Magnetic resonance elastography studies of human skeletal muscle
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Date
02/07/2016Item status
Restricted AccessEmbargo end date
31/12/2100Author
Kennedy, Paul
Metadata
Abstract
A robust, reliable method to non-invasively measure in-vivo mechanical properties of large
tissue areas was unavailable until the advent of a new Magnetic Resonance Imaging (MRI)
technique known as Magnetic Resonance Elastography (MRE). MRE is a phase-contrast
imaging technique that enables quantification of tissue mechanical properties by capturing
the motion of induced shear waves via a synchronised Motion Encoding Gradient (MEG). The
complex shear modulus is determined via mathematical inversion and reported as the
magnitude of the complex shear modulus, |G*|, and phase angle, φ.
The work reported in this thesis focuses on the development of MRE data acquisition and
analysis protocols optimised to study thigh muscle mechanical properties. The protocols are
subsequently applied in healthy volunteers to study natural phenomena such as contraction
and ageing and interventions such as an experimental protocol to produce Exercise Induced
Muscle Damage (EIMD).
Methodological advances made throughout this work include moving from 2D to 3D MRE
data acquisition protocols and the application of advanced inversion software to extract
muscle viscoelastic properties from the acquired MRE data. Results obtained include
observation of reduced muscle stiffness in 6 elderly subjects (>80 years old) compared to 4
young subjects in the Vastus Lateralis (32%), quadriceps muscle group (22%) and entire thigh
cross-section (19%), higher resting stiffness of agonist quadriceps compared to antagonist
hamstrings (18%) and an increase in quadriceps stiffness (40%) during a leg raise task in 11
healthy subjects. Variability in muscle group recruitment patterns during the contraction
were also observed, with the phase angle of the Vastus Intermedius (VI) increasing
significantly during contraction. The final experiment involved the recruitment of 20 healthy
male subjects to perform an eccentric exercise protocol designed to induce EIMD. Subjects
who displayed a Maximum Voluntary Contraction (MVC) force deficit of >10% were
considered to have experienced EIMD. A further severe EIMD group were defined based on
the presence of hyper-intense signal on T2 weighted imaging following the protocol. The T2
hyper-intensity was found to occur exclusively in the Rectus Femoris (RF) and VI muscle
groups. Increased muscle stiffness was observed in the RF muscle in subjects who
experienced moderate EIMD (6%). A greater increase in RF stiffness (48%) was observed in
the severe EIMD group. The severe EIMD group also displayed significantly increased VI
stiffness (14%).
The experiments carried out provide several novel findings which can support the
development of beneficial strategies to promote both healthy ageing and rehabilitation in
athletes, and potentially contribute to improving muscle performance evaluation tests which
will expand the opportunities for clinical applications of muscle MRE.