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Variation of T₂ relaxation times in pediatric brain tumors and their effect on metabolite quantification

Dominic Carlin^1,2, Ben Babourina-Brooks^1,2, Nigel P Davies^2,3

¹Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham, West Midlands, UK.

Journal of Magnetic Resonance Imaging : JMRI

|April 27, 2018

Abstract

Background:

Metabolite concentrations are fundamental biomarkers of disease and prognosis. Magnetic resonance spectroscopy (MRS) is a noninvasive method for measuring metabolite concentrations; however, quantitation is affected by T₂ relaxation.

Purpose:

To estimate T₂ relaxation times in pediatric brain tumors and assess how variation in T₂ relaxation affects metabolite quantification.

Study Type:

Retrospective.

Population:

Twenty-seven pediatric brain tumor patients (n = 17 pilocytic astrocytoma and n = 10 medulloblastoma) and 24 age-matched normal controls.

Field Strength/Sequence:

Short- (30 msec) and long-echo (135 msec) single-voxel MRS acquired at 1.5T.

Assessment:

T₂ relaxation times were estimated by fitting signal amplitudes at two echo times to a monoexponential decay function and were used to correct metabolite concentration estimates for relaxation effects.

Statistical Tests:

One-way analysis of variance (ANOVA) on ranks were used to analyze the mean T₂ relaxation times and metabolite concentrations for each tissue group and paired Mann-Whitney U-tests were performed.

Results:

The mean T₂ relaxation of water was measured as 181 msec, 123 msec, 90 msec, and 86 msec in pilocytic astrocytomas, medulloblastomas, basal ganglia, and white matter, respectively. The T₂ of water was significantly longer in both tumor groups than normal brain (P < 0.001) and in pilocytic astrocytomas compared with medulloblastomas (P < 0.01). The choline T₂ relaxation time was significantly longer in medulloblastomas compared with pilocytic astrocytomas (P < 0.05), while the T₂ relaxation time of NAA was significantly shorter in pilocytic astrocytomas compared with normal brain (P < 0.001). Overall, the metabolite concentrations were underestimated by ∼22% when default T₂ values were used compared with case-specific T₂ values at short echo time. The difference was reduced to 4% when individually measured water T₂ s were used.

Data Conclusion:

Differences exist in water and metabolite T₂ relaxation times for pediatric brain tumors, which lead to significant underestimation of metabolite concentrations when using default water T₂ relaxation times.

Level Of Evidence:

3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:195-203.

Keywords:

MRS MRS quantification T2 relaxation pediatric brain tumors

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