Background and Purpose-Three-dimensional (3-D) vascular ultrasound can be expected to improve qualitative evaluation of vessel pathology and to provide quantitative data on vascular morphology and function. The objective of this study was to develop an ultrafast 3-D vascular system and to validate its performance for quantitation of atherosclerosis and assessment of regional arterial distensibility. Methods-The quantitative analysis of focal atherosclerotic lesions was validated in vitro on 27 phantoms of fibroadipous plaques of known volume (range, 100 to 600 mm 3 ). In vivo reproducibility of plaque volume measurement was tested in 33 patients who had a total of 47 predominantly fibroadipous carotid plaques. Distensibility assessment was validated indirectly through the evaluation of age-related changes in distensibility of common carotid artery in healthy and hypertensive subjects (25 men in each group). Results-The volume of plaque phantoms measured from the 3-D data set showed a very close correlation with the true volume (rϭ0.99; yϭ0.96xϩ12.38; PϽ0.01), with the mean difference between the 2 measurements being Ϫ3.12Ϯ15.1 mm 3 . High reproducibility was found for measurement of carotid plaque volume in vivo: the mean difference between measurements from 2 observers for the same data set was 0.60Ϯ11.2 mm 3 . Indexes of arterial distensibility decreased with age in healthy population, whereas this relationship was lost in hypertensive subjects. Conclusions-Ultrafast 3-D ultrasound imaging of carotid artery demonstrates good accuracy and reproducibility for atherosclerotic plaque volume measurements. The system also allows the study of age-related degenerative vascular changes. (Stroke. 1998;29:1631-1637.)
An approach to dynamic focusing of ultrasound linear array scanners is presented, leading to the unique capability of implementing a focus that continuously tracks the return signal along the penetration depth. An electronically variable lens is obtained by a heterodyning process, in which the phases of echo signals at the array elements are equalized by mixing with suitable reference oscillations. These are generated by control of a single voltage-controlled oscillator, whose frequency is properly varied in synchronism with the delay of signal from different depths. The technique has been experimentally demonstrated by modifying the focusing processor of a conventional echographic linear scanner. Superior performances have been obtained with respect to fixed-focus operation mode. The image quality results are comparable with those of multizone-focus operation mode, in which the focus is varied over more transmit/receive cycles at the expense of lower frame rate.
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