SummaryIn three-dimensional (3D) T1-weighted magnetic resonance imaging used for tissue characterization of coronary plaques, the contrast for electrocardiographic synchronization may vary according to the R-R interval (RR). The coronary artery plaque image shows suppression of the fluid compartment signal for the coronary artery luminal blood as well as the fat signal in the region of interest; in addition, it is necessary to ensure that the value of the plaque-to-muscle signal intensity ratio (PMR) does not change according to the difference in RR. In the current study, the phantom review and clinical data suggested that the PMR changes that occur due to the differences in RR can be minimized by adjusting the inversion time (TI) in the range of the required black blood effect. Moreover, the signal-to-noise ratio (SNR), which varies according to the difference between the RR and the TI, was determined to identify the maximum value flip angle (FA) value that would lead to improvement in the SNR. Thus, signal suppression of the PMR, SNR, and the fluid compartment of the coronary artery luminal blood can be controlled using different RRs with the relational expressions for calculating optimal TI and FA.
緒 言 急性冠症候群,脳血管障害を未然に防ぐには,プ ラークの組織性状評価が有用だといわれている 1, 2) . Magnetic resonance imaging(MRI)を用いたプラーク の組織性状評価は,T1 強調画像,T2 強調画像,プロト ン密度(proton density: PD)強調画像,magnetic reso-nance angiography(MRA)原画像といったマルチコン トラストを用いた評価が行われている 3~9) .なかでも, T1 強調画像が重要だといわれている 10~13) .MRI を用 いたプラークの組織性状評価は,プラークの信号強度 を胸鎖乳突筋や心筋の信号強度で除した値である plaque-to-muscle signal intensity ratio(PMR)によって SummaryIn the tissue characterization of plaques using magnetic resonance imaging (MRI), T1-weighted imaging is important. However, T1-weighted imaging are obtained by various imaging methods, and show different contrasts depending on parameters such as repetition time, echo time, and inversion time. To evaluate the tissue characterization of plaques using MRI, the characteristics are estimated and evaluated using the strength of the plaque-to-muscle signal intensity ratio (PMR), which is the value obtained by dividing the signal intensity of the plaque by that of the sternocleidomastoid muscle or myocardium. In the present research, we aim to obtain the PMR by phantom experiment and grasp the image characteristics for T1 and T2 values of different T1-weighted imaging methods. In addition, since the PMR of the conventional spin echo (SE) method of T1-weighted imaging (twodimensional (2D) T1 WI SE) is reported to have high discrimination ability in plaque tissue characterization, the experimental results were compared with those of 2D T1 WI SE. Among the protocols examined, 3D sampling perfection with application optimized contrasts using different flip angle evolutions, T1-variable, motion-sensitized driven equilibrium (1-axis 300 ms 2* mT/m) + had the same tissue characterization ability as 2D T1 WI SE, and was the most suitable imaging method. Moreover, in the gradient echo method, the effect of T2 values was smaller than that of 2D T1 WI SE, and it was suggested that the PMR of the plaque may be lowered when there is a change in the tissue properties that the T2 value and T1 value are prolonged due to liquefaction. The results of this phantom experiment are expected help in selecting the imaging method aimed at optimization and the image characteristics of different T1-weighted imaging method can be grasped.Key words: magnetic resonance imaging (MRI), T1-weighted image (T1WI), carotid plaque, coronary plaque, plaque-to-muscle signal intensity ratio (PMR)
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