Gradient-echo imaging of hemorrhage at 1.5 Tesla

We report in vitro and in vivo MR studies of hemorrhage using the gradient-echo pulse sequence, FISP (steady state free precession) and FLASH (spoiling of transverse magnetization) at 1.5 Tesla. Phantoms containing methemoglobin, ferromagnetic particles, human serum and blood clot were scanned using both spin-echo and gradient-echo techniques. FLASH signal intensities were more sensitive to methemoglobin concentration than high T₁-weighted spin-echo images. FISP showed little change in signal intensity with varying concentrations of methemoglobin and a contrast relationship similar to T₂-weighted spin-echo techniques. FISP and FLASH showed intensity changes at lower concentrations of ferromagnetic material than T₂-weighted spin-echo sequences. In vitro blood clot was less intense when observed by FISP and FLASH sequences than on the T₂-weighted spin-echo sequences. Maximum contrast between clot and other blood components occurred at a flip andle of 45° for FLASH and 60° for FISP. FISP and FLASH scans of patients with hemorrhage demonstrated a marked decrease in signal intensity in the region of blood clot. This decrease was more pronounced with the gradient-echo sequences than with T₂-weighted spin-echo images. We conclude that FLASH is useful for detecting methemoglobin and that both FISP and FLASH are useful for evaluating hemorrhage because of their sensitivity to methemoglobin.