In Vivo and In Vitro Studies of the Steady State Free Precession-Diffusion-Weighted MR Imagings on Low b-value: Validation and Application to Bone Marrow Pathology

Byun, Woo Mok

Abstract

PURPOSE: The purpose of this study was a phantom study to measure the diffusion properties of water molecules by steady-state free precession diffusion-weighted imaging (SSFP-DWI) with a low b-value and to determine if this sequence might be useful for application to the evaluation of bone marrow pathology.
MATERIALS AND METHODS
1. The phantom study: A phantom study using two diffusion weighted sequences for the evaluation of the diffusion coefficient was performed. Three water-containing cylinders at different temperatures were designed: phantom A was 3degrees C, B was 23degrees C and C was 63degrees C. Both SSFP and echo planar imaging (EPI) sequences (b-value: 1000 s/mm2) were performed for comparison of the diffusion properties. The Signal to noise ratios (SNR) and apparent diffusion coefficient (ADC) values of the three phantoms using each diffusion-weighted sequence were assessed. 2. The Clinical study: SSFP-DWI was performed in 28 patients [sacral insufficiency fractures (10), osteoporotic lumbar compression fractures (10), malignant compression fractures (8)]. To measure the ADC maps, a diffusion-weighted single shot stimulated echo-acquisition mode sequence (650s/ mm2) was obtained using the same 1.5-T MR imager
RESULTS
For the phantom study, the signal intensity on the SSFP as well as the classic EPI-based DWI was decreased as the temperature increased in phantom A to C. The ADC values of the phantoms on EPI-DWI were 0.13x10(-3) mm2/s in phantom A, 0.22x10(-3) mm2/s in B and 0.37x10(-3) mm2/s. in C. The SSFP can be regarded as a DWI sequence in view of the series of signal decreases.
CONCLUSION
Bone marrow pathologies with different diffusion coefficients were evaluated by SSFP-DWI. All benign fractures were hypointense compared to the adjacent normal bone marrow where as the malignant fractures were hyperintense compared to the adjacent normal bone marrow.