The power Doppler imaging method displays intensity information of the Doppler signal generated from moving blood, as opposed to conventional color flow imaging, which displays the mean velocity of blood flow.
Compared with conventional color flow imaging, power Doppler imaging has characteristics such as little angle dependence, no aliasing, and less noise. As a consequence, it can evaluate the blood flow dynamics in small branch vessels distributed in many directions. Power Doppler imaging can also detect small vessels with under noisy conditions which make it difficult for color flow imaging.
On the other hand, power Doppler imaging cannot confirm the direction of blood flow because it only displays intensity information, and the degree of reduction is sacrificed for motion artifact.

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We compared the histological features of carotid plaques obtained from Americans and Japanese patients. Among 36 Japanese plaque specimens obtained between 1976 and 1986 (early Japanese plaques) and American plaque specimens obtained between 1982-1986, we compared the histological findings revealed by H & E staining and immunostaining for macrophages and smooth muscle actin. Japanese plaque specimens obtained between 1987 and 1990 (late Japanese plaques) were also used for detection of histological differences in Japanese plaques between different decades. The only differences we detected were old hemorrhage and calcification, observed predominantly in the American plaques (p<0.01 by chi-square test) . Proliferation of smooth muscle was detected mainly in American plaques (p<0.0I), whereas macrophages predominated in the Japanese plaques (p<0.01) . No histological differences were detected between early and late Japanese plaques. These results indicated that American plaques were in the late stage of atherosclerosis, whereas Japanese plaques were in the early stage of the disease. Further study is needed in order to delineate these differences.

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We reviewed the correlation of histological changes in aherosclerotic carotid arteries and images obtained by in vivo B-mode ultrasonography, based on pathoanatomical studies of carotid arteries obtained at autopsy and carotid endarterectomy specimens in relation to ultrasonographic findings. The crucial purpose of ultrasonography is to detect carotid plaques that pose a risk of ischemic cerebrovascular accidents. Our experience and review of the literature showed that carotid plaques carrying a risk of stroke are characterized by large dimension with severe luminal stenosis, ulcer formation, a large amount of stored lipid, intraplaque hemorrhage and a fragile fibrous cap over a fatty core.
By ultrasonography, fibrous plaque appears as localized thickening of the wall with little change in echogenicity. Fatty cores appear less echogenic than the adjacent tissue. Intraplaque hemorrhages also appear less echogenic, and therefore it is difficult to differentiate them from fatty cores. Calcified foci in plaques are highly echogenic and associated with acoustic shadowing. Ultrasonography cannot detect the detailed morphology of fibrous caps consistently. Plaques carrying a risk of stroke appear heterogeneous by ultrasonography. Even though its function is limited, B-mode ultrasonography is a unique technique for detecting the structural changes which cannot be revealed by angiography.

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The assessment of carotid stenosis and plaque morphology is important for the prevention of cerebral infarction. Power Doppler imaging (PDI) is a new non-invasive technique which can visualize intravascular morphology from the integrated power of the reflected echo mainly from red blood cells. We evaluated PDI and color-flow Doppler imaging (CFDI) for the measurement of carotid stenosis and characterization of the plaque surface and compared the results with surgical specimens. PDI is superior for depicting the vessel lumen with intravascular color signals, but has a tendency to underestimate stenosis due to motion artifacts, whereas CFDI overestimates and underestimates stenosis as determined by angiograms. In hypoechoic stenosis such as radiation-induced angiitis, PDI demonstrates the stenotic vascular lumen clearly. Rough and smooth intrastenotic lumina can be compared, and PDI enhances the surface morphology and depicts rough structures, but fails to delineate ulcerative plaque surfaces clearly. CFDI is useful for assessing ulcerative surfaces due to the presence of turbulent flow. These two types of color-coded Doppler sonography complement each other, and increase the reliability of Doppler imaging for noninvasive diagnosis of carotid artery stenosis.

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A study was performed to clarify the usefulness of an ultrasonic quantitative flow measurement system (QFM) for diagnosis of cerebrovascular disorders. A total of 195 patients including 92 males and 103 females aged 57 to 81 (mean 65) years were enrolled. All patients underwent measurement of common carotid hemodynamics by QFM, and by conventional cerebral angiography. We proposed the following QFM findings as diagnostic criteria for occlusion or stenosis of the internal carotid artery: 1) a difference in mean blood flow volume of over 2.0 ml/s between the opposite side and the involved side; 2) a difference in mean blood velocity of over 5.0 cm/s between the opposite side and the involved side. We also proposed the following QFM findings as diagnostic criteria for hypoplasia or aplasia of the anterior cerebral artery (A, portion) : 1) a difference in mean blood flow volume of over 2.0 ml/s between the opposite side and the involved side; 2) a difference in mean vessel diameter of over 1.0 mm between the opposite side and the involved side. The sensitivity and specificity of the QFM diagnostic criteria for occlusion or stenosis of the interal carotid artery were 74% and 91 % respectively. Sensitivity and specificity of the QFM diagnostic criteria for hypoplasia or aplasia of the anterior cerebral artery (A, portion) were 85% and 98% respectively.
These results suggest that measurement of common carotid hemodynamics by QFM is useful for the screening of cerebrovascular disorders.

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The treatment of spontaneous carotid cavernous fistulas (CCF) has been a challenging problem for neurosurgeons. Recently, with the advent of refined microcatheters and various kinds of embolic materials, endovascular surgery has become the treatment of choice. After embolization, follow-up study is indispensable, because thrombosis of fistulas may continue after the procedure, or reopening of the occluded vessels may occur. The purpose of this study was to evaluate the usefulness of transorbital color Doppler imaging (CDI) as a tool for the diagnosis and follow-up of CCF.
CDI offers simultaneous two-dimensional structural imaging and Doppler measurement of blood flow. Four patients with spontaneous CCF were examined by this technique. CDI demonstrated a dilated superior ophthalmic vein (SOV) with reversed direction of blood flow in all of the patients. They underwent occlusion of the fistula by transvenous embolization with platinum coils. Postembolization CDI revealed shrinkage of the SOV in all cases.
In conclusion, CDI provides a noninvasive means of confirming the presence of CCF, and assists in the evaluation of hemodynamics of carotid cavernous fistulas after endovascular surgery.

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The shock-induced collapse and jet formation of a single air bubble inside a cylinder filled with gelatin and an artificial thrombus were investigated using high-speed photography. A thrombus was prepared in vitro and inserted in a cylinder modeling an artery to establish a treatment for brain embolism by the interaction of an underwater shock wave with an air bubble. When the shock wave was applied to an air bubble of mm in diameter, the liquid jet that formed within the bubble penetrated the thrombus. Liquid jet impact ablation of the for thrombus was found to be very effective, and provided valuable information for the treatment of brain embolism.

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