The value of fast and ultrafast T2-weighted MR imaging sequences in hepatic enhancement with ferumoxides: comparison with conventional spin-echo sequence.

PURPOSE: The efficacy of superparamagnetic iron oxide (SPIO) was evaluated with fast T2-weighted imaging sequences such as turbo spin-echo (TSE), half-Fourier single shot turbo spin echo (HASTE), and echo-planar imaging (EPI) in comparison with the conventional spin-echo (SE) sequence on a 1.5 Tesla MR unit. MATERIALS AND METHODS: In a phantom study, we prepared vials containing different concentrations of ferumoxides (0, 0.25, 0.5, 0.75, and 1 micromol Fe) in 2% agarose simulating the liver. In an animal study, contrast medium in doses of 10, 20, and 30 micromol/kg of ferumoxides was injected into the ear vein of rabbits weighing 3.0-4.0 kg under general anesthesia. MR imaging of the phantom and liver of the rabbits was obtained with the T2-weighted SE sequence (TR/TE=2000/20, 80), TSE sequences (TR/effective TE=2000/90, echo train length=7), HASTE (effective TE=64, 90 msec), and EPI (effective TE=64, 90 msec). Three rabbits in each group were imaged before and 1 hour after ferumoxides administration for in-vivo study. The Signal intensity of pre- and postcontrast imaging of the phantom or rabbits' livers was measured with operator-defined regions of interest, and signal-to-noise ratios (SNR) were obtained. Immediately after imaging, the rabbits were sacrificed and the livers were removed at autopsy, followed by ex-vivo study. In a clinical study, 10 micromol/kg of ferumoxides was given in 34 consecutive patients with 31 solid tumors. The liver SNR were evaluated for all 34 patients, and tumor to-liver contrast-to-noise ratios (CNR) were evaluated for all 31 solid lesions. The same series of imaging techniques as in the experimental studies was performed for quantitative and qualitative analyses. RESULTS: In both in-vitro and in-vivo studies, SNR of the phantom or rabbits' livers significantly decreased after ferumoxides administration. The decrease in SNR on excised rabbits' livers was 72% for EPI, 36% for HASTE, 61% for SE, and 51% for TSE at a dose of 10 micromol/kg of ferumoxides. In the clinical study, HASTE and TSE showed significant improvement in CNRs after ferumoxides administration (p<0.05). Visual analysis revealed improvement in tumor detection for all sequences. On EPI, although contrast was excellent, severe image distortion was seen. Although the signal decrease with HASTE and TSE was somewhat inferior to those with EPI and SE, respectively, the effect of contrast enhancement on HASTE and TSE was marked on visual analysis. CONCLUSION: Although TSE sequences and HASTE sequences are less susceptible to magnetic field inhomogeneities than SE and EPI sequences, the decrease in liver signal on HASTE and TSE sequences was comparable to that on EPI and SE sequences, respectively. These sequences are useful clinically for ferumoxides imaging, because they are less sensitive to motion artifacts.