In vivo 1H2O T2† measurement in the human occipital lobe at 4T and 7T by Carr-Purcell MRI:: Detection of microscopic susceptibility contrast

A high-resolution spin-echo imaging method is presented (called CP-LASER) which exploits the spin refocusing capability of an adiabatic Carr-Purcell (CP) pulse sequence to measure apparent (H2O)-H-1 transverse relaxation (T-2(+)) and generate contrast based on microscopic tissue susceptibility. High-resolution CP-LASER images of the human occipital lobe were acquired at four different echo times from six subjects at 4T and eight subjects at 7T to investigate the effect of magnetic field strength (B-o) and the CP interpulse time (tau(cp)) on T-2(+). Susceptibility contrast was identified and T-2(+) was quantified for long tau(cp) (>10 ms) and short tau(cp) (7 ms at 4T and 6 ms at 7T) in gray matter, white matter, and cerebral spinal fluid. The (H2O)-H-1 relaxation rate constants (1/T-2(+)) of gray and white matter each increased approximately linearly with field strength and T-2(+) was inversely related to tau(cp). The average T-2(+) value of gray matter was 19% and 9% smaller than that of white matter at 4T and 7T, respectively. These results are consistent with higher levels of compartmentalized ferritin and increased blood volume in gray matter compared to white matter in this region of the brain. (C) 2002 Wiley-Liss, Inc.