李晶 馬超 邊云 王馨蕊 史張 王莉 邵成偉 陳士躍 陸建平

小視野高分辨DWI對(duì)胰腺實(shí)性病變的鑒別診斷價(jià)值

李晶 馬超 邊云 王馨蕊 史張 王莉 邵成偉 陳士躍 陸建平

目的探討小視野高分辨擴(kuò)散加權(quán)成像(rFOV DWI)對(duì)胰腺實(shí)性占位的鑒別診斷價(jià)值。方法收集139例胰腺實(shí)性占位患者，其中胰腺導(dǎo)管腺癌(PDAC)105例，神經(jīng)內(nèi)分泌腫瘤(NET)16例，腫塊型慢性胰腺炎(MFCP)7例，實(shí)性假乳頭狀瘤(SPT)11例。招募38名健康成年志愿者作為對(duì)照組。行包括單次激發(fā)平面回波成像(ss-EPI)DWI、rFOV DWI(b值為0和600 s/mm2)的MRI檢查。采用四分法從解剖結(jié)構(gòu)的可視性、胰腺病灶對(duì)比度、運(yùn)動(dòng)及磁敏感偽影3方面評(píng)估rFOV DWI及ss-EPI DWI圖像質(zhì)量，通過工作站自帶軟件測(cè)量感興趣區(qū)(ROI)的表觀擴(kuò)散系數(shù)(ADC)值。比較兩種DWI的圖像質(zhì)量及ADC值在各胰腺疾病及正常胰腺間的差異。繪制ADC 值的受試者工作特征(ROC)曲線，評(píng)價(jià)PDAC與其他胰腺良性腫塊及正常胰腺的差異。結(jié)果b值為0和600 s/mm2的rFOV DWI在顯示胰腺解剖結(jié)構(gòu)、病灶對(duì)比度、偽影評(píng)分均優(yōu)于ss-EPI DWI(b=0 s/mm2時(shí)為2.99±0.51比2.79±0.64、2.37±0.48比1.81±0.63、3.17±0.56比2.91±0.60；b=600 s/mm2時(shí)為3.63±0.50比3.32±0.56、3.45±0.50比3.01±0.49、3.74±0.44比3.12±0.37)，差異均有統(tǒng)計(jì)學(xué)意義(P值均<0.001)。PDAC、NET、MFCP、SPT、正常胰腺rFOV DWI獲得的ADC值分別為(1.38±0.17)×10-3、(1.22±0.35)×10-3、(1.29±0.13)×10-3、(1.04±0.38)×10-3、(1.86±0.15)×10-3mm2/s；ss-EPI DWI的ADC值分別為(1.73±0.24)×10-3、(1.63±0.39)×10-3、(1.58±0.19)×10-3、(1.25±0.26)×10-3、(2.04±0.20)×10-3mm2/s，各組間的差異及同組內(nèi)兩ADC值間的差異均有統(tǒng)計(jì)學(xué)意義(P值均<0.001)。MFCP與PDAC、NET與MFCP、MFCP與SPT間rFOW DWI的ADC值的差異及MFCP與PDAC、PDAC與NET、SPT與MFCP間ss-EPI DWI的ADC值差異無統(tǒng)計(jì)學(xué)意義，而其他兩兩組間差異均有統(tǒng)計(jì)學(xué)意義(P值均<0.05)。PADC與正常胰腺rFOV DWI和ss-EPI DWI的ROC曲線下面積(AUC)分別為0.983(95%CI0.944～0.998)和0.889(95%CI0.822～0.936)，差異有統(tǒng)計(jì)學(xué)意義(P=0.0004)，而PDAC與所有良實(shí)性病變的rFOV DWI和ss-EPI DWI的ADC值的AUC分別為0.799(95%CI0.719～0.864)和0.755(95%CI0.672～0.827)，差異無統(tǒng)計(jì)學(xué)意義。結(jié)論rFOV DWI顯著提高DWI圖像質(zhì)量，并且對(duì)胰腺導(dǎo)管腺癌的診斷效能更佳。

胰腺腫瘤； 磁共振成像； 診斷，鑒別

磁共振擴(kuò)散加權(quán)成像(diffusion-weighted imaging, DWI)通過定量計(jì)算出表觀擴(kuò)散系數(shù)(apparent diffusion coefficient, ADC)從而反映組織內(nèi)水分子擴(kuò)散快慢。臨床DWI應(yīng)用中使用最為廣泛的是單次激發(fā)平面回波成像(single-shot echo-planar-imaging, ss-EPI)序列，其具有成像速度快、對(duì)運(yùn)動(dòng)不敏感等優(yōu)點(diǎn)，但與常規(guī)MRI結(jié)構(gòu)圖像(如T1、T2圖像)相比，DWI因受到偏共振和磁敏感效應(yīng)的影響而導(dǎo)致圖像分辨率偏低。小視野(reduced field-of-view, rFOV)技術(shù)可以實(shí)現(xiàn)高分辨DWI，最初應(yīng)用于脊髓成像[1]。有研究報(bào)道，rFOV在胰腺成像中能提高DWI圖像質(zhì)量并減少偽影，但研究的樣本量較小且未見rFOV DWI對(duì)不同類型胰腺實(shí)性占位診斷的應(yīng)用價(jià)值報(bào)道[2-4]。本研究通過rFOV DWI與ss-EPI DWI圖像質(zhì)量及ADC值的對(duì)比研究，明確rFOV DWI 在胰腺實(shí)性占位診斷中的應(yīng)用價(jià)值。

資料與方法

一、病例資料

研究為前瞻性設(shè)計(jì)，經(jīng)長海醫(yī)院倫理委員會(huì)批準(zhǔn)，所有參與者均簽署知情同意書。收集2014年2月至2016年1月間經(jīng)CT或者B超檢查懷疑胰腺實(shí)性占位的住院患者139例。所有患者檢查前均未行放療或化療，并在長海醫(yī)院行MR檢查后1周內(nèi)手術(shù)治療，有明確的病理檢查結(jié)果。同期招募38名健康志愿者作為對(duì)照組。

139例胰腺實(shí)性占位患者中男性86例，女性53例，平均年齡(57±12)歲。其中胰腺導(dǎo)管腺癌(pancreatic ductal adenocarcinomas，PDAC)105例，男性69例，女性36例，平均年齡(61±9)歲；神經(jīng)內(nèi)分泌腫瘤(neuroendocrine tumor，NET)16例，男、女各8例，平均年齡(51±8)歲；腫塊型慢性胰腺炎(mass-forming chronic pancreatitis，MFCP)7例，均為男性，平均年齡(51±9)歲；實(shí)性假乳頭狀瘤(solid pseudopapillary tumor，SPT)11例，男性2例，女性9例，平均年齡(32±9)歲。38名健康志愿者中男性26名，女性12名，年齡(49±11)歲。

二、MRI掃描方法

MRI檢查均在同一臺(tái)3-T磁共振儀上完成。所有受檢者均于檢查前禁食6 h以上并接受呼吸訓(xùn)練。被檢者采取仰臥位、腳先進(jìn)體位，行包括胰腺橫斷T1加權(quán)像(T1WI)、T2加權(quán)像(T2WI)、磁共振胰膽管造影(MRCP)、動(dòng)態(tài)增強(qiáng)、ss-EPI DWI、rFOV DWI在內(nèi)的胰腺M(fèi)RI掃描。橫斷面呼吸觸發(fā)T2WI序列：重復(fù)時(shí)間(TR)6 316 ms，回波時(shí)間(TE)72 ms，層厚5 mm，視野(FOV)380 mm×400 mm，矩陣320×192；肝臟容積加速采集(liver acquisition with volume acceleration，LAVA)序列：TR 2.5 ms，TE 1.1 ms，層厚5 mm，F(xiàn)OV 440 mm×418 mm，矩陣256×180；厚層塊2D-MRCP序列：TR 7 000 ms，TE 1 221 ms，層厚54 mm，F(xiàn)OV 300 mm×300 mm，矩陣288×288。ss-EPI WDI序列：擴(kuò)散梯度因子(b)值為0、600 s/mm2，TR 6 000 ms，TE 58.6 ms，層厚 5 mm，F(xiàn)OV 380 mm×400 mm，矩陣128×96；rFOV DWI序列：b值為0、600 s/mm2，TR 5 000 ms，TE 58.6 ms，層厚5 mm，F(xiàn)OV 160 mm×80 mm，矩陣128×64。rFOV DWI掃描層數(shù)為6層?；颊呓M最后還要經(jīng)靜脈注射釓噴酸葡胺注射液0.2～0.3 ml/kg體重行動(dòng)態(tài)增強(qiáng)掃描。

三、圖像分析及數(shù)據(jù)測(cè)量

1．DWI圖像質(zhì)量評(píng)估：由一名腹部疾病診斷經(jīng)驗(yàn)豐富的放射科醫(yī)師對(duì)b值為0和600 s/mm2的DWI圖像質(zhì)量進(jìn)行評(píng)分。四分法標(biāo)準(zhǔn)如下：(1)解剖結(jié)構(gòu)的可視性：1分，肉眼無法觀察解剖結(jié)構(gòu)致圖像無法用于診斷；2分，大體顯示解剖結(jié)構(gòu)但胰腺邊緣模糊；3分，較清晰顯示解剖結(jié)構(gòu)且胰腺邊緣清晰；4分，胰管結(jié)構(gòu)清晰可見。(2) 胰腺病灶對(duì)比度：1分，病灶未見顯示；2分，病灶與周圍組織有微弱對(duì)比；3分，病灶與周圍組織有中等對(duì)比度或有強(qiáng)對(duì)比但病灶邊緣模糊；4分，病灶與周圍組織有明顯的對(duì)比度且病灶邊緣清晰。(3)運(yùn)動(dòng)及磁敏感偽影：1分，偽影嚴(yán)重致圖像無法用于診斷；2分，中度偽影；3分，輕度偽影；4分，無偽影。3個(gè)分值之和為DWI圖像質(zhì)量總分[5]。

2．ADC值：ADC值的測(cè)量在工作站自帶軟件(Function 6.3.1e, GE AW VolumeShare 2,GE Healthcare, Milwaukee,WI, USA)上進(jìn)行。數(shù)據(jù)測(cè)量時(shí)避開胰膽管、血管及胰腺邊緣來選取圓形或橢圓形感興趣區(qū)(ROI)測(cè)量ADC平均值。ROI的面積分別為20～287 mm2(ss-EPI DWI)和20～238 mm2(rFOV DWI)。

四、統(tǒng)計(jì)學(xué)分析

結(jié) 果

一、圖像質(zhì)量分析

b值為0和600 s/mm2的rFOV DWI在顯示胰腺解剖結(jié)構(gòu)、病灶對(duì)比度均優(yōu)于ss-EPI DWI，且偽影也明顯少于后者，差異具有統(tǒng)計(jì)學(xué)意義(表1，圖1、圖2)。

二、ADC定量分析

PDAC、NET、MFCP、SPT、正常胰腺rFOV DWI獲得的ADC值分別為(1.38±0.17)×10-3、(1.22±0.35)×10-3、(1.29±0.13)×10-3、(1.04±0.38)×10-3、(1.86±0.15)×10-3mm2/s；ss-EPI DWI的ADC值分別為(1.73±0.24)×10-3、(1.63±0.39)×10-3、(1.58±0.19)×10-3、(1.25±0.26)×10-3、(2.04±0.20)×10-3mm2/s，各組間的差異均有統(tǒng)計(jì)學(xué)意義(P值均<0.001)。此外，同組內(nèi)rFOV DWI獲得的ADC值均顯著小于ss-EPI DWI的ADC值，差異均有統(tǒng)計(jì)學(xué)意義(P值均<0.001)。兩兩組比較時(shí)， rFOV DWI的ADC值在MFCP與PDAC(P=0.078)、NET與MFCP(P=0.937)、SPT與MFCP(P=0.09)的組間差異以及ss-EPI DWI的ADC值在MFCP與PDAC(P=0.104)、PDAC與NET(P=0.133)、SPT與MFCP(P=0.285)的組間差異無統(tǒng)計(jì)學(xué)意義，而其他兩兩組間差異均有統(tǒng)計(jì)學(xué)意義(P值均<0.05)。

表1 rFOV DWI與ss-EPI DWI圖像質(zhì)量評(píng)分(分，

圖1 胰頭部中分化導(dǎo)管腺癌。1A為ss-EPI DWI(b=600 s/mm2)，1B為rFOV DWI(b=600 s/mm2)，1C為軸位T2WI，1D為軸位T1WI。rFOV DWI對(duì)病灶的顯示邊緣結(jié)構(gòu)清晰，信號(hào)顯示較ss-EPIDWI均勻

圖2 胰尾部慢性腫塊型胰腺炎。2A為ss-EPI DWI(b=600 s/mm2)，2B為rFOV DWI(b=600 s/mm2)，2C為軸位T2WI，2D為軸位T1WI。rFOV DWI對(duì)病灶的顯示邊緣結(jié)構(gòu)清晰，信號(hào)顯示較ss-EPIDWI均勻

PDAC與正常胰腺的rFOV DWI和ss-EPI DWI的ADC值的ROC曲線下面積(AUC)分別為0.983(95%CI0.944～0.998)和0.889(95%CI0.822～0.936)，差異有統(tǒng)計(jì)學(xué)意義(P=0.0004，圖3A)。

將NET、MFCP、SPT合并為良實(shí)性病變組，PDAC與良實(shí)性病變組的rFOV DWI和ss-EPI DWI的ADC值的AUC 分別為0.799(95%CI0.719～0.864)和0.755(95%CI0.672～0.827)，差異無統(tǒng)計(jì)學(xué)意義(P=0.4355，圖3B)。

討 論

影響DWI分辨率的因素有兩個(gè)，一個(gè)是FOV，另一個(gè)是采集矩陣。ss-EPI DWI使用的ss-EPI序列TE時(shí)間長且在相位編碼方向的帶寬窄，這有可能會(huì)產(chǎn)生磁敏感偽影和化學(xué)位移偽影，從而導(dǎo)致圖像質(zhì)量欠佳、信噪比較低以及空間分辨率較差。對(duì)于ss-EPI DWI序列來說，采集矩陣的大小直接決定了整體讀出窗口的長度，采集矩陣越大，整體讀出窗口的長度越長，ss-EPI DWI序列的偽影也越重，因此通過增加矩陣提高ss-EPI DWI分辨率是行不通的。此外，可以通過減小FOV實(shí)現(xiàn)圖像的分辨率的提高，因?yàn)镕OV小于成像物體的面積時(shí)，圖像在相位編碼的方向會(huì)產(chǎn)生卷褶偽影，所以ss-EPI DWI的FOV不能隨意縮小。為保證FOV之外的物體不被激發(fā)或激發(fā)之后的信號(hào)對(duì)圖像沒有影響，本研究使用的rFOV DWI利用一種2D選擇性激勵(lì)的射頻脈沖來激發(fā)小范圍的感興趣區(qū)以避免卷褶偽影的干擾，且隨著FOV的增大，b=0 s/mm2時(shí)磁場(chǎng)的不均勻性也會(huì)越明顯，所以rFOV DWI脂肪壓制的效果優(yōu)于ss-EPI DWI，有助于提高小病灶的檢出率[1,6-8]。本研究采用的rFOV DWI的空間分辨率是ss-EPI DWI的4倍以上，可同時(shí)明顯改善DWI圖像的變形和偽影。

圖3 ROC曲線分析。3A為rFOV DWI和ss-EPI DWI對(duì)PDAC與正常胰腺的鑒別診斷ROC分析；3B為rFOV DWI和ss-EPI DWI對(duì)PDAC與胰腺良性病變的鑒別診斷ROC分析

腹部DWI檢查中b值常取值在500～1 000 s/mm2[9-13]。本研究在胰腺DWI成像使用b值為600 s/mm2可以保持較好的信噪比和圖像質(zhì)量[9]?；趕s-EPI DWI的研究可以有效地鑒別胰腺良惡性病變，因胰腺癌的ADC值顯著低于良性病變[10-18]。本研究結(jié)果也顯示胰腺癌的ADC值顯著低于胰腺良性病變，其主要原因是胰腺癌基質(zhì)纖維化含量、增多的腫瘤細(xì)胞限制了細(xì)胞外間隙水分子的運(yùn)動(dòng)，而腫瘤細(xì)胞內(nèi)核質(zhì)比的增加也限制了細(xì)胞內(nèi)水分子的擴(kuò)散運(yùn)動(dòng)[1]。但本研究的ss-EPI DWI及rFOV DWI的ADC值對(duì)MFCP與PDAC的無明顯鑒別診斷價(jià)值，與Philipp等[19]報(bào)道結(jié)果一致。其可能原因一方面是MFCP入組例數(shù)少，另一方面是MFCP富含纖維化基質(zhì)，且其有可能進(jìn)展為胰腺癌。此外，PDAC的腫瘤組織內(nèi)及其周圍可因?yàn)橹饕裙芑蚍种б裙艿淖枞榘l(fā)胰腺炎也可導(dǎo)致MFCP與PDAC的ADC值存在一定程度的重疊[20]。Fattahi等[15]的研究(b為600 s/mm2)則認(rèn)為ADC值可以鑒別這兩種疾病。也有研究認(rèn)為高b值的DWI可以有效地鑒別診斷MFCP與PDAC[21]。目前ADC值對(duì)兩者的鑒別診斷價(jià)值尚存在爭議。

rFOV DWI較ss-EPI DWI對(duì)PADC的診斷準(zhǔn)確性高的可能原因是rFOV DWI的體素體積(7.8 mm3)小于ss-EPI DWI的體素體積(61.8 mm3)，從而有效減少腫瘤組織內(nèi)各成分之間的部分容積效應(yīng)，其ADC值更能反映病變的本質(zhì)。

本研究尚存在一些不足。首先，本研究選取了相對(duì)較低的b值(600 s/mm2)來減少運(yùn)動(dòng)偽影、提高信噪比，但更高的b值才有可能更準(zhǔn)確地反映組織的真實(shí)擴(kuò)散[22-23]。此外，兩個(gè)b值(0和600 s/mm2)的DWI雖然可減少檢查時(shí)間，但多b值DWI成像可能得到更加準(zhǔn)確的ADC值[24-25]。

總之，rFOV DWI對(duì)胰腺解剖結(jié)構(gòu)的顯示、對(duì)病灶的顯示對(duì)比度明顯優(yōu)于ss-EPI DWI，其鑒別診斷胰腺導(dǎo)管腺癌與正常胰腺的效能更高。

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ValueofreducedfieldofviewDWIindifferentiatingsolidpancreaticfocallesions

LiJing,MaChao,BianYun,WangXinrui,ShiZhang,WangLi,ShaoChengwei,ChenShiyue,LuJianping.

DepartmentofRadiology,ChanghaiHospital,SecondMilitaryMedicalUniversity,Shanghai200433,China

LuJianping,Email:cjr.lujianping@vip.163.com

ObjectiveTo study the value of reduced field-of-view (rFOV DWI) in differentiating patients with solid pancreatic focal lesions.Methods139 patients with solid pancreatic mass were enrolled, including 105 patients with pancreatic ductal acinar carcinoma (PDAC), 16 patients with neuroendocrine neoplasms, 7 patients with mass forming chronic pancreatitis (MFCP) and 11 patients with solid papillary tumor (SPT). 38 healthy adult volunteers served as controls, and underwent single stimulated echo planar imaging (ss-EPI)DWI and rFOV DWI(b value=0 and 600 s/mm2)MRI examination. Quartation method was used to evaluate the image quality of ss-EPI)DWI and rFOV DWI in the three terms of the visibility of anatomical structure, contrast of pancreatic lesions, motion and the susceptibility artifacts during MRI. Work station self-carried software was used to measure the ADC value of the region of interest (ROI).The image quality and ADC values of different pancreatic diseases and normal pancreas were compared. ROC curve for ADC value was drawn to evaluate the difference among PDAC, other benign pancreatic masses and normal pancreas.ResultsAt b value of 0 and 600 s/mm2, rFOV DWI was superior to ss-EPI DWI in terms of showing pancreatic anatomic structure, the contrast of the lesion and the score evaluation for susceptibility artifacts(b=0 s/mm22.99±0.51vs2.79±0.64, 2.37±0.48vs1.81±0.63, 3.17±0.56vs2.91±0.60；b=600 s/mm23.63±0.50vs3.32±0.56, 3.45±0.50vs3.01±0.49, 3.74±0.44vs3.12±0.37), and the differences were statistically significant (P<0.001). ADC values of PDAC, NET, MFCP, SPT and normal pancreas were (1.38±0.17)×10-3,(1.22±0.35)×10-3,(1.29±0.13)×10-3,(1.04±0.38)×10-3and(1.86±0.15)×10-3mm2/s for rFOV DWI, and(1.73±0.24)×10-3,(1.63±0.39)×10-3,(1.58±0.19)×10-3,(1.25±0.26)×10-3and(2.04±0.20)×10-3mm2/s for ss-EPI DWI. The difference on ADC values among different groups and within one group were all statistically significant (P<0.001). There were no statistical significant differences on ADC values between MFCP and PDAC, between MFCP and SPT as well as on ss-EPI DWI ADC values between PDAC and NET, but statistical differences were found between other two groups (P<0.05). The area under the ROC curve of rFOV and ss-EPI DWI was 0.983 (95%CI0.944-0.998) and 0.889 (95%CI0.822-0.936), respectively, and the difference was statistically significant (P=0.0004), but rFOV DWI and ss-EPI DWI ADC values for PDAC and all benign solid diseases were 0.799 (95%CI0.719-0.864) and 0.755 (95%CI0.672-0.827), and the difference was not statistically significant.ConclusionsrFOV DWI could significantly enhance the quality of DWI images, and its diagnostic efficacy was much better than ss-EPI DWI.

Pancreatic neoplasms; Magnetic resonance imaging; Diagnosis, differential

FundprogramShanghai Natural Science Foundation(14ZR1408300)；Medical Guidance Project of Shanghai Science and Technology Commission(14411960100)

10.3760/cma.j.issn.1674-1935.2017.06.009

200433 上海，第二軍醫(yī)大學(xué)長海醫(yī)院放射科

陸建平，Email：cjr.lujianping@vip.163.com

上海市自然科學(xué)基金(14ZR1408300)；上海市科委醫(yī)學(xué)引導(dǎo)項(xiàng)目(14411960100)

2017-06-18)

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