Evaluation of focal cerebral perfusion using arterial spin labeling (ASL) technique.

使用动脉自旋标记（ASL）技术评估局灶性脑灌注。

• 批准号: 12670889
• 负责人: KODAMA Takao
• 金额: $ 1.15万
• 依托单位: Miyazaki Medical collage
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12670889/
• 关键词: Magnetic resonance imaging; Arterial spin labeling; Focal cerebral blood flow

During the first year, imaging parameters of the ASL technique affecting the image qualities were evaluated by using a single-slice 2D ASTAR technique in order to optimize the sequence. Because multi-slice imaging is essential for wide clinical applications of ASL techniques, we have evaluated the multi-slice 3D ASTAR technique after the second year. In multi-slice techniques, the influence of magnetization transfer contrast originating from a tagging pulse can't be totally collected with a control pulse. In this study, quality of the 3D ASTAR image was improved by using multiple non-slice selective inversion pulses which suppress the signal intensity of stationary tissues. Signal-to-noise ratio (SNR) of ASTAR images was significantly affected by arterial transit time (ATT), and image contrast changed according to the variation of TI. In the evaluation of the single-slice technique in young normal volunteers, SNR in the posterior watershed areas was lower than other areas probably beca … More use of the longer ATT in these areas. To achieve a proper perfusion map, TI long enough for areas with a long ATT should be selected (TI of 1000 to 1200 ms in normal young subjects). In multi-slice techniques, gap between the tag pulses and imaging slices was larger in more cephalad slices. So, influence of the ATT is more significant in multi-slice techniques than in single-slice ones, especially in cephalad slices. In normal volunteers, TI of longer than 1400 ms was needed to achieve proper signal in the most cephalad slice. In elder subjects, ASL signal of the brain parenchyma tended to be lower and contamination of intravascular signal was more pronounced, compared with younger subjects. These findings suggested the longer ATT in elder subjects due to decreased arterial flow rate. In patients with steno-occlusive vascular disease, elongation of ATT resulted in two errors ; 1) underestimation of focal CBF, and 2) overestimation of focal CBF due to intravascular signal. Influence of ATT was more pronounced in cephalad slices in the 3D ASTAR technique. Though longer TI is necessary to reduce the influence of ATT, longer TI resulted in decreased signal secondary to the longitudinal relaxation and resulted in longer examination time. It seemed to be necessary to decide the proper TI according to the predicted ATT. It, however, is difficult to predict ATT of each area in each subject. And elongation of TI was limited by the longitudinal relaxation and examination time. So, proper evaluation of focal CBF using the ASL technique could be difficult in patients with extremely long ATT, such as patients with progressed moyamoya disease. A saturation pulse could be applied in the same position of a tagging pulse to suppress intravascular signal. However, suppression of signal obtained with this technique was not selective for intravascular signal and could result in lower SNR. Less

在第一年中，通过使用单切片 2D ASTAR 技术评估影响图像质量的 ASL 技术的成像参数，以优化序列。由于多层成像对于 ASL 技术的广泛临床应用至关重要，因此我们进行了研究。第二年后评估了多切片 3D ASTAR 技术 在多切片技术中，源自标记脉冲的磁化传递对比度的影响无法通过控制脉冲完全收集。通过使用多个非切片选择性反转脉冲来抑制静止组织的信号强度，ASTAR 图像得到了改善。ASTAR 图像的信噪比（SNR）受到动脉传输时间（ATT）的显着影响，并且图像对比度根据情况而变化。在对年轻正常志愿者的单切片技术的评估中，后分水岭区域的 SNR 低于其他区域，可能是因为在这些区域使用了较长的 ATT 来实现适当的灌注。对于具有长 ATT 的区域，应选择足够长的 TI（正常年轻受试者的 TI 为 1000 至 1200 毫秒）。在多切片技术中，标签脉冲和成像切片之间的间隙在更多的头侧切片中更大。 ATT 的影响在多切片技术中比单切片技术更显着，尤其是在正常志愿者中，需要超过 1400 ms 的 TI。与年轻受试者相比，老年受试者的脑实质 ASL 信号往往较低，血管内信号污染更明显。这些发现表明，由于动脉减少，老年受试者的 ATT 较长。在狭窄闭塞性血管疾病患者中，ATT 延长会导致两个错误：1）低估局灶性 CBF，2）由于血管内原因而高估局灶性 CBF。 ATT 的影响在 3D ASTAR 技术中的头侧切片中更为明显，尽管需要更长的 TI 来减少 ATT 的影响，但更长的 TI 会导致继发于纵向松弛的信号减少，并导致检查时间更长。需要根据预测的 ATT 来确定适当的 TI，但是很难预测每个受试者每个区域的 ATT，并且 TI 的延长受到松弛纵向和检查时间的限制。对于 ATT 极长的患者，例如患有进展性烟雾病的患者，使用 ASL 技术进行 CBF 可能会很困难，可以在标记脉冲的同一位置应用饱和脉冲来抑制血管内信号。技术对血管内信号没有选择性，可能导致信噪比较低。