Applications of Diffusion-Weighted MRI to the Musculoskeletal System

Diffusion-weighted imaging (DWI) is an established MRI technique that can investigate tissue microstructure at the scale of a few micrometers. Musculoskeletal tissues typically have a highly ordered structure to fulfill their functions and therefore represent an optimal application of DWI. Even more since disruption of tissue organization affects its biomechanical properties and may indicate irreversible damage. The application of DWI to the musculoskeletal system faces application-specific challenges on data acquisition including susceptibility effects, the low T2 relaxation time of most musculoskeletal tissues (2-70 msec) and the need for sub-millimetric resolution. Thus, musculoskeletal applications have been an area of development of new DWI methods. In this review, we provide an overview of the technical aspects of DWI acquisition including diffusion-weighting, MRI pulse sequences and different diffusion regimes to study tissue microstructure. For each tissue type (growth plate, articular cartilage, muscle, bone marrow, intervertebral discs, ligaments, tendons, menisci, and synovium), the rationale for the use of DWI and clinical studies in support of its use as a biomarker are presented. The review describes studies showing that DTI of the growth plate has predictive value for child growth and that DTI of articular cartilage has potential to predict the radiographic progression of joint damage in early stages of osteoarthritis. DTI has been used extensively in skeletal muscle where it has shown potential to detect microstructural and functional changes in a wide range of muscle pathologies. DWI of bone marrow showed to be a valuable tool for the diagnosis of benign and malignant acute vertebral fractures and bone metastases. DTI and diffusion kurtosis have been investigated as markers of early intervertebral disc degeneration and lower back pain. Finally, promising new applications of DTI to anterior cruciate ligament grafts and synovium are presented. The review ends with an overview of the use of DWI in clinical routine. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 3.

The Assessment of Prostate Cancer Aggressiveness Using a Combination of Quantitative Diffusion-Weighted Imaging and Dynamic Contrast-Enhanced Magnetic Resonance Imaging

Objective

To explore the value of combining dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) quantitative parameters with apparent diffusion coefficient (ADC) values in the diagnosis of prostate cancer.

Methods

The clinical data of 146 patients with prostate lesions, including 87 patients with prostate cancer (PCa) and 59 with benign prostatic hyperplasia (BPH), were collected. After DCE-MRI and diffusion-weighted imaging (DWI) prostate scans, the magnitude of the DCE-MRI transfer constant (K^trans), rate constant (k_ep), the volume of the extravascular extracellular space (v_e), and the ADC between the groups were compared, and the correlations between the DCE-MRI parameters and Gleason scores were analyzed. The diagnostic efficacy of these quantitative parameters was assessed by the area under the receiver operating characteristic (ROC) curve.

Results

The DCE-MRI parameters K^trans and k_ep were significantly greater in the PCa group than in the BPH group (p < 0.05). The ROC curve showed the area under the K^trans, k_ep, and ADC curves to be 0.665, 0.658, and 0.782, respectively. When all three quantitative indicators were combined, the area under the ROC curve was 0.904, with sensitivity and specificity rates of 83.6% and 93.7%, respectively. The Gleason scores were positively correlated with the K^trans, k_ep, and v_e (r = 0.39, 0.572, 0.30, respectively; p < 0.05) and negatively correlated with the ADC (r = –0.525; p < 0.05).

Conclusion

The DCE-MRI quantitative parameters K^trans and k_ep, as well as the ADC value, provided effective references for the differential diagnosis of PCa and BPH, as well as more precise and reliable quantitative parameters for grading the aggressiveness of PCa.

Effects of gadoxetic acid on quantitative diffusion-weighted imaging of the liver

PURPOSE

To prospectively evaluate the effect of gadoxetic acid (Gd-EOB-DTPA; Primovist, Bayer-Schering, Berlin, Germany) on quantitative diffusion-weighted imaging (DWI) using the Le Bihan IntraVoxel Incoherent Motion model and considering separately the following parameters: slow diffusion coefficient (D), fast diffusion coefficient (D*), perfusion fraction (PF), and apparent diffusion coefficient (ADC).

MATERIALS AND METHODS

Twenty-four consecutive patients were submitted to the same magnetic resonance (MR)-DWI acquisition before and after gadoxetic acid administration. Patients were divided into four groups according to the time at which the DW sequence was repeated, then 5, 10, 15, 20 minutes after contrast agent administration. A total of 48 manually drawn regions of interest (ROIs) of about 1200 pixels were placed in the middle right liver lobe. The mean and standard deviation (SD) were calculated in each group/patient for every DWI-related parameter. Analysis of variance was performed (threshold P = 0.05). Bonferroni and Games-Howell post-hoc tests were applied if significant differences were found among groups; otherwise, data were averaged together.

RESULTS

D, D*, PF, and ADC did not show any significant difference before and after contrast agent administration, at any time.

CONCLUSION

It is possible to perform DW acquisitions after gadoxetic acid administration without any significant variation of the values of DW-related parameters under consideration in this study.