CHAPTER SUMMARY AND CENTRAL ILLUSTRATION
The modern era of cardiovascular disease management is based on imaging. This chapter seeks to introduce the common imaging modalities—addressing the fundamental imaging considerations of temporal, spatial, and contrast resolution, as well as the underlying pathophysiology examined by each test—and provide the methodology and applications of each technique. Details of test performance are provided in the relevant chapters about disease entities. The main goals of cardiac imaging are the anatomic and functional assessment of the cardiac chambers, valves, great vessels, and coronary arteries. Multiple methodologies are now able to address each one of these goals. We thus risk duplication if we employ the approach of layering multiple tests, particularly when testing begins with a “generic” test, such as a chest x-ray, echocardiogram, or functional test for ischemia. Of course, in a patient with undifferentiated symptoms, this approach is unavoidable. However, given that most cardiovascular diseases are chronic and recurrent, specific questions may arise at particular times. In these settings, selecting a more advanced test that also provides generic information is desirable (see Fuster and Hurst’s Central Illustration).
eFig 3-01 Chapter 3: Cardiovascular Imaging
Cardiac imaging is performed with x-ray, ultrasound, light, nuclear medicine, and magnetic resonance imaging (MRI) techniques. In many clinical situations, multiple modalities can be brought to answer a particular question. Sometimes, the selection of modality pertains to local availability or expertise. However, everything else being equal, the inherent nature of the imaging modalities should be matched to the clinical question. For any imaging methodology, there are three metrics of image resolution: spatial, temporal, and contrast. Spatial resolution is the ability to discriminate small objects and is determined in axial (parallel to the imaging direction; primarily a function of wavelength) or lateral (perpendicular to the beam). Contrast resolution is the distribution of the grayscale of the reflected signal and is often referred to as dynamic range. An image of low dynamic range appears as black and white with a few levels of gray; images at high dynamic range are often softer. Temporal resolution relates to the ability to distinguish events in time. For example, the assessment of myocardial dyssynchrony or contractile dispersion should be done with the highest temporal resolution technique, which is generally ultrasound. On the other hand, the interpretation of the status of atherosclerotic plaque requires very high spatial resolution, and optical coherence tomography (OCT) is more likely to provide this than intravascular ultrasound (IVUS).
The indications for imaging techniques include diagnosis, prognostic assessment, and management decisions. The aspects of the technique that make it desirable for one of these indications may not be the most important in another setting. For example, management decisions may require ...