Exact solution of the CPMG pulse sequence with phase variation down the echo train: Application to R2 measurements

An exact solution for R2,eff in CPMG experiments in the case of two site chemical exchange

“…As this expression is exactly differentiable it has the potential to greatly speed up fitting to experimental data. It is important to note that effects of off resonance [40] and finite time 180° pulses [39] will lead to deviations from ideality [25,28]. Moreover, additional spin-physics such as scalar coupling and differential relaxation are neglected in this approach.…”

Quantitative comparison of errors in 15N transverse relaxation rates measured using various CPMG phasing schemes

“…The alternative phase scheme with a correction factor given to account for longitudinal relaxation during the pulsing was found to provide more accurate transverse relaxation rates covering a wider off-resonance frequency range than the conventional scheme (Bain et al 2011; Yip & Zuiderweg 2004). This conclusion was supported by simulation results as well as experimental results.…”

“…In biomolecular relaxation experiments, accurate error estimation is important in order to compare with NMR-derived dynamics parameters with those obtained by other methods, such as Gibbs free energy estimated from chemical exchange (Farrow et al 1995; Huang & Oas 1995; Szyperski et al 1993), molecular dynamics simulation data (Chandrasekhar et al 1992; Eriksson et al 1993; Horita et al 2000; Smith et al 1995; Wrabl et al 2000; Yamasaki et al 1995), and conformational entropy estimated from generalized order parameters (Akke & Palmer 1996; Li et al 1996; Yang & Kay 1996). The accuracy and precision of R 2 measurements, have been carefully analyzed (Bain et al 2010; Bain et al 2011; Bretthorst et al 2005; Czisch et al 1997; Ishima & Torchia 2005; Istratov & Vyvenko 1999; Korzhnev et al 2000; Long et al 2008; Myint et al 2009; Palmer et al 1991; Ross et al 1997; Skelton et al 1993; Viles et al 2001; Yip & Zuiderweg 2004). However, some of the R 2 measurements remain unclear, yet.…”

“…One approach to improve the accuracy of R 2 measurements, by reducing cumulative pulse error, is an alternative phase scheme that applies pairs of orthogonal 180° pulses ( XXYȲ ) rather than the conventional CPMG ( XXXX ) (Bain et al 2010; Bain et al 2011; Gullion et al 1990; Long et al 2008; Yip & Zuiderweg 2004). The alternative phase scheme with a correction factor given to account for longitudinal relaxation during the pulsing was found to provide more accurate transverse relaxation rates covering a wider off-resonance frequency range than the conventional scheme (Bain et al 2011; Yip & Zuiderweg 2004).…”

Chemical exchange saturation transfer MRI using intermolecular double-quantum coherences with multiple refocusing pulses

“…This is because that the CPMG sequence can well suppress the effects of imperfect hard pulses and field inhomogeneity [30–33]. Inspired by the idea of CPMG sequence, in this paper we utilized multiple refocusing pulses (MRP) to replace the single refocusing pulse in the detection period to increase the intermolecular double-quantum coherence (iDQC) signal intensity (thus, the SNR of acquired iDQC images).…”