Tomo Worksheets
A CT image is made with a 5-mm slice thickness and a 0.5 mm pixel size. What is the size of the voxel?
1.25 mm^3
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
A 120 x 120 matrix will consist of how many pixels?
14,400
Which of the following Hounsfield unit (HU) values most closely represents the value for blood?
20 HU
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 5mm 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
In its simplest configuration, the CT imaging system consists of an x-ray source and which of the following?
A detector
CT imaging systems incorporate
A gantry
Which of the following is characteristic of first-generation CT imaging systems?
A pencil x-ray beam
Each translation of a source detector assembly produces which of the following?
A projection
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
During CT imaging, beam-hardening artifcats
Are due to the polyenergetic beam
Fourth-generation CT imaging systems
Are faster than third-generation CT imaging systems
A CT imaging system produces which type of image?
Axial
Which of the following is characteristic of a CT image but not of a conventional radiograph?
Better contrast resolution is obtained
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 has been used as a detector in a CT imaging system?
Bismuth germanate
Which of the following is specifically characteristic of helical CT?
Continuous x-ray tube rotation in one direction
Slice thickness can also be expressed as which of the following?
Sensitivity profile
The quantity that describes the ability to distinguish between two different tissues is called
Contrast resolution
DAS stands for what?
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
Spatial resolution refers to which of the following?
The ability to identify small high-contrast objects
Which of the following subsystems would normally be associated with the gantry assembly?
The detector array
Which of the following molecules takes on a helical structure?
Deoxyribonucleic acid
The translate-rotate mode
Describes both first and second generation CT imaging systems
Streak artifacts on a CT image are usually due to
Detector imbalance and metal clips
In a CT imaging system, prepatient collimation
Determines patient dose
What is the primary advantage of a dual-source multislice helical CT?
Faster scan time
Second-generation CT imaging systems
Have a multiple detector array
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
Noise on a CT image can be reduced by
Increasing mAs
The ability to reconstruct an image at any z-axis position is due to
Interpolation
When a CT image is described, contrast resolution
Is limited by the noise of the system
During spiral CT examination of a supine patient, the z-axis
Is the long axis of the body
A Hounsfield unit
Is the numeral value of a pixel
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 an artifact in a CT image?
Low z-material
CT angiography relies on a reconstruction process that is called
Maximum intensity projection
The simplest form of three-dimensional imaging is
Maximum-intensity projection
An image matrix contains which of the following?
Picture elements
Noise on a CT image increases with an increase in
Pixel size
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
The thickness of section in CT depends primarily on
Predetector collimation
Sensitivity profile in CT is determined principally by the
Predetector collimator
CT is performed at high kVp principally to
Reduce patient dose
CT mA is modulated to
Reduce patient dose
Which of the following is another advantage of helical CT over conventional CT?
Reduced scanning time
A principal advantage of reconstruction in any z-acis position is due to
Reduction of partial volume
What was originally the primary disadvantage of third-generation CT scanners?
Ring artifact
Third-generation CT imaging systems have which of the following?
Rotate-rotate geometry
Which of the following is another term for slice thickness?
Section sensitivity profile
A weekly test should be performed to ensure that the Hounsfield unit for water is within what range of its standard value?
+/- 10
What is the Hounsfield unit for water?
0
A CT imaging system has a limiting resolution of 7 lp/cm. An object of what size can be resolved?
0.7 mm
What is the pixel size of an image reconstructed from a 24 cm diameter region of interest (ROI) in a 320 x 320 matrix?
0.75 mm
What range of beam pitch is recommended for multislice spiral CT?
1
Spatial resolution for CT imaging systems is approximately
1 mm
A comparision of scintillation and gas-filled detectors show that
The scintillation detectors have higher geometric efficiency
With increasing slice pitch
The section sensitivity profile increases in width
The precise pixel value in HU depends on which of the following?
The x-ray attenuation coefficient
Partial volume artifacts are more likely with
Thicker slices
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
