Diffusion tensor imaging beyond brains: Applications in abdominal and pelvic organs

Does liver diffusion tensor imaging (L-DTI) has a role in differentiation of hepatic focal lesions? Analytic study for assessment of the value of L-DTI in differentiating hepatic focal lesions according to LI-RADS

Background

Magnetic resonance imaging (MRI) plays an important role in the differentiation of hepatic focal lesions and diagnosis of hepatic malignancy, especially hepatocellular carcinoma which is a major health problem worldwide. Diffusion imaging is a functional MRI technique that became an essential part of MRI study of the liver. Recently, diffusion tensor imaging (DTI) is diffusion variant that can provide more information than conventional diffusion imaging based on the tissue anisotropy. The aim of this study was to present the role of DTI in the assessment and differentiation between hepatic focal lesions.

Results

Fifty-one patients having 95 hepatic focal lesions who underwent dynamic MRI with conventional diffusion imaging and DTI acquisition were included in the study. A positive moderate significant correlation was found between Fractional anisotropy (FA) values and Liver Imaging Reporting and Data System (LI-RADS) category while substantial negative significant correlation and moderate negative significant correlation were found between DTI-ADC and DWI-ADC values, respectively, with the LI-RADS category. There was a significant negative correlation between DTI-ADC and FA values. DTI-ADC showed a significant role in differentiation of benign from malignant lesions with cut-off value 0.905 × 10−3 having 88.7% sensitivity and 88.3% specificity compared to 78.5% and 68.7% for DWI-ADC, respectively. Also, it was found that FA value had a significant role in differentiation between benign and malignant lesions with cut-off value 0.34 having 87.1% sensitivity and 73.9% specificity.

Conclusions

DTI can be included in liver MRI studies for better tissue characterization as it may perform better than conventional DWI with higher sensitivity and specificity of DTI-ADC and FA values than conventional DWI-ADC.

The Role of Non-Gaussian Models of Diffusion Weighted MRI in Hepatocellular Carcinoma: A Systematic Review

The importance of Diffusion Weighted Imaging (DWI) in hepatocellular carcinoma (HCC) has been widely handled in the literature. Due to the mono-exponential model limitations, several studies recently investigated the role of non-Gaussian DWI models in HCC. However, their results are variable and inconsistent. Therefore, the aim of this systematic review is to summarize current knowledge on non-Gaussian DWI techniques in HCC. A systematic search of the literature, including PubMed, Google Scholar, MEDLINE, and ScienceDirect databases, was performed to identify original articles since 2010 that evaluated the role of non-Gaussian DWI models for HCC diagnosis, grading, response to treatment, and prognosis. Studies were grouped and summarized according to the non-Gaussian DWI models investigated. We focused on the most used non-Gaussian DWI models (Intravoxel Incoherent Motion (IVIM), Diffusion Kurtosis Imaging (DKI), and Stretched Exponential—SE). The quality of included studies was evaluated by using QUADAS-2 and QUIPS tools. Forty-three articles were included, with IVIM and DKI being the most investigated models. Although the role of non-Gaussian DWI models in clinical settings has not fully been established, our findings showed that their parameters may potentially play a role in HCC. Further studies are required to identify a standardized DWI acquisition protocol for HCC diagnosis, grading, response to treatment, and prognosis.

Diffusion tensor-based fiber tracking of the male urethral sphincter complex in patients undergoing radical prostatectomy: a feasibility study

Objectives

To study the diffusion tensor-based fiber tracking feasibility to access the male urethral sphincter complex of patients with prostate cancer undergoing Retzius-sparing robot-assisted laparoscopic radical prostatectomy (RS-RARP).

Methods

Twenty-eight patients (median age of 64.5 years old) underwent 3 T multiparametric-MRI of the prostate, including an additional echo-planar diffusion tensor imaging (DTI) sequence, using 15 diffusion-encoding directions and a b value = 600 s/mm². Acquisition parameters, together with patient motion and eddy currents corrections, were evaluated. The proximal and distal sphincters, and membranous urethra were reconstructed using the deterministic fiber assignment by continuous tracking (FACT) algorithm, optimizing fiber tracking parameters. Tract length and density, fractional anisotropy (FA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD) were computed. Regional differences between structures were accessed by ANOVA, or nonparametric Kruskal–Wallis test, and post-hoc tests were employed, respectively, TukeyHSD or Dunn’s.

Results

The structures of the male urethral sphincter complex were clearly depicted by fiber tractography using optimized acquisition and fiber tracking parameters. The use of eddy currents and subject motion corrections did not yield statistically significant differences on the reported DTI metrics. Regional differences were found between all structures studied among patients, suggesting a quantitative differentiation on the structures based on DTI metrics.

Conclusions

The current study demonstrates the technical feasibility of the proposed methodology, to study in a preoperative setting the male urethral sphincter complex of prostate cancer patients candidates for surgical treatment. These findings may play a role on a more accurate prediction of the RS-RARP post-surgical urinary continence recovery rate.