A comparison of SNR of two generations of Siemens 1.5T MRI scanners and their associated RF phased array coils

Abstract

Background: The hospital where this study was carried out is in possession of two whole-body MRI Siemens scanners (Siemens Magnetom Aera (2012) and Siemens Magnetom Avanto (2007), Erlangen, Germany). Both machines have field strength of 1.5T but have significant differences between them, namely: the bore size, field of view restrictions and radio frequency receive coils. Despite these differences, the two machines are currently being operated using the same protocol which indicates that the latter may not be optimised for both scanners. Objectives: The primary purpose of this study was to measure and compare Signal to noise ratio (SNR) and SNR uniformity of the two systems. A second objective was to evaluate the different methods of SNR measurement found in MRI literature. Research Design: SNR measurements were carried on spin echo (SE) images using the head coils and combination of body-spine coils. SNR evaluation was carried out on region-of-interests (ROIs) on both phantom and anonymised patient images. The American College of Radiology (ACR) phantom and five cylindrical fluid filled phantoms provided by the manufacturer were used to obtain phantom images. For patient images, neurological and prostate images were used for evaluation of SNR. Different approaches of SNR measurement were compared in phantom measurements with the gold standard multiple-acquisition method (MAM). In patient images only single-image methods could be applied. Results: Deviations from the gold standard were noted. For the head phantom measurements, the Aera produced higher SNR than the Avanto with the highest being 166% and lowest 131%. For the body phantom, SNR values from the Aera were again higher, the highest being 132% and lowest 103%. In general, t-testing indicated that the Aera produces significantly (P<0.05) higher SNR than the Avanto for various ROIs on patient images. Conclusions and recommendations: The Aera scanner produced higher SNR than the Avanto for both phantom and patient images. Based on the assumption that the Avanto SNR is adequate, it is recommended that the increased SNR of the Aera should be used to optimise scanning protocols allowing shorter scan times or improvements in resolution.