Fluoroscopy Lecture Notes PDF

find more resources at oneclass.com Week 11 Lecture 2 What is Fluoroscopy? Allows dynamic/real time radiographic viewing of various body structures/systems (0.5 mA - 5mA) Continuous (or near continuous) x-ray beam (BEAM “ON”) Observe physiology (ie peristalsis, arterial flow, swallowing action, ven...

find more resources at oneclass.com Week 11 Lecture 2 What is Fluoroscopy? Allows dynamic/real time radiographic viewing of various body structures/systems (0.5 mA - 5mA) Continuous (or near continuous) x-ray beam (BEAM “ON”) Observe physiology (ie peristalsis, arterial flow, swallowing action, venous flow) Viewed by TV monitor & able to record images or entire studies Can only see parts that have be enhanced by contrast Fluoroscopy Does so at a fraction of the exposure rate of still imaging (5 mA vs hundreds of mA) Dose still higher than traditional radiography - exposure time in minutes instead of seconds or milliseconds Pulse - reduced dose but maintains temporal component Fluoroscopy Uses Ba studies (upper, lower GI tract) Ba studies are decreasing in major centres & there is less emphasis although still covered in the National Competency Profile Fluoroscopy used in Angiography & Interventional procedures Mobile (C-Arm Fluoro) in OR Intramedullary nailing, hip pinnings, closed reductions, & pacemaker insertions Traditional vs Flat Panel Detector Fluoro Systems Many newer fluoroscopy suites incorporate FPD detectors Traditional - image intensifier system (used more than FPD) Focus of lectures & content Still very widely used Fluoro Instrumentation X-ray tube at bottom General Fluoro Process Transforms the x-ray photons emerging from the patient into a small, bright light image Light image is fed into a TV camera (vidicon), CCD or solid state device that transforms the light image into an electrical signal Electrical signal can be fed into a monitor for real time viewing Images produced fluoroscopically can also be saved digitally & exposed on IR X-ray to electrical to the TV camera Main Components of Fluoro Imaging System Image Intensifier Captures remnant beam Produces continuously updated light image Video camera Captures light image (analog) Provides continuously updated electrical signal (digital) Viewing monitor Receives electrical signal (digital) Produces continuously updated light image (analog) Flat Panel Detector Just x-ray to electrical signal to video/TV camera (no light) Captures remnant beam find more resources at oneclass.com find more resources at oneclass.com Provides continuously updated electrical signal Traditional Fluoro Suite Always wear lead X-ray tube on the bottom Image intensifier at the top Signal goes from bottom to top Mobile Fluoro Unit Used in OR Image Intensifier (II) Basics Function: convert remnant beam to bright visible light image Concept: add brightness to light image from phosphor screen by: Producing more light photons at output than were created at input Concentrating light onto smaller location Glass vacuum tube Enclosed in lead lined metal container Absorbs remnant beam Vacuum inside Image Intensifier Tube 5 Basic Elements 1. Input phosphor (IP) 2. Photocathode (PC) 3. Electrostatic focusing lenses: used once potential difference is applied (kVp drives the potential difference) 4. Accelerating anode 5. Output phosphor (OP) Image Intensifier Construction Large vacuum tube glass/metal envelope Input end CsI phosphor Photocathode (antimony/cesium compounds) Focusing electrodes (electrostatic lenses) Belt-like bands w voltage supplies Output end Anode ZnCdS phosphor Image Intensification find more resources at oneclass.com find more resources at oneclass.com - Input phosphor Made of CsI Photo cathode Responds to light exiting input phosphor Emits electrons Antimony & Cs compounds Electrostatic lenses Focus electrons Output phosphor Receives electrons from PC Emits 50-75x more light than received by PC Allows incoming signal to be intensified, keeping the dose low Image Intensification Operation X-ray photons absorbed by IP Emitted light hits PC, electrons released Electrons pulled by large potential difference b/n anode & cathode Electrons focused by focusing electrodes to cross tube to output side Electrons bombarded output phosphor (OP) Phosphor emits intense light photons Intensification of Signal for 1 Point of the Image Light intensity emitted by IP is proportional to x-ray photon intensity absorbed Electron intensity emitted by PC is proportional to light intensity absorbed by PC Electrons are accelerated by positive voltage (electronic gain) Each electron hits OP, deposits energy Light intensity emitted is proportional to kinetic energy (KE) absorbed by OP Since OP has a smaller diameter, overall light intensity emitted by OP is greater than light intensity emitted by IP; if you change the diameter, it affects dose to the patient, rad would do this not the tech; Brightness Gain Definition: increase in brightness of OP image compared to IP image Not directly measurable Contributors Minification Gain - increase in light intensity due to decrease in image size Flux Gain - increase determined by conversion efficiency of input phosphor, PC, OP Brightness gain = minification gain x flux gain (depends on photons that OP & x-rays at the OP) IP receives x-rays after it goes thru the grid to electrons Electrostatic focusing lense drives electrons to OP & changes it into an electric signal OP is always smaller than IP OP has better spatial resolution Flux gain = # of output light photons/# of input x-ray photons Minification gain = (di/do)^2 Where di is the diameter of input phosphor & do is the diameter of OP Operational Feature of II: Magnification mode Reduced input POV is displayed over entire OP Improves contrast & spatial resolution Good for visibility BUT requires higher input exposure rate to maintain overall light intensity of OP image Less minification gain due to decrease in IP size, therefore must increase exposure rate Magnification Mode: How it works System decreases collimated field size Smaller diameter of IP receives radiation Smaller diameter of PC emits electrons System alters voltage pattern on focusing electrodes Electron beam focusing changes, crossover occurs sooner Electron beam diverges more after crossover, fill entire OP screen Image find more resources at oneclass.com find more resources at oneclass.com Automatic Brightness Control (ABC) Technical factors can be controlled manually (rarely used) Depends on the thickness of the tissue Most often adjusted automatically via ABC Goal: maintain brightness of image regardless of tissue thickness or density, FOV Functions similar to AEC Maintain SNR by maintaining photon fluence to the IP Can adjust mA, kVp, in all fluoro modes In pulsed fluoro, can increase the duration of the pulses Tech needs to make sure the room is prepared, the patient is prepared Image find more resources at oneclass.com