Background and purpose: After radiotherapy (RT), children with diffuse intrinsic pontine gliomas (DIPG) are followed with sequential magnetic resonance imaging (MRI). However, MRI changes do not necessarily reflect tumor progression, and therefore additional noninvasive tools are needed to improve the definition of progression vs. treatment-related changes. In this study, we determined the feasibility and accuracy of multivoxel proton magnetic resonance spectroscopic imaging (1H-MRSI) for monitoring pediatric patients with DIPG.
Methods and patients: Twenty-four serial examinations of MRI/MRSI (7 2D-MRSI and 17 3D-MRSI) were performed on 8 patients with DIPG who received local RT. A total of 1635 voxels were categorized as "normal" or "abnormal" based on corresponding imaging findings on contrast-enhanced T1- and T2-weighted MRI. The choline to N-acetyl-aspartate ratio (Cho:NAA) and choline to creatine ratios (Cho:Cr) within each category of MRI abnormality were compared to their counterpart in normal surrounding tissues. The changes in these ratios corresponding to each type of abnormality were evaluated before RT, at response, and at recurrence, as determined by the clinical status of the patients. The presence or absence of lactate and lipid peaks was noted for each voxel. MRI/MRSI was performed on posterior fossa and supratentorial tissue of 3 volunteer pediatric patients.
Results: The Cho:NAA and Cho:Cr values within the imaging abnormalities (3.8 +/- 0.93 and 3.55 +/- 1.37, respectively) were significantly higher than the mean values in normal-appearing regions (0.93 +/- 0.2 and 1.13 +/- 0.38, respectively) (p < 0.005). Cho:NAA values decreased from studies at diagnosis to the time of response to RT (3.12 +/- 0.5 and 2.08 +/- 0.73, respectively), followed by an increase at the time of relapse (from 1.83 +/- 0.92 to 4.29 +/- 1.08). Loss of lactate and lipid peaks correlated with response, and their presence and stability with relapse. In 3 patients, increased spectral abnormalities preceded the radiological and clinical deterioration by 2-5 months.
Conclusion: Multivoxel MRSI is a feasible and reproducible noninvasive tool for assessing pediatric DIPG. Longitudinal multivoxel MRSI measurements have potential value in assessing response to radiation or other therapies, because they offer more coverage than single-voxel techniques and provide reliable spectral data.