Abstract
Image registration is crucial in multimodal longitudinal skeletal muscle Magnetic Resonance Imaging (MRI) studies to extract reliable parameters that can be used as indicators for physio/pathological characterization of muscle tissue and for assessing the effectiveness of treatments. This paper aims at proposing a reliable registration protocol and evaluating its accuracy in a longitudinal study. The hips of 6 subjects were scanned, in a multimodal protocol, at 2 different time points by a 3 Tesla scanner; the proposed multi-step registration pipeline is based on rigid and elastic transformations implemented in SimpleITK using a multi-resolution technique. The effects of different image pre-processing (muscle masks, isotropic voxels) and different parameters’ values (learning rates and mesh sizes) were quantitatively assessed using standard accuracy indexes. Rigid registration alone does not provide satisfactory accuracy for inter-sessions alignment and a further elastic step is needed. The use of isotropic voxels, combined with the muscle masking, provides the best result in terms of accuracy. Learning rates can be increased to speed up the process without affecting the final results. The protocol described in this paper, complemented by open-source software, can be a useful guide for researchers that approach for the first time the issues related to the muscle MR image registration.
Highlights
Skeletal muscle is one of the largest tissues of the body, accounting for approximately 45–50% of body mass, and besides its main biomechanical role in locomotion, it is involved in physiological and pathological metabolic processes, such as oxygen (O2 ) consumption, energy metabolism, and substrate turnover and storage, and it is the major protein reserve of the human body [1,2]
Absorptiometry (DXA) [5], and Magnetic Resonance Imaging (MRI) [6], allow to non-invasively evaluate skeletal muscle morphological and functional properties related to a broad spectrum of conditions
Regarding the Hausdorff distance (HD), the values exhibited a wider variability among subjects, but again Isotropic voxels with mask (IM) and NM schemes were the best choice
Summary
Skeletal muscle is one of the largest tissues of the body, accounting for approximately 45–50% of body mass, and besides its main biomechanical role in locomotion, it is involved in physiological and pathological metabolic processes, such as oxygen (O2 ) consumption, energy metabolism, and substrate turnover and storage, and it is the major protein reserve of the human body [1,2]. Medical imaging techniques, such as Computed Tomography (CT) [3], Ultrasound (US) [4], Dual-Energy X-ray. Sci. 2020, 10, 7823 dystrophies [10,11], and atrophy [12], and can be used to assess the outcome of motor rehabilitation after an adverse event [13]
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