Optimization of b value in diffusion-weighted MRI for the differential diagnosis of benign and malignant vertebral fractures.

OBJECTIVE

The objective was to explore the optimal b value in diffusion-weighted imaging (DWI) of MRI for differential diagnosis of benign and malignant vertebral fractures.

MATERIALS AND METHODS

Thirty-four consecutive patients with vertebral compression fractures underwent sagittal diffusion-weighted imaging (DWI) with different b values. The group included 14 patients with 18 benign vertebral fractures due to osteoporosis and/or trauma and 20 patients with 27 malignant vertebral fractures due to malignancy. The quality of the images was analyzed qualitatively on a three-point scale and quantitatively by measurement of the signal-to-noise ratio (SNR). Apparent diffusion coefficient (ADC) values were also calculated.

RESULTS

Smaller b values correlated with better DW image quality. We found significant differences in the qualitative points values among the DW images with different b values (F=302.18, p<0.001). The mean SNR of the images ranged from 21.75+/-3.64 at a b value of 0 s/mm2 to 5.31+/-3.17 at a b value of 800 s/mm2. The SNR of DWI with a b value of 300 s/mm2 (18.62+/-2.47) was significantly different from that with other b values (p<0.01). The mean combined ADC values of malignant fractures were significantly lower than those of benign ones on DWI with a b value of 300 s/mm2 (t=9.097, p<0.01). Four cases of benign vertebral fractures were misdiagnosed as being malignant when b values of 0 s/mm2 and 100 s/mm2 were used.

CONCLUSIONS

When DWI with multiple b values is used to differentiate benign from malignant vertebral compression fractures, b values within the range of around 300 s/mm2 are recommended, taking into account both SNR and diffusion weighting of water molecules.