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| We worked with The Herchel Smith Laboratory for Medicinal
Chemistry based at Addenbrookes Hospital in Cambridge, UK.
Prof. Laurie Hall, the group's head, has specialized in micro-MRI
of joints to track action of drugs on the articular surfaces
of bones. His work is used particularly in the development
of drugs to combat arthritis and rheumatism. Until our approach
to him, however, Prof. Hall's work had not been used as the
basis of 3D imagery for medical education. The Herchel Smith
Laboratory build their own scanners and the magnetic coils
into which subjects are placed for scanning. It was decided
that the best way to achieve optimum resolution was to fix
a hand and arm inside a precise jig which would sit neatly
inside the coil. The jig would be cast in fiberglass from
a precision mold of the subject's hand and arm. Into this,
the entire limb could be fixed tightly into place and, using
fixing pegs within the coil, the jig could be relocated
with precision for repeat scans. Maximum resolution transverse
slices at 5mm intervals were acquired across hand and arm,
equating to between 50 and 60 slices. This sequence was
optimized for segmentation by hand of muscles and tendons
(see stage two).
One of Primal Pictures' own employees supplied the hand
and arm for the scanning, which meant, in practice, sitting
with his arm in the jig for hours on end to achieve the
required resolution. Slight cramp was the only temporary
side effect!
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| The imaging data is then processed at Primal Pictures. The
data is delivered as 2D cross-sectional slices. Each slice
then goes through a segmentation process. This involves
outlining by hand individual tissue and tracking the contours
of each anatomical feature through successive slices.
These contours create a wire-frame 3D model for each anatomical
structure. These structures are then amalgamated stage by
stage into an accurate CAD-CAM model of the complete anatomy.
In turn, this model is fed into computer graphics systems
and put through a "texture-mapping" process, a
procedure which adds texture, color, shadows and depth to
the 3D model.
This model is then "rendered", the final process
whereby individual full color frames are created. When the
user moves from frame to frame, the impression is gained
to moving around a 3D object. |
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