Week 4 Lecture 1 Flashcards
6 basic ct equipment
- couch/table
- operating console
- workstation
- contrast media injector
- accessory equipment
- gantry
describe some characteristics of the table.
it is made of carbon fibre to provide it with rigidity
it is controlled by electrical and mechanical controls
there are attachment areas for accessory equipments
it is narrow and concave
2 planes the table can move in
- vertical (y axis)
- horizontal (z axis)
incrementation
when the table moves to a specified distance in the z axis plane
why is table motion important?
it can affect consistency of the scanning and pathology localization
why is table referencing important?
it will help maintain scan consistency between followup exams
scan point
table’s position relative to the gantry; gives you the location of irradiation
scan point should be manually set to _____ by technologist
zero
limitations to the table
- weight restrictions
- scannable range* (must be considered to prevent patient repositioning)
*exceeding the weight limits of the table can…?
affect precision of pitch
operating console
pieces of equipment that allow technologists to input factors prior to acquisition that affect the scan
what are the monitors called at the operating console?
scan monitors & display monitors
what makes up the operating console?
- computer
- keyboard
- multiple monitors
the keyboard at the operating console enables?
- communication with scan room
- manipulation of gantry tilt
- table movement
- irradiation
scan monitors
enables the selection of various factors prior to acquisition (ex. patient’s demographics, scan protocols and parameters)
display monitors
enables image viewing and post-processing functions
what type of data is stored at the operators console?
RAW data
workstation
**access and manipulate IMAGE DATA; post-process images
what is the key difference between the keyboard’s control on the operators console vs. workstation?
keyboard at operators console allows for communication with scan room, gantry tilts, table movement and irradiation
keyboard at workstation only communicates with the computer (*focus here is on image manipulation)
contrast media injector
mechanical device to safely administer large amounts of contrast media through an IV
contrast media injectors can be programmed for?
- to ensure precise volumes and injection rates
*this allows for consistency of image appearance
syringes on the contrast media injectors keep contrast and saline separate. contrast syringes need what special considerations?
a “warming sleeve”
contrast media injectors have audible and visual alerts. why?
to help identify potential problems
warming sleeves
*to maintain the desired temperature of contrast media
what does the contrast media injector comprise of?
- syringes (one or two)
- warming sleeves
- console
consoles on the contrast media injection devices are for?
allows for selection and monitoring
- selection of pre-programmed protocols and other administration factors
accessory equipments
designed to improve patient care and image quality
what are some accessory equipment commonly used in ct?
- specialized headrest
- sponges
- immobilization straps
- shielding
gantry
houses the x-ray tubes + detectors
- opening the patient moves through
what is the average diameter of the gantry aperture?
~70-90 cm
what is the max gantry tilt?
30 degrees
cephalad
towards the head/anterior
caudad
towards the back/posterior
what are the lights on the gantry for?
enables accurate patient positioning – isocenter
what are the components you can find in the gantry?
x-ray tube, detectors, collimators, filtration, das, slip ring
DAS
digital acquisition system
measures the transmitted radiation beam (ex. radiation flux at the detectors)
what is sampling?
how DAS reduces the creation of image artifacts
DAS converts measurements into? with what?
digital signals by using a ADC
converted digital signals are sent to the computer by the ADC for?
reconstruction
slip rings
electromagnetic devices that provides continuous electrical power and electronic communication across rotating surfaces
what type of generators do conventional units use?
3-phase generators
3 phase generators are found (inside/outside) the gantry
outside of the gantry
what type of generators do the modern units use?
high frequency generators
high frequency generators are found (inside/outside) the gantry
inside the gantry
high-frequency inverter circuit
- enables high kV settings
- produces less voltage ripple (consistent power levels)
what generator has better efficiency?
high frequency generators
what are the two common sizes of focal spots?
0.5mm & 1mm
how are the x-ray tube components designed in order to decrease heat loads?
- higher anode rotation speeds
- larger and thicker anodes
- metal envelope
- dual focal spots
power supplied by high frequency generators (increase/decrease) heat loading.
decreases
what is the common range for the high frequency generators?
120-140 kVp
higher kVps = (fewer/more) electrons boiling off the filament
higher kVps = fewer electrons boiling off
filtration
shapes the x-ray beam by absorbing low energy photons
filtration results in (homogeneous/heterogenous) beam
homogenous beam
by increasing the average energy of the beam, what does it do to the patient’s dose?
reduces it
(less to be absorbed by the patient)
a consistent, uniform beam is good for?
increasing the accuracy of HU measurements
**increasing the accuracy of HU measurements results in?
**minimizing the appearance of artifacts caused by beam hardening
what are the two classification of filtration?
- inherent
- added (aka compensating)
what are the 3 factors to inherent filtration?
- built into the system
- can’t be changed
- applied to all exams
what are the 3 factors to compensating filtration?
- located between the tube and patient
- applied anatomically specific exams
- have special shapes to match beam divergence and patient shape
collimators
small, thin pieces of lead that resemble shutters
where are the collimators located?
- pre-patient (source)
- post-patient (pre-detector)
why is the collimator needed post-patient?
- to maintain beam width at the detector
- decrease scatter that reaches the detector
what does “narrowing the x-ray beam” mean?
restricting the x-ray beam to anatomy of interest, which allows for the controlling of the voxel length (z-axis)
***collimators contribute to slice thickness in (SDCT/MDCT)
collimators control slice thickness in (SDCT/MDCT)
contribute - mdct
controls - sdct
detectors
absorb transmitted radiation photons
**detectors convert absorbed x-ray energy into _______
electrical signals
radiation intensity (≠/=) electrical energy
radiation intensity = electrical energy
detectors count the quantity of photons but not quality
quality = energy of the photons
