In a heartbeat: Cardiac FDG PET/MR effective, beneficial for ischemia
Simultaneous PET/MR broke additional ground toward clinical use by showing technical success and potential clinical merit for FDG PET/MR detection of ischemic heart disease, according to a study published May 7 in Radiology.
Felix Nensa, MD, from the department of diagnostic and interventional radiology and neuroradiology at the University Hospital Essen and University of Duisburg-Essen in Essen, Germany, and colleagues tested the capacity of cardiac F-18 FDG PET/MR to evaluate patients with myocardial infarction for ischemia by imaging resting myocardial glucose uptake, with encouraging preliminary results. Successful imaging was achieved for all subjects with the exception of one claustrophobic patient who could not tolerate the scan time.
“Cardiac FDG PET/MR imaging provides quantitative information on metabolic processes that might be incorporated into cardiac MR imaging protocols to improve risk stratification in acute myocardial infarction,” wrote Nensa et al. “Cardiac PET/MR imaging with dedicated tracers for specific targets might complement cardiac MR imaging with valuable information on the pathophysiologic level.”
The study was conducted with a subject population of 20 patients who suffered myocardial infarction and were referred for cardiac assessment with a whole body 3T PET/MR system with Dixon-based attenuation correction after six hours of fasting. Half of the participants also underwent PET/CT imaging of the heart prior to PET/MR.
Specific MR sequencing was used for all sessions. “Two-dimensional half-Fourier acquisition single-shot turbo spin-echo sequences, balanced steady-state free precession cine sequences, two-dimensional turbo inversion-recovery magnitude T2-weighted sequences, and late gadolinium-enhanced (LGE) segmented two-dimensional inversion-recovery turbo fast low-angle shot sequences were performed,” wrote the authors.
Infarct identification and characterization comparisons were conducted according to American Heart Association (AHA) guidelines, with 17-segment left ventricle mapping. Gadolinium enhancement, myocardial wall motion and FDG uptake were evaluated for each segment using a binary scale and categorical intermethod agreement calculation with Cohen K. Comparisons were made between PET/MR and nonfused PET imaging with CT attenuation correction using a five-segment model of maximum standardized uptake value. Scans were assessed by two readers with 10 or more years experience.
Findings showed significant matching between between cine images, k=0.78, and PET and LGE segment images, k=0.76. A total of 93 of 306 segments were determined infarcted in the LGE images, whereas 97 were considered infarcted via PET imaging and 90 in cine. No major differences were found in tracer uptake for the subgrouped PET/CT comparison.
Further studies assessing PET/MR imaging for the detection of ischemia will need to be conducted to replicate these findings. the authors noted a need for standardization of PET/MR imaging protocol, especially in terms of patient management during long fasting and procedural time (about 53 minutes), and diversified comparison studies.
“These findings demonstrate the feasibility of clinical cardiac MR imaging with an integrated PET/MR imaging device,” wrote the researchers. “However, to prove that the integrated design does not interfere with the performance of the device, a systematic intraindividual comparison with a comparable 3-T MR device and identical sequence parameters is still needed.”