Apparent transverse relaxation (R2∗) on MRI as a method to differentiate treatment effect (pseudoprogression) versus progressive disease in chemoradiation for malignant glioma

Introduction Pseudoprogression (psPD) is a transient post‐treatment imaging change that is commonly seen when treating glioma with chemotherapy and radiation. The use of apparent transverse relaxation rate (R2∗), which is calculated from a contrast‐free multi‐echo gradient echo Magnetic Resonance Imaging (MRI) sequence, may allow for quantitative identification of patients with suspected psPD. Methods We acquired a multi‐echo gradient echo sequence using a 3T‐Siemens Prisma MRI. The signal decay through the echoes was fitted to provide the R2∗ coefficient. We segmented the T1‐gadolinium enhancing the image to provide a contrast enhancing lesion (CEL) and the FLAIR hyperintensity to provide a non‐enhancing lesion (NEL). These regions of interest were applied to the multi‐echo gradient echo to acquire a mean R2∗ within the CEL and NEL. We additionally acquired ADC data to attempt to corroborate our findings. Results We found that patients who later exhibited PD exhibited a higher R2∗ within the CEL as well as a higher ratio of CEL to NEL. Our data correctly distinguished pseudoprogression from treatment effect in 9/9 patients, while ADC corrected identified 7/9 patients using an absolute ADC of 1200 × 10−6 mm2/s. Conclusions Our method seems promising for the accurate identification of psPD, and the technique is amenable to evaluation in larger, multi‐centre patient cohorts.