Patient dose in fluoroscopy is what to mA station used
Directly proportional
mA in fluoroscopy
.05 to 5 mA (usually 2-3 mA)
Audible alarm
Goes off every 5 minutes to remind the operator and protect the patient of unnecessary radiation,
Fluoro kVp
usually operating at 125-150. At these energies must be 3mm al eq
STD source to target distance fluoro
12in to 18in
I.I. image intensifier primary barrior
Must be 2mm of lead eq
Exposure switch must be
deadman terminate when pressure is released
Interlocks are
Devices that prevent exposure when parked
Collimators
must be automatic in mag mode and in more than 1-1 mode. Must use smallest size possible to the anatomy of the part required by law. Image quality is improved as x-ray beam is reduced. When auto collimators is on must see boarders at all distances.
X-ray tube housing
Must protect from leakage no more than 100mR/1hr/1 meter
What must be posted
Certifications, radiation control regs and operating procedures and notice to employees
Who is rad monitored
Anyone who asks, persons entering high radiation areas, person who operate mobile equipment. Dose= in excess of 0.1 rem in 1 hour at 30 cm.
Logs required
QC, equipment registration, installation, safety, calibration ect.
Protective curtain and drapes
Must be .25 mm lead eq. should be positioned between the patient and fluoroscopist. W/O dose could be 500 mrads/hr to operator and not required on c-arm units.
Leakage radiation
protective housing so that no more than 100 mR/hr/1 meter is emitted
Protective apparel
Gloves .25 mm Pb MUST be worn
Goggles must be available
Thyroid shields .25 mm Pb must be available
Aprons .25 mm Pb will reduce exposure by 97%
Aprons .5 mm Pb will reduce exposure by 99.9%
Aprons cover 80% of the active bone marrow
MDP exposure rate
MPD (exposure) rate
Before 1974 w/o AEC = 5R/min
After 1974 with AEC
Regular mode = 10 R/ hr
Boost/mag mode = 20 R/hr
The table top intensity should not exceed 2.2 R/min for each mA of current at 80 kVp
Filtration requirements
Inherent and added must equal 2.5 mm Al eq.
Min. permissible source to patient distance
Shortest distance decreases penumbra & dose.
Target to table top shall not be less than 12 & should not be less than 18 inches mobile (12 & 15 on fixed units)
Structural shielding
1/16th of an inch and 7 feet high
HVL
Used to determine quality or barrier thickness
To reduce 100mr/min to 25 mr/min
need 2 HVL
Primary protective barriers
The II - 2mm lead equiv
The lead window = 1.5 mm Pb equivalent
Primary factors associated w/ fluoroscopy
mA is typically less than 5 (spot films =greater than 100)
mA reduced from 5 to 3, dose rate is reduced by 40%
Increased kVp slightly increases internal dose but decreases skin dose
High-level procedures (Boost mode)
10-20 mA
Entrance dose rate is 10-50 r/min at table top
Used for interventional
1994 limits tabletop dose to 20 rads/min w/o recording device
Audible warning must be continuous
Pulsed procedures
5 msec or less
Synchronized to video camera
Significantly reduces pt dose.
Scatter, magnitude, directionality
Patient is the main source
Iso exposure curve
500 mR/hr at 1 foot
100 mR/hr at 2 feet
50 mR/hr at 3 feet
Maximum intensity of beam at 135 and 120 degree from primary beam with under table tube
Dose versus quantum mottle
QM is caused by statistical fluctuation of absorbed photons.
Decrease in photons reduce pt. dose but decrease image quality
2 to 3 mA must be maintained as a minimum to prevent mottle by maintain adequate statistics.
Potential image distortions
Pincushion
Spatial distortion that warps the appearance of the image and is related to vignetting
Vignetting
Decrease in light intensity at the periphery of an image
Image perception
Related to 3 factors:
Image integration (recognition time)=0.2 sec
Intensity discrimination=ability to determine brightness level at the center of the image where it is highest to the periphery where it is the lowest
Visual acuity = the ability of human e
Quality control
Records must be kept for 3 years
Tests must be done after repair or replacement and at acceptance
Tests required on outline and on page 99 of syllabus
Procedure & equipment
Basic fluoro unit is composed of
II
AEC
ABC
Recording system
Viewing system
Cumulative timer
Closed circuit TV
VCR
II
II converts x-ray to light
Increases brightness of radiation by 5000 to 20,000 times to cone vision region where visual acuity is greatest.
Input phosphor is made of cesium iodide look like pointed needles compacted to improve spatial resolution
10-35 cm
II Functions
II's main function is converting X-ray photons to amplified light energy
Electronically amplifies the brightness of an image
Image Intensifier-main component pathway
input phosphor
x-rays to light
photocathode
light to electrons
electrostatic focusing lens
steer those electrons
accelerating anode
speed up those electrons
output phosphor
electrons to light
Image intensifier component
Input screen: conversion of incident X Rays into light photons (CsI)
1 X Ray photon creates 1,000 light photons
Photocathode: conversion of light photons into electrons
only 10 to 20% of light photons are converted into photoelectrons
Electrodes (lenses)
Image Intensifier: Input phosphor�Cesium Iodide
X-ray photons emitted from patient hit input phosphor made of Cesium Iodide (CsI) crystals of II
Input phosphor coverts x-ray photons to visible light
Image Intensifier: Photocathode�Cesium & Antimony
Visible light then hits the adjacent transparent adhesive layer called "photocathode" composed of cesium & antimony compounds
Photocathode converts visible light to electrons (photoelectrons) through Photoemission
Photoemission : e- emission that follows
Image Intensifier�electrostatic focusing lenses & anode
Photo e- are accelerated and focused in the vacuum of the II.
Photo e- are focused, accelerated and controlled w/out geometric distortion via negatively charged electrostatic focusing lenses & through the anode
Image Intensifier: Output phosphor-Zinc Cadmium Sulfide
Photo e- hit the smaller Output phosphor with much greater kinetic energy then they had leaving the photocathode.
They also maintain the input phosphors undistorted image in minified form
Most modern I.I.'s have a 1inch output phosphor.** CCS pg17
Acceler
Image Intensifier Tube
Vacuum tube encased in 2mm Pb equivalent (primary barrier)
1. Input phosphor (CsI)
X-rays light
2. Photocathode(Cs & Antimony)
Photoemission
Light electron beam
3. Electrostatic lenses
Maintain, focus & minify e-
4. Anode
Attracts & speed up e- in beam
Brightness Gain
overall ability of II to increase the illumination level of the image via image minification & the acceleration of e-
This value will decrease with age approximately 10% each year & eventually requires replacement
Minification gain
Increased illumination due to the compression of e- (electrostatic focusing lenses) from a large input screen to a smaller output screen.
Flux gain
Increase in light photons due to gain created by the e- to light conversion at the output phosphor.
Brightness Gain formula
BG =
Minification Gain x Flux Gain
Minification gain (MG): The ratio of the squares of the input and output phosphor diameters. This corresponds to "concentrating" the light into a smaller area, thus increasing brightness
MG = (Input Diameter )2
(Output D
Conversion Factor
Brightness gain can degrade as much as 10% per year due to age
Degradation leads to increased pt dose as a result of increasing exposure factors to maintain a optimal image.
A periodic check of brightness gain can be made by measuring the conversion facto
Magnification pg 19 CSS
Mag used to visualize smaller structures or to penetrate through larger parts
Achieved by applying different (increased) voltages to the electrostatic lenses
Results in overall increase in pt dose
Overall, less incident e- hit the smaller FOV therefore AB
Magnification Tubes
Greater voltage to electrostatic lenses
Increases acceleration of electrons
Shifts focal point away from anode
Identified by input phosphor FOV size
Dual focus
23/15 cm 9/6 inches
Tri focus
25/17/12 cm 12/9/6 inches
MAG MODE FORMULA
Normal Mode Size = Magnification
Mag Mode Size
MAG MODE FORMULA to calculate pt dose
(Normal mode size) 2
(Mag mode size) 2
= Increase in pt dose
Magnification-results in:
Smaller FOV
Better image quality
Increased pt dose
Output phosphor
Made of zinc cadmium sulfide
Converts electrons to light 50-75 times more than at the photocathode (FG = ratio of # of light photons at OP/IP)
That is the flux gain (almost always 50)
Size is 2.5 to 5 cm which also causes an increase in brightness (1 inch
Image quality
Central portion possesses greatest resolution
Resolving power is principally determined by input phosphor
Tube moved quickly results in lag
Fluoro quality is poor compared to radiograph
2 important factors to evaluate are statistical quality and level of
Quantum mottle
Grainy appearance in an image caused by statistical fluctuation of absorbed x-ray photons�is seen more with low levels of mA
Viewing systems
Closed circuit TV
Cineflorography
Spot films with conventional IR (mA is typically over 100 mA)
Spot film cameras (photograph image off output phosphor
Video disc recording
Vignetting and quantum noise
Repeats = lack of light at periphery and stats fluction
AEC
After 1974 with AEC shall not be operable at any settings which result in an exposure rate in excess of 10.0 R/minute where it enters the patient
After 1974 without AEC shall not be operable at any settings which result in an exposure rate in excess of 5.
ABC
Allows selection of image brightness level that is maintained by varying kV or mA
Lambert is unit of image brightness
Brightness gain is ability of II to increase the illumination
BG=FG X MG
Usually 5,000 to 20,000 in most II and decreases with age and us
Resolution
Process or capability of distinguishing closely adjacent optical images
Lag
The amount of time for image to build up and decay on the vidicon target. occurs when tube is moved.
Closed circuit systems
# of horizontal lines is 525 regardless of size of monitor
Signals carried through cables
OP coupled directly to TV camera tube
Plumicon TV camera results in least exposure (lead oxide)
Vidicon most often used (antimony trisulphide)
Able to control bright
Type of TV camera
VIDICON TV camera
improvement of contrast
improvement of signal to noise ratio
high image lag
LOWER PATIENT DOSE
PLUMBICON TV camera (suitable for cardiology)
lower image lag (follow up of organ motions)
higher quantum noise level
CCD TV camera (digital f
TV monitor
made of 1000's of tiny dots of differing brightness - arranged in horizontal scan lines
525 system= total # of line - regardless of screen size
1000+ systems = double resolution
Resolution/quality determined by:
Total # of cycles /sec available for displa
Bandwidth or Bandpass-
total # of cycles/sec
Product of scan lines, scan rate & frequency
Horizontal resolution - resolve dots
? bandwidth = camera tube to turn off & on more times/sec
? ? bandwidth ? resolution
Image recording
Video disc and video tape recording systems has a frame rate of 30 frames/sec
Cine uses synchronization to operate
Larger film size used by spot filming camera, the greater the dose to the patient (90 vs. 105 mm)
Reducing room light increases viewing cond
CINE/ CINEFLUORGRAPHY
Synchronized with camera shutters - no exp while closed
Movie camera intercepts image
16 mm and 35 mm formats
Record series of static exposures at high speed
30 - 60 frames per second
Offer increased resolution
At the cost of increased patient dose
Framin
VIDEO DISC RECORDING
like a laser disc - size of an LP record)
Combines radiography with fluoro
Image is stored as a single frame on a video disc recorder - newer uses CD
95% dose reduction when
VIDEO TAPE RECORDING
Provides a permanent record w/o ? pt dose
Instant play back - Real time images
Poor image quality
CASSETTE SPOT FILMING vs PHOTOSPOT FILMING
First type of recording used
9x9 cassettes then later up to 14x 14
9 on 1, 4 on 1, 2 on 1
Delay while filming (anatomy still moving)
Radiographic mA - must boost up to
100 - 200 mA for filming
And moving cassettes around inside tower
Higher patient dose
R
SPOT FILMS - CASSETTES
BETWEEN PT & II
? Ma (100 -200) ? time
High resolution
PHOTOSPOT -
� - 1/3 DOSE OF FILM CASSETTES
TAKEN FROM OP OF II
? Ma , ? time (LESS THAN CASSETTE)
? image quality than cassettes
Contrast media
Iodinated, water soluble, barium, ionic, non-ionic
High atomic number and low toxicity
Complications include extravasation, phlebitis, flushing hives nausea shock hypotension
First aid includes reassurance to CPR
Know what to use in cases of perforated bo
Patient protection
A 2 minute UGI results in an exposure of 4.4 R (5)
Approximate exposure after 5 minutes of fluoro is between 10 and 30 R
Minimum distance shall not be less than 12 (SOD)
II shall always be closer to the pt as possible
AEC and under table tube will up dose
Gonad shielding & dose
? receive 3x more dose than
? for pelvic x-rays
1 mm lead will reduce exposure (primary) by about 50% ?
by about 90 - 95 % ?