Role of Diffusion and Perfusion Imaging Measurements in Grading of Glioma and Quantitative Assessment of Temporal Change in These Measurements in Glioma Patients Undergoing Radiotherapy

Abstract

Introduction: Conventional neuro imaging of brain tumors is anatomy based and differentiates low grade (LGG) and high grade glioma (HGG) based on pattern recognition which at times may be difficult to comprehend. Functional MRI incorporates morphologic abnormality with physiologic alterations.  Quantification of ADC (apparent diffusion coefficient) and rCBV (relative cerebral blood volume) values using functional MRI have been explored to characterize these tumors. The present study purposes to determine the temporal change in diffusion (ADC) and perfusion (rCBV) in glioma patients treated by radiotherapy.

Material and Methods: 3Tesla MRI diffusion & perfusion imaging was done postoperatively before radiotherapy (RT), during RT at 4^th week & subsequently on follow-up on 18 glioma patients (LGG=5 and HGG=13). Quantification of ADC_minimum (ADC_min) and rCBV_maximum (rCVB_max) value was done and the temporal changes of these parameters with RT were evaluated.

Results: In pre-RT MRI, the mean ADC_min for LGG was significantly higher in comparison to HGG  (mean ± SD, 1.10 ± 0.11; 0.83 ± 0.13, respectively, all values x 10^-3 mm² sec^-1; t-test p=0.00). The mean ADC_min for LGG during RT increased compared to baseline value and thereafter remained stable at the first follow-up imaging, although the difference was non-significant (p=.33 and 0.8, respectively), while for HGG, mean ADC_min significantly increased during RT from baseline value and consistently increased at the time of follow-up imaging (p=.00, p=.01, respectively).

The rCVB_max for LGG (1.98 ± 0.70) was significantly lower in comparison to HGG (5.07 ± 0.04).  In both LGG and HGG the rCVB_max decreased during RT from baseline pre-RT values and remained constant at the follow-up. The mean difference in rCVB_max values was significant (LGG: p = 0.00 & 0.03; HGG: p = 0.00 & 0.002, respectively).

Conclusion: There is a change in diffusion (ADC_min) and perfusion (rCVB_max) parameters in glioma patients treated by radiotherapy with values differing based on the grade of tumor, and these measurements shows a temporal change in their values with radiation response.