釓劑對MR IDEAL-IQ骨髓脂肪定量影響的實驗研究

林苑，查云飛，2*，邢棟，胡磊，王嬌，曾菲菲，陸雪松

釓劑對MR IDEAL-IQ骨髓脂肪定量影響的實驗研究

林苑1，查云飛1，2*，邢棟1，胡磊1，王嬌1，曾菲菲1，陸雪松2，3

骨髓；脂肪類；磁共振成像；對比劑

骨髓脂肪組織作為骨質(zhì)疏松、糖尿病等代謝性疾病、神經(jīng)厭食癥、血液系統(tǒng)疾病及良惡性骨腫瘤等的重要生物學(xué)標記物，與骨髓的各種生理性、病理性改變都密切相關(guān)[1-3]，迭代最小二乘法六回波梯度回波非對稱采集水脂分離磁共振成像(iterative decomposition of water and fat with echoasymmetry and least square estimationironquantification，IDEAL-IQ)是在IDEAL技術(shù)上改良的MR三維脂肪定量技術(shù)，其在肝臟、骨髓組織脂肪定量的準確性已得到充分肯定[4-6]。

常規(guī)MRI增強和動態(tài)對比磁共振成像(DCEMRI)對鑒別骨髓良惡性病變、評估惡性腫瘤預(yù)后、監(jiān)測腫瘤對放化療和抗血管基因治療的反應(yīng)以及評價骨髓病變血流灌注具有重要意義[7-9]。IDEAL-IQ序列定量評估骨髓脂肪分數(shù)(FF)是否受到釓對比劑增強掃描的影響尚未見專題研究報道，本研究旨在探討靜脈注射釓對比劑對IDEALIQ定量兔腰椎體骨髓脂肪含量的影響，以評估增強掃描后應(yīng)用IDEAL-IQ技術(shù)定量骨髓脂肪含量的可行性。

1 材料與方法

1.1 研究對象

于武漢大學(xué)動物實驗中心購進新西蘭大白兔8只，雌雄不限，3～5月齡。所有實驗兔在武漢大學(xué)實驗動物中心單籠飼養(yǎng)，予以標準兔飼料及衛(wèi)生水喂養(yǎng)，室溫控制在25℃。本實驗遵循武漢大學(xué)關(guān)于保護和使用實驗動物的相關(guān)規(guī)定。

1.2 MRI成像方法

將實驗兔固定后，用留置針(20 G)穿刺耳緣靜脈，注射3%戊巴比妥鈉溶液1.5 ml/kg進行麻醉。取仰臥位、足先進置于8通道膝關(guān)節(jié)專用相控陣線圈，運用3.0 T超導(dǎo)MR機(Discovery MR 750 Plus，GE Healthcare)行三平面定位掃描后，對每只兔常規(guī)行腰椎矢狀面FSE-T1WI、FSE-T2WI和IDEALIQ掃描，掃描范圍包括第3～7腰椎。隨后采用MEDRAD Spectris Solaris EP磁共振壓力注射器，經(jīng)兔耳緣靜脈留置針注射釓貝葡胺(Gd-BOPTA，商品名：莫迪司)3 ml，用6 ml生理鹽水以相同流率(0.5 ml/s)進行沖洗。注射后5 min、30 min分別行腰椎矢狀面IDEAL-IQ序列掃描，注射釓對比劑前后IDEAL-IQ掃描參數(shù)保持一致，掃描參數(shù)如下。

矢狀面T1WI掃描參數(shù)：TR 400 ms，TE 13 ms，掃描層厚3 mm，視野16 cm×16 cm，矩陣512×512，激勵次數(shù)為1，掃描時間2 min 20 s。

矢狀面T2WI掃描參數(shù)： TR 2500 ms，TE 102.9 ms，掃描層厚3 mm，視野16 cm×16 cm，矩陣512×284，激勵次數(shù)為1，掃描時間3 min 25 s。

矢狀面IDEAL-IQ掃描參數(shù)：反轉(zhuǎn)角6°，TR 19.6 ms，TE1 1.2 ms，ΔTE 2 ms，帶寬125 kHz，掃描層厚3 mm，視野16 cm×12.8 cm，矩陣288×288，激勵次數(shù)為2，掃描時間4 min 22 s。

1.3 組織病理學(xué)檢查

于MR掃描后當日采用空氣栓塞法將實驗兔處死，取出第3～7腰椎，4%多聚甲醛固定24 h后，用EDTA脫鈣液進行脫鈣3周，隨后脫水、石蠟包埋、切片，沿每個椎體短軸切4 μm厚薄片兩張，分別行HE染色和普魯士藍鐵染色。

1.4 數(shù)據(jù)分析

1.4.1 IDEAL-IQ骨髓脂肪分數(shù)(FF)及R2*測定

1.4.2 HE染色骨髓脂肪含量

在Image-Pro Plus 6.0圖像分析系統(tǒng)對骨髓脂肪含量進行定量分析，按照下列公式計算脂肪含量：FCHIS=選中空泡區(qū)域的面積/整體面積。每張HE病理切片隨機選擇5個200倍光鏡視野計算平均值。

1.4.3 普魯士藍染色椎體骨髓鐵沉積

在顯微鏡(OLYMPUS BX51)下觀察腰椎普魯士藍染色切片，確定腰椎骨髓內(nèi)有無鐵沉積。

1.5 統(tǒng)計學(xué)分析

2 結(jié)果

注射釓對比劑前IDEAL-IQ骨髓脂肪分數(shù)值(FF0min)與注射釓對比劑5 min后骨髓脂肪分數(shù)值(FF5min)、30 min后骨髓脂肪分數(shù)值(FF30min)均服從正態(tài)分布，且組間方差齊，應(yīng)用單變量重復(fù)測量的方差分析，各時間點骨髓脂肪分數(shù)(FF)無明顯統(tǒng)計學(xué)差異(F=3.118，P＞0.05，組間比較結(jié)果分別為P=0.835、0.916和0.754)

Pearson相關(guān)分析結(jié)果顯示HE染色計算的脂肪含量(FCHIS)與注射釓劑前FF0min(r=0.813)存在高度正相關(guān)性(P＜0.05)(圖3)。

Bland-Altman分析顯示注射釓劑前FF0min與注射釓劑5 min后FF5min(0.90、1.10)及注射釓劑30 min后FF30min(0.94、1.07)均具有良好的一致性(測量值比率95%置信區(qū)間)，提示95%置信區(qū)間內(nèi)骨髓脂肪分數(shù)測量值最大差值分別為2.89%、2.42%(圖4，5)。

圖1兔腰椎矢狀面IDEAL-IQ圖像。A、B分別為注射釓劑前FF圖、R2*圖；C、D分別為注射釓劑5 min后FF圖、R2*圖；E、F分別為注射釓劑30 min后FF圖、R2*圖圖2A：兔腰椎骨髓HE染色(HE ×200)。紅色箭頭所示為脂肪空泡，黑色箭頭所示為骨髓細胞；B：兔腰椎骨髓普魯士藍染色( ×400)光鏡下細胞排列整齊，形態(tài)規(guī)則，未見明顯鐵顆粒Fig. 1The fat fraction (FF) and R2*mappings of the spleen. A, B: The spine fat fraction (FF) and R2*mappings before administration of Gd-BOPTA. C, D: The spine fat fraction (FF) and R2*mappings 5 min after administration of Gd-BOPTA. E, F: The spine fat fraction (FF) and R2*mappings 30 min after administration of Gd-BOPTA.Fig. 2A: Bone marrow HE staining (HE ×200), the fat cell (red arrow) and the bone marrow cells (black arrow). B: Bone marrow (BM) iron deposits were assessed by Prussian blue staining( ×400).

表1注射釓劑前后兔腰椎骨髓FF值和R2*值時序性變化Tab. 1Fat fractionfor the spine before and after gadolinium-based contrast media injection

表1注射釓劑前后兔腰椎骨髓FF值和R2*值時序性變化Tab. 1Fat fractionfor the spine before and after gadolinium-based contrast media injection

Notes: 40 vertebrae, FF measurements of revealed no signif i cant systematic bias between the three measurements(P＞0.05 for all), R2*increased (P=0.046, P=0.024) after administration of gadolinium.

±s (s-1) Pre-contrast After-contrast 5 min After-contrast 30 min F value P valuePre-contrastAfter-contrast 5 min After-contrast 30 min F value P value 40 31.77±2.66 31.89±2.54 31.71±2.520.0510.950121.64±20.28125.70±19.15125.21±19.18 3.1180.048 FF x n ±s (%) R2*x

圖3注射釓劑前IDEAL-IQ定量的骨髓脂肪分數(shù)(FF0min)與HE染色計算的骨髓脂肪含量(FCHIS)的相關(guān)性圖4IDEAL-IQ定量的注射釓劑前及注射釓劑5 min后兔腰椎FF值Bland-Altman分析結(jié)果圖5IDEAL-IQ定量的注射釓劑前及注射釓劑30 min后兔腰椎FF值Bland-Altman分析結(jié)果Fig. 3Correlation between the IDEAL-IQ fat fraction (FF0min) and the historic fat content(FCHIS).Fig. 4Pre- and post-contrast (5 min) Bland-Altman plots.Fig. 5Pre- and post-contrast (30 min) Bland-Altman plots.

3 討論

本實驗中根據(jù)釓對比劑在體內(nèi)的代謝時間曲線特點[10]，設(shè)定在注射釓劑前及注射后5 min、30 min 三個時間點分別采用IDEAL-IQ序列對兔腰椎進行掃描，將相應(yīng)時間點椎體骨髓脂肪分數(shù)進行分析且將增強前脂肪分數(shù)與組織病理學(xué)脂肪含量進行對比，結(jié)果顯示注射釓劑前后各時間段IDEAL-IQ測得的椎體骨髓脂肪分數(shù)無明顯差異，且增強前脂肪分數(shù)與組織病理學(xué)脂肪含量具有高度相關(guān)性。Bland-Altman一致性分析顯示注射釓劑前IDEAL-IQ測得的脂肪分數(shù)與注射后各時間段測得的脂肪分數(shù)一致性良好。這證明了IDEAL-IQ序列定量骨髓脂肪含量準確度高，穩(wěn)定性及可重復(fù)性好，且不受釓對比劑增強掃描的影響，即在靜脈注射釓對比劑后采用IDEAL-IQ序列定量骨髓脂肪含量具有可行性。

DIXON方法可利用水脂分離技術(shù)測得組織脂肪含量，傳統(tǒng)的兩點式DIXON[11]技術(shù)通過調(diào)節(jié)回波時間TE做兩次采集，得到同相位及反相位圖像，對兩幅圖像進行加減，可得到水像和脂像，進一步算出脂肪分數(shù)，然而傳統(tǒng)的兩點式DIXON方法受T2*效應(yīng)影響，在進行水脂分離時產(chǎn)生相位誤差，導(dǎo)致測量結(jié)果誤差[12]。IDEAL-IQ采用小角度激發(fā)降低T1偏倚，采集多個(≥6)梯度回波擬合T2*衰減曲線，將生成的T2*值用來校正源數(shù)據(jù)，從而修正T2*效應(yīng)的影響[13]。并用fly-back方法進行k空間填充，生成水像、脂像以及脂肪比像等六幅圖像，在脂肪比圖像上及弛豫率圖像放置ROI可以直接得到脂肪分數(shù)(FF)及R2*值而無需進一步計算。本實驗將骨髓脂肪分數(shù)(FF)與病理學(xué)定量的骨髓脂肪細胞面積比(FCHIS)進行相關(guān)性分析，進一步驗證IDEAL-IQ技術(shù)定量骨髓脂肪含量準確度高。

MR釓類對比劑具有一定程度的T1弛豫時間和T2、T2*弛豫時間縮短效應(yīng)。橫向弛豫率R2*是T2*的倒數(shù)，釓劑能縮短T2*弛豫時間，相對應(yīng)增加R2*值，本實驗注射釓劑后骨髓R2*值升高，亦予以證實。Ge等的研究[14]顯示IDEAL-IQ技術(shù)定量的肝臟脂肪分數(shù)不受靜脈注射釓對比劑帶來的R2*值變化的影響而保持較高的穩(wěn)定性，但是無法排除鐵沉積對R2*定量參數(shù)測量的影響。Liau等[15]通過實驗證實IDEAL-IQ定量的肝臟脂肪分數(shù)不受鐵劑的影響，但是Hines等[16]通過對不同濃度的水-脂-鐵試劑進行定量分析，發(fā)現(xiàn)隨著鐵劑濃度的增高，IDEAL-IQ定量的脂肪分數(shù)與實際脂肪含量差異增大，其原因可能是鐵劑對水組織的T2*弛豫的影響大于對脂肪組織的影響。本實驗中，對兔腰椎椎體切片后進行普魯士藍染色，在400倍顯微鏡下觀察骨髓內(nèi)鐵沉積情況，見細胞排列整齊，形態(tài)規(guī)則，未見明顯鐵顆粒，參照 Sehgal等[17]鐵沉積半定量分析評價標準可歸為0級即無鐵沉積。因此，可基本排除椎體骨髓內(nèi)鐵沉積對R2*值的影響，在本實驗中R2*值的變化主要代表釓劑對骨髓組織T2*弛豫的影響。

本實驗結(jié)果顯示由于釓劑可通過加快骨髓的T2*弛豫率而導(dǎo)致R2*值的升高，然而進行骨髓脂肪定量時，通過采集多個回波擬合T2*衰減曲線，能修正T2*效應(yīng)的影響，因此在注射釓劑后，IDEAL-IQ序列定量的脂肪分數(shù)值(FF)依然能保持一定的穩(wěn)定性，這與Ge等[14]證實的IDEAL-IQ對靜脈注射釓噴酸葡胺保持良好穩(wěn)定性的結(jié)果一致，進一步提示磁共振釓類對比劑等影響T2*弛豫率的物質(zhì)對IDEAL-IQ定量組織脂肪含量影響較小。

本研究的局限性：(1)本研究試驗樣本量較小，增大樣本量及變異程度的改變可能會得到不同的結(jié)果，所以仍需后續(xù)大樣本實驗研究證實；(2)本實驗未對IDEAL-IQ技術(shù)T2*校準效應(yīng)對骨髓脂肪分數(shù)(FF)的影響進行評估，即未比較經(jīng)T2*校準的FF值和未經(jīng)T2*校準的FF值的差異。然而根據(jù)Meisamy等[18]的報道，在未注射釓劑的情況下，肝臟經(jīng)T2*校準的FF值和未經(jīng)T2*校準的FF值有統(tǒng)計學(xué)差異，筆者推斷IDEAL-IQ可修正骨髓T2*效應(yīng)而保持FF測量結(jié)果的穩(wěn)定性。

總之，在靜脈注射釓劑引起的R2*值增高的情況下，IDEAL-IQ定量椎體骨髓脂肪分數(shù)的準確度高，且仍維持較高的穩(wěn)定性和一致性。在靜脈注射釓對比劑后采用IDEAL-IQ序列定量骨髓脂肪含量具有可行性。

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Effect of gadolinium on vertebral fat fraction content using IDEAL-IQ technique

LIN Yuan1, ZHA Yun-fei1,2*, XING Dong1, HU Lei1, WANG Jiao1, ZENG Fei-fei1, LU Xue-song2,3

1Department of Radiology, Renmin Hospital of Wuhan University, Wuhan 430060, China

2Hubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis &Treatment, Wuhan 430060, China

3Department of Biological Engineering, School of Biomedical Engineering, South-Central University for Nationalities, Wuhan 430060, China

ACKNOWLEDGMENTSThis thesis is sponsored by the Opening Foundation of Hubei Key Laboratory of Medical Information Analysis and Tumor Diagnosis & Treatment (No. PJS140011511). Scientif i c Research Funding Project of Hubei Provincial Department of Health (No. JX6B68).

Objective:This study evaluates the robustness of a magnetic resonance (MR) fat quantification method to changes in R2*caused by an intravenous infusion of gadolinium.Materials and Methods:The R2*and fat fraction content (FF) were measured in vertebral marrow in eight New Zealand white rabbits using an investigational sequence (IDEAL IQ) provided by the MR scanner vendor. Measurements were made once before and twice after Gd-BOPTA infusion (5 min, 30 min). Then HE stain was performed for calculating vertebral fat content (FCHIS), Prussian blue stain was performed for showing iron in vertebral.Results:Vertebral marrow FF measurements revealed no significant systematic bias between the three measurements (P＞0.05 for all). Good agreement (95% confidence interval) of FF measurements were demonstrated between FF0minand FF5min(0.90, 1.10) and FF0minand FF30min(0.94, 1.07). A signif i cant positive correlation is found between FF0minand FCHIS(r=0.813, P＜0.05). R2*increased after administration of gadolinium.Conclusion:Although under the impact of an increased R2*in vertebral marrow post-contrast, the investigational sequence can still obtain accurate and stable fat fraction content. the IDEAL IQ method of fat quantif i cation is robust to changes in R2*.

Bone marrow; Fats; Magnetic resonance imaging; Contrast media

Zha YF, E-mail: zhayunfei@hotmail.com

Received 26 Sep 2016, Accepted 20 Oct 2016

醫(yī)學(xué)信息分析及腫瘤診療湖北省重點實驗室開放課題基金項目(編號：PJS140011511)；湖北省衛(wèi)生廳科研資助項目(編號：JX6B68)

1. 武漢大學(xué)人民醫(yī)院放射科，武漢430060

2. 醫(yī)學(xué)信息分析及腫瘤診療湖北省重點實驗室，武漢 430060

3. 中南民族大學(xué)生物醫(yī)學(xué)工程學(xué)院，武漢 430060

查云飛，E-mail：zhayunfei@hotmail. com

2016-09-26

接受日期：2016-10-20

R445.2

A

10.12015/issn.1674-8034.2016.11.012

林苑, 查云飛, 邢棟. 等. 釓劑對MR IDEAL-IQ骨髓脂肪定量影響的實驗研究. 磁共振成像, 2016, 7(11): 856-860.*