Heiland S, Dietrich O, Sartor K
Department of Neuroradiology, University of Heidelberg Medical School, Germany.
Neuroradiology. 2001 Jun;43(6):442-7. doi: 10.1007/s002340000537.
We used a rat model of focal cerebral ischaemia to compare stimulated-echo (STE) and spin-echo (SE) echo planar (EPI) diffusion-weighted sequences as regards image quality and accuracy of calculation of apparent diffusion coefficients (ADC). Focal cerebral ischaemia was induced by endovascular occlusion of the middle cerebral artery in five rats. MRI was performed on a 2.35 tesla imager. For diffusion-weighted imaging (DWI) we used STE-EPI and SE-EPI with different diffusion times (delta) of 15, 30, 45, 60, 75 and 90 ms using values of b of 200, 300, 400, 500, 600 and 700 s/mm2. We assessed image quality, the signal-to-noise-ratio (SNR) and the accuracy of the ADC calculated from both sequences. Infarcts were delineated in all cases, independent of sequence type and delta. The image quality and SNR of the SE-EPI images were significantly better, with a higher SNR than STE-EPI images for short and intermediate values of delta. However, when delta reached 75 ms STE-EPI became superior to SE-EPI. ADC calculated from STE-EPI images were smaller than those from SE-EPI images for short and intermediate diffusion times, possibly because of the lower SNR of the former. We suggest that SE-EPI sequences be used for DWI of the brain, particularly on experimental systems and whole-body imagers with enhanced gradient hardware, where it is possible to run highly diffusion-weighted sequences (b > 500 s/mm2) with delta less than 50 ms. However, when using very long values of delta because of hardware restrictions or for measurement of restricted diffusion, STE sequences give better results.
我们使用局灶性脑缺血大鼠模型，比较刺激回波（STE）和自旋回波（SE）回波平面（EPI）扩散加权序列在图像质量和表观扩散系数（ADC）计算准确性方面的差异。通过对5只大鼠进行大脑中动脉血管内闭塞诱导局灶性脑缺血。在一台2.35特斯拉成像仪上进行磁共振成像（MRI）。对于扩散加权成像（DWI），我们使用STE-EPI和SE-EPI，扩散时间（δ）分别为15、30、45、60、75和90毫秒，b值分别为200、300、400、500、600和700秒/平方毫米。我们评估了图像质量、信噪比（SNR）以及从这两种序列计算得到的ADC的准确性。在所有情况下均能勾勒出梗死灶，与序列类型和δ无关。对于较短和中等δ值，SE-EPI图像的图像质量和SNR明显更好，SNR高于STE-EPI图像。然而，当δ达到75毫秒时，STE-EPI变得优于SE-EPI。在较短和中等扩散时间下，从STE-EPI图像计算得到的ADC小于从SE-EPI图像计算得到的ADC，这可能是因为前者的SNR较低。我们建议，SE-EPI序列可用于脑部DWI，特别是在实验系统和具有增强梯度硬件的全身成像仪上，在这些设备上可以运行δ小于50毫秒的高扩散加权序列（b>500秒/平方毫米）。然而，由于硬件限制或为了测量受限扩散而使用非常长的δ值时，STE序列会给出更好的结果。
