A cylindrical-window NMR probe with extended tuning range for studies of the developing heart

Three matched cylindrical-window NMR probes were designed and constructed in graduated sizes (16, 25, and 30 mm) for neonatal, immature, and adult heart spectroscopy. The cylindrical probes were made of copper foil and had two symmetrical cylindrical conductive blades separated by openings subtending 90° arcs. The tuning range included both sodium-23 (52.9 MHz) and phosphorus-31 (81.0 MHz). The ability to tune to sodium-23 expedited shimming for phosphorus-31 experimental measurements. Standardization of phosphorus-31 spectra was achieved with an MDPA-filled capillary tube placed outside the cylindrical window. The finite element method was used to derive the electrical potential, magnetic field, and current densities. B₁ field mappings showed uniformity throughout the usable areas, an attribute facilitating comparisons of spectra from hearts of different sizes. We summarize the current designs for low-inductance NMR probes of this type.