Jeffrey C. Hellinger, MD

The cardiovascular community has witnessed historic changes in the way cardiovascular disease is evaluated. Recently, the greatest growth has been in cardiac CT to noninvasively diagnose coronary (Figure 1) and noncoronary cardiac disease (Figure 2).

Despite its clear advantages and broad-based support, CCT practice varies widely among imaging communities. Many early-adopting radiologists and cardiologists have developed active clinical services. Others are still waiting to see how the technology evolves, local politics progresses, and Medicare and Medicaid policies are further defined. As we are clearly still in the early phase of modern day CCT, it is key that all of those involved with CCT strive for clinical excellence in acquisition, interpretation, and reporting.

Excellence begins with physician and technologist education and training, as the ability to acquire and interpret CCT images with high quality is only as good as one's skill. Participants in training programs can be categorized into three groups: The first consists of those seeking to become familiar with the technology and clinical applications. Decisions have not yet been made in their group practices. The training program will provide more direct understanding, regardless of whether exploratory committees have been established. The second consists of those who understand the clinical utility of CCT and want to get credentialed in anticipation of their groups eventually offering the procedure. The third consists of physicians and technologists whose practices have decided to pursue a clinical service. These individuals require training immediately and often design an accelerated training schedule.

The training process includes didactic lectures, static case review, and hands-on workstation case review. At present, training opportunities are available through academic centers, professional societies, educational organizations, workstation vendors, and private sector physician groups. Most programs offer courses remotely and have self-study CD-ROMs. Onsite training is also available (www.cvctraining.com). This is often ideal for groups whose travel logistics, cost limitations, and call schedules preclude remote training.

Each program typically includes several learning objectives:

to understand CCT acquisitions, contrast medium delivery, and workstation principles;

to understand cardiac anatomy on 2D, 3D, and 4D workstation displays;

to understand cardiac pathology and pathophysiology;

to recognize cardiac pathology on CCT, including but not limited to coronary atherosclerotic disease;

to develop a methodology for image analysis; and

to develop an efficient reporting structure for CCT.

To ensure standardized skill and knowledge, the American College of Radiology and the American College of Cardiology have established credentialing requisites for radiology and cardiology practices.1,2 Most insurance carriers will not reimburse without documentation that physicians and practices have met these standards. Local forces lead many radiologists to target their training to meet both ACR and ACC requirements.

In the future, the Society for Cardiovascular Computed Tomography will take this standardization to the next level with the initiation of cardiovascular CT board certification.

One of the most critical learning objectives is developing an efficient methodology for rendering anatomy and interpreting cardiovascular disease on a workstation. This can be achieved only through hands-on training courses.

After reviewing the workstation features, trainees should review cardiovascular and noncardiovascular anatomy using 2D, 3D, and 4D visualization techniques. It is important to demonstrate the principles of each technique and emphasize their advantages and disadvantages.

Trainees are then ready to develop a logical approach to systematically analyzing cardiac and vascular structures and to optimize interpretation accuracy and efficiency. As opposed to catheter angiography, in which contrast is injected directly into the vascular structures or the cardiac chambers and 2D cardiovascular structures appear on a screen, interpretation of CCT requires the operator to actively engage the workstation to display anatomy. The operator must "seek out" the anatomy and generate renderings that can be interpreted.

This requirement applies not only to coronary arteries, but also to the pericardium, right and left cardiac chambers, valves, pulmonary arteries and veins, coronary veins, and thoracic aorta. Anatomic segments do not necessarily need to be viewed with each visualization technique. Rather, techniques are utilized based on the anatomic segment of interest, the specific goals of the operator, and the advantages of each technique. By employing this approach, the operator can swiftly interchange techniques. Each trainee should develop an order of preference for evaulating and reporting the coronary and imaged noncoronary structures. This approach also applies to display and interpretation of noncardiovascular structures included in the data set.

Hands-on workstation training programs should offer a balanced caseload that reflects real clinical practice. Trainees should first be shown normal cases of high image quality. Next, normal cases of adequate and poor image quality should be presented, so the trainee can recognize suboptimal enhancement, motion (cardiac, respiratory, and patient), streak artifact, blooming artifact, incorrect field-of-view selection, and other pitfalls that can limit interpretation of the coronary arteries. Later, high-quality cases with < 50%, 50% to 70%, > 70%, and occlusive native coronary atherosclerotic lesions should be presented and reviewed, preferably with correlation to catheter angiography. High-quality studies with stents and bypass grafts should be presented at this time.

As the patterns of disease become understood, similar cases of less robust image quality should be presented. Following this, CCT cases showing coronary anomalies and myocardial, pericardial, valvular, pulmonary arterial, pulmonary venous, and thoracic aortic disease should be reviewed. Common adult congenital heart disease cases should also be presented. Over subsequent days, trainees should see as many cases as possible, often in a random order. Once trainees are exposed to basic pathology and workstation use, repetition and discussion are vital to pattern recognition, establishing a fundamental base that trainees can then apply in their own imaging practices.

Hands-on workstation training programs have become known as the most sophisticated method for learning the advanced skills essential to performing and interpreting CCT.

Dr. Hellinger is an assistant professor of radiology and cardiology at the Children's Hospital of Philadelphia, University of Pennsylvania, and is director of cardiovascular imaging and the 3D laboratory for radiology. He can be reached at 

Weinreb JC, Larson PA, Woodard PK, et al. American College of Radiology clinical statement on noninvasive cardiac imaging. Radiology 2005;235:723-727.

Budoff MJ, Cohen MC, Garcia MJ, et al. ACCF/AHA Clinical competence statement on cardiac CT and MR. JACC 2005;46(2):383-402.

Articles

Clinical excellence in cardiac CT must begin with education

The Stanford International Symposium on Multidetector-Row CT has gained such momentum in its nine-year history that the next meeting will be in a larger venue in Las Vegas. The growing importance of multislice CT is reflected in the wide range of topics presented this year. Several themes stood out as important:

striving for the highest image quality using protocols recommended by the lecturers;

achieving this performance while adhering to an ALARA (as low as reasonably achievable) principle for radiation exposure;

adapting contrast medium protocols for current and future CT scanners; and

understanding current and future image processing techniques and tools, and future IT models for clinical workflow and enterprise solutions.

At the end of the four-day symposium, the team of lecturers provided a comprehensive update for mid-2007 and offered a preview of what to expect for MSCT technology and clinical practice in the next six to 12 months.

While technological advances are opening new opportunities, radiation safety and data overload present serious challenges.

CT scanners. Researchers frequently reported on experience and applications with Siemens Medical Solutions' dual-source CT and Toshiba Medical System's 256-slice CT. Investigators also gave presentations on GE Healthcare's experimental high-definition CT, inverse-geometry CT, and Siemens' C-arm CT.

The dual-source scanner has two x-ray tubes, resulting in a half-gantry rotation time of 83 msec. The two tubes can combine their individual 80-kW output at similar kVp and mA settings to increase the effective mA. Cynthia McCollough, Ph.D., a medical physicist at the Mayo Clinic in Rochester, MN, pointed out that this may allow use of higher pitch values, which could lead to shorter scans, improved enhancement, or thinner collimation.

Alternatively, the x-ray tubes can be set at different kVp and mA settings to generate dual-energy data sets. Data sets can be separated using postprocessing algorithms. Applications include CTA bone and calcium removal (i.e., peripheral arterial disease), generation of virtual unenhanced images, and characterization of renal calculi (Figures 1 and 2).

Dr. Kazuhiro Katada, a professor of radiology at Fujita Health University in Toyoake, presented his experience with Toshiba's 256-slice CT system. Johns Hopkins University Medical Center has a prototype of this scanner installed, and Toshiba anticipates commercial availability next year. The 256-slice system can scan a maximum of 128 mm. Depending on the distance to be covered, no more than a single rotation may be necessary, obviating the need for helical scanning. Complete coverage of the head or heart is possible with a single rotation. Scan time is significantly reduced, which is advantageous for critically ill patients and those who may require sedation. Scans are acquired with isophasic imaging, which permits more uniform delivery of contrast medium. Alternatively, the same organ can be scanned sequentially without table motion, allowing for dynamic functional evaluation, including perfusion and time-resolved CT angiography. This technique can also be used to generate unenhanced and contrast-enhanced images (subtraction). An interesting adjunct is its ability to perform scans at two different energies within 0.5 seconds of each other for tissue characterization.

Radiation safety. Radiation safety was very much on everyone's mind. The excellent clinical performance of volumetric MSCT scanning has led to a rapid growth in CT studies. This growth in utilization, in turn, has led to a rise in radiation exposure attributable to CT. Direct morbidity and mortality risk, however, remain the focus of discussion and outcomes research.

The clear message was ALARA. Achieving ALARA begins with patient selection, adherence to exam indications, and eliminating unnecessary repeat exams. Consideration must be given to a patient's age, sex, and radiosensitivity, as well as the possibility that clinical problems could be addressed with a nonionizing modality such as ultrasound or MRI. Risks of radiation should always be weighed against the benefits of the exam. Multiple lectures stressed the importance of consistently using radiation reduction strategies when acquiring a study: using lead shielding, limiting the scan range, decreasing the tube voltage (kVp), and using attenuation-tube current (mA) modulation.

When using ECG gating for a cardiac or thoracic aortic study, ECG tube-current modulation should also be employed and a low heart rate targeted to ensure effective modulation. However, very low may necessitate increased scan redundancy and therefore increase dose. In discussions on ECG-gated radiation exposure reduction, the liveliest interest centered on multisource versus prospectively gated step-and-shoot scanning. Speakers presented data showing radiation exposure reduction with both approaches. Which approach will prove most effective remains an area of active research.

Contrast medium administration. The art of administering contrast with advanced MSCT scanners depends directly on fundamental knowledge of contrast medium pharmacokinetics, particularly with cardiovascular CTA. Contrast should be delivered with suitable iodine dose and iodine flux that reflect a patient's weight (measure of central blood volume) and cardiac output. Iodine dose is controlled by contrast volume and concentration, while iodine flux is controlled by injection rate and concentration. The targeted injection rate should always be balanced with the caliber of the intravenous catheter and the vein used for injection. As discussed by Dr. Dominik Fleischmann, an associate professor of radiology at Stanford University, 64-slice and greater scanners, fixed scan time, and injection duration can be used to synchronize the scan acquisition and contrast delivery by way of variable scan delays.

Image processing. Data overload is a critical issue with MSCT. Workstation vendors and software developers recognize this challenge and are actively pursuing hardware and software solutions to help imagers achieve high efficiency while maintaining accuracy.

MSCT exams may be viewed on PACS, workstation, or both. Assessment on a workstation can be performed by a thin-client, thick-client, or stand-alone 3D system. With the increasing data load in imaging practices, stand-alone systems and thick-client solutions can put a significant strain on productivity. On the one hand, there is redundant data transmission and archiving. On the other, these workstations may not be readily accessible to all who need to interrogate an exam with advanced tools. The coming solution will be full integration of 3D workstation applications (e.g., vessel analysis, lung nodule analysis, lumen fly-through, CT perfusion, etc.) into PACS, using a thin-client model. Imagers and physicians will be able to view MSCT studies and perform advanced processing with a single hospital enterprise system, onsite or remotely, by intranet or over the Internet, depending on the available user bandwidth. TeraRecon, the first vendor to enter the market with a thin-client solution, leads this drive with the planned release of its iNtuition workflow architecture at the 2007 RSNA meeting.

Continued advancements in automated intelligent preprocessing, clinical analysis tools, multimodality integration, and time-resolved study analysis are all actively being pursued. It is anticipated that only thin-section source data will be stored and diagnostic images reconstructed in real-time on PACS to the desired section thickness. On-demand or automatically launched computer-aided detection algorithms (e.g., lung and colon MSCT exams) will be more widely used with PACS to improve reader performance in high-volume practices. Finally, as the technology places greater demand on clinical workflow, the role of a 3D laboratory for quantitative analysis and treatment planning will likely gain more prevalence in imaging practices.

Many of these issues came to light during the symposium's workstation face-off. Veteran participants Siemens, GE, Vital Images, TeraRecon, and Philips Medical Systems were joined by Carestream and Barco. Each vendor presented four cases: an aortic stent-graft CT, pancreas protocol CT, cardiac CTA, and renal artery CTA. The aortic stent-graft was a noncontrast follow-up to a prior CTA. The challenge was to demonstrate study coregistration with image processing. TeraRecon seemed to be the fastest, using automatic segmentation.

The purpose of the pancreas case was to use advanced tools to segment out the pancreas, pancreatic duct, and vasculature. Variability between presenters was wide, with some producing oblique minimum intensity projections (MinIPs) and others generating curved planar reformations (CPRs). This was also an opportunity for some vendors to demonstrate labeling tools, with TeraRecon and GE using a menu option system and Vitrea using manual labeling. The cardiac CT case was a standard multiphase 4D data set. However, the task was to analyze morphology and function using a thin-client solution at 4 MHz bandwidth. For this case, GE's Advantage Windows had no thin-client server, and Siemens' Leonardo was operated at a 10-MHz connection, as it could not perform at the mandated modem speed. While load times varied, TeraRecon, Carestream, and Vital Images were noticeably faster than Barco and Philips. TeraRecon was the obvious leader in the cardiac CT demonstration, with near seamless processing of wall motion, ejection fraction, coronary artery autosegmentation, and vessel analysis.

Applications in many areas of clinical practice were discussed.

Cardiovascular imaging. The cardiac session was an intense, comprehensive overview of the current and expected future practice of cardiac CT. Topics ranged from training and credentialing to exam indications, applications, acquisition, and reporting. A quarter of the day-long session was dedicated to technique. Speakers discussed strategies for improved temporal resolution, reduced radiation exposure, and improved coronary artery disease assessment. Debate between dual-source and 256-slice over whole-heart imaging for improved temporal resolution is just beginning. Add prospective ECG gating to these scanners for the most efficient approach to radiation reduction, and the debate gets livelier. Expand the discussion to include one-stop evaluation for morphology, perfusion, and function, using a PET/CT or a 256-slice CT scanner, and it becomes challenging to recommend the best CT scanner for cardiac disease diagnosis and management.

Lectures on cardiac CT use for coronary artery disease stressed the importance of patient selection and preparation, particularly for patients presenting to the emergency department with acute chest pain. Calcium scoring, plaque morphology, and CT performance for coronary artery disease were all reviewed. Lectures on noncoronary artery disease addressed aortic valve assessment, pulmonary vein mapping, and noncardiac anatomy and findings on a cardiac CT exam.

The vascular session focused on aortic, renal, peripheral arterial, and venous MSCT applications. The key take-home messages from these vascular lectures were that high clinical utility is achieved with CTA and CT venography in the vascular system, and that clinical success relies on technical success. Aorta topics included practical reviews of dissection, acute inflammatory conditions of the aorta, ulcer like lesions of the aorta, and endoleaks. The renal CTA lecture emphasized broad application, including renal donor evaluation, renal artery stenosis (ostial and fibromuscular dysplasia), dissection, vasculitis, and aneurysms. Discussions of the peripheral arterial system and occlusive disease focused on MSCT technique, CTA pitfalls, the role of MRI, and dual-energy application with dual- and single-source 64-slice scanners for bone and calcium removal. The lecture on indirect and direct MSCT venography addressed clinical indications, technique, and pitfalls.

Abdominal imaging. The first part of the abdominal lectures addressed hepatic, pancreaticobiliary, and renal MSCT technique and applications, with emphasis on solid tumor imaging. Focused subtopics included tumor characterization with CT perfusion and mass and stone characterization with dual-energy CT. Speakers stressed the importance of vascular and parenchymal multiphase acquisitions to comprehensively define tumor morphology and assess resectability. Image processing with MPR, MIP, MinIP, average intensity projection, CPR, and/or volume rendering was presented with discussion on strengths and weaknesses for each anatomical display.

The second part of the abdominal lectures addressed virtual CT colonography and CT enterography. The main issues raised in CTC were the use of minimal, noncathartic preparation and CAD. Minimal-preparation CTC employs barium and iodine oral contrast for fecal tagging, which can then be electronically subtracted, although this results in artifacts that interfere with CAD. The overall consensus was that minimal preparation CTC with CAD is a technology that is very nearly ready for widespread clinical use, but some significant software innovations will be necessary first.

The main points addressed in CT enterography were the use of negative enteric contrast and the necessity of multiplanar reformats. Negative contrast, such as E-Z-EM's VoLumen or a suspension of mannitol, increases the conspicuity of the submucosa, vessels, and calcifications. The use of coronal imaging for improved characterization of jejunal folds and for mesenteric processes was stressed.

Pediatric imaging. Given its capability for rapid acquisition and minimal need for sedation, MSCT can be a valuable tool for pediatric imaging. MSCT applications discussed in the pediatric section included congenital heart disease, vascular rings and other congenital and acquired vascular abnormalities, congenital lung lesions, congenital airway anomalies, pulmonary infections, diaphragmatic hernias, ureteropelvic junction obstruction, ectopic ureters, and musculoskeletal anomalies. The message from the speakers was that these applications and others in pediatrics must be strictly balanced between image quality and ALARA. Protocols must strive for a low kV and must use dose-modulation software. When evaluating congenital heart disease, ECG gating should be used selectively.

Musculoskeletal/trauma. Isotropic, submillimeter data sets are standard practice for musculoskeletal MSCT. These data sets produce robust volume renderings and multiplanar reformations, which can be used to evaluate the axial and appendicular skeleton in the setting of trauma, degenerative disease, tumors, dysraphic disorders, and postoperative surveillance, according to Dr. Lawrence Tanenbaum, section chief of CT, MRI, and neuroradiology at JFK Medical Center in Edison, NJ. Image quality is further maximized by positioning the targeted anatomy parallel to the gantry table, using a small field-of-view, and prescribing an appropriate voltage and tube current for the anatomical application.

From the same isotropic acquisition, a soft-tissue data set can be reconstructed using a different filter. This second data set can then be applied to display and render skin, soft tissues, tendons, muscles, viscera, and vessels. This multireconstruction approach has revolutionized the assessment, triage, and management of polytrauma patients. As discussed by Dr. Jorge Soto, an associate professor of radiology at Boston Medical College, vascular, visceral, soft-tissue, and musculoskeletal structures can be evaluated using a single bolus of contrast.

Neurologic imaging. Neurovascular imaging and related 3D postprocessing was the dedicated focus of this year's symposium. Dr. Jay Cinnamon, of Quantum Radiology Northwest in Georgia, began the session discussing diagnostic algorithms for MRA, ultrasound, CTA, and/or catheter angiography for evaluation of cerebrovascular disease. Cinnamon and others presented excellent cases, emphasizing the role of CTA and advanced 3D imaging to diagnose atherosclerotic disease, thromboembolism, aneurysms, dissection, arteriovenous malformations, dural AV fistulas, and traumatic carotid injury. CT brain perfusion was discussed as an adjunct tool for evaluating patients with acute stroke. This will likely become more standard as whole-brain imaging (possible with a 256-slice scanner) moves into clinical practice.

Thoracic imaging. Pulmonary nodules and their morphology, behavior, detection, and management were the focus for the majority of thoracic imaging lectures. This discussion was appropriate, as thin-section MSCT acquisitions have enhanced practitioners' ability to detect subcentimeter nodules, including those 

PET/CT can be used to characterize nodules and assess tumor physiology. However, false-positive results due to infectious and inflammatory diseases are not uncommon. Additional topics in the thoracic section addressed reducing radiation in routine thoracic CT, advanced applications and strategies to ensure appropriate utilization and radiation protection for CT pulmonary angiography, and, finally, strategies to optimize CTPA enhancement when a patent foramen ovale may be present.

For more information regarding this symposium, or to order a symposium CD-ROM complete with the speakers' exam protocols, please go to mdct.stanford.edu.

The 10th Annual International Symposium on Multidetector-Row CT will be held May 13-16, 2008, at the Wynn Hotel in Las Vegas.

Dr. Hellinger is director of cardiovascular imaging and 3D imaging at The Children's Hospital of Philadelphia, and Dr. Margolis is an assistant professor of radiology at the University of California, Los Angeles.

The Stanford International Symposium on Multidetector-Row CT has gained such momentum in its nine-year history that the next meeting will be in a larger venue in Las Vegas. The growing importance of multislice CT is reflected in the wide range of topics presented this year.

Stanford CT symposium ignites both excitement and concern

One of the early applications of CT angiography in the 1990s was assessment of the renal arteries.1-2 Using single-detector-row technology, CTA was well suited for this use. Moderately thin sections (~3 mm) could be acquired through the renal vasculature in a relatively short duration. Researchers demonstrated reliable performance in evaluating suspected renal artery stenosis (RAS)2 and in screening potential living related kidney donors.3 Renal CTA was quickly adopted by many clinicians and imagers as an alternative to invasive catheter angiography.

Introduced in 1998, multidetector-row CT technology presented key advantages over single-detector-row scanners to improve the use of renal CTA. Thinner sections (0.63 to 1.5 mm) could be acquired through similar volume coverage with faster speed. The result has been improved spatial resolution along the z-axis, reduced breath-hold durations, and improved quality of 2D and 3D images. Multislice CT technology has afforded multiphase acquisitions through different physiologic renal states and multi-data set reconstructions from the original scan.

Since MSCT technology was introduced, assessment of RAS (Figure 1) and scanning of living related kidney donors remain core applications. Other clinical applications include evaluation of renal transplants, suspected crossed ureteropelvic junction vessels, renal aneurysms (Figure 2), arteriovenous fistulae (congenital and acquired), vasculitis, dissection, thromboembolism, suspected trauma, and renal masses. Early work also suggests that MSCTA may be a useful modality to quantify the glomerular filtration rate.4

Renal CTA requires synchronizing a high-flow intravenous contrast medium injection with a thin-section helical acquisition through the kidneys and their vascular supply. Images are interpreted using a combination of 2D and 3D displays. The ability to render high-quality images and interpret the exam is dependent on the quality of the CT acquisition and contrast medium administration.

To image the kidney, main renal arteries and veins, potential accessory arteries and veins, and normal variant anatomy, scan coverage should include from the supraceliac aorta through to the iliac bifurcation. If the exam is meant to assess transplant kidney vasculature, coverage is through the transplant kidney, which is typically in the right or left iliac fossa.

In general, MSCTA slice thickness should not exceed 1.5 mm. Depending on the number of MSCT channels (four to 10 versus 16 to 64), scan distance, body habitus, and noise, submillimeter slice thickness is recommended to generate isotropic data sets and improve small vessel depiction. Additional potential acquisitions include an initial unenhanced scan, a delayed nephrographic scan, and a delayed urographic scan.

For contrast medium administration, high-concentration material, high iodine flux (injection rate of 4 to 5 cc/sec), and injection duration of at least 20 seconds are essential. Timing is synchronized to enhancement of the midabdominal aorta, using either automated bolus-triggering software or a test bolus. For acquisitions greater than 20 seconds, the injection duration should be prescribed to equal the scan duration. If automated bolus triggering is used, the injection duration is extended to account for the inherent delay when using this software. For acquisitions less than 20 seconds, either slowing the table speed or increasing the scan delay should ensure that the acquisition and injection durations are equal, approaching 20 seconds.

I interpret the vasculature from a volumetric approach on a 3D workstation. I first use interactive volume-rendered images to form a structural overview of the aorta, iliac arteries, mesenteric arteries, and renal vasculature. Next, I interrogate the vessels of interest using either an interactive thin-slab maximum intensity projection, thin-slab volume-rendered image, or multiplanar reformation. To characterize segments of vessels, I use targeted orthogonal MPR projections.

Renal MSCTA can be used to investigate a broad spectrum of renal vascular pathology. Combined with visceral imaging, a comprehensive kidney and urologic evaluation can also be performed.

- Renal artery stenosis. RAS accounts for up to 5% of patients with hypertension, most commonly from atherosclerosis (90%, Figure 1) or fibromuscular dysplasia ( < 10%). The objective of CTA is to determine renal artery patency and characterize the vessel wall, including ostial, postostial, and segmental regions. Equally important is the assessment of parenchymal findings that suggest the presence of hemodynamically significant stenoses. These include renal atrophy, cortical thinning, and decreased cortical enhancement. In both instances, initial unenhanced images can aid diagnoses by detecting calcium, stents, and surgical clips. Evaluating suspected RAS with four-channel MSCT, authors report a sensitivity of 86% to 100%, specificity of 98.6% to 100%, and accuracy of 96.9% to 99%.5,6 Evaluating renal stent patency can also be achieved with reliable confidence.7

- Living related kidney donor. Determining which kidney may be more suitable for transplantation requires a more comprehensive exam. In addition to noncontrast and first-pass phases, delayed nephrographic and urographic phases are essential, as nonvascular findings such as nephrolithiasis, cysts, solid masses, cortical scarring, hydronephrosis, and ureteral duplications may preclude donation. Interpretation of a living related kidney donor CTA begins with the noncontrast images to identify any calculi or vascular calcifications. Vascular assessment addresses the number, location, patency, and branching pattern of renal arteries and veins, including accessory vessels and normal variants. Parenchymal assessment addresses the presence of masses and scarring in addition to calculating kidney dimensions such as length and volume. Finally, thorough evaluation of the upper and lower collecting systems addresses the draining pattern and patency.

- Renal transplants. Many post-renal transplant patients have multiple surgical clips in the pelvis, which can degrade MR image quality. CTA is therefore an excellent alternative to catheter angiography to assess renal transplant arteries and veins. The imaging objectives and protocol are similar to RAS evaluation, with two exceptions: Coverage is limited to the pelvis, and acquisition occurs in the angionephrographic phase so that arteries and veins can be evaluated.

- Renal artery aneurysms. Renal artery aneurysms (RAA) are uncommon, occurring in approximately 0.09% of patients.9 RAA have a slight female predominance and are typically unilateral and solitary, occurring slightly more frequently in the right kidney. Most patients with RAA are asymptomatic (Figure 2). However, RAA are associated with hypertension and can cause flank pain, hematuria, and renal function demise, depending on their size, the presence of microemboli, and occurrence of rupture. CTA is a reliable means to define the location, type, and size of RAA as well as the presence of calcification, thrombus, and other renal arterial pathology.

In these and other clinical applications of renal MSCTA, it is important to remember that success depends on a fundamental understanding of scan acquisition, contrast medium administration, and image display principles.

Dr. Hellinger is an assistant professor of radiology and cardiology at The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, and director of cardiovascular imaging and of the 3D laboratory.

1. Rubin GD, Dake MD, Napel SA, et al. Three-dimensional spiral CT angiography of the abdomen: initial clinical experience. Radiology 1993;186(1):147-152.

2. Rubin GD, Dake MD, Napel SA, et al. Spiral CT of renal artery stenosis: comparison of three-dimensional rendering techniques. Radiology 1994;190(1):181-189.

3. Rubin GD, Alfrey EJ, Dake MD, et al. Assessment of living renal donors with spiral CT. Radiology 1995;195(2):457-462.

4. Sommer G, Olcott EW, Chow LC, et al. Measurement of renal extraction fraction with contrast-enhanced CT. Radiology 2005;236:1029-1033.

5. Willmann JK, Wildermuth S, Pfammatter T, et al. Aortoiliac and renal arteries: prospective intraindividual comparison of contrast-enhanced three-dimensional MR angiography and multi-detector row CT angiography. Radiology 2003;226(3):798-811.

6. Fraioli F, Catalano C, Bertoletti L, et al. Multidetector-row CT angiography of renal artery stenosis in 50 consecutive patients: prospective interobserver comparison with DSA. Radiol Med (Torino) 2006;111(3):459-468.

7. Raza SA, Chughtai AR, Wahba M, et al Multislice CT angiography in renal artery stent evaluation: prospective comparison with intra-arterial digital subtraction angiography. Cardiovasc Intervent Radiol 2004;27(1):9-15.

8. Frauscher F, Janetschek G, Helweg G, et al. Crossing vessels at the ureteropelvic junction: detection with contrast-enhanced color Doppler imaging. Radiology 1999;210(3):727-731.

9. Henke PK, Cardneau JD, Welling TH, et al. Renal artery aneurysms: a 35-year clinical experience with 252 aneurysms in 168 patients. Ann Surg 2001;234(4):454-462.

Careful contrast timing and sophisticated acquisition techniques address new applications ranging from transplants to aneurysms

Jeffrey C. Hellinger, MD

Articles

Clinical excellence in cardiac CT must begin with education

Stanford CT symposium ignites both excitement and concern

Renal CTA moves past arterial stenosis to vessel anomalies