If necessary, the filter can be applied several times; it operates by removing the magnetization of spins that reside

at the immobile site and therefore the diffusional decay detected at the end is, if the filter applied repeatedly, contributed only by those spins that resided on the “free” and mobile site during the whole diffusion time. In other words, the detected decay is supposed to be single-component with setting D = Df in Eq. (1). The pulse sequence with a single T2-filter was proposed previously [39] but without a detailed analysis, evaluation, and without having identified its possible use for eliminating exchange effects. The signal attenuation in the pulse sequence given in Fig. 2 can be found by analyzing the same set of coupled of differential selleck inhibitor equations as above, Eq. (2a) and (2b).

The effect of the T2-filter is to re-establish after having applied the filter the same initial condition as in Eq. (6). As the other initial condition, at the end of the first τex delay and after having applied the first T2-filter, the free-pool magnetization is expressed similarly to that in Eq. (7a). equation(8a) Mz(q,τex)∝P′e-(2πq)2D1τex+(1-P′)e-(2πq)2D2τexMz(q,τex)∝P′e-(2πq)2D1τex+(1-P′)e-(2πq)2D2τex Hence, the selleckchem effect of any subsequent delay τex and T2-filter is to simply multiply the free-pool magnetization by the same factor; for n filters and thereby (n + 1) τex delays the obtained signal becomes equation(8b) S(q,n,τex)∝Mz(q,n,τex)∝(P′e-(2πq)2D1τex+(1-P′)e-(2πq)2D2τex)n+1S(q,n,τex)∝Mzq,n,τex∝P′e-(2πq)2D1τex+(1-P′)e-(2πq)2D2τexn+1

(We provide in Appendix A the formal solutions for those situations where delays τ1 and τrel are not of negligible length.) In that limit where the filter is applied with sufficiently high (τex ≪ 1/kb) frequency, the original exchange equation Eq. (2a) becomes modified by having suppressed any magnetization returning form the “bound” site equation(9) dMf(t)dt=-(2πq)2Df+kf+RfMf(t) As a result, the effect of exchange on the diffusional decay is removed and one retains the original Stejskal–Tanner expression with exchange Staurosporine chemical structure solely exhibited as an intensity reduction equation(10) S=(S0e-kfΔ)e-γ2δ2g2(Δ-δ/3)DS=(S0e-kfΔ)e-γ2δ2g2(Δ-δ/3)Dby the factor exp(−kfΔ) that arises because longitudinal magnetization transferred to the “bound” site is eliminated. With τ1 ≫ T2b as is under consideration here, the system is selectively excited so that in the beginning of the τ2 period it is only the “free” site that exhibits nonzero longitudinal magnetization. This situation is similar to that explored in exchanging systems where spectral resolution permits the excitation of individual resonances by selective RF pulses [41]. As compared to conventional PGSTE experiments with nonselective RF pulses, the effect of exchange is reduced with selective excitation.