2D ¹H sLASER Long‐TE and 3D ³¹P Chemical Shift Imaging at 3 T for Monitoring Fasting‐Induced Changes in Brain Tumor Tissue

BackgroundEmerging evidence suggests that fasting could play a key role in cancer treatment. Its metabolic effects on gliomas require further investigation.PurposeTo design a multi‐voxel 1H/31P MR‐spectroscopic imaging (MRSI) protocol for noninvasive metabolic monitoring of cerebral, fasting‐induced changes on an individual patient/tumor level, and to assess its technical reliability/reproducibility.Study TypeProspective.PopulationMRS phantom. Twenty‐two patients (mean age = 61, 6 female) with suspected WHO grade II‐IV glioma examined before and after 72‐hour‐fasting prior to biopsy/resection.Field Strength/Sequence3‐T, 1H decoupled 3D 31P MRSI, 2D 1H sLASER MRSI at an echo time of 144 msec, 2D 1H MRSI (as water reference), T1‐weighted, T1‐weighted contrast‐enhanced, T2‐weighted, and FLAIR. sLASER and PRESS sequences were used for phantom measurements.AssessmentPhantom measurements and spectral simulations were performed with various echo‐times for protocol optimization. In vivo spectral analyses were conducted using LCModel and AMARES, obtaining quality/fitting parameters (linewidth, signal‐to‐noise‐ratio, and uncertainty measures of fitting) and metabolite intensities. The volume of glioma sub‐regions was calculated and correlated with MRS findings. Ex‐vivo spectra of necrotic tumor tissues were obtained using high‐resolution magic‐angle spinning (HR‐MAS) technique.Statistical TestsWilcoxon signed‐rank test, Bland–Altman plots, and coefficient of variation were used for repeatability analysis of quality/fitting parameters and metabolite concentrations. Spearman ρ correlation for the concentration of ketone bodies with volumes of glioma sub‐regions was determined. A P‐value <0.05 was considered statistically significant.Results1H and 31P repeatability measures were highly consistent between the two sessions. β‐hydroxybutyrate and acetoacetate were detectable (fitting‐uncertainty <50%) in glioma sub‐regions of all patients who completed the 72‐hour‐fasting cycle. β‐hydroxybutyrate accumulation was significantly correlated with the necrotic/non‐enhancing tumor core volume (ρ = 0.81) and validated using ex‐vivo 1H HR‐MAS.Data ConclusionWe propose a comprehensive MRS protocol that may be used for monitoring cerebral, fasting‐induced changes in patients with glioma.Evidence Level1Technical EfficacyStage 4