CT Acquisition 1A

Question 1

What is Tomography?

Answer 1

It is an imaging technique used to eliminate the structures below the focal plane.

Question 2

What is IVU Tomography?

Answer 2

It is an x-ray machine that moves over in an arc and blurs out the top and bottom of a structure for example, the kidney, to be able to see the calluses filled with contrast

Question 3

What is overcome with Tomography?

Answer 3

Super imposition

Question 4

What is the limitations of Tomography?

Answer 4

Fails to demonstrate the slight differences in the subject contrast which are characteristics of soft tissues.

This means that the similar attenuation of all tissues are difficult to differentiate

Question 5

Why is CT used?

Answer 5

Because it overcomes radiography and tomography by achieving-
- minimal superimposition
- improved image contrast
- recording of small differences in tissue contrast due to the shades of grey of the Hounsfiled units)

Question 6

How does CT work?

Answer 6

The beam of the x-ray is transmitted through a specific cross section of the patient, this removes superimposition of structures above and below the specific cross section of slice of tissue.

Question 7

How does CT minimise scatter production?

Answer 7

The beam of x-rays is higher collimated into a thin beam that only passes through the cross section of tissue to be imaged.

This done to minimise scatter and improve contrast of the image.

Question 8

How does CT measure very small differences in tissue contrast?

Answer 8

When the x-ray beam passes through the patient it strikes the detector, these detectors are attenuated and can measure very small differences in the tissue contrast

Question 9

How is the data processed in CT?

Answer 9

The data is processed by a digital computer that uses algorithm to reconstruct an image from the information of the cross sectional

Question 10

What are the CT components?

Answer 10

X-ray tube
Filter
Collimator
Where the patient lays
Detector array
Gantry

Question 11

What is the CT Bow Tie filter?

Answer 11

This placed between the x-ray source and the patient. It removes the lower energy x-rays that don’t contribute to the image formation but increases patient dose.

It affects dose and image quality

Question 12

How is a monochromatic beam made?

Answer 12

As the low energy x-rays are removed there is a narrower spectrum of x-ray energies creating a monochromatic beam

Question 13

What is image reconstruction based on?

Answer 13

It is based on the assumption of a single monochromatic beam

Question 14

Where is the Bow Tie filter in CT?

Answer 14

It is built into the CT scanner.

In some scanners the filer is shaped to the beam and in others it isn’t which gives it the bow tie shape.

Question 15

Why is there less attenuation of the x-ray beam due to the bow tie filter?

Answer 15

There’s less attenuation of the x-ray beam as the lateral edge of the body are thinner than the centre

Question 16

What are the different types of collimator?

Answer 16

Source
Detector (acts like a grid as it reduces scatter so there won’t be image degradation)

Question 17

How does CT converts x-rays into visible light pluses?

Answer 17

CT scanners use scintillation crystals to convert x-rays to visible light pluses which can be detected and counted by electronic circuits

Question 18

What does conventional detectors produce?

Answer 18

They produce light pulses and voltage pulses resulting in a simple count of x-ray photons

Question 19

What does CT detectors do?

Answer 19

They use fast scintillator ceramic crystals and the intensity of light pulses which is proportional to the total energy of photons, striking the crystals

The light is converted into a current and hence a voltage across the resistance which is detected as digital data for use by the reconstruction system

This allows for change of information on the depth of providing a third dimension to that so that a voxel is produced from this data and it can be converted into other planes