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

在第一年，成像参数的ASL技术影响图像质量进行了评估，通过使用单片二维ASTAR技术，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，因此我们在第二年后对多层3D ASTAR技术进行了评估。在多切片技术中，由标记脉冲引起的磁化传递对比度的影响不能用控制脉冲完全收集。在这项研究中，三维ASTAR图像的质量提高，通过使用多个非切片选择性反转脉冲，抑制信号强度的静止组织。动脉通过时间（ATT）对ASTAR图像的信噪比（SNR）有显著影响，图像对比度随TI的变化而变化。在年轻正常志愿者的单层技术评价中，后分水岭区域的SNR低于其他区域，这可能是因为 ...更多信息 在这些领域使用较长的ATT。为了获得适当的灌注图，应选择对于ATT较长的区域足够长的TI（正常年轻受试者的TI为1000至1200 ms）。在多层面技术中，标记脉冲和成像切片之间的间隙在更多的头部切片中更大。因此，ATT的影响在多层面技术中比在单层面技术中更显著，尤其是在头部层面。在正常志愿者中，需要长于1400 ms的TI才能在最头侧切片中获得适当的信号。与年轻受试者相比，老年受试者的脑实质ASL信号趋于降低，血管内信号污染更明显。这些结果表明，在老年受试者的ATT较长，由于动脉流速下降。在狭窄闭塞性血管疾病患者中，ATT延长导致两个错误：1）低估局灶性CBF，2）由于血管内信号而高估局灶性CBF。ATT的影响在3D ASTAR技术的头部切片中更为明显。虽然较长的TI是必要的，以减少ATT的影响，较长的TI导致信号降低继发于纵向松弛，并导致较长的检查时间。因此，有必要根据预测的ATT来确定合适的TI。然而，很难预测每个学科每个区域的ATT。TI的延长受纵向松弛和检查时间的限制。因此，使用ASL技术正确评估局灶性CBF对于ATT极长的患者（如进行性烟雾病患者）可能是困难的。饱和脉冲可以应用在标记脉冲的相同位置以抑制血管内信号。然而，用这种技术获得的信号的抑制对于血管内信号没有选择性，并且可能导致较低的SNR。少

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