CT chapter 4
which CT scanner is based on fan-beam geometry and complete rotation of the x-ray tube and detectors
3rd generation
in which scanner is the apex of the fan-beam located outside the detector?
4th generation
which generation is classified as a high-speed scanner
5th
scanner that uses an electron gun to shoot electrons towaex a target ring is the
5th generation
Which generation of scanner, also called dual-source CT scanners, consists of two x-ray tubes and two sets of detectors?
6th
T/F first generation scanners were first to use fan-beam geometry
False 2nd generation
T/F: multirow CT detectors fall into two categories, namely, matrix array detectors and pixel array detectors
False matrix array detectors and adaptive array detectors
T/F: Gas-ionization CT detectors convert x-ray photons into electrical signals with no light conversion process in-between
True
which of the following refers to size, shape, motion, and path traced by x-ray beam as it scans the patient
beam geometry
filtration
beam hardening
What style of filter is common in CT filtration because it compensates for the difference in beam path length through the axial plane of the object such that a more uniform fluence can be delivered to the detector?
bowtie filter
the following crystals have been used in scintillation CT detectors except calcium tungstate NaI crystals calcium flouride bismuth germanate
calcium tungstate
compared with conventional CT scanners, slip-rings offer all of the following advantages except: facilitates continuous rotation of the x-ray tube capacity for interrupted acquisition protocols. minimal interscan delays elimination of start-stop process removal of wraparound process
capacity for interrupted acquisition protocols.
View in CT is
collection of rays from one translation across the object
The slice thickness in CT is determined by the :
collimator width
slip-ring design
continuous gantry rotation
which of the following refers to a method by which the patient is systematically scanned by the x-ray tube and detectors to collect enough information for image reconstruction?
data acquisition
detector electronics
data acquisition system
what detector innovation allows for acquisition for both low and high energies for every exposure in CT imaging
dual-layer detector
the ratio of the largest signal to the smallest measured by a CT detector is the:
dynamic range
refers to the ability of the CT detector to capture, absorb, and convert x-ray photons into electrical energy
efficiency
T/F Anistrophic is a term used to describe detector channels that are equal in size
false
T/F contactless slip-ring design uses a conductive wire as its sliding contact
false
T/F gas-ionization detector are prone to afterglow problems
false
T/F high-frequency generators use a low-frequency inverted circuit to convert low-voltage current from the main power supply to high-voltage current required by the CT x-ray tube
false
T/F streaking artifacts are the result of too many samples being measured by the detectors
false
T/F gas-ionization chambers where first introduced in second-generation scanners
false 3rd gen
T/F: 6th generation scanners are referred to as the cine CT scanner because of its high-speed acquisition for imaging the heart and circulation
false 5th generation
T/F: Straton x-ray tube was designed by Toshiba
false siemens
T/F: overall goal of the electron-beam CT (EBCT) scanner is to produce low-resolution images of moving organs that are free of artifacts caused by motion
false high-resolution
4th generation ct scanners are characterized by
fan-beam geometry and complete rotation of x-ray tube around a stationary ring of detectors
Scintillation
flashes of light
which x-ray generator is used in modern ct scanners
high-frequency
All of the following are radiation beams produced by an x-ray tube designed for CT except: polyenergetic polychromatic heterogenous homogeneous
homogeneous beam
What category of multirow detector array utilizes an isotropic design
matrix array detectors
total number of data samples per scn or per slice in CT
number of data samples per view times the number of views
In one type of 4th generation CT scanner, the tilting action of the detector ring is referred to as:
nutating
Collimation plays a role in:
patient dose ensures constant beam width at the detectors reduces scatter radiation
semiconductor
photodiode
the data acquisition system performs each of the following except:
powers the rotating components of the gantry Feedback: The DAS is located between the detectors and the computer, and it performs three major functions: (1) it measures the transmitted radiation beam, (2) it encodes these measurements into binary data, and (3) it transmits the binary data to the computer.
what design of collimation is influenced by size of the focal spot
prepatient collimation
Ct detectors generate a signal that represents the attenuation as the ray moves across the slice. This signal is called:
profile
The main purpose of a filter used in CT is to:
protect the patient
speed with which CT detector can detect an x-ray event and recover to detect another event
response time
which x-ray tube is most likely used in spiral/helical CT scanners
rotating anode with a rhenium tungsten disk
a single ray in computer tomography is
single straight line path of x-ray beam
method does not affect sampling information
slice thickness
collimation
slick thickness
electromechanical devices made up of rings and brushes to transmit electrical energy across a rotating interface
slip-rings
which scanner is based on slip-ring technology
spiral/ helical scanner
which scanner allows for continuous rotation of the x-ray tube while the patient moves simultaneously through the gantry aperture
spiral/helical scanner
which scanner results in a volume of the patient being scanned during single breath-hold (rather than a single slice of tissue)?
spiral/helical scanner
Which detector characteristic refers to the steadiness of the detector response
stability
T/F Adaptive section collimation is a design to overcome overscanning, an issue of exposing the patient outside the imaged range which occurs for spiral CT with multirow detectors at the start and the end of the scan.
true
T/F afterglow refers to the persistence of the image even after the radiation has been turned off
true
T/F optoelectronics refer to the used of lens and light diodes to facilitate data transmission
true
T/F: 7th generation scanners use flat-panel digital area detectors
true
T/F: photodiodes are now used in CT scintillation detectors
true
T/F: scintillation detectors convert x-ray photons to light and subsequently to electrical signals
true
T/F: the high-voltage generator of slip-ring scanners are located in the gantry
true
t/f configuration of the dual-row detector system results in faster volume coverage compared with single-row CT systems
true
which of the following is commonly used in gas-ionization CT detectors
xenon
ionization detector
xenon gas
What provides double sampling by obtaining two overlapping slices for each detector row per 360-degree rotation
z-flying focal spot technique