The distribution of the magnetic field in the spine depends on the composition of bone marrow.

Although the composition of bone marrow with hemopoietic cells, fat cells, and extracellular fluid can be roughly assessed by standard MR-imaging techniques and especially water and lipid-selective chemical-shift-imaging methods, a new approach to the characterization of the magnetic properties of marrow was performed by special field-mapping techniques. The distribution of the magnetic field inside and outside vertebral bodies containing paramagnetic substances was systematically studied for phantoms and by measurements in vivo. Nineteen healthy volunteers and 26 patients with alterations of the bone marrow due to hematologic disease were examined. The amount of paramagnetic substances in the marrow was estimated by measuring steps of Larmor frequency of the water resonances at the transition between vertebral bodies and adjacent intervertebral disks. These frequency steps were exhibited by MAGSUS imaging on a 1.5 Tesla whole-body imager. Additional volume-localized 1H spectroscopy allowed a more quantitative assessment of the spectral components. The measured frequency steps of the water resonances ranged between 0 and 26 Hz for the healthy volunteers examined. In contrast, patients with pathologically altered marrow and high amount of paramagnetic substances revealed frequency steps of up to 85 Hz. The frequency steps in 8 patients after bone marrow transplantation (BMT) with slow reconstitution (mean 48.9 Hz, standard deviation (s.d.) 21.7 Hz) were significantly (p < 0.001) higher than in normal volunteers. Seven BMT patients with good reconstitution (frequency steps: mean 16.7 Hz, s.d. 13.9 Hz) were not clearly different from the healthy subjects. Six patients with acute leukemia showed significantly (p < 0.01) increasing frequency steps during initial cytotoxic treatment: The frequency steps increased from a mean of 4.7 Hz (s.d. 2.7 Hz) before treatment to a mean of 30.2 Hz (s.d. 14.6 Hz) after a few months of therapy.