 |
This photo simulates the path that
the x-ray beam makes as spiral CT data acquisition of the abdomen is being made. The
highlighted area is a man's stomach (man is lying on his back with his arms over his
head). |
In all original CT scanners (1974 to
1987), the x-ray power was transferred to the x-ray tube using high voltage cables wrapped
around an elaborate set of rotating drums and pulleys. The rotating frame (or gantry)
would spin 360° in one direction and make an image (or a slice), and then spin 360° back
in the other direction to make a second slice. In between each slice, the gantry would
come to a complete stop and then reverse directions while the patient table would be moved
forward by an increment equal to the slice thickness.
In the mid 1980's, an innovation called
the power slip ring was developed so that the elaborate x-ray cable and drum system could
be abandoned. The slip ring allows electric power to be transferred from a stationary
power source onto the continuously rotating gantry. State of the art CT scanners with slip
rings can now rotate continuously and do not have to slow down to start and stop. The
innovation of the power slip ring has created a renaissance in CT called spiral or helical
scanning.
These spiral CT scanners can now image
entire anatomic regions like the lungs in a quick 20 to 30 second breath hold. Instead of
acquiring a stack of individual slices which may be misaligned due to slight patient
motion or breathing (and lung/abdomen motion) in between each slice acquisition, spiral CT
acquires a volume of data with the patient anatomy all in one position. This volume data
set can then be computer-reconstructed to provide three-dimensional pictures of complex
blood vessels like the renal arteries or aorta. 3D CT images from volume data allow
surgeons to visualize complex fractures, for example of facial trauma, in three dimensions
and can help them plan reconstructive surgery.
MR, ultrasound and digital x-ray fluoroscopy have all made
significant improvements in their ability to image the chest, lungs and abdomen. However,
spiral CT has kept computed tomography as the primary digital technique for imaging the
chest, lungs, abdomen and bones due to its ability to combine fast data acquisition and
high resolution in the same study. CT is also unique in that it can provide detailed
information of nearly every organ in the upper abdomen and pelvis in one quick
examination.
Advanced 3D CT Images and
"Virtual Reality" Images
Spiral CT allows the acquisition of CT
data that is perfectly suited to three-dimensional reconstruction. A wide range of
software techniques and advanced computer systems are being developed that enable creation
of amazing 3D "virtual reality" images.
| Virtual reality 3-D image of the
lungs. The bronchial trees are colored in green and the heart, aorta and vertebrae are
colored in red |
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