Fluoro Equipment Review RHB Fluoro Syllabus & Rad Prot

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Presentation transcript:

Fluoro Equipment Review RHB Fluoro Syllabus & Rad Prot June 2008 ccrt55 revised

History of fluoroscopy Thomas Edison invented the fluoroscope in 1896 He was the first one to try to image the brain Fluoroscopy was performed in total darkness so the eyes had to be adjusted for 30 minutes by wearing red goggles

General Fluoroscopic Concepts 1. Primary factors associated with fluoroscopy 2. High-level fluoroscopic procedures 3. Pulsed fluoroscopic procedures 4. Scatter, magnitude, directionality & leakage radiation 5. Dose trade offs versus quantum mottle 6. Potential image distortions

Basic “Imaging Chain”

Basic Componets of “old” Fluoroscopy “Imaging Chain” Primary Radiation EXIT Radiation Fluoro TUBE PATIENT 105 Photospot Image Intensifier Image Recording Devices Cassette ABC Fiber Optics OR CINE CONTROL UNIT VIDICON Camera Tube TV

Basic Componets of “NEW DIGITAL” Fluoro“Imaging Chain” Primary Radiation EXIT Radiation Fluoro TUBE PATIENT Analog to Digital Converter ADC Image Intensifier ABC CCD TV

Modern fluoroscopic system components

The image intensifier (I.I.) I.I. Input Screen Electrode E1 Electrode E2 Electrode E3 Electrons Path I.I.Output Screen Photocathode +

Image Intensifier VACUUM TUBE ENCASED IN A LEAD HOUSING = 2MM PB (PRIMARY BARRIER)

Cesium Iodide (CsI) Phosphor on Input Phosphor CsI crystals grown linear and packed closely together The column shaped “pipes” helps to direct the Light with less blurring Converts x-ray photons to visible light SIDE VIEW

Input phosphor X-rays hit this concave surface first. It is made of cesium iodide crystals shaped like tiny needles packed tightly together. The more crystals, the better the spatial resolution. The crystals convert the x-ray photons to light energy so the more crystals, the more energy converted to light the less radiation needed so patient dose goes down.

photocathode The photocathode is close to the input phosphor but can’t touch it otherwise there would be a chemical reaction that would destroy the phosphor. The photocathode is made of antimony and cesium compounds. When these compounds come into contact with light they emit electrons The photocathode has the job of turning the light into photoelectrons.

Veiling glare Scatter in the form of x-rays, light & electrons can reduce contrast of an image intensifier tube.

Functioning of Image Intensifier

Intensifier Format and Modes Note focal point moves farther from output in mag mode

BG = MG X FG FLUX GAIN – increase of light brightness due to the conversion efficiency of the output screen 1 electron = 50 light photons is 50FG Can decrease as II ages Output phosphor almost always ____ inch Made of _____________phosphor Flux gain is almost always 50

Raster pattern scan lines Video Field Interlacing

Horizontal resolution The number of dots on the horizontal scan line. How close together are they? It is the product of scan lines, frame rate and frequency rate

Vertical resolution How far apart are the horizontal scan lines? Since we can’t have more than 525 scan lines, we can have more dots that are smaller The Kell factor is a component of vertical resolution. Memorize the number 0.7 and know that it is the Kell factor & part of vertical resolution

Viewing Fluoroscopic Images

Image Quality Contrast Resolution Distortion Quantum mottle

Contrast Controlled by amplitude of video signal Affected by: Scattered ionizing radiation Penumbral light scatter

Resolution Video viewing Limited by 525 line raster pattern of monitor Newer digital monitors 1024 - better resolution

Size Distortion Affected by same parameters as static radiography Primarily OID Can be combated by bringing image intensifier as close to patient as possible

Shape Distortion Geometric problems in shape of input screen Concave shape helps reduce shape distortion, but does not remove it all Vignetting or pin cushion effect

Image distortion PINCUSHION EFFECT PINCUSHION ?? WHAT IS VIGNETTING??

Image Quality Terms that are necessary to know: Vignetting is the loss of brightness at the periphery of the II due to the concave surface Pincushion effect is the drop off at the edges of the II due to the curved surface Quantum mottle is the grainy appearance on the image due to statistical fluctuations The center of the II will always have the best resolution. Lag is the blurry image from moving the II too fast

Regulations about the operation Fluoroscopic tubes operate at currents that range from0.5 to 5 mA with 3 - 4 the most common AEC rate controls: equipment built after 1974 with AEC shall not expose in excess of 10 R/min; equipment after 1974 without AEC shall not expose in excess of 5 R/min

Other regulations Must have a dead man switch Must have audible 5 min. exposure timer Must have an interlock to prevent exposure without II in place Tube potential must be tested weekly Brightness/contrast must be tested annually Beam alignment and resolution must be tested monthly Leakage cannot exceed 100mR/hr/meter

more regulations Must have a device to prevent operation at a SOD of less than 12” A bucky slot cover must be provided Aprons must be at least 0.25 mm Pb equivalent 2.5 mm Al equivalent filtration is required Must provide at least 12” and preferably 15” between source and table top

Fluoroscopy exposure rate For radiation protection purposes the fluroscopic table top exposure rate must not exceed 10 mR/min. The table top intensity should not exceed 2.2 R/min for each mA of current at 80 kVp

Patient Protection A 2 minute UGI results in an exposure of approximately 5 R!! After 5 minutes of fluoro time the exposure is 10-30 R Use of pulsed fluoro is best (means no matter how long you are on pedal there is only a short burst of radiation) ESE must not be more than 5 rads/min W/0 AEC 10 WITH & 20 BOOST

Always keep the II as close to the patient as possible to decrease dose Highest patient exposure happens from the photoelectric effect (absorption) Boost control increases tube current and tube potential above normal limits Must have continuous audible warning Must have continuous manual activation

ESE FOR FLUORO TLD PLACED AT SKIN ENTRACE POINT for fluoro 1 – 5 R/MINUTE AVE IS ________R/MIN

ESE FOR FLUORO TLD PLACED AT SKIN ENTRACE POINT 1 – 5 R/MINUTE AVE IS 4 R/MIN (now closer to 1 – 3 R/min) When not known – assume 4 R

Framing and patient dose syll = Pg 31 which is BEST The use of the available film area to control the image as seen from the output phosphor. Underframing Exact Framing, (58 % lost film surface) Overframing,(part of image is lost) Total overframing

EXPOSURE RATES FLUORO MA IS 0.5 MA TO 5 MA PER MIN AVE DOSE IS 4 R / MIN IF MACHINE OUTPUT IS 2 R/MA/MIN = WHAT IS PT DOSE AT 1.5 MA FOR 5 MIN STUDY?

DOSE REGULATIONS BEFORE 1974 - AT TABLETOP 5R/MIN (WITHOUT AEC) 5R/MIN (WITHOUT AEC) – BOOST MODE After 1974 with AEC 10 R/MIN 20R/MIN BOOST

ISOEXPOSURE CURVES

Where should a dosimeter badge be worn?

RHB “RULES” RHB RP PG61 LICENTIATES OF THE HEALING ARTS (MD, DO, DC, DPM) MUST HAVE A RADIOLOGY SUPERVISOR & OPERATORS PERMIT & CERTIFICATE TO OPERATE OR SUPERVISE THE USE OF X-RAYS ON HUMANS SUPEVISORS MUST POST THEIR LICENSES

RHB “RULES” RHB RP PG62 ALL XRAYS MUST BE ORDERED BY A PHYSICIAN VERBAL OR WRITTEN PRESCRIPTION See Section C – “Technologist Restrictions”

Declared Pregnant Worker Must declare pregnancy – 2 badges provided 1 worn at collar (Mother’s exposure) 1 worn inside apron at waist level Under 5 rad – negligible risk Risk increases above __________rad Recommend abortion (spontaneous) 25 rad (“Baby exposure” approx 1/1000 of ESE 1/50 th dose of mother***) www.ntc.gov/NRC/RG/08/08-013.html

CARDINAL RULES TIME DISTANCE SHEILDING

RHB – Rad Prot – CH. IX p 51 ALARA (no minimum threshold) STOCHASTIC EFFECTS – NON TRESHOLD (CA + GENETIC) NON STHOCAHSTIC (DETERMINISTIC) SEVERITY OF EFFECTS VARIES WITH RADIATION DOSE (THRESHOLD) (CATARACTS, SKIN, BONE MARROW, STERILITY

# 7 – Dose Response Relationships LINEAR NON THRESHOLD ASSUMES ANY AMOUNT OF RADIATION IS CAPABLE OF CAUSING A BIOLOGIC RESPONSE THE RELATIONSHIP BETWEEN THE RADIATION DOSE AND BIOLOGIC RESPONSE IS CONSIDERED TO BE DIRECTLY PROPORTIONAL