QUANTIFICATION AND ASSESSMENT OF CAROTID-ARTERY LESIONS - DEGREE OF STENOSIS AND PLAQUE VOLUME

Various methods were developed for the quantification of the degree of stenosis: B-mode imaging, CW Doppler with spectral analysis, PW-duple x, and color-flow imaging. The degree of stenosis can be evaluated usi ng transverse views of the carotid in conventional B-mode imaging. The diameters of the residual lumen (Ds) and the external diameter (De) o f the artery at the same level are measured and the degree of stenosis (in area) is calculated. Two different Doppler methods have been desi gned and validated for the quantification of the stenosis degree. The first one is based on the determination of the maximal velocity inside the stenosis and requires the use of a duplex device. The second one, based on the quantification of the hemodynamic disturbances at the ou tlet of the stenosis, can be used either with a duplex system or with a continuous-wave Doppler system (pencil probe). The color display mod e facilitates the determination of the residual lumen and therefore co ntributes to making the B-mode method more accurate. Moreover, it prov ides a visualization of the blood flow which avoids most of the misint erpretations of B-mode or Doppler data. Several classification systems based on subjective or semi-quantitative criteria (morphological or h emodynamic) were used to identify different grades of stenosis (<40%, 40% to 60%, 60% to 90%, etc.) These classifications provide an evaluat ion of the degree of stenosis accurate enough to discuss the possibili ty of performing an endarterectomy on a symptomatic patient. When the surgical treatment seems to be inappropriate, the patient is treated m edically; the follow-up of the lesion (ie, every 6 months) requires a more precise evaluation of the plaque changes than does stenosis class ification. Several parameters have been designed and validated for the quantification of the degree of stenosis by ultrasound. These paramet ers, whether measured with the B-mode and color image or with the Dopp ler spectrum, allow quantification of the stenosis degree in percentag e of lumen reduction with a precision of approximately +/- 10%. Such a quantitative assessment of carotid lesions for a long period of time may be very helpful in evaluating the beneficial effects of medical tr eatment or in detecting any significant increase of the stenosis that could lead to surgical treatment. A new method for the plaque volume a ssessment has been recently validated. The plaque volume index express ed in mm(3) is calculated from logitudinal and transversal B mode view s of the bifurcation. (C) 1995 John Wiley and Sons, Inc.