Reverse Redistribution on Stress-redistribution Thallium ...

[Pages:1]Reverse Redistribution on Stress-redistribution Thallium301 Myocardial SPECT :Comparison with Delayed Contrast-enhanced MRI and Cine MRI

yukako YAHARA', Hajirne SAKUMA2,Kakuya KITAGAWA', Tadanori HIRANO', Kan TAKEDA', Satoshi OHTA', Tamaki KITAI', Katsutoshi MAKNO'

'Mmusaka Central Hospital, 102 Kobo, Matsusaka, Mie Japan; 2Mie university school ofmedicine, 2-174 Edohashi, Tsu, Mie Japan;

Abstrtact

Purpose: To evaluate the pathophysiological significance of reverse redistribution (r-RD) on stress-redistribution thallium-20 1 SPECT using delayed-enhanced(DE) MRI. Methods: DE and cine MR images were evaluated in 16 patients demonstrating r-RD on SPECT. Results: DE-MRI revealed non-transmural infarction in 8 of 16 patients with r-RD (Group A). No infarction was found on MRI in the remaining 8 patients (Group B). Regional wall motion was preserved in both groups. Conclusions: Reverse RD can be interpreted as evidence of myocardial scar within a viable myocardium in patients with CAD. However, r-RD may only represent normal variability of thallium-20 1 dynamics in subjects with low lokelihood of CAD such as patients in Group B. These two conditions can be easily differentiated with DE-MRI.

Introduction Exercise thallium scintigraphy has been widely

used in evaluating patients with known or suspected coronary artery disease. It has been noted that, not uncommonly, a thallium-20 1 perfusion defect develops or becomes more evident on delayed redistribution images compared with the initial stress images. The prevalence of this phenomenon, referred to as "reverse redistribution" can be found in up tp 75% of patients with acute myocardial infarction[l]. It has

been suggested that resverse redistribution can be interpreted as an admixture of scar and viable myocardium in patients with coronary artery disease. And in subjects with a low liklihood of coronary artery disease, it may represent only normal variability of thallium-201 clearance. However, the

pathophysiology and clinical significance of reverse redistribution remain unclear.

The purpose of this study was to evaluate whether reverse redistribution on stress-redistribution tlallium-20 1 SPECT myocardial scintigraphy actually represents myocardial scar within a segment containing viable myocardium, by using delayed contrast-enhanced MR images which can provide an accurate identification of necrotic myocardium (2).

Methods Delayed contrast-enhanced MR images and cine

MR images were retrospectively evaluated in patients demonstrating reverse redistribution on stress-redistribution thallium-201 images. The diagnosis of reverse redistribution was made when perfusion defect develops or becomes more evident on delayed redistribution thallium-20 1 images in comparison with the initial stress images, by using quantitative criteria in addition to visual assessments. Reverse redistribution was observed in 16 patients (10 men and 6 women) with a mean age of 6919 years. Nine of the patients had a history of previous myocardial infarction. Nine patients had undergone previous revascularization therapy (5 coronary angioplasty, 4 coronary artery bypass surgery). Thallium-201 imaging and MR imaging were obtained within approximately 1 month. No coronary intervention was performed during the period between two examinations.

Stress-redistribution thallium-201 single-photon emission computed tomographic (SPECT) images were obtained with a three-head gamma camera system (GCA9300A, Toshiba). Stress involved either standard

treadmill exercise (n=lO) or intravenous dipyridamole pharmacological stress (n=6). Thallium-201 (2 mCi) was injected either 4 min after the end of dipyridamole infusion or at peak exercise in those undergoing treadmill stress. Image acquisition started 5 min after radionuclide injection. Redistribution images were acquired 2-3 hour after stress

thallium imaging. Reverse redistribution was defined as >lo% decrease in normalized thallium activity on redistribution images in comparison with stress thalium-201 images.

MR images were obtaied by using a 1.5-Tesla MR scanner (Siemens Magnetom Vision) equipped with phased-array body coils. Delayed contrast-enhanced MR images were obtained with an inversion-recovery prepared segmented turboFLASH sequence. Breath-hold MR images were acquired 20 minutes after administration of Gd-DTPA (0.15mmolkg). Inversion time was adjusted in each patient to minimize the signal intensity of normal myocardium. Breath-hold cine MR images on short axis planes were obtained with a segmented turboFLASH sequence (TR, 50ms; TE, 4.8ms; flip angle, 25 degree). Regional myocardial contractile function was assessed by measuring

wall thickening of the left ventricular wall. These findings on SPECT and MR images were compared with the results by coronary angiography and clinical findings.

Results

Delayed contrast-enhanced MR imaging revealed subendocardial infarction or small area of infarction in 8 (50%) of the 16 regions demonstrating reverse redistribution(Gr0up A). No infarcted tissue was found on delayed contrast- enhanced MR images in the remaining 8 (50%) of 16 regions(Group B). No transmural infarction was observed on delayed contrast-ehnahcned MR images. Regional wall motion was generally preserved in Group A and Group B (13 normal and 3 mild hypokinesis). On selective coronary angiography, no flow-limiting stenosis was found in the coronary arteries supplying the blood to the regions showing reverse redistribution. In 7 (87.5%) patients in group A, there was a previous history of myocardial infarction in the segments with reverse redistribution. Conclusions

The pathophysiological significance of reverse redistribution on stress-redistribution thallium-201 scintigraphy was evaluated by using delayed contrast enhanced MR imaging and breath-hold cine MR imaging. The results in this study indicated that reverse redistribution can be interpreted as evidence of myocardial scar within a segment containing viable myocardiun in patients with coronary artery disease. However, in subjects with a low likelihood of coronary artery disease, reverse redistribution may only represent normal variability of thallium-20 1 dynamics. These two conditions showing reverse redistribution can be easily differentiated with use of delayed contrast-enhanced MR imaging. References 1. Weiss AT, et al. JACC 1986;7:61-67 2. Dudzic EM. Et al. Eur J Nucl Med 1994;21:449-453 3. Kim RJ, et al. Circulation1999; 100:1992-2002

? Proc. Intl. Soc. Mag. Reson. Med. 10 (2002)

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