Texture analysis of magnetic resonance images of rat muscles during atrophy and regeneration

doi:10.1016/j.mri.2005.10.002

Magnetic Resonance Imaging

Volume 24, Issue 2, February 2006, Pages 167-171

https://doi.org/10.1016/j.mri.2005.10.002 Get rights and content

Abstract

Objectives

The goals of the current study were (i) to introduce texture analysis on magnetic resonance imaging (MRI-TA) as a noninvasive method of muscle investigation that can discriminate three muscle conditions in rats; these are normal, atrophy and regeneration; and (ii) to show consistency between MRI-TA results and histological results of muscle type 2 fibers' cross-sectional area.

Method

Twenty-three adult female Wistar rats were randomized into (i) control (C), (ii) immobilized (I) and (iii) recovering (R) groups. For the last two groups, the right hind limb calf muscles were immobilized against the abdomen for 14 days; then, the hind limb was remobilized only for the R group for 40 days. At the end of each experimental period, MRI was performed using 7-T magnet Bruker Avance DRX 300 (Bruker, Wissembourg); T1-weighted MRI acquisition parameters were applied to show predominantly muscle fibers. Rats were sacrificed, and the gastrocnemius muscle (GM) was excised immediately after imaging. (A) Histology: GM type 2 fibers (fast twitch) were selectively stained using the adenosine triphosphatase (ATPase) technique. The mean cross-sectional areas were compared between the three groups. (B) Image analysis: regions of interest (ROIs) were selected on GM MR images where statistical methods of texture analysis were applied followed by linear discriminant analysis (LDA) and classification.

Results

Histological analysis showed that the fibers' mean cross-sectional areas on GM transversal sections represented a significant statistical difference between I and C rats (ANOVA, P<.001) as well as between R and I rats (ANOVA, P<.01), but not between C and R rats. Similarly, MRI-TA on GM transversal images detected different texture for each group with the highest discrimination values (Fisher F coefficient) between the C and I groups, as well as between I and R groups. The lowest discrimination values were found between C and R groups. LDA showed three texture classes schematically separated.

Conclusion

Quantitative results of MRI-TA were statistically consistent with histology. MRI-TA can be considered as a potentially interesting, reproducible and nondestructive method for muscle examination during atrophy and regeneration.

Introduction

Although atrophy has been observed as a post-immobilization drawback in muscles, immobilization remains a frequently used clinical process in musculoskeletal injuries. Previous studies on animal using cast immobilization have shown that the severity of atrophic changes depends on muscle composition (slow or fast twitch) [1], immobilization position (extended or shortened) [2] and duration [3]. Histological results concerning muscle atrophy and regeneration are not always convergent, probably due to the diversity of animal model, immobilization method and analysis procedures.

Measurements of relaxation times T₁ and T₂ in magnetic resonance imaging (MRI) have been suggested to characterize myopathy and training effects in vivo [4], [5]. However, authors did not always find a significant correlation between biopsy analysis and relaxation time measurements of dystrophic human muscles [6]. Texture analysis (TA) is a method of image analysis that has been first applied on satellite images before it was implemented on MR images [7]. An MRI signal belonging to a certain component of tissue can predominate other signals of other components if the proper acquisition parameter are selected. In addition, TA is characterized by its high sensitivity, specificity and its reproducibility. These factors made texture analysis on Magnetic Resonance Imaging (MRI-TA) a promising method for noninvasive studies. In muscle studies, MRI-TA was able to discriminate normal from dystrophic tissues with sensitivity higher than that of the human eye [8]. Moreover, MRI-TA was able to discriminate different types of bovine muscles of different genetic origin with results statistically consistent with fat and collagen quantitative chemical contents [9]. Although there are evidences that MRI-TA is directly influenced by muscle structure and composition, the interpretation of its patterns is still rather speculative. To our knowledge, no previous studies tended to correlate between muscle histology and MRI-TA results.

The goals of the current study were (i) to introduce MRI-TA as a noninvasive method of muscle investigation that can discriminate three muscle conditions in rats; these are normal, atrophy and regeneration; and (ii) to show consistency between MRI-TA results at square-pixel resolution and histological results of muscle fibers' cross-sectional area at optical microscopy scale. For this purpose, we are going to use an experimental model of rat gastrocnemius muscle (GM) during atrophy and regeneration induced by cast immobilization and free-cage recovery, respectively. We have chosen the GM in this study as it is sensitive to immobilization and is known to respond well to recovery [10]. Moreover, it represents a recognizable form and size on MR transversal images adequate for our study.

Section snippets

Animals and immobilization technique

Twenty-four adult Wistar female rats weighing 200±7 g were randomized into control group (C) composed of 8 rats and one test group of 15 rats. Under anesthesia (pentobarbital 40 mg/kg ip), the right hind limb was immobilized against the abdomen so that the GM is maintained in the dorsal flexion position. The cast is composed of water hardening heavy bandage with small amount of quinine sulfate solution to inhibit rats from damaging the bandage. The test rats were housed in individual cages and

Histological analysis

Under light microscopy, the GM appears to be composed of two regions: a homogenous region (80% of the total area) of type 2 fibers only and a heterogeneous region (20% of the total area) including both type 2 fibers (80%) and type 1 fibers (20%). The mean cross-sectional area of type 2 fibers only was calculated for each histological section (Table 1). For the three groups, no inflammation or signs of necrosis were observed. One histological section belonging to the C group was removed from the

Discussion and conclusion

In this work, we used two different methods to quantify GM modifications after cast immobilization followed by free-cage recovery in Wistar rats. The first method was the conventional histological analysis of type 2 fibers' cross-sectional areas for normal, immobilized and remobilized muscles, which gave results similar to previous works in the literature: authors have detected a significant decrease in the fibers' mean cross-sectional area after experimental immobilization of the GM in rats

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Original contributionTexture analysis of magnetic resonance images of rat muscles during atrophy and regeneration

Abstract

Objectives

Method

Results

Conclusion

Introduction

Section snippets

Animals and immobilization technique

Histological analysis

Discussion and conclusion

Magn Reson Imaging

Neuromuscul Disord

Magn Reson Imaging

Magn Reson Imaging

Magn Reson Imaging

Muscle fiber atrophy and degeneration induced by experimental immobility and hindlimb suspension

Int J Sports Med

Collagen synthesis and proteolytic activities in rat skeletal muscles: effect of cast-immobilization in the lengthened and shortened positions

Arch Phys Med Rehabil

Original contribution
Texture analysis of magnetic resonance images of rat muscles during atrophy and regeneration