早期脑缺血MR灌注成像的实验研究

Experimental study on early brain ischemia with perfusion MRI

目的应用脑灌注ＭＲＩ技术研究早期脑缺血血流动力学改变并探讨其临床应用价值。方法经右侧颈内动脉逆行注入自体血凝块制作１０只兔大脑中动脉栓塞永久性脑缺血模型，利用动态快速梯度回波（ＤｙｎａｍｉｃＴＦＥ）和ＧｄＤＴＰＡ团注技术做同层动态扫描，计算双侧深部灰质、颞部、颞顶部和顶部最大信号下降率（ＭａｘＳＲ），最大准Ｔ２磁化率（ΔＲ２ｐｅａｋ）、信号开始下降时间（Ｔｓｔａｒｔ），信号下降达峰值时间（Ｔｐｅａｋ）和相对循环时间（ｒＭＴＴ），结果作配对ｔ检验并与四氮唑红（ＴＴＣ）组织染色对照。结果脑灌注ＭＲＩ于脑缺血后３０分钟即清楚显示缺血区。缺血侧平均ＭａｘＳＲ和ΔＲ２ｐｅａｋ分别为０．２２±０．０５和（２．４２±０．６５）×１０－２，非缺血侧为０．３８±０．０４和（４．７３±０．７０）×１０－２（Ｐ＜０．０１）；缺血侧Ｔｓｔａｒｔ、Ｔｐｅａｋ和ｒＭＴＴ明显延长，分别为：１８．５３±１．６８、２７．６０±２．４４和１４．９５±１．４９秒，非缺血侧分别为：１５．４３±１．００、２４．７６±２．７０和９．８２±０．９６秒（Ｐ＜０．０１），缺血区于缺血后１小时内未见高信号改变。结论脑灌注ＭＲＩ是一种对脑缺血敏感的技术?

Purpose To investigate the value of perfusion MRI on the early brain ischemia. Methods Dynamic turbo field echo sequence(TFE)with Gd DTPA bolus injection was used in 10 rabbits with the right middle cerebral artery(MCA)and the right internal carotid artery(ICA) occluded to induce permanent ischemia with autocoagulated clot through the external carotid artery retrogradely.TTC stained postmortem specimens were correlated with perfusion MRI images. Maximum signal reduction rate(MaxSR), peak ΔR 2 *(ΔR 2 *peak), signal reduction starting time (Tstart),time to peak signal reduction(Tpeak)and relative mean transit time(rMTT) were measured based on the S T curve. Results Perfusion MRI clearly delineated non perfused and hypoperfused regions as early as 30 minutes after ischemic ictus, when T 2 weighted images appeared normal. Data showed that MaxSR and ΔR 2 * peak were decreased, Tstart, Tpeak and rMTT were increased in the ischemic hemisphere as compared with those of the contralateral healthy hemisphere. The mean values of MaxSR, ΔR 2 *peak,Tstart, Tpeak and rMTT were 0.22±0.05,(2.42±0.65)×10 -2 ,18.53±1.68s,27.60±2.44 and 14.95±1.49s respectively in the ischemic hemisphere and 0.38±0.04,(4.73±0.70)×10 -2 ,15.43±1.00s、24.76± 2.70s and 9.82±0.96s respectively in the non ischemic hemisphere ( P <0.01 or P <0.05). ΔR 2 *(t) time curve revealed the regions of non perfusion and hypoperfusion(ischemic penumbra). Conclusion Perfusion MRI, is an effective technique in the evaluation of early brain ischemia and assessment of hemodynamics. It is more sensitive than the conventional T 2 weighted MR technique. Delayed and slow perfusion can be demonstrated in the ischemic region.