arXiv:physics/0406051v1 [physics.med-ph] 10 Jun 2004 Effects of T 2 Relaxation and Diffusion on Longitudinal Magnetization State and Signal Build for HOMOGENIZED Cross Peaks Curtis A. Corum 1 , Arthur F. Gmitro 1,2 ISMRM 2004, Poster 2323, Thursday, May 20 1 Optical Sciences Center (corum@email.arizona.edu), 2 Department of Radiology, University of Arizona, Tucson, AZ, USA Abstract An analytical expression has been developed to describe the effects of T 2 relaxation and diffusing spatially modulated longitudinal spins during the signal build period of an HOMOGENIZED cross peak. Diffusion of the longitudinal spins results in a lengthening of the effective dipolar demagnetization time, delaying the re-phasing of coupled anti-phase states in the quantum picture. In the classical picture the unwinding rate of spatially twisted magnetization is no longer constant, but decays exponentially with time. The expression is experimentally verified for the HOMOGENIZED spectrum of 100mM TSP in H 2 O at 4.7T. Introduction HOMOGENIZED[13] and its variants[2, 9] and the recently proposed IDEAL[14] sequences have great potential for in-vivo spectroscopy[10]. Diffusion weighting in HOMOGENIZED is present both to give intentional diffusion weighting and as a side effect of the various gradients present. Stekjsal-Tanner (ST) diffusion weighting[12] during the t1 (mix) and t2 (build) periods of the sequence can be used to suppress radiation dampening. Enhanced diffusion weighting[15, 4, 3] is obtained during t1. There is an additional t2 dependent diffusion weighting possible, due to the iZQC gradient G zq and β pulse combination. The weighting results from diffusing modulated longitudinal magnetization, and does not behave as ST diffusion weighting. Kennedy et al.[11] have shown recently that this diffusion weighting has the novel property of being insensitive to object motion. We have concentrated our efforts on the 2d HOMOGENIZED sequence shown in figure 1. The sequence consists of three RF pulses, α for excitation, β to convert helical transverse magnetization to M z modulation, and π to form a spin echo. The G a1 , G a2 gradient pair yields ST diffusion weighting and radiation damping suppression during t1. The G b1 , G b2 gradient pair accomplishes the same during t2. The G c1 , G c2 gradient pairs crush transverse magnetization created at π due to pulse imperfections and B 1 inhomogeneity, as well as introduce some additional diffusion weighting. The G zq gradient selects intermolecular zero quantum coherences (iZQCs) in the quantum picture. In the classical picture the G zq gradient in combination with β creates spatially modulated longitudinal magnetization whose magnetic field causes unwinding (and eventually rewinding) of helically twisted transverse magnetization[8]. A 2d HOMOGENIZED experiment (see figure 3) is carried out by incrementing t1 over multiple acqui- sitions. In a two (or multiple) component system where only one component is present in high concentration 1