In the past few years, the term“Noh Dok”has become popular in Japan. This is a cerebral screening system based on MR angiography (MRA), which can obtain angiographic images noninvasively. Since the advent of MRA, the position of Doppler ultrasonography as the representative noninvasive diagnostic method has been under challenge. However, ultrasonography has several advantages over MRA, such as real-time imaging, bedside diagnosis, simplicity, cost-effectiveness, and freedom from the dangers of magnetic materials. These advances are in favor of its use for health screening. Recent advances in ultrasonography, such as transcranial Doppler, color Doppler-assisted duplex imaging, distal beams, broad-band-width scanning, color capture, and ultrasonic contrast medium, have enabled the development of new methods of clinical diagnosis. This article reviews the diagnostic potential of these new ultrasonic tools and discusses the role of ultrasonography in screening of the brain. In order to maintain its position as a health screening tool, ultrasonography must not be used as the sole fool for diagnosis.
Accuracy and limitations of medical ultrasound are described in terms of several kinds of resolution, such as temporal, spatial, contrast and velocity resolution. Ultrasound speed of about 1500 m/s in human soft tissue, limits the number of frames per second, the viewing area and the scanning line density. There are trade-offs among these parameters. In color Doppler flow imaging, frame rate limitation is much more severe. Three kinds of spatial resolutions are defined as the range resolution, the lateral resolution and the slice width. A simple and practical drawing method for ultrasound beam width representing the lateral resolution is shown for non-focusing and focusing transducers. Upper and lower limitations of Doppler blood velocity measurements are described.
Chronological changes of cerebral hemodynamics and cerebral oxygen metabolism in patients with head injuries associated with TSAH were analyzed by TCD and SjO2to evaluate disturbances accompanying traumatic vasospasm and the final outcome. The subjects were 44 head injury patients with Glasgow Coma Scale (GCS) scores of 3-15 (mean, 7) . Mean velocity (Vm) and pulsatility index (PI) in the middle cerebral artery were monitored continuously for 3 weeks after injury. The subjects were classified into Group S (19 cases) with and Group N (25 cases) without TSAH based on the initial CT findings, they were subdivided into two groups of initial GCS≤8 and 9≤. Sequential changes in the TCD findings in the periods 0-2, 3-7, 8-14, 15-21 and 22- days after injury were compared. In cases with GCS≤8, there was a weak correlation between the patient's outcome one and six months after injury and increased Vm (≥100 cm/s) on the 7th day after injury. Comparison between Group S and N showed: 1) Significant Vm increase and lower PI increase in group S compaired with group N (GCS≤8 cases) . 2) In both groups, Vm tended to increase and PI to decrease in correlation with TSAH (Fisher's classification) .3) Craniotomy did not influence Vm or PI in either group. 4) SjO2increase (>80%) tended to be correlated with increase in Vm (≥100 cm/s) cases. 5) Angiography demonstrated vasospasm and SPELT hypoperfusion in two of three cases of increased Vm (≥100 cm/s), but did not show development to cerebral infarction. 6) Poor outcome was predominant in cases with increased Vm in Group S. Increases in Vm and PI in patients with TSAH were probably related to localized ischemia and increased cerebrovascular resistance due to vasospasm after severe head injury, but global hyperemia based on oxygen metabolism indicated a poor outcome. Therefore, it is necessary to take account of abnormal hyperemia associated with TSAH after severe head injury.
In 20 healthy subjects the right middle cerebral artery TCD Doppler shift was monitored over 10 minutes and on-line analyzed. During minutes 3, 4 and 5 the subjects smoked a cigarette of their choice making a deep inhalation every 20 seconds and respiring normally in between. Blood pressure and heart rate were externally measured every 30 seconds. Cigarette smoking significantly increased blood pressure, heart rate and flow velocity. The TCD pulsatility index increased only after smoking. Flow velocity dropped to an average of 94+/-8% over postsmoking minutes 4 and 5. Repeated smoking spaced by several days done only in 1 subject so far having the middle cerebral artery Doppler signal recorded and analyzed bilaterally resulted in increased flow after smoking on one side and in decreased flow on the other. In conclusion the increase in heart rate and blood pressure and results indicate dilation of the cerebral resistance arteries during smoking followed by constriction of these vessels. The vasculature of one individual hemisphere may react differently on repeated smoking.
Cases of cerebral aneurysm in the aged has increased recently due to the advance of diagnostic methods. To obtain satisfactory results, complete neck clipping is not the only requisite factor, but also preservation of the blood flow in the parent arteries and perforators is needed. Monitoring of arterial blood flow velocity might be helpful in determining the possibility of stenosis or occlusion in the parent arteries. Forty cases with the mean age of 61 years are included in this study. Measurement of the blood flow velocity of the parent arteries was carried out before and after neck clipping of the aneurysm. The degree of flow change was evaluated as the percent change of the velocity. When the velocity increased or decreased more than 20% to the pre-clipping level, the result was evaluated as abnormal. Twelve cases were evaluated as abnormal, and ten cases of these were found to be aged 65 years and over. Five cases remained at the abnormal level even after topical application of papaverine. Controlled angiography revealed arterial occlusion in one case, and arterial stenosis in 4 out of 5 cases. Monitoring of arterial blood flow velocity shows blood flow in the vessels precisely during aneurysm neck clipping. Accordingly, better results can be expected through the use of this technique.