Applied Radiology

This publication was supported by an educational grant from Amersham Health, Princeton, NJ. The opinions expressed in this publication are those of the authors and not necessarily those of Amersham Health.

Dr. Fishman is a Professor of Radiology and Oncology, and Director of Diagnostic Radiology and Body CT at Johns Hopkins Medical Institutions, Baltimore, MD.

Radiologists at leading institutions have been performing CT angiography (CTA) for more than a decade. Even in 1989, when single-slice CT was introduced, it was possible to produce reasonable-quality CT angiographic images of certain vessels, particularly the aorta. By the late 1990s, following the introduction of 4-slice scanners, most CTA applications had become both easier to do and more robust. Sixteen-slice technology, introduced in 2002, promises to make CTA a standard procedure in most radiology departments.

As shown in Table 1, CT has undergone an extraordinary evolution during the last 20 years. Today it is characterized by subsecond scan times, submillimeter scan thicknesses, and the acquisition of approximately 1000 slices per examination. Sixteen-slice scanners have been particularly important in advancing CTA, offering the ability not only to optimize contrast enhancement but also to acquire data in isotropic voxels. Having equal spatial resolution in the X, Y, and Z directions greatly improves three-dimensional (3D) reconstructions.

CTA is not a study that is used occasionally for unique or difficult cases. Instead, it has become part of standard practice. Indeed, growth in CTA has exceeded expectations, in large part as a result of technological innovation. In fiscal year 2000, we performed 1160 body CTA examinations at Johns Hopkins. In 2001, that number climbed to 2037 and in 2002, to 2818. Prior to acquiring a 16-slice scanner, we projected a CT volume of 3150 for fiscal year 2003. Instead, the final volume was 3800.

The clinical applications of CTA continue to increase in number and range. Today, CTA is performed in the chest, abdomen, kidney, liver, brain, and heart with increasing ease.

It is possible to examine the pulmonary vasculature (Figure 1), the aorta, and the mediastinum, among other
thoracic structures. Routinely, CTA is used to examine the carotid arteries for stenosis (Figure 2), an application that markedly reduces patient risk and has substantially increased CT volume in many radiology practices.

CTA of the coronary arteries, while not yet routine, can be readily performed with the newest scanners. Whether in the examination of patients for stenosis or in the evaluation of graft patency, CTA of the coronary vasculature represents an application of great promise.

In approximately 90% of diagnostic studies, CTA can replace conventional angiography. The evaluation of pulmonary embolism is a perfect example of a clinical application in which CTA has become the diagnostic standard. Even more important, in the case of cancer, CTA can not only diagnose disease but can also provide accurate information on staging, all in a single examination (Figure 3).

In hepatic imaging, CTA can be used for vascular mapping and to look for such conditions as cavernous transformation of the portal vein or collateral vessels in the abdominal wall of a patient with cirrhosis (Figure 4). CTA is useful not only for detecting lesions, but also for looking at the pattern of contrast enhancement; such as in the case of hemangioma. Similarly, in the case of
a metastatic neuroendocrine tumor, arterial-phase imaging can nicely reveal arteriovenous shunting.

CTA offers numerous opportunities to increase the capability of CT, not by improving the definition of pathology but, as shown in Figure 5, by detecting lesions that might otherwise be overlooked because they are infiltrative rather than mass-like. Detection of neovascularity in a patient with hepatoma is an example.

CTA is becoming the state of the art for examining a wide range of problems, including those in which CT has always played an important role. Preoperative evaluation of the mesenteric vessels in a patient with a recurrent small bowel tumor, or examination for ischemic bowel in a patient with abdominal pain represent classic applications of CT that are strengthened by advances in scanning technology.

With scan times of <10 seconds, and delays from scanning to visualization of only 1 to 2 minutes, advanced CT technology is markedly changing how we practice. As our experience increases, and as scanners continue to improve, many questions remain to be answered. The importance of good contrast enhancement is clear. However advanced image processing techniques may be, whether maximum-intensity projection or volume rendering, they rely on the quality of the initial data sets. With adequate vessel opacification and optimally timed image acquisition, the quality of the images we are able to create is truly impressive.

Figure Captions

FIGURE 1. (A and B) Maximum-intensity projections reveal pulmonary vasculature.

FIGURE 2. (A and B) Occluded left internal carotid artery. CTA is routinely used to examine carotid arteries for stenosis.

FIGURE 3. (A and B) In hypervascular right renal cell carcinoma, CT can not only detect disease but also provide accurate information on staging.

FIGURE 4 . Collateral vessels in the abdominal wall of a patient with cirrhosis.

FIGURE 5. CTA detects neovascularity in a patient with hepatoma in a cirrhotic liver.

Please note that you must read all 8 articles and complete the quiz in order to earn 8 CME credits.

In order to take the quiz please click here .