Deck 3: Physical Principles of Computed Tomography

Question 1

When a beam of X-rays passes through the patient, the relative transmission or penetration measurement can be calculated by using which of the following?

A) Log of the ratio of intensity of X-rays at the source to the intensity of the detector
B) Log of the ratio of the detector intensity to the source intensity
C) Ratio of the source intensity to the detector intensity
D) Ratio of the detector intensity to the source intensity

Answer 1

Log of the ratio of intensity of X-rays at the source to the intensity of the detector

Question 2

The attenuation used by Hounsfield in his original experiments was:

A) a heterogeneous beam.
B) a monoenergetic beam.
C) a polychromatic beam.
D) a hardened beam.

Answer 2

a hardened beam.

Question 3

In which of the following data acquisition methods is a volume of tissue (rather than a single slice) scanned during a single breath-hold?

A) Spiral/helical CT
B) Conventional radiography CT
C) Conventional CT
D) Slice-by-slice CT

Answer 3

Spiral/helical CT

Question 4

The total number of X-ray transmission measurements is equal to the:

A) total number of detectors.
B) number of views in each scan.
C) product of the number of views and the number of rays in each view.
D) the number of views divided by the number of rays in each view.

Question 5

All of the following changes occur in the attenuation of a heterogeneous beam of radiation except:

A) the beam quality.
B) the beam quantity.
C) the beam intensity.
D) the beam direction.

Question 6

Which of the following best describes the term "data acquisition geometry" in CT?

A) The size and shape of the X-ray beam
B) The arrangement of the X-ray tube and detectors
C) The stationary ring of detectors
D) The rotation of the X-ray tube

Question 7

The limitations of conventional tomography include all of the following except:

A) superimposition of structures above and below the focal plane.
B) image blur from movement of the tube and film.
C) contrast degradation from the open beam geometry.
D) the presence of ghost images on the film.

Question 8

Which of the following is not true of a homogeneous beam of radiation?

A) All the photons have different energies
B) All the photons have the same energy
C) Equal thicknesses of the absorber remove equal amounts of radiation
D) Equal thicknesses of the absorber remove different amounts of radiation

Question 9

The reduction of the intensity of a beam of X-rays as it passes through the patient is:

A) the relative transmission value.
B) attenuation.
C) the natural logarithm.
D) the linear attenuation coefficient.

Question 10

The most obvious difference between CT and radiography is that:

A) CT shows cross-sectional images or transaxial anatomy.
B) radiography uses sodium iodide detectors.
C) a computer is used to produce the film in radiography.
D) radiography shows cross-sectional images.

Question 11

The radiation beam produced from a conventional X-ray tube is:

A) homogeneous.
B) heterogeneous.
C) monoenergetic.
D) monochromatic.

Question 12

The unit of the linear attenuation coefficient ( $\mu$ ) is:

A) per centimeter.
B) cm¹.
C) 1/cm.
D) per cm^-2

Question 13

Attenuation of a beam of radiation depends on each of the following except:

A) the electrons per gram of tissue.
B) the energy of the radiation.
C) the speed of the radiation.
D) the atomic number of the tissue.

Question 14

Which of the following obeys Lambert-Beer's law?

A) A homogeneous beam of radiation
B) A heterogeneous beam of radiation
C) A polyenergetic beam of radiation
D) A polychromatic beam of radiation

Question 15

In which of the following are slices taken at specific locations on the patient?

A) Spiral CT
B) Helical CT
C) Conventional slice-by-slice CT
D) Volumetric CT

Question 16

Data acquisition in CT refers to:

A) acquiring the information from the detectors.
B) acquiring the information from the computer.
C) acquiring information from the patient by using special motions of the X-ray tube and detectors.
D) processing the information from the patient.

Question 17

The radiation beam used by Hounsfield in his original experiments was:

A) gamma rays.
B) X-rays.
C) cosmic rays.
D) microwaves.

Question 18

Which of the following is a limitation of radiography?

A) Image blur caused by patient breathing
B) Contrast degradation because of low peak kilovoltage techniques
C) The presence of ghost images caused by the tube movement
D) Superimposition of structures

Question 19

CT overcomes the limitations of radiography and conventional tomography by achieving all of the following except:

A) reducing the problem of superimposition.
B) improving the contrast of the image.
C) using quantitative detectors and a computer.
D) reducing a patient's radiation dose.

Question 20

All of the following apply to computed tomography (CT) except:

A) a computer is used to reconstruct cross-sectional images of the patient.
B) mathematical methods are used to reconstruct images.
C) X-ray film is used as the detector.
D) special detectors are used to detect X-rays that have passed through the patient at multiple angles.

Question 21

A scaling factor of 1000 in the Hounsfield scale (H scale) for K results in a:

A) contrast scale of 0.2% per CT number.
B) contrast scale of 0.1 % per CT number.
C) contrast scale of 0.5% per CT number.
D) contrast scale of 0.8% per CT number.

Question 22

A high-kilovolt (kV) technique is necessary in CT imaging for all of the following reasons except:

A) to reduce the contrast of bone relative to soft tissues.
B) to increase the probability of beam hardening.
C) to reduce the dependence of attenuation coefficients on photon energy.
D) to produce a high-radiation flux at the detector.

Question 23

If the FOV for an examination is 30 cm and the matrix size is 1024 * 1024, what is the approximate pixel size?

A) 25 mm
B) 0.5 mm
C) 0.3 mm
D) 0.05 mm

Question 24

The center or midpoint of the range of CT numbers is called the:

A) WW.
B) WL.
C) ROI.
D) contrast factor.

Question 25

The CT number for water is:

A) (-1000).
B) (-100).
C) 0.
D) 100.

Question 26

A limitation of conventional radiography is that it is qualitative rather than quantitative.

Question 27

How many pixels make up a CT image whose matrix size is 512 * 512?

A) 100,000
B) 1024
C) 262,144
D) 512

Question 28

Data from the CT detectors are first sent to the _________ before going to the computer.

A) array processor
B) host computer
C) back-projector
D) digitizers

Question 29

Data processing includes all of the following except:

A) raw data preprocessing.
B) analog to digital conversion.
C) image reconstruction.
D) image storage.

Question 30

A CT image of 12 bits per pixel means :

A) each pixel can have a total of 4096 shades of gray.
B) the matrix is 4096 * 4096.
C) the pixel size is 12 mm.
D) the voxel size is 12 mm.

Question 31

The second step of data acquisition is scanning.

Question 32

The field of view (FOV) is:

A) the reconstruction circle.
B) the ROI.
C) a mathematical technique.
D) a digital processing technique.

Question 33

The display FOV can ________________ the scan FOV (sFOV).

A) be greater than
B) be less than
C) be replaced by
D) be reversed by

Question 34

The range of CT numbers in an image is called the:

A) window width (WW).
B) window level (WL).
C) region of interest (ROI).
D) dynamic range.

Question 35

The WW controls the image contrast and the WL controls the image brightness.

Question 36

Which of the following is used to calculate CT numbers?

A) CT number = $\mu$ water + $\mu$ tissue $\mu$ K
B) CT number = $\mu$ tissue - $\mu$ water *K/ $\mu$ tissue
C) CT number = $\mu$ water - $\mu$ tissue * K/ $\mu$ water
D) CT number = $\mu$ tissue- $\mu$ water * K/ $\mu$ water

Question 37

If the linear attenuation coefficients for bone and water are 0.380 and 0.190, respectively, and the scaling factor of the scanner is 1000, the CT number for bone is:

A) +1000.
B) (-1000).
C) +380.
D) +190.

Question 38

The Compton effect occurs largely in soft tissues.

Question 39

Conversion of the attenuation readings into a CT image is accomplished by reconstruction algorithms.

Question 40

Which of the following is a limitation of CT compared with conventional radiography?

A) Decreased spatial resolution
B) Increased contrast resolution
C) Decreased patient dose
D) Decreased visualization of artifacts

Question 41

Please match the following concepts for each group. All answer selections will be used just once.

Superimposition of all structures on film

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 42

Please match the following concepts for each group. All answer selections will be used just once.

All photons do not have the same intensity

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 43

Please match the following concepts for each group. All answer selections will be used just once.

Sections of image blur

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 44

A polychromatic beam is better known as a homogeneous beam.

Question 45

Please match the following concepts for each group. All answer selections will be used just once.

Cross-section or slice of tissue

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 46

Please match the following concepts for each group. All answer selections will be used just once.

Reduction of the X-ray intensity as the beam passes through the patient

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 47

Please match the following concepts for each group. All answer selections will be used just once.

Range of CT numbers

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 48

CT numbers are established by referencing the linear attenuation coefficient of air.

Question 49

Please match the following concepts for each group. All answer selections will be used just once.

Cathode ray tube

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 50

Please match the following concepts for each group. All answer selections will be used just once.

Center of the Hounsfield unit range

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 51

A spiral or helical beam is used to scan the patient in slice-by-slice data acquisition.

Question 52

Please match the following concepts for each group. All answer selections will be used just once.

All photons have the same energy

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL

Question 53

CT is better at recording very small differences in tissue contrast compared to conventional tomography.

Question 54

The photoelectric effect occurs mainly in tissues with a low atomic number.

Question 55

Please match the following concepts for each group. All answer selections will be used just once.

Collecting data from the patient

A)Radiography
B)Heterogeneous beam
C)WW
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)CT
J)WL