Transcript Medical Imaging and Anatomy - Computer Graphics at Stanford

Medical Imaging and Anatomy
Mike Houston, Anthony Sherbondy,
Ruwen Hess
Where do the pictures come from?
• The imagination
• Dissection
• X-ray, CT, MRI, Cryosection, PET/SPECT,
etc.
X-Ray Transmission Imaging
• Shoot x-rays through the patient onto detector film.
• Different tissues absord and deflect x-rays to
different degrees. The film is exposed less when xrays encounter higher density material like bone.
• Low resolution. Hard to distinguish between blood
vessals and tissue without an injection of iodine or
barium
Computed Tomography (CT)
• Sort of a 3D x-ray. An x-ray emitter is rotated
around the patient and a receiver measures the
intensity of the transmitted rays from different
angles
• Uses an electronic receiver instead of film.
• Became generally available in mid 1970's and have
gotten MUCH better in resolution and accuracy.
Still have problems with metal in the body...
Magnetic Resonance Imaging
(MRI)
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Subject body to strong magnetic field (0.08-4T) causing the
nuclei of magnetic isotopes to align their orientation.
This causes the nuclei to absorb energy and enter a higher
energy state.
When magnetic field is turned off, nuclei return to
equilibrium state emitting energy.
Each element has a unique energy signature that can then be
measured.
Getting more common and very cheap. Can now get a full
body MRI scan for ~$500
Cryosection
• Freeze specimen or embed in a plastic
polymer
• Cut specimen into as many slices as possible
along an axis
• Photograph each slice
• Example: Visible Male and Visible Female
Positron Emission Tomography
(PET)
• Inject a metabolically active tracer into subject
with an affinity to a certain molecule.
• 18F will accumulate in the brain where glucose is
used as primary energy source.
• The radioactive nuclei decay by positron
emmission which collides with a free electron
resulting in a gamma ray
• Detectors pick up the events and the a
reconstruction is computed
Medical Imaging for Education
Exploring the human body
• The "Ancients"
• Gray's Anatomy
• Visible Human Project
The Visible Human Project
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Create a digital image dataset of complete human male and
female cadavers in MRI, CT and anatomical modes.
MR –256x256 resolution at 4mm intervals, 12-bit/pixel
CT –512x512 resolution at 1mm intervals, 12-bits/pixel
Cryosection
– Low res: 2048x1216 at 1mm intervals, 24bits/pixel
– High res: 4096x2700 at 1mm intervals, 24bits/pixel
1871 slices per mode
Note: specs are for visible male
So what?
• We now have a digitized model of an
"average" male and female using the current
major medical imaging techniques
• We can now get views of the body that were
previously difficult if not impossible
• But, we know have LOTS of data and have
to figure out how to visualize it effectively
Lots of examples