Amplitude-modulated composite pulses
1988; Elsevier BV; Volume: 80; Issue: 2 Linguagem: Inglês
10.1016/0022-2364(88)90312-5
ISSN1557-8968
AutoresDavid B. Zax, Gadi Goelman, Shimon Vega,
Tópico(s)Advanced MRI Techniques and Applications
ResumoOne of the most important developments in the field of magnetic resonance in the past decade has been the introduction of composite pulse sequences (I). These may be either several pulses of specified length and phase applied sequentially or a single complex pulse of continuously varying phase and/or amplitude which compensate for the imperfections (most notably, finite RF power) or other undesirable qualities of normal pulses. In this power we describe a set of RF pulses with “broadband” character in that they elicit some desired behavior in a two-level spin system over a larger bandwidth for a specified RF power than do normal pulses. Additionally, these pulses compare favorably with other pulses designed with a similar goal in mind (26). We were led to explore these questions and to some of the answers by our continuing interest in the application of the Floquet formalism for periodic time-dependent Hamiltonians to problems in NMR (7,8). The detailed description of the formalism and the full theoretical grounding for the results we present here will appear elsewhere as part of a significantly extended study of the problem. In this Communication we focus instead on the results themselves rather than their derivation and on the experimental verification of the theoretical predictions in the realm of broadband RF pulse sequences. Composite and/or broadband pulses have been developed to cover a multitude of experimental situations, and via several theoretical approaches (9-12). Generally, the goal is to design a pulse sequence H,(t) such that, for a total Hamiltonian
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