Recently, it has become possible to measure blood flow velocity by MRI flow mapping. This study was designed to evaluate the accuracy of MRI flow mapping for measuring blood flow velocity in the common carotid artery (CCA), in comparison with a conventional ultrasonic quantitative flow measurement system (QFM) .
We studied 58 patients aged 19-74 years (mean age, 40 years; 20 males, 38 females) without cerebrovascular disorders, essential hypertension, diabetes mellitus, or hyperlipidemia. The maximum and mean blood flow velocity of the CCA were determined by QFM 2000 XA (Nippon Koden Co.) and MRI (Siemens Co. 1.0T) based on MRI phase-contrast measurement. Technical parameters of MRI were: TR/TE/FA=31 ms/6 ms/25, slice=6 mm, matrix=256 × 256, field of view = 200 × 200 mm.
The maximum blood flow velocity was 55.2 ± 16.8 cm/s by QFM, and 56.8 ± 15.5 cm/s by MRI. The maximum flow velocity in the CCA determined by MRI was significantly correlated with that determined by QFM (r=0.69, p<0.001), and the two methods were in good agreement. The mean flow velocity in the CCA was 22.6±5.6cm/s by QFM, and 25.3±7.3 cm/s by MRI. The mean flow velocity measured by MRI was higher than that measured by QFM, but the two values were significantly correlated (r=0.59, p<0.001) .
These results indicate that the maximum blood flow velocity in the CCA as measured by MRI is in good agreement with that determined by QFM.

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Recently, high-intensity transient signals (HITS) obtained by transcranial Doppler ultrasonography (TCD) were reported to reflect micro-emboli in cerebral arteries. Frequent detection of HITS in patients with mechanical valve replacement has been reported for many years. However, the mechanism and significance of these signals has remained unclear. We attempted to elucidate whether HITS indicate a risk of cerebral infarction in patients with mechanical valve (St. Jude Medical valve: SJM) replacement, and also carried out an animal experimental study to clarity the mechanism of HITS formation.
HITS was frequently detected in patients with SJM valves. The HITS count after surgery in patients with cerebral infarction (83 ± 66/15 min) was significantly higher than that in patients without a history of stroke (7 ± 7/15 min) (p<0.001) . The HITS count in patients with mechanical valve replacement appeared to increase with time after surgery. Thus, the HITS count appeared to indicate the risk of cerebral infarction after mechanical valve replacement. In the experimental study, injection of clotted blood into the aorta produced low-frequency and small-intensity HITS. Introduction of micro-bubbles into the aorta produced high-frequency and large-signal-intensity HITS. These two kinds of HITS were detected in patients with SJM valves. Thus, HITS in patients with SJM valves may be produced by both gaseous and solid micro-emboli.

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Harmonic imaging (HI) は, tissue harmonic imagingとして実質画像の空間分解能を上げるだけでなく, 超音波造影剤を用いて血管画像, ひいては実質臓器の微小血流の評価にまで応用されつつある.すなわちneurosonologyの領域では, emission CTやXe CTなどのいわゆる脳循環測定法としての意義が見込まれる.そこで, 最近発表されたこれに関する研究を紹介する.
【背景と目的】超音波造影剤静注後のgray-scaleHIは, 脳血流が毛細管レベルに至る脳灌流状態を画像化する初あての手法である.本研究は, 経頭蓋超音波法により脳の異なった部位の造影剤による一過性の増強効果を, second harmonic imaging (SHI) を用いて評価することを目的とした.
【対象と方法】脳血管障害のない各種神経疾患の患者18例 (22-56, 平均39歳) に対し, 6.5mlのガラクトースを基材としたmicrobubbleの混濁液 (Levovist, Schering AG) 400mg/mlを用いて, 両側の側頭窓から評価した.SONOS5500 (HP) の2.5MHzセクタ探触子で, frame rateは4心拍毎, 1.8MHz送信で3.6MHz受信のSHIとして画像化された.脳局所の増強効果を, まず視覚的に評価し, オフラインでtime-intensity curveを用いて定量的に評価した.脳の関心領域 (ROI) は, 視床の後部 (a) と前部 (b) , レンズ核 (c) , 大脳白質 (d) におき, 増強効果のpeak intensity, time-intensity curve下の面積 (AUC) , peak intensityまでの時間, ROIcとa, dとa, cとb, dとbの比を算出した.
【結果】全例で, 脳実質の増強効果が視認された.144のROI中131で, 増強効果を示す特徴的なtime-intensity curve (baseline phase, peak intensity, slow washout phase) が描出可能であった.とくにROIcとROIdで, 特徴的なtime-intensity curveが得られる頻度が最も高く (68/72) , ROIaとROIbでは増強不良で72検査のうち9回のみであった.peak intensityに至るまでの時間は, 20-52心拍と変動があり, 1例では88心拍であった.全例におけるAUCsと18例中16例のROIcとROIdにおけるpeak intensityは, ROIaとROIbと比較し2-10倍増強された.AUC比が2以上の左右差を示すROIはみられなかった.
【結論】SHIにより脳実質の異なった部位において, 超音波造影剤による増強効果を本研究では初あて描出し, 脳実質の血液灌流に関連した超音波診断法を導入した.しかし, 側頭骨の厚さの違いや超音波造影剤の濃度と描出される測定強度との関連は複雑で, 定量的評価としての増強効果の絶対値はバラツキがみられた.脳実質の増強効果の比較に, 異なった関心領域における増強効果の比が有用であった.SHIを用いた増強効果の減衰は測定深度に依存するため, HIによる脳灌流測定はpositron emission tomographyなど他の画像診断法と直接比較することはできない.
結局本研究では, 脳循環測定法として定量的な信頼性を確立することが出来ず, 定性的な意義しか見いだすことは出来なかった.しかし著者らも述べているように, 実時間性を生かしたdigital subtraction法の併用など今後の技術の改善により, 超音波を用いた局所脳循環測定法としての確立が切望されるところである.

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A 52-year-old man with aortic regurgitation (AR) presented with a subarachnoid hemorrhage (SAH) due to a ruptured mycotic aneurysm. Transcranial Doppler sonography (TCD) of the left middle cerebral artery demonstrated an increased peak systolic flow velocity (FV_max) of 95 cm/s and no flow during the end-diastolic phase. Management of cerebral vasospasm giving consideration to cardiac function was successful, and no further increase of FV_max was observed. After replacement of the aortic valve, TCD showed normalization of the wave contour compared with that before replacement. As AR patients are prone to cerebral vasospasm due to end-diastolic cerebral hypoperfusion, serial observation by TCD is helpful for management.

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We evaluated the clinical usefulness of three-dimensional (3-D) echoencephalography in infants. The transducer was placed on the anterior fontanel and all the sections were serially and automatically scanned in a few seconds. A 3-D image was constructed by an internal computer in a few seconds.
We could produce B-mode images at any direction, including those which could not be achieved via conventional methods. By using 3-D imaging, we could easily grasp the three-dimensional structure of the central nervous system. Further, we could measure ventricular volumes. We concluded that 3-D echoencephalography in infants is very useful.

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Background and Purpose: To assess the influence of the skull on blood flow signals detected by transcranial Doppler, we measured bone density in the skull using dual energy X-ray absorptimetry. Methods: Bone mineral density (BMD) was studied in 219 normal volunteers (mean age±SD 53.5±17.9 years, 80 men, 139 women) . In 37 of the subjects (mean age ±SD 56.4±15.8 years, 17 men, 20 women), blood flow signals were also measured using a 2-MHz range-gated pulsed-wave Doppler. Results: BMD in women was lower than that in men over 60 years of age (p<0.05) . The rate of unsuccessfully recorded flow signals increased with age, especially in women (14 of 17 women aged 60 years or over) . BMD in the unsuccessful recording group (1.482 ± 0.123 g/cm², mean ± SD) was significantly lower than that in the successful recording group (1.835±0.058 g/cm²) (p<0.05) . Conclusion: The rate of unsuccessfully recorded blood flow signals increased with advancing age, especially in women, and with lower BMD in the skull.

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From the viewpoint of safety, it is necessary for the diagnostic ultrasonic equipment used in clinical practice to satisfy the FDA 510 (k) requirement track III. The new requirement requires medical doctors and staff to have a greater understanding of ultrasonic bioeffects as indicated by the mechanical index (MI) and the thermal index (TI), on the real-time display of recently developed diagnostic ultrasonic devices.
This article describes the significance of MI and TI and the variables in clinical use. Also it is noted that the ultrasonic examiner should uphold the principle of ALARA (as low as reasonably achievable) in clinical use.

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