Summary
We evaluated the effect of changes in the direction of the coronary artery
in terms of the accuracy and precision of vessel diameter measurement in
a quantitative coronary angiography system (QCA system). Vessel phantoms
sized 0.3, 0.5, 1.O, 1.5, 2.O, and 2.5 mm in diameter were evaluated. The
phantoms were aligned on an acrylic plate, and the angle to the television
(TV) camera was altered. The deployed angles were 0(perpendicular), 45,
9O, and 135 degrees in clockwise order. The phantoms were imaged with matrices
of 1024×1024 (10242), 512×512 (5122), and 512×1024. Image size was 7inches,
and the frame rate was 15 frames per second. Minimal lumen diameters were
measured on the ACA system. The results revealed that, in the 10242 matrix,
overall accuracy for the 90-degree angle was significantly underestimated
compared with the O-degree angle (-4.14 vs. -0.014 mm; p=0.007). Accuracy
for the 90-degree angle was better than that for the O-degree angle when
the vessel diameter was 1 mm or smaller (-0.02±0.16 vs. 0.10±0.22 mm).
In addition, precision was better at the 90-degree angle than with the
other angles in the 10242 matrix (overall precision=0.002 mm). In the 5122
matrix, overall accuracy for the 90-degree angle was significantly underestimated
compared with the 45-degree angle (-0.077 vs. 0.096 mm; p=0.02). In addition,
accuracy for the 90-degree angle was better than that for the 45-degree
angle below 1 mm (0.05±0.24 mm vs. 0.26±0.47 mm). In terms of overall accuracy,
the 45-degree angle in the 5122 matrix showed significant overestimation
compared with that in the 10242 matrix (0.096 vs. -0.069 mm; p=O.015).
There was no difference in accuracy in the 512x1024 matrix. Our results
suggest that the direction of the vessel against the TV image affects accuracy
of measurement in the QCA system.
目的
1995年、デジタル画像のフォーマットの標準化が、米国循環器学会(ACR)と国際電子機器工業界(NEMA)によってDICOM 3.0(Digital Imaging and Communication In Medicine)として規格化された。この規格化により、循環器X線撮影システムのデジタルシネ画像は、DICOM 3.Oに準拠したCD-Rへの記録が可能となり、CD-Rはシネフィルムに変わる保存メディアとなりつつある。
定量的冠動脈造影法(Quantitative Coronary Angiography:QCA)は、PTCAなどインターベンション時のデバイスサイズ決定のための支援、治療の効果判定、薬剤投与による冠状動脈の狭窄予防効果の判定などに用いられ、従来からシネフィルムがゴールデンスタンダードとして用いられてきた。今後は、シネリプレースメントが進む中で、QCAはDICOMフォーマットされたデジタル画像で施行される可能性が高いと予想される。そこで、循環器画像技術研究会では、DICOMフォーマット画像によるQCAの有用性を検討するため、血管狭窄ファントムを用いて評価したので報告する。