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1 System Operation & Components > Study Unit 1 > Flashcards

Study Unit 1 Flashcards

1
Q

CT system console

A

Where instructional commands are initiated by the technologist, including: information about the patient, imaging parameters, post-processing techniques, and filming & archiving instructions.

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2
Q

host computer

A

Commands from console are shuttled through host computer, translated into the system’s machine language, and passed to the scan controller.

Receives calculated images after scanning is completed where they may be maintained on a storage device, displayed on the console monitor, or transmitted to a remote location.

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3
Q

scan controller

A

Responsible for timing and operation of patient table, gantry, and high voltage generator.

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4
Q

digital-to-analog converter (DAC)

A

Electronic signals from host computer are converted into analog to be sent to gantry control.

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5
Q

gantry

A

Contains physical components of scanner, including: x-ray tube and detectors.

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6
Q

high-voltage generator

A

Produces high-voltage potential that exists between cathode and anode.

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7
Q

amplifier

A

Amplifies the electrical signals received from DELs, which are then sent to the sample-and-hold component (S/H)

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8
Q

sample-and-hold component (S/H)

A

Amplified electrical (analog) signals are sampled and sent to analog-to-digital converter (ADC)

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9
Q

analog-to-digital converter (ADC)

A

Converts electrical (analog) signals to digital signals to be processed in the array processor.

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10
Q

array processor

A

Digital signals are calculated into image data.

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11
Q

Date CT systems commercially introduced

A

1973

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12
Q

first-generation scanners

A

-pencil beam
-single detector
-translate-rotate process
-long scan time (shortest approx. 5 min)
-only used for head imaging due to motion limitations

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13
Q

translate-rotate

A

-tube and detector translated across gantry while patient remained stationary
-after one complete projection, assembly rotated by 1-degree for next projection
-180-degrees necessary to construct image

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14
Q

second-generation scanners

A

-fan beam geometry introduced
-approx. 30 detectors
-translate-rotate process
-assembly rotation by 5-degrees per projection
-reduced amount of time required (about 10x faster than first-gen)
-scan time reduced to about 20 seconds
-used for more than head only
-rendered first-gen systems obsolete

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15
Q

fan beam geometry

A

x-ray beam generated in a shape similar to an opened paper fan

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16
Q

third-generation scanners

A

-first introduced in 1975
-most scanners used today are third-gen
-fan-beam
-introduced curved arc arrangement of detector array
-tube/detectors rotate around patient, instead of translating across the patient
-several hundred to several thousand detectors
-greatly reduced time required for data collection

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17
Q

arc arrangement of detector array

A

-improves reproducibility of projection data
-minimizes certain artifacts that were common to second-gen

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18
Q

fourth-generation scanners

A

-fan beam rotates around patient
-detectors form a complete circle around the gantry
-design was not more advantageous than third-gen

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19
Q

continuous rotation scanners

A

-third-gen scanners started with cable technology that needed to be unwound
-slip-ring technology introduced

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20
Q

slip-ring

A

large, rotating ring which surrounds the gantry aperture, conveying electrical power and data

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21
Q

slip ring transfers…

A

-electrical power
-scanning instructions
-detected signals
between stationary components and rotating gantry components

22
Q

multi-row detector scanners (MDCT)

also called multi-slice scanners (MSCT) and multi-array scanners

A

-a form of third-generation scanners
-collect information from multiple anatomical slices in each rotation of the x-ray tube
-anatomy can be scanned faster without increasing slice thickness or varying the pitch

23
Q

cone-beam

A

fan beam which has increased in thickness (as in MDCT), which causes it to be diverged over z-axis

24
Q

benefits of multi-row detector scanners (MDCT)

A

-faster scans
-increased anatomical coverage
-scanning with thinner slices to improve resolution along the slice direction

25
Q

electron beam CT scanner (EBCT)

A

-an alternative design that has no x-ray tube, instead uses electron beam, directed at tungsten target
-no moving parts, so very fast acquisition times
-suited for cardiac and coronary artery imaging

26
Q

PET/CT scanners

A

-fusion of positron emission tomography (PET) and computed tomography (CT)
-low resolution images obtained from PET are overlaid on higher resolution CT images

27
Q

positron emission tomography (PET)

A

A nuclear imaging modality involving injection of a slightly radioactive pharmaceutical into the body, which accumulates in tissues having rapid growth. The images obtained, however are of low resolution

28
Q

cone beam CT in oncology

A

-used in oncology to verify patient positioning prior to receiving radiation therapy, ensuring that radiation is delivered with extreme accuracy only to the tissue that needs it
-applications are growing outside of oncology (ex: dental)

29
Q

operator’s console

A

key point of interaction between technologist and imaging system

30
Q

Components of operator’s console

A

-graphic monitor
-keyboard
-mouse or trackball

31
Q

host computer

A

-primary link between the technologist and the other components of imaging system
-controls storage devices, such as hard disks and removable media (archiving and retrieval of patient data)

32
Q

gantry

A

-contains: tube, detectors, patient table is fed through aperture of gantry, slip ring, high voltage generator
-oblique slices can be obtained by tilting the gantry by up to approx. +/- 30-degrees

33
Q

rotating frame assembly

A

located toward the central aspect of the gantry, contains tube, detector array, and data acquisition system

34
Q

bremsstrahlung radiation

A

-also called “braking radiation”
-electron collides with the nucleus (uncommon) or passes near and changes direction (common), the loss of energy and slowing of the electron produces an x-ray photon

35
Q

characteristic radiation

A

-electron collides with target atom’s inner shell electron, ejecting it; an outer shell electron will move in to take its place and releases excess energy in the form of x-ray photon
-called characteristic because the energy level of the resulting photon is a characteristic of the specific target atom

36
Q

distribution of radiation interactions in large population of x-ray photons

A

-distribution is made up of both bremsstrahlung and characteristic radiation
-only 10% to 12% is characteristic

37
Q

kVp

A

x-ray photon energy level is related to the energy level of the electron beam originating from the tube cathode which collides with the anode target.

38
Q

space charge compensator

A

cools the filament slightly as the kV is increased to reduce the unintentional and unavoidable, slight increase in number of electrons emitted from the cathode

39
Q

high-voltage generator

A

produces the high voltage needed to create high-voltage potential between cathode and anode and heats the cathode filament

40
Q

atomic number of tungsten

A

74

41
Q

melting point of tungsten

A

around 3400-degrees celcius

42
Q

interscan delay time

A

the minimum amount of time that must transpire between the end of one scan and the initiation of the next scan (includes idle time between scans to allow tube cooling)

43
Q

Pre-patient collimation

A

-restricts the x-ray beam immediately after it exits the CT tube and before any x-ray photons enter the patient’s body by the use of thick metal plates attached to the bottom of tube housing
-minimizes dose to the patient

44
Q

effects of pre-patient collimation on single-slice vs multi-slice detectors

A

SINGLE SLICE: collimator assembly specifies the thickness of the slices

MDCT: collimator specifies the thickness of the x-ray beam, which spreads out over multiple rows of detectors

45
Q

Post-patient collimation

A

-also called “pre-detector collimation”
-restricts unwanted x-rays from entering the detector assembly from arbitrary angles (scatter radiation)

46
Q

detectors

A

-two basic categories: gas and solid state
-first component of data acquisition system (DAS)
-measure incoming x-ray photons if three conditions are met: x-ray must be able to enter the chamber of the detector and be “captured”, x-ray must collide with atom in detector material, collision of the photon and detector material must produce a result that can be measured (e.g., electricity or light)

47
Q

gas detector

A

-most contain xenon
-pressurized by up to 30x normal atmospheric pressure to compress the gas and increase probability that photon will collide with xenon atom
-when photon collides with xenon atom, the atom splits into xenon ion and an electron and the charged particles (ion+, e-) are attracted to the oppositely charged sides of the chamber, creating a measurable event
-tiny signal from the electrical event goes to amplifier, then to array processor, where it’s used to reconstruct the image

48
Q

solid state detector

A

-currently the detector of choice
-sometimes called “scintillation detectors”
-made of solid crystalline substance which is much more dense than xenon gas
-when x-ray photon collides with the solid state material, detector emits brief flash of light
-light is converted into a usable electrical impulse by a photodiode attached to the bottom of solid state material on the detector
-tiny signal from the electrical impulse goes to amplifier, then to array processor, where it’s used to reconstruct the image

49
Q

array processor

A

-primarily functions to reconstruct the projected attenuation raw data into CT images
-also the site of calculations required to generate retrospective reconstructions, and sometimes, to post-process image data

50
Q

network

A

-includes: operator’s console, image workstations, image viewing stations, image storage devices, printers, and personal computers
-close proximity uses copper cables, wider distance (but still within the same building) uses fiber optic cables, long distances require high speed circuits through telephone lines (T1)

51
Q

server

A

archive device that stores the images

52
Q

client

A

image workstation which needs access to images stored on the server

1 System Operation & Components (2 decks)

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