vascular imaging

Radiol Clin N Am 40 (2002) xi xii

Preface

Vascular imaging

Klaus D. Hagspiel, MD Alan H. Matsumoto, MD Guest Editors

It has been 7 years since an issue of Radiologic Clinics of North America was devoted to vascular imaging. Now, as then, cardiovascular disease remains the leading cause of death and morbidity in the United States; however, in the ensuing 7 years, noninvasive vascular imaging modalities have improved significantly, and there has also been a significant change in their utilization pattern. Gadolinium-enhanced 3D magnetic resonance angiography (MRA) has matured into a robust and accurate vascular imaging technique. Its use is no longer confined to a few dedicated centers; rather, 3D gadolinium-enhanced MRA is now successfully used in many clinical settings throughout the world and has replaced other diagnostic imaging modalities in a number of vascular territories. Although it was not considered a primary vascular imaging modality 7 years ago, computed tomography angiography (CTA) has experienced a technological quantum leap forward. The introduction of multislice detector systems with isotropic imaging capabilities has enabled CTA to surpass MRA with regard to spatial resolution. In many centers, CTA is now the modality of choice for the diagnosis of pulmonary embolism and the assessment of diseases of the aorta. The acquisition of CTA data is rapid, and the postprocessing algorithms continue to improve, allowing for the use of various fly-through and 3D reconstructions. In addition, in its most recent implementation using an EKG-gated technique, CTA allows for the

acquisition of images of the coronary arteries with resolution and vessel definition surpassing those of coronary MRA. Another innovation in vascular imaging is the development of both MR and CT for the detection and characterization of atherosclerotic plaque. The ability to define plaque morphology reveals a whole new realm of vascular imaging application. It has become apparent that atherosclerotic plaques are heterogenous, with some being more prone to calcify, rupture, or progress depending on the constitution of the plaque. In addition, by being able to more clearly define a plaque and its morphology, the effect of various therapies on the progression or regression of plaque can be monitored. Catheter-based angiography is now synonymous with digital subtraction angiography (DSA). Although DSA is used less in the setting of vascular diagnosis, its application in interventional procedures or to reconcile the inconsistencies of noninvasive studies continues. Newer, catheter-based methods have also been developed and refined to add to our armamentarium. 3D rotational angiography and the use of alternative contrast media are two examples of catheter-based techniques that have been developed in the past decade. Nevertheless, there can be no doubt that the role of catheter-based angiography as a diagnostic tool will be further reduced over the next decade given the rapid pace of technological advancements in both CT and MR imaging. In addition, the

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field of interventional MRI has progressed to a level that vascular interventions are now feasible in an MR environment and may ultimately challenge fluoroscopically guided techniques. We hope that this issue of Radiologic Clinics of North America provides the reader with a greater understanding of some of the recent developments in the field of vascular imaging and helps to put their potential use and application into a practical clinical context. We would like to thank the authors for their outstanding and timely contributions. Undoubtedly, vascular imaging is an area within the field of cardiovascular medicine that is experiencing rapid growth, and every radiology department should attempt to become intimately involved in its clinical application.

Klaus D. Hagspiel, MD Associate Professor of Radiology Department of Radiology Division of Angiography and Interventional Radiology University of Virginia Health System Charlottesville, VA 22908 0170, USA Alan H. Matsumoto, MD Professor of Radiology Division Head Department of Radiology Division of Angiography and Interventional Radiology University of Virginia, Health System Charlottesville, VA 22908-0170, USA

Radiol Clin N Am 40 (2002) 689 692

The future of catheter-based angiography: implications for the vascular interventionalistBarry T. Katzen, MD*Miami Cardiac and Vascular Institute, Baptist Hospital, 8900 North Kendall Drive, Miami, FL 33176, USA Department of Radiology, University of Miami School of Medicine, Miami, FL 33176, USA

The title of this article implies that there is a problem that will result in changes in the way invasive angiography is performed or used. Clearly the impact of less invasive imaging methods will result in reduced need and benefit of catheter-based angiography in the future. Does this mean the need for angiographic equipment, qualified interventionalists, and catheter technologies will be eliminated? Before addressing these questions, it is important to understand the current clinical applications of invasive angiography and the modalities that may offer practical replacements.

Current applications of catheter-based angiography Historically, catheter-based angiography has provided the gold standard for visualization of the circulatory system. After Seldingers historic description of a simple technique to introduce catheters into the circulation without surgical incision in 1953, angiography was explored for its value in providing diagnostic information about a broad spectrum of disease entities. These included not only atherosclerotic occlusive disease and other primary vascular diseases, but also neoplastic diseases and other masses [1]. With the advent of computed tomography (CT) in the 1970s and body CT in the latter part of that decade, there was a gradual transition away from

* Correspondence. Miami Cardiac and Vascular Institute, Baptist Hospital, 8900 North Kendall Drive, Miami, FL 33176, USA.

the vascular anatomy as a distinguishing characteristic. Technology also affected the safety and efficacy of angiography in the late 1970s and early 1980s. The advent of digital techniques and, specifically, digital subtraction angiography (DSA) made angiographic examinations much safer with reduction in contrast and significant reduction in size of sheaths and catheters necessary to perform procedures. Following a short period of time where intravenous (IV) contrast was used to promote outpatient procedures, it became rapidly apparent that with smaller catheters and meticulous technique, outpatient angiography could be a reality. Because imaging was far superior with arterial compared with venous injections of contrast material, arterial DSA became the standard. Image quality improved to the point that film changers were eliminated and replaced by DSA components that produced real-time information, with reduced contrast needs and the potential for filmless and dynamic imaging. This improvement in imaging was accompanied by the development and advancement of catheter-based therapeutic procedures, including angioplasty, thrombolysis, and stent placement. Over the past fifteen years, angiography has become irrelevant in the diagnosis of pancreatitis, cancer of the pancreas, liver, kidney, and other organs. Yet it remains critical to the detection and pretreatment planning for vascular occlusive disease by either surgical or endovascular techniques. Catheter-based angiography remains the primary method of evaluating the severity and specific location of occlusive disease of the extracranial carotid arteries, the renal and visceral arteries, and the thoracic and abdominal aorta and peripheral arteries. Invasive approaches also are used widely for assessment of


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venous structures and vascular malformations. Anatomic evaluation of the coronary arteries also is completed predominantly by invasive angiography. Clearly other modalities are improving their spatial and contrast resolution and ability to demonstrate simply the vasculature. As a result, even at the time of this writing, change that will affect the future of invasive imaging is occurring rapidly.

Advances in percutaneous therapeutic techniques Since the first description of transluminal angioplasty by Dotter in 1963, percutaneous therapy for vascular occlusive disease, and other forms of vascular disease, has become the standard of care for many patients. The radiologist and other specialists are dependent on high-quality imaging to make the complex treatment decisions necessary to insure high-quality outcomes with low morbidity [2]. Some of the components of endovascular therapy include: 1. Percutaneous revascularization. In the treatment of noncoronary vascular disease, percutaneous techniques are the first line of management in many patients. Techniques such as percutaneous transluminal angioplasty (PTA), intravascular stent placement, and use of thrombolysis have proven efficacy, but depend on high-quality imaging to identify patients who might be candidates. In addition, imaging is critical in determining the specific anatomic features of lesions, distal runoff vessels, presence of collateral flow, and other characteristics for the interventionalist to perform adequately treatment planning. Areas of application include all parts of the circulatory tree including the aorta, iliac and femoral arteries, renal and visceral branches, and the brachiocephalic circulation. 2. Embolization. A large part of vascular intervention includes the occlusion of blood vessels for therapeutic purposes. Conditions such as neoplasm, vascular malformations, aneurysm, and hemorrhage may require the skills of the interventionalist. Recently, uterine fibroid embolization has become an important interventional alternative in symptomatic patients. The role of imaging is not only to detect disease, but also to provide sufficient information for treatment planning. 3. Drug delivery. In the treatment of neoplastic disease, patients may benefit from direct

delivery of agents for greater efficacy. Thrombolytic agents, and perhaps other agents directed at restenosis, may become more important as a therapeutic technique. Other agents include vasodilators for cholesterol embolization, and vasoconstrictors for some types of gastrointestinal hemorrhage. 4. Endograft placement. Endografts represent a combination of fabric and stent technology and can be used to treat a variety of types of aneurysm disease in large- and medium-sized vessels. These include disease in the abdominal and thoracic aorta and branch aneurysms, such as visceral and brachiocephalic. Additionally, this technology may have benefit in occlusive disease, particularly in the future, perhaps in conjunction with the delivery of drug. For all these procedures, catheter-based angiography is the gold standard in obtaining information for treatment planning, but if noninvasive modalities could provide sufficient quality information, the need for invasive angiography for diagnosis alone would be greatly reduced.

Current status of vascular imaging Vascular imaging has changed significantly in the past decade and this rate of change is accelerating dramatically. These changes are of great benefit to patient care through early detection of disease in some cases and avoidance of invasive procedures in others. The development of ultrasound-based technologies, including imaging, Doppler shift velocity measurements, and combinations resulting in color-flow imaging, allow precise physiologic and morphologic measurements of significant occlusive disease. While there are limitations to these technologies in deeper vessels, superficial vessels such as carotid, infrainguinal, and other arteries are reliably imaged without difficulty. The rapid expansion of noninvasive vascular laboratories and vascular imaging programs within imaging departments has facilitated early detection of disease and stimulated multidisciplinary accrediting bodies such as the Intersocietal Commission on the Accreditation of Vascular Laboratories. For many clinical problems, ultrasonography offers the benefit of reduced cost, in addition to being noninvasive. CT has also advanced rapidly as scan times are reduced by spiral and multidetector technologies [3,4]. Using iodinated contrast and rapid CT scanning


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techniques, many vascular structures can be imaged effectively. The detection of renal artery stenosis, carotid artery disease, diseases of the thoracic, and abdominal aorta is accomplished effectively with relatively short imaging times. Even the infrainguinal peripheral circulation can be identified. The advantage of volumetric acquisition and data analysis associated with CT is useful, especially in the diagnosis and treatment of aneurysms. Despite these benefits, CT angiography requires large volumes of iodinated contrast and significant doses of radiation. Dynamic imaging is possible but not optimal with this modality. Magnetic resonance angiography (MRA) [5] has improved rapidly in resolution and speed of acquisition and has thereby become a more practical modality for general application in angiography. The lack of ionizing radiation and use of non-nephrotoxic contrast agents offer great advantages to our patients, in particular those with abnormal renal function or allergic manifestations to contrast agents. A variety of techniques allow high-resolution angiography of virtually all parts of the circulation [6 11]. In addition, dynamic imaging of cardiac structures can be achieved without contrast injections. The potential for head-to-toe angiography represents an exciting possibility for changing how patients with vascular disease are assessed. MRA is not applicable in patients with pacemaker implants and has limited use in the presence of indwelling metallic implants. Detection of in-stent restenosis is not possible, but if implants are altered or developed to be more MR friendly, certainly this could change. The quality of MRA varies from excellent to substandard. Nonetheless, overall it has improved to the point that many types of invasive angiographic procedures are significantly reduced, but not entirely eliminated. Some pitfalls of MRA include overestimation of the degree of stenosis and other occasional artifacts. With the use of gadolinium, accuracy and image quality increase significantly. MRA is useful in detection of renal artery stenosis and other types of peripheral vascular disease.

niques. In many ways, these changes will complete the transition, which has occurred in our discipline during the past two decades, from angiographers to interventionalists. The improvement in the quality of MRA, CT angiography, and color-flow duplex imaging increases early and late diagnosis of vascular disease, which will result in significant increases in the vascular interventional case volume. At the Miami Cardiac and Vascular Institute, these predictions are incorporated into our capital equipment and space planning. It is reasonable to ask whether diagnostic angiography will be eliminated by these technologies. Clearly, most types of stand-alone elective diagnostic procedures will be eliminated. The author believes that diagnostic angiography will increase, but as an immediate prelude to therapeutic procedures. The interventionalist will have very precise anatomic information available prior to therapy, but will perform documentary angiography prior to intervention. Thus, the use of diagnostic catheters will remain necessary.

What is the impact of these changes on the interventionist? It is of critical importance for the interventionist to be involved in new imaging modalities to avoid being excluded from patient care algorithms and maintain patient access. Harvey et al [12] and others prove that high-quality patient- and clinically-oriented vascular imaging programs, linked to the interventional service, are effective in the detection of vascular disease and linkage to endovascular solutions for appropriate stages of disease. Conversely, if all vascular imaging excludes the interventionalist, the risk of being excluded from interventional therapy is significant [13].

Summary Based on the assumptions mentioned previously, the author makes the following predictions regarding catheter-based angiography and related procedures: 1. Most diagnostic angiography will be performed with noninvasive methods. In the peripheral circulation, MRA will be the predominant method, with CTA having an important role in aortic imaging and coronary imaging. MRA will have increased use for elective diagnosis and in clinical emergencies.

What does it all mean for invasive angiography? Is the catheter for diagnosis finished? Two trends are converging and diverging significantly. The movement toward less invasive therapies is growing and involving more procedures, more disease processes, and more disciplines of medicine in the delivery of vascular care. This growth in treatment methods and efficacy is associated with dramatic improvement in noninvasive imaging tech-

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2. Catheter-based angiography will have an important role as an adjunct or preliminary procedure related to interventions. This is significant for planning catheter development and functionality of future angiographic equipment. 3. The need for angiographic equipment will continue to grow despite this decrease in diagnostic application,as a result of increase in interventional therapy. This increase in therapy will be a result of a variety of factors, including aging population, early diagnosis, and increasing acceptance of less invasive therapy. 4. Interventionists should be considering and planning for vascular imaging devices MRA, CTA, and USto be included as part of the interventional sections and the workload. 5. Cardiovascular imaging should be a clinical imaging specialty, with patient interaction at the time of imaging. 6. These changes should be embraced by vascular interventionalists, who should incorporate these tools into their clinical practice. 7. The changes, if they occur as predicted, will create significant problems in training skilled interventionists who will not have the foundation of diagnostic angiography on which to build complex endovascular skills.

[4]

[5] [6]

[7]

[8]

[9]

[10]

References[1] Seldinger SI. Catheter replacement of needle in percutaneous arteriography: new technique. Acta Radiol (Stockh) 1953;39:368. [2] Dotter CT, Judkins MP. Transluminal treatment of arteriosclerotic obstruction: description of a new technique and a preliminary report of its application. Circulation 1964;30:654 70. [3] Rubin GD, Shiau MC, Schmidt AJ. Computed tomo-

[11]

[12]

[13]

graphic angiography: historical perspective and new state-of-the-art using multi detector-row helical computed tomography. J Comput Assist Tomogr 1999; 33(Suppl):S83 90. Katz DS, Hon M. CT Angiography of the lower extremities and aortoiliac system with a multi-detector row helical CT scanner: promise of new opportunities fulfilled. Radiology 2001;221:7 10. Prince MR. Peripheral vascular MR angiography: the time has come. Radiology 1998;206:592 3. Serfaty JM, Chirosel P, Chevallier JM. Accuracy or three-dimensional gadolinium-enhanced MR angiography in the assessment of extracranial carotid artery disease. AJR Am J Roentgenol 2000;175:455 63. Korst MB, Joosten FB, Postma CT, et al. Accuracy of normal-dose contrast-enhanced MR angiography in assessing renal artery stenosis and accessory renal arteries. AJR Am J Roentgenol 2000;174:629 34. Nelson H, Gilfeather M, Holman J, et al. Gadoliniumenhanced breathold three-dimensional time of flight renal MR angiography in the evaluation of potential renal donors. JVIR 1999;10:175 81. Ernst O, Asner V, Sergent G, et al. Comparing contrast-enhanced breath-hold mr angiography and conventional angiography in the evaluation of mesenteric circulation. AJR Am J Roentgenol 2000;174: 433 9. Kreitner KR, Kalden P, Neufang A, et al. Diabetes and peripheral arterial occlusive disease: prospective comparison of contrast-enhanced three dimensional mr angiography with conventional digital subtraction angiography. AJR Am J Roentgenol 2000;174:171 9. Baum RA. Peripheral vascular diagnosis using magnetic resonance angiography [abstract]. JVIR 1999;10 (Suppl 5):387. Harvey RT, Soulen MC, Siegelman ES. Impact of screening mr angiography on referrals for percutaneous intervention in renovascular disease. JVIR 1999;10: 559 64. Stein B, Katzen BT. Magnetic resonance angiography use it or lose it. . . .ALL. SCVIR Newsletter MRA. January 2001.

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Gadolinium-based contrast agents in angiography and interventional radiologyDavid J. Spinosa, MD*, J. Fritz Angle, MD, Gary D. Hartwell, DSc, Klaus D. Hagspiel, MD, Daniel A. Leung, MD, Alan H. Matsumoto, MDDepartment of Radiology, University of Virginia Health System, Post Office Box 800170, Charlottesville, VA 22908, USA

Limited use of gadolinium-based contrast agents (Gd) in place of iodinated contrast material for angiography and interventional procedures in patients with renal insufficiency or a history of a severe reaction to iodinated contrast material can be helpful. Contrast nephrotoxicity is reported to occur in approximately 10% to 30% of patients with pre-existing renal insufficiency when intravascular iodinated contrast material is used [1 4]. Although recovery of renal function occurs in most patients, a 10% to 25% incidence for a transient need for dialysis in patients developing contrast nephrotoxicity is reported, particularly when oliguria develops [5,6]. In addition, in up to 30% of the patients, renal function fails to return to baseline [6]. Equally disturbing are reports of a mortality rate of 34% in patients developing contrast nephrotoxicity while hospitalized, compared with a mortality rate of 7% in similar patients who do not develop contrast nephrotoxicity [7]. Even though significant coexisting medical problems such as sepsis and transient hypotension contribute to deterioration in renal function in some patients, contrast nephrotoxicity results in prolongation of the hospital stay, the occasional need for dialysis, and predisposition of some patients to permanent worsening of renal function and death. Occasionally, patients with a history of a severe, life-threatening reaction to iodinated contrast material require an iodinated contrast study. More frequently, some patients state that they are told never to receive iodinated contrast material because of a pre-

* Corresponding author. E-mail address: [email protected] (D.J. Spinosa).

vious reaction that they or their physician may not be able to recall. In these patients, the radiologist must decide whether or not to administer iodinated contrast material. Frequently, traditional diagnostic angiograms or venograms can be avoided and noninvasive studies, such as duplex sonography or magnetic resonance angiography/venography, can be performed. When these noninvasive studies are inconclusive, however, or if a percutaneous procedure for treatment is contemplated, angiographic studies requiring the use of an intravascular contrast agent may be necessary. Recently, fenoldopam and acetylcysteine have been proposed as possible premedications to reduce the risk for contrast-induced nephrotoxicity [8,9]. Both strategies require the administration of the drug for some period of time prior to the procedure. Although there is limited clinical experience with these two agents, nephrotoxicity can occur [9], and these agents do not obviate the risk for a contrastinduced allergic reaction. Use of carbon dioxide (CO2) as a contrast agent is advocated in selective patients to reduce the risk of nephrotoxicity [10]. With experience, CO2 can serve as a satisfactory alternative to iodinated contrast material for many diagnostic angiograms and interventional procedures. CO2 is non-nephrotoxic and inexpensive. Unfortunately, CO2 is not approved by the Food and Drug Administration (FDA) for intravascular use. In addition, CO2 angiography has limitations in defining the anatomy of large diameter vessels, such as the aorta or inferior vena cava (IVC), and in high-resistant vascular beds, such as the tibial vessels in patients with poor runoff [11,12]. Cerebral arteries should not be studied with CO2. Use of small amounts of


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iodinated contrast material can be used to supplement a CO2 study; however, it is unclear if the amount of iodinated contrast material used correlates with the risk for developing contrast nephrotoxicity [13,14]. The use of Gd in place of iodinated contrast material, either alone or in conjunction with CO2, is another strategy recently employed. Because of the ability of Gd to attenuate radiographs, its use with digital subtraction angiography (DSA) can produce diagnostic images for angiography and interventional radiologic procedures [15 18]. When used in doses similar to those recommended for magnetic resonance imaging (MRI), use of Gd during angiography is reported to result in a markedly reduced incidence of contrast nephrotoxicity when compared with iodinated contrast material. The safety of intravenous (IV) Gd administration in patients with pre-existing renal insufficiency for MRI studies is well known [19 21].

higher (approximately doubled) in patients with a history of a reaction to iodinated contrast material [24,25]. The intra-arterial use of Gd represents an offlabel use of these FDA-approved contrast agents. The FDA-approved dosages for IV use are listed in Table 1. Deterioration in renal function, although infrequent, has been reported when doses up to and above the 0.3 to 0.4 mmol/kg dose limits are used [26,27]. It is unclear, however, whether the Gd alone is responsible for the deterioration in renal function in these patients. Therefore, even though higher doses of Gd ( > 0.4 mmol/kg) are administered safely in some patients [28], the clinical use of these higher doses has not been studied to any great extent. Thus, it seems prudent to limit the total dose of Gd used for angiographic studies to 0.3 to 0.4 mmol/kg at this time.

Properties of gadolinium agents Adverse effects Even though there is substantial literature documenting the clinical safety of Gd agents, adverse reactions are reported in association with their administration. The total incidence of adverse effects is less than 5%, and the incidence of a severe adverse event is less than 1% in all patients [22]. The most common side effects with Gd use are nausea, headaches, and emesis. Anaphylactoid reactions also are reported with the use of Gd. The incidence of these reactions probably is in the range of 1 in 100,000 to 1 in 500,000 [23]. Not surprisingly, the risk of adverse reactions is Free Gd, a rare earth element, is toxic and excreted by the body slowly, with a biologic half-life of several weeks [23]. Therefore, free Gd must be chelated to another chemical that limits the availability of free Gd in solution, thereby limiting its toxicity. Four Gd-based contrast agents are available for use in the United States: gadodiamide (GdDTPA-BMA, Omniscan1, Nycomed, Princeton, NJ), gadopentetate dimeglumine (Gd-DTPA, Magnevist1, Berlex, Wayne, NJ, United States, and Schering, AG, Germany), gadoteridol (Gd-HP-DO3A, ProHance1, Bracco Diagnostics, Princeton, NJ), and Gadoversetamide (Gd-DTPA-BMEA, OptiMARK1, Mallinckrodt

Table 1 Gadolinium chelates Thermodynamic equilibrium constantc log keg 22.2

Trade name Magnevist

Chemical compound Gadopentetate dimeglumine (Gd-DTPA) Gadodiamide (Gd-DTPA-BMA) Gadoversetamide (Gd-DTPA-BMEA) Gadoteridol (Gd-HP-DO3A)

FDA-approved dosea 0.1 mmol/kg

Osmolalityb 1960

Omniscan OptiMARK ProHancea b c

0.3 mmol/kg 0.2 mmol/kg 0.3 mmol/kg

783 1110 630

16.9 16.6 23.8

Approved for venous administration (total dose). Mosmol/kg water at 37C. Higher values are better.


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Inc, St. Louis, MO) (see Table 1). These four agents have similar biodistributions, pharmakinetics, and half-lives [29 32]. The biologic half-life of these agents is approximately 1.5 hours. These chelated agents demonstrate a 500-fold increase in renal ex-

cretion when compared with the excretion of free Gd [33,34]. These chelates have a high affinity for Gd (see Table 1). Nevertheless, when Gd complexes remain in the body for prolonged periods of time, Gd ions

Fig. 1. (A) Gadolinium abdominal aortogram performed using a pigtail catheter injecting 10 ml in 0.5 seconds demonstrates a high-grade stenosis (small arrow) at the origin of the left renal artery and probable occlusion of the proximal right renal artery (large arrow). (B) Injection of 6 ml of gadolinium via a vascular sheath demonstrating a widely-patent origin of the left renal artery after stenting (small arrow) and occlusion of the proximal right renal artery (large arrow). (C) Injection of 5 ml of gadolinium via an end-hole catheter into the origin of the right renal artery after recanalization and stenting (arrow) demonstrates a widely-patent right renal artery.

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patients with markedly reduced renal function, the half-life of Gd chelates is up to 10 times longer than normal, creating a theoretical concern for the accumulation of free Gd [25]. Despite this theoretic concern regarding the in vivo release of free Gd, no harmful effects in humans are reported from the clinical use of these agents [39]. In patients with renal insufficiency who receive IV Gd chelates for MRI studies, there is no evidence to suggest that these agents result in Gd toxicity or deterioration in renal function [19 21,25,40 42]. More than 96% of

Fig. 2. (A) Injection of 8 ml of gadolinium via a vascular sheath demonstrates a severe stenosis at the origin of the right main renal artery (arrow). (B) Injection of 8 ml of gadolinium via the vascular sheath demonstrates a widely-patent right renal artery origin after renal artery stenting (arrow).

can be released in the presence of a high concentration of competing cations such as copper and zinc. These circulating cations can displace Gd ions from the chelating complex (transmetalation) and result in the release of free Gd. Transmetalation is observed in vitro and in vivo [35 38]. In patients with normal renal function, excretion of the Gd complexes is rapid and the concentration of free Gd is very low. In

Fig. 3. (A) Injection of 16 ml of gadolinium at 8 ml/second via an end-hole catheter into the right common iliac artery demonstrates high-grade stenosis in the midtransplant renal artery (arrow). (B) Injection of 10 ml via an end-hole catheter in the right common iliac artery demonstrates a widely-patent renal transplant artery after intravascular stenting (arrow).


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suspected stenosis or occlusion seen during CO2 angiography and to help guide endovascular interventions. Intraarterial gadolinium is less effective in evaluating the aorta because of its large diameter and high flow rate. In these situations, Gd is useful as a problem solver to supplement CO2 angiography. In contrast to the vascular system, full-strength Gd is visualized satisfactorily in the genitourinary (GU) system and biliary tree with fluoroscopy. The osmolality of the Gd agent also plays an important role in obtaining quality DSA images. Lower-osmolality contrast agents, such as gadodiamide or gadoteridol, are helpful in evaluating upper and lower extremities because their use is associated with less pain, which helps to minimize patient motion during image acquisition (see Table 1). Finally, the K-edge of Gd (50.2 KeV versus 33 KeV for iodine) allows imaging with a higher range of kilovoltages (77 96 KVp) compared with those typically used for iodinated contrast studies (63 73 KVp). The ability to use higher KVps for Gd angiography can result in a decrease in skin radiograph exposure compared with the lower-kilovoltage techniques used with iodinated contrast material [44]. This benefit,

Fig. 4. Injection of 18 ml of gadolinium at 9 ml/second using a power injector via a multisided-hole catheter positioned in the left common iliac artery demonstrates high-grade stenosis at the origin of the transplant renal artery (arrow). Quantum mottle effect, a result of the steep angulation (57) required to profile the transplant renal artery origin, is evident.

Gd can be removed from the circulation after three dialysis sessions [41]. Gadolinium also can be removed using peritoneal dialysis; however, approximately three weeks is required to clear approximately 70% of the circulating Gd [43].

Technical considerations and imaging Gadolinium is difficult to visualize with fluoroscopy because of the high flow rates typically present in the arterial system, the low concentration (0.5 mmol/ml) of agents, and the recommended total dose limits of Gd (0.3 0.4 mmol/kg). To maximize image quality, full-strength Gd should be administered for intraarterial injections, and high-quality DSA techniques limiting motion and distortion should be used. Gadolinium is best used with selective angiography in small- to medium-sized vessels (less than 1 cm in diameter) to confirm areas of

Fig. 5. Injection of 16 ml of gadolinium at 8 ml/second delivered with a power injector via an end-hole catheter demonstrates a web-like stenosis (small arrow) in the right common iliac artery. Note the patent renal transplant artery (large arrow).

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however, is partially offset by the need to increase the radiation dose administered for each radiograph exposure to help decrease the noise (predominantly quantum mottle effect) in the image. In general, for an average-sized adult patient, obtaining radiographs at 96 KVp results in reducing the skin dose by approximately 50%. Because of the reduced concentration of Gd agents, however, the authors typically increase the dose by approximately 180% to reduce the quantum mottle effect. Therefore, there is approximately a 10% overall reduction in radiation dose to the patient from adjusting the imaging acquisition parameters. The benefit in-

creases as patient size decreases and decreases as patient size increases. Laboratory phantom experiments demonstrate that radiographic images of Gd and various dilutions of iodine containing agents result in Gd images that exhibit image contrast equal to an iodine preparation containing 37.5 to 75.0 mg/ml of iodine (ie, one eighth- to one quarter-strength of a 300-mg/daily iodine preparation). As soft-tissue attenuation increases, however (body parts increase in thickness), image contrast remains relatively unchanged at these higher KVps for Gd, but deteriorates with iodine images. Therefore, when imaging using a 20 cm of

Fig. 6. (A) Gadolinium angiogram demonstrates total occlusion of the left popliteal artery by an embolus (arrow). (B) A multisided-hole infusion catheter is placed across the occlusion in the left popliteal artery. Injection of 8 ml of gadolinium into the multisided-hole catheter after a six-hour infusion of tissue plasminogen activator (TPA). The study demonstrates persistent thrombus in the left popliteal artery (arrow) with excellent filling of the distal popliteal artery and proximal peroneal artery. (C) Injection of 10 ml of gadolinium via a vascular sheath in the left common femoral artery after 22 hours of TPA and balloon angioplasty of the left popliteal artery demonstrates a widely-patent left popliteal artery (arrow).


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dose (0.3 0.4 mmol/kg) considerations necessitate careful planning prior to each injection. It is paramount to use the smallest amount of contrast agent possible, but each angiogram should be performed with enough Gd to produce diagnostic images. Optimization of Gd use typically takes some practice as the interventionalist learns to account for vessel size, vessel flow, and vessel location. As stated previously, Gd agents are best used as problem solvers to confirm the findings of CO2 angiography, define areas incompletely evaluated with CO2 angiography, guide interventional treatment, or replace CO2 when CO2 injections are not well tolerated by the patient (ie, abdominal pain). Gadolinium agents are used in many vascular beds, most frequently renal and peripheral (upper and lower extremities) vascular beds, and with dialysis fistulography. Upper extremity venography, transjugular intrahepatic portosystemic shunts (TIPS) construction and repair, IVC filter placement, and interventional urinary and biliary procedures also can be performed with use of these agents. Although CO2 angiography should not be used to evaluate upper extremity or cerebral arterial anatomy, gadolinium agents are used safely in these vascular territories.

Fig. 6 (continued ).

Renal vascular disease An abdominal aortogram usually can be obtained with the use of CO2. The renal arteries can be identified and the optimum projection for profiling the origin can be defined with CO2 angiography. If the renal artery is incompletely visualized, or confirmation of the results of the CO2 angiogram is desired, Gd can be injected, acquiring the DSA images in the optimum projection. An injection of 10 to 20 ml in 0.5 seconds via a pigtail catheter positioned just above the renal arteries usually provides diagnostic images of the aorta and renal artery origins at the level of the renal arteries and renal artery origins (Fig. 1A). This method is particularly useful in confirming the presence of renal artery occlusion. Once proceeding with a renal intervention, a small hand injection of 2 to 4 ml of Gd via an end-hole catheter, while acquiring DSA images, confirms satisfactory catheter position across the renal artery lesion and opacifies the distal main renal artery and its branches. The intervention is monitored with the use of small hand injections (4 8 ml) of gadolinium through a vascular sheath or catheter (Fig. 1B,C). CO2 angiography usually is adequate to allow precise positioning of the intravascular stent, so that it covers the origin of the main renal artery. In patients with

water phantom model, image contrast with fullstrength Gd seems similar to an iodine preparation containing approximately 100 to 150 mg/ml of iodine (ie, one third- to one half-strength of a 300-mg/daily iodine preparation). Increased tissue attenuation results in hardening of the radiograph beam (shift in the spectrum of energy towards higher energy values). Beam hardening results in increased image contrast for a given concentration of Gd relative to that of iodine and accounts for some of the differences noted between the theoretical model calculations and in vivo observations of image contrast.

Gadolinium agents in angiography and interventional radiology Typically, Gd agents are used either alone or to supplement CO2 angiography to answer diagnostic questions and guide interventional procedures [15 18,27]. When used alone, dose limitations reduce the number of angiographic images that are acquired. Gadolinium can be administered with the use of a power injector or by hand injection. Total

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Fig. 7. (A) Left lower-extremity Gd angiogram performed using a stepping-table technique. A single 40-ml bolus of Gd was injected at 5 ml/second using a power injector via an end-hole catheter in the midleft superficial femoral artery. Stations at the knee, calf, and foot were obtained. Gadolinium angiogram demonstrates high-grade stenosis at the level of the mid-left popliteal artery (small arrow) and at the origins of the left anterior tibial and peroneal arteries (large arrow). (B) Gadolinium angiogram demonstrates a patent peroneal artery (small arrow) to the level of the ankle and poor flow distally in the anterior tibial artery (large arrow). (C) Angiogram at the level of the left foot demonstrates reconstitution of the left posterior tibial artery (small arrow) from peroneal collaterals. Note that the left anterior tibial artery is occluded at the level of the ankle (large arrow). (D) Delayed images of the left foot demonstrate a patent left plantaris pedis artery (small arrow) and occlusion of the left anterior tibial artery above the ankle (large arrow).


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extensive bowel gas, marked irregularity of the abdominal aorta as a result of severe atheromatous plaque formation, or aneurysmal dilatation of the aorta at the renal artery level, the renal artery and its origin often are identified better using Gd angiography (Fig. 2A,B). Gadolinium images are particularly helpful in defining complications that occur during the intervention, such as dissection or intravascular throm-

bus formation. Gadolinium angiography also provides a more detailed completion angiogram, especially for evaluating the intrarenal branches for dissection, perforation, spasm, or thrombus/embolus after treatment. In renal transplant patients in whom there is concern for renal vascular disease, CO2 angiography usually is adequate. If the CO2 angiogram study is suboptimal, however, power injection of 16 to 20 ml

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provides adequate visualization of the inflow iliac artery, transplant artery, and intrarenal branches (Figs. 3 5). CO2 angiograms still are helpful as the initial study to determine the optimum projection in which to perform the Gd study.

Peripheral vascular disease The volume of Gd agent necessary to perform a complete angiographic study of the lower extremity usually exceeds the total recommended dose limits; therefore, CO2 angiography is used to evaluate as much of the lower-extremity anatomy as possible. The use of Gd agents is reserved for answering specific questions not answered by the CO2 angiogram and is especially helpful in problem solving during interventional therapy (Fig. 6A C). CO2 angiography usually is adequate in defining lowerextremity anatomy to the level of the popliteal artery, especially when using stacking-software algorithms that are available on most current DSA equipment. Occasionally, small amounts of Gd delivered by hand injection via an end-hole catheter are necessary to answer specific questions regarding disease in the iliac vessels obscured by overlying bowel gas. When CO2 angiography fails to visualize the infrapopliteal vessels, positioning of an end-hole catheter in the

Fig. 8. Injection of 6 ml of gadolinium via an angiocatheter in the arterial limb of an upper arm arteriovenous dialysis graft refluxed into the brachial artery demonstrates a widelypatent arterial anastomosis (arrow).

of Gd at a rate of 8 to 10 ml/second via a pigtail catheter in the lower-abdominal aorta or multisidedhole straight catheter in the ipsilateral iliac artery

Fig. 9. Injection of 10 ml of gadolinium via a vascular sheath in a left upper arm arteriovenous gortex dialysis graft after balloon angioplasty of a high-grade stenosis at the junction of the left brachiocephalic vein and superior vena cava (arrow) demonstrates excellent flow into the superior vena cava.


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mid- or distal superficial femoral artery (SFA) in conjunction with small boluses (5 10 ml) of Gd can be used to image these vessels. If the SFA is patent, but there is significant distal occlusive disease, larger volumes of Gd are necessary to visualize the more distal outflow and runoff vessels. A digital subtraction stepping program to evaluate the lower two stations of the extremity of interest (lower leg and foot) frequently maximizes the information obtained when injecting a single large bolus (5 6 ml/second for a total volume of 30 40 ml) of Gd (Fig. 7A D). Reducing patient motion is critical under these circumstances. In the authors experience, lower-osmolar contrast agents, such as gadodiamiole or gadoteridol, cause less discomfort and less patient motion than the higher osmolar Gd preparations. If the SFA is occluded, but numerous collaterals are present, the use of larger volumes of Gd (40 50 ml) usually is necessary to offset the dilutional effects. The quality of the lower-extremity angiogram in this setting is variable. Fortunately, CO2 angiography is particularly useful in visualizing the runoff vessels when there is a lower-resistance vascular bed in the lower leg and foot because of a proximal occlusion and less helpful when there is a high resistance vascular bed in the lower leg and foot because of distal occlusive disease. Evaluation of the proximal upper extremity can be performed with the use of a selective hand injection of 8 to 10 ml of Gd in the subclavian, axillary, or proximal brachial artery. The evaluation of the forearm vessels and palmar arch requires the use of larger volumes of contrast injected via a power injector (15 36 ml delivered at 5 6 ml/second via an end-hole catheter positioned in the distal axillary or proximal brachial artery). Again, use of lower-osmolality agents results in less patient discomfort and motion, thereby producing better quality images. Because of total dose limits, it is best to evaluate and treat only one extremity at a time. Evaluation and treatment of the other extremity should be delayed until the majority of Gd is cleared from the patients system (2 5 days in patients with moderate to severe renal insufficiency).

CO2 into the vertebral arteries seizures [46]. Therefore, Gd angiography can be used to evaluate more safely the arterial anastomosis (Fig. 8) and to verify the

Central veins and dialysis access Gadolinium and CO2 are used in the evaluation of arteriovenous grafts and fistulas [45]. CO2 is useful for evaluation of the arterial-venous graft and outflow veins. CO2 angiography, however, occasionally overestimates the degree of stenosis present, and attempts at refluxing CO2 to evaluate the arterial anastomosis are reported occasionally to result in retrograde flow of

Fig. 10. Gadolinium cavogram performed injecting 30 ml at 15 ml/second using a power injector via a calibrated pigtail catheter (small arrow) positioned in the lower inferior vena cava above the iliac vein bifurcation demonstrates a widely patent inferior vena cava without evidence of thrombus. Note the origin of the left and right (large arrows) renal veins, hepatic vein inflow (open arrow), and left and right iliac veins (hatched arrows). The double exposure appearance of the pigtail catheter is a result of catheter motion during the study and image stacking during image postprocessing.

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severity of disease in the dialysis graft or outflow veins. The central veins can be imaged using a hand injection of approximately 8 to 10 ml of Gd via an endhole catheter positioned in the axillary or subclavian vein or by delivering 20 to 25 ml of Gd at a rate of 4 to 5 ml/second via a catheter in the fistula (Fig. 9). A hand injection of 8 to 10 ml of Gd also can be used for evaluating malfunctioning central catheters to detect the presence of a thrombus or fibrin sheath in patients. An injection of Gd at 10 to 15 ml/second for two seconds is adequate for evaluating the IVC in preparation for IVC filter placement (Fig. 10). Inferior vena cavograms also can be obtained using half-strength gadolinium and higher total volumes (50 60 ml) [47]. IVC size, renal vein location, the presence of IVC thrombus, and IVC anatomy all can be determined with Gd cavography if CO2 inferior vena cavography does not successfully define the IVC anatomy.

Aortography and visceral angiography Imaging of the aorta and mesenteric vessels is limited by the total recommended dose of Gd (0.3

0.4 mmol/kg). A single injection of Gd at 20 to 25 ml/ second for 2 seconds produces reasonable images of the thoracic aortic arch and origins of the great vessels [48]. An abdominal aortogram can be acquired by administering Gd at 15 to 16 ml/second for two seconds (Fig. 11). Assessment of aortic aneurysm disease is more difficult because of the higher volumes of Gd that are needed. As stated previously, when evaluating for renovascular disease, CO2 angiograms are useful in determining the optimal angle to visualize the renal artery origins prior to performing a Gd aortogram. Fortunately, MR angiography with Gd enhancement provides diagnostic images in most of these patients. A selective celiac or mesenteric artery injection is helpful for evaluating the origin and proximal portions of these vessels, but is not helpful for evaluating the more distal anatomy because of dilution of the Gd. Therefore, it is best to use gadolinium for problem solving or for selective injections of visceral branches when evaluation of more distal anatomy is required. CO2 particularly is helpful in evaluating the origins of the celiac and superior mesenteric arteries because of their anterior position when the patient is supine (Fig. 12A, B).

Fig. 11. Gadolinium abdominal aortogram performed injecting 32 ml at 16 ml/second with a power injector via a pigtail catheter positioned in the upper abdominal aorta.


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Miscellaneous gadolinium applications Cerebral angiograms also are obtained using Gd. Selective carotid angiograms with Gd can be performed to evaluate for carotid artery stenosis in patients with renal insufficiency or a history of a

severe contrast reaction [49]. After a hand injection of 2 to 3 ml of Gd confirms catheter position within the common carotid artery, a power injection of Gd at 7 ml/second for a total volume of 11 ml is performed. Additional projections are obtained as needed to visualize the extent of carotid artery disease. Cerebral

Fig. 12. (A) CO2 angiogram demonstrates what seems to be a high-grade stenosis (small arrow) in the origin of the superior mesenteric artery and mildstenosis in the origin of the celiac artery (large arrow). (B) Lateral abdominal aortogram performed injecting 15 ml of Gd in 0.5 seconds by power injector via pigtail catheter demonstrates no evidence of significant stenosis involving the origin of the superior mesenteric artery (small arrow). There is mild stenosis at the origin of the celiac artery (large arrow).

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Fig. 13. After creation of a transjugular intrahepatic portosystemic shunt (TIPS), a final Gd angiogram is performed injecting 18 ml at 9 ml/second by power injector via a multisided-hole catheter positioned in the portal vein. Note the widely-patent TIPS shunt (arrow).

angiograms to evaluate the intracerebral circulation also are performed using Gd agents [50,51]. TIPS also can be evaluated using Gd angiography in patients with renal insufficiency or hepatorenal syndrome (Fig. 13). Gadolinium portal-vein studies are useful for confirming anatomy, evaluating stenotic or occluded TIPS shunts, and studying and treating varices. Hand injections of 8 to 10 ml of Gd via an end-hole or multiside-hole catheter typically provides diagnostic images, while power-injecting 16 to 20 ml at a rate of 8 to 10 ml/second via a multisidehole catheter is helpful in defining a high-flow portal system (Fig. 14).

the biliary and genitourinary tracts, although the images are inferior to images obtained with fullstrength iodinated contrast agents. A hand injection of 6 to 10 ml of Gd into a drainage catheter frequently can determine catheter patency and confirm satisfactory positioning of the catheter (genitourinary or biliary). Percutaneous nephrostomy can be aided by Gd injection into the renal pelvis or calyx if a CO2 injection into the urinary collecting system is difficult to visualize. In patients with a history of severe iodine reactions, percutaneous transhepatic cholangiography and biliary drainage catheter placement also can be performed using Gd as the sole contrast agent (Fig. 15A C).

Genitourinary and biliary studies Summary Opacification of the urinary and biliary tracts can be performed by direct injection of Gd into the renal pelvis or intrahepatic biliary tree [52]. These images are similar to images obtained with approximately 100 to 150 mg/ml iodine contrast agent preparations. Use of Gd is particularly helpful in patients with a history of a severe reaction to iodinated contrast material. Unlike Gd injected into arteries and highflow veins, Gd can be visualized fluoroscopically in Gadolinium is useful as an alternative contrast agent for diagnostic angiographic and interventional procedures in patients with renal insufficiency or a history of a severe reaction to iodinated contrast material. Gadolinium usually is used as a problem solver to answer specific diagnostic questions or guide interventional procedures that cannot adequately be defined with CO2 angiography. Because of dose limi-


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Fig. 14. (A) Splenic-vein angiogram performed in a patient with renal insufficiency, splenomegaly, and gastric varices. A noninvasive study suggests narrowing of the splenic vein near its hilum. An end-hole catheter was positioned in the distal splenic vein placed via a transhepatic portal vein puncture. Gadolinium angiogram performed injecting 10 ml of Gd demonstrates a highgrade stenosis of the splenic vein at the splenic hilum (arrow). (B) Delayed images of the Gd splenic venogram demonstrate the remainder of the splenic vein (small arrow) and portal vein (large arrow) to be patent.

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Fig. 15. (A) A percutaneous transhepatic cholangiogram is performed injecting 8 ml of Gd into a 22-gauge needle with its tip positioned within a small branch of the right biliary ductal system (small arrow). Note opacification of the right (large arrow) and left (open arrow) intrahepatic ducts and high-grade obstruction at the anastomosis of the common hepatic duct with the Roux-en-Y limb (hatched arrow). (B) Access into a larger right intrahepatic bile duct is obtained and a guide wire passed across the obstruction into the Roux-en-Y limb (arrow). (C) A biliary drainage catheter (arrow) is successfully placed across the obstruction into the Roux-en-Y limb.


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tations with Gd, careful planning is required prior to its use with angiography or interventional procedures.

Acknowledgment A special thanks to Sherry Deane, Geneva Shifflett, and Shirley Naylor for their expert assistance in preparation of this manuscript.

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Lower extremity arteriography utilizing iodinated contrast or gadodiamide to supplement CO2 angiography in patients with renal insufficiency. JVIR 2000;11:35 43. Gemmete JJ, Foraver AR, Kazanjian S, et al. Safety of large volume gadolinium angiography [abstract]. JVIR 2001;12(1):528. Harpur E, Worah D, Hals PA, et al. Preclinical safety assessment and pharmocokinetics of gadodiamide injection, a new magnetic resonance imaging contrast agent. Invest Radiol 1993;28:S28 43. Oksendal A, Hals P. Biodistribution and toxicity of MR imaging contrast media. J Magn Reson Imaging 1993;3:157 65. Tweedle MF. Physiochemical properties of gadoteridol and other magnetic resonance contrast agents. Invest Radiol 1992;27(S1):S2 6. Tweedle MF, Eaton S, Eckelman W, et al. Comparative chemical structure in pharmocokinetics of MRI contrast agents. Invest Radiol 1988;23(S1):S236 9. Cacheris WP, Quay SC, Rocklage SM. The relationship between thermodynamics and the toxicity of gadolinium complexes. 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Radiol Clin N Am 40 (2002) 711 728

Current technology and clinical applications of three-dimensional angiographyRichard P. Klucznik, MDDepartment of Radiology, Division of Interventional Neuroradiology, Baylor College of Medicine, The Methodist Hospital, 6565 Fannin Street, Houston, TX 77030-2707, USA

History of three-dimensional imaging There has been a recent evolution in the angiographic evaluation of patients with the development of three-dimensional (3D) rotational angiography. To understand this evolutionary process, it is worthwhile to understand the history of 3D imaging. The first 3D images were produced by a British scientist, Charles Wheatstone, in the 1830s. Other British inventors, David Brewster and the famous 3D photographer Louis Daguere, created photographs with dimension, providing the basis for much of 3D imaging. Two separate photographs of an individual object were taken 2.5 inches apart (the distance between a humans pupils). Using stereoscope lenses, which directed the image to its corresponding eye, the images were viewed side by side, giving the perception of depth. By the early 20th century, 3D photography was commonplace. William Gruber, an organ maker from Portland, OR, and Harold Graves created a device that became known as The Viewmaster. The Viewmaster was designed principally for taking scenic photography, but it came into prominence during World War II when it was used to produce pictures for the United States government to aide in military site identification and range estimation. In 1952, 3D cinema began with the films Bwana Devil and House of Wax. The world of 3D imagery in medicine also has changed dramatically. With the need for precise anatomic definition, 3D imaging has grown slowly

from holographic images of the spine to true 3D pictures of the body using a variety of cross-sectional modalities. Digital subtraction angiography (DSA) has made great advances and has gradually become the gold standard for the delineation of vascular anatomy. With the development of endovascular treatments for occlusive vascular disease, aneurysms, arteriovenous malformations, and tumors, it became necessary to visualize the specific and detailed vascular anatomy on a more real-time basis. Threedimensional angiography was first proposed by Cornelius and advanced into clinical practice by Voigt in 1975 [1]. Since then, a variety of improvements have been developed as a result of the increased speed and data transfer afforded by modern computers. Recent publications by Fahrig and others [2 6] have brought 3D angiographic imaging to the forefront. The 3D evaluation of cerebral aneurysms and arteriovenous malformations no longer is a clinical curiosity, but an absolute necessity.

Techniques In the Endovascular Center, Department of Radiology at The Methodist Hospital (Houston, TX), all 3D rotational studies are performed on a biplane neuroangiography unit (Neurostar Plus, Siemens, Erlangen, Germany). The procedure can be performed with the patient awake using neuroleptic analgesia. The best images, however, are obtained with the patient under general anesthesia, where absolute control of the patients movements and respiration is maintained. The patient is situated in the isocenter of the C-arm of the angiographic unit.

E-mail address: [email protected] (R.P. Klucznik).


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R.P. Klucznik / Radiol Clin N Am 40 (2002) 711728

Fig. 1. A diagramatic representation of the C-arm movement during an acquisition. The first 200 C-arm provides the mask images. With a prolonged contrast injection, the return sweep of the C-arm acquires the data for creation of the 3D images.

Fig. 2. The approximate contrast injection for the varied parameters. All images are obtained using Omnipaque 300 mg/ml (Amersham Health, Princeton, NJ). The contrast flow rates and duration of contrast injection match the speed of rotation with a more prolonged injection for a 14-second acquisition.


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Fig. 3. Adjusting the speed of rotation to more than 40/ second results in decreased image sharpness. The optimumimaging mode for the 3D acquisition is approximately 40. A 20 swing offers good spatial resolution, but may involve higher contrast loads.

The C-arm rotates in a continuous 200 arc around the patients head in a period of 5 seconds. The initial acquisition phase has two actions. The first sweep of the C-arm acts as the mask for the subsequent data acquisition during the injection of contrast. The return sweep of the C-arm in an arc of 200 is performed while contrast is injected during the

entire period of data acquisition (Fig. 1). The rotating C-arm is calibrated for correction of distortion as a result of deviations in the rotational path. For cerebral arteriography, the usual injection is approximately 2.5 to 3 mL/second for a total of 30 to 35 mL (Fig. 2). Abdominal imaging requires higher contrast injection rates, with a typical rate of 10 mL /second for a total of 150 mL. The speed of rotation can be varied, with the rate selected based on the area of interest. The rotational speed can be 5, 8, or 14 seconds. All image acquisition is performed at a constant rate of 10 frames/ second. Therefore, depending on the speed of rotation, the number of projection images is between 50 and 140 images. The maximum rotational speed is 40/second. There currently is no benefit to faster C-arm rotation. Increasing the speed of rotation to 60/second tends to decrease the resolution of the acquisition (Fig. 3). Typically, the image intensifier is set at either a 33- or 20-cm field of view. Once the acquisition is performed, the images are transferred via a high-speed data link to the 3D Virtuoso workstation (Siemens Medical), which can perform high-speed data manipulation. The 2D images are then converted into pseudo-computed tomography (CT) slices using the convolution back projection technique (fan beam principle). Instead of

Fig. 4. Strother has quantified the accuracy of 3D angiographic imaging relative to intravascular ultrasound using a bifurcation model of an aneurysm (Courtesy of Charles Strother, MD, University of Wisconsin).

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Fig. 5. The pitfall with 3D pictures is the potential of inappropriate window and level settings obscuring anatomic detail on the images. If the viewing parameters are set to create shadows, the size of the dome and neck of tan aneurysm may be underestimated. If the window and level are set to bright, the dome size and neck measurements may be overestimated (Courtesy of Charles Strother, MD, University of Wisconsin, 2001).

a CT detector, the Dynavision system (Siemens Medical) uses the image intensifier as a multiline detector. Specific algorithms are performed to correct

for image intensifier and contrast distortion. The data is reconstructed into a volume-rendered technique (VRT) (Fig. 4). In addition, other methods visualize

Fig. 6. Biplane digital angiography dose is listed on the left side of the chart. As one proceeds from a 5-second to 14-second acquisition, the dose with the 3D angio increases, but not significantly above that of a routine biplane digital subtraction acquisition.


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the images, including surface-shaded display (SSD), maximum intensity projection (MIP), or multiplanar reformatting (MPR) (Fig. 7). The most beneficial and widely-used postprocessing technique is the volumerendered technique, where the image is viewed at any chosen angle. True stereo 3D images with depth can be seen at the computer monitor, using glasses manufactured by Stereographics Corp (Crystal Eyes III, Stereographics Corp, San Raphael, CA). The Virtuoso workstation

manipulates the images and transfers them to each corresponding eye at a rate of speed fast enough to allow for the perception of depth. All 3D imaging is based on the principle that if images are separated by 7 or more, they can be viewed in stereo. In a 14-second acquisition, more than 260 images are obtained, including the mask images. Therefore, true stereoscopic images can be rendered in any projection. In the initial acquisition phase, before the transfer is made to the Virtuoso workstation, the

Fig. 7. Some of the methods to display intracranial aneurysms are illustrated. The typical representation (A) is a volume-rendered (VR) acquisition, which has exquisite anatomic delineation. This is a carotid terminus aneurysm with a relatively wide patulous neck that extends directly superiorly. The vessels can be made radiolucent (shadow) in order to evaluate to the aneurysm neck (B). Notice some contrast resolution is lost with this technique, and one may underestimate the size of the neck, but it still can be useful for seeing the entrance into the aneurysm in an end-on position. A grid can be used, which accurately depicts vessel size (C). In addition, direct distance measurements can be made on the VR image. Another aneurysm is used to show that a geometric box can be placed on the image (D), which delineates all quadrants, so that while reviewing the image in real time, a sense of orientation can be maintained.

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Fig. 8. A single image from a biplane acquisition (A) shows a large left paraophthalmic segment aneurysm with a wide patulous neck. The 3D images (B,C) illustrate how the anatomic delineation of the true size and nature of the aneurysm is visualized as it extends over the cribriform plate, and the true size of the neck is identified. The indentations on the fundus are from intra-aneurysmal clot. Comparison can then be made to a 3D CT acquisition (D,E), which may show the overall relationship of the aneurysm and the remainder of the cerebral vasculature to the bone of the cribriform plate and anterior cranial fossa. The 3D CT does not have the contrast and spatial resolution necessary to decide the planned treatment. The wide patulous nature of the neck excludes the patient from constructive endovascular treatment. The patient requires either an attempt at surgical clipping or parent vessel occlusion.


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images can be delivered either in a subtracted or a nonsubtracted mode. Transferring images in the subtracted mode naturally will double the transfer and volume reconstruction time. The total process from the acquisition of data to the rendering of 3D images varies, depending on the mode selected. The fastest method is a 5-second acquisition transferred in a

nonsubtracted mode, where the reconstruction time can be as little as 5 minutes. If, however, one selects a 14-second acquisition delivered in a subtracted mode, the total time from acquisition to image rendering can be as long as 15 minutes. Conspicuity is a combination of spatial and contrast resolution. The typical spatial resolution in

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Fig. 9. Middle cerebral artery aneurysms may be difficult to treat via an endovascular approach as branches of the middle cerebral artery often originate from the aneurysm base. Multiple digital-subtraction acquisition runs are usually necessary to quantify the aneurysm neck. A single image from the biplane acquisition is represented, showing the irregular nature of the ruptured aneurysm. The 3D acquisition allows quantification of the true size of the neck, making endovascular treatment of this aneurysm possible.

the isotropic volume obtained is between 0.2 and 0.3 mm. Even smaller objects (eg, microcatheter systems) may be visible although not fully resolved. The limitations in spatial resolution are secondary to patient movement, breathing, swallowing, and hemodynamics, including cardiac output. Other limitations include C-arm reproducibility, as the system may not remain in perfect calibration. The selected volume of interest is set at the workstation and adjusted to outline the specific region of interest

(ie, the anterior communicating artery rather than the entire cerebral vasculature) and is used to determine the theoretical resolution. Most reconstruction algorithms involve a 256 256 matrix. Higher matrices are available (512 512 and 1024 1024) but involve a longer reconstruction time for little overall increase in resolution. The contrast resolution depends on the speed and volume of contrast injection. Three-dimensional imaging requires an increased volume of contrast


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injection. For neuroimaging, 35 mL is injected for a single acquisition. Abdominal imaging can require 120 to 150 mL of contrast for a single acquisition. The resolution also depends on the number of projections obtained and the radiation dose setting (quantum noise is a function of the dose setting on the digital equipment). There also are choices for recontruction algorithms (sharp versus smooth). The sharp (or edge-enhancement algorithm) is used

mostly when metallic devices, stents, or surgical clips are in the field of the view. This algorithm increases the dose to produce a sharper image. There is always a question of accuracy of images procured. The accuracy of rotational angiography has been compared with intravascular ultrasound (IVUS) in an animal model (Charles Strothers, MD, University of Wisconsin, personal communication, 2001). An excellent correlation between the measurements

Fig. 10. In patients who harbor multiple intracranial aneurysms, delineation of the nature of each aneurysm is difficult, because they begin to overlie each other on different projections. This patient harbors three aneurysms on the left side, which cannot fully be appreciated on the digital acquisition runs. (A) The patient harbored two additional aneurysms on the right, one of which was treated via an endovascular approach at the time of rupture. The 3D images (B,C) are two rotated views and can be compared with the single digital subtracted angiographic image. Here, all three aneurysms are visualized, the necks delineated, and the relationship to the internal carotid identified. On the Virtuoso workstation, these images are manipulated into any angle, allowing quantification of any of the three aneurysms before deciding on a treatment course. The left posterior communicating artery aneurysm was treated via an endovascular approach. The patient is to return for possible endovascular treatment of the remaining aneurysms.

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obtained with MPR, 3D angiography, and intravascular ultrasound is found (Fig. 4). A pitfall is seen when inappropriate window/level settings are used to film or review the study, especially when the region of interest, such as aneurysm neck and fundus, is artifactually narrow (Fig. 5). Always of concern is radiation dosage (skin dose) to patients. Radiation dose for a 14-second acquisi-

tion is similar to that of a biplane digital subtraction acquisition during a routine cerebral arteriogram. The parameters used are 3 frames/second for the first 4 seconds, 2 frames/second for the next 4 seconds, and 1 frame/second until the venous phase is visualized. An 8-second acquisition approximates a singleplane acquisition of a cerebral angiogram. A 5-second acquisition has a radiation dose less than a single-plane

Fig. 11. Two posterior communicating artery aneurysms are illustrated. Both aneurysms are large in size, making it difficult to identify the origin of the posterior communicating artery itself. From the routine angiographic runs, the necks of both aneurysms seem patulous (A,C). In the first aneurysm (A,B), the actual size of the aneurysm neck is very small and the aneurysm has an overall heart-shaped appearance, easily treated via an endovascular approach. The second aneurysm (C,D) has a somewhat larger neck, but when the 3D images are rotated posteriorly, the origin of the posterior communicating artery clearly is identified. This patient also was treated successfully using endovascular techniques.


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acquisition; therefore, the radiation dose to the patient and the volume of contrast administered are well within defined safety limits (Fig. 6).

Clinical use Three-dimensional imaging has come to the forefront in the diagnosis and treatment of cerebral aneurysms and arteriovenous malformations because of the exquisite anatomic detail defined [7 13]. The important factors necessary for treatment of a cerebral aneurysm include neck size, morphology of the neck

and its relationship to surrounding vessels, and the origin of vessels from the aneurysm base (Figs. 8 15), as seen with middle cerebral artery or posterior communicating artery aneurysms. The 3D stereoscopic view and the surface shaded-display images of the aneurysm are imperative for defining the anatomy for all those practitioners involved in the treatment of aneurysms [5,10]. From an endovascular viewpoint, the true size of the neck determines whether the patient is a candidate for Guglielmi detachable coils (GDC) or a new liquid agent, such as Onyx. If the neck is patulous in nature or if vessels originate from the aneurysm base, surgical interven-

Fig. 12. An example of a carotid terminus aneurysm. The routine frontal projection of the angiogram (A) does not reflect the nature of the aneurysm as well as the 3D image (B). This view is then used to treat the aneurysm with platinum coils. The posttreatment single plane (C) view shows complete obliteration with preservation of the carotid terminus.

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tion is then required (Fig. 13). The 3D imaging then becomes important for a surgeon to plan not only the surgical approach, but also what type of clip may be

used. Because the patient is in isocenter and a true isotrophic volume is obtained, direct measurements are obtained on the screen. Therefore, the true size of

Fig. 13. Two anterior communicating artery aneurysms. The lateral view of a digital subtraction run (A) shows a large aneurysm that seems to have a small neck. Three successive views from the 3D images (B D), however, show that the aneurysm has a wide, patulous neck that encompasses the entire anterior communicating artery complex. The patient underwent successful surgical clipping. Having knowledge of the precise anatomy of the aneurysm was invaluable to the neurosurgeon for surgical planning. The anatomic findings at the time of the surgery correlated exactly to those on the 3D images. A second anterior communicating artery aneurysm (E,F) also is seen and can be treated either with endovascular techniques or surgically. The angiographic planes used for the endovascular treatment (E) matches the best image from the 3D acquisition (F).


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an aneurysm or arteriovenous malformation is determined. An accurate measurement of the degree of

stenosis and vessel size also can be directly obtained in preparation for stenting or carotid endarterectomy

Fig. 14. Superior hypophyseal artery aneurysms are difficult to approach surgically, because the treatment involves drilling through the anterior clinoid process. These aneurysms, however, usually are easily accessible via an endovascular approach. (A) This superior hypophyseal aneurysm has a relatively narrow neck (B) and is more easily discernible with the 3D study than with the routine biplane acquisitions. This also illustrates one of the features of the 3D imaging called surface shading, which may not increase any specific information, but does allow the images to have a more realistic appearance by adding a shaded-light appearance to the vessel.

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(Fig. 16). In those patients who have multiple aneurysms on a single vessel, 3D imaging supplants the innumerable views that may be required to obtain the relationship of all the aneurysms (Fig. 10). In this case, a single-shot 3D study would involve a lower contrast dose and radiation exposure. In the evaluation and treatment of cerebral and spinal arteriovenous malformations, 3D imaging is imperative in the definition of aneurysms and its feeding vessels, intranidal fistula, and relationship of the nidus to the draining veins [6]. The amount of information available in 3D and 3D stereo vastly overshadows a biplane DSA (Fig. 17). Whether planning endovascular, surgical, or radiation treat-

ment of the malformation, information as to the size of the nidus, the entrance of feeding pedicles, and the presence of intranidal draining veins, venous aneurysms, or fistulae is extremely important. With endovascular treatment, the feeding pedicles that may harbor intranidal fistula can be approached first, with subsequent treatment of the remaining or residual nidus. Any high-flow fistula, such as carotid-cavernous, dural, or spinal fistula may also be evaluated using 3D techniques (see Fig. 18). In abdominal-pelvic imaging, abdominal aortic aneurysms are easily demonstrated (Fig. 19), but the definition of anatomy sometimes may be limited because of patient motion and breathing artifacts.

Fig. 15. Dissections and dissecting aneurysms are some of the most difficult disease processes to evaluate and treat. The routine angiogram (A) shows a large fusiform dilatation of the basilar artery with a large pseudoaneurysm. The 3D images (B,C) better delineate the nature of the dissection and dissecting aneurysm. There were no surgical options once the true nature of the disease was identified. The patient underwent coiling of the pseudoaneurysm with parent vessel occlusion of both vertebral arteries, allowing retrograde flow to fill the basilar artery.


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Fig. 16. Because the 3D acquisition is isotropic in nature, true measurements are identified, which are useful in the evaluation of a stenosis for possible stenting. These are two separate patients with significant stenosis of the vertebrobasilar system. The first patient (A,B) shows a significant stenosis of the proximal basilar artery. The 3D pictures allow exact measurements so that a stent size is chosen accurately for placement across the area of stenosis. The second patient shows a significant stenosis of the distal vertebral artery, with poststenotic dilatation (C).

There is, however, the potential that with one injection of contrast, all the information necessary for treatment is obtained: the relationship of the aneurysm to the renal arteries, the number of renal arteries, the diameter and length of the aneurysm, the diameter and length of the infrarenal aortic neck, the degree of calcification or thrombus formation in the neck of the aneurysm, stenoses of celiac artery, renal anterior superior mesenteric artery (SMA), the patency of the inferior mesenteric artery, and the degree of involvement of the iliac arteries. In the future, with the advancement of endovascular stent-grafting for

the treatment of aortic aneurysmal disease, 3D imaging may be invaluable for detecting the site and significance of an endoleak and allow planning of the treatment.

Future plans Three-dimensional imaging is on the cusp of an evolutionary development in the evaluation of vascular lesions. The future will bring real-time 3D imaging during the performance of endovascular

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Fig. 17. The true microarchitecture of arteriovenous malformations can be delineated only on 3D imaging. This figure illustrates a small vermial arteriovenous malformation with two principal feeding arteries on the superior and inferior surfaces. With rotation, the entrance site is delineated. The venous drainage and fistula sites are delineated. The best method of evaluation, however, is true steroscopic imaging, which is only available at the Virtuoso workstation with the use of the Crystal Eyes# (Stereo Graphics Corp, San Raphael, CA) glasses, with which one perceives depth and identifies the architecture of

vascular imaging

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