Superparamagnetic iron oxide (SPIO) MRI contrast agent for bone marrow imaging: differentiating bone metastasis and osteomyelitis.

PURPOSE We explored appropriate scan timing for bone marrow imaging enhanced using superparamagnetic iron oxide (SPIO) and evaluated the usefulness of SPIO in differentiating metastasis and osteomyelitis in patients. METHODS To determine the adequate scan timing after administration of SPIO, 5 healthy subjects were examined using a 1.5T magnetic resonance (MR) imaging scanner. Sagittal images of their lumbar spines were obtained using short-TI inversion recovery (STIR) sequence before and 3, 6, 9, 24, and 48 hours after intravenous injection of 8 micromol Fe/kg SPIO (ferucarbotran). MR signal intensities (SIs) were evaluated. Based on the results, 12 patients, five with bone metastasis and seven with vertebral osteomyelitis, were examined using the same procedure before and 3 hours after intravenous injection of ferucarbotran at the same dose. SIs of the bone metastases, osteomyelitis, and surrounding normal bone marrow were measured, and relative enhancement (RE) was calculated for each lesion. RESULTS In the healthy volunteers, maximum reduction in signal was observed 3 to 24 hours (P<0.05) after administration of SPIO; thereafter and up to 48 hours, the SI gradually recovered. In the patients, the RE of the bone metastases was -12.2%, which was significantly higher than that in the osteomyelitis (-35.0%, P<0.001) and normal bone marrow (-46.6%, P<0.0005). CONCLUSION Maximum suppression of signal intensity in bone marrow was seen 3 hours after injection of ferucarbotran, the point at which ferucarbotran allows differentiation of bone metastasis from ostoemyelitis.