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Another Data Source
September 30, 2009

So far, we have discussed using medical images to extract human bone shapes for analysis. This is not, however, the only source of data for human bone shapes. Another accurate source of human bone geometry are human bones from human remains.

Actual samples of human bones are quite common since, of all the organs in the body, bones are the most durable. Skeletons can be recovered many years after the individual's death, as long as the body has not been cremated. They are also easy to handle and store and do not require as much care as other organs to maintain. For this reason, many human bone collections exists throughout the world for studies in anthropology, forensics, and medicine. The various collections are listed at this website.

Note that bony remains are very different that the actual living bone. Human bone is composed of living and non-living components. Living components include bone-depositing cells (osteoblasts), bone-resorbing (removing) cells (osteoclasts), blood vessels, and blood cells to name a few. The non-living tissue is a mixture collagen and hydroxyapatite and provides the structure and strength of the bone. This is the bony tissue that remains long after the living tissue has died.

human tibia samples

The image above shows 5 human tibia samples that have been cleaned for use in teaching. Preparing these samples is a labor intensive process. First, all the muscle, tendon, and ligament tissues must be removed from the bone. This is done through boiling, composting, or using dermestid beetles. Bones also store fat inside (yellow marrow), so they must be degreased. Finally, they are typically whitened using hydrogen peroxide before they are sold for academic use.

To create a digital model of the shape of the bone we use a FARO Laser ScanArm mounted on a FaroArm Quantum measuring arm. This system is simply a hand-held, 3D laser triangulation scanner that generates 3D position measurements on the surface of an object quickly and accurately. The principles of how it works is very simple: the scanner shines a laser beam, spread out in a thin line, on the object to be scanned. Then, a camera placed at a specific angle to the beam captures the image and looks for the bright red laser light. Using the angle between the beam and the camera and the position of the red beam in the camera image, a 3D point is computed where the surface of the object reflects the laser beam. A wonderful depiction of this is shown here. The images below show the scanner in action and the results on the computer screen.

scanner in action scanner screen shot

We have set up a lab to scan complete human skeletons such as the sample shown below. We are very near completion of our first, mostly complete skeleton (unfortunately, we are missing the skull, the sacrum, and one tibia).

scanned specimen scanned specimen detail

Our scanning sessions proceed as follows: in the morning, we check our e-mail or read the latest news while we sip our coffee and allow the laser scanner to warm up. Next, we recalibrate the scanner as seen below, on the left. Finally, we grab the next bone in the spreadsheet and begin to scan. Our spreadsheet is a template for a database we will design and build which will include, in addition to all of the bone shapes, the geographic origin of the specimen, sex, and age at death (if known), and tagged landmarks of salient anatomical features. We are also including some extra slots for anomalies--the specimen we are currently scanning, for example, has an extra pair of cervical ribs! This will require massive amounts of storage: our scan files run between 1 and 8 million vertices per bone!

calibration scanning a bone

We typically scan each bone twice, once from either side (for example, a superior and inferior view for a vertebra, or palmar and dorsal views for a metacarpal). There are, however, some bones which require more than two scans to capture all the nooks and crannies in their shape digitally (the triquetral, for example). Due to the scanning technology, some of the scans will invariably have holes where the laser light cannot reach. So far, this has only been the case for some of the cervical and thoracic vertebrae, but we expect to have the same issue with the skull. The scanning software provides features that allow us to clean up the scans and register the pieces together into the final product.


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