Fluoroscopy Flashcards
What is Fluoroscopy?
Real time imaging viewed on a display monitor in the clinical room
What is the matrix size and grey scale for Fluoroscopy?
512 x 512 pixels and 8 bits of grey scale
What types of images can Fluoroscopy acquire?
Continuous (cine) or pulsed fluorographic images
What is Fluorography?
Images usually formed and viewed after the x-ray exposure is complete
What are the advantages of Fluorography over Fluoroscopy?
Better quality images but at higher doses
What is the matrix size and grey scale for Fluorography?
1024 x 1024 pixels with each pixel representing 10 bits of grey scale information
What are ‘Greyscale’ digital x-ray imaging modes?
Fluoroscopy, digital cardiac, and digital spot imaging
What is Subtractive digital imaging?
Base image taken which is then subtracted from the image with contrast to result in an image showing the contrast only
What is an Image intensifier (II)?
A system that converts the input light into a much higher output (gain or intensification)
What is the formula for brightness gain (Gbrightness)?
Gbrightness = Gminification x Gflux
What does Gminification describe?
The increase in brightness due to the demagnification of the image in the II tube
What is the formula for Gminification?
Gminification = (Dinput / Doutput)^2
What is the Image intensifier conversion factor (Gx)?
Gx = L / X’ where L = luminance of the II output and X’ = II entrance dose rate
What factors affect the brightness gain of an II tube?
Magnification and Flux
What are the standard configurations of radiography/fluoroscopy equipment?
Under table x-ray tube with an over-couch II system, Table can be tilted and rotated, Radiologist stands beside patient
What are the configurations of Remote control R/F equipment?
X-ray tube mounted over the bed and II system underneath, Higher scattered dose so radiologist stands behind screen
What is a Fixed C-arm?
II x-ray tube and II system attached to a C-structure that allows rotation and movement
What is a Mobile C-arm?
System that can be transported on wheels to different locations
What is the II input window?
Convex metal shield, usually aluminium or titanium foil, that covers the input face of the II
What is the Input phosphor made of?
Layer of sodium activated caesium iodide (CsI:Na)
What is the thickness of CsI:Na in the Input phosphor?
400-500μm
What does the Photocathode do?
Absorbs fluorescent light photons and releases a pattern of electrons
How many electrons are released per absorbed x-ray photon in the Photocathode?
Approximately 200 electrons
What does the Electron focusing system do?
Focusing electrodes direct electrons to the output screen to create an exact but minified image
What is the material used for the Output screen in an II tube?
Thin layer of silver-activated zinc cadmium sulphide (ZnCdS:Ag) crystals
What is the purpose of the Output Window?
Optically transparent glass block port through which the intensified light image exits the II tube
What are the methods to minimize halation in the Output Window?
Smoked glass, Special optical coatings, Very thick glass, Fibre-optic bundle
What is Magnification in fluoroscopy?
Achieved electronically with electronic focusing of the electron beam
What is the effect of Magnification on image brightness and dose?
Less bright image and increased dose required
What is the benefit of using a Charged Coupled Device (CCD) sensor over a TV camera tube?
Small, inexpensive, compact, low-power consumption, self-scanning image readout, negligible lag, excellent stability, long life-time, compatibility with digital x-ray imaging modalities
What does Automatic brightness control (ABC) do?
Maintains constant viewing condition by regulating mA and kV
What are the modes of Automatic brightness control (ABC)?
Minimum patient dose rate mode, Standard patient dose rate mode, High patient dose rate mode
What is the purpose of Digital image processing in fluoroscopy?
To improve the appearance of the image on the screen
What are the types of Digital image processing?
Greyscale processing, Spatial filtering, Temporal filtering
What is a Flat Panel Detector (FP detector)?
Flat panel of detectors that provide a direct electronic readout instead of requiring the conversion of analogue to digital
What are the benefits of Flat Panel Detectors?
Smaller equipment, digital video signal, better temporal resolution, better image quality, fewer artefacts, higher detective quantum efficiency, zoom option
What is Digital Subtraction Angiography (DSA)?
Procedure that highlights contrast-outlined structures by removing background anatomical structures
What is the dose limit for Maximum entrance skin dose rate?
100 mGy per minute
What is the dose range for Digital fluoroscopy?
10 to 30 mGy per minute for larger patients
What is the main contribution to staff dose?
Scatter of x-rays from the patient
What are the methods to minimize staff dose?
Use of lead aprons and other radiation shields, Maintain maximum possible distance from patient, Monitor individual staff doses
What are the methods to minimize patient dose?
Tight collimation of x-ray beam, Appropriate x-ray beam spectral filter, Increase distance between patient and x-ray source, Minimize gap between patient and II entrance, Remove anti-scatter grid if possible
What is Fluoroscopy in simple terms?
Real-time imaging viewed on a display monitor
What is Fluorography in simple terms?
Image displayed after x-ray exposure
How is image intensification measured in IITV?
Brightness gain = minification gain x flux gain
What factors affect brightness gain in IITV?
More minimisation, reduction in input field area, higher voltage across II tube
What materials are used in the II input window?
Aluminium or titanium foil
What is the purpose of the input phosphor in IITV?
Good x-ray absorption efficiency
What is the main function of the photocathode in IITV?
Releases electrons into the II tube
What happens during electron focusing in IITV?
Electrons are directed to create an exact but minified image
What is the output screen made of in IITV?
ZnCdS:Ag that converts electrons into light photons
What does the II TV camera do?
Scans photoconductive target to create a flow of electrons corresponding to light intensity
What is the function of CCD sensors in IITV?
Each pixel has an associated electrode, charge accumulation proportional to light intensity
What technology do Flat Panel Detectors use?
Same as digital radiography
What is Automatic brightness control (ABC)?
Maintains constant viewing condition by regulating mA and kV
What are the types of digital processing in IITV?
Greyscale processing, Spatial filtering, Temporal filtering
What is the main source of staff dose in fluoroscopy?
Scatter of x-rays from the patient
What are the strategies to minimize staff dose in fluoroscopy?
Use lead aprons, maximize distance from patient, monitor doses
