fluoroscopic system: flat panel (modern) Flashcards
what is the difference between the production of xrays in flat panel and image intensifier fluroscopu
flat panel = receives xrays from high spec medium frequency generator
image intensifier = receives xrays from regular xray tube
what is the power range of the frequency generator in flat panel fluroscopy
65-126kw
what is the exposure range of the xrays the frequency generator makes for static images and fluroscopy
static imaging = 40-150kV, 32-63mA
Fluroscopy = 40-125kV, 0.5-4mA
both have 5ms-5 second times
what is the range of pulsed images per second the can be produced by the frequency generator
1 - 8 per second
(cardiac systems up to 30/sec)
describe the process of how a flat panel fluoroscopic system works
- xrays converted to light using caesium iodide in a scintillator
(no electron acceleration or minification to reduce noise)
- light then reaches a low-noise amorphous silicon (a-Si) photodiode array where it is converted into an electrical charge
- Each photodiode represents a single pixel, and each produces an electrical charge that is read out digitally by the TFT array layer underneath
- then finally being sent to the image processor
why is the caesium iodide layer thicker in flat panel than image intensifier system
for greater xray absorption/sensitivity
flat panel does not have electron acceleration to minimise noise production, so what does it do instead to reduce noise
pixel binning
- adding together groups of pixels to make a smoother image
what is a negative of pixel binning
reduced resolution
how can pixel binning affect frame rate
increase/faster frame rates as it reduces the amount of data to be handled
what are the 2 ways to magnify an image using the flat panel system
- electronic zoom of binned pixels (no increase in resolution, just part of panel is displayed magnified
- pixels unbanned in centre of detector, increases resolution
both fluroscopy and recorded images are dynamic methods
achieved nu pulsing xrays at several frames per second
what controls the xray pulses in fluroscopy
gridded tube, it suspends electrons ready to expose
compare the dosage of pulsed and continuous fluroscopy
pulsed fluroscopy significantly reduces dose to patient
pulsed fluroscopy does reduce dosage to patient however there are disadvantages associated, what are they
- blurred when patient moves
for very slow pulse rates as in pulsed fluroscopy, when several frames have been averaged to smooth out the noise what can happen to the contrast of the imageq
- have higher contrast resolution due to reduced noise
what is the typical fluroscopy pulse rate
1-15 frames per second
what are the 5 things you can adjust to control flat detector image quality
- ABC, AGC, AEC
- collimation
- edge-enhancement
- noise reduction filter
- pulsed imaging to reduce dose
what are the 4 types of noise reduction filters/systems
- temporal/recursive filtering / frame averaging
- motion tracking
- background supression
- pixel binning
what type of artefact/effect will you find in image intensifier but not flat panel system
no pin-cushion effect due to curvature of front of image intensifier causing blur at the edges
why is there no s-distortion found in flat panel but is in image intensifior
- no magnets accelerating electrons in flat panel
- so no s-distortion caused by earths magnetic field acting on focussing electrodes
what is done to correct s-distortion in image intensifier system
s-distortion corrections are made to the system by the service engineer
what is another advantage that flat panel has over image intensifier system
no vignetting, where the periphery of the image is less bright than the center and has lower resolution
know that overall the flat panel has 3 major benefits over image intensifier in terms of artefacts/errors that can occur in image production
- pin cushion effect
- s-distortion
- vignetting
what are edge detection filters used for
edge enhancement
how does the fluoroscopic machine differ from the catheter lab/ high-performance systems to regular
- gantry c-arm suspended from floor or ceiling mount
describe how the additional advantages/features found in high performance systems
anti-collision software, gantry and table (predictive and actual)
fast moving (moves 180 degrees in 30 seconds)
all high performing systems use flat panel not image intensifier
high performance systems have virtual collimation, what is this
allows you to quickly collimate or perform adjustments at the workstation right before X-ray exposure
high performance systems have roadmapping, what is this
can overlay the vessel to reduce fluroscopy to check location of guide wire
what is LIH
last image hold
high performance systems have live stent enhancement, what is this
real-time verification of the stent positioning while moving the device.
high performance systems can image fuse with CT, US etc
what are the highest risk dose procedures in R&F and other fluoroscopic systems
R&F (continuous xray image) = multiple lateral images of the pelvis/lower spine
other systems = cardiac and neurological intervention
what is the optimal distance of the patient to the tube and patient from detector
patient to tube distance = 80cm
patient to detector (flat panel or image intensifier) = 30cm
why is there an optimal distance of the detector and tube from patient?
- reduces the scatter pattern of the radiation to minimise risk to operator and surrounding ppl
what is dose awareness
back scatter to operator when they normally work from the right
when the c arm is lateral, where is the back scatter the highest
on the tube side of the patient (right beside where the x-rays are coming out of tube)
left lateral, a common projection gives highest operator dose when operators put catheters into femoral and radial arteries
what are the ranging radiation protection equipment when using fluroscopy
- lead curtains/suspended drapes (mobile or suspended from table)
- lead apron
- lead gloves
- lead goggles
- lead thyroid collar
- mask
- lead shoes
- lead panties
what are some dose control activities you can do
- dosimeter under lead apron, fingers or next to eyes
- never stand within 2m of patient
- keep fluroscopy to minimum (use it pulsed)
- last image hold to avoid need for further xrays
- use 2nd monitor for reference images to avoid live fluroscopy
- store fluoroscopic images when image quality is enough
- keep operator aware of flare time and patient dose displayed
- keep image receptor close to patient as possible
- dont magnify imaging unless needed
- collimate
greatest patient dose risk in order of different imaging:
- angiography system with 3D
- catheter lab
- R&F system
- Surgical mobiles
5.finger xray
