Role of Multidetector CT(MDCT)

Dr. Peter JohnsonConsultant Radiologist

University Hospital of the West Indies

• What does MDCT mean ?

CT-Principle

Advantages of MDCT over SDCT

• Improved spatial resolution• Improved temporal resolution

MDCT & Spatial Resolution

• 16 Slice scanners : Isotrophic• No appreciable improvement in quality

(spatial resolution) with > 16 detectors

Multiplanar Reconstructions (MPR)

Multiplanar Reconstructions (MPR)

Multiplanar Reconstructions (MPR)

Multiplanar Reconstructions (MPR)

Volume Rendering

Surface Rendering

MDCT & Temporal Resolution

• > number of detectors, greater volume covered per unit time

• > number of detectors, faster scanning• Better for CTA and Cardiac (esp)• Advantage of 64 slice over 16 slice etc.

Temporal Resolution

• Useful for:– Vascular work eg. CTA, CTV– Phased scanning eg. Liver, Kidneys– Functional work eg. CT Perfusion, Cardiac CT

• Reduces scan time hence great for:– Uncooperative patients• SOB• Confused (eg. Head injury etc)• Paediatric

Reduced Frequency of Sedation of YoungChildren with Multisection Helical CTPappas John N., Donnelly Lane F., Frush Donald P.

CONCLUSION: The rate of sedation was reduced threefold with multisection helical CT compared with standard helical CT, and the need for sedation was eliminated in some age groups.

Radiology 2000; 215:897-899

Temporal Resolution

Clinical Applications

• General body imaging (Chest, Abdomen & Pelvis)• Trauma• CT Angiography (CTA)• Cardiac CT• Virtual Colonoscopy (and other virtual endoscopy)• CT perfusion• Other

Clinical Applications

• Cardiac….driving force in MDCT– CT Coronary Angiography– 4D Cardiac CT…..ventricular function etc.– Cardiac calcium scoring

Coronary CTA

Interpreting the evidence: How accurate is coronary computedtomography angiography?

Abstract: Coronary CT angiography (CTA) has evolved rapidly into a powerful diagnostic tool. More than 30 accuracy studies have reported accuracy results in >2000 patients. A meta-analysis of 29 studies found per-patient accuracy of 96% sensitivity, 74% specificity, 83% positive predictive value, and 94% negative predictive value. Several clinical studies support the safety and accuracy of coronary CTA for acute chest pain, after inconclusive stress testing, and in preoperative evaluation of patients before cardiac valve surgery. Accuracy studies suffer from selection bias because of the inclusion only of patients previously selected to undergo invasive angiography. This increases the incidence of true disease, raising apparent sensitivity and lowering negative predictive value, although the latter remains high at 94%. CTA has relatively low accuracy for the quantitative assessment of stenosis severity. CTA accuracy studies show high figures for sensitivity and negative predictive value in detection of coronary lesions. CTA less accurately shows lesion severity, and intermediate-grade lesions require physiologic evaluation. Clinical studies support the effectiveness of CTA for exclusion of significant coronary disease.

Gilbert L. RaffJournal of Cardiovascular Computed Tomography (2007) 1, 73-77

Coronary CTA

• High sensitivity and negative predictive value• Good selection tool for excluding patients

who are not candidates for invasive cardiac catheterization

• Good screening tool• Less acurate at demonstrating lesion severity– These patients need intervention anyways !

Coronary CTA• The greater the detectors….better temporal

resolution• MDCT scanners with greater detector numbers

perform better than lower numbers

Coronary Arteries: Diagnostic Performance of 16-versus 64-Section Spiral CTCompared with Invasive Coronary Angiography-Meta-Analysis

Conclusion: Sixty-four-section spiral CT has significantly higher specificity and PPV ona per-patient basis compared with 16-section CT for the detection of greater than 50% stenosis of coronary arteries.

Michele Hamon, MD Remy Morello, MD John W. Riddell, MD Martial Hamon, MDRadiology: Volume 245: Number 3-December 2007

Pulmunary Thrombo-embolism

– CT Pulmunary Angiography (CTPA) +/- CT venography

– Recommended by PIOPED II

CTPASuspected Acute Pulmonary Embolism: Evaluation with Multi-Detector RowCT versus Digital Subtraction Pulmonary Arteriography

PURPOSE: To determine diagnostic accuracy of four-channel multi-detector rowcomputed tomography (CT) in emergency room and inpatient populations suspectedof having acute pulmonary embolism (PE) who prospectively underwent both CT andpulmonary arteriography (PA).

CONCLUSION: Multi-detector row CT has an accuracy of 91% in the depiction ofsuspected acute PE when conventional PA is used as the reference standard.

Winer-Muram HT, Rydberg J, Johnson MS, Tarver RD, Williams MD, Shah H, Namyslowski J, Conces D, Jennings SG, Ying J,Trerotola SO, Kopecky KK.Radiology 2004; 233:806-815

Virtual Colonoscopy

• Utilizes endo-luminal rendering• Similar bowel prep as optical colonoscopy• No need for sedation

• Several studies demonstrate Virtual Colonoscopy performance on par with optical colonoscopy. Some indicate superior performance

Johnson CD, Dachman AH. CT colonography: the next colon screening examination. Radiology 2000;216:331–341

Macari M, Bini EJ, Milano A, et al. Clinical significance of missed polyps at CT colonography. AJR Am J Roentgenol2004;183:127–134.

Pickhardt PJ, Choi JR, Hwang I, et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia inasymptomatic adults. N Engl J Med 2003;349:2191–2200

Virtual Colonoscopy:Patient Tolerance

“Patients undergoing colorectal cancer screening prefer CT colonography to both colonoscopy and DCBE. The

majority of patients experience discomfort and inconvenience with cathartic bowel preparation.”

Thomas M. Gluecker, MD, C. Daniel Johnson, MD, William S. Harmsen, MS, Kenneth P. Offord, MS, Ann M. Harris, BA, Lynn A.Wilson, RN and David A. Ahlquist, MDRadiology 2003;227:378-384

“CT colonography was considered less painful and less difficult overall than colonoscopy and was thepreferred examination”Maria H. Svensson, MD, Elisabeth Svensson, PhD, Anders Lasson, MD and Mikael Hellström, MD, PhDRadiology 2002;222:337-345

“Patients preferred CT colonography to colonoscopy; however, this preference decreased in time, whileoutcome considerations gradually replaced temporary experiences of inconvenience”Rogier E. van Gelder, MD, Erwin Birnie, PhD, Jasper Florie, MD, Michiel P. Schutter, Joep F. Bartelsman, MD, Pleun Snel, MD, PhD,Johan S. Laméris, MD, PhD, Gouke J. Bonsel, MD, PhD and Jaap Stoker, MD, PhdRadiology 2004;233:328-337

Virtual Colonoscopy

Virtual Colonoscopy

Virtual Colonoscopy

• No established international or even national protocol for:– Performing study– Evaluating and reporting studies

• Some differences in performance of VC software by manufacturer

Virtual Colonoscopy

• Problems:– Poor detection rate for “flat” lesions– Artefacts– No consensus in performance and reporting of

studies– No tissue sampling– Patient compliance– Cost

Virtual Colonoscopy

• Current Established Indications:– Failed Optical Colonoscopy (OTC)– Evaluation of colon proximal to an obstructing

lesion– Patients with contraindications to OTC

• Future:– Screening….pending outcomes of Trials

Brain Imaging

• MDCT rarely adds to routine brain imaging• Useful for:– CTA (SAH)– CT perfusion (Stroke)– ENT imaging

Cerebral CTA

• Has replaced catheter angiography as the initial evaluation of the cause of acute subarachnoid haemorrhage in many centres

Cerebral CTAMDCT Angiography for Detection and Quantification of Small IntracranialArteries: Comparison with Conventional Catheter Angiography

CONCLUSION: Except for the recurrent artery of Heubner and the anteriorchoroidal artery, MDCT angiography depicted 90% or more of all examinedsmall intracranial arteries detected with digital subtraction angiography.

Themean sensitivity was 0.91, and the mean specificity was 0.7.

Villablanca JP, Rodriguez FJ, Stockman T, Dahliwal S, Omura M, Hazany S, Sayre J.AJR 2007; 188:593-602

Cerebral CTA

Intracranial Aneurysms: Role of Multidetector CT Angiographyin Diagnosis and Endovascular Therapy Planning

Conclusion: Multidetector CT angiography offers high diagnostic accuracy-equivalent to that of DSA-in the detection of intracranial aneurysms. Also,the possibility of coil embolization can be reliably determined with

multidetector CT angiography.

Karsten Papke, MD Christian K. Kuhl, MD Martin Fruth, MD Cornel Haupt, MD Martin Schlunz-Hendann, MDDieter Sauner, MD Martin Fiebich, PhD Alan Bani, MD Friedhelm Brassel, MDRadiology: Volume 244: Number 2-August 2007

Peripheral CTA

• Good non-invasive tool for evaluating peripheral arterial disease.

Peripheral CTAAortoiliac and Lower Extremity Arteries Assessed with 16–Detector Row CTAngiography: Prospective Comparison with Digital Subtraction Angiography

“In this study, the improved spatial resolution obtained with a 16–detector row CTscanner is reflected in the total sensitivity and specificity (96% and 97%, respectively,for both readers) in the detection of hemodynamically significant arterial stenosis ofaortoiliac and lower extremity arteries. In particular, excellent sensitivities (ie, 96% and97% for readers 1 and 2, respectively) and specificities (ie, 95% and 96% for readers 1and 2, respectively) for grading small popliteocrural arteries were obtained in thisstudy”

Jürgen K. Willmann, MD, Bernhard Baumert, MD, Thomas Schertler, MD, Simon Wildermuth, MD, Thomas Pfammatter, MD,Francis R. Verdun, PhD, Burkhardt Seifert, PhD, Borut Marincek, MD and Thomas Böhm, MDRadiology 2005;236:1083-1093

Peripheral CTA

Whole Body CT

Cost-effectiveness of Whole-Body CT Screening

“Compared with routine care, whole-body CTscreening provided minimal gains in life expectancy(0.016 6 years or 6 days) at an average additional costof $2513 per patient, or an incremental costeffectiveness ratio of $151 000 per life-year gained”

Molly T. Beinfeld, MPH, Eve Wittenberg, PhD and G. Scott Gazelle, MD, MPH, PhD

However….

• MDCT is not indicated for everything !• It isn’t indicated at all in certain cicumstances• Not the study of choice in many circumstances• Should be used with caution in some

circumstances

e.g.

Not the study of Choice:

• MRI:– Intra and extra-axial intracranial tumours– Congenital brain anomalies– Myelopathy & Radiculopathy (Traumatic & Non-

traumatic)

Not the study of Choice:

• Ultrasound:– Initial evaluation of neonatal intracranial events

e.g. Germinal Matrix Haemorrhage (CT not indicated for this pathology), ? Hydrocephalus.

– Acute gynecologic events e.g. ? Ectopic, ruptured ovarian cysts, ovarian torsion

Use with caution……

• Pregnant patients (especially 1st trimester)• Paediatric patients

Radiation Effects

Radiation Dose“On the basis of such risk estimates and data on CT use from 1991 through1996, it has been estimated that about 0.4% of all cancers in the United

Statesmay be attributable to the radiation from CT studies. By adjusting thisestimate for current CT use, this estimate might now be in the range of 1.5 to2.0%”

David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc.NEJM 2007; 357:2277-2284

Radiation Risks

Radiation Dose

“Relative to CT scanners from the early 1990s,present-day MDCT scanners result in doses thatare ~1.5 and -1.7 higher per unit mAs in headand body phantoms, respectively.”

Huda W, Vance AAJR 2007; 188:540-546

However……..

• To date, no example of cancer definitely attributable to exposure to diagnostic x-ray doses has been reported.

• Data represent extrapolated risk estimates related to known cancer incidences from exposure at Hiroshima and “therapeutic Xray treatments” in the early 20th century.

Radiation

• Care and good judgement should be excersised….esp. paediatric population.

• Risk/Benefit• Indications• Contraindications (including no indication !)

And so…….

• MDCT has revolutionized diagnostic imaging• Tremendous potential• High radiation dose• Not indicated for everything !• Not a replacement for other modalities

Thank you