Bushong ch 28-3 worksheet_ computed tomography
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?
1.5
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?
30 cm
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?
30 s
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?
5 cm
Approximately what is the minimum power requirement for the high-voltage generator and x-ray tube for helical CT?
50 kW
How often should patient dose measurements be taken on a multislice helical CT?
Annually
During CT imaging, beam hardening artifacts:
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:
Better spatial resolution
Which of the following is specifically characteristic of helical CT?
Continuous x-ray tube rotation in one direction
The quantity that describes the ability to distinguish between two different tissues is called:
Contrast resolution
DAS stands for which of the following?
Data acquisition system
Which of the following technique developments made helical CT possible?
Slip rings
Which of the following terms is equivalent to helical?
Spiral
When a shaded surface display reformation is implemented, the image will appear:
Surface-rendered
which of the following molecules takes on a helical structure?
Deoxyribonucleic acid
The ability to reconstruct an image at any z-axis position is due to:
Extrapolation
What is the primary advantage of a dual-source multislice helical CT?
Faster scan time
Which of the following characteristics is specific to a helical CT x-ray tube?
High anode heat capacity
Which of the following is an advantage of iterative reconstruction methods?
Higher contrast resolution
The standard deviation of a uniform image can help determine:
Image noise
The single most important advantage of helical CT is which of the following?
Imaging of a large volume of anatomy in one breath-hold
During spiral CT examination of a supine patient, the z-axis:
Is the long axis of the body
Which of the following is one advantage of helical CT over conventional CT?
Lack of motion artifact
What type of material is least likely to produce artifact in a CT image?
Low Z-material
Noise on a CT image increases with an increase in:
Matrix size
CT angiography relies on a reconstruction process that is called:
Maximum intensity projection
The simplest form of three-dimensional imaging is:
Maximum-intensity projection
Spatial resolution in CT imaging depends principally on:
Pixel size
Why is it recommended that beam pitch should not exceed 2.0?
Poor z-axis resolution
Which of the following is another advantage of helical CT over conventional CT?
Reduced scanning time
A principal advantage of reconstruction in any z-axis position is:
Reduction of partial volume
What was originally the primary disadvantage of third-generation CT scanners?
Ring artifact
Which of the following is another term for slice thickness?
Section sensitivity profile
What is the Hounsfield unit for water?
0
What range of beam pitch is recommended for multislice spiral CT?
1
With increasing slice pitch:
The section sensitivity profile increases in width.
Today all CT scanners are what generation?
Third generation
The largest number of individual detectors in a multislice CT imager is approximately:
Thousands
Which of the following statements about multislice CT is true?
Wider multislices allow imaging of a greater tissue volume.
A weekly test should be performed to ensure that the Hounsfield unit for water is within what range of its standard value?
± 10
