31 P MR Spectroscopy in the Pancreas: Repeatability, Comparison With Liver, and Pilot Pancreatic Cancer Data.

BACKGROUND: Non-invasive evaluation of phosphomonoesters (PMEs) and phosphodiesters (PDEs) by 31-phosphorus MR spectroscopy (31 P MRS) may have potential for early therapy (non-)response assessment in cancer. However, 31 P MRS has not yet been applied to investigate the human pancreas in vivo.

PURPOSE: To assess the technical feasibility and repeatability of 31 P MR spectroscopic imaging (MRSI) of the pancreas, compare 31 P metabolite levels between pancreas and liver, and determine the feasibility of 31 P MRSI in pancreatic cancer.

STUDY TYPE: Prospective cohort study.

POPULATION: 10 healthy subjects (age 34 ± 12 years, four females) and one patient (73-year-old female) with pancreatic ductal adenocarcinoma.

FIELD STRENGTH/SEQUENCE: 7-T, 31 P FID-MRSI, 1 H gradient-echo MRI.

ASSESSMENT: 31 P FID-MRSI of the abdomen (including the pancreas and liver) was performed with a nominal voxel size of 20 mm (isotropic). For repeatability measurements, healthy subjects were scanned twice on the same day. The patient was only scanned once. Test-retest 31 P MRSI data of pancreas and liver voxels (segmented on 1 H MRI) of healthy subjects were quantified by fitting in the time domain and signal amplitudes were normalized to γ-adenosine triphosphate. In addition, the PME/PDE ratio was calculated. Metabolite levels were averaged over all voxels within the pancreas, right liver lobe and left liver lobe, respectively.

STATISTICAL TESTS: Repeatability of test-retest data from healthy pancreas was assessed by paired t-tests, Bland-Altman analyses, and calculation of the intrasubject coefficients of variation (CoVs). Significant differences between healthy pancreas and right and left liver lobes were assessed with a two-way analysis of variance (ANOVA) for repeated measures. A P-value <0.05 was considered statistically significant.

RESULTS: The intrasubject CoVs for PME, PDE, and PME/PDE in healthy pancreas were below 20%. Furthermore, PME and PME/PDE were significantly higher in pancreas compared to liver. In the patient with pancreatic cancer, qualitatively, elevated relative PME signals were observed in comparison with healthy pancreas.

DATA CONCLUSION: In vivo 31 P MRSI of the human healthy pancreas and in pancreatic cancer may be feasible at 7 T.

EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: Stage 2.