超音波変位法 (Stiffness Parameter β) による脳動脈硬化判定に関する研究

Abstract

Because of the rapid increase of the aged population, arteriosclerosis of the cerebral artery has become one of the most important cerebral pathologies in the adult patients. Unfortunately, a reliable and non-invasive method for estimation of sclerotic changes in the cerebral artery has not yet been established. We developed a new method for this purpose, using an ultrasonic phaselocked echo tracking technique. As we reported in our previous papers, the grade of arteriosclerosis was estimated by the magnitude of pulsatile movement of the arterial wall. In this study, grading of cerebral arteriosclerosis by our method was compared with grading or rating by other methods of investigation.In our method, a linear scan ultrasonograph (Aloka-SSD610) was used, which contains an ultrasonic phase-locked echo tracking system and is combined with a 10 MHz transducer and a RF-I echo monitor. The common carotid artery, internal carotid artery, carotid sinus and vertebral artery were examined separately by this method. A stiffness parameter, i.e. β value, was calculated from the diameter of an examined artery (Dd), pulsatile changes in a diameter of the artery (ΔD), systolic arterial pressure (Ps) and diastolic arterial pressure (Pd), using the following equation; β = In {(Ps/Pd) / (ΔD/Dd)}. It is apparent, therefore, that a higher β value suggests a less pulsatile deformation of an arterial wall, i.e. a higher hardness of the arterial wall. On the other hand, a severity of cerebral arteriosclerosis was rated with a five-grade scale (0 to IV) according to angiographical changes such as irregularity of the wall, stenosis, tortuosity and dilatation. Additionally, an arteriosclerotic rating due to the funduscopic findings and evaluation of cerebral perfusion by a single photon emission CT (SPECT) with 123I-IMP were tried. Included in this study were 196 cases of obstructive cerebrovascular disease.Our data accumulated so far has revealed that: (1) β value become high as an sclerotic change in the arterial wall increased, (2) β value tended to be higher in the hypertensive group than in the non-hypertensive group, (3) β value was proved to correlate well with the angiographic rating of cerebral arteriosclerosis, (4) Keith-Wagener grading based on funduscopic findings also correlate well with β value, (5) β value was elevated in patients with cerebral hypoperfusion demonstrated by SPECT with 123I-IMP.Our conclusion is that assessment of cerebral arteriosclerosis by our method has a clinical usefulness because of its good correlation with other ratings of cerebral arteriosclerosis and its non-invasiveness.