Noise contamination from PET blood sampling pump: Effects on structural MRI image quality in simultaneous PET/MR...

To fully quantify PET imaging outcome measures, a blood sampling pump is often used during the PET acquisition. With simultaneous PET/MR studies, a structural magnetization-prepared rapid gradient-echo (MP-RAGE) may also be acquired while the pump is generating electromagnetic noise. This study investigated whether this noise contamination would be detrimental to the quantification of volume and cortical thickness measures obtained from automated segmentation of the MP-RAGE image.

MP-RAGE T1w structural images were acquired for a phantom and 10 healthy volunteers (five female, 27.2 ± 5.1 y old) with the blood sampling pump and without. The white matter signal-to-noise ratio (SNR) was computed for all images. Region-wise cortical thickness and volume were extracted with Freesurfer 5.3.0.

The phantom SNR and the white matter human subject SNR was degraded in the MP-RAGE images acquired with the pump (P = 0.005; white matter SNR: 43.9 and 50.8 with the pump and without). Intrasession, region-wise volume and cortical thickness estimates were significantly overestimated with the pump (percent difference: 1.14 ± 2.67% for volume (P = 0.0003) and 0.34 ± 1.59% (P = 0.02) for cortical thickness). Regions with percent differences greater than 5% between pump conditions were those close to tissue-air interfaces: entorhinal, frontal pole, parsorbitalis, temporal pole, and medial orbitofrontal. Synthetically adding Gaussian noise to the without pump MP-RAGE images yielded similar, significant detriments to cortical morphometry compared to without the pump.

This study provides evidence that the use of PET blood sampling pumps may generate unstructured, Gaussian-distributed noise in MP-RAGE images that significantly alters the accuracy of Freesurfer-derived volume and cortical thickness estimates. While many cortical regions showed a percent difference of less than 1% with the pump, regions close to tissue-air interfaces, subject to larger susceptibility artifacts, were significantly affected. This potential for decreased accuracy should be considered in PET/MR research studies utilizing blood sampling pumps, as well as any MRI study utilizing radiofrequency noise producing devices such as functional MRI task equipment and physiologic monitoring devices.