31P NMR spectral editing technique for blood with short T2 values

Abstract

Since the work of Moon and Richards (I), the 3’P chemical shift of inorganic phosphate (Pi) has been widely used as an indicator of the pH of biological systems. In blood, the Pi resonance often overlaps the doublet resonance of 2,3-diphosphoglycerate (2,3-DPG) and several spectral editing techniques to separate them have been suggested (2-4). However, all of those techniques require a delay of 1/2J,n(n in this method the delay between excitation and acquisition can be much less than 1/2n the 180” pulse refocuses any dephasing due to magnetic field inhomogeneity and the evolution due to chemical shift. Any evolution due to heteronuclear scalar coupling is also refocused. Consequently, both the components of the DPG doublet and Pi will have the same phase. In the second sequence, a 180” pulse is applied at the 31P and ‘H frequencies. Since the 180” proton pulse inverts the spin states of the proton spins, the evolution due to the heteronuclear scalar coupling of the DPG doublet is not refocused. Therefore at the end of the sequence, one of the resonances of the doublet would have evolved through an angle of hJpH, and the other through -rJpH (= kq5). However, the magnetization of the Pi singlet will have the same phase as before. The positions of the magnetization vectors after the two sequences are illustrated in Fig. 2 as EXP 1 a and EXP lb. The phase of the FID acquired with the sequence in Fig. 1 b is now rotated through k,$. When this FID is subtracted from that resulting from the sequence in Fig. lA, one peak of the DPG doublet cancels out, leaving the singlet from the Pi, plus the