Quiz 3

Axial slices lie parallel to one another. A) True B) False

A

Higher mA settings allow shorter scan times to be used. A) True B) False

A

In which type of scans does the CT table move to the desired location and remain stationary while the x-ray tube rotates? A) Step-and-shoot scans B) Localizer scans C) Helical scans D) Spiral scans

A

MDCT designs were responsible for the demise of fourth-generation scanning systems. A) True B) False

A

On CT images, objects with a 5% contrast variation can be distinguished. A) True B) False

A

What is another name for the radiation emitted from the collimated x-ray source in multidetector row systems? A) cone beam B) misregistration C) adaptive array D) pitch

A

What is low-contrast resolution? A) The ability of the system to differentiate between objects with similar densities. B) The ability of the system to differentiate between objects of similar sizes. C) The system's ability to resolve, as separate forms, small objects that are very close together. D) The level of detail that is visible on the image.

A

Which is a reason why a technologist should take one cross-sectional slice to check the accuracy of a localizer image? A) It is impossible to use readily identifiable landmarks. B) The intravenous contrast material is critical. C) The patient is placed head first in the gantry. D) The localizer image will be an anterior-posterior projection.

A

Which is another name for step-and-shoot scanning? A) Axial scanning B) Spiral scanning C) Helical scanning D) Localizer scanning

A

Which statement is true? A) The higher the mAs setting, the longer the time between scans. B) The higher the mAs setting, the shorter the time between scans. C) The lower the mAs setting, the longer the time between scans.

A

Axial scans are typically used in protocols in which the acquisition speed is a major concern and optimal resolution is not required. A) True B) False

B

Localizer images are cross-sectional in nature. A) True B) False

B

Milliampere level and scan time together define the quality of the beam. A) True B) False

B

Slice thickness has no impact on image quality. A) True B) False

B

The DFOV used for a study is 30 cm and a 512 matrix is used. What is the approximate pixel size in mm? A) 0.06 mm B) 0.59 mm C) 1.71 mm D) 17.07 mm

B

The selection of 160 mA and a 2-second scan time provides a greater quantity of x-ray energy than 640 mA and a 0.5-second scan. A) True B) False

B

The terms scout, surview, topogram, scanogram, preview, and pilot are alternative names for step-and-shoot scans. A) True B) False

B

What is the most common range for pitch values in both SDCT and MDCT systems? A) 0-1 B) 1-1.5 C) 1-2 D) 1.5-2

B

What is the name for the slight pause in scanning between data acquisitions? A) Convolution B) Interscan delay C) Interpolation D) Back projection

B

What is the unit of measurement for current of electrons that flow from the filament to the anode? A) kVp B) mA C) kW D) HU

B

What percent reduction in radiation dose do automatic tube current modulations provide without degrading image quality? A) 10% to 25 % B) 15% to 40% C) 5% to 50% D) 15% to 60%

B

Where does a localizer image for a CT of the chest usually begin? A) At the base of the spine B) At the lower neck C) At the top of the head D) At mid-abdomen

B

Which generation of CT systems typically used a 360 degree rotation for each acquisition? A) Fourth B) Third C) Second D) First

B

Which is not a factor that affects contrast resolution? A) Reconstruction algorithm B) CTDI phantoms C) Patient size D) Slice thickness

B

Why doesn't the uncoupling effect play a role when the mA or kVp setting is too low? A) Because there is no relationship between dose and image quality when the mA or kVp setting is too low. B) Because quantum noise will result and provide evidence of the inadequate exposure settings. C) Because when the settings are too low, the radiation dose cannot be at a dangerous level.

B

Why is it important to correctly input the patient's position before the localizer image is obtained? A) The optimal display field of view will be distorted B) Subsequent images will be incorrectly annotated which can result in misdiagnosis and serious medical errors C) Data acquired during axial scanning will not be contiguous

B

An examination protocol calls for contiguous, 5-mm slices to be taken and 70 slices are planned. How much of the patient anatomy in the z direction will be covered with sross-sectional slices? A) 75 mm B) 159 mm C) 350 mm D) 700 mm

C

If 30 lines can be seen in a 1-cm section in an image of a line pairs phantom, what is the spatial resolution? A) 1 lp/cm B) 15 lp/cm C) 30 lp/cm D) 60 lp/cm

C

If an image reproduced the object exactly, what is the MTF of the system? A) 0 B) 0.5 C) 1 D) 1.5

C

The DFOV used for an abdominal study is 42 cm and a 256 matrix is used. What is the approximate pixel size in mm? A) 0.164 mm B) 0.61 mm C) 1.64 mm D) 6.10 mm

C

The General Electric Lightspeed QX/I scanner system uses 16 detector rows, each 1.25 mm wide, arranged side-by-side along the z axis. If three detector rows are combined, how thick will the resultant slices be? A) 1.25 mm B) 2.5 mm C) 3.75 mm D) 5 mm

C

What does it mean for an axial scan to be clustered? A) Scanners can repeat scans at the same slice location B) The pauses between each data acquisition will be less than 30 seconds C) More than one scan can be taken during a single breath-hold

C

What is the pitch for a 64-slice MDCT with 0.5-mm slice thickness and a table-feed of 48 mm per rotation? A) 1.75 B) 0.75 C) 1.5 D) 0.6

C

What is tube current? A) The loss of resolution caused by a larger filament B) The time the x-ray beam is on for the collection of data for each slice C) The product of milliampere setting and scan time

C

Which equation correctly describes the relationship between pixel size, matrix size, and DFOV? A) pixel size = DFOV x matrix size B) pixel size = matrix size/DFOV C) pixel size = DFOV/matrix size D) pixel size = (DFOV/matrix size) + 1

C

Which is an advantage of step-and-shoot scanning? A) Misregistration often occurs during scanning B) Data acquired are more limited in how they can be reconstructed C) On phantoms, they result in the highest quality image D) The cumulative effect of the pauses between each data acquisition adds to the total examination time

C

Which is another name for helical scanning? A) Axial scanning B) Step-and-shoot scanning C) Spiral scanning D) Localizer scanning

C

Which is not a benefit of localizer images? A) They help the technologist select the correct image center. B) They allow the technologist to prescribe the location of cross-sectional slices. C) They speed up the examination process. D) They help the technologist select the optimal display field of view.

C

Which is not another name for reconstruction algorithm? A) FC filter B) convolution filter C) spatial frequency algorithm D) algorithm

C

Which statement about interpolation is true? A) As the angle of the slice becomes less steep, the interpolation required to adjust the data increases. B) As the angle of the slice becomes less steep, the interpolation required to adjust the data decreases. C) As the angle of the slice becomes steeper, the interpolation required to adjust the data increases. D) As the angle of the slice becomes steeper, the interpolation required to adjust the data decreases.

C

A scanner allows mA choices in 20-mA increments from 20 to 700, and offers a choice of scan times from 0.4, 0.6, 0.8, 1.0, and 2.0 seconds. Which combination of mA and scan time will produce an mAs of 336? A) 0.6 second and 500 mA B) 1.0 second and 320 mAs C) 0.4 second and 680 mAs D) 0.8 second and 420 mA

D

What is slice thickness blooming? A) A parameter that is commonly used to describe the CT table movement B) The delay in axial scanning sequences C) Grouping more than one scan in a single breath-hold D) When interpolation methods result in a scan that is wider than that selected by the operator

D

What is the kVp range for routine body CT for adult patients? A) 100 kVp to 160 kVp B) 80 kVp to 100 kVp C) 80 kVp to 140 kVp D) 120 kVp to 140 kVp

D

What is the tube rotation of an overscan? A) 180° B) 360° C) 380° D) 400°

D

What is the typical range of values for scan time for a full rotation? A) 1 second to 5 seconds B) 0.1 second to 3 seconds C) 1 second to 2 seconds D) 0.5 second to 2 seconds

D

Which is not a basic attribute of a helical scan process? A) Uninterrupted table movement B) Constant x-ray output C) A continually rotating x-ray tube D) Each slice of the image is parallel to every other slice

D

Which is not a scanning parameter? A) Field of view B) Slice thickness C) Reconstruction algorithm D) Patient size

D

Which is not true about the effect of mAs and kVp setting on the radiation dose? A) Excessively lowering the kVp may result in a dramatic increase in the amount of x-ray attenuated by patient tissue. B) Reducing the kVp while holding the mAs constant reduces the radiation dose to the patient. C) Reducing the mAs while holding the kVp constant reduces the radiation dose to the patient. D) It is more common to manipulate the kVp, rather than the mAs.

D

Which of the following statements is true? A) A large object will have a high spatial frequency, and small objects will have no spatial frequency. B) A large object will have no spatial frequency, and a small object will have a high spatial frequency. C) A small object will have a low spatial frequency, and a large object will have a high spatial frequency. D) A large object will have a low spatial frequency, and small objects will have a high spatial frequency.

D

Which type of scans are digital image acquisitions that are created while the tube is stationary and the table moves through the scan field? A) Axial scans B) Spiral scans C) Helical scans D) Localizer scans

D

The ___is the ratio of the accuracy of the image compared with the actual object scanned.

MTF

____ pitch is defined as table movement per rotation time divided by the selected slice thickness of the detector.

detector

_______CT uses two sets of x-ray tubes and two corresponding detector arrays in a single CT gantry.

dual source

In ___scanning, the x-ray output is continually on while the table moves through the gantry.

helical

____is the undesirable fluctuation of pixel values in an image of a homogeneous material. (2 words)

image noise

_____delay is the time between each acquisition when the table moves to the next scan position and the scanner readies itself for the next acquisition.

interscan

Resolution in the z direction is called_____resolution.

longitudinal

The travel distance of the CT scan table per 360 degree rotation of the x-ray tube, divided by the x-ray beam collimation width is called __

pitch

____is the relationship between slice thickness and table travel per rotation during a helical scan acquisition.

pitch

____resolution is another term used for detail resolution.

spatial