Deck 4: Physical Principles of Computed Tomography

Question 1

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

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

Answer 1

per centimeter

Question 2

When a beam of x rays passes through the patient, the relative transmission or penetration measurement can be calculated by use of 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 2

log of the ratio of intensity of x rays at the source to the intensity of the detector

Question 3

Data acquisition in computed tomography 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

Answer 3

acquiring information from the patient by using special motions of the x-ray tube and detectors

Question 4

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 5

Computed tomography overcomes the limitations of radiography and conventional tomography by: I. reducing the problem of superimposition
II) improving the contrast of the image
III) using quantitative detectors and a computer

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 6

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 7

All of the following apply to 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 8

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

Question 9

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

Question 10

Attenuation of a beam of radiation depends on: I. the atomic number
II) the electrons per gram of tissue
III) the energy if the radiation

A)I and II
B)II and III
C)I and III
D)I, II, and III

Question 11

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 12

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 13

The most obvious difference between computed tomography and radiography is that:

A)computed tomography 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 14

The second step of data acquisition is scanning.

Question 15

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

A)spiral computed tomography
B)helical computed tomography
C)conventional slice-by-slice computed tomography
D)volumetric computed tomography

Question 16

The Compton effect occurs largely in soft tissues.

Question 17

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 18

The window width controls the image contrast and the window level controls the image brightness.

Question 19

Which of the following represents the correct expression of Lambert Beer's law?

A)I = I₀e ^-µ
B)I = I₀e ^+µb
C)I₀ = I₀e ^-µa
D)I = I₀e ^-µx

Question 20

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 computed tomography
B)conventional radiography computed tomography
C)conventional computed tomography
D)slice-by-slice computed tomography

Question 21

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

A)contrast scale of 0.2% per computed tomography number
B)contrast scale of 0.1 % per computed tomography number
C)contrast scale of 0.5% per computed tomography number
D)contrast scale of 0.8% per computed tomography number

Question 22

The radiation beam from an x-ray tube is:

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

Question 23

Data processing includes all of the following except:

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

Question 24

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

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

Question 25

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 computed tomography number for bone is:

A)+1000
B)1000
C)+380
D)+190

Question 26

In the attenuation of a heterogeneous beam of radiation:
I. the beam quality changes, II. the beam quantity changes, III. the beam intensity changes

A)I and II
B)I and III
C)I and III.
D)I, II, and III

Question 27

The center or mid point of the range of computed tomography numbers is called the:

A)window width
B)window level
C)region of interest
D)contrast factor

Question 28

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

A)decreased spatial resolution
B)increased contrast resolution
C)decreased patient dose
D)decreased visualization of artifacts

Question 29

The range of computed tomography numbers in an image is called the:

A)window width
B)window level
C)region of interest
D)dynamic range

Question 30

If the field of view 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 31

If the linear attenuation coefficients for fat and water are 0.185 and 0.205, respectively, and the scaling factor for the scanner is 1000, the CT number for fat is approximately:

A)+1000
B)-1000
C)+100
D)-100

Question 32

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

A)gamma rays
B)x rays
C)cosmic rays
D)microwaves

Question 33

Which of the following is used to calculate computed tomography numbers?

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

Question 34

The attenuation used by Hounsfield in his original experiments was: I. a heterogeneous beam
II) a homogeneous beam
III) a monoenergetic beam
IV) a polychromatic beam

A)I and III
B)II and IV
C)I and II
D)II and III

Question 35

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

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 36

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 37

The photoelectric effect occurs more frequently in tissues with a: I. high atomic number
II) low atomic number
III) high Z number
IV) low Z number

A)I and II
B)III and IV
C)I and III
D)II and IV

Question 38

The field of view is:

A)the reconstruction circle
B)the region of interest
C)a mathematical technique
D)a digital processing technique

Question 39

The computed tomography number for water is:

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

Question 40

A computed tomography 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 41

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)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography

Question 42

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

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

Question 43

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)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography

Question 44

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

Image blur

A)Radiography
B)Heterogeneous beam
C)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography

Question 45

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)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography

Question 46

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

Superimposition of structures

A)Radiography
B)Heterogeneous beam
C)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography

Question 47

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)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography

Question 48

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)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography

Question 49

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)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography

Question 50

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

Range of computed tomography numbers

A)Radiography
B)Heterogeneous beam
C)Window width
D)Conventional tomography
E)Homogeneous beam
F)Display device
G)Attenuation
H)Data acquisition
I)Computed tomography