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Ⅰ.はじめに
Magnetic resonance angiography(MRA)は非侵襲的な脳血管検査として普及しているが,狭窄・閉塞病変を過大評価する傾向があることが知られている1, 11).その原因としては,狭窄が高度でMRAの解像度で検出できない場合や血流速度が低下しtime-of-flight(TOF)効果が十分でない場合などが考えられる.頸部頸動脈狭窄症においても,高度狭窄の場合MRA上は閉塞に見えることがあり,carotid endarterectomy(CEA)やcarotid artery stenting(CAS)の適応症例を見逃す可能性がある.今回MRA上の頸部頸動脈閉塞症例におけるMRA所見の精度をdigital subtraction angiography(DSA)所見との対応において検討した.
また,MRAに加えて,造影剤を用いて血行動態を描出するtime-resolved imaging of contrast kinetics(TRICKS)12)や,流血を無信号化することで血管壁やプラークを詳細に描出するblack blood imaging(BBI)4)を併用することが診断能の向上に寄与するかどうかを検討した.
Magnetic resonance angiography (MRA) is one of the most popular tools for imaging cerebral arteries. However, it may overestimate steno-occlusive lesions. The purpose of the present study was to investigate the diagnostic accuracy of cervical MRA for carotid steno-occlusive lesions.
This study included 13 sides of 12 patients (male: female=11: 1, 53-83 years old) who showed cervical carotid occlusion on MRA at 3 tesla. The MRA was performed along with time-resolved imaging of contrast kinetics (TRICKS) and/or black blood imaging (BBI) when detailed evaluation was considered necessary after routine 1.5 tesla MRA. All patients underwent digital subtraction angiography (DSA) for definitive diagnosis. Cervical duplex scan was also performed in 12 sides. DSA demonstrated occlusion in only 6 sides (46.2%). In the remaining 7 sides, in spite of occlusion on MRA, DSA demonstrated stenoses in 4 sides and pseudoocclusions in 3 sides. Adding TRICKS or BBI resulted in correct diagnosis (same as DSA) in 6 sides.
In comparison to DSA, sensitivity and specificity of combination of TRICKS and BBI were 100% and 85.7%, respectively, for the diagnosis of cervical carotid occlusion.
In conclusion, MRA alone does not accurately demonstrate severe stenosis of the cervical carotid artery and may miss surgical candidates. TRICKS and BBI are useful adjunct tools for an accurate diagnosis.
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