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Here are the main category of the techniques used

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for obtaining dual energy CT,

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and here is an example. One of the ways it's done is like a

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single X-ray source with fast kV switching.

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We call it as rapid switching dual energy CT technique.

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The second one is a dual source with dual detector

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array. We also call this a dual source dual

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energy CT.

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The third one is a single X-ray source with a filter,

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which we call it as a twin beam dual energy CT.

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Fourth one is a single source with a dual detector

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layer, called as dual layer dual energy CT.

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And the fifth type is basically with a regular CT scan, but

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doing twice by each time setting the kV differently,

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thereby you're obtaining two data set of different kV.

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So here is the one which is obtained by one vendor manufacturer

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called GE Healthcare. They do the dual energy CT

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as follows.

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It's a single source with fast kV switching.

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As shown here in this particular diagram, at every

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point of acquisition, there is two X-ray beams are

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produced, one with 80 kV

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beam and the other one is 140 kV.

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Fast switching between 80 and 140 kV generates

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two energy X-ray spectrum.

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While doing this one, the vendor adjusts the tube

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current so that for the 80 kV, the

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exposure time is slightly more compared to the 140 kV

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at about 35%.

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The second type is called the dual source with dual detector array,

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and this is quite commonly seen across the board in the clinic

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because the Siemens have started doing this dual source

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CT technology back in 2005 or

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2006. So they have two X-ray tube with the two

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detector arrays. You acquire two different image sets

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simultaneously. Therefore, two different X-ray tubes allow

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beam filtration and tube current adjustment to optimize the image quality.

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The only thing which you need to understand is at every point, there is an

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offset of one-quarter time rotation difference between the two

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spectra.

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Here is an example of the dual source CT.

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You have two X-ray tubes installed in the CT gantry.

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Simultaneously, there is two detector arrays at the opposite end.

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The second detector array is slightly smaller than the first

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one, and that's what this is a circle telling.

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If you want to utilize the dual energy CT

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protocol, the object or the patient has to be in this red

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area, which covers for both the detector size of this

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particular dual energy CT.

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The way it's obtained here is you're obtaining two spectrum.

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This is the 80 kV spectrum and 140 kV spectrum.

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You can see that by having this filter, you're

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separating these two separately.

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The single source dual energy technique, again, is another

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way the vendor is doing is they have only one

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X-ray tube. However, as it's acquiring the image, there is a

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tin filter passed halfway through the beam.

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That way, the tin filter will distribute the energy

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into two different spectrum, thereby obtaining dual

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spectrum.

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Another methodology obtaining dual sources or dual

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energy is obtaining with the same X-ray tube,

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but the detector has two layers. The top

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layer will absorb the lower energy, and the bottom layer will absorb

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the high energy. Thereby, we call this as a sandwich detector

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type, and this modified detector array will

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result in two X-ray spectrum utilized for dual energy.

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The single source sequential scan is done one over the other, and

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again, it can create a low or high energy spectrum.

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This is less done compared to the other way.