CH 25 - CT

* A relative comparison of x-ray attenuation of a voxel of tissue to an equal volume of water is a(n): a. CT number b. matrix c. FOV d. pixel

a. CT number

* All of the following effect radiation dose in CT EXCEPT: a. FOV b. beam energy c. tube current d. section/slice thickness

a. FOV

* The number used to describe the average density of a tissue: a. Hounsfield unit b. voxel c. window level d. window width e. pixel

a. Hounsfield unit

* Which 3D imaging technique is commonly used for CTA? a. MIP b. SSD c. VR d. helical

a. MIP ( maximum intensity projection )

* All of the following scan parameters effect the temporal resolution EXCEPT: a. algorithm b. multidetector CT c. tube/gantry rotation time d. dual-source CT

a. algorithm

* Reconstruction algorithms affect all of the image quality factors EXCEPT: a. artifact b. noise c. contrast resolution d. spatial resolution

a. artifact

* Which of the following is the most significant geometric factor that contributes to spatial resolution? a. detector aperture width b. focal spot size c. slice thickness d. detector array

a. detector aperture width

* What is based on the principle that different structures enhance at different rates after contrast administration? a. dynamic scanning b. 3D imaging c. spiral CT d. image misregistration

a. dynamic scanning

* The part of the scanner that houses the x-ray tube, cooling system, detector assembly and DAS: a. gantry b. table c. control console d. computer e. aperture

a. gantry

* The 4 main factors that affect CT image quality include all of the following EXCEPT: a. patient size b. spatial resolution c. contrast resolution d. noise e. artifact

a. patient size

* One individual cell surface within an image matrix used for CRT image display: a. pixel b. voxel c. FOV d. Hounsfield unit

a. pixel

* Random variations in photon detection results in: a. quantum noise b. streak artifacts c. beam hardning d. image misregistration

a. quantum noise

* The amount of blurring in a CT image is described as the image's: a. spatial resolution b. contrast resolution c. noise d. artifact

a. spatial resolution

* What is the aperture of the CT machine? a. the opening within the gantry b. the part of the detector assembly that converts analog signals to digital signals c. the part of the scanner that houses the x-ray tube, cooling system, detector assembly, and DAS d. the electronic component of the scanner that measures remnant radiation exiting the patient and converts it to a proportional analog signal

a. the opening within the gantry

* The midpoint of the range of gray levels to be displayed on the monitor is the: a. window level b. window width c. Hounsfield number d. algorithm

a. window level

* The ability to differentiate between small differences in density within the CT image is called: a. spatial resolution b. contrast resolution c. temporal resolution d. gray level mapping

b. contrast resolution

* The ability to differentiate between small differences in density within the image describes the image's: a. spatial resolution b. contrast resolution c. noise d. artifact

b. contrast resolution

* CT is the examination of choice for: a. limb fractures b. head trauma c. the GI tract d. the genitourinary system

b. head trauma

* CT scanners produce _______ scatter than x-rays, creating an image with ______ contrast resolution. a. more b. less c. higher d. lower

b. less; c. higher

* The array of numbers arranged in a grid that comprises the digital image: a. FOV b. matrix c. pixel d. voxel

b. matrix

* Converting axial raw data into another plane is known as: a. algorithm b. multiplanar reconstruction c. curved planar reformations d. mapping

b. multiplanar reconstruction

* The scan parameters that effect the spatial resolution include all of the following EXCEPT: a. slice thickness b. patient size c. display FOV d. matrix size e. algorithm

b. patient size

* The most common cause of noise in a CT image arises from the random variation in photon detection, known as: a. scatter b. quantum noise c. artifact d. noise

b. quantum noise

* Which new CT data acquisition method involves the continuous rotation of the gantry as the table moves through the gantry? a. dynamic scanning b. spiral c. multislice spiral d. CTA

b. spiral

* High resolution CT scans are made using: a. shorter scan times b. thinner sections or slices c. wider window widths d. volume rendering algorithms

b. thinner sections or slices

* CT protocols for pediatric patients are based on: a. age b. weight c. suspected pathologic conditions d. all of the above

b. weight

* The __________ determines the midpoint of the range of gray levels displayed. a. FOV b. window level c. window width d. Hounsfield unit

b. window level

* The range of CT numbers that are used to map signals into shades of gray is called the: a. window level b. window width c. image registration d. matrix display

b. window width

* What is the CT number of water? a. -1000 b. -100 c. 0 d. 1000

c. 0

* Tissue densities of less than ______ can be distinguished by CT. a. 0.01% b. 0.1% c. 0.5% d. 1%

c. 0.5%

* The 3 common techniques used for creating 3D images from CT data include all of the following EXCEPT: a. MIP b. SSD c. CTA d. VR

c. CTA ( CTA = CT angiography )

* The area of anatomy displayed by the monitor: a. matrix b. window c. FOV d. gantry

c. FOV

* All of the following can result in "streaking" artifact on a CT image EXCEPT: a. residual barium b. thick bone density c. absesses d. artificial joints

c. absesses ( these can cause a "halo" appearance when injected with contrast )

* Radiation exiting the patient is measure by the: a. matrix b. gantry c. detector assembly d. DAS

c. detector assembly

* Which new CT data acquisition technology has detector arrays containing multiple rows of elements along the z-axis, instead of a single row of detectors? a. dynamic scanning b. spiral c. multislice spiral d. CTA

c. multislice spiral ( aka helical )

* What term is applied to a single square, or picture element, in the image display matrix? a. CT number b. Hounsfield number c. pixel d. raw data

c. pixel

* All of the following are methods of 3D reconstruction EXCEPT: a. maximum intensity projection b. volume rendering c. segmentation d. shaded surface display

c. segmentation

* Which 2 of the following scan parameters effect all 3 of the main image quality factors? ( contrast resolution, spatial resolution, noise ) a. FOV b. matrix size c. slice thickness d. beam energy e. reconstruction algorithm f. patient size

c. slice thickness; e. reconstruction algorithm

* MR is the preferred imaging modality for which of the following? ( select all that apply ) a. bony structures b. less scan time c. soft tissue d. claustrophobic patients e. better low-contrast resolution f. less costly

c. soft tissue; e. better low-contrast resolution

* The amount of blurring in a CT image is termed: a. noise b. artifact c. spatial resolution d. contrast resolution e. temporal resolution

c. spatial resolution

* Which image quality factor is affected by focal spot size? a. noise b. artifact c. spatial resolution d. contrast resolution

c. spatial resolution

* "Beam hardening" affects which of the following image qualities? a. spatial resolution b. contrast resolution c. noise d. artifact

d. artifact ( beam hardening = thick density bones absorbing x-rays, obscuring underlying structures )

* Which of the following can be selected at the operator's console? 1. slice thickness 2. table index 3. imaging technique factors a. 1 and 2 b. 1 and 3 c. 2 and 3 d. 1, 2, and 3

d. 1, 2, and 3

* Which of the following contribute to image noise in CT? 1. detector aperture width 2. matrix size 3. patient size a. 1 and 2 b. 1 and 3 c. 2 and 3 d. 1, 2, and 3

d. 1, 2, and 3

* Which of the following quality factors is affected by x-ray beam energy? 1. contrast resolution 2. spatial resolution 3. noise a. 1 and 2 b. 1 and 3 c. 2 and 3 d. 1, 2, and 3

d. 1, 2, and 3

* The part of the detector assembly that converts analog signals to digital signals: a. matrix b. Hounsfield unit c. voxel d. DAS e. gantry

d. DAS ( data acquisition system )

* What determines the amount of data displayed on the monitor? a. number of volume elements b. pixel size c. tissue density d. FOV

d. FOV

* The electronic component of the scanner that measures remnant radiation exiting the patient and converts it to a proportional analog signal: a. DAS b. gantry c. aperture d. detector assembly e. matrix

d. detector assembly

* The image that appears on the monitor depends on the: a. focal spot size b. detector array c. detector aperture width d. display FOV

d. display FOV

Which generation of CT is pictured? a. first b. second c. third d. fourth e. fifth f. sixth

d. fourth

* A narrow window width would display: a. a long gray scale b. many shades of gray c. low contrast d. high contrast

d. high contrast

* What new CT data acquisition method involves continuous gantry rotations combined with constant table movement through the aperture? a. dynamic scanning b. maximum intensity projection c. volume rendering d. spiral / helical CT

d. spiral / helical CT

* The window level should be set to: a. one half of the algorithm point b. the Hounsfield center c. the average level of the voxel d. the CT number of the tissue of interest

d. the CT number of the tissue of interest

* All of the following scan parameters effect the contrast resolution EXCEPT: a. slice thickness b. algorithm c. windowing d. tube/gantry rotation time e. beam energy

d. tube/gantry rotation time

* The ________ is determined by the slice thickness: a. Hounsfield unit b. window level c. window width d. voxel

d. voxel

* The following scan parameters effect the level of noise in the CT image EXCEPT: a. matrix size b. slice thickness c. beam energy d. algorithm e. display FOV

e. display FOV ( patient size and scatter also effect the level of noise )

Which generation of CT is pictured? a. first b. second c. third d. fourth e. fifth f. sixth

e. fifth

* The range of CT numbers used to map signals into shades of grey: a. matrix b. Hounsfield units c. voxel d. window level e. window width

e. window width

Which generation of CT is pictured? a. first b. second c. third d. fourth e. fifth f. sixth

f. sixth