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Papers Published

1. Karis, JP; Allan Johnson, G; Glover, GH, Signal-to-noise improvements in three-dimensional NMR microscopy using limited-angle excitation, Journal of Magnetic Resonance (1969), vol. 71 no. 1 (January, 1987), pp. 24-33, Elsevier BV [doi] .
   (last updated on 2025/02/12)

   Abstract:
   The 3D FT variant of spin-echo imaging has previously been successfully used to yield images at microscopic resolution. In obtaining such high resolution, optimization of signal to noise for a given acquisition time is crucial. Using a limited-angle (<60) slice-selective pulse one can improve the effective signal to noise or reduce the experimental time. The spin echo is generated through gradient refocusing. A phantom with T1 of 800 and 1200 ms was used to simulate white and gray matter. Signal intensity was modeled by the expression M= M0sinθ[1-exp(- TR T1)] 1-exp(- TR T1)cosθ For TR < 200 ms, limited-angle excitation can yield improvements in signal to noise by greater than a factor of two. These results were experimentally verified on a 1.5 T prototype system (General Electric, Milwaukee, Wis.) configured with gradient and rf coils designed for NMR microscopy. In those cases where signal-to-noise concerns do not require signal averaging beyond that which is inherent in the 3D FT technique, the limited-angle approach can reduce the acquisition time by as much as a factor of four. These results were verified in small animal studies of the brain of a 200 g rat. © 1987.