Hydrogen magnetic resonance spectroscopy follow-up after radiation therapy of human brain cancer: Unexpected inverse correlation between the changes in tumor choline level and post-gadolinium magnetic resonance imaging contrast

RATIONALE AND OBJECTIVES The anatomic and metabolic changes in human brain tumors treated by radiation therapy were compared using gadolinium–enhanced magnetic resonance imaging and hydrogen (¹H) magnetic resonance spectroscopy. The study was intended to assess the potential of ¹H magnetic resonance spectroscopy in monitoring response to therapy. METHODS Thirteen cases of brain cancer treated by radiation therapy were examined by ¹H magnetic resonance spectroscopy and gadolinium–enhanced T1–weighted magnetic resonance imaging and reexamined at 2–month intervals. RESULTS Follow–up after radiation therapy showed changes in post–gadolinium magnetic resonance imaging contrast that are inversely correlated with the changes in choline level (r = –0.69, P < 0.00001) and in tumor volume (r = –0.35, P < 0.05). CONCLUSIONS The choline loss in tumors gaining post–gadolinium magnetic resonance imaging contrast after therapy is unexpected in view of previously reported correlation between the two in untreated metastatic brain tumors. Indicated is the use of ¹H magnetic resonance spectroscopy to discriminate enhancing brain tumors with a high content of vital tumor cells (high choline) from tumors, combining decreased cell density with increased interstitial space (low choline).

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