Feasibility Study of MRI Muscles Molecular Imaging in Evaluation of Early Post-Mortem Interval

Diffusion Tensor Imaging of Rat Rotator Cuff Muscle With Histopathological Correlation: An Exploratory Study

The purpose of this exploratory study was to quantify the relationship between scalar-based measures of diffusion tensor imaging (DTI) and histologically derived microstructural measurements in precisely colocalized rat rotator cuff muscle tissue and to compare the results when imaged at 0.25- and 0.5-mm isotropic resolutions. Four Lewis rats subject to a unilateral chronic massive rotator cuff tear model were evaluated on a 3-T preclinical MRI scanner using spin echo DTI sequences at 0.25- and 0.5-mm isotropic resolutions, and histology was subsequently performed. Fractional anisotropy (FA), mean diffusivity (MD), and radial diffusivity (RD) were calculated. Whole muscle myofiber boundary segmentation was performed, and muscle fiber diameter and cross-sectional area were calculated on slides that passed rigorous histologic quality control. Scatter plots were generated on a pixel-by-pixel basis from meticulously colocalized DTI and histology data. Pearson's correlations were performed. Twenty-two distinct supraspinatus and infraspinatus muscle locations from two rats were included. Negligible correlations were found between DTI metrics, including FA, MD, and RD, and histological measurements, including muscle fiber diameters and cross-sectional areas. Using the most commonly employed spin echo DTI sequences with intermediate diffusion times, there may be negligible sensitivity to direct measures of muscle tissue microstructure. Our findings underscore the need for further research with optimized imaging parameters to enhance our knowledge regarding the capability of DTI to determine important features of muscle microstructure.

Diffusion Tensor Imaging of Rat Rotator Cuff Muscle with Histopathological Correlation: An Exploratory Study

Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) technique that can be used to assess microstructural features of skeletal muscle that are related to tissue function. Although widely used, direct correlations between DTI derived metrics such as fractional anisotropy and spatially matched tissue microstructure assessed with histology have not been performed. This study investigated the relationship between scalar-based DTI measurements and histologically derived muscle microstructural measurements in rat rotator cuff muscles. Despite meticulous co-localization of MRI and histology data, negligible correlations were found between DTI metrics and histological measurements including muscle fiber diameter, cross-sectional area, and surface-to-volume ratio. These findings highlight the challenges in validating DTI with histology due to requirements in anatomical co-localization, necessity of high-quality histology, and consideration of diffusion measurement scales. Our findings underscore the need for further research with optimized imaging parameters to enhance our knowledge regarding the sensitivity of DTI to important features of muscle microstructure.

Magnetism of materials: theory and practice in magnetic resonance imaging

All substances exert magnetic properties in some extent when placed in an external magnetic field. Magnetic susceptibility represents a measure of the magnitude of magnetization of a certain substance when the external magnetic field is applied. Depending on the tendency to be repelled or attracted by the magnetic field and in the latter case on the magnitude of this effect, materials can be classified as diamagnetic or paramagnetic, superparamagnetic and ferromagnetic, respectively. Knowledge of type and extent of susceptibility of common endogenous and exogenous substances and how their magnetic properties affect the conventional sequences used in magnetic resonance imaging (MRI) can help recognize them and exalt or minimize their presence in the acquired images, so as to improve diagnosis in a wide variety of benign and malignant diseases. Furthermore, in the context of diamagnetic susceptibility, chemical shift imaging enables to assess the intra-voxel ratio between water and fat content, analyzing the tissue composition of various organs and allowing a precise fat quantification. The following article reviews the fundamental physical principles of magnetic susceptibility and examines the magnetic properties of the principal endogenous and exogenous substances of interest in MRI, providing potential through representative cases for improved diagnosis in daily clinical routine.