Simultaneous PET and MRI is providing important diagnostic information about soft tissues and physiological functions throughout the body, and scans focused on screening lesions for cancer are already comparable to more conventional molecular imaging methods, according to preliminary research presented this week at SNM's 58th annual meeting in San Antonio, Texas.
Alexander Drzezga, MD, of the department of nuclear medicine at the TU Muenchen in Munich, Germany, and colleagues sought to compare clinical performance between PET/CT and recently introduced whole-body PET/MR (Biograph mMR, Siemens Healthcare) for simultaneous acquisition of PET and MR data in humans.
Eleven patients with oncological diagnoses underwent a dual-imaging, single-injection protocol including PET/CT and subsequent PET/MR.
The researchers performed PET/CT scans according to standard clinical protocols (83 minutes post-injection (pi) of 427 MBq 18F-FDG, two minutes/BP). Subsequently (145 minutes pi), PET/MRI was performed (five minutes/BP). They reconstructed PET images iteratively (OSEM3D), performed attenuation correction using CT-data for PET/CT and segmented DIXON-MR sequences for PET/MR. Comparison between PET/MR and PET/CT was performed by semi-quantitative analysis of tracer uptake in different organs and lesions versus reference tissue (musculature).
Simultaneous PET/MR acquisition was feasible with good quality of the MR and PET data, according to Drzezga and colleagues.
Organ to reference (rf) ratios of tracer-uptake were not significantly different concerning lung, liver, spleen and bone: Median lung/rf: PET/CT=0.45, PET/MR=0.39; liver/rf: PET/CT=2.8, PET/MR=2.3; spleen/rf: PET/CT=2.2, PET/MR=2.7; bone/rf: PET/CT=2.7, PET/MR=3.6.
“Tracer-uptake was similar in relation to lung, liver, spleen and bone scanning, all acquired within a short examination timeframe,” the authors wrote. All 13 tumors/lesions detected in PET/CT also could be identified in PET/MR, and there was no significant difference between PET/CT and PET/MR regarding the uptake ratios in tumors/lesions (median lesion/rf: PET/CT=6.4, PET/MR=9.6), they reported.
"Combining MRI technology with PET in a single integrated system adds the advantages of the extremely broad spectrum of diagnostic MRI procedures to the arsenal of available PET procedures," said Drzezga. "This could potentially result in the development of new imaging agents that bring together specific diagnostic strengths of PET and MRI. It offers exciting scientific options to image physiologic and pathophysiologic processes at the same time and to improve our understanding of both. This and further studies could potentially open a whole new hybrid imaging discipline within the field of nuclear medicine."
The next step for PET/MR, Drzezga and colleagues said, is studying the added benefit of introducing sophisticated MRI sequences to the diagnostic imaging protocol. They hypothesized that this and other related studies may lead to the establishment of hybrid PET/MR imaging as a new diagnostic imaging system similar to PET/CT for its effectiveness and ability to provide a wealth of both functional and anatomical information about the body.