Fluoroscopy

What is fluoroscopy?

Imaging technique using a fluoroscope to capture realtime images of internal structures of a patient in real time

What is an image intensifier?

Evacuated electron-optical device

Captures time varying image in fluoroscopy

Computerised image processing enhances presentation

What is the physical structure of the image intensifier?

Glass/ceramic envelope

Surrounded by metal housing

Non-magnetic

What are the three main components of the image intensifier?

Input screen

Electron-optics

Output screen

What are the three features of the input screen?

Input window

Inout phosphor

Photocathode

What is the function of the input window?

Supports vacuum

Can’t be too thick and prevent most X-ray photons penetrating through

What are the effects of excessive interactions of x-ray beams with input screen components?

What is the structure and function of the input phosphor?

Layer of fluorescent material on a thin metal layer

Needle-like crystalline structure

Primary x-ray detector

What is the structure and function of the photocathode layer?

Converts light photons to electrons

Layer of Caesium Antimonide well matched to the blue light of the input phosphor

No of electrons produced is directly proportional to x-ray intensity

What is the function of the electron-optics?

Electrons accelerated through a positively charged anode

All electrons have the same path length due to curvature of input

Focusing electrodes ensure electrons travel in straight line

What is the function of the output window?

Focusing electrons on a smaller area to amplify brightness

Thin aluminium layer prevents back scatter

What is the image intensifier conversion process?

X-rays converted to light in input phosphor

Light converted to electrons in photocathode and electrons accelerated

Electrons converted to light in output phosphor

What image display is used in modern fluoroscopy imaging?

TV cameras produce analogue signals that are converted to digital

Charged Coupled Device store charge proportional to light hitting it

What is flux gain?

Extent to which the light output has been intensified

What is minimisation gain?

Intensification from reducing the image size at the output

What is overall gain?

Combination of flux gain and minimisation gain

How can magnification be used in fluoroscopy?

Change voltages of focussing electrodes

More electrons cross over at a single point closer to the input

Reduces minimisation gain and brightness

What is automatic gain control?

Automatically adjusting sensitivity to maintain brightness

At excess of higher dose or noise

What is automatic brightness control?

Controls dose and therefore brightness

Measures light intensity or camera signal to adjust x-ray generator

Can increase kVp or mA

What is flat panel fluoroscopy?

Uses flat panel detectors rather than image intensifiers

No distortions, no magnification and high quality image captures

What are the advantages of using flat panel fluoroscopy?

Smaller an less bulky

Lacks distortion

Incorporates more digital applications

What are the disadvantages of flat panel fluoroscopy?

Lower signal to noise ratio

Slower response

What is pulse fluoroscopy?

Pulsing x-ray beam not detectable to the eye that reduces patient dose

Where are low pulse rates used?

Little or slow movement such as imaging fractures

When are higher pulse rates used?

Fast movement such as imaging of the heart to avoid blurring

What is the purpose of filtration in fluoroscopy?

Uses interchangeable filters to harden x-ray beam and reduce dose

What is the process of recording images on digital systems?

Store the signal from the detector

Fluorography

What are the ways images can be recorded?

Last image hold left on the monitor for review

Digital spot images are single shots taken wit high mA

What s digital subtraction angiography?

Produces image of contrast filled vessels in isolation form other tissues

Images taken in quick succession

Mask (non-contrast image) and contrast image subtracted from each other pixel by pixel

What is pixel shifting?

Corrects misalignment of successive images

Only corrects translational motion

What is CBCT fluoroscopy?

Rotational imaging tool that takes successive images at different angles

Reconstructed 3D images

What are some radiation monitoring metrics for patients?

Dose area product calculates total procedure dose

Reference air KERMA is an indicator for patient entrance dose

Exposure time uses a five minute warning system

What are the patient considerations for fluoroscopy procedures?

Far from x-ray tube and close to detector

Reduce dose and reduce magnification

What are the clinical considerations for fluoroscopy procedures?

Tube under imaging table to reduce scatter

Clinician positioned on receptor side to reduce scatter from patient