WEEK 5 - Fluoroscopy

main function of fluro

provides dynamic imaging that allows for functional pathology to be visualized

• swallowing

• peristalsis

• heartbeat

types of systems

• fixed fluoro systems

• mobile fluoro systems

Fixed Fluoro

permanent room arrangements

how is the fixed fluoro usually set up

x-ray tube is under table, image intensifier (receptor) above the patient

Mobile Fluoro are also known as

portable fluorography systems / C-arms

operating system types

• II

• FPD (DF)

diff between II and DF

II

• uses lower mA ranges (1-5)

• purpose is to make image brighter

DF / FPD

• uses higher ranges

image intensifier

• older technology

• can be fixed or portable

x-ray tube in fluoro

same design as general x-ray equipment but the capture mechanism of the II tube is unique

Components of II

1. input phosphor

2. photocathode

3. glass envelope

4. electrostatic lenses

5. anode/focal point

6. output phosphor

Image capturing steps in II

1. input phosphor: xrays are converted into light photons/visible

2. photocathode: exposure to visible light releases -e (photoemission)

3. glass envelope: high voltage (25,000-30,000 volts) is applied to accelerate -e across

4. electrostatic lenses: negatively charged metal focuses and narrows the -e stream

5. anode: part of electrostatic lenses which help -e crossover at the focal before reaching the output phosphor

6. output phosphor: converts electrons into light

input phosphor is made of

microscopic needle-shaped CsI crystals

photocathode is made of

cesium and antimony compounds

minification

the process of narrowing and focusing the -e emitted from the photocathode onto the much smaller output

effect of minification

-e concentrated into a smaller region = screen to glow more brightly = brighter image

output phosphor is made of

zinc cadmium sulphide

size of output phosphor

1/10 of the input phosphor size

larger ratio of input size : output size

increases the brightness and resolution

flux gain and its influence

# of output light photons / number of input x-ray photons

• higher flux gain = better IQ, brighter image

significance of II

amplifies the light emission from the original input phosphor without increasing exposure

minification gain and calculation

• change in image size from the input phosphor to the output phosphor

• input phosphor diameter (d1), divided by output phosphor diameter (d0), all squared

• (d_1/ d_o )²

brightness gain and calculation

• allows us to monitor the decreasing image brightness as the II ages (exposure will increase to maintain IQ)

• minification gain x flux gain

Digital Fluoro advantages

increased acquisition speed and the ability to post-process digital images

interrogation rate - DF

time required for the generator to activate the tube to the desired exposure

extinction time - DF

time required to terminate the exposure

pulsed acquisition rate function and defined by

• manages the high mA and heat load

• interrogation rate x extinction time

duty cycle

fraction of time that the tube is activated compared to when it’s off

• important for assessing a device's performance and durability

• used to determine how long a device can run without overheating or needing maintenance 

significance of Pulsed DF

reduces patient dose and should be routinely used

types of DF receptors

• Charge-Coupled Device (CCD)

• Flat Panel DR

CCD

• coupled to output phosphor directly or by fiberoptics

• converts light to electrical charge

• improves IQ

Flat Panel Detectors (FPD) advantages

extremely fast duty cycles, allowing further exposure reduction yet providing improved image quality

FPD design lincludes

• improved image accuracy (no distortion)

• consistent image quality across the whole image

• more compact and lighter than II → easy movement and positioning

• High Detector Quantum Efficiency (DQE)

FPD types

• indirect: uses phosphor which first transforms x-ray
  photons → light → electrical signal

• direct: converts photons → electrical signal for data
  quantization

magnification mode usage and why

should be limited as it increases image noise and exposure

how does mag mode work

by reducing the size of the input phosphor and adjusting the focal point further from the output phosphor

Automatic Brightness Control (ABC)

system that maintains the desired level of brightness when using magnification mode

Exposure Increase and Calculation - mag mode

• to see the exposure increase when using mag mode

• IP_1² / IP_2²

• (x cm)2 / (y cm)2

operating FPD

fluoro equipment is activated by either a footswitch or a hand switch

SOD for exposure safety

minimum SOD

• 38cm in FIXED

• 30cm in MOBILE

short SOD causes

skin damage or exposure burns

fluoro exposure safety procedures

• position tube beneath pt to reduce scatter exposure of the head, neck, torso (lower extremities are less radiosensitive)

• personnel lead aprons (≥ 0.5 mm of lead)

• bucky slot covers (0.25 mm of lead)

• protective curtain (0.25 mm of lead)

cause of fluoro artifacts

II shape and lensing can generate artifacts

typical brightness gain of fluoroscopy systems

500-3000