造影剤非使用時のDSAによる左心動態の検討—時間—濃度曲線および位相解析を用いて

A quantitative evaluation of left ventricular function by digital subtraction angiography without contrast medium:Time-activity curve and Fourier analysis

　Digital Subtraction Angiography （DSA）は経静脈性に造影剤を注入して，動脈系の造影を可能にするために開発された装置である。本装置の第2の大きな特徴はvideodensitometryを用いて，computer画像解析を行なうことにより，機能的かつ定量的評価が可能なことである。我々もDSA画像のvideodensitometryの直線性に関する基礎的検討を行ない，臨床応用が可能であることをすでに報告した^1）。したがってDSAの濃度情報の変化から，左心動態^2）や局所心筋灌流動態^3,4）などの臨床的評価が試みられている。

　一方，DSAの画像はマスク像を差し引いた差分像であるため，微細なX線通過強度の差が増幅されて表示されている。このため，造影剤を使用しない時のDSA画像でも，通常のX線像では把握し得ない心臓の収縮，拡張に伴う心陰影のX線通過強度の変化が，比較的明瞭に観察し得る。そこで我々はこの差分像の画像特性に着目して，造影剤非使用（non-contrast）時のDSA画像を用いて，左心室領域の一心周期におけるX線通過強度の変化をcomputer解析し，globalおよびregionalな左心動態の評価を試みた。

Digital subraction angiography (DSA) is a sub-traction image, in which a difference in X-ray absorption from a mask image is linearly amplified. Therefore, it seems possible to evaluate a small change in X-ray absorption of the cardiac silhouette during a cardiac cycle, even without using contrast medium. Utilizing this property of DSA image, we have developed a new approach to evaluate global and regional left ventricular (LV) function by DSA without contrast medium.

The study subjects included 17 patients with myocardial infarction and 13 patients with various heart disease who showed normal wall motion. DSA images of the LV were obtained without contrast medium in the right anterior oblique projection. Image analysis was performed with an image-pro-cessing computer and LV time-activity curves were contructed for one cardiac cycle with videodensito-metry. As the present study could not determine background density of DSA image without contrast medium, the first third ejection and filling index (1/3EI, 1/3FI) were calculated as the first third systolic and diastolic density changes normalized by stroke density. These indices were compared with the first third ejection and filling fraction (1/3EF, 1/3FF) which were derived from LV angio-graphy using contrast medium. The pattern of time-density curve for one cardiac cycle without contrast medium was nearly identical to LV volume curve with contrast medium. 1/3EI and 1/3FI without contrast medium showed good correlations with 1/3 EF and 1/3FF with contrast medium (r=0.75 and r=0.62, p<0.005) . To determine regional wall motion abnormality of the LV, phase analysis of the non-contrast DSA image was performed using first harmonic Fourier analysis. The phase images with-out contrast medium was comparable to those with contrast medium. As compared with conventional cineangiography, diagnostic accuracy of regional wall motion abnormality by phase analysis without contrast medium was : sensitivity of 100%, specific-ity of 83% and efficiency of 93%. In addition, there was a good relationship between the standard deviation (SD) of the LV phases with contrast medium and that without contrast medium (r= 0.75, p<0.005). The SD of the LV phase analysis in patients with myocardial infarction were sig-nificantly greater than those in patients with normal wall motion (p<0.005) , in both analysis without contrast medium and with contrast medium.

From the above findings, the present study indi-cated that the computer analysis of DSA image without contrast medium is a valuable noninvasive method for assessing global and regional LV func-tion.