來源：磁共振成像傳媒

李俊彤, 苗豐, 王效春. 高分辨MR顱內(nèi)血管壁成像技術(shù)研究及臨床應(yīng)用新進(jìn)展. 磁共振成像, 2018, 9(5): 376-380.

隨著人類生活水平的提高及生活方式的改變，腦卒中已成為嚴(yán)重威脅人類健康的致死性疾病之一。在我國，腦卒中是成人致殘或致死的首要危險(xiǎn)因素[1]且發(fā)病年齡呈年輕化趨勢。Wang等[2]研究發(fā)現(xiàn)，我國約46.6%的急性缺血性卒中(acute ischemic stroke)由顱內(nèi)動(dòng)脈粥樣硬化疾病(intracranial atherosclerotic disease， ICAD)引起，相關(guān)的腦血管事件每年復(fù)發(fā)率極高。顱內(nèi)動(dòng)脈夾層、Moyamoya病、腦動(dòng)脈炎等也可導(dǎo)致缺血性腦卒中， 因此早期鑒別診斷腦血管病對(duì)臨床指導(dǎo)治療和患者預(yù)后十分重要。

目前臨床主要應(yīng)用管腔狹窄程度來評(píng)估腦血管病變的嚴(yán)重程度。常用的影像學(xué)檢查技術(shù)有CT血管成像(computed tomography angiography， CTA)、數(shù)字減影血管造影(digital subtractionangiography，DSA)和MR血管成像(magnetic resonance angiography，MRA)等，DSA為有創(chuàng)檢查，現(xiàn)已逐步被CTA及MRA取代。上述腦血管檢查技術(shù)只能顯示管腔狹窄程度，不能明確狹窄處管壁結(jié)構(gòu)及導(dǎo)致其狹窄原因[3-4]。Leng等[5]認(rèn)為單純研究管腔狹窄程度對(duì)腦血管病變的診斷，評(píng)估病變特征及預(yù)防繼發(fā)卒中的風(fēng)險(xiǎn)分層明顯不足，而對(duì)病變處動(dòng)脈管壁結(jié)構(gòu)的研究更有意義。

高分辨率MR成像(high resolution magnetic resonanceimaging，HR-MRI)在顱外頸動(dòng)脈斑塊研究和臨床應(yīng)用中日漸成熟，其病理結(jié)果與高分辨率MR成像定義的斑塊成分有很好的相關(guān)性，近年來逐漸被用于顱內(nèi)動(dòng)脈的研究，是目前唯一可在體進(jìn)行腦血管成像的方法[6]。高分辨率MR成像與常規(guī)MRI相比，具有更高的信噪比(signal/noise ratio，SNR)、空間分辨率等優(yōu)勢[7]。

HR-MRI采用3.0 T高場強(qiáng)MR掃描設(shè)備及多通道頭部線圈，顯著提高了圖像空間分辨率、對(duì)比噪聲比(contrast/noise ratio，CNR)、信噪比(signal/noise ratio，SNR)，提高了圖像質(zhì)量[8]。高分辨率MR成像在腦血管成像中，較成熟的掃描技術(shù)有“亮血技術(shù)”和“黑血技術(shù)”。

“亮血技術(shù)”即三維時(shí)間飛躍法MR血管成像(3D time of flight magnetic resonanceangiography， 3D-TOF MRA)，是一種擾相梯度回波序列，采用短回波時(shí)間(echo time，TE)，短重復(fù)時(shí)間(repetitiontime，TR)及較小激發(fā)角度，使斑塊顯示為低信號(hào)、血流為高信號(hào)，在顱外頸動(dòng)脈斑塊成像中能夠區(qū)分出管壁、血流及斑塊等不同成分[9]，在顯示低信號(hào)的纖維帽和高信號(hào)的斑塊內(nèi)出血(intraplaquehemorrhage，IPH)等方面具有優(yōu)勢。

“黑血技術(shù)”即使用雙反轉(zhuǎn)恢復(fù)、飽和脈沖法等方法來抑制管腔內(nèi)血液信號(hào)，使血流呈低信號(hào)、管壁軟組織和斑塊呈較高信號(hào)，從而更好地顯示管壁和斑塊等結(jié)構(gòu)。有學(xué)者研究發(fā)現(xiàn)，雙反轉(zhuǎn)恢復(fù)法較飽和脈沖法對(duì)血流的抑制效果更好， 該血管壁成像方法臨床應(yīng)用較廣泛， 近年來被國內(nèi)外學(xué)者用于顱內(nèi)動(dòng)脈管壁的成像研究，并獲得了較好的病理印證， 是HR-MRI黑血技術(shù)現(xiàn)階段比較公認(rèn)的標(biāo)準(zhǔn)方法。

Mugler等[10]于1990年首次提出三維磁化準(zhǔn)備快速梯度回波序列(3D magnetization prepared rapid gradient echo，3D MP-RAGE)序列，并將其應(yīng)用于腹部與頭顱的MR成像。3D MP-RAGE序列依賴反轉(zhuǎn)恢復(fù)脈沖能很好地抑制血流信號(hào)和背景組織，較為敏感地識(shí)別出斑塊內(nèi)出血(intraplaque hemorrhage，IPH)信號(hào)，與傳統(tǒng)的T1W和TOF序列相比，3DMP-RAGE序列可對(duì)IPH進(jìn)行較準(zhǔn)確的定量測量，其測量結(jié)果與病理結(jié)果具有較高的一致性[11]。Kwak等[12]采用3D MP-RAGE序列對(duì)大腦中動(dòng)脈(middle cerebral artery，MCA)夾層進(jìn)行高分辨率MR管壁成像研究，發(fā)現(xiàn)該序列能很好地顯示假腔內(nèi)出血信號(hào)。

三維同時(shí)非對(duì)比增強(qiáng)血管成像和斑塊內(nèi)出血(3D simultaneous noncontrast angiography and intraplaque hemorrhage，3D SNAP)成像序列充分利用選擇性相位敏感反轉(zhuǎn)恢復(fù)(slab-selectivephase-sensitive inversion-recovery，SPI)技術(shù)的優(yōu)勢(IPH 顯示為高信號(hào)，血流顯示為低信號(hào))，只需一次掃描就可區(qū)分出狹窄管腔和IPH；該技術(shù)既能在一次掃描過程中檢測出ICAD管腔狹窄程度及IPH兩個(gè)重要危險(xiǎn)因素，又能靈活地對(duì)這兩個(gè)因素進(jìn)行獨(dú)立分析或聯(lián)合分析[13]。Wang等[14]分別用3D SNAP 序列和3D TOF序列對(duì)大腦中動(dòng)脈(middle cerebral artery，MCA)成像，發(fā)現(xiàn)兩者在顯示動(dòng)脈狹窄病變方面具有較高的一致性，且3D SNAP成像對(duì)大腦中動(dòng)脈最小可見分支的顯示優(yōu)于TOF圖像。

3D快速自旋回波(3D turbo spin echo，3D TSE)序列采用非選擇脈沖和變角度回聚脈沖，使回波間距明顯縮短，掃描效率得到提高[15]。該技術(shù)由不同的MR平臺(tái)優(yōu)化后形成了GE公司的CUBE序列、Siemens公司的SPACE序列和Philips 公司的VISTA序列。Edjlali等[16]在3.0 T下采用變翻轉(zhuǎn)角度3D快速自旋回波T1(CUBE T1)非對(duì)比增強(qiáng)成像對(duì)11例頸動(dòng)脈夾層患者進(jìn)行研究，發(fā)現(xiàn)該序列可準(zhǔn)確識(shí)別動(dòng)脈夾層管壁壁間血腫，彌補(bǔ)了傳統(tǒng)2D軸位成像的不足。2010年Fan等[17]將運(yùn)動(dòng)敏感散相脈沖(flow-sensitive dephasing，F(xiàn)SD)與3D SPACE序列相結(jié)合，提高了管壁與大管腔之間的CNR (P＜0.001)及管壁與殘余血流區(qū)域的CNR (P＜0.001)。Zhu等[18]認(rèn)為3D VISTA成像可以區(qū)分獲得性動(dòng)脈粥樣硬化性狹窄與椎動(dòng)脈發(fā)育不全(vertebralartery hypoplasia，VAH)。Qiao等[19]對(duì)13例健康志愿者及4例患者行3D VISTA成像研究，并與傳統(tǒng)的2D TSE成像對(duì)比，發(fā)現(xiàn)管壁SNR 提高了約60%，管腔與管壁的CNR提高了約74%。

顱內(nèi)動(dòng)脈粥樣硬化性病變(intracranialatherosclerotic disease，ICAD)是缺血性腦卒中主要風(fēng)險(xiǎn)之一。在中國，缺血性腦卒中患者約33%～50%存在顱內(nèi)動(dòng)脈粥樣硬化[20]。Turan等[21]報(bào)道，3.0 T HR-MRI在體粥樣硬化斑塊成分與癥狀性ICAD患者斑塊的病理標(biāo)本具有較高一致性，可研究在體顱內(nèi)動(dòng)脈粥樣硬化狹窄的病理改變，定性及定量分析斑塊成分大小，探測管壁、管腔結(jié)構(gòu)。HR-MRI可用于測量管壁厚度、管腔面積和管壁面積，分析斑塊負(fù)荷、管壁重構(gòu)及判斷斑塊易損性。Chung等[22]將HR-MRI應(yīng)用于椎動(dòng)脈腦卒中患者的成像研究并獲得其病理結(jié)果，發(fā)現(xiàn)HR-MRI能夠確定其潛在的病理生理機(jī)制， 從而改善癥狀性顱內(nèi)動(dòng)脈疾病的風(fēng)險(xiǎn)分層和治療決策。

煙霧病(Moyamoya disease，MMD)是一種由于單側(cè)或雙側(cè)頸內(nèi)動(dòng)脈終末端、MCA或大腦前動(dòng)脈起始段狹窄或閉塞性腦血管疾病，常伴有異常血管網(wǎng)形成，其發(fā)病率僅次于動(dòng)脈粥樣硬化性MCA閉塞[23-24]。臨床表現(xiàn)與動(dòng)脈粥樣硬化性疾病相近，常難以鑒別，且有時(shí)可并發(fā)。Kim等[25]對(duì)Moyamoya病、顱內(nèi)動(dòng)脈粥樣硬化患者M(jìn)CA管壁進(jìn)行高分辨率掃描，發(fā)現(xiàn)Moyamoya病患者M(jìn)CA 狹窄部位血管外徑較小，少見偏心斑塊，增強(qiáng)掃描局部未見明顯強(qiáng)化。與動(dòng)脈粥樣硬化病變組相應(yīng)病變部位比較，MMD患者同心圓型管壁更加均勻，伴有側(cè)支血管形成，?？梢奙CA病理收縮現(xiàn)象，可作為病程進(jìn)展的一個(gè)重要征象[26-27]，從而對(duì)MMD病程不同階段進(jìn)行監(jiān)測及治療。

顱內(nèi)動(dòng)脈夾層多發(fā)于椎基底動(dòng)脈，是青年患者缺血性腦卒中及自發(fā)性蛛網(wǎng)膜下腔出血(subarachnoid hemorrhage，SAH)的常見病因，在東亞人群中發(fā)病率達(dá)67%～90%。Jung等[28]采用3.0 T HR-MRI對(duì)自發(fā)性破裂和未破裂的急性顱內(nèi)動(dòng)脈夾層(spontaneous and unruptured acute intracranial artery dissection，SID)患者進(jìn)行定量解剖研究，并對(duì)各腦動(dòng)脈之間的差異進(jìn)行了探討，從而擴(kuò)寬了HR-MRVWI的研究方向。Natori 等[29]對(duì)16例顱內(nèi)椎基底動(dòng)脈夾層(intracranial vertebrobasilarartery dissection，iVBD)患者進(jìn)行前瞻性研究，發(fā)現(xiàn)與多序列MRI相比，T1W (3D-vascular wall imaging) 3D-VWI能直接顯示腦卒中急性期血管壁異常病變，可清楚的顯示夾層內(nèi)膜瓣、雙腔征以及假腔內(nèi)血腫等。Chung等[22]認(rèn)為HR-MRI可以發(fā)現(xiàn)大腦前動(dòng)脈和MCA等顱內(nèi)更加細(xì)小分支血管夾層。

顱內(nèi)動(dòng)脈炎性病變是一種因感染、藥物或變態(tài)反應(yīng)等因素導(dǎo)致腦動(dòng)脈管腔狹窄、閉塞，病變供血區(qū)腦組織缺血、梗死的腦血管疾病，是缺血性腦卒中的發(fā)病原因之一。Saam等[30]報(bào)道，采用脂肪抑制技術(shù)下的HR-MR對(duì)比增強(qiáng)T1WI序列可對(duì)顱內(nèi)動(dòng)脈炎性病變進(jìn)行診斷，該技術(shù)可代替常規(guī)血管造影和腦活檢等有創(chuàng)性檢查；此外，HR-MRI還能提供疾病相關(guān)炎性活動(dòng)信息，可用于監(jiān)測抗炎治療。Siemonsen等[31]經(jīng)活檢證實(shí)HR-MRI能可靠地檢測出巨細(xì)胞性動(dòng)脈炎(giant cell arteritis， GCA)，發(fā)現(xiàn)病變顳淺動(dòng)脈和枕動(dòng)脈管壁呈彌漫性同心圓型增厚，病變處管壁光滑，對(duì)比增強(qiáng)明顯強(qiáng)化，該方法檢測GCA的靈敏度和特異性均可達(dá)80%。

有學(xué)者將3D HR-MRI管壁成像應(yīng)用于顱內(nèi)動(dòng)脈瘤、VAH等疾病導(dǎo)致缺血性腦卒中機(jī)制的研究[18，32]。Li等[33]對(duì)放療后患者大腦中動(dòng)脈行HR-MRI檢查，發(fā)現(xiàn)病變管壁呈同心圓增厚，增強(qiáng)掃描均勻強(qiáng)化，其特征與動(dòng)脈炎一致。近年有學(xué)者認(rèn)為MRI管壁成像在鑒別血管炎與可逆性腦血管收縮綜合征(reversiblecerebral vasoconstriction syndrome，RCVS)方面也有重要價(jià)值[34-35]。

高分辨率MR血管壁成像(high resolution magnetic resonancevascular wall imaging，HR-MR VWI)是目前唯一可在體進(jìn)行顱內(nèi)血管壁成像的無創(chuàng)檢查技術(shù)，具有高空間分辨率、對(duì)比-噪聲比(contrast/noise ratio，CNR)及信噪比(signal/noise ratio，SNR)等優(yōu)勢；可在體、無創(chuàng)、無輻射地評(píng)估顱內(nèi)血管壁病變情況，為腦血管病變鑒別診斷、對(duì)因治療提供極大幫助和影像依據(jù)，具有很大的潛力和臨床應(yīng)用前景，有望成為臨床腦血管病鑒別診斷、預(yù)后評(píng)估及早期預(yù)防的重要檢查手段之一。目前，HR-MR顱內(nèi)血管壁成像仍存在掃描序列及參數(shù)不統(tǒng)一、掃描時(shí)間較長、病人耐受差、受運(yùn)動(dòng)偽影影響較大等問題，需要更多科研團(tuán)隊(duì)積極開展相關(guān)研究，并對(duì)成像參數(shù)及掃描序列做進(jìn)一步改進(jìn)和統(tǒng)一，相信隨著相應(yīng)研究的進(jìn)展，這些問題即將被解決，HR-MRI將成為腦血管病變的一項(xiàng)常規(guī)檢查手段。

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