Biology Reference
In-Depth Information
CT and Geometric Morphometrics
Geometric morphometric techniques based on bony landmarks are replacing traditional
linear measurement as the preferred method of capturing cranial shape and size. This can
be accomplished by using a 3-D digitizer to capture the landmarks in a Cartesian coordinate
system (i.e., x, y, z) or by using laser surface scans. The advantages to a landmark approach
are that it can be much less expensive than using medical imaging and the methods therein
are more readily available to most skeletal biologists. Studies have used a geometric morpho-
metric approach to analyze the three-dimensional form of the vertebrae, os coxa, and femur,
to mention just a few (
Manfreda et al., 2006; Gu et al., 2008; De Groote et al., 2010
). The
requirement of corresponding landmarks, however, has made the application of these tech-
niques to the post-crania difficult since most long bones lack sufficient, well-defined land-
marks. See McKeown and Schmidt (Chapter 12), this volume, for more information on
geometric morphometrics. Computed tomography scanning provides data potentially suit-
able for the application of geometric morphometric techniques to post-cranial elements,
but has the added benefit of visualizing the internal structure, which is not possible from
most geometric morphometric methods.
Peripheral Quantitative Computed Tomography (pQCT) and Micro-CT
Two different variations of CT that may be of interest to the skeletal biologist are micro-
CTand pQCT. Micro-CT provides extremely high resolution, as small as 1
m, but the level
of radiation at this resolution is lethal to living subjects. This method could be extremely
valuable for nondestructive histological analysis of skeletal samples. One study compared
micro-CT to histological analysis of osteochondritis dissecans (a disease in a joint caused by
avascular necrosis or loss of blood supply) in three subjects and found it of great speed and
utility, though they were not able to image cells or different tissue types (
Mohr et al., 2003
).
Compared to DEXA, peripheral quantitative computed tomography (pQCT) allows for
the assessment of trabecular and cortical bone separately, and the ability to measure the volu-
metric density. The pQCT is often used to take bone mineral density readings of the smaller
peripheral parts of the body (e.g., arms, hands, and feet). The pQCT has lower radiation than
CT, but with higher precision and higher predictive capabilities for peripheral fractures
(
Groll et al., 1999
). The pQCT is only able to measure the smaller peripheral appendages
of a living individual or just a portion of a dry long bone. This method works well for
comparing shape variation of the hands and feet in living subjects.
Briggs and colleagues
(2010)
compare the quality and the advantages and disadvantages of bone mineral density
calculations of the vertebrae from DEXA, pQCT, and micro-CT.
m
CASE STUDY: FUNCTIONAL MORPHOLOGY, CT, AND BONE
DENSITY IN ACTION
Research questions from a perspective of functional morphology tend to be considerable
undertakings. The researcher should have an understanding of biomechanics, bone biology,
and the different medical imaging methods available to best suit the study. A study that
