✍ Scribed by A.C. Hsu; C.D. Gregory
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In vivo spectroscopic experiments are commonly done under as well. This is of no consequence with sufficiently long partially T 1 saturated conditions and saturation factors (observed repetition times (TR), since M z would return to its fully signal intensity divided by fully relaxed intensity) used for quantirelaxed state between excitations. However, short TR values tative analysis of absolute and relative metabolite concentrations. are commonly used in practice. Under these conditions, par-The conventional calculation of the saturation factor assumes unitial saturation is observed and the nonuniform M z becomes form excitation across the spectrum. This assumption is violated important. when selective-excitation solvent peak suppression techniques, Quantitative correction for partial saturation can be such as binomial sequences, are used. In this case, the degree of achieved by dividing the amplitudes or areas of the observed partial saturation, and hence the saturation factor, is dependent spectral peaks by their respective saturation factors (SF) on the resonance offset. This has implications for the frequency (8), where SF is the partially saturated peak area divided offset of maximum excitation, solvent suppression effectiveness, absolute and relative quantitative measurements, and progressive by the fully relaxed peak area. For the simple case of nonsesaturation T 1 measurements. In this paper, the jump and return lective p/2 pulses, a saturation factor of (JR) and jump and return echo (JRE) sequences are examined in detail with regard to these implications. It is shown that offset-SF Å 1 0 exp(0TR/T 1 ) [1] dependent partial saturation depends on the sequence used and can become significant. A saturation factor which is a function of offset can be used to correct for this effect and allow for proper is typically used. However, with the JR and other binomial quantitative interpretation of experimental results under partially solvent suppression techniques, the true saturation factor is saturated conditions. ᭧ 1998 Academic Press
offset dependent since the steady-state M z is offset dependent. This paper will examine two pulse sequences, JR and JRE, to investigate the impact of offset-dependent saturation.
Although it has been noted that there is an offset-dependent
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