Measurement of metabolite levels and treatment-induced changes in hepatic metastases of gastro-esophageal cancer using 7-T phosphorus magnetic resonance spectroscopic imaging

Abstract

Methods for early treatment response evaluation to systemic therapy of liver metastases are lacking. Tumor tissue often exhibits an increased ratio of phosphomonoesters to phosphodiesters (PME/PDE), which can be noninvasively measured by phosphorus magnetic resonance spectroscopy (³¹P MRS), and may be a marker for early therapy response assessment in liver metastases. However, with commonly used ³¹P surface coils for liver ³¹P MRS, the liver is not fully covered, and metastases may be missed. The objective of this study was to demonstrate the feasibility of ³¹P MRS imaging (³¹P MRSI) with full liver coverage to assess ³¹P metabolite levels and chemotherapy-induced changes in liver metastases of gastro-esophageal cancer, using a ³¹P whole-body birdcage transmit coil in combination with a ³¹P body receive array at 7 T. 3D ³¹P MRSI data were acquired in two patients with hepatic metastases of esophageal cancer, before the start of chemotherapy and after 2 (and 9 in patient 2) weeks of chemotherapy. 3D ³¹P MRSI acquisitions were performed using an integrated ³¹P whole-body transmit coil in combination with a 16-channel body receive array at 7 T, with a field of view covering the full abdomen and a nominal voxel size of 20-mm isotropic. From the ³¹P MRSI data, 12 ³¹P metabolite signals were quantified. Prior to chemotherapy initiation, both PMEs, that is, phosphocholine (PC) and phosphoethanolamine (PE), were significantly higher in all metastases compared with the levels previously determined in the liver of healthy volunteers. After 2 weeks of chemotherapy, PC and PE levels remained high or even increased further, resulting in increased PME/PDE ratios compared with healthy liver tissue, in correspondence with the clinical assessment of progressive disease after 2 months of chemotherapy. The suggested approach may present a viable tool for early therapy (non)response assessment of tumor metabolism in patients with liver metastases.

Keywords: 7 T; cancer; liver metastasis; magnetic resonance spectroscopy; membrane turnover; phosphorus; treatment response.