Correlation of Thallium Uptake With Left Ventricular Wall Thickness by Cine Magnetic Resonance Imaging in Patients With Acute and Healed Myocardial Infarcts

Myocardial infarction (MI) is characterized by cellular necrosis which undergoes fibrotic transformation over time. Cine magnetic resonance imaging (MRI) offers high-resolution 3-dimensional images of the left ventricular myocardium, allowing sampling of the myocardial wall thickness over the entire left ventricle. Tomographic (single-photon emission computed tomography [SPECT]) thallium images also provide 3-dimensional information on the location and level of thallium uptake, which has been shown to correlate with myocardial viability. The purposes of this study were: (1) to examine the relation between both end-diastolic and end-systolic wall thickness and normalized thallium-201 uptake over the left ventricle in a group of patients with MI, (2) to examine the relation between regional wall thickening and normalized thallium uptake, and (3) to examine the relation between thallium uptake and wall thickness both early and late after infarction. Twenty-four patients with MI underwent stress, redistribution, and reinjection thallium SPECT imaging and cine MRI within several days. Seventeen patients underwent imaging late after infarction and 7 underwent imaging early after infarction. Normalized thallium activity was correlated with MRI wall thicknesses at both end-diastole and end-systole for 18 segments for each ventricle. In addition, end-diastolic and end-systolic wall thicknesses were grouped by their corresponding thallium activity levels into percentiles. End-systolic wall thickness correlated significantly with normalized thallium uptake in 14 of 18 segments, end-diastolic wall thickness in only 4 of 18 segments, and wall thickening in only 3 of 18 segments. Mean values for end-diastolic and end-systolic wall thicknesses corresponding to severely reduced (<50%) normalized thallium activity were 9.9 ± 1.1 and 8.5 ± 0.6, respectively. Using receiver-operating curve analysis, end-systolic wall performed as a better diagnostic parameter than end-diastolic wall for identifying severely reduced thallium activity levels. For all levels of thallium activity, end-diastolic wall thicknesses were all thinner late versus early after MI, whereas end-systolic wall thickness was thinner only in the segments corresponding to severely reduced thallium activity. Based on these results, end-systolic wall thickness is the best noninvasive anatomic parameter of myocardial scar.