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