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Two‐Dimensional Doppler (Color) Flow Imaging: State‐of‐the‐Art

The field of echocardiography continues to expand with new information and applications for the evaluation of patients with cardiovascular disease. Stress echocardiography is being utilized more widely, and is beginning to play an important role in the evaluation of patients with coronary artery disease. Progress in contrast echocardiography is slow but sure, and the potential applications for this technique continue to be delineated at the experimental level. Advances also are being made in the field of tissue characterization by ultrasound, and this technique appears to be on the threshold of fulfilling the potential that it has promised for so many years. However, of all of the technology on the drawing board or currently being introduced into echocardiography, the one that recently has drawn the most attention and excitement has been two-dimensional Doppler flow imaging. The technical development of color flow imaging has proceeded relatively rapidly. The earliest units were large, immobile, subject to artifacts such as ghosting, and not entirely well integrated with pulsedand continuous-wave Doppler spectral recordings. The newest units are smaller, portable, and provide an entire package of capabilities including two-dimensional and Mmode echo, flow imaging, and pulsedand continuous-wave Doppler. In addition, other improvements are being evaluated, such as displays of aliasing only. Progress in the clinical application of Doppler flow imaging has proceeded at a slower, but still steady pace. Much time has been devoted toward recognizing the multiple patterns that may be recorded in various areas within the central circulation in normal flow states. The optimal technique for performing the Doppler mapping examination has been sought, and realization of the benefit of nonstandardized views has been reached. There has been an increasing appreciation of the relative value of each Doppler technique to the assessment of a given patient. This work has led to documentation of the ability of Doppler flow imaging methods to identify cardiovascular abnormalities. Doppler flow mapping perhaps has been most sensational in the evaluation of valvular regurgitation. Thus, the presence, number, size, shape, and direction of regurgitant jets have been well tracked and visualized by color flow methods. The appearance of intracardiac shunting also has been dramatic, and color flow imaging techniques have identified the presence, location, and direction of blood flow of such communications in the central circulation. In regard to valvular stenosis, work has emerged that has shown a clear pattern of disturbed flow due to an obstruction at a valve orifice. Despite these qualitative observations, quantitative information has been slow in coming. Although intuitively it would seem that visualization of a regurgitant jet should convey quantitative data regarding either the volume of regurgitation or the effect of the lesion upon cardiac function, such a relationship has not been easily documented. In regard to the evaluation of stenotic lesions, the enhancement of gradient estimation conveyed by the ability to delineate jet direction has apparently not yet reached a level sufficient to alter clinical practice. Doppler flow imaging has done much to strengthen the conviction in the overall noninvasive assessment of any individual patient, but has not provided an objective measurement of comparable magnitude