CT Quick Prep

Question 1

How does filament size affect image quality?

Answer 1

A smaller filament produces images with superior spatial resolution.

Question 2

When the pitch is increased from 1:1 to 2:1, what happens to the effective slice thickness?

Answer 2

it increases (widened)

Question 3

In CT, why is the beam heavily filtered?

Answer 3

To reduce beam-hardening artifacts & scatter radiation.

Question 4

The ability to resolve, as separate forms, small objects that are very close together is called:

Answer 4

Resolution.

Question 5

The area of pt tissue exposed during a CT scan is controlled by the:

Answer 5

Scan field of view (SFOV).

Question 6

The ability of the detector to capture transmitted photons and change them to electronic signals is called:

Answer 6

Detector efficiency.

Question 7

A speckled appearance of the CT image caused by insufficient photons reaching the detectors is known as:

Answer 7

Noise.

Question 8

What fundamental property accounts for beam hardening artifacts?

Answer 8

The polychromatic nature of the x-ray beam.

Question 9

What unit quantifies a structure’s ability to attenuate the x-ray beam?

Answer 9

Hounsfield Unit (HU).

Question 10

What takes up more computer space when stored, raw data or image data?

Answer 10

Raw Data.

Question 11

A cube of data acquired in CT is called:

Answer 11

A voxel.

Question 12

What is the process by which different tissue attenuations are averaged to produce a single less accurate pixel reading?

Answer 12

Volume averaging or partial volume effect.

Question 13

What is the process of converting the data from the attenuation profile to a matrix?

Answer 13

Back Projection

Question 14

The __________ is often called the “Brain” of the CT system.

Answer 14

Central processing unit (CPU).

Question 15

An artifact that results from beam hardening & appears on the image as a vague area of increased density in a somewhat concentric shape around the periphery of an image, similar to the shape of a cup is called a:

Answer 15

Cupping artifact.

Question 16

Visible fluctuations in the image which result in a salt and pepper look is called

Answer 16

Quantum noise.

Question 17

The CT process be broken down into these three segments:

Answer 17

1. data acquisition.
2. image reconstruction.
3. image display.

Question 18

The way the detectors are placed, relative to one another, affects the:

Answer 18

Amount of scatter radiation that reaches the image (geometric efficiency).

Question 19

With what type of scanner are ring artifacts more common?

Answer 19

3rd generation.

Question 20

What part of the CT system is responsible for sampling each of the detector cells?

Answer 20

The data acquisition system (DAS).

Question 21

What do the initials ROC stand for in the term “ROC curve”?

Answer 21

Receiver Operating Characteristics.

Question 22

What is the current of electrons produced by the filament referred to as?

Answer 22

Milliamperes (mAs).

Question 23

What is the unit of measure for the heat dissipation rate of a system?

Answer 23

KHU (thousand heat units).

Question 24

What will happen to the CT image if too low an mAs setting is used?

Answer 24

The image will be noisy (grainy)

Question 25

The amount of CT number variance within the region of interest is called

Answer 25

Standard deviation

Question 26

What is a disadvantage to a tube with a small focal spot?

Answer 26

It decreases the amount of heat the tube can tolerate.

Question 27

"The ability to resolve anatomy in an image" is the definition of:

Answer 27

Image quality

Question 28

What effect does decreasing the slice thickness have on volume averaging?

Answer 28

A thinner slice results in less volume averaging.

Question 29

What is a two-dimensional square of data called?

Answer 29

A pixel.

Question 30

The space occupied by the detector collimator plates relative to the surface area of the detector determines the:

Answer 30

Geometric efficiency.

Question 31

A measure of the beam-attenuation capability of a specific structure is expressed in:

Answer 31

Hounsfield unit (HU), pixel value or CT number.

Question 32

Why are solid-state detectors sometimes called scintillators?

Answer 32

B/C they emit a flash of light when struck by an x-ray beam.

Question 33

How can out-of-field artifiacts be avoided?

Answer 33

Proper pt centering within the gantry.

Question 34

A volume elemnt is also called:

Answer 34

A voxel.

Question 35

A manifestation that is seen on an image but is not present in the object scanned is called:

Answer 35

An artifact.

Question 36

The ability to represent small objects & differentiate between closely spaced objects is called:

Answer 36

Spatial resolution.

Question 37

The mechanism in some CT scanners that allows the x-ray tube to rotate continually in the same direction is known as a:

Answer 37

Slip-ring.

Question 38

All the measurements obtained from the detector array are called:

Answer 38

Scan data or raw data.

Question 39

A picture element is known as a:

Answer 39

Pixel.

Question 40

How will creating a more uniform x-ray beam intensity affect the CT image?

Answer 40

Beam-hardening artifacts will be reduced, therefore the image will be improved.

Question 41

Sodium iodide, bismuth germanate, cadmium tungstate, cesium iodide, and ceramic rare earth are all materials that have been used for:

Answer 41

Making solid-state detectors.

Question 42

In the formation of x-ray how will increasing the kilovoltage affect the electrons which will later strike the target material?

Answer 42

Increase thier speed.

Question 43

Which type of detectors are more sensitive to fluctuations in temperature & moisture?

Answer 43

Solid-state detectors.

Question 44

What parameter controls the number of detectors used to create an image?

Answer 44

The scan field of view (SFOV).

Question 45

To create an image, info from the DAS must be translated into a:

Answer 45

Matrix

Question 46

What device is used to convert the electric signal from the detectors into a digital format?

Answer 46

Analog-to-digital converter (ADC)

Question 47

What device reduces the beam intensity at the periphery of the beam, corresponding to the thinner parts of a pt?

Answer 47

Bow-tie filters.

Question 48

The ability of the detector to capture transmitted photons & change them to electronic signals is called:

Answer 48

Detector efficiency.

Question 49

Prior to a colonography, the patient may undergo a bowel cleansing termed:

Answer 49

Catharsis.