Biomedical Solid State NMR : An ADRF Cross Polarization Study of Calcium Phosphates and Bone Mineral

This thesis investigates the application of a low power solid state NMR technique, using proton to phosphorus-31 cross polarization via adiabatic demagnetization in the rotating frame (ADRF-CP), to study samples of synthetic calcium phosphate and bone mineral. The first section describes the use of ADRF-CP, with a surface coil, to detect monohydrogen phosphate ions in the presence of a large background of non-protonated phosphate ions in porcine bone and a mixture of synthetic calcium phosphates. Transient oscillations were observed in the transfer of polarization between the proton dipolar and phosphorus Zeeman nuclear spin reservoirs after the initiation of thermal contact. Suppression of the non-protonated phosphate was achieved by detecting the signal when the oscillation was passing through zero, and adjusting the phosphorus rf field to achieve optimal cross polarization with the proton local fields of the monohy-drogen phosphate ions. An adiabatic remagnetization of the phosphorus eliminated the oscillations, while increasing the strength of the observed total phosphorus signal. The second section describes the investigation of three variants of the ADRF process as well as a Jeener-Broekaert pulse sequence to create proton dipolar order in the calcium phosphates. The relative efficiencies of the different techniques were sample dependent, with the ADRF techniques performing well in hydroxyapatite and poorly in brushite. The reason for this poor performance in brushite is not well understood. The third section describes experiments demonstrating an ADRF-CP variant of the differential cross polarization technique. The inversion of the phosphorus Zeeman temperature is performed by changing the phase of the phosphorus rf by 180 degrees during the cross polarization. Transient oscillations were observed on inverting the phosphorus temperature. The final section of the thesis describes the design and construction of a two-port double resonance probe with interchangeable coils for a 4.7 T magnet. The plug-in design for the coils facilitates the use of coils of different circuits and geometries with the same set of variable tuning and matching capacitors. Two double resonance coils were constructed, a surface coil using a novel circuit design, and a previously described cylindrical resonator. Acknowledgments There have been so many people who have taught me so much and enriched my life over the last six years here at MIT that I don't really know where to begin. None of this work would have been possible without the support and guidance of Jerry Ackerman. He has been both a friend and a mentor over the …