Evaluation of myocardial viability with contrast-enhanced magnetic resonance imaging - comparison of the late enhancement technique with positron emission tomography

Purpose: To compare contrast-enhanced magnetic resonance imaging (MRI) and positron emission tomography (PET) in the evaluation of myocardial viability. Methods: [F-18]-FDG-PET, [Tl-201]-TlCl-SPECT and contrast-enhanced MRI were performed in 29 patients with proven coronary artery disease and impaired left ventricular function to assess myocardial viability. MRI scans were done on a 1.5 T scanner (Magnetom Sonata, Siemens, Germany). After the steady-state free precession cine study, 0.2 mmol/kg BW of Gd-DPTA (Magnevist(R), Schering, Germany) were administered i.v. For the detection of "late enhancement" (LE) indicating scar, left ventricular long axes and contiguous short axis slices of 8 mm thickness were scanned using an inversion recovery turbo gradient echo sequence (TR 8.0 ms; TE 4.0 ms; Tl 180 - 240 ms; FA 20degrees). The evaluation of LE and FDG uptake in PET with perfusion defect in SPECT was done using an 8 (basal, mid) and 4 (apical) segment model in all short axes to cover the entire ventricle. The transmural extent of LE was assessed using a 4-point score system. Comparison between the two modalities was performed on a segmental basis. Results: A total of 1753 segments were assessed. In MRI, 40% of the segments showed myocardial scar, whereas PET revealed impaired uptake in 25%. MRI obtained a very low interobserver variability in detecting myocardial scar (kappa 0.92). Using PET as the standard of reference in the segmental comparison, contrast-enhanced MRI yielded a sensitivity of 84% and a specificity of 76% for the detection of scar. 18% of all segments showed LE but normal FDG uptake, 83% of them referred to subendocardial scars. Conclusions: There is close agreement between contrast-enhanced MRI and PET in detecting transmural moycardial scars. Superior spatial resolution enables MRI to detect and quantify even subendocardial scar. Therefore, larger studies using functional recovery after revascularisation as an endpoint have to prove whether MRI might replace PET as the standard of reference in the assessment of myocardial viability.