工藤 信樹, 張 旭, 山本 克之

Nobuki KUDO, Xu ZHANG, Katsuyuki YAMAMOTO

北海道大学工学部

Division of Biomedical Systems Engineering, Hokkaido University

キーワード : Arterial wall thickness, Atherosclerosis, Carotid artery, Radiofrequency echo signal, Ultrasound

Use of B-mode ultrasonograghy to measure the wall thickness of the carotid artery is a promising method for detecting and diagnosing atherosclerosis in its early stage. Accurate measurement is essential, however, because the change in wall thickness is very small. Here we propose a new method for measuring arterial wall thickness using the frequency spectrum of a radiofrequency (RF) echo signal and validate the usefulness of the method by comparing its results with those obtained with the conventional method, which is based on B-mode ultrasound imaging. The measurement system uses a diagnostic ultrasound unit equipped with a 7.5 MHz annular array probe and a personal computer. RF echo signals from the inner and outer walls of the carotid artery were obtained from 12 healthy subjects. Wall thickness was determined from the interval of dips that appeared in the power spectrum of the captured RF echo signals. For purposes of comparison, thickness was also measured using two threshold methods, which simulated the conventional B-mode-based measurement by processing A-mode signals with a computer. The average of 110 measurements of wall thickness made by using the power spectrum method, the constant threshold method, and the normalized threshold method were 0.59±0.095 mm, 0.41±0.095 mm, and 0.56±0.083 mm, respectively. The fact that the magnitude of the echo signals from the inner and outer walls differs so greatly in the constant threshold method, which is widely used for B-mode-based measurement, suggests that this method may underestimate wall thickness by about 30%.