Absolute quantification of human in vivo hepatic 31P magnetic resonance spectroscopy at 7 tesla

Thesis

Phosphorus (³¹P) metabolites are emerging liver disease biomarkers. This work aims to develop a quantification protocol for human hepatic ³¹P magnetic resonance spectroscopy (MRS) at 7 tesla (T). It should have high SNR, deliver robust measurements of metabolite concentrations with high reproducibility, and be feasible to use in clinical studies. This will allow detailed characterization of liver metabolism in diseases such as cirrhosis, increasing the utility of ³¹P-MRS as a clinical tool.

A 3D chemical shift imaging method using a 16 channel ³¹P array at 7 T is chosen to give high SNR ³¹P spectra from the human liver in vivo, while also providing good spatial localization and spectral resolution.

The Oxford Spectroscopy Analysis (OXSA) toolbox, our MATLAB-based processing software package, is introduced and adaptations for analysis of liver spectra are described.

Five volunteers were scanned to determine T₁s for the ten visible ³¹P metabolites. Simulations were used to determine design criteria for calibration phantoms at 1.5, 3 and 7 T. I compare three candidate approaches to give "absolute" concentrations in mmol/L wet tissue using a 10 cm loop coil, and then extend these approaches to data acquired using the 16 element receive array.

The final protocol was applied to data acquired in ten healthy volunteers and eleven patients with cirrhosis to determine reproducibility and the differences between healthy and diseased livers. This protocol allows distinction between healthy and cirrhotic livers with 90% specificity and sensitivity, using cut-offs in either γ-adenosine triphosphate or inorganic phosphate concentrations.

This ³¹P-MRS absolute quantification protocol is an important first step in fully utilising the increased SNR afforded by the 7 T scanner, offering valuable insight into liver metabolism, and paving the way for other novel ³¹P-MRS methods to be developed in the liver at 7 T.

Authors: Purvis, L

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: phosphorus; liver; magnetic resonance spectroscopy; human; 31P; in vivo; absolute quantification
• Subjects: Nuclear magnetic resonance spectroscopy