fluroscopic systems: image intensifier (traditional) Flashcards
what is fluroscopy used for
to retrieve static image of body part
what is R & F system
radiography and fluoroscopy system
- a type of medical imaging that shows a continuous X-ray image on a monitor
be aware that you need a static image for archiving in fluroscopy
what is the difference between a dynamic and static image in fluroscopy
dynamic = a picture that has a certain amount of motion e.g only a swallow
static = fixed image
(fluroscopy uses dynamic imaging)
be aware that there is blur/lag with fast movement in dynamic imaging
give an example of a fluorescent molecule found in producing fluorescence
caesium iodid
explain the process of how fluorescence is made
- fluorescent molecule excited by incident xray photon
- electron in an orbiting shell jumps into a shell in a higher state but is unstable and drops back down
- energy is emitted to return to ground state in the form of visible light
because fluroscopy is more efficient than using xrays directly to create an image, what does this mean about patient dose
- fewer xrays used due to increased efficiency
- lower patient dose
what are the 3 general configurations of fluroscopic machinery/system
- under couch
- over couch
- C arm
what is under couch fluroscopy
- xray tube underneath a couch for the patient to lie on and image capture above
- uses image intensifier
what is over couch flurosopy
- image receptor under couch and xray tube over head
what is c arm flurosocpy
mounted on opposite sides of c arm to be able to move around the patient
why type of fluoroscopic machinery is used in theatre
c arm
what are 3 reasons why under couch fluroscopy (traditional R&F) superior
- image receptor can come down close to the patient for best image quality
- most scattered radiation downwards away from operator eyes
- can Han lead rubber stops off the side of the image receptor to protect operator
what are some negatives of under couch fluoroscopy
- needs separate xray tube to do plain radiography as mixed application room
- needs wall bucky
- large screening carriage needs to be pushed backwards to pelvis or similar
- high to do extremities on
- have to remember to move the bucky to top or bottom end of table to use screening carriage
why was an over couch/remote system invented after the under couch/traditiional system
- allows operator easier access to patient for interventional procedures with sterile area
- less claustrophobic
- operator can step away from scattered radiation and move system with joystick
- doesnt need second xray tube for projection radiography (theres bucky under the table)
lastly why was a c arm system invented/ benefits it provides
- has all the benefits of a remote system
- many of the benefits of interventional room where instead of turning the patient, you turn the system
what are the 2 main issues with c arm system
- needs dedicated fluroscopy room
- not designed for plain radiography use
which of the 3 fluoroscopic systems is used for angiography
c arm
why is the c arm used for angiography / what benefits does it provide
- outstanding image quality to demonstrate small vessels and guidewares
- fast frame rates, minimal dose to patient and operator
- functions for long time without over heating
-
what body compartment is most demanding for fluroscopy
cardiology
be aware that cardiology is the most demanding fluroscopy with the highest dose risk
what are the 6 body systems scanned using R&F
- upper and lower gastro intestinal tract
- urinary system
- genito-urinary system and gynaecology
- billiary system with endoscope
- joints
what is a defecography/proctogram and what is it used for
examination of the lower bowel and rectum using x-rays
- for rectal incontinence
what contrast is used for fluroscopy of GI tract
barium (meal/swallow or enema)
what is an antegrade pyelogram
Antegrade pyelography is a diagnostic test that uses special contrast agent (dye) to produce detailed X-ray pictures of the upper urinary tract (kidney and ureter).
what is retrograde pyelogram
uses special contrast agent (dye) to produce detailed X-ray pictures of the ureters and kidneys.
- The difference is that in retrograde pyelography the dye is injected directly into the ureters rather than into a vein. It is better suited to see the definition of the upper urinary tract, particularly the ureter and kidney
what is antegrade pyelogram used for
to assess obstruction, insert shunts
what is retrograde pyelogram used for
haematuria, stone removal
what is a urethrogram and what is it used to assess
- xray imaging to asses structure of urethers
- used to see if there are strictures
what is hysteria-salpingogram
utilizes radiopaque dye injected into the uterus and is visualized with an x-ray.
- assess patency of Fallopian tubes
what is micturating/ voiding cystogram and what is it used to assess
- uses contrast to image urinary system
- used to identify UTI or incontinece
why do all the R&F systems have tilting tables
- need to move patient around on motor controlled top
- air and liquids. might be used to coat and outline the anatomy
- may ask patient to do things which are easier not supine
what are 2 common table tilts/ table positioning in R&F
- standard angulation 90 degree
- 30 trendelenburgh (head down)
what are the standard weight limitations on R&F table
150-240kg
how many focal spots does a R&F x-ray tube have
2
what main characteristics must the anode in an R&F have
- high anode heat capacity
what material filtration should a R&F xray tube have
copper
what material insert does the xray tube in R&F have
ceramic
an R&F xray tube has a gridded tube, what is this
- electrostatic ‘grid’ that holds the electrons close to the cathode, acting like a switch so they can be pulsed
what type of anode does the R&F xray tube have
- heavy, combination anode
what do all the features of an R&F xray tube allow/ benefit
all factors/ component of R&F xray tube contribute to not overheating and shutting the system down
what are the 2 types of anti-scatter grids used in R&F
- oscillating
- fixed grid
where would u find the grid in under couch, over couch or c arm
under couch = in screening carriage
over couch = in bucky under table
c-arm = static, fixed but removable grid in front of image receptor
why is a grid needed in fluroscopy
- you are usually imaging thick body parts at 80kV+ so lots of scattered radiation both backwards from patient and towards image receptor
a medical LED display monitor is the system used in R&F, what are the pros associated with this sytem
- short response time
- high definition (large pixel range)
the imaging storage system for R&F is short term, what does this mean
- enough space for 1-3 months
- need to archive onto PACS
what does PACS stand for and what is it
- picture archiving and communication system
- a computerised means of replacing the roles of conventional radiological film: images are acquired, stored, transmitted, and displayed digitally.
how does an R&F system using an image intensifier (traditional way) work
- xrays strike input phosphor (caesium iodide)
- phosphor glows
- light picked up by photocathode and turned into electrons
- electrons accelerated up image intensifier by high kV (increase in energy)
- magnetic field focuses electrons
- electrodes intensify energy more by focussing it on small output phosphor
- output phosphor (ZnCdS) glows
- light captured by CCD (charged couple device)
what material is the output and input phosphor in image intensifier
input = caesium iodide
output = zinc cadmium sulphide
what is image intensification gain
by how much does the image intensifier, intensify the image
define flux gain (FG)
increase in number of photons from output phosphor compared with input phosphor
what is the approx value of increase in number of output compared to input phosphor
x50 to x100
define minification gain (MG)
diameter of output compared to input
how do you calculate brightness gain
flux gain x magnification gain
what is the range of modern amplification
x5000 to x9000
find image of image intensifier component and label and state what each thing does
find image of R&F xray tube and label each thing and state what each thing does
what is the typical diameter of a circular field of view
32cm
what is the diameter of circular field of view for small or larger size
large = 38-40cm
small = 23cm
explain how an image is magnified on R&F system + the consequences related
- smaller central area on input phosphor is focussed onto the same output phosphor
- causes loss of brightness and increase in noise from smaller FOV
how would you regain signal to noise ration due to image magnification
double the dose (approx) to compensate and maintain same image quality
what is the relation between FOV and dose and image quality
the smaller the FOV, the higher the dose to maintain image quality
what is seen differently on live fluoroscopic image and acquired recorded imaged
- on live fluroscopy the image is reversed black and white (air is white and density is dark)
what are the standard pixel size of images on any fluoroscopic system
1024 x 1024 pixels, 8 bits
what is pre-set LUT
- lookup table
- preset that can adjust a much wider range of image parameters, things like exposure, sharpening and vignetting.
A preset can contain a LUT, but a LUT is not generally referred to as a preset.28 N
what is ABC and why do we need it
- automatic brightness control
- amount of light reaching output phosphor is adapted so image doesnt become too birght or dark and with adequate penetration
automatic brightness control is automatic, what function controls this and how does this adapt depending on the body part being screened
it is controlled from a sensing window in centre of image (red box seen)
- the shape and size of the sensing window should be set to match the anatomy expected for the preset protocol
what is FLARE artefact in fluroscopy and what causes it
- extraneous light around anatomy seen from raw radiation striking the input phosphor and gets included in sensor calculations
- Caused by a transition from heavy attenuation to minimal attenuation.
how does automatic brightness control work in practice (what 2 physical factors are adjusted for brightness control if not using ABC)
- POSITIONING
- COLLIMATION
how does positioning and collimation affect image quality in fluroscopy
- positioning and collimation controls the light
- the dose is then controlled
- which controls the brightness
- and positively or negatively impacts image quality
be aware that you must know how the system works to be able to optimise the images
e.g u see sensing window is too large which will make image too bright and cause insufficient penetration
how can too much flare and anatomy within the image affect the image quality
- becomes dark and noisy as the exposure and gain are reduced
how is the image quality affected if there is too much dense barium-filled, bones, metallic implants or heart
- image becomes over bright and saturated
what is AGC and why is it used
- automatic gain control
- when light intensity within image drops, system can automatically increase electronic signal (GAIN) to compensate without increasing xray dose
in practical terms, AGC can maintain the signal of a movie object whilst giving time for the ABC to react
what practical issues are there with the physics of the image intensifier
- has a curved surface which distorts the image (pin-cushion effect)
- edges of image are long way from source so fade
- image is intensified using electrons and magnets which susceptible to earths magnetic field
- image made with light and when here’s less light you must increase radiation dose to compensate
what is the difference in dosage for a general view and a diagnostic view in fluroscopy
low dose per Fram for general view
higher dose, higher quality images for diagnosis and archiving
what are the 2 types of imaging in fluroscopy and the difference between them
- fluroscopy (screening) (lower dose)
- fluorography (acquisition/record images) (higher dose)
how much higher is the dose for fluorography (acquisition image) than fluroscopy (screening
x5 to x10
what are 3 types of image capturing done on fluroscopy system
what are the difference between them
- fluoroscopic screen captures (can store fluroimage currently on screen)
- last image hold
- fluorography ( 1 acquired image at a time or a sequence)
