X-rays and CT I - Imaging in medicine (4/13)


Uploaded by OUlearn on 25.07.2008

Transcript:
Now, what about rotation of the gantry?
For a standard CT scan we need to acquire projection data
over a full rotation of 360 degrees.
At the time when the high voltage was still supplied with the tube via cables,
we had to reverse the direction of rotation from scan to scan
in order not to twist the cables.
Of course, continuous data acquisition wasn't possible at this time.
Only stop and go from scan to scan.
But things are different today - look at this.
Continuous rotation of the gantry was impossible
before the development of electrical slip rings,
for getting power into the X-ray tube and data out of the detectors.
The weight of the rotating parts adds up to almost a ton,
and we can accelerate the machine to an angular speed
of one rotation in three quarters of a second.
The radio acceleration at this speed
is 45 times the gravitation of acceleration.
In the original version of the third generation scanner,
the problem of the twisted cables
meant that the scanner had to reverse direction after each slice.
This limited the speed of the scan,
as well as causing wear and tear on the components
through repeated accelerations and decelerations.
Continuous rotation overcomes all the disadvantages of stop and go,
and when combined with continuous patient feed into the scanner,
creates the so-called spiral scan.