Purpose: In acceptance and annual testing of MR systems, physicists are key in assuring the high performance in acquisition, hardware fidelity and image quality. With the increase in dependence on quantitative measurements for patient management, there is an urgent need for physicists to commission the post-processing software used to generate this information. Here we illustrate a commissioning process developed for an FDA-cleared R2* mapping software package, which is used for such tasks as quantifying liver iron concentration.
Methods: For initial commissioning, we created a digital reference object (DRO) to represent ground truth measurements for comparison with software output. DROs were generated using in-house software, with and without additive noise (SNR=5-20 on first TE), and logarithmically spaced R2* values with signal modeling to replicate the output of a clinical multi-echo gradient-echo protocol. R2* calculations using both a two-parameter and three-parameter fit were used to compare to the ground truth DRO value. For assuring for consistency in a software upgrade, six patients with recent iron overload scans were evaluated. A three-parameter fit was applied to calculate the R2* map on both software platforms. According to our clinical standard operating procedure, three ROIs were made on each R2* map from both software platforms. Results from two software were compared to assess their agreement.
Results: DRO analysis demonstrated that the software’s accuracy is dependent on the native liver R2*, acquisition parameters and that a 3-parameter fit should be used especially if moderate or higher liver iron overload is suspected. In our patient data for a range of 38-815 Hz, there was perfect agreement of mean ROI measurements between both software platforms.
Conclusion: Using both DRO and patient data, we tested available software for its performance in calculating MR R2* measurements. This methodology can be applied to other applications when commissioning software for clinical use.