趙莉蕓，周純武，李靜

2012年北美放射學(xué)年會(RSNA)共收錄乳腺影像學(xué)摘要約339篇，其中大會發(fā)言133篇，科學(xué)展板82篇，教育展覽124篇。從成像技術(shù)方面，涉及MRI的文章約占30%，其次分別為超聲成像、數(shù)字X線攝影(digital mammography,DM)、數(shù)字合成乳腺X線體層成像(digital breast tomosynthesis,DBT)和乳腺分子影像(molecular breast imaging,MBI)。從研究內(nèi)容方面，主要集中在乳腺成像和診斷新技術(shù)的應(yīng)用、乳腺癌篩查、新輔助化療(neoadjuvant chemotherapy,NAC)療效評價和定位活檢等，筆者將從以上四個方面分別進行闡述，以期對今后乳腺影像學(xué)研究提供參考。

1 乳腺成像和診斷新技術(shù)

1.1 分子影像

以X線攝影和超聲為代表的形態(tài)學(xué)成像是乳腺傳統(tǒng)的檢查方法，磁共振擴散、灌注及波譜等功能成像也正逐漸應(yīng)用于臨床；而MBI可從細胞、分子甚至基因水平反映活體的生理和病理過程，目前已成為乳腺影像學(xué)研究的新熱點。

2002年，Brem等[1]率先將乳腺專用伽馬成像(breast-specific gamma imaging,BSGI)應(yīng)用于臨床并取得成功。BSGI具有無痛、易于被患者接受、檢查時間短、比較經(jīng)濟等特點，因而適合于乳腺篩查。Coffey等[2]對364例X線表現(xiàn)正常的乳腺癌高危人群行BSGI，認為BSGI是常規(guī)乳腺篩查的有益補充，可使檢出率提高2.5%，尤其對于致密型乳腺。Velez等[3]研究顯示將BSGI引入傳統(tǒng)乳腺篩查中，可提高乳腺癌和高危病變檢出的敏感度，但特異度卻無明顯改變。除此之外，Rapelyea等[4]研究顯示，BSGI上表現(xiàn)為彌漫性放射性攝取增高的乳腺浸潤性導(dǎo)管癌，經(jīng)保乳手術(shù)后陽性切緣的發(fā)生率較高，往往需要再次手術(shù)，因此術(shù)前BSGI可提示這類患者要擴大手術(shù)切除范圍。PET領(lǐng)域的研究主要集中在乳腺癌治療效果評價和預(yù)后預(yù)測方面。Koo等[5]回顧性分析了548例乳腺癌患者的PET-CT圖像，發(fā)現(xiàn)不同分子亞型的乳腺癌，其18F-FDG攝取也不同，三陰性乳腺癌FDG攝取最高(SUVmax 9.55±5.90)，而Luminal A型者最低(SUVmax 4.62±3.42)。說明PET-CT可從分子水平反映疾病的生物學(xué)特性。Kiyoto等[6]分析了87例乳腺癌(90個病灶)患者NAC前后PET-CT上SUVmax，結(jié)果顯示ΔSUVmax>80.8%往往提示為完全病理緩解者(pathological complete response,pCR)，且可獲得相對延長的無病生存(disease-free survival，DFS)。Nakajima等[7]對49例經(jīng)過乳腺切除和術(shù)后放療的患者行術(shù)前PET-CT檢查，認為治療前的SUV-max是這類患者預(yù)后的獨立預(yù)測指標(biāo)。

光學(xué)分子成像仍處于發(fā)展的初期，是分子影像領(lǐng)域新的研究方向。Ahn等[8]的研究認為，與單獨超聲檢查相比，擴散光學(xué)成像(optical diffusion imaging)聯(lián)合超聲可明顯提高乳腺病變診斷的準(zhǔn)確度和特異度，減少假陽性的產(chǎn)生。Choi等[9]對240例乳腺癌患者行術(shù)前擴散光學(xué)成像和PET-CT檢查，結(jié)果顯示擴散光學(xué)成像參數(shù)氧飽和度(SO2)與SUVmax存在相關(guān)性，SO2高者，SUVmax也相應(yīng)較高，NAC后pCR率也較高。Sklair-Levy等[10]采用一種新型紅外線 (RUTH) 成像技術(shù)獲得了乳腺超分辨率3D血管圖像，結(jié)果顯示乳腺浸潤性癌的血管密度評分高于正常乳腺，而大多數(shù)患者血管圖像中顯示的異常增多血管是人眼無法識別的；因此，認為這種快速、非侵入性的成像方式有望檢出早期乳腺癌。

1.2 MRI

擴散加權(quán)成像(diffusion weighted imaging，DWI)在乳腺MRI的應(yīng)用已較為廣泛，DWI與動態(tài)增強MRI聯(lián)合可提高乳腺癌診斷的準(zhǔn)確度、特異度和陽性預(yù)測值[11-13]；DWI亦可鑒別乳腺浸潤性癌與導(dǎo)管原位癌[14]。Pediconi等[15]研究顯示DWI聯(lián)合T2 IDEAL序列評價乳腺癌NAC療效的敏感度和特異度等同于MRI動態(tài)對比增強，而前者不需注射對比劑。Schiani等[16]研究認為ADC值與乳腺癌預(yù)后因子(ER、PR、HER2和Ki-67)間存在相關(guān)性，Benveniste等[17]的研究結(jié)果則不然。

擴散張量成像(diffusion tensor imaging，DTI)已廣泛應(yīng)用于中樞神經(jīng)系統(tǒng)，而在乳腺的應(yīng)用鮮有報道。由于乳腺導(dǎo)管的平均直徑(約60 μm)要比腦白質(zhì)纖維束(1～2 μm)大得多，因此需延長擴散時間來充分實現(xiàn)各向異性。Cho等[18]行6個方向擴散敏感梯度的乳腺DTI，結(jié)果顯示不同擴散時間獲得的各向異性指數(shù)FA和擴散特征值λ3有顯著性差異，因而證實延長擴散時間可增加乳腺組織對各向異性的敏感度，有望鑒別正常乳腺組織與惡性腫物及獲得乳腺導(dǎo)管結(jié)構(gòu)的擴散張量圖。Penn等[19]對36例患者行DTI檢查，發(fā)現(xiàn)ADC值聯(lián)合DMB(diffusion morphological blooming)有助于鑒別乳腺良惡性腫瘤，ROC曲線下面積達0.90(單獨應(yīng)用ADC值為0.77)；而與對比增強MRI相比，DTI不需注射對比劑、費用更低。

1.3 超聲剪切波彈性成像(shear wave elastography，SWE)

SWE定量參數(shù)(如彈性評分、彈性指數(shù)等)的測定具有可重復(fù)性，常規(guī)超聲檢查聯(lián)合SWE可提高乳腺腫瘤診斷的準(zhǔn)確度和特異度，而不降低敏感度[20-24]。Evans等[25]分析了266例乳腺癌患者術(shù)前SWE，有17例表現(xiàn)為良性，其中5例為導(dǎo)管原位癌(5/11)，12例為浸潤性癌(12/255)，可見導(dǎo)管原位癌在SWE上更容易被誤診為良性病變，而SWE上表現(xiàn)為良性征象的浸潤性癌在組織學(xué)上多為Ⅰ級且易被X線檢出；而這些SWE誤診為良性的病例在常規(guī)超聲檢查中不易被誤診，因此二者聯(lián)合可提高病變診斷的準(zhǔn)確度。Chang等[26]研究了乳腺浸潤性癌SWE上彈性指數(shù)與腫瘤大小、受體狀態(tài)、組織學(xué)類型和分級之間的相關(guān)性，結(jié)果顯示Luminal A型乳腺癌的平均彈性指數(shù)最低，腫瘤體積較大、組織學(xué)分化較差和三陰性乳腺癌的平均彈性指數(shù)則較高。

2 乳腺篩查

X線攝影和超聲檢查是最基本的乳腺影像學(xué)篩查手段，MRI在乳腺篩查，特別是乳腺癌高危人群和致密型乳腺者篩查中的價值也逐漸被肯定。2007年美國癌癥協(xié)會的篩查指南建議乳腺癌高危人群需行每年一次MRI檢查作為乳腺X線篩查的補充。No等[27]研究顯示，許多患者和醫(yī)師由此夸大了MRI在乳腺篩查中的作用，從而使這些患者摒棄了每年一次的X線篩查。MRI是乳腺癌高危人群篩查的有益補充，而不可替代常規(guī)X線攝影。Schrading等[28]評估了乳腺MRI在一般人群篩查中的價值，結(jié)果顯示對于X線和超聲無法發(fā)現(xiàn)的乳腺癌，MRI的額外檢出率為5.4‰，因此認為MRI用于一般人群的乳腺篩查亦是非常必要的。另外兩項研究結(jié)果顯示，MRI可作為常規(guī)X線的有益補充而用于乳腺癌病史患者的篩查，其檢出率分別為4.4%[29]和2.1%[30]。Kaiser等[31]研究認為，與單獨行乳腺X線篩查相比，MRI檢查的費用盡管較高，但從長遠考慮，則是一種經(jīng)濟的篩查策略。Johnson等[32]研究認為乳腺癌高危人群MRI篩查的召回率與讀片者的經(jīng)驗關(guān)系不大，而與X線篩查的召回率相關(guān)，因此其客觀性相對較強。以往考慮到女性體內(nèi)激素水平隨月經(jīng)周期而出現(xiàn)波動，乳腺背景的強化程度亦隨激素水平的波動而發(fā)生變化，因此推薦MRI篩查應(yīng)安排在月經(jīng)周期的早期(即受檢者體內(nèi)激素水平最低時)進行。Dontchos等[33]回顧性分析了243名未絕經(jīng)婦女的319項MRI檢查，認為MRI的診斷結(jié)果不受月經(jīng)周期影響，因而婦女可選擇月經(jīng)周期的任何時段行乳腺MRI檢查。

數(shù)字合成體層成像技術(shù)用于乳腺X線檢查的時間并不長，DBT可呈現(xiàn)三維空間的影像信息，從而消除常規(guī)DM檢查中組織重疊造成的觀察障礙。Miravete等[34]回顧了5718名乳腺篩查者的普查數(shù)據(jù)，結(jié)果顯示與傳統(tǒng)的DM篩查比較，引入DBT后的聯(lián)合篩查的檢出率可由原來的1.50%提高到2.33%，且對于不同密度的乳腺腺體的檢出率無明顯差別。Rose等[35]、Hass等[36]、Destounis等[37]的研究結(jié)果顯示DM聯(lián)合DBT篩查可減少召回率，尤其是對于致密型乳腺和<50歲的患者。盡管DBT是一種很有前景的篩查方式，但也存在一定局限性，如工作時間延長、射線劑量高于常規(guī)DM等。Kalra等[38]的研究結(jié)果顯示DM聯(lián)合DBT閱片時間約為傳統(tǒng)DM的2倍，這將會影響臨床工作的效率。Garrett等[39]利用先驗圖像壓縮感知算法(prior image constrained compressed sensing,PICCS)降低DBT檢查約60%的劑量，而其診斷效果與常規(guī)劑量DBT相當(dāng)，且PICCS可提高低對比病灶的信噪比而不影響其重要細節(jié)的顯示。

3 乳腺癌NAC療效評價和預(yù)測

NAC前后MRI參數(shù)(血流動力學(xué)參數(shù)、ADC值等)的改變評價乳腺癌NAC療效的價值已得到大量研究證實[40-42]。Arlinghaus等[43]對25例乳腺癌患者行化療前和NAC 1周期后MRI檢查，結(jié)果顯示NAC 1周期后ADC值的改變可早期預(yù)測pCR，因此有望提早幫助臨床醫(yī)師決定治療方案，避免不必要的化療。Li等[44]對28例乳腺癌患者NAC早期療效預(yù)測的研究亦顯示，NAC 1周期后動態(tài)增強定量參數(shù)Ktrans、Kep和Vp的改變可早期預(yù)測NAC的療效。然而，這些僅僅是小樣本研究，NAC 1周期的MRI參數(shù)能否預(yù)測NAC最終療效還需大宗病例和Meta分析的進一步證實。Telesca等[45]使用一種高弛豫率對比劑釓貝葡胺(Gd-BOPTA，莫迪司)行3.0 T增強 MRI評價乳腺癌NAC療效，結(jié)果顯示其測得的病灶最大徑與病理標(biāo)本的測量值呈正相關(guān)(r=0.746)，因此認為這種方法可準(zhǔn)確評價乳腺癌NAC后殘余病灶的大小。由于Gd-BOPTA的弛豫率約為Gd-DTPA的2倍，因此1/2劑量即可達到同樣的強化效果，適用于灌注成像；且初步研究顯示[46]，Gd-BOPTA還可用于肝腎功能不全者，從而拓展了其應(yīng)用范圍。另外，亦有學(xué)者報道了影響MRI評價乳腺癌NAC療效準(zhǔn)確性的一些因素。Ko等[47]的174例大樣本研究顯示，對于導(dǎo)管原位癌、分化程度較好、基線MRI表現(xiàn)為非腫塊樣強化或NAC后殘余病灶較大者，腫瘤大小評價NAC療效的準(zhǔn)確性較低。Drisis等[48]對91例乳腺癌患者行動態(tài)增強MRI檢查，發(fā)現(xiàn)定量參數(shù)評價和預(yù)測乳腺癌NAC療效的能力受分子亞型影響，對于三陰性和HER2陽性乳腺癌，其評價效能較高，對luminal型則較低。

4 乳腺定位技術(shù)

導(dǎo)絲定位由于置入的導(dǎo)絲容易移位脫落，且手術(shù)陽性切緣率較高、患者易產(chǎn)生不適感及并發(fā)癥，近年來受到質(zhì)疑。Ananyhasivan等[49]采用放射性同位素引導(dǎo)隱匿性病灶定位(radio-guided occult lesion localization,ROLL)技術(shù)對乳腺腫瘤及前哨淋巴結(jié)進行術(shù)前定位，即在超聲或X線引導(dǎo)下將放射性同位素锝標(biāo)記硫膠體注入病灶內(nèi)，術(shù)中用伽馬探針對病灶進行精確定位，結(jié)果顯示與導(dǎo)絲定位相比，ROLL是一種準(zhǔn)確、簡便、性價比高且容易被患者接受的定位方法。然而ROLL的手術(shù)陽性切緣率還需進一步評價。King等[50]采用放射性粒子125I植入定位(radioactive seed localization，RSL)技術(shù)對195名婦女行乳腺術(shù)前定位，結(jié)果顯示單獨采用RSL定位者手術(shù)陽性切緣率為10%，RSL和導(dǎo)絲聯(lián)合定位者為14%，兩者無統(tǒng)計學(xué)差異。因而，RSL是一種安全、有效、快速且并發(fā)癥較少的定位方法。

縱觀2012年RSNA乳腺影像學(xué)報道，MRI在乳腺疾病診斷和研究中具有廣闊前景，分子成像等新技術(shù)的興起將會開辟乳腺影像學(xué)研究的新局面；同時，尋找更好的、適合本國國情的早期發(fā)現(xiàn)和診斷乳腺癌的影像篩查手段，降低死亡率，仍是放射科醫(yī)師今后繼續(xù)努力的方向。

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