Ernst angle

Abstract: The parameters of a spoiled gradient-echo (SPGR) pulse sequence have been optimized for in vivo localization of a focused ultrasound beam. Temperature elevation was measured by using the proton resonance frequency shift technique, and the phase difference signal-to-noise ratio (SNR delta phi) was estimated in skeletal muscle and kidney cortex in 10 rabbits. Optimized parameters included the echo time equivalent to T2* of the tissue, the longest repetition time possible with a 20-s sonication, and the flip angle equivalent to the Ernst angle. Optimal SPGR phase imaging can detect a sonication beam with a peak phase difference of 0.55 radian, which corresponds to a temperature elevation of 7.3 degrees C. The sonication beam can be localized within one voxel (0.6 x 0.6 x 5 mm3) at power levels that are below the threshold for thermal damage of the tissue.

Abstract: The application of Ernst angle pulses in multidimensional NMR spectroscopy is theoretically and experimentally investigated. Theory shows that only for a few pulse sequences employed at high repetition rate, a remarkable gain in sensitivity is possible using Ernst angle pulses. As an example, a new variant of the heteronuclear multiple quantum coherence (HMQC) experiment, the fast-(1H,15N)-HMQC, is described. This sequence allows, with a 1 mM protein sample in H2O, the acquisition of a highly resolved two-dimensional (1H,15N) correlated spectrum within 37 s. The high efficiency of the fast-HMQC to detect ligand binding to a target protein is demonstrated.

Abstract: T1 is often ill-determined This means that an Ernst angle excitation often cannot be precisely defined for the simple pulse and acquire experiment Here, published 31P T1 values of metabolites in human muscle, liver, heart, and brain are archived, some new data on heart and brain added, and overall confidence intervals determined Strategies for setting the flip-angle based on the confidence intervals are examined, and an optimum flip-angle derived which minimizes the signal loss relative to what could have been realized if T1 were precisely known With such optimized pulses, signal loss can be limited to < or = 14% for up to a 10-fold variation in T1, with TR < or = T1 The effect that an uncertainty in T1 by a factor of two has on the saturation corrected signal is limited to < or = 20% in the optimum flip-angle experiment Adiabatic B1-independent rotation phase-cycled (BIRP) excitation pulses are ideal as optimum flip-angle pulses as they can be prescribed without calibration

Abstract: Radial acquisition (RA) techniques have been extended to produce isotropic, three-dimensional images of lung in live laboratory animals at spatial resolution down to 0.013 mm 3 with a signal-to-noise ratio of 30:1. The pulse sequence and reconstruction algorithm have been adapted to allow acquisition of image matrices of up to 256 3 in less than 15 min. Scan-synchronous ventilation has been incorporated to limit breathing motion artifacts. The imaging sequence permits randomizing and/or discarding selected views to minimize the consequences of breathing motion. The signal in lung parenchyma was measured as a function of flip angle (α) for different repetition times and found to follow the predictions for which there is an optimum excitation (Ernst) angle. A single T 1 relaxation value of 780 ± 54 ms fits all data from six guinea pigs at 2.0 T. This T 1 value parameterizes the signal and allows for a priori optimization, such as calculation of the Ernst angle appropriate for lung imaging.