陳利軍,陳士新,孫澤棟,馬寧,徐琳
陜西省漢中市3201醫(yī)院影像科, 漢中723000
曲面重建(curvature plane reconstruction,CPR)是醫(yī)學(xué)影像診斷較常用的三維重建技術(shù)之一,其特點(diǎn)是將組織的不同斷面通過曲面重建使得組織結(jié)構(gòu)得以在同一個(gè)面上完整顯示。目前由于其在血管、膽管、輸尿管等方面的應(yīng)用價(jià)值已得到臨床廣泛認(rèn)可。該技術(shù)在CT成像中運(yùn)用極為普遍,然而在磁共振成像中卻很少被運(yùn)用,這可能是CT的重建技術(shù)在某種程度上影響或限制了磁共振重建的發(fā)展,或是放射科醫(yī)生還沒有對(duì)磁共振重建工作給臨床帶來的價(jià)值有足夠的認(rèn)識(shí)和意識(shí)?,F(xiàn)今的MR血管神經(jīng)重建技術(shù)從既往的多平面重組[1](multi-plane reformation,MPR)進(jìn)展為采用血管神經(jīng)圖像融合技術(shù)[2-3]以及仿真內(nèi)窺鏡重建(megnatic resonance virtual ebdoscopy,MRVE)技術(shù)[4],目前的重建方法在顯示雙側(cè)神經(jīng)的完整形態(tài)以及信號(hào)方面缺乏較為直觀的對(duì)比,以提供客觀的判斷依據(jù)。本文采用雙激發(fā)平衡式穩(wěn)態(tài)自由進(jìn)動(dòng)序列對(duì)81例患者進(jìn)行掃描,利用CPR技術(shù)顯示責(zé)任血管與神經(jīng)的關(guān)系,并對(duì)照65例術(shù)后結(jié)果,探討該技術(shù)在顯示血管神經(jīng)解剖關(guān)系的價(jià)值。
收集自2012年4月至2014年6月在我院接受MR神經(jīng)血管成像檢查的臨床診斷的48例三叉神經(jīng)痛(trigeminal nevralgia,TN)及33例面肌痙攣(hemifacial spasm,HFS)患者材料。81例中男32例,女49例;年齡26~79歲,中位年齡53歲;患者病程4周至3年;81例中46例患高血壓病,8例為糖尿病,8例為冠心病;65例接受微血管減壓(microvacular decompression,MVD)治療,其中TN 35例,HFS 30例。
81例均采用GE公司Hdxt 3.0 T雙梯度超導(dǎo)磁共振掃描儀,8通道相控陣線圈,3D-FIESTA-C掃描參數(shù):TR 4.1 ms,TE 1.6 ms,反轉(zhuǎn)角度60°,矩陣256×288,掃描視野18cm×18cm,層厚1 mm,無層間距,NEX為2,相位編碼方向?yàn)榍昂?A/P)方向,掃描層數(shù)為50層,掃描范圍包括中腦至橋腦延髓溝,掃描時(shí)間為4 min30 s。本研究經(jīng)醫(yī)院倫理委員會(huì)批準(zhǔn),所有受試者或是法定監(jiān)護(hù)人均簽署知情同意書。
將3D-FIESTA-C原始圖像輸入GE AW4.5工作站選擇curved進(jìn)行CPR,在三叉神經(jīng)層面將曲面端點(diǎn)定于視神經(jīng)管附近,聽面神經(jīng)層面將曲面端點(diǎn)定于視神經(jīng)管下方約5 mm處,沿神經(jīng)走行做單側(cè)神經(jīng)曲面重建,然后沿對(duì)側(cè)神經(jīng)至端點(diǎn),通過角度調(diào)節(jié),觀察不同角度雙側(cè)神經(jīng)的形態(tài)以及與血管的關(guān)系。
CPR需觀察雙側(cè)神經(jīng)形態(tài)及信號(hào)、腦池間距;腦干雙側(cè)形態(tài)。將患側(cè)神經(jīng)關(guān)系分為無接觸、接觸、壓迫。無接觸為神經(jīng)周圍無血管影像;接觸為神經(jīng)形態(tài)自然,輪廓光滑,血管神經(jīng)無間隙,神經(jīng)信號(hào)均勻;壓迫為神經(jīng)受壓變形,神經(jīng)輪廓毛糙模糊,神經(jīng)信號(hào)強(qiáng)度減弱,或中斷缺失。將血管神經(jīng)相鄰腦池間距分為雙側(cè)對(duì)稱等寬,患側(cè)腦池間距變窄。將患側(cè)腦干外緣較對(duì)側(cè)受壓變形定為壓迫,雙側(cè)腦干外緣對(duì)稱自然定為接觸。
結(jié)果采用統(tǒng)計(jì)軟件SPSS 18.0進(jìn)行分析,計(jì)算出81例3D-FIESTA-C、CPR各自以及兩者聯(lián)合運(yùn)用檢測(cè)責(zé)任血管的靈敏度、特異度、陽性預(yù)測(cè)值、陰性預(yù)測(cè)值,與MVD結(jié)果比較,得出K值。K<0.40為一致性弱,0.40~0.60為一致性一般,0.61~0.80為一致性強(qiáng),0.81~1.00為一致性極強(qiáng),并對(duì)其結(jié)果進(jìn)行分析。
圖1~4 右側(cè)小腦上動(dòng)脈與三叉神經(jīng)REZ段接觸。圖1為單側(cè)曲面圖,圖2~4為不同角度曲面圖,血管與神經(jīng)無間隙,與對(duì)側(cè)比較,右側(cè)神經(jīng)輪廓光整,形態(tài)自然,信號(hào)均勻,右腦池間距較對(duì)側(cè)窄小 圖5~8 右側(cè)巖靜脈屬支壓迫三叉神經(jīng)REZ段。圖5為單側(cè)曲面圖,圖6~8為不同角度曲面圖,右三叉神經(jīng)REZ段局部信號(hào)缺失,右側(cè)腦池間距較對(duì)側(cè)窄小,神經(jīng)長(zhǎng)度較對(duì)側(cè)縮短,REZ段腦干外緣較對(duì)側(cè)可見淺弧形壓跡 圖9~12左側(cè)椎動(dòng)脈及小腦后下動(dòng)脈共同壓迫面神經(jīng)REZ段。圖9為單側(cè)曲面圖,圖10~12為不同角度曲面圖,左椎動(dòng)脈明顯迂曲擴(kuò)張,與內(nèi)側(cè)小腦后下動(dòng)脈共同壓迫REZ段,與對(duì)側(cè)相比,左面神經(jīng)局部信號(hào)減弱,輪廓毛糙模糊,神經(jīng)長(zhǎng)度縮短,REZ段腦干外緣與對(duì)側(cè)相比輕度變形 圖13~16左側(cè)小腦前下動(dòng)脈血管袢壓迫面神經(jīng)REZ段,REZ段神經(jīng)信號(hào)減弱,REZ段腦干外緣較對(duì)側(cè)可見弧形壓跡Fig.1—4 Right suporior creballar artery contacted with REZ segment of trigeminal never.Fig.1 Unilateral curve plane reformation.Fig.2—4 curve plane reformation of different angles.Without space between blood vessels and nerves.Nerve on the right side contour finishing,natural shape,signal uniformity.Compared with the contralateral,the right nerve’s contour was fi nishing and signal was uniformity.Right cistern space was narrow the contralateral.Fig.5—8 Right petrosal vein branch compressed REZ segment of trigeminal never.Fig.5 Unilateral curve plane reformation.Fig.6—8 curve plane reformation of different anglesand the local signal missing for REZ segment right trigeminal nerve.compared with the contralateral the right cistern spacing was narrower and nerve was shorter and there was a light arc pressure trace in the REZ segment out of brain stem.Fig.9—12 Left vertebral artery and posterior inferior cerebellar artery compressed REZ segment of facial never.Fig.9 Unilateral curve plane reformation.Fig.10—12 curve plane reformation of different angles.Left vertebral artery was significantly tortuous expansion,and compressed REZ segment accompanying with medial cerebellar artery.Compared with the contralateral,the left facial nerve local signal was weak and the outline was rougher and the nerve was shorter and REZ segment of brainstem outer was mild deformation.Fig.13—16 Left vascular loop of anterior inferior cerebellar artery compressed REZ segment of facial nerve,REZ segment nerve signal was weak,compared with the contralateral the left cistern spacing was a light arc pressure trace in the REZ segment out of brain stem.
81例均為單側(cè),其中48例TN右側(cè)22例,左側(cè)26例;33例HFS右側(cè)13例,左側(cè)20例。81例中血管神經(jīng)無接觸8例(均為TN),接觸25例,壓迫48例。接觸及壓迫部位位于神經(jīng)出腦干段(root emerging zone,REZ)者58例,表現(xiàn)為神經(jīng)出腦干3 mm以內(nèi);位于腦池段者15例,表現(xiàn)為神經(jīng)出腦干3 mm以外。接觸與壓迫病例中腦池間距窄小者33例,腦干變形者12例。剔除8例血管神經(jīng)無接觸的TN,其余40例TN顯示責(zé)任血管為小腦上動(dòng)脈者31例,巖靜脈屬支5例,基底動(dòng)脈2例,小腦前下動(dòng)脈2例;其中小腦上動(dòng)脈與巖靜脈屬支共同壓迫2例,小腦上動(dòng)脈與巖靜脈共同接觸1例,巖靜脈主干單獨(dú)壓迫2例,小腦上動(dòng)脈與小腦前下動(dòng)脈共同壓迫2例。33例HFS責(zé)任血管為小腦前下動(dòng)脈12例,小腦后下動(dòng)脈13例,椎動(dòng)脈7例,巖靜脈1例;其中小腦前下動(dòng)脈與后下動(dòng)脈共同壓迫5例,前下動(dòng)脈與椎動(dòng)脈共同壓迫2例,后下動(dòng)脈與椎動(dòng)脈共同壓迫2例,椎動(dòng)脈壓迫與巖靜脈接觸1例。血管神經(jīng)無接觸表現(xiàn)見圖1~4,壓迫表現(xiàn)見圖5~8,腦池間距窄小表現(xiàn)見圖9~12,神經(jīng)REZ段腦干受壓表現(xiàn)見圖13~16。2名放射醫(yī)師對(duì)65例CPR圖像診斷結(jié)果的Kappa一致性檢驗(yàn)見表1,3D-FIESTA-C以及聯(lián)合CPR與65例MVD術(shù)中所見責(zé)任血管來源、壓迫部位以及神經(jīng)受壓程度方面一致性檢驗(yàn)以及CPR檢測(cè)責(zé)任血管的靈敏度、特異度、陽性預(yù)測(cè)值、陰性預(yù)測(cè)值見表2、3。65例術(shù)后30例HFS癥狀消失,30例TN疼痛癥狀消失,5例疼痛癥狀較前明顯減輕。
表1 2名觀察者對(duì)CPR結(jié)果的一致性評(píng)價(jià)Tab.1 Consistency evaluation of CPR by two observes
表2 3D-FIESTA-C與MVD結(jié)果的一致性評(píng)價(jià)Tab.2 Consistency evaluation of 3D-FIESTA-C and MVD
表3 3D-FIESTA-C聯(lián)合CPR與MVD結(jié)果的一致性評(píng)價(jià)Tab.3 Consistency evaluation of 3D-FIESTA-C combining with CPR and MVD
TN和HFS盡管臨床特征有所不同,但是由于血管的搏動(dòng)性壓迫而導(dǎo)致臨床癥狀的產(chǎn)生,卻是兩者共有的特性。這種搏動(dòng)性壓迫易發(fā)生于相應(yīng)腦神經(jīng)在出腦干前中樞與周圍髓鞘的交界區(qū),神經(jīng)髓鞘的再生受影響后,傳遞痛覺和觸覺的突觸相接觸,導(dǎo)致神經(jīng)傳導(dǎo)通路產(chǎn)生“短路”[5],即產(chǎn)生相應(yīng)的TN和HFS癥狀。雖然血管壓迫學(xué)說目前已得到臨床的普遍認(rèn)可,但仍有部分學(xué)者對(duì)其發(fā)病機(jī)理提出質(zhì)疑,尤其是TN的發(fā)病,因?yàn)樵谡H巳褐校?%~32%亦存在血管神經(jīng)接觸壓迫的情況[6],與TN相比,HFS的病因較為明確。微血管減壓術(shù)是目前公認(rèn)的對(duì)TN和HFS最有效的首選治療方法[7-8],其在TN的總有效率平均約為83.5%[7],而HFS有效率約為94.1%[9]。責(zé)任血管與神經(jīng)壓迫部位主要發(fā)生于神經(jīng)的出腦干段(root emerging zone,REZ)[10-12],本組三叉神經(jīng)痛主要的責(zé)任血管為小腦上動(dòng)脈(約占77.5%),而偏側(cè)面肌痙攣的主要血管為小腦后下動(dòng)脈(約占36.3%)、小腦前下動(dòng)脈(約占39.3%),及椎動(dòng)脈(約占21.2%),其結(jié)果與MVD術(shù)后結(jié)果相符[13-14]。與動(dòng)脈相比,靜脈壓迫少見,本組責(zé)任靜脈主要為巖靜脈及其屬支(約占12.5%),其主要與TN相關(guān),在被證實(shí)的責(zé)任靜脈中巖靜脈的屬支橋橫靜脈較為常見[15-16]。責(zé)任血管可為單支或多支,動(dòng)脈或靜脈接觸與壓迫也可同時(shí)存在。
梯度回波序列(grdient recalled echo,GRE)是高場(chǎng)強(qiáng)磁共振掃描儀上較常用的一組MRI射頻脈沖序列。臨床應(yīng)用主要包括擾相GRE序列、普通穩(wěn)態(tài)自由進(jìn)動(dòng)序列(steady state free precession,SSFP)和平衡式穩(wěn)態(tài)自由進(jìn)動(dòng)序列(Balance SSFP)。雙激發(fā)Balance SSFP是Balance SSFP的改進(jìn)序列,不同公司設(shè)備上其名稱亦有所不同,如西門子公司稱3D CISS,而GE公司則稱3D-FIESTA-C。目前雙激發(fā)Balance SSFP主要應(yīng)用于腦、脊神經(jīng)根以及內(nèi)耳的成像,需要指出的是,雙激發(fā)Balance SSFP(3D-FIESTA-C或3D-CISS為代表)與Balance SSFP(3D-FEISTA為代表)有所不同,因?yàn)橛袑W(xué)者認(rèn)為Balance SSFP是MR三維高分辨率成像的代表[9]。然而與一般的Balance SSFP相比,雙激發(fā)Balance SSFP序列可明顯減輕圖像的條紋偽影,在TR相對(duì)較長(zhǎng)的情況下仍可保持圖像具有較高的信噪比。由于3D-FIESTA-C組織的圖像對(duì)比取決于T2/T1的比值,組織的對(duì)比特點(diǎn)主要表現(xiàn)在液體由于T2值長(zhǎng)而呈現(xiàn)很高信號(hào),而軟組織呈現(xiàn)相對(duì)低信號(hào),故該序列就是通過在腦脊液高亮信號(hào)的襯托下,與低信號(hào)的血管與神經(jīng)形成顯著對(duì)比為特征。由于該序列血管神經(jīng)均表現(xiàn)為低信號(hào),血管神經(jīng)信號(hào)強(qiáng)度差異不及3D-TOF-MRA顯著,故該序列僅能根據(jù)解剖形態(tài)區(qū)分血管神經(jīng)。在既往的研究中,雙激發(fā)Balance SSFP在空間分辨力及信噪比方面優(yōu)于3D-TOF-MRA[11],其亦比3D-TOF-MRA明顯提高了責(zé)任靜脈的顯示能力[17]。
在三維高分辨率成像的基礎(chǔ)上應(yīng)用曲面重建技術(shù),其目的就是能夠在同一平面上完整顯示雙側(cè)神經(jīng)的形態(tài),以提供患側(cè)與健側(cè)有效的對(duì)比,通過對(duì)比提高判斷血管神經(jīng)接觸及壓迫的敏感度,以及神經(jīng)移位變形的程度。筆者發(fā)現(xiàn),可能是由于手術(shù)視角的局限性,使得MVD術(shù)中對(duì)血管神經(jīng)接觸及壓迫的敏感度以及神經(jīng)移位變形程度方面的顯示好像并沒有比曲面重建表現(xiàn)的顯著,然而對(duì)手術(shù)醫(yī)生而言,這似乎并不影響手術(shù)方法的改變以及術(shù)后療效,故可能多數(shù)手術(shù)醫(yī)生持有接觸即壓迫的觀點(diǎn)。在顯示雙側(cè)神經(jīng)完整形態(tài)的同時(shí),曲面重建還提供了雙側(cè)腦池間距以及腦干形態(tài)的對(duì)比,通過對(duì)比可輔助提高判斷血管神經(jīng)接觸及壓迫的特異性,對(duì)術(shù)前準(zhǔn)確了解血管神經(jīng)周圍組織結(jié)構(gòu)的形態(tài)提供了更為豐富的解剖信息。本組中,患側(cè)腦池間距窄小約占接觸與壓迫病例的45.2%,該表現(xiàn)在TN中尤為顯著,說明患側(cè)腦池間距窄小是導(dǎo)致血管神經(jīng)接觸及壓迫的一個(gè)重要因素。有報(bào)道稱,患側(cè)橋小腦池窄小可作為輔助診斷TN的一個(gè)重要指標(biāo)[18]。由于腦池間距的窄小,給手術(shù)操作帶來一定的困難,甚至可能導(dǎo)致手術(shù)失敗,故術(shù)前對(duì)腦池間距的評(píng)估具有重要意義。曲面重建通過對(duì)神經(jīng)輪廓及信號(hào)的觀察,提高了對(duì)血管神經(jīng)接觸與壓迫判斷的診斷效能。神經(jīng)的輪廓不光整以及神經(jīng)局部信號(hào)減弱,甚至信號(hào)中斷缺失,均是提示存在壓迫的可靠依據(jù)。腦干變形提示壓迫存在,主要表現(xiàn)為REZ段腦干外緣與對(duì)側(cè)相比可見弧形壓跡,在本組中導(dǎo)致這一表現(xiàn)的責(zé)任血管主要為基底動(dòng)脈和椎動(dòng)脈,小腦后下動(dòng)脈及前下動(dòng)脈相對(duì)較少,高血壓動(dòng)脈硬化引起的血管迂曲擴(kuò)張,是導(dǎo)致腦干受壓變形的一個(gè)主要原因。本組病例表明,3D-FIESTA-C聯(lián)合CPR經(jīng)兩名觀察者判斷具有較高的一致性,其診斷結(jié)果與MVD術(shù)中所見亦具有較好的一致性,3D-FIESTA-C聯(lián)合CPR在判斷責(zé)任血管來源方面優(yōu)于術(shù)中所見,可能是手術(shù)視野的局限性以及血管迂曲、變異均會(huì)對(duì)MVD術(shù)中準(zhǔn)確判斷血管來源產(chǎn)生影響,而3D-FIESTA-C可以較為準(zhǔn)確的追溯血管來源。
在近來的研究中,運(yùn)用不同場(chǎng)強(qiáng)的MR掃描儀所進(jìn)行的血管神經(jīng)成像,3.0 T MR在顯示解剖細(xì)節(jié)方面優(yōu)于1.5 T MR[19]。其原始圖像的空間分辨率的提高勢(shì)必對(duì)重建圖像質(zhì)量帶來一定的影響,這樣,重建圖像才可能為臨床提供更加清晰準(zhǔn)確的解剖信息。MR曲面重建技術(shù)突破了既往MPR單側(cè)判斷的局限性,拓寬了解剖信息的觀察視野,故該技術(shù)必將在今后的臨床應(yīng)用中發(fā)揮重要作用,尤其是應(yīng)用于血管神經(jīng)成像,其操作簡(jiǎn)單,分析診斷以及相應(yīng)的測(cè)量方便快捷,具有較高的臨床應(yīng)用價(jià)值。
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