紀(jì)曉鵬,劉 洋,王錫明,楊世鋒,李 霞,馮 娟
(1.山東大學(xué)附屬省立醫(yī)院醫(yī)學(xué)影像科,超聲診療科,山東濟(jì)南250021;2.泰山醫(yī)學(xué)院研究生院,山東泰安271000;3.山東省醫(yī)學(xué)影像學(xué)研究所CT室,山東濟(jì)南250021)
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雙源CT大螺距掃描在雙側(cè)雙向Glenn術(shù)后評(píng)估中的應(yīng)用
紀(jì)曉鵬1a,劉洋2,王錫明3,楊世鋒1a,李霞1b,馮娟1b
[摘要]目的:探討128層雙源CT低劑量大螺距掃描在雙側(cè)雙向Glenn術(shù)后形態(tài)學(xué)評(píng)估中的臨床應(yīng)用價(jià)值。方法:收集雙側(cè)雙向Glenn術(shù)后患兒20例,均行低劑量大螺距掃描和DSA檢査。大螺距掃描管電壓為80 kV,管電流根據(jù)患兒體質(zhì)量調(diào)節(jié),螺距3.4。由2名醫(yī)師采用5分法對(duì)圖像質(zhì)量進(jìn)行主觀評(píng)價(jià)。測(cè)量升主動(dòng)脈根部、胸背部肌肉、雙側(cè)上腔靜脈及肺動(dòng)脈的CT值和噪聲。記錄劑量長(zhǎng)度乘積以計(jì)算有效輻射劑量(effective dose,ED)。采用Kappa檢驗(yàn)比較2名醫(yī)師對(duì)圖像質(zhì)量主觀評(píng)分的一致性。觀察患兒術(shù)后形態(tài)學(xué)改變情況,并以DSA結(jié)果作為標(biāo)準(zhǔn),評(píng)價(jià)CT的準(zhǔn)確性。結(jié)果:所有患兒均成功完成低劑量大螺距掃描,圖像均未出現(xiàn)運(yùn)動(dòng)偽影。升主動(dòng)脈根部、雙側(cè)上腔靜脈及肺動(dòng)脈的CT值均超過(guò)250 HU,圖像強(qiáng)化良好。圖像質(zhì)量主觀評(píng)價(jià)平均得分(4.15±0.67)分,2名醫(yī)師的一致性好(K=0.65,P<0.05)。CT發(fā)現(xiàn)上腔靜脈擴(kuò)張7處,肺動(dòng)脈狹窄4處,體-肺循環(huán)側(cè)支血管19支,以DSA結(jié)果作為標(biāo)準(zhǔn),CT診斷準(zhǔn)確率均為100%。患兒平均CTDIvol為(0.59±0.15)mGy,平均DLP為(14.6±6.0)mGy·cm,平均ED為(0.33±0.11)mSv。結(jié)論:128層雙源CT低劑量大螺距掃描在雙側(cè)雙向Glenn術(shù)后形態(tài)學(xué)評(píng)估中可獲取滿足診斷的圖像,且患兒無(wú)需屏氣,具有較好的應(yīng)用價(jià)值。
[關(guān)鍵詞]心轉(zhuǎn)流術(shù),右;體層攝影術(shù),X線計(jì)算機(jī);輻射劑量
雙向Glenn術(shù)是將上腔靜脈橫斷后與右肺動(dòng)脈行端-側(cè)吻合的術(shù)式,近年來(lái)多作為功能性單心室的復(fù)雜性先天性心臟病患兒的過(guò)渡性手術(shù),可有效促進(jìn)患兒的肺動(dòng)脈發(fā)育,為下一步行改良Fontan術(shù)提供有利條件[1-3]。對(duì)部分伴永存左上腔靜脈的患兒,將其雙側(cè)上腔靜脈分別與同側(cè)肺動(dòng)脈行端-側(cè)吻合即為雙側(cè)雙向Glenn術(shù)。與單側(cè)雙向Glenn術(shù)相比,雙側(cè)雙向Glenn術(shù)死亡率更高,形成血栓的風(fēng)險(xiǎn)更大,最終完成根治術(shù)的概率更低[4-5],故對(duì)雙側(cè)雙向Glenn術(shù)后患兒密切隨訪具有重要意義。
影像學(xué)在雙側(cè)雙向Glenn術(shù)后隨訪中發(fā)揮著十分重要的作用,其中DSA是常規(guī)檢查項(xiàng)目,但其操作復(fù)雜、費(fèi)用高、有并發(fā)癥且輻射劑量較高[6-7]。近年來(lái),CTA在先天性心臟病患兒的術(shù)后評(píng)估中應(yīng)用日益廣泛,其簡(jiǎn)便易行,準(zhǔn)確率高,但CT伴隨的輻射一直是人們關(guān)注的重點(diǎn)。128層雙源CT前瞻性心電門控大螺距掃描(簡(jiǎn)稱大螺距掃描)可清晰地顯示心臟大血管的畸形且輻射劑量極低(多低于0.5 mSv)[8-9],已用于先天性心臟病患兒的術(shù)前評(píng)價(jià)。該技術(shù)能否用于雙側(cè)雙向Glenn術(shù)后評(píng)估,國(guó)內(nèi)目前尚無(wú)文獻(xiàn)報(bào)道。本研究以DSA結(jié)果作為標(biāo)準(zhǔn),探討128層雙源CT低劑量大螺距掃描在雙側(cè)雙向Glenn術(shù)后患兒中進(jìn)行形態(tài)學(xué)評(píng)估的可行性及準(zhǔn)確性。
1.1一般資料收集2014年8月至2015年10月來(lái)山東省立醫(yī)院隨訪的雙側(cè)雙向Glenn術(shù)后患兒20例,年齡1~10歲,平均(5.6±3.1)歲;男9例,女11例;體質(zhì)量10~31 kg,平均(20.2±6.8)kg。所有患兒于低劑量大螺距掃描后1周內(nèi)行DSA檢查。本研究已通過(guò)山東省立醫(yī)院倫理委員會(huì)的批準(zhǔn)。行低劑量大螺距掃描和DSA檢查之前,告知患兒家屬含碘對(duì)比劑的不良反應(yīng)和接受X線輻射的風(fēng)險(xiǎn),并由家屬簽署知情同意書。
1.2 CT檢查
1.2.1所有檢查使用Siemens第2代雙源CT機(jī)(Somatom Definition Flash,Siemens Healthcare,F(xiàn)orchheim,Germany)完成。掃描參數(shù):球管旋轉(zhuǎn)時(shí)間0.28 s/r,探測(cè)器準(zhǔn)直2×64×0.6 mm,借助Z軸飛焦點(diǎn)技術(shù),層面采集厚度為2×128×0.6 mm,螺距3.4,管電壓80 kV,管電流根據(jù)患兒體質(zhì)量調(diào)節(jié):體質(zhì)量超過(guò)6 kg,超出部分在60 mAs基礎(chǔ)上每1 kg增加5 mAs。掃描范圍從胸廓入口至心底,掃描方向由頭側(cè)向足側(cè)。所有患兒均未服用β受體阻滯劑控制心率。大螺距掃描數(shù)據(jù)采集起始時(shí)相設(shè)置在心動(dòng)周期的10%[8]。記錄CT機(jī)顯示的大螺距掃描的掃描長(zhǎng)度及掃描時(shí)間。
在患兒?jiǎn)蝹?cè)手背靜脈或肘部靜脈建立靜脈通道,掃描前行對(duì)比劑(碘海醇,350mgI/mL)過(guò)敏試驗(yàn)。試驗(yàn)陰性后,體質(zhì)量不超過(guò)15 kg的患兒口服10%水合氯醛(劑量0.5 mg/kg體質(zhì)量)進(jìn)行鎮(zhèn)靜[10];體質(zhì)量超過(guò)15 kg的患兒囑其平靜呼吸,不必進(jìn)行屏氣訓(xùn)練。所有患兒均未進(jìn)行麻醉。
對(duì)比劑注射方案:對(duì)比劑(碘海醇,350 mgI/mL)劑量為2.0 mL/kg體質(zhì)量,注射時(shí)間20 s,以相同的注射流率追加生理鹽水(劑量1.0 mL/kg體質(zhì)量)。于對(duì)比劑開(kāi)始注射50 s后開(kāi)始大螺距掃描。
1.2.2圖像后處理將采集的數(shù)據(jù)以層厚0.75 mm、層距0.5 mm重建薄層圖像,卷積核為B26f。所有薄層圖像傳輸至工作站(Multiple Modality Workplace,Siemens Healthcare,F(xiàn)orchheim,Germany)進(jìn)行后處理。
1.2.3圖像評(píng)估及分析觀察圖像是否出現(xiàn)由呼吸運(yùn)動(dòng)引起的錯(cuò)層偽影。分別測(cè)量升主動(dòng)脈根部、胸背部肌肉、雙側(cè)上腔靜脈及肺動(dòng)脈的CT值和噪聲。CT值采用1.0cm2的圓形ROI測(cè)量,將CT值的標(biāo)準(zhǔn)差定義為噪聲。計(jì)算升主動(dòng)脈根部、雙側(cè)上腔靜脈及肺動(dòng)脈的SNR和對(duì)比噪聲比(contrast noise ratio,CNR)。以升主動(dòng)脈為例,SNR=升主動(dòng)脈CT值/圖像噪聲,CNR=(升主動(dòng)脈CT值-胸背部肌肉CT值)/圖像噪聲。
由2名具有5年以上心血管影像診斷經(jīng)驗(yàn)的放射科醫(yī)師獨(dú)立對(duì)心外大血管的圖像質(zhì)量進(jìn)行主觀評(píng)價(jià)。采用5分法:5分,大血管顯示清晰,無(wú)搏動(dòng)偽影;4分,大血管顯示較清,無(wú)搏動(dòng)偽影;3分,大血管顯示較清,有輕微搏動(dòng)偽影;2分,大血管顯示不清,有明顯搏動(dòng)偽影;1分,大血管顯示不清,搏動(dòng)偽影嚴(yán)重[11]。3分及以上的圖像質(zhì)量滿足診斷需要。對(duì)評(píng)價(jià)得分不一致的圖像,經(jīng)討論給出最終評(píng)分。
1.2.4 CT形態(tài)學(xué)評(píng)價(jià)指標(biāo)觀察上腔靜脈擴(kuò)張及肺動(dòng)脈狹窄情況:在MPR圖像上取上腔靜脈管腔最寬處及肺動(dòng)脈管腔最窄處的截面,測(cè)量相應(yīng)管徑并與上腔靜脈遠(yuǎn)心端、肺動(dòng)脈近心端管徑比較,以管徑增寬或狹窄超過(guò)20%[12]作為判斷局部擴(kuò)張或狹窄的標(biāo)準(zhǔn)。此外,重點(diǎn)觀察患兒是否存在血栓形成、體-肺循環(huán)側(cè)支血管(數(shù)量、起源)及肺動(dòng)靜脈畸形等并發(fā)癥。
1.2.5輻射劑量評(píng)估記錄CT機(jī)顯示的CT容積劑量指數(shù)(volume CT dose index,CTDIvol)和劑量長(zhǎng)度乘積(dose length product,DLP),將DLP乘以2.3得到校正后的DLP’[7],將DLP’乘以轉(zhuǎn)換系數(shù)k即得到有效輻射劑量(effective dose,ED)[其中1~6歲,k=0.018 mSv/(mGy·cm);6歲以上,k=0.014 mSv/ (mGy·cm)[13]]。
1.3 DSA檢查使用Philips X線造影機(jī)(Allura CV20,Phillips Medical Systems,The Netherlands)完成。采用咪唑安定(劑量0.1 mg/kg體質(zhì)量)和氯胺酮(劑量1~2 mg/kg體質(zhì)量)對(duì)患兒進(jìn)行全身麻醉,運(yùn)用Seldinger法穿刺股動(dòng)脈、股靜脈和頸內(nèi)靜脈,建立動(dòng)脈和靜脈通道。在操作開(kāi)始時(shí)給予肝素(劑量80 U/ kg體質(zhì)量)。對(duì)比劑為碘海醇(350 mgI/mL),最大劑量為5 mL/kg體質(zhì)量。形態(tài)學(xué)評(píng)價(jià)同CTA。
1.4統(tǒng)計(jì)學(xué)分析運(yùn)用SPSS 19.0軟件進(jìn)行統(tǒng)計(jì)分析。數(shù)值變量采用x±s表示,分類變量采用百分?jǐn)?shù)表示。2名醫(yī)師對(duì)圖像質(zhì)量主觀評(píng)分的一致性采用Kappa檢驗(yàn)(K>0.81,一致性強(qiáng);0.61≤K≤0.80,一致性好)。以P<0.05為差異有統(tǒng)計(jì)學(xué)意義。
20例均順利完成大螺距掃描,掃描長(zhǎng)度(156.1± 29.3)mm,掃描時(shí)間(0.34±0.07)s。
2.1 CT圖像質(zhì)量所有圖像均未出現(xiàn)運(yùn)動(dòng)偽影。圖像質(zhì)量客觀評(píng)價(jià)指標(biāo)見(jiàn)表1,升主動(dòng)脈、雙側(cè)上腔靜脈及肺動(dòng)脈的CT值均達(dá)到250 HU以上,血管強(qiáng)化程度滿足圖像診斷要求[14]。圖像質(zhì)量主觀評(píng)價(jià)5分6例,4分11例,3分3例,均滿足診斷要求,平均得分(4.15±0.67)分,2名醫(yī)師主觀評(píng)價(jià)的一致性好(K= 0.65,P<0.05)。
表1圖像質(zhì)量客觀評(píng)價(jià)情況(x±s)
2.2術(shù)后形態(tài)學(xué)評(píng)價(jià)CT發(fā)現(xiàn)擴(kuò)張的上腔靜脈7支,其中右側(cè)4支,左側(cè)3支(圖1a~1c);肺動(dòng)脈狹窄4處,其中肺動(dòng)脈起始部至吻合口的近心端發(fā)現(xiàn)局部狹窄3處,肺動(dòng)脈遠(yuǎn)段狹窄1處。10例發(fā)現(xiàn)體-肺循環(huán)側(cè)支血管19支,其中起自降主動(dòng)脈9支、肋間后動(dòng)脈5支、右胸廓內(nèi)動(dòng)脈2支、主動(dòng)脈弓1支、左胸廓內(nèi)動(dòng)脈1支、右鎖骨下動(dòng)脈1支(圖1d)。所有患兒均未發(fā)現(xiàn)血栓形成與肺動(dòng)靜脈畸形。以上結(jié)果均經(jīng)DSA檢查證實(shí),準(zhǔn)確率為100%。
2.3輻射劑量CTDIvol為0.38~0.83 mGy,平均(0.59±0.15)mGy;DLP為6.5~27.1 mGy·cm,平均(14.6±6.0)mGy·cm;ED為0.16~0.52 mSv,平均(0.33±0.11)mSv。
3.1大螺距掃描概述大螺距掃描得益于雙源CT具備2套球管與探測(cè)器系統(tǒng),第2套探測(cè)器所獲得的數(shù)據(jù)能夠填補(bǔ)第1套探測(cè)器大螺距掃描時(shí)的間隙。其最大螺距達(dá)3.4,進(jìn)床速度達(dá)46 cm/s,特別適合屏氣配合欠佳甚至無(wú)法配合屏氣的患者,可明顯降低因呼吸導(dǎo)致圖像錯(cuò)層的概率。本研究中大螺距掃描的平均時(shí)間在0.4 s以內(nèi),在非鎮(zhèn)靜患兒平靜呼吸的狀態(tài)下,所有圖像均未出現(xiàn)呼吸運(yùn)動(dòng)偽影,圖像質(zhì)量明顯提高。
大螺距掃描最初應(yīng)用于成人冠狀動(dòng)脈CTA,能夠在1個(gè)心動(dòng)周期內(nèi)完成心臟的數(shù)據(jù)采集,輻射劑量可降低至1 mSv以下[15-17],且不會(huì)出現(xiàn)因需要多個(gè)心動(dòng)周期重建而產(chǎn)生的階梯狀偽影?,F(xiàn)該模式也已應(yīng)用于先天性心臟病的檢查,可準(zhǔn)確地評(píng)價(jià)心臟大血管的畸形,輻射劑量也顯著降低[8-9],且與前瞻性心電門控序列掃描相比,在相同管電壓、管電流條件下,大螺距掃描的ED更低[8]。焦北魚等[18]在雙側(cè)雙向Glenn術(shù)后評(píng)估中采用雙源CT前瞻性心電門控序列掃描,其平均ED為(0.43±0.21)mSv,本研究平均ED較其降低約23.3%。
3.2CT檢查在術(shù)后形態(tài)學(xué)方面的評(píng)估價(jià)值由于上腔靜脈出現(xiàn)擴(kuò)張往往提示上腔靜脈內(nèi)血流受阻或血流動(dòng)力學(xué)情況不理想,且上腔靜脈擴(kuò)張至一定程度可形成靜脈瘤,本研究7支上腔靜脈出現(xiàn)擴(kuò)張,左、右側(cè)上腔靜脈出現(xiàn)擴(kuò)張的例數(shù)相近。術(shù)后肺動(dòng)脈的局部狹窄同樣是心外科醫(yī)師關(guān)注的重點(diǎn)。本研究中,3處狹窄位于肺動(dòng)脈起始部至吻合口近心端,該狹窄可使來(lái)自主肺動(dòng)脈或?qū)?cè)上腔靜脈的血液減少,不利于同側(cè)肺動(dòng)脈的發(fā)育;1處狹窄位于肺動(dòng)脈遠(yuǎn)段,提示該肺動(dòng)脈發(fā)育不良。
體-肺循環(huán)側(cè)支在Glenn和Fontan術(shù)后很常見(jiàn),Triedman等[19]報(bào)道36.2%(71/196)的患兒術(shù)后DSA檢查時(shí)發(fā)現(xiàn)體-肺循環(huán)側(cè)支。體-肺循環(huán)側(cè)支血管大多起自主動(dòng)脈及其主要分支,其血液供應(yīng)肺組織后回流入左心,繼而進(jìn)入主動(dòng)脈,這一血液循環(huán)過(guò)程在氧合方面基本可視為無(wú)效循環(huán)。體-肺側(cè)支血管帶來(lái)的額外血流也可能是術(shù)后早期出現(xiàn)滲出較多或乳糜胸的原因之一[20]。本研究中,10例出現(xiàn)側(cè)支血管,略高于Triedman等[19]的報(bào)道,可能與患兒例數(shù)較少有關(guān),但也提示在雙側(cè)雙向Glenn術(shù)后患兒出現(xiàn)體-肺循環(huán)側(cè)支十分常見(jiàn);在側(cè)支的起源中,以起自降主動(dòng)脈和肋間后動(dòng)脈較為常見(jiàn),占73.7%(14/19)。
血栓形成是術(shù)后嚴(yán)重的并發(fā)癥之一[21],CTA能夠顯示血栓及周圍組織的情況,從而為取栓提供更加豐富的信息。對(duì)術(shù)后出現(xiàn)肺動(dòng)靜脈畸形,目前臨床可根據(jù)患兒情況進(jìn)行介入封堵、部分肺葉切除等處理。本組患兒均未發(fā)現(xiàn)血栓形成及肺動(dòng)靜脈畸形,但仍需長(zhǎng)期隨訪觀察。
CT在形態(tài)學(xué)評(píng)價(jià)方面與DSA的評(píng)估高度一致,但與DSA的二維圖像相比,CT以其直觀清晰的三維重組圖像可更好地顯示術(shù)后的形態(tài)學(xué)改變(圖1),使心外科醫(yī)師對(duì)患兒術(shù)后心臟大血管形態(tài)的認(rèn)識(shí)更加全面深刻。128層雙源CT低劑量大螺距掃描在雙側(cè)雙向Glenn術(shù)后形態(tài)學(xué)評(píng)估中可獲取滿足診斷的圖像,且患兒無(wú)需屏氣,具有較好的應(yīng)用價(jià)值。
本研究不足:①樣本數(shù)量較少,由于雙側(cè)雙向Glenn術(shù)不僅增加了手術(shù)難度,患兒預(yù)后也較單側(cè)Glenn術(shù)差[4-5],故接受雙側(cè)雙向Glenn術(shù)進(jìn)行修復(fù)的先天性心臟病患兒較少。可以考慮將低劑量大螺距掃描應(yīng)用于接受其他術(shù)式進(jìn)行修復(fù)的先天性心臟病患者。②雖已將平均輻射劑量降至(0.33±0.11)mSv,但仍有X線輻射,在以后的研究中可以結(jié)合超聲、MRI等檢查手段減少CT的輻射危害。
圖1男,10歲,30 kg,雙側(cè)雙向Glenn術(shù)后,大螺距掃描,80 kV,180 mAs,有效輻射劑量為0.47 mSv 圖1a VR示左上腔靜脈近吻合口管腔局部擴(kuò)張,右上腔靜脈近心段管腔局部擴(kuò)張 圖1b VR示右上腔靜脈近心段管腔局部擴(kuò)張 圖1c DSA證實(shí)右上腔靜脈近心段管腔局部擴(kuò)張 圖1d MIP示體-肺循環(huán)側(cè)支血管分別起自右鎖骨下動(dòng)脈(APC1)和降主動(dòng)脈(APC2)(RSVC:右上腔靜脈;LSVC:左上腔靜脈;RSA:右鎖骨下動(dòng)脈;DA:降主動(dòng)脈)
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Low-dose prospectively ECG-gated high pitch spiral dual-source CT angiography in patients with bilateral bidirectional Glenn shunt
JI Xiaopeng,LIU Yang,WANG Ximing,YANG Shifeng,LI Xia,F(xiàn)ENG Juan. CT R
CT Room,Shandong Medical Imaging Research Institute,Jinan,250021,China.
[Abstract]Objective:To explore the clinical value of low-dose prospectively ECG-gated high pitch spiral dual-source CT angiography(low-dose HP scanning)in patients with bilateral bidirectional Glenn shunt(bBDG). Methods:Twenty patients with bBDG were prospectively enrolled. Low-dose HP scanning and DSA were performed within one week. The scanning parameters were 80 kV tube voltage and weight adapted setting for tube current. Two cardiac radiologists interpreted the image quality of great vessels using a 5-grade scoring system. The CT attenuation and the noise in the ascending aorta,chest muscles,bilateral superior vena cava(SVC)and pulmonary artery(PA)were measured. The dose length product was recorded to calculate the effective dose(ED). Interobserver agreement on grades of subjective image quality was assessed by kappa statistics. Based on the findings of DSA,the accuracy of low-dose HP scanning was calculated. Results:The low-dose HP scanning and DSA were carried out in all the patients. There was no motion artifact due to the breath. The attenuation of the ascending aorta,bilateral SVC and PA was more than 250 HU. Overall interobserver agreement on subjective image quality was good(K=0.65,P<0.05). The average subjective image quality score was(4.15±0.67). The morphological evaluation of HP scanning was quite consistent with that of DSA. The mean ED was(0.33±0.11)mSv. Conclusion:Low-dose HP scanning is a convenient and noninvasive post-operative method of assessment for patients with bBDG,and there is a great clinic prospective with regard to the postoperative evaluation of patients with bBDG.
[Key words]Heart bypass,right;Tomography,X-ray computed;Radiation Dosage
收稿日期(2015-11-29)
[通信作者]王錫明,E-mail:wxming369@163.com。
[基金項(xiàng)目]國(guó)家自然科學(xué)基金項(xiàng)目(81371547);泰山學(xué)者工程專項(xiàng)經(jīng)費(fèi)資助;山東省自然科學(xué)基金項(xiàng)目(ZR2012HM006)。
DOI:10.3969/j.issn.1672-0512.2016.03.006