Quality assurance for MRI: practical experience

Abstract

The aim of this study is to propose guidelines for quality assurance (QA) in MRI, based on a comprehensive assessment of QA parameters undertaken on a busy clinical MRI scanner over the course of 1 year. QA phantoms supplied by the scanner manufacturer were used together with the Eurospin MRI phantom set. Signal-to-noise ratio (SNR) and image uniformity were measured daily from spin echo images acquired using a quadrature send-receive head coil and from a gradient echo sequence using the Helmholtz body coil. The voltage of the transmit radiofrequency (RF) amplifier was noted. Monthly measurements of slice thickness, geometric distortion, slice position, image resolution and image ghosting were acquired using the head coil. In addition, SNR was measured monthly on a selection of commonly used coils. Apart from some drift of the RF amplifier voltage, all measurements were within acceptable limits and were stable over the course of 1 year. Satisfactory measurements of SNR were possible using the simple phantom supplied with the scanner. The SNR, geometric distortion and RF amplifier voltage are simple to determine and can be measured in less than 15 min by the scanner operator, using the scanner software. Weekly recording of these parameters is recommended for busy clinical MRI scanners, as this should allow deviations from acceptable limits to be identified early. Such in-house checks can usefully be compared with the less frequent estimations performed by the service engineer. Comprehensive QA routines are discussed for systems used for quantitative measurements.