Modifications and Accuracy Evaluations of Vascular Space Occupancy Method for Measuring Absolute Cerebral Blood Volume

以血管空間佔據方法量測絕對腦血量的改進與準確性評估

盧凱玲(Kai-Ling Lu)

指導教授 ： 王福年

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2011年)

https://doi.org/10.6843/NTHU.2011.00284

摘要

腦血量主要用以評估腦生理狀態和病理狀態，而腦血量的絕對定量可藉由血管空間佔據 (Vascular Space Occupancy, VASO) 磁振造影技術來完成。其原理是利用可縮短血液T1值的Gd對比劑打入生物體內，以反轉回復序列獲知其血液訊號抑制時間點打藥前後訊號的變化，將前後兩張影像相減後，根據參考訊號進一步絕對定量腦血量。

前人利用EPI序列去計算絕對腦血量，容易造成影像扭曲和部分體積
效應，為了解決此問題，在這個研究中我們採用RARE序列來計算絕對腦血量，並且進行參數的調整與準確性的評估。實驗的過程分成三個部分 : (1) 磁振造影參數最佳化的模擬，(2) 利用假體實驗比較不同參數所評估出的絕對腦血量準確性，(3) 以正常大鼠進行動物實驗。

從假體結果得知，絕對腦血量的準確性於IR-RARE序列比單純使用RARE序列來的好，推測原因是IR可以抑制組織訊號所造成的干擾。而使用IR-RARE序列時，短TR(1600 ms)在假體上定量的絕對腦血量準確性較長TR(4000 ms)準確，且在動物實驗上測得的絕對腦血量數值也在之前文獻中的範圍內。因此我們相信此種方法對於血管空間佔據磁振造影技術將能有效的評估絕對腦血量。

關鍵字

絕對腦血容積 ； 血管空間佔據核磁共振 ； 假體模擬

並列摘要

Cerebral blood volume (CBV) plays an important role for quantitative assessment of the brain physiology and pathophysiology state, which can be obtained with vascular-space-occupancy (VASO) MRI. One approach to determine absolute cerebral blood volume (aCBV) in humans is VASO MRI, which has been reported previously by Lu et al. The VASO MRI technique uses an inversion recovery pulse to null
blood signal. Then, the signal difference before and after injection of T1 shortening Gd contrast agent can be used to calculate absolute CBV values with a reference signal.

The aCBV was estimated by EPI sequence in previous reports, which may cause image distortion and partial volume effect. In order to overcome these problems, the RARE sequence was utilized in this study. Aiming to optimize the imaging parameters and evaluating the accuracy of VASO MRI, three experiments were preformed. First, we conducted computer simulations to estimate optimal imaging parameters. Second, phantom experiments were performed to assess the accuracy of aCBV with different parameters. Finally, the in vivo experiments were performed on a normal rat model.

The results of the phantom experiments showed that the accuracy of aCBV value was higher for RARE sequence with IR preparation than without it. It is speculated that the interference of tissue signal is suppressed by the IR preparation. Compared with longer TR (4000ms), the aCBV estimated with shorter TR (1600 ms) was more accurate for IR-RARE sequence in phantom studies. In animal experiments, using the optimized parameters, the aCBV estimated with shorter TR is in good agreement with values reported in the literatures. Therefore, it is believed that our modified VASO MRI method will be beneficial for assessing aCBV.

並列關鍵字

absolute Cerebral blood volume ； vascular-space-occupancy MRI ； phantom model

參考文獻

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