Biomedical subjects

M Yasaka

Publications and source records attributed to M Yasaka.

57 records · Page 4Linked to original sources

PubMedDate not supplied

Microembolic signals and diffusion-weighted MR imaging abnormalities in acute ischemic stroke.

BACKGROUND AND PURPOSE: The clinical significance of microembolic signals (MESs) detected by transcranial Doppler sonography (TCD) in acute ischemic stroke remains unclear. The purpose of the present study was to assess the findings of diffusion-weighted MR imaging (DWI) and other clinical characteristics in patients with acute ischemic stroke and MESs. METHODS: We performed TCD and DWI within 48 hours and 7 days, respectively, after stroke onset in 28 patients with acute brain infarction. The relationship between the number of MESs and DWI findings, risk factors for stroke, National Institutes of Health Stroke Scale (NIHSS) score on admission, and arterial disease was examined. RESULTS: Ten patients had MESs detected by TCD (MES group) and 18 had no MESs (control group). The frequency of hypertension, diabetes mellitus, hyperlipidemia, and smoking; NIHSS score; blood-coagulation parameters; and interval between stroke onset and DWI study did not differ between the two groups. However, arterial disease was more frequent in the MES group than in the control group. Small, multifocal ischemic lesions (<10 mm in diameter) on DWI were more frequent in the MES group than in the control group. Conventional CT and MR imaging often failed to show these lesions. CONCLUSION: Small, often asymptomatic DWI abnormalities were more frequent in patients with MESs detected by TCD and with large-vessel occlusive diseases than in stroke patients without MESs. TCD and DWI may provide early clues to the mechanism of stroke in the acute phase.

Acute Disease↗

PubMedDate not supplied

Imaging of the basal cerebral arteries and measurement of blood velocity in adults by using transcranial real-time color flow Doppler sonography.

We report an attempt to obtain images of the basal cerebral arteries and to measure the quantitative flow velocity in these arteries from outside the skull via the color Doppler imaging method. In 25 healthy volunteers, 22-41 years old, the transducer was positioned just superior to the zygomatic arch and anterior to the external ear canal. The absolute flow velocity was calculated by dividing the measured velocity by the cosine of the incident angle. The middle cerebral artery was readily identified in all subjects, but the anterior cerebral artery was seen in only 7/50, and the posterior cerebral artery in 27/50. The corrected mean velocity of the horizontal middle cerebral artery was 86 +/- 17 cm/sec at an average incident angle of 49 degrees. However, it was difficult to calculate the absolute flow velocity in the anterior and posterior cerebral arteries because the length of those arteries delineated was too short to read the incident angle. The reproducibility of the mean blood velocity in the middle cerebral artery was tested by two examiners on two different occasions, and showed a linear regression with a correlation coefficient of 0.93 (p less than .001) when the correction with the incident angle was made. Transcranial real-time color-flow Doppler imaging permits more accurate noninvasive quantification of cerebral hemodynamic consequences than previous methods do.

Adult↗

PubMedDate not supplied

Diagnosis of middle cerebral artery stenosis by transcranial color-coded real-time sonography.

BACKGROUND & PURPOSE: This study was performed to determine the usefulness of transcranial color-coded real-time sonography (TCCS) in detecting stenosis in the horizontal portion of the middle cerebral artery (MCA). METHODS: Using TCCS and the incident angle correction technique, we measured the peak-systolic flow velocity in bilateral MCAs in 45 consecutive patients in whom cerebral angiography was carried out within 1 week before or after TCCS. Three patients had a stenosis of 75% or greater and four had a unilateral occlusion of the extracranial internal carotid artery (ICA) (the ICS and ICO groups, respectively). Eight patients had a stenosis of 50% or greater (one bilateral and seven unilateral) (the M1S group). Four patients had unilateral distal occlusion of the horizontal portion of the MCA (the M1O group). Twenty-six patients had no significant extra- or intracranial stenosis on the ipsilateral or contralateral side (the control group). RESULTS: Mean peak-systolic flow velocity on the affected side was 83.0 +/- 20.8 cm/s in the ICS group, 59.8 +/- 23.2 cm/s in the ICO group, and 62.3 +/- 33.7 cm/s in the M1O group. In the control group, the mean peak-systolic flow velocity was 116.0 +/- 31.5 cm/s. In the M1S group, however, the mean peak-systolic flow velocity (334.2 +/- 35.7 cm/s) on the affected side always exceeded 180 cm/s (mean value +/- 2 SD in the control group), and was significantly higher than that in the other groups. The mean peak-systolic flow velocity in the M1S group increased with the grade of stenosis. CONCLUSION: The M1S group members could easily be distinguished from the other group members by their peak-systolic flow velocity in excess of 180 cm/s. Measurement of the peak-systolic flow velocity of the MCA by TCCS may help to identify a significant stenosis in the horizontal portion of the MCA.

Blood Flow Velocity↗