A nuclear magnetic resonance study of vacancy and interstitial motion in scandium hydrides and deuterides

Nuclear Magnetic Resonance (NMR) methods have been used to study the nonstochiometric dihydrides and dideuterides of high purity scandium. For the first time, measurements have been made of the spin relaxation times T(,1) and T(,2) of all three nuclear species present ((\u2745)Sc, (\u272)D, (\u271)H) in a metal hydride (deuteride) system, permit- ting a comparison of the main features of both atomic and vacancy motion on the hydrogen sublattice. In the regions of the conventional diffusion induced (\u2745)Sc- and (\u272)D-T(,1) minima ( 0.03 and shows a weaker frequency dependence than expected. The jump-attempt frequencies (nu)(,o) obtained from the (\u2745)Sc-T(,1) data agree well with the values obtained from neutron scattering measurements, whereas the (\u271)H-T(,1) data yield anomalously low jump frequency prefactors. We interpret the departure of the (\u2745)Sc results from the Lorentzian model as indicating the formation of vacancy pairs and the importance of particle-particle interactions. The (\u2745)Sc- and (\u272)D- T(,1) data also reveal the importance of three particle correlations and conduction elec- tron screening for the quadrupolar relaxation mechanism. At high temperatures (\u3e800K), we have observed a new, previously unfore- seen and essentially frequency independent decrease of T(,1) and T(,2) for all three nuclear species ((\u2745)Sc, (\u272)D and (\u271)H). This second, high temperature T(,1) minimum suggests the formation of short-lived clusters on the H(D) sublattice similar to that occurring in superionic fluorides and the existence of highly correlated modes of motion. Large amplitude vibrations of the hydrogen (deuterium) atoms at high temperatures lead to an effective slowdown of atom diffusion and the T(,1) decrease. Several other high temperature relaxation;mechanisms have been considered and can be excluded on both theoretical and experimental grounds; (\u271)DOE REport IS-T-1237. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy

Quantification of myocardial perfusion by cardiovascular magnetic resonance

The potential of contrast-enhanced cardiovascular magnetic resonance (CMR) for a quantitative assessment of myocardial perfusion has been explored for more than a decade now, with encouraging results from comparisons with accepted "gold standards", such as microspheres used in the physiology laboratory. This has generated an increasing interest in the requirements and methodological approaches for the non-invasive quantification of myocardial blood flow by CMR. This review provides a synopsis of the current status of the field, and introduces the reader to the technical aspects of perfusion quantification by CMR. The field has reached a stage, where quantification of myocardial perfusion is no longer a claim exclusive to nuclear imaging techniques. CMR may in fact offer important advantages like the absence of ionizing radiation, high spatial resolution, and an unmatched versatility to combine the interrogation of the perfusion status with a comprehensive tissue characterization. Further progress will depend on successful dissemination of the techniques for perfusion quantification among the CMR community

Cardiac Function Evaluation with Cine MRI of the Heart

This unit describes how to determine hemodynamic parameters of cardiac function such as ejection fraction (EF), end diastolic volume (EDV), end systolic volume (ESV), stroke volume (SV), and cardiac mass, based on experience using a Siemens 1.5 T Sonata scanner. Briefly, cine loops are acquired over several heartbeats, synchronized with the heart cycle by gating of the encoding steps with the patients electrocardiogram (ECG). Recently, it has become feasible to acquire cine loops in real time, although the temporal resolution is not optimal. Options discussed in this unit include breath hold versus free breathing, prospective triggering versus retrospective gating, and volumetric data sets versus biplanar approaches. Patient parameters such as heart rate or rhythm, degree of functional impairment, the presence of valvular disease, and the need to assess for jets from shunts or valve dysfunction are also treated.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145342/1/cpmia1104.pd

Cardiac Function Evaluation with Cine MRI of the Heart

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145199/1/cpmia1104.pd

T1 Mapping Basic Techniques and Clinical Applications

AbstractIn cardiac magnetic resonance (CMR) imaging, the T1 relaxation time for the 1H magnetization in myocardial tissue may represent a valuable biomarker for a variety of pathological conditions. This possibility has driven the growing interest in quantifying T1, rather than just relying on its effect on image contrast. The techniques have advanced to where pixel-level myocardial T1 mapping has become a routine component of CMR examinations. Combined with the use of contrast agents, T1 mapping has led an expansive investigation of interstitial remodeling in ischemic and nonischemic heart disease. The purpose of this review was to introduce the reader to the physical principles of T1 mapping, the imaging techniques developed for T1 mapping, the pathophysiological markers accessible by T1 mapping, and its clinical uses