Metabolic magnetic resonance imaging: A case for bioscales in medicine

Abstract

The demand to constrain the increasing costs of medical care in an aging population while improving the quality of services is a contradiction of goals that provides the opportunity to rethink the medical service paradigm. It is not a new idea to promote preventive medicine or to attempt to intervene at the earliest stages of disease when treatment costs are low and outcome is improved. However, current imaging modalities are geared toward assessment of disease through detection of altered anatomy that is a late marker of disease. The emphasis has been on higher spatial resolution imaging with improved contrast of tissues in less time in an effort to improve sensitivity of disease detection while maintaining patient throughput to reduce cost escalation. Although exquisite anatomical images are obtained, the large variation in anatomic parameters across the population handicaps such an approach for improving sensitivity of disease detection. An alternative approach is to change the nature of the questions to be answered by measuring parameters that more directly relate to disease. Disease is a disturbance of cellular metabolic processes that are manifested by abnormal genetic expression or external disruption of the cellular homeostatic processes. Metabolic magnetic resonance (MR) imaging of MR signals from proton and non-proton elements such as sodium, oxygen, and phosphorus can be performed in a quantitative manner to yield spatially resolved maps of parameters that are directly interpretable in terms of biological processes. As these processes are tightly controlled in normal tissue, the small biological variation of these metabolically based parameters enhances the sensitivity for detection of early disease. The term bioscale has been coined to reflect that these quantitative metabolic maps have a direct biological interpretation, to be distinguished from the term biomarker that is usually a qualitative term, usually predicting risk for disease. The bioscale of tissue sodium concentration is used to demonstrate the method of measurement of metabolic MR imaging and its application in important clinical roles of determining tissue viability in the setting of stroke and during radiation treatment of brain tumor.