Fluroscopic Imaging Flashcards
what is fluoroscopy?
- Real time imaging of internal structures displayed on a monitor
- it allows the imaging of moving internal structures by the use of continuous x-rays
what are the essential components in analogue fluoroscopy?
- X-ray tube
- flat panel detector
- image intensifier
where is fluoroscopy used?
- It is widely used in radiography to produce images of moving structures which can be used for real-time diagnostic imaging and treatment guidance.
- commonly used for evaluation of various parts of GI tract. These examinations use barium sulphate as contrast media (barium swallow, barium meal and barium enema)
- Fluoroscopy maybe useful in detection of certain GI tract cancers. However, the hepatocellular carcinomas can not be detected by this imaging technique.
how is image formed in fluoroscopy?
- X-ray photons enter tube through aluminium or titanium window
- x-ray photons hit the input phosphor layer of sodium activated caesium iodide (CsI:Na) and release light photons
- Light photons detected by photocathode and converted into electrons to be released into the II tube
- Electrons accelerated and focused onto the output screen (silver-activated zinc cadmium sulphide crystals) as a minified and inverted image
- then electrons are converted into light photons by the thin layer on the inner surface of output window and released from the output window
what are the features of FPD in fluoroscopy?
- Flat panel detectors utilise the same technology as digital radiography
- FPD provide a direct electronic readout instead of requiring the conversion of analogue to digital as is seen in the IITV.
- Similar to digital radiography dynamic FPDs can be direct or indirect.
- However, they are more commonly indirect with a CsI:Tl x-ray scintillator layer which is superimposed onto an a-Si high resolution active matrix.
what are the advantages of FPD in fluoroscopy?
- compact construction
- both dynamic and static images recorded 3. rectangular field allows more information
- wider dynamic range
- post processing options common to all digital images
- do not suffer from image distortions like Its
- may provide 50% reduction in dose
how to minimise patient dose in fluoroscopy through equipment set up?
- Tight collimation of x-ray beam
- Appropriate x-ray beam spectral filter to minimise patient skin dose rate
- Increase distance between patient and x-ray source
- Minimise gap between patient and II (image intesifier) entrance
- Remove anti-scatter grid if possible
how to minimise patient dose in fluoroscopy through imaging procedure?
- Avoid constantly imaging at same projection angle
- Minimise x-ray beam on time
- ABC mode with lowest dose rate possible for diagnostic images
- Pulsed fluoroscopy with minimum acceptable pulse rate if possible
- Avoid use of II zoom
what are the various ways to minimise a patient and operator dose?
Patient dose
1. regulating set up equipment
2. imaging procedure
3. digital process
4. fluoroscopy
Operator/Staff dose
1. Use of lead aprons and other radiation shields e.g. gloves, glasses and thyroid protection
2. Lead-rubber drapes and movable lead glass shields
3. Maintain maximum possible distance from patient
4. Monitor individual staff doses
5. by regulating the stray radiation
what are the two forms of FPD?
- indirect capture - caesium iodide amorphous silicon
2. direct capture - amorphous selenium
what are the features of FPD?
- 60 fps (frame per second, rapid readout via fibre optic cable)
- low dose application needs high fill. factor (area sensitive to x-rays) specially with indirect systems
- back lighting system erases detectors/charge from previous frame or in b/w frames to prevent ghosting
- individual frames stored digitally
- sometimes LIH (last image hold) used instead of conventional spot film images
- photospot images have. same characteristics as digital fluoroscopy
what are the limitations of FPDS
- nosier than Its, contrast to noise ratio. (CNR) may be a problem
- resolution usually little lower than II (due to comparatively lower spatial resolution?)
outline the imaging options available for the following
- mouth, pharynx, oesophagus
- oesophagus, stomach, duodenum
- small bowel
- large bowel
- mouth, pharynx, oesophagus - videofluroscopy, barium swallow, endoscopy
- oesophagus, stomach, duodenum - barium meal, endoscopy, CT
- small bowel - small bowel enerma, CT, isotope scan, M2A capsule imaging
- large bowel - barium. enema, CT colonography, colonoscopy, conventional CT
what is capsule endoscopy?
it is a capsule fitted with a disposable mini video camera to examine parts of small intestine for diagnosing unexplained bleeding or other abnormalities where standard scope cannot reach
what is the procedure involved in capsule endoscopy?
- fasting is necessary prior to the capsule swallowing
- capsule glides smoothly through the digestive tract
- wireless recorded worn on a belt to receive signals from transmitter on capsule through sensors placed on patients body
- capsule naturally excreted
