首波灌流影像的檢查首波灌流影像是以SE/EPI (multislice spin echo/echo-planar images)技術來偵測相對大腦血流體積 ( r-CBV) 。其重覆循環時間 (TR):1900毫秒,迴旋時間(TE ):80毫秒
結果:
在中風病人中(5位病人,6個病變),在梯度迴旋動脈質子標記灌流影像與首波灌流影像中,皆可發現區域灌流減少(hypoperfusion)。在類中風病人中 (18位病人,19個病變) 在梯度迴旋動脈質子標記灌流影像中,除了出血病變之外,並沒有呈現出區域低灌流現象。 我們初步經驗發現梯度迴旋動脈質子標記灌流影像的診斷效力與首波灌流影像相當甚至更好。
結論:
在梯度迴旋技術的協助下,梯度迴旋動脈質子標記灌流影像有較好的雜訊比(signal to noise ratio, SNR)、空間解析度(spatial resolution),而且迴旋時間極短,所以可以將磁場屏蔽雜訊(magnetic susceptibility artifact) 降到最低。 而且梯度迴旋動脈質子標記灌流影像在不須使用外來顯影劑的情形下,可以增加核磁共振檢查在臨床上的應用。
Purpose: A simple gradient-echo arterial spin tagging (GREAST) technique, allowing a quick look at the tissue perfusion state without administration of exogenous contrast agent, was compared with the first-pass dynamic MR imaging technique in differential diagnosis of stroke and stroke-liked patients.
Materials and methods: The GREAST technique uses a combination of a spoiled gradient-echo sequence with an ordinary selective pre-saturation radio-frequency (RF) pulse that allows acquiring each tagged and control image within 10-20 seconds. The spatial pre-saturation RF pulse was used to saturate the inflowing spins and was applied in a short repetition time to achieve a steady-state effect. The imaging parameters were TR=15 msec, TE=1.5 msec, flip angle=20 degrees, matrix=256x160. The total scanning time was 19 seconds per image. MR perfusion images of 23 patients (25 lesions) with symptoms and signs of stroke acquired with the GREAST and first-pass perfusion techniques by using 1.5T MR system. Qualitative and visual analyses were performed to evaluate the diagnostic efficacy of GREAST.
Results: In stroke patients (five patients and six lesions), regional hypo-perfusion was identified in both GREAST and first-pass perfusion images except in reperfusion lesions. Almost all lesions in non-stroke group (eighteen patients and nineteen lesions) had iso- to hyper- perfused characteristics except in hemorrhagic lesions. Our preliminary results revealed that the diagnostic efficacy of GREAST is as good as or better than that of the first-pass perfusion imaging technique.
Conclusion: With the indigenous advantage of gradient echo sequences, GREAST allows much higher signal-to-noise (SNR), spatial resolution, and especially much shorter TE, which is very effective in minimizing the magnetic susceptibility artifact. Without administration of exogenous contrast agents, GREAST would be clinically useful to expand the brain MR applications in routine examinations.