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Visualising the 3D anatomy and muscle architecture of the human foot using MRI and fibre-tracking software for education and research

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Abstract

The amount and value of digital resources available for anatomical education and research is continuously growing with more advanced imaging technologies. Computed tomography (CT) and magnetic resonance imaging (MRI) have been used extensively in anatomy to build 3D models and compare digital dissection methods with traditional dissection. Diffusible iodine contrast-enhanced computed tomography (diceCT) is becoming a valuable tool to visualise and reconstruct soft-tissue anatomy of smaller structures, including muscle fascicles. However, the preparation for diceCT is time consuming and often requires multiple test scans to determine if the desired level of straining has been reached for maximum soft-tissue contrast. Here, we test if high resolution MRI can achieve similar results for visualising muscle fibres. We scanned and digitally segmented the tendons and intrinsic muscles of the foot and used algorithmic fibre-tracking software to visualise the muscle fibres as curved cylinders. Fibre-specific information, such as length and orientation, was gathered, as well as muscle-wide information of muscle architecture by modelling numerous fibres within a whole muscle. We then compared these results with length, mass and pennation angle measured from the dissection of the left and right foot of two individuals, including the specimen that was scanned. The digital fibres required some editing to remove obvious traces that were not part of the muscles; however, we found that the length of the digital fibres were within mm of the results obtained from dissection, and in agreement with measurements in the literature. The values for muscle volume and mass were also similar, although the volume was consistently higher for all muscles. This method has allowed comprehensive quantitative and qualitative visual data to be collected that could aid in biomechanical modelling and understanding individual anatomical variation. The volume and fibre models are also an excellent teaching resource for anatomical and medical education as both digital and printed models. This research was conducted with ethical approval from The University of Liverpool’s Central University Research Ethics Committee, reference number 5844.
Visualising the 3D anatomy and muscle architecture of the human foot
using MRI and fibre-tracking software for education and research
Alana C. Sharp1, Misha Folker2, Oliver McHugh2, Andrew Fisher3
1Institute of Life Course and Medical Sciences, University of Liverpool, Liverpool, UK, @AlanaCSharp; 2School of Life
Sciences, University of Liverpool, Liverpool, UK; 3Human Anatomy Resource Centre, University of Liverpool, Liverpool, UK
Introduction
Computed tomography (CT) and magnetic resonance imaging (MRI) have been used extensively in anatomy to build 3D
models and compare digital dissection methods with traditional dissection. Diffusible iodine contrast-enhanced computed
tomography (diceCT) is becoming a valuable tool to visualise and reconstruct soft-tissue anatomy of smaller structures,
including muscle fascicles [1,2]. However, the preparation for diceCT is time consuming and often requires multiple test
scans to determine if the desired level of straining has been reached for maximum soft-tissue contrast. Here, we test if high
resolution MRI can achieve similar results for visualising muscle fibres.
Abductor digiti minimi
Flexor digitorum brevis
Abductor hallucis
Quadratus plantae
Flexor digiti minimi brevis
Interossei
Adductor hallucis oblique head
Flexor hallucis brevis
Materials & Methods
Scanning
A formalin fixed right foot and ankle was
scanned using a Siemens 3.0T Prisma. A
T2 weighted sequence with water excitation
(Fig.1A) and without water excitation
(Fig.1B) were used in order to more clearly
visualise the bones and muscles
respectively. The voxel size was 0.5 x 0.5 x
0.5 mm.
Segmentation and fibre tracking
The scans were loaded in Avizo (Thermo
Fisher Scientific) and each bone and
muscle was segmented using a
combination of automatic and manual
selection tools. For fibre tracking, the
segmented muscle volumes were combined
with the MRI to isolate each muscle. A
Cylinder Correlation module was then used
to set parameters for approximate fibre
length and radius to more clearly define the
fibres. A Trace Correlation Lines module
was then added to the output “correlation
fields” data to trace each fibre, specifying
settings for densely packed fibres and if
fibres were more or less straight. The
resulting cylinders could then be used to
estimate average fibre length and
orientation for each muscle.
A
B
Figure 1. T2 weighted MRI of right foot
Results
Most of the muscles and tendons
were visualised and segmented
successfully the lumbricals could
not be identified. An accessory flexor
digitorum longus muscle was also
identified.
Fibre tracking was successful and
the mean fibre length for each
muscle agreed with measurements
taken from dissection and compared
with the literature [3].
Outcomes and conclusions
The amount and value of digital resources available for
anatomical education and research is continuously
growing with more advanced imaging technologies.
This method has allowed comprehensive quantitative
and qualitative visual data to be collected that could aid
in biomechanical modelling and understanding
individual anatomical variation. The volume and fibre
models are also an excellent teaching resource for
anatomical and medical education as both digital and
printed models.
Volumetric model
Fibre model
Acknowledgments and references
This research was conducted with ethical approval from The University of Liverpool’s
Central University Research Ethics Committee, reference number 5844, and we would
like to thank the donors and their families for their valuable contribution.
1. Gignac PM, Kley NJ, Clarke JA, et al. (2016) Diffusible iodine-based contrast-enhanced
computed tomography (diceCT): an emerging tool for rapid, high-resolution, 3-D imaging of
metazoan soft tissues. J Anatomy, 228, 889-909.
2. Dickinson E, Stark H, Kupczik K (2018) Non-Destructive Determination of Muscle
Architectural Variables Through the Use of DiceCT. The Anatomical Record, 301, 363-377.
3. Kura H, Luo Z-P, Kitaoka HB, An K-N (1997) Quantitative analysis of the intrinsic muscles
of the foot. The Anatomical Record, 249, 143-151.
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