aapm/rsna physics tutorial 1495 aapm/rsna physics … · ©rsna, 2007 note: this copy is for your...

of 18 /18
AAPM/RSNA PHYSICS TUTORIAL 1495 AAPM/RSNA Physics Tuto- rial for Residents Physics of Cardiac Imaging with Multiple-Row Detector CT 1 Mahadevappa Mahesh, MS, PhD Dianna D. Cody, PhD Cardiac imaging with multiple-row detector computed tomography (CT) has become possible due to rapid advances in CT technologies. Images with high temporal and spatial resolution can be obtained with multiple-row detector CT scanners; however, the radiation dose asso- ciated with cardiac imaging is high. Understanding the physics of car- diac imaging with multiple-row detector CT scanners allows optimiza- tion of cardiac CT protocols in terms of image quality and radiation dose. Knowledge of the trade-offs between various scan parameters that affect image quality—such as temporal resolution, spatial resolu- tion, and pitch—is the key to optimized cardiac CT protocols, which can minimize the radiation risks associated with these studies. Factors affecting temporal resolution include gantry rotation time, acquisition mode, and reconstruction method; factors affecting spatial resolution include detector size and reconstruction interval. Cardiac CT has the potential to become a reliable tool for noninvasive diagnosis and pre- vention of cardiac and coronary artery disease. © RSNA, 2007 Abbreviations: ECG electrocardiographic, MPR multiplanar reformation, 3D three-dimensional RadioGraphics 2007; 27:1495–1509 Published online 10.1148/rg.275075045 Content Codes: 1 From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, 601 N Caroline St, Baltimore, MD 21287-0856 (M.M.); and the Department of Imaging Physics, University of Texas M. D. Anderson Cancer Center, Houston, Tex (D.D.C.). From the AAPM/RSNA Physics Tutorial at the 2005 RSNA Annual Meeting. Received March 12, 2007; revision requested April 4 and received May 21; accepted June 8. M.M. receives research support from Siemens; D.D.C. is a speaker for the Medical Technology Management Insti- tute, Milwaukee, Wis. Address correspondence to M.M. (e-mail: [email protected]). © RSNA, 2007 Note: This copy is for your personal, non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, use the RadioGraphics Reprints form at the end of this article.

Author: others

Post on 22-May-2020

2 views

Category:

Documents


0 download

Embed Size (px)

TRANSCRIPT

  • AAPM/RSNA PHYSICS TUTORIAL 1495

    AAPM/RSNA Physics Tuto-rial for ResidentsPhysics of Cardiac Imaging withMultiple-Row Detector CT1

    Mahadevappa Mahesh, MS, PhD ● Dianna D. Cody, PhD

    Cardiac imaging with multiple-row detector computed tomography(CT) has become possible due to rapid advances in CT technologies.Images with high temporal and spatial resolution can be obtained withmultiple-row detector CT scanners; however, the radiation dose asso-ciated with cardiac imaging is high. Understanding the physics of car-diac imaging with multiple-row detector CT scanners allows optimiza-tion of cardiac CT protocols in terms of image quality and radiationdose. Knowledge of the trade-offs between various scan parametersthat affect image quality—such as temporal resolution, spatial resolu-tion, and pitch—is the key to optimized cardiac CT protocols, whichcan minimize the radiation risks associated with these studies. Factorsaffecting temporal resolution include gantry rotation time, acquisitionmode, and reconstruction method; factors affecting spatial resolutioninclude detector size and reconstruction interval. Cardiac CT has thepotential to become a reliable tool for noninvasive diagnosis and pre-vention of cardiac and coronary artery disease.©RSNA, 2007

    Abbreviations: ECG � electrocardiographic, MPR � multiplanar reformation, 3D � three-dimensional

    RadioGraphics 2007; 27:1495–1509 ● Published online 10.1148/rg.275075045 ● Content Codes:

    1From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, 601 N Caroline St,Baltimore, MD 21287-0856 (M.M.); and the Department of Imaging Physics, University of Texas M. D. Anderson Cancer Center, Houston, Tex(D.D.C.). From the AAPM/RSNA Physics Tutorial at the 2005 RSNA Annual Meeting. Received March 12, 2007; revision requested April 4 andreceived May 21; accepted June 8. M.M. receives research support from Siemens; D.D.C. is a speaker for the Medical Technology Management Insti-tute, Milwaukee, Wis. Address correspondence to M.M. (e-mail: [email protected]).

    ©RSNA, 2007

    Note: This copy is for your personal, non-commercial use only. To order presentation-ready copies for distribution to your colleagues or clients, use the RadioGraphics Reprints form at the end of this article.

  • IntroductionCoronary heart disease (CHD) represents themajor cause of morbidity and mortality in West-ern populations (1). In 2003 alone, more than450,000 deaths were associated with CHD in theUnited States; that translates to nearly one of ev-ery five deaths (1). The economic burden onhealth care due to CHD is also enormous. Ad-vances in multiple-row detector computed to-mography (CT) technology have made it feasiblefor imaging the heart and to evaluate CHD non-invasively. Calcium scoring, CT angiography,and assessment of ventricular function can beperformed with multiple-row detector CT (2).Coronary artery calcium scoring (3,4) allows pa-tients at intermediate risk for cardiovascularevents to be risk stratified. Coronary arterial anat-omy and both noncalcified and calcified plaquesare visible at coronary CT angiography (5,6).Vessel wall disease and luminal diameter are de-picted, and secondary myocardial changes mayalso be seen (5–7).

    Even though the prime diagnostic tool toevaluate and treat CHD is coronary angiography(an x-ray fluoroscopy–guided procedure) and thefluoroscopically guided images are considered thestandard of reference for comparing coronary ar-tery image quality, the procedure is invasive andrequires longer examination times than CT an-giography, including patient preparation and re-couping times. Images obtained with 16-row and16�-row detector CT scanners are increasinglybecoming comparable to those of the standard ofreference (8).

    The prospect of imaging the heart and coro-nary arteries with CT has been anticipated sincethe development of CT more than 3 decades ago.The lack of speed and poor spatial and temporalresolution of previous generations of CT scannersprevented meaningful evaluation of the coronaryarteries and cardiac function. Most early assess-ments of the coronary arteries with CT were per-formed with electron beam CT, developed in theearly 1980s (9). Electron beam CT has been usedmostly for noninvasive evaluation of coronaryartery calcium (10), but other applications in-cluding assessment of coronary artery stenosishave been reported in limited cases. However,electron beam CT is expensive and is not widelyavailable.

    Recent advances in CT technologies, especiallymultiple-row detector CT, have dramaticallychanged the approach to noninvasive imaging ofcardiac disease. With submillimeter spatial reso-

    lution (�0.75 mm), improved temporal resolu-tion (80–200 msec) (11), and electrocardio-graphically (ECG) gated or triggered mode ofacquisition, the current generation of CT scan-ners (16–64-row detectors) makes cardiac imag-ing possible (12–17) and has the potential to ac-curately characterize the coronary tree.

    The purpose of this article is to describe thephysics of cardiac imaging with multiple-row de-tector CT. The factors affecting temporal andspatial resolution are discussed along with scanacquisition and reconstruction methods, recon-struction algorithms, reconstruction interval,pitch, radiation dose, and geometric efficiency.

    Key Issues in Cardiac Imag-ing with Multiple-Row Detector CT

    The primary challenge required to image a rap-idly beating heart is that the imaging modalityshould provide high temporal resolution. It isnecessary to freeze the heart motion in order toimage coronary arteries located close to heartmuscles, since these muscles show rapid move-ment during the cardiac cycle. Since the mostquiescent part of the heart cycle is the diastolicphase, imaging is best if performed during thisphase. Hence, it is required to monitor the heartcycle during data acquisition. The subject’s elec-trocardiogram (ECG) is recorded during scan-ning because the image acquisition and recon-struction are synchronized with the heart motion.Also, the imaging modality should provide highspatial resolution to resolve very fine structuressuch as proximal coronary segments (right coro-nary ascending and left anterior descending arter-ies) that run in all directions around the heart.These requirements impose greater demands onmultiple-row detector CT technology. One ofthe primary goals of the rapid development ofCT technology has been to achieve these de-mands in order to make cardiac CT imaging aclinical reality.

    Understanding thePhysics of Cardiac Imaging

    To better demonstrate and understand the neces-sity for high temporal resolution in cardiac imag-ing, Figure 1 shows how the length (in time) ofthe diastolic phase changes with heart rates. Theleast amount of cardiac motion is observed duringthe diastolic phase; however, the diastolic phasenarrows with increasing heart rate. With rapidheart rates, the diastolic phase narrows to such anextent that the temporal resolution needed to im-age such subjects is less than 100 msec. The de-

    1496 September-October 2007 RG f Volume 27 ● Number 5

  • sired temporal resolution for motion-free cardiacimaging is 250 msec for heart rates up to 70 beatsper minute and up to 150 msec for heart ratesgreater than 100 beats per minute. Ideally, mo-tion-free imaging for all phases requires temporalresolution to be around 50 msec. The standard ofreference for comparing the temporal resolutionobtained with multiple-row detector CT is fluo-roscopy, wherein the heart motion is frozen dur-ing dynamic imaging to a few milliseconds (1–10msec). Therefore, the demand for high temporalresolution implies decreased scan time requiredto obtain data needed for image reconstructionand is usually expressed in milliseconds.

    The demand for high spatial resolution thatenables the visualization of various coronary seg-ments (such as the right coronary artery, left ante-rior descending artery, and circumflex artery) thatrun in all directions around the heart with de-creasing diameter is high. These coronary seg-ments range from a few millimeters in diameter(at the apex of the aorta) and decrease to a fewsubmillimeters in diameter as they traverse awayfrom the aorta in all directions. The need to im-age such small coronary segments requires smallvoxels, and this is key to cardiac imaging withmultiple-row detector CT. Spatial resolution isgenerally expressed in line pairs per centimeter orline pairs per millimeter. Like temporal resolu-tion, the standard of reference for comparing spa-tial resolution is the resolution obtained duringfluoroscopy. However, one of the major goals ofmultiple-row detector CT technology develop-

    ment has been to obtain similar spatial resolutionin all directions, also expressed as isotropic spatialresolution (18).

    In addition, a sufficient contrast-to-noise ratiois required to resolve small and low-contraststructures such as plaques. In CT, low-contrastresolution is typically excellent. However, it candegrade with the increasing number of CT detec-tors in the z direction due to increased scatteredradiation that can reach detectors in the z direc-tion. It is important to achieve adequate low-con-trast resolution with minimum radiation expo-sure. The need to keep radiation dose as low asreasonably possible is essential for any imagingmodality that uses ionizing radiation.

    Overall, cardiac imaging is a very demandingapplication for multiple-row detector CT. Tem-poral, spatial, and contrast resolution must all beoptimized with an emphasis on minimizing radia-tion exposure during cardiac CT imaging.

    Temporal ResolutionThere are a number of factors that influence thetemporal resolution achieved with multiple-rowdetector CT scanners. Among them, the key fac-tors are the gantry rotation time, acquisitionmode, type of image reconstruction, and pitch.

    Gantry Rotation TimeGantry rotation time is defined as the amount oftime required to complete one full rotation (360°)of the x-ray tube and detector around the subject.The advances in technology have considerablydecreased the gantry rotation time to as low as330–370 msec. The optimal temporal resolutionduring cardiac imaging is limited by the gantryrotation time. The faster the gantry rotation, thegreater the temporal resolution achieved. How-ever, with increasing gantry rotation speed, thereis also an increase in the stresses on the gantrystructure, since rapid movement of heavy me-chanical components inside the CT gantry resultsin higher G forces, making it harder to achieve afurther reduction in gantry rotation time. In fact,even a small incremental gain in the gantry rota-tion time requires great effort in the engineeringdesign.

    In the past, the minimum rotation time was ashigh as 2 seconds; in the past few years, gantryrotation time has decreased steadily to less than400 msec. As discussed in the previous sectionand in Figure 1, since the currently available gan-try rotation time is not in the desired range forobtaining reasonable temporal resolution, various

    Figure 1. Diagram shows the range of diastolicregions for varying heart rates. The desired tem-poral resolution for cardiac CT is approximately250 msec for average heart rates of less than 70beats per minute; for higher heart rates, the de-sired temporal resolution is approximately 100msec.

    RG f Volume 27 ● Number 5 Mahesh and Cody 1497

  • methods have been developed to compensate,such as different types of scan acquisitions or im-age reconstructions to further improve temporalresolution.

    Acquisition ModeFor imaging the rapidly moving heart, projectiondata must be acquired as fast as possible in orderto freeze the heart motion. This is achieved inmultiple-row detector CT either by prospectiveECG triggering or by retrospective ECG gating(19).

    Prospective ECG Triggering.—This is similarto the conventional CT “step and shoot” method.The patient’s cardiac functions are monitoredthrough ECG signals continuously during thescan. The CT technologist sets up the subjectwith ECG monitors and starts the scan. Instruc-tions are built into the protocol to start the x-raysat a desired distance from the R-R peak, for ex-ample at 60% or 70% of the R-R interval. Thescanner, in congruence with the patient’s ECGpulse, starts the scan at the preset point in theR-R internal period (Fig 2). The projection dataare acquired for only part of the complete gantryrotation (ie, a partial scan).

    The minimum amount of projection data re-quired to construct a complete CT image is 180°plus the fan angle of the CT detectors in the axialplane. Hence, the scan acquisition time dependson the gantry rotation time. The best temporal

    resolution that can be achieved in the partial scanmode of acquisition is slightly greater than half ofthe gantry rotation time. Once the desired dataare acquired, the table is translated to the nextbed position and, after a suitable and steady heartrate is achieved, the scanner acquires more pro-jections. This cycle repeats until the entire scanlength is covered, typically 12–15 cm (dependingon the size of the heart).

    With multiple-row detector CT, the increasingnumber of detectors in the z direction allows alarger volume of the heart to be covered per gan-try rotation. For example, using a multiple-rowdetector CT scanner capable of obtaining 16 axialsections (16 rows of detectors with 16 data acqui-sition system channels in the z direction) and witheach detector width of 0.625 mm, one can scan a10-mm (16 � 0.625-mm) length per gantry rota-tion. Similarly, with a 64-section multiple-rowdetector CT scanner (64 rows of detectors with64 data acquisition system channels) and eachdetector 0.625 mm wide, one can scan about 40mm per gantry rotation. Typically, the cardiacregion ranges from 120 to 150 mm, which can becovered in three to four gantry rotations with a64-row detector CT scanner. This has a majoradvantage in terms of the decreased time requiredfor breath holding to minimize motion artifacts(critical when scanning sick patients).

    One of the advantages of the prospective trig-gering approach is reduced radiation exposure,because the projection data are acquired for shortperiods and not throughout the heart cycle. Tem-poral resolution with this type of acquisition canrange from 200 to 250 msec. Prospective trigger-

    Figure 2. During the prospectiveECG-triggered scan mode, the pa-tient’s ECG is continuously moni-tored but the x-rays are turned on atpredetermined R-R intervals to ac-quire sufficient scan data for imagereconstruction. The table is thenmoved to the next location for fur-ther data acquisition. These types ofscans are always sequential and nothelical and result in a lower patientdose because the x-rays are on for alimited period. Calcium scoringscans are typically performed in thisscan mode.

    1498 September-October 2007 RG f Volume 27 ● Number 5

    TeachingPoint Teaching

    Point

    Teaching PointThe minimum amount of projection data required to construct a complete CT image is 180° plus the fan angle of the CT detectors in the axial plane.

    Teaching PointOne of the advantages of the prospective triggering approach is reduced radiation exposure, because the projection data are acquired for short periods and not throughout the heart cycle.

  • ing is the mode of data acquisition used for cal-cium scoring studies, since calcium scoring analy-sis is typically performed in axial scan mode. Thescan technique such as tube current (milliam-peres) for a calcium scoring protocol can be quitelow, yielding low radiation dose, since calciumhas a high CT number and is easily visible evenwith a noisier background. Also, each data set isobtained during the most optimal ECG signal toreduce motion artifacts.

    Retrospective ECG Gating.—Retrospectivegating is the main choice of data acquisition incardiac coronary artery imaging with multiple-row detector CT. In this mode, the subject’sECG signals are monitored continuously and theCT scan is acquired continuously (simulta-neously) in helical mode (Fig 3). Both the scanprojection data and the ECG signals are re-corded. The information about the subject’s heartcycle is then used during image reconstruction,which is performed retrospectively, hence thename retrospective gating. The image reconstruc-tion is performed either with data correspondingto partial scan data or with segmented reconstruc-tion.

    In segmented reconstruction, data from differ-ent parts of the heart cycle are chosen, so that thesum of the segments equates to the minimal par-tial scan data required for image reconstruction.This results in further improvements in temporal

    resolution. Temporal resolution with this type ofacquisition can range from 80 to 250 msec.

    The disadvantage of the retrospective gatingmode of acquisition is the increased radiationdose, because the data are acquired throughoutthe heart cycle, even though partial data are actu-ally used in the final image reconstruction. Also,since this scan is performed helically, the tissueoverlap specified by the pitch factor is quite low,indicating excessive tissue overlap during scan-ning, which also increases radiation dose to thepatients. The need for low pitch values or exces-sive overlap is determined by the need to haveminimal data gaps in the scan projection data re-quired for image reconstruction. The need forlow pitch values is discussed in detail in the sec-tion on pitch.

    Reconstruction MethodCardiac data acquired with either prospectiveECG triggering or retrospective ECG gating areused in reconstructing images. High temporalresolution images are obtained by reconstructingthe data either with partial scan reconstruction orwith multiple-segment reconstruction.

    Partial Scan Reconstruction.—Among themethods of image reconstruction in cardiac CT,the most practical solution is the partial scan

    Figure 3. During the retrospectiveECG-gated scan mode, the patient’sECG is continuously monitored andthe patient table moves through thegantry. The x-rays are on continu-ously, and the scan data are col-lected throughout the heart cycle.Retrospectively, projection datafrom select points within the R-Rinterval are selected for image recon-struction. Radiation dose is higher inthis type of scan mode comparedwith that in the prospective trigger-ing mode. Pos � position.

    RG f Volume 27 ● Number 5 Mahesh and Cody 1499

    TeachingPoint

    Teaching PointThe disadvantage of the retrospective gating mode of acquisition is the increased radiation dose, because the data are acquired throughout the heart cycle, even though partial data are actually used in the final image reconstruction.

  • reconstruction. Partial scan reconstruction canbe used for both prospective triggering and retro-spective gating acquisitions. The minimumamount of data required to reconstruct a CT im-age is at least 180° plus the fan angle of data inany axial plane. This determines the scan time toacquire projection data needed for partial scanreconstruction and also limits the temporal reso-lution that can be achieved from an acquisition.The CT detectors in the axial plane of acquisitionextend in an arc that covers at least a 30°–60° fanangle. Therefore, during partial scan reconstruc-tion, the scan data needed for reconstruction areobtained by rotating the x-ray tube by 180° plusthe fan angle of the CT detector assembly (Fig 4).

    If the gantry rotation time is 500 msec, thetime required to obtain the minimum scan data isslightly greater than half of the gantry rotationtime. This means that, for a gantry rotation of500 msec, the scan time for acquiring data forpartial scan reconstruction is around 260 to 280msec. This value represents the limit of temporalresolution that can be achieved through partialscan reconstruction. To achieve further improve-ments in temporal resolution, the CT manufac-turers are driving scanner gantry rotation timefaster and faster. To date, the fastest commer-cially available gantry rotation time is 330 msec.In such scanners, the partial scan reconstructiontemporal resolution can be as high as 170–180msec. At the same time, the G force generateddue to rapid gantry motion is growing exponen-tially and is reaching a limit for the existing tech-nology. The demand for even higher temporalresolution has led to the development of dual-

    source CT, and some are even considering devel-oping multiple x-ray source CT scanners.

    Multiple-Segment Reconstruction.—The pri-mary limitation to achieving high temporal reso-lution with the partial scan approach is the gantryrotation time. To achieve even higher temporalresolution, multiple-segment reconstruction wasdeveloped (12). The principle behind multiple-segment reconstruction is that the scan projectiondata required to perform a partial scan recon-struction are selected from various sequentialheart cycles instead of from a single heart cycle(Fig 4). This is possible only with a retrospectivegating technique and a regular heart rhythm. TheCT projection data are acquired continuouslythroughout many sequential heart cycles.

    The multiple-segment reconstruction methodselects small portions of projection data from vari-ous heart cycles, so that when all the projectionsare combined, they constitute sufficient data toperform partial scan reconstructions. For ex-ample, if one chooses to select half of the data setrequired for partial scan reconstruction from oneheart cycle and the rest from another heart cycle,this results in temporal resolution that is aboutone-fourth of the gantry rotation time. This isdone by using projection data from two separatesegments of the heartbeat cycle for image recon-struction. Further improvement in temporal reso-lution can be achieved by cleverly selecting pro-jection data from three or four different heartcycles, resulting in temporal resolution as low as80 msec.

    In general, with multiple-segment reconstruc-tion, the temporal resolution can range from amaximum of TR/2 to a minimum of TR/2M,where TR is the gantry rotation time (seconds)

    Figure 4. Differences betweenpartial scan reconstruction versusmultiple-segment reconstruction.Top: During partial scan reconstruc-tion, sufficient data from a pre-scribed time range within the R-Rinterval of one cardiac cycle are se-lected for reconstruction. Bottom: Inmultiple-segment reconstruction,sufficient data segments of the samephase from multiple cardiac cyclesare selected for image reconstruc-tion. Higher temporal resolution(TR) can be achieved with this typeof reconstruction.

    1500 September-October 2007 RG f Volume 27 ● Number 5

    TeachingPoint

    Teaching PointThe principle behind multiple-segment reconstruction is that the scan projection data required to perform a partial scan reconstruction are selected from various sequential heart cycles instead of from a single heart cycle (Fig 4).

  • and M is the number of segments in adjacentheartbeats from which projection data are usedfor image reconstruction. Usually, M ranges from1 to 4.

    TRmax �TR2M

    .

    If TR � 400 msec and M � 1, then TRmax is asfollows:

    TRmax �TR2

    � 200 msec.

    If TR � 400 msec and M � 2, then TRmax is asfollows:

    TRmax �TR4

    � 100 msec.

    If TR � 400 msec and M � 3, then TRmax is asfollows:

    TRmax �TR6

    � 67 msec.

    The advantage of multiple-segment recon-struction is the possibility to achieve high tempo-ral resolution. The disadvantage is that becauseprojection data sets are obtained from differentheartbeat cycles, a misregistration due to rapid

    motion can result in the degradation of imagespatial resolution. This method also allows selec-tion of different packets of data for reconstructingan image for patients with irregular heart rates.

    Overall, the temporal resolution of cardiac CTdepends on the gantry rotation time. A gantryrotation time of 330–500 msec is possible with16–64-channel multiple-row detector CT scan-ners. With such rapid gantry rotation time, onecan achieve a temporal resolution of 80–250msec through multiple- and partial-segment re-construction, respectively. Temporal resolutionimproves with multiple-segment reconstruction(Fig 5); however, the spatial resolution can de-grade due to misregistration of motion artifacts,since projection data sets are selected from differ-ent heartbeats.

    With both types of reconstruction, there is ademand for a significant amount of projectionoverlap during data acquisition, which is indi-cated by the pitch. Usually, the pitch ranges from0.2 to 0.4 for cardiac CT protocols. This is quitedifferent from routine body CT protocols, whichare typically performed with pitch values of 0.75–1.50.

    Spatial ResolutionThere are a number of factors that influence thespatial resolution achieved with multiple-row de-tector CT scanners. Among them are the detectorsize in the longitudinal direction, reconstructionalgorithms, and patient motion.

    Figure 5. Effect of temporal resolution on reconstructed images from the same patient.(a) Partial scan reconstruction with temporal resolution of approximately 250 msec.(b) Multiple-segment reconstruction (two segments) yields a temporal resolution of approxi-mately 105 msec. The stair-step artifacts are less visible and the structures in the sagittalplane have a smooth edge compared with the appearance of partial scan reconstruction.

    RG f Volume 27 ● Number 5 Mahesh and Cody 1501

  • Effect of Detector SizeThe effect of detector size in the z direction orout-of-plane spatial resolution is very significantand has become one of the driving forces in theadvancement of multiple-row detector CT tech-nology. Also, larger volume coverage in combina-tion with a larger number of thin images requiresmore detectors in the z direction, which is thehallmark of technological advance in multiple-row detector CT. On the other hand, scan planeor axial spatial resolution has been very high fromthe beginning and is dependent on the scan fieldof view (SFOV) and image reconstruction matrix.Axial pixel size is the ratio of SFOV to image ma-trix; for example, for a conventional 512 � 512matrix, the transverse pixel size for a 25-cmSFOV is 0.49 mm. On the other hand, the longi-tudinal or z-axis resolution mainly depends on theimage thickness. The z-axis spatial resolution(image thickness) ranges from 1 to 10 mm in con-ventional (nonhelical) and in helical single-rowdetector CT. With multiple-row detector CT, thez-axis detector size is further reduced to submilli-meter size.

    Initially, with the introduction of multiple-rowdetector CT technology, the thinnest detectorsize was 0.5 mm and there were only two suchdetectors. However, within a few years, the tech-nology improved to provide 16 of these thin de-tectors, ranging from 0.625 to 0.5 mm. With 64-section multiple-row detector CT scanners, thedetector array designs are as shown in Figure 6;64 thin detectors (0.625 mm) are currently avail-able, resulting in z-axis coverage of up to 40 mmper gantry rotation (11). The increased spatialresolution with multiple-row detector CT scan-ners is demonstrated in Figure 7. Cardiac CTimages can be comparable in delineating detailsof the coronary vessels to the cardiac images ob-tained with fluoroscopy (8).

    Reconstruction IntervalThe reconstruction interval defines the degree ofoverlap between reconstructed axial images. It isindependent of x-ray beam collimation or imagethickness and has no effect on scan time or pa-

    tient exposure. The reason for decreased recon-struction interval (or increased overlap) is to im-prove z-axis resolution, especially for three-di-mensional (3D) and multiplanar reformation(MPR) images. If the reader is making a diagnosisbased on only axial images, reconstruction inter-val is not an issue. But frequently, physicians arealso reading MPR and 3D images; this is espe-cially true for cardiac CT.

    For example, in a single examination the samecardiac data set (acquired at 0.5-mm detectorconfiguration) was reconstructed with three dif-ferent values of reconstruction interval (Fig 8).Overlapping axial images results in a relativelylarge number of images but can also result in im-proved lesion visibility in MPR and 3D imageswithout increasing the patient dose. For routineMPR and 3D applications, a 30% image overlapis generally sufficient (1-mm section thicknesswith 0.7-mm reconstruction interval). For cardiacimages, at least 50% overlap is desirable (0.5-mmsection thickness with 0.25-mm reconstructioninterval).

    It should be recognized that too much overlapresults in a large number of images, increases re-construction time, can result in longer interpreta-tion periods, and can put undue strain on imagehandling overhead costs (image transfer, imagedisplay, image archiving, etc) with no significantgain in image quality.

    Overall, spatial resolution in the axial or x-yplane has always been quite high and is on the

    Figure 6. Detector array designs for multiple-row detector CT scanners that can yield 64 sec-tions per gantry rotation.

    1502 September-October 2007 RG f Volume 27 ● Number 5

  • order of 10–20 line pairs per centimeter. The z-axis spatial resolution is influenced by the detec-tor size, reconstruction thickness, and other fac-tors such as pitch and is around 7–15 line pairs

    per centimeter. The efforts toward obtaining iso-tropic resolution are leading further developmentsin multiple-row detector CT technology.

    Figure 7. Images from cardiac CT angiography (a) and fluoroscopically guided coronaryangiography (b) show a right coronary artery (long arrow) with calcification (short arrows).The spatial resolution and delineation of details of CT angiography are comparable withthose of coronary angiography. (Reprinted, with permission, from reference 8.)

    Figure 8. Effect of reconstruction interval on imagequality. All three sets of images are from the same dataset reconstructed with 0.5-mm section thickness. How-ever, the reconstruction intervals are different, whichaffects the number of reconstructed images and 3Dimage quality. (a) A reconstruction interval of 0.3 mmyields 301 images and implies a 60% overlap. (b) Areconstruction interval of 5 mm yields only 19 imagesand results in a staggered appearance of 3D images.(c) A reconstruction interval of 0.5 mm yields 184 im-ages and results in image quality similar to that of a.Normally, a 50% overlap is sufficient for optimum im-age quality for MPR and 3D images.

    RG f Volume 27 ● Number 5 Mahesh and Cody 1503

  • PitchThe concept of pitch was introduced with the ad-vent of spiral CT and is defined as the ratio oftable increment per gantry rotation to the totalx-ray beam width (20,21) (Fig 9). Pitch valuesless than 1 imply overlapping of the x-ray beamand higher patient dose; pitch values greater than1 imply a gapped x-ray beam and reduced patientdose (18). Cardiac imaging demands low pitchvalues because higher pitch values result in datagaps (Fig 10), which are detrimental to imagereconstruction. Also, low pitch values help mini-mize motion artifacts, and certain reconstructionalgorithms work best at certain pitch values,which are lower than 0.5 in cardiac imaging.Typical multiple-row detector CT pitch factorsused for cardiac imaging range from 0.2 to 0.4.

    The pitch required for a particular scanner isaffected by several parameters, as shown in the fol-lowing equation. For single-segment reconstruc-tion (partial scan acquisition), the pitch factor isinfluenced heavily by the subject’s heart rate (22).

    P ��N�1N � TRTRR � TQ ,where N � number of active data acquisitionchannels, TR � gantry rotation time (millisec-onds), TRR � time for a single heartbeat (millisec-onds), and TQ � partial scan rotation time (milli-seconds). For heart rates of 45–100 beats perminute (TRR of 1333–600 msec), TR of 500 msec,and TQ of 250–360 msec, the required pitch fac-tor ranges from 0.375 to 0.875. At higher pitch,there are substantial data gaps. As a result, most

    cardiac CT protocols require injecting beta-block-ers (23) to lower the subject’s heartbeat within thedesirable range of less than 70 beats per minute.

    When the subject’s heart rates are rapid anddifficult to control, the diastolic ranges aresmaller, so images are reconstructed using mul-tiple-segment reconstruction in order to improvetemporal resolution. With multiple-segment re-construction, the number of segments used in thereconstruction further restricts the pitch factors.

    P ��N�M�1NM � TRTRR ,where N � number of active data acquisitionchannels, M � number of segments or subse-quent heart cycles sampled, TR � gantry rotationtime (milliseconds), and TRR � time for a singleheartbeat (milliseconds). For a heart rate of 60beats per minute with a TR of 400 msec, N � 16,and M � 2, the required pitch is �0.21; similarly,for M � 3, the required pitch is �0.15.

    The pitch factor plays a significant role in im-proving both the temporal and spatial resolutionbut at the same time has a dramatic effect on theoverall radiation dose delivered during a cardiac

    Figure 9. Pitch is defined as the ratio oftablefeed per gantry rotation to the total x-ray

    beamwidth. This definition is applicable to bothsingle-row detector CT and multiple-row detectorCT(21). I � table travel (millimeters) per

    rotation,N � number of active data acquisitionchannels,T � single data acquisition channel width

    (milli-meters), W � beam width (millimeters).

    Figure 10. Graphs demonstrate the necessityfor scanning at low pitch values during helicalcardiac CT data acquisition. If the table feed be-comes greater than the beam width, it results ina data gap, which is detrimental for imagereconstruction.

    1504 September-October 2007 RG f Volume 27 ● Number 5

    CT examination. Because radiation dose is in-versely proportional to the pitch, the low pitchvalues characteristic of cardiac CT protocols sub-stantially increase radiation dose to patients un-dergoing cardiac imaging with multiple-row de-tector CT.

    TeachingPoint

    Teaching PointThe pitch factor plays a significant role in improving both the temporal and spatial resolution but at the same time has a dramatic effect on the overall radiation dose delivered during a cardiac CT examination. Because radiation dose is inversely proportional to the pitch, the low pitch values characteristic of cardiac CT protocols substantially increase radiation dose to patients undergoing cardiac imaging with multiple-row detector CT.

  • In cardiac CT imaging, the need for high spa-tial and temporal resolution in turn requires thepitch values to be as low as 0.2–0.4. This resultsin a radiation beam overlap of nearly 80%–60%,respectively, and an increase in radiation dose ofup to a factor of five times compared to a pitch of1. Hence, proper choice and optimization of pitchfactor is critical in cardiac imaging. In fact, thedemand for reducing radiation dose and fasterscans is driving the technology to introduce eitheran even higher number of thin detectors in the zdirection (256 rows) or flat panel technology sothat the entire cardiac area can be covered in asingle gantry rotation without the necessity fortissue overlap (low pitch values).

    Radiation RiskOne of the disadvantages of cardiac imaging withmultiple-row detector CT is its use of ionizingradiation. The radiation dose delivered is highlydependent on the protocol used in cardiac CT(24). Among the most widely known protocolssuch as calcium scoring studies, the effective doseis relatively small, 1–3 mSv (25). However, forretrospective gating, used for coronary vessel ste-nosis assessment and CT angiography, effectivedoses of 8–22 mSv and higher have been re-ported. By comparison, the radiation dose of anuncomplicated diagnostic coronary angiographystudy performed under fluoroscopic guidanceranges from 3 to 6 mSv (11,25) and for typicalbody CT protocols ranges from 2 to 10 mSv (26)

    (Table). Across the board, radiation doses arehigher with multiple-row detector CT comparedwith the doses delivered with electron beam CTand fluoroscopically guided diagnostic coronaryangiography and similar procedures (25).

    One approach to reduce the high dose associ-ated with retrospective gating is called ECG dosemodulation (27) and is directed at reducing thetube current during specific parts of the cardiaccycle, particularly during systole, where imagequality is already degraded by motion artifactsand these portions of the cardiac cycle are notused in the image reconstruction. When dosemodulation is implemented, a 10%–40% dosereduction (27) can be achieved; however, the sav-ings must be evaluated for each specific CT pro-tocol. It is important that any steps taken to re-duce radiation exposure should not jeopardize theimage quality, because poor image quality mayresult in repeat scans, which would result in addi-tional radiation doses to patients.

    Geometric EfficiencyDose efficiency (also called geometric efficiency)is of particular concern with the earlier four-chan-nel multiple-row detector CT scanners, for whichthe x-ray photon beam has to be quite uniform asit strikes the detector array. This requirementmeans that the natural shadowing of the beam(penumbra) attributable to the finite-sized focalspot is intentionally positioned to strike the neigh-boring nonactive detector elements. Thus, someamount of radiation transmitted through the pa-tient does not contribute to image generation.The width of the penumbra is fairly constant witheach scanner, generally in the range of 1–3 mm.

    Typical Effective Doses for Various Cardiac Imaging and Routine CT Procedures

    Imaging Procedures Modality Effective Dose (mSv)*

    Cardiac proceduresCalcium scoring Electron beam CT 1.0–1.3

    Multiple-row detector CT 1.5–6.2†

    Cardiac CT angiography Electron beam CT 1.5–2.0Multiple-row detector CT 6†–25

    Cardiac SPECT with 99mTc or 201T1‡ Nuclear medicine 6.0–15.0Coronary angiography (diagnostic) Fluoroscopy 2.1†–6.0Chest radiography Radiography 0.1–0.2

    Routine CT proceduresHead CT Multiple-row detector CT 1–2Chest CT Multiple-row detector CT 5–7Abdominal and pelvic CT Multiple-row detector CT 8–11

    *10 mSv � 1 rem.†Indicated data are from reference 25.‡SPECT � single photon emission CT, 99mTc � technetium 99m, 201T1 � thallium 201.

    RG f Volume 27 ● Number 5 Mahesh and Cody 1505

  • The proportion of radiation wasted relative tothe overall width of the x-ray beam varies with theprotocol used. If very thin images are requiredand the overall x-ray beam width is small—5 mm,for example—then the proportion of wastedx-rays could be 20%–60% (resulting in a doseefficiency of 40%–80%). If thin images are notrequired and a wider x-ray beam can be used—20mm, for example—then the proportion of wastedx-rays would be 5%–15% (resulting in a dose effi-ciency of 85%–95%). Dose efficiency may be dis-played on the scanner console. More recent mul-tiple-row detector CT scanners have been engi-neered such that this problem is very muchdiminished.

    ArtifactsIn cardiac imaging, owing to the inherent natureof imaging a rapidly moving organ, there arisemany unique artifacts (28,29); among them, the

    most common artifacts are due to cardiac pulsa-tion (29). Figure 11 shows disconnect in the lat-eral reconstructed image due to pulsation. Thesetypes of artifacts are minimized by multiple-seg-ment reconstruction or by scanning at evenhigher temporal resolution on the order of 50msec. The second types of artifacts are the band-ing artifacts due to increased heart rate during thescan. In the example shown in Figure 12, theheart rate varied from 51 to 69 beats per minuteduring the scan and resulted in banding artifacts(29). The other types of cardiac artifacts com-monly observed are due to incomplete breathholding. These types of artifacts are not observedon axial images but are visible on coronal or sagit-tal views (Fig 13).

    When subjects with previous stents or coils inthe coronary artery undergo CT imaging, we ob-serve streak artifacts around these highly attenu-ating objects. Often these artifacts can dominatethe artery region and obscure other structures. Asshown in Figure 14, the metallic structures

    Figure 11. Left anterior oblique (a) and anterior (b) MPR images show cardiac pulsationartifacts due to a rapid heartbeat. (Reprinted, with permission, from reference 29.)

    Figure 12. Banding artifacts due to an increased heart rate from 51 to 69 beats perminute. Coronal (a) and sagittal (b) reformatted images of the heart obtained from CT datashow banding artifacts (arrowheads). (Reprinted, with permission, from reference 29.)

    1506 September-October 2007 RG f Volume 27 ● Number 5

  • Figure 13. Artifacts due to incomplete breath holding. (a) Axial images show no motion artifacts.(b, c) Coronal (b) and sagittal (c) reformatted images show banding artifacts. (Reprinted, with permis-sion, from reference 29.)

    Figure 14. Streak artifacts visible in thepresence of a stent. Thin-slab maximum in-tensity projection image (a), MPR image (b),and thin-slab maximum intensity projectionimage obtained with a wide window (c) showstreak artifacts (arrows in a). (Reprinted, withpermission, from reference 29.)

    RG f Volume 27 ● Number 5 Mahesh and Cody 1507

  • appear on axial images with no streak artifact butare very distinct and disturbing in coronal or sag-ittal planes (29). These types of artifacts are tosome extent handled by special artifact reductionsoftware developed by manufacturers. Theblooming artifacts are caused primarily by thecombination of very highly attenuating objectsand the inherent limiting resolution of the scan-ner.

    Future Directionsin Cardiac Imaging

    The demand for higher temporal and spatial reso-lution has already led to the development of adual-source CT scanner (30) and a 256-row de-tector CT scanner (31). In dual-source CT, thereare two x-ray tubes positioned 90° apart provid-ing 64 axial sections for a complete gantry rota-tion, which yields further improvement in tempo-ral resolution. As mentioned earlier, the mini-mum amount of data needed to reconstruct animage is 180° plus the fan angle; therefore, withtwo tubes positioned at 90°, it is sufficient to ac-quire data for one-fourth of a gantry rotation andthen coordinate the data from two sets of detec-tors to reconstruct the image. This can yield tem-poral resolution as low as one-fourth the gantryrotation speed. With scanner gantry rotationspeeds at below 330 msec, the temporal resolu-tion can be as low as 80 msec. With this scanner,the pitch factor may be increased for higher heartrates with a potential to reduce radiation dose.

    Similarly, the demand for higher spatial resolu-tion has led to the development of a 256-row de-tector CT scanner, which can cover the entireheart in one gantry rotation (12.8-cm beam widthat isocenter). In the 256-row detector CT scan-ner, the 256 detectors in the longitudinal direc-tion can cover an area of 12.8 mm per gantry ro-tation and therefore can eliminate the need foroverlapping pitch. In this type of scanner, it is

    possible to obtain complete data from one heartcycle, further diminishing the need for excessivetissue overlaps (low pitch values) and thereforereducing radiation dose and also reducing motionartifacts. Ideally, the combination of a 256-rowdetector assembly in the dual-source CT scannerwould be phenomenal because that would notonly give high temporal resolution but also highspatial resolution with minimal motion artifacts.

    ConclusionsCardiac imaging is a highly demanding applica-tion of multiple-row detector CT and is possibleonly due to recent technological advances. Un-derstanding the trade-offs between various scanparameters that affect image quality is key in opti-mizing protocols that can reduce patient dose.Benefits from an optimized cardiac CT protocolcan minimize the radiation risks associated withthese cardiac scans. Cardiac CT has the potentialto become a reliable tool for noninvasive diagno-sis and prevention of cardiac and coronary arterydisease.

    References1. American Heart Association. International cardio-

    vascular disease statistics. Dallas, Tex: AmericanHeart Association, 2003.

    2. Mahnken AH, Wildberger JE, Koos R, GuntherRW. Multislice spiral computed tomography ofthe heart: technique, current applications, andperspective. Cardiovasc Intervent Radiol 2005;28:388–399.

    3. Budoff MJ, Achenbach S, Duerinckx A. Clinicalutility of computed tomography and magneticresonance techniques for noninvasive coronaryangiography. J Am Coll Cardiol 2003;42:1867–1878.

    4. Ulzheimer S, Kalender WA. Assessment of cal-cium scoring performance in cardiac computedtomography. Eur Radiol 2003;13:484–497.

    5. Dewey M, Borges AC, Kivelitz D, et al. Coronaryartery disease: new insights and their implicationsfor radiology. Eur Radiol 2004;14:1048–1054.

    6. Pannu HK, Jacobs JE, Lai S, Fishman EK. Coro-nary CT angiography with 64-MDCT: assessmentof vessel visibility. AJR Am J Roentgenol 2006;187:119–126.

    1508 September-October 2007 RG f Volume 27 ● Number 5

  • 7. Schoenhagen P, Halliburton SS, Stillman AE, etal. Noninvasive imaging of coronary arteries: cur-rent and future role of multi–detector row CT.Radiology 2004;232:7–17.

    8. Hoffmann MH, Shi H, Schmid FT, Gelman H,Brambs HJ, Aschoff AJ. Noninvasive coronary im-aging with MDCT in comparison to invasive con-ventional coronary angiography: a fast-developingtechnology. AJR Am J Roentgenol 2004;182:601–608.

    9. McCollough CH, Morin RL. The technical designand performance of ultrafast computed tomogra-phy. Radiol Clin North Am 1994;32:521–536.

    10. Detrano RC. Coronary artery scanning using elec-tron beam computed tomography. Am J Card Im-aging 1996;10:97–100.

    11. Mahesh M. Cardiac imaging: technical advancesin MDCT compared with conventional x-ray an-giography. In: Boulton E, ed. US cardiology 2006:the authoritative review of the clinical and scien-tific issues relating to cardiology with perspectiveson the future. London, England: Touch Briefings(http://www.touchcardiology.com), 2006; 115–119.

    12. Flohr TG, Schaller S, Stierstorfer K, Bruder H,Ohnesorge BM, Schoepf UJ. Multi–detector rowCT systems and image-reconstruction techniques.Radiology 2005;235:756–773.

    13. Gerber B, Rosen BD, Mahesh M, Araujo LI, StJohn Sutton M, Lima JAC. Physical principles ofcardiovascular imaging. In: St John Sutton M,Rutherford J, eds. Clinical cardiovascular imaging:a companion to Braunwald’s heart disease. Phila-delphia, Pa: Elsevier-Saunders, 2004; 1–77.

    14. Klingenbeck-Regn K, Flohr T, Ohnesorge B,Regn J, Schaller S. Strategies for cardiac CT imag-ing. Int J Cardiovasc Imaging 2002;18:143–151.

    15. Klingenbeck-Regn K, Schaller S, Flohr T, Ohne-sorge B, Kopp AF, Baum U. Subsecond multi-slice computed tomography: basics and applica-tions. Eur J Radiol 1999;31:110–124.

    16. Nikolaou K, Flohr T, Knez A, et al. Advances incardiac CT imaging: 64-slice scanner. Int J Car-diovasc Imaging 2004;20:535–540.

    17. Pannu HK, Flohr TG, Corl FM, Fishman EK.Current concepts in multi–detector row CTevaluation of the coronary arteries: principles,techniques, and anatomy. RadioGraphics 2003;23(spec issue):S111–S125.

    18. Mahesh M. Search for isotropic resolution in CTfrom conventional through multiple-row detector.RadioGraphics 2002;22:949–962.

    19. Desjardins B, Kazerooni EA. ECG-gated cardiacCT. AJR Am J Roentgenol 2004;182:993–1010.

    20. Mahesh M, Scatarige JC, Cooper J, Fishman EK.Dose and pitch relationship for a particular multi-slice CT scanner. AJR Am J Roentgenol 2001;177:1273–1275.

    21. International Electrotechnical Commission. Medi-cal electrical equipment, part 2-44: particular re-quirements for the safety of x-ray equipment forcomputed tomography. IEC Publication No.60601-2-44. Geneva, Switzerland: InternationalElectrotechnical Commission, 2002.

    22. Ohnesorge B, Becker C, Flohr T, Reiser MF.Multi-slice CT in cardiac imaging. Heidelberg,Germany: Springer, 2002.

    23. Pannu HK, Alvarez W Jr, Fishman EK. Beta-blockers for cardiac CT: a primer for the radiolo-gist. AJR Am J Roentgenol 2006;186(6 suppl 2):S341–S345.

    24. Gerber TC, Kuzo RS, Morin RL. Techniques andparameters for estimating radiation exposure anddose in cardiac computed tomography. Int J Car-diovasc Imaging 2005;21:165–176.

    25. Hunold P, Vogt FM, Schmermund A, et al. Ra-diation exposure during cardiac CT: effectivedoses at multi–detector row CT and electron-beam CT. Radiology 2003;226:145–152.

    26. Morin RL, Gerber TC, McCollough CH. Radia-tion dose in computed tomography of the heart.Circulation 2003;107:917–922.

    27. Jakobs TF, Becker CR, Ohnesorge B, et al. Multi-slice helical CT of the heart with retrospectiveECG gating: reduction of radiation exposure byECG-controlled tube current modulation. EurRadiol 2002;12:1081–1086.

    28. Choi HS, Choi BW, Choe KO, et al. Pitfalls, arti-facts, and remedies in multi–detector row CT cor-onary angiography. RadioGraphics 2004;24:787–800.

    29. Nakanishi T, Kayashima Y, Inoue R, Sumii K,Gomyo Y. Pitfalls in 16–detector row CT of thecoronary arteries. RadioGraphics 2005;25:425–438; discussion 438–440.

    30. Flohr TG, McCollough CH, Bruder H, et al. Firstperformance evaluation of a dual-source CT(DSCT) system. Eur Radiol 2006;16:256–268.

    31. Mori S, Endo M, Obata T, et al. Clinical poten-tials of the prototype 256-detector row CT-scan-ner. Acad Radiol 2005;12:148–154.

    RG f Volume 27 ● Number 5 Mahesh and Cody 1509

  • RG Volume 27 • Volume 5 • September-October 2007 Mahesh and Cody

    Physics of Cardiac Imaging with Multiple-Row Detector CT Mahadevappa Mahesh, MS, PhD, and Dianna D. Cody, PhD

    Page 1498 The minimum amount of projection data required to construct a complete CT image is 180° plus the fan angle of the CT detectors in the axial plane. Page 1498 One of the advantages of the prospective triggering approach is reduced radiation exposure, because the projection data are acquired for short periods and not throughout the heart cycle. Page 1499 The disadvantage of the retrospective gating mode of acquisition is the increased radiation dose, because the data are acquired throughout the heart cycle, even though partial data are actually used in the final image reconstruction. Page 1500 The principle behind multiple-segment reconstruction is that the scan projection data required to perform a partial scan reconstruction are selected from various sequential heart cycles instead of from a single heart cycle (Fig 4). Page 1504 The pitch factor plays a significant role in improving both the temporal and spatial resolution but at the same time has a dramatic effect on the overall radiation dose delivered during a cardiac CT examination. Because radiation dose is inversely proportional to the pitch, the low pitch values characteristic of cardiac CT protocols substantially increase radiation dose to patients undergoing cardiac imaging with multiple-row detector CT.

    RadioGraphics 2007; 27:1495–1509 ● Published online 10.1148/rg.275075045 ● Content Codes:

  • RadioGraphics 2007 This is your reprint order form or pro forma invoice

    (Please keep a copy of this document for your records.)

    Author Name _______________________________________________________________________________________________ Title of Article _______________________________________________________________________________________________ Issue of Journal_______________________________ Reprint # _____________ Publication Date ________________ Number of Pages_______________________________ KB # _____________ Symbol RadioGraphics Color in Article? Yes / No (Please Circle) Please include the journal name and reprint number or manuscript number on your purchase order or other correspondence. Order and Shipping Information Reprint Costs (Please see page 2 of 2 for reprint costs/fees.) ________ Number of reprints ordered $_________

    ________ Number of color reprints ordered $_________

    ________ Number of covers ordered $_________

    Subtotal $_________

    Taxes $_________ (Add appropriate sales tax for Virginia, Maryland, Pennsylvania, and the District of Columbia or Canadian GST to the reprints if your order is to be shipped to these locations.)

    First address included, add $32 for each additional shipping address $_________

    TOTAL $_________

    Shipping Address (cannot ship to a P.O. Box) Please Print Clearly Name ___________________________________________ Institution _________________________________________ Street ___________________________________________ City ____________________ State _____ Zip ___________ Country ___________________________________________ Quantity___________________ Fax ___________________ Phone: Day _________________ Evening _______________ E-mail Address _____________________________________ Additional Shipping Address* (cannot ship to a P.O. Box) Name ___________________________________________ Institution _________________________________________ Street ___________________________________________ City ________________ State ______ Zip ___________

    Country _________________________________________ Quantity __________________ Fax __________________ Phone: Day ________________ Evening ______________ E-mail Address ____________________________________ * Add $32 for each additional shipping address

    Payment and Credit Card Details Enclosed: Personal Check ___________ Credit Card Payment Details _________ Checks must be paid in U.S. dollars and drawn on a U.S. Bank. Credit Card: __ VISA __ Am. Exp. __ MasterCard Card Number __________________________________ Expiration Date_________________________________ Signature: _____________________________________ Please send your order form and prepayment made payable to: Cadmus Reprints P.O. Box 751903 Charlotte, NC 28275-1903 Note: Do not send express packages to this location, PO Box.

    FEIN #:541274108

    Invoice or Credit Card Information Invoice Address Please Print Clearly Please complete Invoice address as it appears on credit card statement Name ____________________________________________ Institution ________________________________________ Department _______________________________________ Street ____________________________________________ City ________________________ State _____ Zip _______ Country ___________________________________________ Phone _____________________ Fax _________________ E-mail Address _____________________________________ Cadmus will process credit cards and Cadmus Journal

    Services will appear on the credit card statement. If you don’t mail your order form, you may fax it to 410-820-9765 with

    your credit card information. Signature __________________________________________ Date _______________________________________ Signature is required. By signing this form, the author agrees to accept the responsibility for the payment of reprints and/or all charges described in this document.

    Reprint order forms and purchase orders or prepayments must be received 72 hours after receipt of form either by mail or by fax at 410-820-9765. It is the policy of Cadmus Reprints to issue one invoice per order.

    Please print clearly.

    Page 1 of 2 RB-9/22/06

  • RadioGraphics 2007 Black and White Reprint Prices

    Domestic (USA only) # of

    Pages 50 100 200 300 400 500

    1-4 $213 $228 $260 $278 $295 $313 5-8 $338 $373 $420 $453 $495 $530

    9-12 $450 $500 $575 $635 $693 $755 13-16 $555 $623 $728 $805 $888 $965 17-20 $673 $753 $883 $990 $1,085 $1,185 21-24 $785 $880 $1,040 $1,165 $1,285 $1,413 25-28 $895 $1,010 $1,208 $1,350 $1,498 $1,638 29-32 $1,008 $1,143 $1,363 $1,525 $1,698 $1,865

    Covers $95 $118 $218 $320 $428 $530

    International (includes Canada and Mexico) # of

    Pages 50 100 200 300 400 500

    1-4 $263 $275 $330 $385 $430 $485 5-8 $415 $443 $555 $650 $753 $850

    9-12 $563 $608 $773 $930 $1,070 $1,228 13-16 $698 $760 $988 $1,185 $1,388 $1,585 17-20 $848 $925 $1,203 $1,463 $1,705 $1,950 21-24 $985 $1,080 $1,420 $1,725 $2,025 $2,325 25-28 $1,135 $1,248 $1,640 $1,990 $2,350 $2,698 29-32 $1,273 $1,403 $1,863 $2,265 $2,673 $3,075

    Covers $148 $168 $308 $463 $615 $768 Minimum order is 50 copies. For orders larger than 500 copies, please consult Cadmus Reprints at 800-407-9190. Reprint Cover Cover prices are listed above. The cover will include the publication title, article title, and author name in black. Shipping Shipping costs are included in the reprint prices. Domestic orders are shipped via UPS Ground service. Foreign orders are shipped via a proof of delivery air service. Multiple Shipments Orders can be shipped to more than one location. Please be aware that it will cost $32 for each additional location. Delivery Your order will be shipped within 2 weeks of the journal print date. Allow extra time for delivery.

    Color Reprint Prices

    Domestic (USA only) # of

    Pages 50 100 200 300 400 500

    1-4 $218 $233 $343 $460 $579 $697 5-8 $343 $388 $584 $825 $1,069 $1,311 9-12 $471 $503 $828 $1,196 $1,563 $1,935 13-16 $601 $633 $1,073 $1,562 $2,058 $2,547 17-20 $738 $767 $1,319 $1,940 $2,550 $3,164 21-24 $872 $899 $1,564 $2,308 $3,045 $3,790 25-28 $1,004 $1,035 $1,820 $2,678 $3,545 $4,403 29-32 $1,140 $1,173 $2,063 $3,048 $4,040 $5,028

    Covers $95 $118 $218 $320 $428 $530

    International (includes Canada and Mexico)) # of

    Pages 50 100 200 300 400 500

    1-4 $268 $280 $412 $568 $715 $871 5-8 $419 $457 $720 $1,022 $1,328 $1,633 9-12 $583 $610 $1,025 $1,492 $1,941 $2,407 13-16 $742 $770 $1,333 $1,943 $2,556 $3,167 17-20 $913 $941 $1,641 $2,412 $3,169 $3,929 21-24 $1,072 $1,100 $1,946 $2,867 $3,785 $4,703 25-28 $1,246 $1,274 $2,254 $3,318 $4,398 $5,463 29-32 $1,405 $1,433 $2,561 $3,788 $5,014 $6,237

    Covers $148 $168 $308 $463 $615 $768 Tax Due Residents of Virginia, Maryland, Pennsylvania, and the District of Columbia are required to add the appropriate sales tax to each reprint order. For orders shipped to Canada, please add 7% Canadian GST unless exemption is claimed. Ordering Reprint order forms and purchase order or prepayment is required to process your order. Please reference journal name and reprint number or manuscript number on any correspondence. You may use the reverse side of this form as a proforma invoice. Please return your order form and prepayment to: Cadmus Reprints P.O. Box 751903 Charlotte, NC 28275-1903 Note: Do not send express packages to this location, PO Box. FEIN #:541274108 Please direct all inquiries to:

    Rose A. Baynard 800-407-9190 (toll free number) 410-819-3966 (direct number) 410-820-9765 (FAX number)

    [email protected] (e-mail)

    Reprint Order Forms and purchase order or prepayments must be received 72 hours after receipt of form.

    Page 2 of 2