Sodium MRI of the Brain, Cartilage, and Heart
Thursday, April 20, 2006
Presented by the Imaging Discussion Group
Organizers: Joseph Helpern, Alexej Jerschow and Ravinder Regatte, New York University School of Medicine
In most living organisms, sodium maintains physiological water levels, normal cell membrane functions, and acid—base balance. Sodium is the second-most NMR-sensitive nucleus but despite its importance in biological systems, sodium MRI has not achieved the utility of conventional proton MRI. The recent introduction of high field MRI systems (3T and greater) along with improved hardware and software, however, makes sodium MRI more attractive and attainable as a routine imaging tool.
5:00 pm - 7:30 pm: Presentations
Keith Thulborn, University of Illinois, Chicago, "The Role of Clinical Sodium MR Imaging in Management of Tissue Viability in Stroke and Brain Tumors."
Paul Bottomley, Johns Hopkins University, "Imaging Sodium Content in Patients with Heart Disease and Cancers."
Ravinder Reddy, University of Pennsylvania, "Sodium MRI for Molecular and Diagnostic Imaging of Cartilage."
Keith Thulborn, "The Role of Clinical Sodium MR Imaging in Management of Tissue Viability in Stroke and Brain Tumors."
The central question in the diagnosis and treatment of disease in the brain relates to tissue viability. Interventions to salvage tissue in the setting of acute stroke require a measure of the ongoing metabolic status of the tissue under threat during the responsive stage of therapy. Treatments of neoplasia are aimed at selective cell death, balancing immediate detrimental effects of toxic agents on normal tissues against cell kill in the neoplasm to produce improved outcome. Current methods for rapid non-invasive measurement of tissue viability are limited. The diffusion-perfusion mismatch has been used as an indicator of tissue death in strokes as loss of oxygen consumption measured by positron emission tomography (PET). The importance of determining tissue viability in these major healthcare areas of stroke and cancer is clear. The implementation of the technology is best achieved by integration into existing practices. The routine availability of magnetic resonance imaging (MRI) and its extensive use in the evaluation of diseases of the central nervous system makes this modality a more favorable approach. As was first proposed almost two decades ago before the appropriate technology was available, sodium MRI holds the potential to measure a tissue property intimately related to viability —sodium ion and water homeostasis. This presentation will focus on my most recent experiences with sodium imaging in the clinical environment in combination with a comprehensive water proton MRI protocol at 3 Tesla. Sodium imaging in humans at 9.4 Tesla offers further opportunities for ultra-high field MRI in humans.
Paul A Bottomley, Johns Hopkins University, "Imaging Sodium Content in Patients with Heart Disease and Cancers."
The concentration of sodium in normal soft human tissues is 20-80 micromol/g wet weight, or about 1/1600th of the water hydrogen concentration which forms the basis of conventional magnetic resonance imaging (MRI). In addition, sodium's MRI sensitivity is only about 9 percent of hydrogen's. Despite these enormous handicaps, sodium imaging at clinical MRI field strengths of 1.5 Tesla with ~0.2 ml resolution is practical in ~15 min scan times or less. Total tissue sodium, derived from both intra- and extra-cellular pools, is quantifiable using external references. Sodium elevations of 10-50 percent are seen when either pool is increased, as with stimuli that increases perfusion, in breast and brain cancers, and in myocardial infarction. Progress with patient studies to evaluate the role of sodium MRI in diagnosis and for monitoring therapeutic response is reviewed.
Ravinder Reddy, "Sodium MRI for Molecular and Diagnost