Evaluation of Metabolic Characteristics of Brain Tumours Utilising 31-Phosphorus MR Spectroscopy in 3T MRI: A Cross-sectional Study

Introduction: The characterisation of brain tumours is predominantly based on Magnetic Resonance Imaging (MRI) for structural details and invasive histopathology for certainty. MR spectroscopy, a non invasive technique has provided access to the novel field of metabolomics in-vivo. Proton (H+) MR spectroscopy has gained unanimous acceptance as a neuroimaging technique. In addition, 31-Phosphorus MR spectroscopy provides insight into the energetics of normal and abnormal tissues. Aim: To metabolically characterise brain tumours and compare them with normal brain parenchyma using 31-Phosphorus spectroscopy by obtaining applicable parameters for evaluation, diagnosis and grading of brain tumours. Materials and Methods: This cross-sectional study was conducted at the Barnard Institute of Radiology, Madras Medical College, Chennai, Tamil Nadu, India, from December 2019 to December 2021. The study included 32 patients diagnosed with brain tumours based on conventional MR imaging, followed by histopathology, and 10 normal healthy volunteers who underwent 31-Phosphorus MR spectroscopy using a customised birdcage 31-P dual-tuned head coil on a Siemens 3-Tesla MRI scanner (Rapid Biomedical, Wurzburg, Germany). The phosphorus metabolites and ratios analysed included Phosphodiesters {Glycerophosphoethanolamine (GPE) and Glycerophosphocholine (GPC)}, Gamma Adenosine Triphosphate (γ-ATP), Phosphocreatine (PCr), and Inorganic Phosphate (Pi). The metabolite ratios assessed were GPC/GPE, GPC/Pi, GPC/PCr, GPC/γ-ATP, GPE/Pi, GPE/PCr, GPE/γ-ATP, PCr/Pi, PCr/γ-ATP, and Pi/γ-ATP. Additionally, pH was derived. The values were recorded within the tumour, in the peritumoural oedema, and in the normal-appearing contralateral brain parenchyma. These values were compared with each other and also with the brain parenchymal values of the controls. Oneway Analysis of Variance (ANOVA) was used to compare the metabolite ratios observed in various sites. Results: The subjects included 13 females and 19 males, with a mean age of 41.7 years and 43.4 years respectively. A mild alkalinisation trend was observed within the brain tumours (pH 7.1±0.12) compared to the control group (7.05±0.02). Significantly increased GPE/γ-ATP and PCr/γ-ATP values, as well as significantly decreased PCr/Pi values, were observed within the tumour in comparison to the control group (p-value <0.05). Gliomas and metastases showed relatively higher pH compared to the controls (7.05±0.02). High-grade gliomas exhibited alkaline pH compared to low-grade gliomas, with a p-value of 0.000439. Significant differences were noted between gliomas and metastases compared to the control group. Conclusion: A 31-Phosphorus MR spectroscopy has provided new insights into cellular metabolism in the pathological brain and has enhanced the understanding of the ongoing pathomechanisms in various brain tumours.