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Now I just want to talk a little bit about the multi-detector CT.

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That is the world we are in now, and what is the principle

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behind the multi-detector CT is what I want to explain now.

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So with the helical CT, which revolutionized the CT,

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however, with helical CT or spiral CT, we only have

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one row of detector in the Z direction.

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Means every rotation provides only one slice at a

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time.

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In 1998, vendors started introducing what is called a

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multi-detector row CT. So instead of one row of

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detector, they introduced multiple rows of detectors.

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So this opened up all new application,

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faster CT, because the principle is still the same.

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The X-ray tube going around the patient,

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collecting the data,

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and in the early days, you are only able to do one rotation and get

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only one slice. Therefore, for chest area, for a chest

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CT, the CT tube has to go around the patient at least 30

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times to cover the entire chest. Now with the

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multiple row detector CT, the beam is slightly opened

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up and the detectors now will collect more information,

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but it can be reconstituted back into four slices or

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16 slices and so forth. Therefore,

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immediately there was a major evolution of the CT technology

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because now instead of one slice, you are able to do four slices.

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Means for the same scan time, you are able to cover

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a larger area. That is the principle behind it.

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The way it worked is as follows. I'm just going to show two examples.

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For example, the detector configuration in these following ways,

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where four is called the number of channels, and

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1.25 is the size of the detector. So in this

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case,

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the vendor has large number of detectors.

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However, they only had a capability to pull out only

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four channel of data in the beginning.

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So in the early days of the multi-detector CT, it was an all

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four-slice CT scanner because it was limited by

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the number of

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data channel.

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Therefore, by having the X-ray beam collimated to

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cover these four detector, you are able to reconstruct four

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slices of 1.25 millimeter.

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If you want to have it covering a larger area, the way it was done is the

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beam was opened up larger,

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but now the data from two different detectors were combined

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to get a slice thickness of 2.5. Therefore, you are able to

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get four slices of 2.5 millimeter.

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And this was how it was done around 1998 and

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2000.

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Within a year, every manufacturer started increasing the

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capability to acquire more data, faster

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data by the principle of this particular principle of

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multi-detector CT.

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So here is the different configuration of detector.

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We are not going to go into the detail, just to give an appreciate.

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GE 16-slice CT scanner had a volume coverage of

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20 millimeter at any one rotation, 20 millimeters, two

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centimeter size. And this 16-slice scanner had a

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maximum up to 32 millimeter, 3.2 millimeter.

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This was the detector configuration, how the detector

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technology evolved, and how the CT protocols were developed.

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So what is the advantage of this multi-slice CT scanner is

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shown here is with a four-slice scanner,

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if you're acquiring a three-millimeter slice thickness, you can

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cover with the following parameter.

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You can cover the entire body, about 100 millimeter, that is

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100 centimeter of length, in less than 30 second.

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Earlier, it is not possible. It used to take about 300 seconds,

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now 30 second.

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Now, within a year, the 16-slice scanner further advanced

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the speed by basically covering a larger

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volume therefore it took less than eight second.

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Now we are at a point where we can scan the whole body in a couple

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of seconds because the volume of data collected per

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rotation has increased.

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With the 16-slice scanner, the maximum was 40 millimeter.

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Means if you want to cover an entire chest, which is about 30

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centimeter, you

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don't need to rotate only about seven to eight times to cover

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the entire chest. They also introduced lot of

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slices for radiologist to review, but the fundamental principle

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is this one.