1H-MRSI of Radiation Effects in Normal-appearing White Matter: Dose-dependence and Impact on Automated Spectral Classification

Purpose: To identify radiation-induced changes in healthy white-matter spectra in the first six months following radiotherapy, and assess the impact of these changes on an automated algorithm for detecting spectral abnormalities.

Materials And Methods: 1H-MRSI was performed on 10 patients with grade IV gliomas who were to undergo radiation therapy. Choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) ratios were studied as a function of dose and time. The impact of these spectral changes on a spectral analysis algorithm was evaluated.

Results: The Cho/NAA ratios rose to values of 0.66 +/- 0.15, 0.75 +/- 0.21, and 0.73 +/- 0.15 two months after therapy, compared to immediate post-therapy values of 0.56 +/- 0.15, 0.60 +/- 0.16, and 0.61 +/- 0.15 for the < 25, 25-50, and > 50 Gy dose groups, respectively. These maxima were followed by a dose-dependent recovery. A similar trend was found in the Cho/Cr ratio. The automated spectral analysis system incorporated the changing Cho/NAA ratio into a global redefinition of healthy tissue, but did not account for dose-dependent spatial variations in Cho/NAA ratios.

Conclusion: Radiation significantly alters the spectra of healthy tissues in the first six months after radiotherapy. This suggests that the radiation dose distribution should be considered during analysis of post-therapy spectra.