# Comparison of Magnetic Resonance Spectra Acquired With Hybrid PET/MR and Standalone MR Scanners

## TL;DR

This study compares brain MR spectroscopy quality between hybrid PET/MR and standalone MR scanners, finding that PET/MR does not significantly compromise MR spectral quality.

## Contribution

The study provides empirical evidence on the impact of PET modality on MR spectral quality in hybrid scanners.

## Key findings

- Hybrid PET/MR scanners showed comparable MR spectral quality to standalone MR scanners in terms of signal-to-noise ratio and repeatability.
- In vitro tests showed higher signal-to-noise ratio in PET/MR compared to standalone MR but lower than another standalone MR scanner.
- Metabolite concentrations were significantly higher in standalone MR spectra compared to PET/MR.

## Abstract

The effect of the positron emission tomography (PET) modality in hybrid PET/MR scanners on MR spectral quality is unclear.

To evaluate spectral quality, quantification, and repeatability of brain MR spectroscopy (MRS) acquired on PET/MR and standalone MR scanners.

Prospective.

23 healthy adults (male/female = 11/12, age = 27 ± 11 years).

3T, semi‐localized by adiabatic selective refocusing.

Single voxel MR spectra were acquired with GE Signa PET/MR and Siemens Prisma Fit MR scanners in healthy volunteers, and additionally with a GE Premier MR scanner in vitro. Spectral quality, metabolite concentrations, and repeatability were evaluated.

Linear mixed models assessed signal‐to‐noise ratio (SNR), full width at half maximum (FWHM), and metabolites/total creatine (tCr). Intraclass correlation coefficients (ICCs) determined repeatability; mean squared error (MSE) evaluated accuracy of quantification. Values are reported as mean ± standard deviation. Significance was determined by p ≤ 0.05.

In vivo spectra acquired using the Siemens standalone MR showed significantly higher SNR (PET/MR: 118.8 ± 19.1, MR: 132.2 ± 24.4) but significantly broader FWHM (PET/MR: 7.2 ± 1.8 Hz, MR: 8.4 ± 2.5 Hz) compared to PET/MR. All metabolite ratios were significantly higher in spectra acquired on the standalone MR. Within‐session repeatability was good (ICC > 0.75), and between‐session repeatability was moderate to excellent (ICC 0.5 to > 0.90) for all metabolites in vivo. In vitro spectra acquired with the PET/MR had significantly higher SNR (329.1 ± 46.1) than the Siemens standalone MR (150.8 ± 49.3) but significantly lower than the GE standalone MR (395.9 ± 33.7). The PET/MR produced narrower FWHM (2.1 ± 0.4 Hz) than the Siemens standalone MR (4.1 ± 1.7 Hz) but broader than the GE standalone MR (1.6 ± 0.1 Hz) and lower MSE for some metabolites.

MR spectral quality appears uncompromised when acquired with hybrid PET/MR compared to standalone MR.