Assessment of the myocardium on 2-phase cardiac multidetector computed tomography: does cyclic cardiac contraction influence myocardial attenuation?

OBJECTIVE: To analyze changes in attenuation of non-contrast-enhanced and contrast-enhanced myocardium throughout the cardiac cycle and to determine the effect of myocardial location, cardiac phase, and dominant coronary perfusion type on myocardial attenuation to evaluate the impact of contraction-dependent factors on multidetector computed tomography (MDCT) perfusion studies.

MATERIAL AND METHODS: Cardiac computed tomography imaging was performed on a 40-row MDCT scanner. Myocardial attenuation was assessed in 50 men during 20 cardiac phases. Ninety myocardial regions of interest were placed in the distribution of the right, left anterior descending, and left circumflex coronary arteries on contrast-enhanced MDCT. In 26 patients, myocardial attenuation was also assessed on non-contrast-enhanced MDCT. Myocardial attenuation was analyzed on isopycnic graphs. Attenuation changes due to myocardial contraction were evaluated on non-contrast-enhanced MDCT. The impact of cyclic perfusion on myocardial enhancement was determined on contrast-enhanced MDCT. Student t test and Pearson correlation were used. The influence of dominant coronary perfusion type, supplying coronary artery, and cardiac phase were evaluated using univariate general linear model analysis.

RESULTS: Isopycnic graphs revealed that myocardial contraction during systole led to significant increase in myocardial attenuation on non-contrast-enhanced MDCT [ HU systole = 33.2 vs HU diastole = 29.1, P < 0.001]. Reduction in myocardial perfusion during systole led to decrease in myocardial attenuation in contrast-enhanced MDCT [ HU systole = 92.4 vs HU diastole = 111.9, P < 0.001]. Systolic increase in attenuation due to myocardial contraction was far outweighed by the effects of intramyocardial contrast enhancement (correlation Pearson = 0.941). Dominant coronary perfusion did not lead to significant changes in contrast-enhanced myocardium (P = 0.299). Anatomical location and underlying cardiac phase represented significant factors in myocardial attenuation variation (P < 0.001).

CONCLUSION: Myocardial attenuation is influenced by cardiac phase and myocardial location. These factors must be considered when analyzing myocardial perfusion with MDCT.