Amplitude- and frequency/phase-modulated refocusing pulses that induce plane rotations even in the presence of inhomogeneous B1 fields

Amplitude- and frequency/phase-modulated 180† plane rotation pulses that can achieve both inversion and refocusing transformations in the presence of large B1 variations are presented. Such pulses are required especially in in vivo applications where some of the most commonly used coils generate highly inhomogeneous RF fields. The principles involved in constructing such pulses are discussed in detail together with five different types of problems encountered that affect performance of these pulses off resonance. The refocusing transformation is achieved by inverting the effective field halfway through the pulse. The different pulses discussed tolerate very large and similar range of variations in B1 magnitude on resonance, but behave differently off resonance. Two of the pulses achieve 180† plane rotations with constant phase over a useful off resonance range and in the presence of large B1 variations. Therefore, these pulses are expected to be useful in high-resolution as well as in vivo NMR applications.

[1]  D. I Hoult,et al.  Rotating frame zeugmatography , 1979 .

[2]  M. S. Silver,et al.  Highly selective {π}/{2} and π pulse generation , 1984 .

[3]  M. Bendall,et al.  Portable NMR sample localization method using inhomogeneous rf irradiation coils , 1983 .

[4]  M. Bendall.  Elimination of high-flux signals near surface coils and field gradient sample localization using depth pulses , 1984 .

[5]  D. Rothman,et al.  Phase cycling of composite refocusing pulses to eliminate dispersive refocusing magnetization , 1985 .

[6]  M. Bendall,et al.  Depth and refocusing pulses designed for multipulse NMR with surface coils , 1983 .

[7]  J. Eberly,et al.  Optical resonance and two-level atoms , 1975 .

[8]  C. Slichter.  Principles of magnetic resonance , 1963 .

[9]  Michael Garwood,et al.  Amplitude- and frequency-modulated pulses to achieve 90° plane rotations with inhomogeneous B1 fields , 1987 .

[10]  Christopher J. Hardy,et al.  Efficient adiabatic fast passage for NMR population inversion in the presence of radiofrequency field inhomogeneity and frequency offsets , 1986 .

[11]  David T. Pegg,et al.  Uniform sample excitation with surface coils for in vivo spectroscopy by adiabatic rapid half passage , 1986 .

[12]  A Sotgiu,et al.  High‐order coils as transmitters for NMR imaging , 1986, Magnetic resonance in medicine.

[13]  A. Pines,et al.  Iterative schemes for broad-band and narrow-band population inversion in NMR , 1984 .

[14]  D. Gadian,et al.  Mapping of metabolites in whole animals by 31P NMR using surface coils , 1980, Nature.

[15]  A. J. Shaka,et al.  Composite pulses with dual compensation , 1983 .

[16]  Michael Garwood,et al.  Spatial localization of tissue metabolites by phosphorus-31 NMR rotating-frame zeugmatography , 1984 .

[17]  Peter Styles,et al.  Towards biochemical imaging , 1980 .

[18]  E. Schneider,et al.  Composite pulses without phase distortion , 1985 .

[19]  Michael Garwood,et al.  A modified rotating frame experiment based on a fourier series window function. Application to in vivo spatially localized NMR spectroscopy , 1985 .

[20]  D. T. Pegg,et al.  Adiabatic refocusing pulse which compensates for variable of power and off‐resonance effects , 1987, Magnetic resonance in medicine.

[21]  G. Radda,et al.  A method for localizing high‐resolution NMR spectra from human subjects , 1985, Magnetic resonance in medicine.

[22]  D. T. Pegg,et al.  Improved fourier series windows for localization in in vivo NMR spectroscopy , 1985 .

[23]  G. Radda,et al.  Spatial localization of high resolution 31P spectra with a surface coil , 1983 .

[24]  Pines,et al.  Broadband and adiabatic inversion of a two-level system by phase-modulated pulses. , 1985, Physical review. A, General physics.