28-3 Worksheet Questions

What is the Hounsfield unit for water? a.) 0 b.) 30 c.) -100 d.) 1000 e.) -20

a.) 0

How much z-axis tissue will be imaged during a 20-s procedure if the slice width is 5 mm at a pitch of 1 and the gantry rotation time is 2 s? a.) 5 cm b.) 10 cm c.) 100 cm d.) 5 mm e.) 10 mm

a.) 5 cm

During CT imaging, beam hardening artifacts: a.) Are due to the polyenergetic beam. b.) Can be corrected by preprocessing. c.) Produce CT numbers higher in the periphery. d.) Result in brighter pixels in the center of the patient. e.) Result in higher attenuation in the center of the patient.

a.) Are due to the polyenergetic beam.

A principal advantage of multislice helical CT compared with step and shoot CT is all of the following, except: a.) Better spatial resolution b.) Faster imaging c.) Larger tissue volume d.) Lower patient dose e.) None of the above

a.) Better spatial resolution

The quantity that describes the ability to distinguish between two different tissues is called: a.) Contrast resolution b.) Spatial resolution c.) Point spread function d.) Filtered backprojection e.) Signal-to-noise ratio

a.) Contrast resolution

DAS stands for which of the following? a.) Data acquisition system b.) Digital acquired space c.) Digital activation signal d.) Digital analog server e.) Digital analog system

a.) Data acquisition system

Which of the following characteristics is specific to a helical CT x-ray tube? a.) High anode heat capacity b.) High rotation speed c.) Large effective focal spots d.) Large target angle e.) Small effective focal spot.

a.) High anode heat capacity

If a 20-s helical CT examination is acquired at a pitch of 1.5 with collimation of 10 mm, what was the length of the scan if gantry rotation time was 1 s? a.) 3 cm b.) 30 cm c.) 300 cm d.) 3 mm e.) 30 mm

b.) 30 cm

Which of the following is specifically characteristic of helical CT? a.) Continuous bidirectional rotation of the x-ray tube. b.) Continuous x-ray tube rotation in one direction. c.) Rotating detector array. d.) Stationary patient couch. e.) Steplike motion of the patient couch.

b.) Continuous x-ray tube rotation in one direction.

Which of the following molecules takes on a helical structure? a.) Carbohydrate b.) Deoxyribonucleic acid c.) Free radical d.) Lipid e.) Protein

b.) Deoxyribonucleic acid

The standard deviation of a uniform image can help determine: a.) Spatial resolution b.) Image noise c.) Contrast resolution d.) Patient dose e.) Scan time

b.) Image noise

The single most important advantage of helical CT is which of the following? a.) Imaging of a large volume of anatomy at a low patient dose. b.) Imaging of a large volume of anatomy to one breath-hold. c.) Improved contrast resolution. d.) Improved spatial resolution. e.) Improved z-axis resolution.

b.) Imaging of a large volume of anatomy to one breath-hold.

What type of material is least likely to produce artifact in a CT image? a.) High z-material b.) Low z-material c.) Lead-based material d.) Aluminum e.) Copper

b.) Low z-material

CT angiography relies on a reconstruction process that is called: a.) Longitudinal reformation b.) Maximum intensity projection c.) Shaded surface display d.) Surface-rendered e.) Volume-rendered

b.) Maximum intensity projection

The simplest form of three-dimensional imaging is: a.) Isometric b.) Maximum-intensity projection. c.) Shaded surface display. d.) Shaded volume display. e.) Slip-ring technology.

b.) Maximum-intensity projection.

Which of the following terms is equivalent to helical? a.) Elliptical b.) Spiral c.) Interpolation d.) Paraboloid e.) Trispiral

b.) Spiral

Thirty centimeters of tissue along the z-axis is to be imaged with a 5-mm slice thickness at a pitch of 2.0. What imaging time is required if gantry rotation time is 1 s? a.) 20 s b.) 25 s c.) 30 s d.) 35 s e.) 40 s

c) 30 s

A weekly test should be performed to ensure that the Hounsfield unit for water is within what range of its standard value? a.) +/- 1 b.) +/- 5 c.) +/- 10 d.) +/- 20 e.) +/- 100

c.) +/- 10

During a 360 degree x-ray rotation, the patient couch moves 15 mm during each revolution. Slice thickness is 10 mm. What is the slice pitch? a.) 0.66 b.) 1.25 c.) 1.5 d.) 1.66 e.) 2.0

c.) 1.5

Noise on a CT image increases with an increase in: a.) kVp b.) mA c.) Matrix size d.) Pixel size e.) Slice thickness

c.) Matrix size

Spatial resolution in CT imaging depends principally on: a.) Focal-spot size b.) kVp c.) Pixel size d.) Postpatient collimation e.) Slice thickness

c.) Pixel size

Today all CT scanners are what generation? a.) First generation b.) Second generation c.) Third generation d.) Fourth generation e.) Fifth generation

c.) Third generation

What range of beam pitch is recommended for multislice spiral CT? a.) 0.5 to 1 b.) 0.5 to 2 c.) 0.5 to 4 d.) 1 e.) 1 to 2

d.) 1

Which of the following is an advantage of iterative reconstruction methods? a.) Higher patient dose b.) Higher spatial resolution c.) Faster scan time d.) Higher contrast resolution e.) Shorter reconstruction time

d.) Higher contrast resolution

The ability to reconstruct an image at any z-axis position is due to: a.) Extrapolation. b.) Filtered back projection. c.) Fourier transformation. d.) Interpolation e.) Linear estimation.

d.) Interpolation.

During spiral CT examination of a supine patient, the z-axis: a.) Is the anterior-posterior axis. b.) Is the lateral axis, left to right. c.) Is the lateral axis, right to left. d.) Is the long axis of the body. e.) Varies with the examination.

d.) Is the long axis of the body.

Which of the following is one advantage of helical CT over conventional CT? a.) Better patient dose use. b.) Improved contrast resolution. c.) Improved spatial resolution. d.) Lack of motion artifact. e.) Large matrix reconstruction.

d.) Lack of motion artifact.

What was originally the primary disadvantage of third-generation CT scanners? a.) Long imaging time b.) Low spatial resolution c.) Motion artifact d.) Ring artifact e.) High heat load

d.) Ring artifact

Which of the following is another term for slice thickness? a.) Dose profile b.) Interpolation profile c.) Reconstruction index d.) Section sensitivity to profile e.) Z-axis profile

d.) Section sensitivity to profile

Which of the following technique developments made helical CT possible? a.) Dose-efficiency detectors b.) High-frequency generators c.) Interpolation algorithms d.) Slip rings e.) Volume imaging

d.) Slip rings

When a shaded surface display reformation is implemented, the image will appear: a.) As CT angiography. b.) As z-axis reformation. c.) Isometric d.) Surface-rendered e.) Volume-rendered

d.) Surface-rendered

Approximately what is the minimum power requirement for the high-voltage generator and x-ray tube for helical CT? a.) 10 kW b.) 20 kW c.) 30 kW d.) 40 kW e.) 50 kW

e.) 50 kW

How often should patient dose measurements be taken on a multislice helical CT? a.) Daily b.) Weekly c.) Monthly d.) Semiannually e.) Annually

e.) Annually

What is the primary advantage of a dual source multislice helical CT? a.) Lower patient dose b.) Higher spatial resolution c.) Less noise d.) Higher signal-to-noise ratio e.) Faster scan time

e.) Faster scan time

Why is it recommended that beam pitch should not exceed 2.0? a.) Increased noise b.) Poor contrast resolution c.) Poor patient dose use d.) Poor spatial resolution e.) Poor z-axis resolution

e.) Poor z-axis resolution

Which of the following is another advantage of helical CT over conventional CT? a.) Better patient dose use. b.) Improved contrast resolution. c.) Improved spatial resolution. d.) Large matrix reconstruction e.) Reduced scanning time.

e.) Reduced scanning time.

A principal advantage of reconstruction in any z-axis position is: a.) Image acquisition during a single breath-hold. b.) Improved contrast resolution. c.) Improved spatial resolution. d.) Larger volume of tissue imaged. e.) Reduction of partial volume.

e.) Reduction of partial volume.

With increasing slice pitch: a.) Image noise is reduced. b.) Patient dose is increased. c.) Sagittal/coronal reconstruction is improved. d.) The section sensitivity profile decreases in width. e.) The section sensitivity profile increases in width.

e.) The section sensitivity profile increases in width.

The largest number of individual detectors in a multislice CT imager is approximately: a.) Two b.) Four c.) Ten d.) Hundreds e.) Thousands

e.) Thousands

Which of the following statements about multislice CT is true? a.) Higher-resolution multislice helical CT results in low patient radiation dose. b.) Larger detector size results in better spatial resolution. c.) Narrower slice scanning results in better contrast resolution at the same mA. d.) The simplest approach to multislice scanning is the use of eight detector arrays, each of equal width. e.) Wider multislices allow imaging of a greater tissue volume.

e.) Wider multislice allow imaging of a greater tissue volume.