Imaging evaluation of the pregnant patient with suspected pulmonary embolism.

Pulmonary embolism is the leading cause of maternal death in the developed world. The clinical diagnosis of pulmonary embolism is particularly challenging in pregnant patients as physiologic changes of pregnancy can mimic symptoms of pulmonary embolism or deep venous thrombosis. Clinical decision and imaging algorithms for venous thromboembolic disease have been proposed in the literature for the general population, but have not undergone wide-scale validation in pregnant patients. Laboratory evaluation of D-dimer levels has likewise been established as a viable screening method in the general population but remains controversial in pregnant patients. Regardless of whether D-dimer levels are used in this population, the clinician must often rely on imaging tests to confirm or exclude a clinical suspicion of pulmonary embolism. Additional factors beyond test performance must be weighed during pregnancy: radiation exposure to the fetus and maternal breast tissue, the safety of intravenous contrast administration and the diagnostic accuracy of the various testing options so that diagnosis and proper management are not delayed. The epidemiology of pregnancy-related venous thromboembolic disease and the different diagnostic methods are reviewed, with emphasis on the pregnant patient. Finally, a diagnostic imaging algorithm is proposed for the evaluation of the pregnant patient when a clinical suspicion of pulmonary embolism exists.

Single-shot diffusion measurement in laser-polarized Gas.

A single-shot pulsed gradient stimulated echo sequence is introduced to address the challenges of diffusion measurements of laser polarized 3He and 129Xe gas. Laser polarization enhances the NMR sensitivity of these noble gases by >10(3), but creates an unstable, nonthermal polarization that is not readily renewable. A new method is presented which permits parallel acquisition of the several measurements required to determine a diffusive attenuation curve. The NMR characterization of a sample's diffusion behavior can be accomplished in a single measurement, using only a single polarization step. As a demonstration, the diffusion coefficient of a sample of laser-polarized 129Xe gas is measured via this method.

Shimming a high-resolution MAS probe.

A systematic and efficient approach to shimming a high-resolution, magic angle sample spinning probe is introduced. The method takes into account the different symmetries of the normal shim coils and the MAS experiment.

RF gradient BIRD/TANGO sequence to eliminate uncoupled magnetization.

A modification of the BIRD and TANGO sequences is presented which employs radiofrequency field gradients to eliminate the net magnetization from uncoupled spins, while completely preserving coupled magnetization. The standard BIRD and TANGO sequences cause selective nutation of protons directly bound to a coupling partner, while returning uncoupled magnetization to +z. These sequences lend themselves naturally to modification using RF gradients, which require no increase in pulse-sequence complexity while providing substantial suppression of uncoupled resonances and elimination of typical antiphase and multiple-quantum error terms that arise from improperly set pulse lengths or delays. In the RF-gradient BIRD/TANGO sequence, the uncoupled magnetization is dephased in a plane orthogonal to the RF axis, while the desired signal components are refocused, effectively in a rotary echo. The sequence has applications to solvent suppression and selective isotopomer excitation. It is demonstrated for selective excitation of the satellites in a sample of chloroform, yielding suppression of the uncoupled magnetization by factor of approximately 800.