Bendick et al. [24] evaluated the accuracy of 3-D power Doppler angiography in the carotid artery bifurcation compared with digital subtraction contrast angiography and surgical findings at carotid endarterectomy. Thirty-two patients were studied, with sixty-four vessels available for correlation. Luminal narrowing was categorized according to standard gradations of percent stenosis or total occlusion, using direct measurements from the 3-D images without knowledge of the angiographic results and applying the methodology of stenosis measurement of the NASCET study (Fig. 56.3). In addition, surface morphology of the 3-D images was evaluated to determine the extent of luminal narrowing, defined as focal, moderate (<1 cm), or lengthy (>1 cm), as well as the presence of plaque ulceration. Three carotid bifurcations had atherosclerotic lesions that were too heavily calcified for adequate power Doppler angiography and could not be classified by 3-D imaging. Of the remaining 61 bifurcations, 53 were accurately classified as to percent stenosis, giving an overall accuracy of 87%, similar to results obtained when Doppler velocity criteria are used to categorize lesion severity. The sensitivity of 3-D imaging to a >50% diameter stenosis was 100%; the positive predictive value for >50% diameter stenosis was 81% (21 of 26 bifurcations) (Fig. 56.4). All four total occlusions were correctly identified by 3-D imaging.

In the evaluation of the extent of lesions, 11 of 13 (85%) were correctly classified as focal, 24 of 29 (83%) as being of moderate extent of <1 cm, and 14 of 14 (100%) as extended lesions of >1 cm. Five lesions were considered to be ulcerated by 3-D angiography (Fig. 56.2) with four of these ulcerations shown by subtraction angiography. 3-D power Doppler angiography was believed to provide an accurate noninvasive technique comparable to subtraction angiography for the anatomic evaluation of carotid bifurcation atherosclerotic disease, with selectable viewing projections that helped eliminate vessel overlap and other artifacts. The technique complemented the hemodynamic data already available from conventional 2-D duplex ultrasound, but at this time could not replace it; instead it allowed a more thorough evaluation of any obstructive disease present without significant additional testing.

Delcker et al. [25] investigated 3-D power Doppler angiography for transcranial imaging of the major intracranial vessels. Previous studies have shown improved ability for transcranial duplex ultrasound to detect and image the intracranial vessels using power Doppler compared with color Doppler imaging [26, 27]. Delcker et al. also studied the use of a transpulmonary-stable ultrasound contrast agent. When their 3-D studies were compared with diagnostic cerebral angiography, they had imaging success rates of 100% for the ipsilateral anterior cerebral artery, middle cerebral artery (with three or more branches), posterior cerebral artery, and posterior communicating artery and 90% for the anterior communicating artery. On the side contralateral to the transducer, imaging success rates were 90% for the anterior cerebral artery, 80% for the middle cerebral artery (again with three or more branches), and 100% for the posterior cerebral artery. They concluded that 3-D transcranial power Doppler angiography with contrast agent enhancement provided significant improvements in the visualization and evaluation of the major intracranial arteries.

A number of other reports have been published on the clinical utility of power Doppler ultrasound in vascular patients [28–31]. The most recent report evaluated 53 patients referred to the vascular laboratory who had conventional color duplex ultrasound followed by power Doppler imaging [32]. All 53 patients had conventional arteriography to verify the duplex ultrasound results. Patients were seen for the following indications:

The color duplex imaging and the power Doppler examinations were performed by experienced registered vascular technologists in an accredited vascular laboratory using an HDI 5000 Philips, ATL system (Bothell, WA). Sequential parallel longitudinal views and perpendicular cross-sectional views were obtained on both color duplex and power Doppler imaging. The display quality of both sonographic examinations was classified as satisfactory or unsatisfactory by both the technologist and the interpreting physician. A satisfactory image was defined as one with clearly seen anatomy and well-visualized pathology of the examined vessel. Power Doppler imaging was considered to be of positive diagnostic value if the results of that examination were helpful in differentiating subtotal from total occlusion, optimizing image quality, or visualizing deep-lying vessels (e.g., renal artery) that were not seen on conventional duplex examination. If the two portions of the duplex examination were inconsistent, the final conclusion was decided based on the results obtained by conventional arteriography.

A positive diagnostic value was achieved using power Doppler imaging in 22 out of 29 (76%) carotid artery examinations. Similarly, 10 out of 14 (71%) peripheral artery examinations had a positive diagnostic value. Four out of five (80%) renal artery examinations had a positive diagnostic value, while three out of five (60%) aortoiliac examinations had a positive diagnostic value. Overall, a positive diagnostic value was achieved by adding power Doppler imaging in 39 out of 53 arteries (74%, Table 56.1). The overall sensitivity of power Doppler imaging in patients with a positive diagnostic value was 95%, and the positive predictive value was 97%.

Table 56.2 summarizes the indications of power Doppler imaging and the positive diagnostic value in carotid artery applications. As noted, five out of six patients (83%) who were believed to have total carotid occlusion by conventional color duplex were confirmed to have subtotal occlusion by adding power Doppler imaging. Ten out of fourteen (71%) carotid artery patients who were believed to have suboptimal images had an improved image on power Doppler imaging. Table 56.3 summarizes the findings in patients for whom the indications included peripheral arteries, renal arteries, and aortoiliac arteries. Six out of eight (75%) patients with a questionable subtotal versus total occlusion by conventional duplex examination were confirmed to have subtotal occlusion by power Doppler imaging. Overall, 10 out of 14 (71%) patients with peripheral arterial examinations had a positive diagnostic value. Four out of five (80%) renal examinations resulted in a positive diagnostic value, which included three patients in whom the origin of the renal arteries was not seen by conventional duplex examinations. Three out of five (60%) aortoiliac examinations resulted in a positive diagnostic value. Figures 56.5, 56.6, 56.7, 56.8, 56.9, 56.10, 56.11, 56.12, and 56.13 illustrate various clinical scenarios where a positive diagnostic value was achieved by adding power Doppler imaging.