AbstractID: 6733 Title: Quality Assessment of Magnetic Resonance Images and
Variations of Image Quality Over Time
Introduction: The American College of Radiology (ACR) sets guidelines by which
clinical magnetic resonance imaging (MRI) scanners are judged for image quality.
Specific quality indices are calculated from the MRI images and compared to the limits
for acceptable levels established by the ACR to determine whether a scanner is eligible
for accreditation. We hypothesized that the variations in image quality acquired over
many months on a typical MRI scanner might be significant compared to the acceptable
limits established by the ACR.
Methods: The tests were conducted on a 1.5 T Philips Gyroscan ACSNT using the
standard ACR phantom and ACR scanning protocols. We measured geometric accuracy,
percent signal ghosting, percent integral uniformity, slice position accuracy, and slice
thickness accuracy. The quality indices were measured once a month for several months,
and the mean and standard deviations were calculated.
Results: The mean value and standard deviation for each measurement (followed by the ACR
acceptable limits in parenthesis) were: geometric accuracy 191.75 ± 0.96 mm (192 ± 2 mm),
slice thickness 5.04 ± 0.16 mm (5.0 ± 0.7), slice position 1.4 ± 0.4 mm (<4 mm) , percent
integral uniformity 91.79 ± 0.93 (>87.5), and ghosting (9.5 ± 4.5)×10-4 (<2.5×10-3).
Conclusions: We found quality indices to be fairly robust parameters. Variations in the
indices were typically a small fraction of the of the overall acceptable range set by the
ACR, suggesting that the ACR protocol on a typical MRI scanner gives well defined and
stable values over time.