在過(guò)去的十余年間，術(shù)中成像已成為神經(jīng)外科熱點(diǎn)之一。在術(shù)中就能客觀地評(píng)估腫瘤的切除程度是非常有利的。如果術(shù)中發(fā)現(xiàn)有殘留，術(shù)者可繼續(xù)進(jìn)行腫瘤切除。相對(duì)傳統(tǒng)方式術(shù)者主觀判斷來(lái)說(shuō)，術(shù)中影像能夠提供更為客觀的術(shù)中評(píng)估信息，是一種很好的術(shù)中質(zhì)量控制手段［1－6］。 除此之外，借助于計(jì)算機(jī)輔助外科，能夠同時(shí)進(jìn)行神經(jīng)導(dǎo)航［5，7，8］。導(dǎo)航系統(tǒng)使得術(shù)者對(duì)手術(shù)野術(shù)前和術(shù)中影像進(jìn)行必要的聯(lián)系，從而實(shí)時(shí)反饋信息。而更重要的是，不僅術(shù)中影像能夠發(fā)現(xiàn)遺漏的殘留腫瘤，并使得術(shù)者進(jìn)一步擴(kuò)大切除范圍，還能夠借助術(shù)中導(dǎo)航來(lái)避免損傷腦重要結(jié)構(gòu)，防止增加新的神經(jīng)功能障礙。

在傳統(tǒng)導(dǎo)航系統(tǒng)（又稱為無(wú)框架立體定向?qū)Ш剑┲?，手術(shù)區(qū)域是與三維空間內(nèi)的解剖影像相關(guān)聯(lián)的。顯微鏡下導(dǎo)航在實(shí)際使用中更具優(yōu)勢(shì)。借助于現(xiàn)代顯微鏡的抬頭顯示器功能，導(dǎo)航影像能被疊加并投射在顯微鏡下的手術(shù)視野內(nèi)。傳統(tǒng)的解剖結(jié)構(gòu)導(dǎo)航在很多中心已常規(guī)使用，近年來(lái)，更逐漸演化至整合多種影像信息的多模態(tài)神經(jīng)導(dǎo)航。

進(jìn)行多模態(tài)神經(jīng)導(dǎo)航的首要步驟就是開(kāi)發(fā)功能神經(jīng)導(dǎo)航，譬如將腦磁圖（MEG）［9－11］或功能磁共振（fMRI）［5，12］顯示的腦重要功能區(qū)（如語(yǔ)言區(qū)和運(yùn)動(dòng)區(qū)皮層）整合進(jìn)導(dǎo)航系統(tǒng)，并生成個(gè)體化的導(dǎo)航計(jì)劃。功能神經(jīng)導(dǎo)航的使用，使得在重要功能區(qū)更徹底地切除腫瘤，而不增加術(shù)后致殘率成為可能。彌散張量成像纖維束示蹤技術(shù)（DTI）整合進(jìn)導(dǎo)航系統(tǒng)后，將功能神經(jīng)導(dǎo)航的范圍擴(kuò)展至皮層下區(qū)域［13－16］。 而整合 PET 或磁共振波譜（MRS）則使導(dǎo)航系統(tǒng)能夠根據(jù)腫瘤的代謝情況進(jìn)行多模態(tài)神經(jīng)導(dǎo)航［17－22］。

1 將導(dǎo)航整合進(jìn)外科常規(guī)流程

神經(jīng)外科手術(shù)室應(yīng)該使手術(shù)者方便的獲取患者的資料和信息。多模態(tài)神經(jīng)導(dǎo)航能夠借助于手術(shù)區(qū)域周邊的顯示器和手術(shù)顯微鏡內(nèi)的投射影像顯示病人的多模態(tài)腦功能影像，是整合過(guò)程中的主要部分。

與傳統(tǒng)導(dǎo)航系統(tǒng)使用的觀察棒相比，顯微鏡下導(dǎo)航可以直接在手術(shù)野中觀察各重要結(jié)構(gòu)。因?yàn)橛^察棒只能在導(dǎo)航圖像上顯示其尖端，因此在術(shù)中進(jìn)行導(dǎo)航時(shí)，術(shù)者常常需要將視線離開(kāi)顯微鏡并觀察導(dǎo)航屏幕，中斷了正常的手術(shù)流程。而顯微鏡下導(dǎo)航具備的抬頭顯示功能可以將腦功能結(jié)構(gòu)的信息以不同的顏色投射在手術(shù)視野內(nèi)，與此同時(shí)，顯微鏡焦點(diǎn)或是手術(shù)器械尖端可以顯示在導(dǎo)航系統(tǒng)屏幕上。

盡管如此，現(xiàn)有的導(dǎo)航系統(tǒng)仍有很大的改進(jìn)潛力。在大多數(shù)情況下，手術(shù)視野內(nèi)顯示的是二維圖像，對(duì)手術(shù)視野內(nèi)深度的立體結(jié)構(gòu)顯示不佳，未來(lái)將有可能改進(jìn)為視野內(nèi)三維圖像。而目前常用的導(dǎo)航系統(tǒng)的圖像質(zhì)量尚需提高。另外的一個(gè)重要問(wèn)題是，導(dǎo)航系統(tǒng)應(yīng)該避免因同時(shí)投射過(guò)多的影像資料而影響手術(shù)者的判斷。下一代的高級(jí)導(dǎo)航系統(tǒng)需要開(kāi)發(fā)相應(yīng)功能以使系統(tǒng)在不同的手術(shù)階段智能顯示相關(guān)的重要腦功能結(jié)構(gòu)，以免誤導(dǎo)手術(shù)者或中斷正常的外科手術(shù)流程。

那么，在術(shù)中磁共振環(huán)境下的導(dǎo)航應(yīng)該是什么樣的概念？一種方式是磁共振機(jī)本身就作為一個(gè)導(dǎo)航儀，如使用0.5T的GE磁共振機(jī)的系統(tǒng)，患者在磁體內(nèi)接受手術(shù)，手術(shù)同時(shí)進(jìn)行磁共振掃描。用此方式，手術(shù)時(shí)可以在磁共振圖像上實(shí)時(shí)觀察到手術(shù)器械的位置［1，23，24］。 這種導(dǎo)航方式基于實(shí)時(shí)磁共振成像，也被稱為實(shí)時(shí)立體定向，常被用來(lái)進(jìn)行穿刺置管或是立體定向活檢［25－27］。

另一種術(shù)中磁共振和導(dǎo)航的整合概念是術(shù)中磁共振和導(dǎo)航不是同時(shí)進(jìn)行。大多數(shù)系統(tǒng)將導(dǎo)航設(shè)備安放在磁體5高斯（5G）線外，以便能使用非磁共振兼容的標(biāo)準(zhǔn)手術(shù)器械進(jìn)行手術(shù)。如果僅僅將普通導(dǎo)航系統(tǒng)放置于磁體附近有可能引起相關(guān)的安全事故，因此，吊頂式導(dǎo)航系統(tǒng)是一個(gè)比較好的選擇。整合術(shù)中影像和導(dǎo)航對(duì)于優(yōu)化術(shù)中導(dǎo)航流程至關(guān)重要。術(shù)前、術(shù)中的影像學(xué)數(shù)據(jù)高效地傳輸至導(dǎo)航系統(tǒng)必不可少。優(yōu)化排列術(shù)中成像序列的順序，以便充分利用時(shí)間，在進(jìn)行磁共振掃描的同時(shí)進(jìn)行導(dǎo)航計(jì)劃的更新。

在進(jìn)行神經(jīng)導(dǎo)航輔助腫瘤切除的過(guò)程中，導(dǎo)航信息的準(zhǔn)確性是非常重要的。在所有可能導(dǎo)致導(dǎo)航誤差的因素當(dāng)中，患者手術(shù)開(kāi)始時(shí)的首次注冊(cè)最易導(dǎo)致誤差。目前最常用的導(dǎo)航注冊(cè)方法是在皮膚表面粘貼導(dǎo)航標(biāo)記物，并以影像學(xué)方法顯示標(biāo)記物，然后通過(guò)計(jì)算機(jī)注冊(cè)計(jì)算將標(biāo)記物的實(shí)際空間位置與導(dǎo)航系統(tǒng)內(nèi)虛擬位置相對(duì)應(yīng)，完成注冊(cè)和配準(zhǔn)的過(guò)程。自動(dòng)注冊(cè)法由于無(wú)需操作者的操作，因此，可以減少操作者相關(guān)的注冊(cè)誤差［28］。

2 自動(dòng)注冊(cè)

導(dǎo)航準(zhǔn)確性受一系列因素影響，如操作誤差、注冊(cè)系統(tǒng)的移位、術(shù)中腦組織的變形（腦組織移位）等。操作誤差常見(jiàn)影響因素包括：影像系統(tǒng)成像質(zhì)量，導(dǎo)航系統(tǒng)本身設(shè)備精度和患者注冊(cè)過(guò)程的質(zhì)量［29］。磁共振成像過(guò)程中的影像變形常由成像過(guò)程中的化學(xué)位移和掃描物體的非勻質(zhì)性產(chǎn)生［30］。對(duì)使用者來(lái)說(shuō)，由此原因產(chǎn)生的導(dǎo)航誤差和導(dǎo)航系統(tǒng)技術(shù)缺陷產(chǎn)生的誤差很難被克服。因此，通過(guò)改進(jìn)使用者的注冊(cè)操作和積累經(jīng)驗(yàn)是更為現(xiàn)實(shí)的減少導(dǎo)航誤差的方法。

有多種方法可以完成標(biāo)準(zhǔn)導(dǎo)航注冊(cè)。一方面，可以利用導(dǎo)航標(biāo)記物（粘貼于皮膚表面或是釘入顱骨）或是頭部解剖部位進(jìn)行注冊(cè)。另一方面，還可利用面部或頭部解剖輪廓進(jìn)行注冊(cè)。多個(gè)研究［31－34］證實(shí)了上述注冊(cè)方法的可靠性，而借助于影像自動(dòng)或半自動(dòng)探測(cè)標(biāo)記物技術(shù)，也可以比較快速地完成此類(lèi)導(dǎo)航注冊(cè)［35］。盡管如此，上述注冊(cè)過(guò)程仍然需要人工進(jìn)行操作，因此不僅費(fèi)時(shí)，而且容易產(chǎn)生誤差。

雖然自動(dòng)注冊(cè)的基本原理仍是基于空間位置的點(diǎn)對(duì)點(diǎn)注冊(cè)，但是它避免了使用點(diǎn)對(duì)點(diǎn)注冊(cè)時(shí)常規(guī)注冊(cè)方式容易產(chǎn)生誤差的環(huán)節(jié)。自動(dòng)注冊(cè)的主要任務(wù)是將導(dǎo)航所用影像學(xué)數(shù)據(jù)與導(dǎo)航參考架關(guān)聯(lián)起來(lái)。參考架帶有反光標(biāo)記物，并被剛性固定在手術(shù)頭架上，其作用是給導(dǎo)航系統(tǒng)追蹤手術(shù)器械提供一個(gè)參照物。從數(shù)學(xué)角度看，參考架和患者影像數(shù)據(jù)構(gòu)成了兩個(gè)獨(dú)立的坐標(biāo)系統(tǒng)。一個(gè)系統(tǒng)以參考架為基準(zhǔn)，定位導(dǎo)航器械與參考架的空間相對(duì)位置。另一個(gè)系統(tǒng)則將導(dǎo)航器械的三維圖像投射在患者的影像圖像上，從而在屏幕上顯示在患者影像資料上的器械位置，或是將圖像投射在手術(shù)顯微鏡內(nèi)，進(jìn)行鏡下導(dǎo)航。

通常我們認(rèn)為上述兩個(gè)坐標(biāo)系統(tǒng)通過(guò)一個(gè)剛性配準(zhǔn)系統(tǒng)關(guān)聯(lián)在一起，從而使這兩個(gè)系統(tǒng)通過(guò)旋轉(zhuǎn)和移位吻合在一起，或是將一個(gè)坐標(biāo)系內(nèi)的導(dǎo)航器械位置，轉(zhuǎn)化為另一坐標(biāo)系內(nèi)影像資料上的相應(yīng)位置。為了達(dá)成上述目的，必須分別在實(shí)際空間內(nèi)及影像資料上至少定義三個(gè)相應(yīng)標(biāo)記點(diǎn)。然后，點(diǎn)對(duì)應(yīng)算法將選擇最優(yōu)旋轉(zhuǎn)和移位參數(shù)，減少注冊(cè)誤差，并進(jìn)行最優(yōu)化注冊(cè)配準(zhǔn)。這種標(biāo)記點(diǎn)注冊(cè)法的一大改進(jìn)是自動(dòng)注冊(cè)法的引入。此法需使用自動(dòng)注冊(cè)架，該器材由一系列位置相對(duì)固定的標(biāo)記點(diǎn)和導(dǎo)航反光球組成。注冊(cè)架附加在磁共振上片射頻線圈上，并使各標(biāo)記點(diǎn)盡量靠近患者頭部，以便進(jìn)行磁共振成像時(shí)能顯示各標(biāo)記點(diǎn)。掃描完成后，圖像資料被傳送至導(dǎo)航工作站，操作者僅需簡(jiǎn)單調(diào)整導(dǎo)航紅外攝像頭，追蹤導(dǎo)航參考架和自動(dòng)注冊(cè)架的反光球部分，然后導(dǎo)航系統(tǒng)即可計(jì)算出參考架和自動(dòng)注冊(cè)架之間的空間關(guān)系。當(dāng)自動(dòng)注冊(cè)架的反光球空間位置確定后，自動(dòng)標(biāo)記物探測(cè)算法可以在影像圖像上定位出各個(gè)標(biāo)記點(diǎn)。因?yàn)橄到y(tǒng)已內(nèi)置了關(guān)于各個(gè)標(biāo)記點(diǎn)確切位置和排列的空間位置信息，所以上述信息可直接被用來(lái)進(jìn)行標(biāo)記物配準(zhǔn)注冊(cè)。綜合自動(dòng)注冊(cè)架和導(dǎo)航參考架的相對(duì)位置，自動(dòng)注冊(cè)架內(nèi)各標(biāo)記物的空間位置，以及各標(biāo)記物在影像上和患者頭部的相對(duì)位置，通過(guò)計(jì)算，就可以定義患者頭部在空間的具體位置并開(kāi)始導(dǎo)航。通?？稍诨颊哳^皮上放置一個(gè)額外標(biāo)記物，并不將其列入注冊(cè)標(biāo)記物，以便可以在注冊(cè)后，借助該標(biāo)記物判斷注冊(cè)誤差（通常在0.3～2.5 mm之間）。而針對(duì)自動(dòng)注冊(cè)系統(tǒng)進(jìn)行的磁共振水膜測(cè)試證實(shí)該方法誤差為0.88～2.13 mm，與傳統(tǒng)方法的誤差相當(dāng)。在大多數(shù)的測(cè)試中，自動(dòng)注冊(cè)甚至比使用4或7個(gè)標(biāo)記物的注冊(cè)方法精度更佳［28］。

3 多模態(tài)導(dǎo)航

降低術(shù)后并發(fā)癥的發(fā)生率至關(guān)重要，尤其是對(duì)于高級(jí)別膠質(zhì)瘤來(lái)說(shuō)。因?yàn)榇祟?lèi)患者，擴(kuò)大切除范圍往往只能延長(zhǎng)數(shù)周生存時(shí)間，而術(shù)后長(zhǎng)期的并發(fā)癥將嚴(yán)重影響患者的生存質(zhì)量。因此，必須同時(shí)兼顧最大化的病灶切除和最大化的神經(jīng)功能保護(hù)。術(shù)中成像不僅有助于術(shù)中最大化的切除病變，還能夠通過(guò)整合術(shù)中多模態(tài)神經(jīng)功能導(dǎo)航來(lái)最小化神經(jīng)功能損傷［13，36］。隨著外科技術(shù)和圍手術(shù)期技術(shù)的發(fā)展，現(xiàn)在已能夠?qū)ε徶匾δ軈^(qū)的惡性膠質(zhì)腫瘤進(jìn)行最大化切除而并不明顯增加術(shù)后致殘率。有關(guān)研究表明，大于98%的病變切除率將明顯延長(zhǎng)惡性膠質(zhì)腫瘤患者術(shù)后的生存時(shí)間，尤其是對(duì)Karnofsky評(píng)分較好的年輕患者而言［37］。

為達(dá)到上述目標(biāo)，整合腦解剖和功能信息的功能神經(jīng)導(dǎo)航是術(shù)中磁共振的良好補(bǔ)充。借助功能神經(jīng)導(dǎo)航，可以避免過(guò)于激進(jìn)的切除，并降低術(shù)后新發(fā)神經(jīng)功能障礙的發(fā)生率。同時(shí)，將MEG和fMRI影像整合進(jìn)功能神經(jīng)導(dǎo)航系統(tǒng)有助于定位重要腦功能區(qū)，如運(yùn)動(dòng)區(qū)和語(yǔ)言區(qū)等［11-12］。

我們?cè)M(jìn)行了一項(xiàng)回顧性研究，目的是評(píng)估腦磁圖對(duì)于膠質(zhì)瘤切除決策的影響［9］。研究包括了5年內(nèi)所有患有波及功能區(qū)的膠質(zhì)瘤患者，共有191例，其中119例幕上膠質(zhì)瘤。根據(jù)腦磁圖檢查的結(jié)果，約有26.8%的病例在術(shù)后有很大可能性發(fā)生神經(jīng)系統(tǒng)嚴(yán)重并發(fā)癥，因此被認(rèn)為不適合手術(shù)。該研究結(jié)果與另一項(xiàng)已發(fā)表的研究結(jié)果吻合。在該研究中，約30%（12／40例）的腫瘤或動(dòng)靜脈畸形患者由于腦磁圖的結(jié)果而選擇了非手術(shù)治療［38］。當(dāng)腦功能成像結(jié)果融合進(jìn)無(wú)框架導(dǎo)航系統(tǒng)用于手術(shù)后，術(shù)后致殘率低至2.3%，而總體的致殘率為6.8%。與其他使用常規(guī)手段的研究（致殘率6%～31.7%）相比，上述數(shù)據(jù)說(shuō)明了功能神經(jīng)導(dǎo)航能夠降低術(shù)后的致殘率［39-43］。當(dāng)然，我們也能將該數(shù)據(jù)解讀為，由于術(shù)前進(jìn)行了全面細(xì)致的腦功能成像，從而使病例的選擇更為仔細(xì)和謹(jǐn)慎，使得術(shù)后致殘率降低。術(shù)前的腦功能成像對(duì)膠質(zhì)瘤術(shù)前風(fēng)險(xiǎn)評(píng)估有幫助，而功能神經(jīng)導(dǎo)航能降低術(shù)后致殘率。同時(shí)，運(yùn)動(dòng)區(qū)和語(yǔ)言區(qū)皮層的術(shù)前定位，也對(duì)臨床有很大指導(dǎo)意義［44-45］。

腦磁圖或功能磁共振只能定位腦皮層功能區(qū)。然而，在膠質(zhì)瘤切除過(guò)程中，對(duì)腦深部結(jié)構(gòu)，如重要白質(zhì)纖維束的損傷，同樣能夠?qū)е律窠?jīng)功能障礙。彌散張量成像技術(shù)，不僅能夠描繪腫瘤邊界，也能被用來(lái)顯示錐體束等白質(zhì)纖維束。了解纖維束的走行及與腫瘤的解剖關(guān)系，對(duì)預(yù)防術(shù)后神經(jīng)功能障礙很有幫助［46-47］。將DTI生成的纖維束圖像融合進(jìn)導(dǎo)航系統(tǒng)指導(dǎo)手術(shù)可以實(shí)現(xiàn)術(shù)中對(duì)這些重要結(jié)構(gòu)的保護(hù)［16，48－49］。但有一個(gè)重要前提，就是必須對(duì)術(shù)中腦解剖結(jié)構(gòu)的變化 （亦稱為腦移位）加以考慮。和功能磁共振、腦磁圖相比，腦移位對(duì)DTI成像的影響更大，因?yàn)樾g(shù)中皮層結(jié)構(gòu)的移位，能被直接觀察到，而手術(shù)創(chuàng)腔深部接近白質(zhì)纖維束的地方，幾乎是不可能在直視下觀察到移位的。術(shù)中的DTI纖維束成像，顯示腫瘤切除過(guò)程中，纖維束有顯著的移位［15，50］。 因?yàn)槔w維束的移位，術(shù)前的相關(guān)功能成像信息將不再準(zhǔn)確，所以，只要腦移位沒(méi)有獲得補(bǔ)償，則術(shù)中導(dǎo)航將不再可靠。因此，在術(shù)中不僅有必要更新解剖影像，同時(shí)也需要更新腦功能影像。術(shù)中的DTI纖維束示蹤能夠顯示殘余腫瘤與重要白質(zhì)纖維束的相對(duì)關(guān)系［15，50］。術(shù)中電刺激正中神經(jīng)來(lái)進(jìn)行被動(dòng)刺激的功能磁共振則能顯示感覺(jué)區(qū)皮層［51］。

除了腦解剖和功能成像之外，還有一些其他影像數(shù)據(jù)可以用來(lái)進(jìn)行多模態(tài)影像導(dǎo)航。如PET、磁共振波譜（MRS）和磁共振彌散成像能提供腫瘤邊界的信息。將代謝影像融合進(jìn)導(dǎo)航系統(tǒng)能將代謝信息和病理信息進(jìn)行關(guān)聯(lián)［52－53］。上述信息能否用于手術(shù)中，目前正在研究中。而新興技術(shù)，如磁共振分子成像，也許會(huì)在未來(lái)成為術(shù)中成像的手段之一。

4 導(dǎo)航更新

腫瘤切除、腦腫脹、腦壓板牽拉以及釋放腦脊液，都會(huì)引起術(shù)中的腦組織變形，又稱為“腦移位”［24，54］。 因此，如果單純依賴術(shù)前的影像學(xué)數(shù)據(jù)，導(dǎo)航系統(tǒng)的準(zhǔn)確率在術(shù)中將下降。術(shù)中影像數(shù)據(jù)提供了術(shù)中補(bǔ)償腦移位的手段。借助于術(shù)中成像，能夠顯示術(shù)中的腦移位情況，同時(shí)也能顯示腫瘤切除程度［24，55－57］。 通過(guò)術(shù)中重新注冊(cè)來(lái)進(jìn)行腦移位的補(bǔ)償，并更新導(dǎo)航計(jì)劃操作繁瑣［56－57］。 在我們使用低場(chǎng)強(qiáng)術(shù)中磁共振系統(tǒng)的臨床實(shí)踐中，必須在開(kāi)顱骨窗周邊固定標(biāo)記物，然后進(jìn)行術(shù)中再注冊(cè)。然而，低場(chǎng)強(qiáng)術(shù)中MRI系統(tǒng)的圖像質(zhì)量較差，從而使得在術(shù)中圖像上分辨這些標(biāo)記物變得十分復(fù)雜。除此之外，更新導(dǎo)航計(jì)劃本身也很費(fèi)時(shí)，因?yàn)樯鲜鰳?biāo)記物首先要被固定在骨窗周邊，然后再在術(shù)中MR圖像上辨認(rèn)并將其標(biāo)記出來(lái)，隨后再使用導(dǎo)航觀察棒逐個(gè)定位實(shí)際標(biāo)記物，并將標(biāo)記物的空間位置和影像上的位置一一對(duì)應(yīng)起來(lái) （亦稱為術(shù)中患者再注冊(cè)）。正因?yàn)樯鲜龇爆嵉牟僮?，使得在我們進(jìn)行的330例低場(chǎng)強(qiáng)術(shù)中磁共振手術(shù)患者中，盡管有26%的病例在進(jìn)行術(shù)中成像時(shí)，發(fā)現(xiàn)有腫瘤殘留（如膠質(zhì)瘤）且能被繼續(xù)切除，最終只有 16 例（4.8%）進(jìn)行了真正的術(shù)中導(dǎo)航更新［56，58］。

高場(chǎng)強(qiáng)術(shù)中磁共振和顯微鏡下導(dǎo)航使得術(shù)中導(dǎo)航更新成為現(xiàn)實(shí)［5］。除了傳統(tǒng)的顱骨標(biāo)記物方法之外，還有另外兩種方法可以進(jìn)行術(shù)中患者再注冊(cè)，一個(gè)經(jīng)過(guò)校準(zhǔn)的注冊(cè)參考架可以固定在術(shù)中磁共振的上片線圈上，并能被導(dǎo)航系統(tǒng)追蹤［28］。在導(dǎo)航注冊(cè)前，先需要進(jìn)行一次三維磁共振掃描，掃描范圍需包括整個(gè)參考架，以便參考架上的所有標(biāo)記物能顯示出來(lái)并被用來(lái)進(jìn)行注冊(cè)。同樣的過(guò)程也能用于術(shù)中再次注冊(cè)。此時(shí)，使用一個(gè)消毒的注冊(cè)參考架，將其與消毒的術(shù)中上片磁共振線圈連接，該方法也可作為其他注冊(cè)手段失敗時(shí)的后備方法。

如果不需要患者術(shù)中再注冊(cè)，術(shù)中的導(dǎo)航更新則更為簡(jiǎn)單。首先將術(shù)中影像與術(shù)前影像進(jìn)行剛性配準(zhǔn)，然后描繪殘余腫瘤輪廓，最后恢復(fù)患者的初始注冊(cè)數(shù)據(jù)。這樣可以將原來(lái)的注冊(cè)空間坐標(biāo)用于術(shù)中影像上來(lái)完成快速地術(shù)中影像注冊(cè)。術(shù)中更新導(dǎo)航數(shù)據(jù)能夠可靠地定位殘留腫瘤或修正穿刺導(dǎo)管位置。而鏡下導(dǎo)航則能夠在手術(shù)視野內(nèi)快速準(zhǔn)確地定位殘留腫瘤，有非常重要的作用。術(shù)后病理結(jié)果顯示，擴(kuò)大切除的部分均為腫瘤組織，沒(méi)有假陽(yáng)性的結(jié)果。這當(dāng)然是由于殘留腫瘤被可靠地描繪出來(lái)并用來(lái)更新導(dǎo)航所致。而將術(shù)前和術(shù)中影像并列顯示也對(duì)影像判讀大有幫助，并且有效地減少了創(chuàng)腔邊緣手術(shù)痕跡對(duì)影像判讀的干擾。

通過(guò)將術(shù)中和術(shù)前的影像并列顯示，可以清楚顯示殘留腫瘤，也可以同時(shí)顯示腦移位程度。重復(fù)的解剖標(biāo)志確認(rèn)可以證實(shí)通過(guò)剛性配準(zhǔn)，進(jìn)行可靠的術(shù)中導(dǎo)航更新，而無(wú)需再次進(jìn)行導(dǎo)航注冊(cè)。剛性配準(zhǔn)注冊(cè)法不太容易受腦移位或是腫瘤切除的影響。這可以通過(guò)對(duì)比剛性配準(zhǔn)后的比較固定的解剖位置來(lái)證實(shí)，比如對(duì)比眼眶和頭釘?shù)?。一?xiàng)關(guān)于導(dǎo)航自動(dòng)注冊(cè)的研究顯示，通過(guò)術(shù)中和術(shù)前影像的剛性配準(zhǔn)，注冊(cè)誤差在2 mm以內(nèi)［59］。當(dāng)然，為避免發(fā)生嚴(yán)重注冊(cè)誤差，在進(jìn)行剛性配準(zhǔn)后，必須進(jìn)行人工確認(rèn)。

利用術(shù)中影像學(xué)資料更新導(dǎo)航是目前校正腦移位的最可靠方法。同樣的工作流程也可以用來(lái)更新多模態(tài)的腦功能數(shù)據(jù)。腦功能成像信息，如fMRI或DTI等可以在術(shù)中獲取并直接用于術(shù)中導(dǎo)航更新。當(dāng)然，在實(shí)際臨床操作中，有時(shí)上述工作比較費(fèi)時(shí)，如在顯像進(jìn)行連接語(yǔ)言區(qū)的纖維束時(shí)。

另外，非線性配準(zhǔn)及模式識(shí)別等更為復(fù)雜的技術(shù)有可能使包含腦功能信息的術(shù)前影像與術(shù)中磁共振影像融合配準(zhǔn)［60，61］。該技術(shù)在無(wú)法進(jìn)行高場(chǎng)強(qiáng)術(shù)中磁共振，但能進(jìn)行其他形式的腦解剖成像時(shí)可能會(huì)很有幫助。因?yàn)榇藭r(shí)，可以將術(shù)前的多模態(tài)腦功能數(shù)據(jù)與術(shù)中獲得的較低質(zhì)量的腦解剖數(shù)據(jù)進(jìn)行非線性注冊(cè)配準(zhǔn)，從而預(yù)測(cè)腦功能結(jié)構(gòu)在術(shù)中的位置。一個(gè)比較好的替代手段是術(shù)中超聲，尤其是術(shù)中 3D 超聲［62－64］。 當(dāng)然，使用術(shù)中超聲等其他替代手段能否清晰顯示膠質(zhì)瘤切除范圍目前尚存在爭(zhēng)議。但是，作為一種真正的術(shù)中實(shí)時(shí)成像方法，術(shù)中超聲可以提供術(shù)中解剖影像，從而能將術(shù)前腦功能影像通過(guò)非線性配準(zhǔn)變形后，來(lái)顯示術(shù)中腦功能結(jié)構(gòu)位置，抵消腦移位的影響。此時(shí)，術(shù)前的磁共振影像根據(jù)非線性配準(zhǔn)生成的腦移位數(shù)學(xué)模型進(jìn)行相應(yīng)的形變，從而反應(yīng)術(shù)中腦功能結(jié)構(gòu)的移位［65－69］。

關(guān)于使用數(shù)學(xué)模型來(lái)模擬腦移位，目前尚無(wú)法準(zhǔn)確預(yù)測(cè)術(shù)中的實(shí)際情況。術(shù)中的多種因素，如腦室系統(tǒng)開(kāi)放，患者體位變動(dòng)或腦水腫等，都可能影響腦移位的程度和方向。然而，數(shù)學(xué)模型加上術(shù)中的部分三維影像數(shù)據(jù)，則有可能調(diào)整術(shù)前影像來(lái)反映術(shù)中移位［67，69－71］。術(shù)中高場(chǎng)強(qiáng)磁共振，結(jié)合術(shù)中解剖和腦功能影像是驗(yàn)證和改進(jìn)這些數(shù)學(xué)模型的最佳工具。

5 結(jié)論

融合了多模態(tài)腦功能成像的鏡下導(dǎo)航技術(shù)和術(shù)中高場(chǎng)強(qiáng)磁共振，是目前最有希望做到最大程度切除腫瘤且最大程度保留神經(jīng)功能的方法之一。多模態(tài)神經(jīng)功能導(dǎo)航融合了腦常規(guī)解剖，功能及代謝信息。定位殘留腫瘤，分辨腫瘤周邊的重要功能結(jié)構(gòu)，以及將影像信息與病理結(jié)果關(guān)聯(lián)是多模態(tài)功能神經(jīng)導(dǎo)航的主要目的。利用術(shù)中影像資料更新導(dǎo)航后，可以修正腦移位的影響，并準(zhǔn)確地定位殘留腫瘤。

同英文版）

（中國(guó)人民解放軍總醫(yī)院 陳曉雷譯）

doi：10.3969 ／j.issn.1002－0152.2012.04.002

Department of Neurosurgery，University Marburg，Marburg，Germany

Intraoperative imaging has attracted increasing interest in the last decade.The ability to objectively determine the extent of tumour removal during surgery is highly advantageous.If the resection is incomplete，one can attempt to remove the tumour residues that were initially missed during the same operation.In contrast to a subjective estimation by the neurosurgeon，intraoperative imaging allows an objective evaluation of the intraoperative situation，thus acting as quality control during surgery［1－6］.In addition to intraoperative imaging，an integral part of our concept of computer aided surgery is the possibility to apply navigation simultaneously［5，7，8］.Navigation allows essentially visualizing the results of pre-and intraoperative imaging in the surgical field，so that the image data provide an immediate feedback.The most important aspect is to prevent increased neurological deficits despite increased resections that might result from the attempt to remove initially overlooked tumor remnants that are detected by intraoperative imaging.

In standard navigation，also known as frameless stereotaxy，the real space of the surgical field is registered to the 3-D image space，which is based on anatomical data only.We prefer the application of microscope-based navigation，where the extent and localization of a tumour is superimposed on the microscope field of view through contours using the headsup display technology of the modern operating microscopes.Standard navigation based on anatomical information only，which has become a routine tool in many neurosurgical departments，was developed further by the integration of further information from other modalities resulting in the so-called multimodal navigation.

A first step in the direction of multimodal navigation was the development of functional navigation，where preoperative data from magnetoencephalography（MEG）［9－11］and functional magnetic resonance imaging （fMRI）［5，12］defining localizations of cortical eloquent brain areas，such as the motor and speech areas，in individual patients，were integrated in the navigation setup.This method of functional neuronavigation allowed more a thorough resection of tumours in risk zones with low morbidity.Integration of diffusion tensor imaging （DTI） data delineating the course of major white matter tracts extended this concept also to subcortical areas［13－16］，while the co-registration of PET data and information from MR spectroscopy （MRS）added metabolic information leading to true multimodal navigation［17－22］.

1 Implementation of navigation in the surgical workflow

The neurosurgical operating room should be the integrative place where all patient data can be visualized in a surgeon-friendly fashion.Multimodal navigation with the visualization of multimodal data on several screens close to the surgical site，as well as，the parallel superimposition of the relevant structures visualized by contours in different colours in the microscope field of view，is the main tool to achieve this integration.

In contrast to pointer-based navigation，microscope-based navigation provides a more intuitive data visualization directly in the surgical field.Pointer-based systems only delineate the position of an instrument，e.g.typically the tip of a pointer，in the image space，so that during surgery when navigation information is needed the surgical workflow is interrupted by necessitating that the surgeon is looking away from the surgical field to a navigation screen.Microscopebased navigation has the advantage of heads-up displays superimposing additional information on the surgical field by colour contours or semi-transparent 3-D objects，while in parallel still the position of an instrument，e.g. the autofocus position of the microscope is still additionally displayed on the navigation screen.

However，there is still much room for further enhancements of these display technologies.In most setups there is only a 2-D visualization，lacking real depth information，which would be possible in a real 3-D image injection setup.Also the realtime rendering of the displayed objects in the current standard commercial systems does not represent what is nowadays possible with near photo-realistic visualizations in other fields of computer graphics.One of the most important aspects in such systems is to avoid a confusion of the neurosurgeon by a potential information overload.Sophisticated systems have to be developed that present the most relevant information at a certain stage of surgery without impeding the surgical workflow and without distracting the neurosurgeon from his main task.

What are the navigation concepts in an intraoperative MR environment？ Either the MR scanner serves as a navigational device per se，as it was the basic principle in the 0.5T double-doughnut GE scanner concept，where the patient was operated directly in the scanner，so that surgical space and imaging space were identical，so that an instrument in the surgical space could be tracked in image space without much additional effort［1，23，24］.Direct navigation in the MR scanner is often based on realtime imaging，like in the so-called prospective stereotaxy，a method for trajectory alignment for placements of catheters or sampling biopsies［25－27］.

Other attempts to integrate intraoperative MRI and navigation result in a classical navigation setup because image space and surgical space are not identical，so that some kind of patient registration has to be applied.Most setups implement navigation at the 5 G line，so that standard non-MR-compatible instruments can be used.Ceiling mounted solutions of the navigation camera and screens［5］are an optimal solution in the intraoperative scenario，since just placing a standard navigation system close to an MR scanner increases the risk of potential magnetic accidents.To optimize the navigation workflow a close integration of imaging and navigation is necessary.For pre-and also intraoperative registration an efficient data transfer between scanner and navigation computers is mandatory，as well as an optimized order of the different imaging sequences allows navigation planning and preparation，while scanning is still going on.

High navigation accuracy is a prerequisite if the navigation information is to be used at critical steps during the resection of a tumor.Among all errors contributing to the overall navigation accuracy，the initial patient registration process is mostly prone to errors.The most common strategy for patient registration relies on placement of skin-adhesive fiducials，which can be detected in the images，so that their position in virtual and real physical space can be correlated to define the registration coordinate system.Automatic registration setups，allowing an user-independent registration of patient space and image space，try to reduce the user dependent errors［28］.

2 Automatic registration

Navigation accuracy is influenced by a variety of factors，among them are the so-called application accuracy，factors relating to a unwanted movement of the registration coordinate system （positional shift），and intraoperative events like brain deformation，which is known as brain shift.The application accuracy is influenced by the quality of imaging，by the technical accuracy of the system itself，and by the quality of patient registration，which defines the process of registering image space and real／surgical space［29］.While the spatial distortion of MR images，which is due to gradient field non-linearities and resonance offsets（chemical shifts and magnetic field inhomogenities）［30］，and the technical accuracy of the navigation system are not easily influenced by the user，the patient registration process is much user-dependent and is influenced by the individual registration strategy and user experience.

Standard patient registration can be achieved in different ways.On the one hand there are “marker-fit”-techniques using either extrinsic markers（so-called fiducials either self-adhesive or implanted in the skull bone） or anatomical landmarks for registration.On the other hand there are “surface-fit”-techniques using the outer contour of the face and the skull for the referencing process.Several studies［31－34］showed the reliability of these registration methods and rapid progress was made towards automatic marker detection in image space and a semiautomatic registration［35］.Nevertheless，the registration process itself still has to be performed manually and therefore remains time-consuming and prone to error.

The concept of an automatic registration is based on paired point registration but sparing the user all the error prone steps associated with it.The main task of the automatic registration is to create an unambiguous relationship between the reference array and the acquired images used for navigation.The reference array is an important reflective marker structure rigidly attached to the patient head via the head clamp.It is used as a relative reference for the system to be able to track instruments，even when the stereoscopic camera is moved into a different position.Looking from the mathematical standpoint the reference array and the volumetric images span two independent coordinate systems.One coordinate system is used to describe the position of tracked instruments in the surgical field or relative to the reference array，the other to render a 3-D model of the tracked instrument in the volumetric images，which in return then is projected on a 2-D view on a screen，or superimposed in the operating microscope，allowing the user to navigate on the images.

It is generally assumed that these two coordinate systems relate to each other via a rigid transformation matrix，describing the rotation and translation between these coordinate systems，or how to transform one position of the instrument，in the surgical space into a corresponding position in the virtual／image space.In order to be able to calculate the rotation and translational parameters，at least 3 points in the patient space and corresponding points in the virtual space have to be defined.A paired point matching algorithm then optimizes the rotation and translational parameters to minimize the root-mean-square-error between these point pairs or even to permute the pairs to achieve an optimal result.An additional indirection for fiducial registration is of importance to implement the automatic registration method.A so-called registration matrix is introduced，which already contains a fixed constellation of fiducials relative to a reflective marker structure，making it possible to use the registration matrix as a tracked instrument.The registration matrix is attached to the upper part of the head coil，so that the fiducials from the registration matrix are automatically imaged，when placed close enough to the patient’s head.Once the scan is completed and the acquired images are transferred to the navigation system，the user only has to adjust the navigation camera so that it can identify the reflective marker structure of the registration matrix and the reference array for a brief moment，so that the navigation system can determine the spatial relation between registration matrix and reference array.Once the acquisition of the reflective marker structures has been completed，an automatic marker detection algorithm detects the fiducials from the registration matrix in the image data set.Since the system knows the exact arrangement and position of the fiducials integrated in the registration ma-trix this information can be used as input for the paired point matching algorithm.Combining the information where the registration matrix was in relation to the reference array and how the detected fiducials in the images relate to the fiducials of the registration matrix and also knowing how the fiducials from the registration matrix relate to the spatial position of the matrix itself by the defined construction，a transforma-tion matrix can be calculated directly relating the refer-ence array with the acquired images，so that then the relation between image space and physical／surgical space is defined and navigation can be used.An additional skin fiducial that is not used for the registration process is localized after patient registration to docu-ment a target registration error，which is typically in the range between 0.3 and 2.5 mm.Phantom studies resulted in median localization errors between 0.88 and 2.13 mm for the automatic registration approach，which was at least not worse，in most test series even signifi-cantly better，than that of the standard registration no matter whether 4 or 7 fiducial markers were used［28］.

3 Multimodal navigation

Low postoperative neurological deficits are mandatory，especially in surgery of high grade tumors it is of no benefit for the patient to maximize the extent of a resection to potentially increase the survival time by only some weeks，when risking permanent neurological deficits right after surgery.It is absolutely mandatory to combine the goal of maximum resection with the goal of preservation of function.Intraoperative imaging helps not only to maximize the extent of resection but in combination with functional multimodal navigation also minimization of postoperative neurological deficits is possible［13，36］.With the advances in surgical techniques and perioperative technology，it is now possible to maximally resect malignant intrinsic glial neoplasms，even close to functionally critical areas，without increased morbidity. Studies have demonstrated a survival advantage of these lesions with a resection extent of 98%or greater，particularly in younger patients with good Karnofsky scores［37］.

To achieve this，functional navigation，i.e.integrating functional data into anatomical navigational datasets，is an important add-on to intraoperative MRI since it prevents too extensive resections，which would otherwise result in new neurological deficits.Meanwhile，data from MEG and fMRI are routinely integrated in functional navigation allowing identification of eloquent brain areas such as the motor area and speech related areas［11，12］.

In a retrospective study we focused on how the decision to resect a glioma was influenced by MEG［9］.In a time period of 5 consecutive years we have investigated every patient proposed for surgery，who harboured a lesion adjacent to an eloquent brain area.Altogether 191 patients were examined，119 of them harboured supratentorial gliomas.About every forth patient （26.8%） yielded a severe possible danger of postoperative neurological morbidity according to MEG and thus was not considered being a good candidate for surgery.This is a corresponding result to published data where 12 out of 40 investigated patients （30%）with tumours and vascular malformations underwent non-surgical therapy according to the MEG results［38］.When functional data were used in combination with frameless stereotactic devices the postoperative morbiditywasaslowas2.3%.Overallmorbidityhoweverwas 6.8%.These data reflect the beneficial effects of functional navigation in comparison to data of other studies with morbidity rates varying from 6 to 31.7%［39－43］.These figures can also be interpreted as a result of a more careful patient selection through the help of preoperative brain mapping.Preoperative identification of eloquent brain areas has an impact in the risk evaluation in glioma surgery，as well as functional navigation reduces the risk for postoperative neurological deficits.Besides identification of the motor strip，the localisation of language areas is of great clinical impact［44，45］.

Functional data from MEG and fMRI only localize function at the brain surface.However，neurologi-cal deficits can also occur during tumor resection due to damaging of deeper structures，such as major white matter tracts.DTI can be used not only to delineate tumor borders，but also to display the course of white matter tracts，such as the pyramidal tract.The knowledge of the course of major white matter tracts in relationship to a tumor helps to prevent new postoperative neurological deficits［46，47］.Registration of diffusion data with the navigational dataset［16，48，49］facilitates the intraoperative preservation of these eloquent structures.A prerequisite is that intraoperative changes of the brain anatomy，known as brain shift，are taken into account.In contrast to the use of fMRI and MEG，brain shift clinically effects much more the DTI data，because the intraoperative shifting of cortical areas during surgery can be well detected by the naked eye，however changes in the depth of a resection cavity，close to major white matter tracts，is nearly undetectable for the neurosurgeon during tumor resection.Intraoperative DTI，revealed a marked shifting of the pyramidal tract due to tumor resection［15，50］.As a consequence of this shifting the preoperative functional data are no longer valid，so navigation can no longer relied on，if this shifting is not compensated for.Therefore，it is necessary that not only intraoperative anatomical data are used to compensate for the effects of brain shift but also functional data have to be updated.Intraoperative acquisition of DTI data enables intraoperative fiber tracking to visualize how a tumor remnant is localized in relation to major white matter tracts［15，50］.Even intraoperative fMRI applying electrical stimulation of median and tibial nerves as a passive stimulation paradigm is possible and enables identification of the somatosensory cortex［51］.

Besides functional and structural data further information is available for a multimodal navigation setup.PET，MRS，and diffusion weighted imaging may provide information on the diffuse tumor border.Integration of metabolic maps into the navigation datasets enables a spatial correlation of metabolic data and histopathological findings［52，53］.Whether these techniques can also be used intraoperatively，so that these data can also be updated，is under investigation.Furthermore，upcoming techniques such as MR-based molecular imaging may find its role in the intraoperative imaging armamentarium.

4 Navigation updating

Tumor removal，brain swelling，the use of brain retractors，and cerebrospinal-fluid drainage all result in an intraoperative brain deformation，which is known as brain shift［24，54］.Thus，navigation systems relying on preoperative image data only have a decreasing accuracy during the surgical procedure.Intraoperative imaging offers a possibility to compensate for the effects of brain shift，because it provides a virtual reproduction of the actual intraoperative physical reality，on how the brain is deformed and on the achieved extent of tumor removal［24，55－57］.Compensation for brain shift by intraoperative registration of the intraoperative MRI data to update the navigation setup has been a cumbersome process［56，57］.In our low-field MRI setting bone fiducial markers had to be placed around the craniotomy opening，which were then used for intraoperative patient re-registration.With the restricted image quality of the low-field MRI system it was quite complicated to identify these markers in the intraoperative images.Furthermore，updating was a time consuming process，because these bone fiducials had to be placed around the craniotomy opening； then they had to be identified and marked in the intraoperative images and then they had to be individually identified in physical space using the tip of a pointer and correlated to the position in the intraoperative images to define the navigation coordinate system，i.e.intraoperative patient re-registration.This is the main reason why only in 16 out of 330 patients investigated with low-field MRI an actual navigation update was performed，despite intraoperative imaging had detected tumor remnants e.g.in the gliomas that could undergo further resection in about 26%［56，58］.

The setup integrating high-field MRI and micro-scope-based navigation offered to facilitate this intraoperative update procedure［5］.Besides the bone-fiducial placement for intraoperative re-registration two alternative patient registration methods and thus update strategies are available.A calibrated registration matrix can be attached to the upper part of the head coil and tracked by the navigation system.28 This automatic registration matrix can be used for an initial patient registration.Before the patient registration it is required that the anesthetized patient gets a preoperative 3-D MR scan after head fixation，which fully covers the registration matrix，so that all markers integrated in the registration matrix are visible and can be detected and used for registration.This approach is also a possibility to perform a registration of intraoperatively acquired images.A sterile registration matrix has to be connected to the sterile upper part of the head coil before it is attached to the head holder.This method serves as a backup approach if other registration strategies fail.

Navigation updating without an intraoperative patient re-registration is an even more straightforward approach.It is based on a rigid registration of the intraoperative image data with the preoperative image data，subsequent segmentation of the tumor remnant，and final restoring of the initial patient registration，so that the registration coordinate system of the preoperative image data is applied on the intraoperative images，allowing an immediate intraoperative image update.Updated image data allow a reliable identification of a tumor remnant or correction of a catheter.Microscope-based image injection with the direct visualization of the segmented tumor remnant in the surgical field plays a crucial role in the precise localization and orientation in the resection cavity.Histological analysis of the extended resections proved pathological tissue in all cases； there were no false positive findings.This is of course due to the fact that only areas of reliably identified tumor remnants were segmented and used for updating.The side-by-side analysis of preand intraoperative images greatly facilitates image interpretation and to exclude misinterpretations due to surgically induced changes at the resection border.

After updating also a side-by-side display of preand intraoperative images visualizing the segmented tumor remnant in both of them，is possible，facilitat ing orientation and image interpretation-therefore，also the extent of brain shift is easily visible.Repeated landmark checks have proved that the rigid registration approach is a reliable approach to update the navigation system without a repeated patient registration.The rigid registration algorithm is robust enough to accomplish a registration that is not sensitive to the effects of brain shift and the actual reduction of the tumor mass.This could be shown by analyzing the registration accuracy of structures that are not affected by brain shift，such as the position of both orbits and the position of the skull fixation pins.An extensive analysis comparing the automatic registration，which is used to register pre-and intraoperative images，with an independent reference registration showed，that the registration error is below 2 mm even in a worst case scenario［59］.Nevertheless，to prevent a mis-registration a visual control after rigid registration of pre-and intraoperative images is mandatory.

Updating the navigation system with intraoperative MR image data seems to be the most reliable method to compensate for the effects of brain shift.In contrast to previous setups this framework is also open to update multimodal information.Functional data，such as fMRI or DTI data can also be acquired intraoperatively and directly used for intraoperative updating，which in the clinical routine might be a time-consuming effort，especially when in case of e.g. visualization of speech connecting fiber tracts some sophisticated time-consuming non-standard tracking algorithms have to be applied.

Alternatively either non-linear registration techniques，as well as sophisticated techniques from pattern recognition analysis may allow a matching of preoperative MR data sets containing functional information with intraoperative MR image volumes［60，61］.This might also be a possibility in case where intraoperative MRI is not available，but other imaging modalities provide intraoperative 3-D information about the brain configuration，so that high-resolution multi-modality data can be registered non-linearly onto the ‘low-quality’ intraoperative data.An alternative to intraoperative MR imaging might be intraoperative ultrasound，especially intraoperative 3-D ultrasound［62－64］.Whether the image quality to evaluate the extent of a glioma resection is equivalent among the different imaging modalities is still discussed controversially.However，it is out of doubt that intraoperative ultrasound has the advantage of being a real-time modality.Ultrasound data may provide information on how to deform high-quality preoperative MR image data in order to represent the intraoperative real situation，thus compensating for the effects of brain shift.This approach relies on the non-linear registration of intraoperative ultrasound data with preoperative MR volume data.Consecutively the MR data are deformed using a mathematical model describing the deforma tion of the brain during surgery［65－69］.Mathematical models trying to simulate brain shift behavior will not be able to predict the actual intraoperative situation without further data.Intraoperative events such as opening of the ventricular system and CSF drainage，patient positioning，and brain swelling all influence the extent and direction of brain shift. However，mathematical models together with some sparse data describing the actual intraoperative 3-D situation may be able to adjust high-quality preoperative data to represent the intraoperative reality［67，69－71］.Intraoperative high-field MRI with anatomical and functional imaging possibilities is the ideal tool to validate and refine these models.

5 Conclusion

Microscope-based navigation serving as a common interface for the presentation of multimodal data in the surgical field in combination and close integration with intraoperative high-field MRI seems to be one of the most promising setups allowing avoiding unwanted tumor remnants while preserving neurological function.Multimodal navigation integrates standard anatomical，structural，functional，and metabolic data.Visualizing the initial extent of a lesion，identification of neighboring eloquent brain structures，as well as allowing a direct correlation of histology and multimodal data are the main tasks of navigation.After intraoperative imaging navigation data can be updated，so that brain shift is compensated for and initially missed tumor remnants can be localized reliably.

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