Influence of magnetic field strength on t2* decay and phase effects in gradient echo mri of vertebral bone marrow

Objective: The goal of this study was twofold: First, to quantify the influence of magnetic field strength (fl₀) on T2* and T2_susceptibmty relaxation rates in vertebral bone marrow; and second, to determine the significance of in-phase/ out-of-phase phenomena in GE MRI as a function of TEs at different B₀ values. Materials and Methods: Magnetic resonance imaging of the spine was performed at 1.5, 1.0, and 0.2 T using a GE sequence (2D-FLASH) with variable TE. Vertebral body signal intensities were measured and plotted against TE values. These curves were used to calculate T2* decay of bone marrow at different B₀ values. Results: At all field strengths, we observed exponential signal decay, modulated by a cosine function, the periodicity of which was proportional to B₀. The T2* values of vertebral bodies were 9.7 ± 1.8 ms at 1.5 T, 17.2 ± 2.4 ms at 1.0 T, and 53 ± 5 ms at 0.2 T. True T2 relaxation time (independent of field strength) was 62 ± 4 ms. The T2_susccptibmty was 11.7 ms at 1.5 T, 24.8 ms at 1.0 T, and 585 ms at 0.2 T. Conclusion: We conclude that at low B₀, susceptibility effects become less important and T2* approaches true T2 relaxation.