Effect of MRI Acoustic Noise on Cerebral Fludeoxyglucose Uptake in Simultaneous MR-PET Imaging

Abstract

Integrated scanners capable of simultaneous PET and MRI data acquisition are now available for human use. Although the scanners’ manufacturers have made substantial efforts to understand and minimize the mutual electromagnetic interference between the two modalities, the potential physiological inference has not been evaluated. In this work, we have studied the influence of the acoustic noise produced by the MR gradients on brain FDG uptake in the Siemens MR-BrainPET prototype. While particular attention was paid to the primary auditory cortex (PAC), a brain-wide analysis was also performed. Methods The effects of the MR on the PET count rate and image quantification were first investigated in phantoms. Next, ten healthy volunteers underwent two simultaneous FDG-PET/MR scans in the supine position with the FDG injection occurring inside the MR-BrainPET, alternating between a “quiet” (control) environment in which no MR sequences were run during the FDG uptake phase (the first 40 minutes after radiotracer administration) and a “noisy” (test) case in which MR sequences were run for the entire time. Cortical and subcortical regions of interest (ROIs) were derived from the high-resolution morphological MR data using FreeSurfer. The changes in FDG uptake in the FreeSurfer-derived ROIs between the two conditions were analyzed from parametric and static PET images, and on a voxel-by-voxel basis using SPM8 and FreeSurfer. Results Only minimal to no electromagnetic interference was observed for most of the MR sequences tested, with a maximum drop in count rate of 1.5% and a maximum change in the measured activity of 1.1% in the corresponding images. The ROI-based analysis showed statistically significant increases in the right PAC in both the parametric (9.13±4.73%) and static (4.18±2.87%) images. SPM8 analysis showed no statistically significant clusters in any images when a p<0.05 (corrected) was used; however, a p<0.001 (uncorrected) resolved bilateral statistically significant clusters of increased FDG uptake in the area of the PAC for the parametric image (left: 8.37±1.55%, right: 8.20±1.17%), but only unilateral increase in the static image (left: 8.68±3.89%). Conclusion Although the operation of the BrainPET prototype is virtually unaffected by the MR scanner, the acoustic noise produced by the MR gradients causes a focal increase in FDG uptake in the PAC, which could affect the interpretation of pathological (or brain-activation related) changes in FDG uptake in this region, if the expected effects are of comparable amplitude.

Comparison of hybrid FDG PET/MRI compared with PET/CT in colorectal cancer staging and restaging: a pilot study

“…PET/CT was acquired before PET/MR with a delay of 38 min. b [24]. Another challenge involves the administration of glucagon prior to MRI acquisition to help reduce bowel motion and artifacts during MRI scanning.…”

Precuneus and Cingulate Cortex Atrophy and Hypometabolism in Patients with Alzheimer’s Disease and Mild Cognitive Impairment: MRI and18F-FDG PET Quantitative Analysis Using FreeSurfer

“…Few recent studies used FreeSurfer ROIs to quantify the buildup of amyloid [ 11 , 29 ]. However, few studies focused on the use of FreeSurfer to analyze 18 F-FDG data [ 30 ].…”

Principles of Simultaneous PET/MR Imaging

“…This device was called BrainPET and was designed to fit into the bore of the standard 3T whole body MRI scanner (Magnetom Trio, Siemens, Erlangen, Germany). Although only a handful of BrainPET prototypes were ever built and only three of them are still in use, these inserts have been used for many studies ranging from those aimed at investigating the mutual interference between the two devices and the performance of the APD-based PET detector technology (21, 22), developing methods to use the information obtained from one device to improve the other modality (23–26), and demonstrating the tremendous potential of PET/MRI through proof-of-principle studies in small animal, non-human primates and humans (27–35). …”