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Terms in this set (105)
What percent of US population gets fluoro each year?
Number of fluoro exams per person
what is the average number of spot films taken per fluoroscopic examination?
1. GI tract - 53%
2. Barium enema- 28%
3. Other- 19%
Fluoro exam by body area?
First injury from x-rays was when?
First case of cancer from x-rays?
What percent of the average population exposure from man made radiation source comes from medical use of radiation?
What percent of exposure from diagnostic x-ray examination can be eliminated without decreasing patient benefits?
1. Determine if patient needs x-rays
2. Perform the x-rays (fluoroscopy supervisor and operator who can perform it or supervising a technologist)
3. Interpret the imagine
What are the 3 phases of radiologic service?
Non-threshold linear dose effect
What amount of radiation causes adverse effects?
How much exposure does the patient get from a GI fluoroscopy exam that is 120 seconds of fluoroscopy?
How much exposure does the patient get from one AP abdominal film?
Studying dynamic procedures
What is fluoroscopy used for?
Licentiates of the healing arts who hold a Supervisor and Operator Radiology Certificate or a Supervisor and Operator Fluoroscopy Permit, and have been properly trained
Who can perform fluoroscopy procedures?
1. x-ray tube, x-ray equipment, use of equipment
2. allowable exposure rates
3. exposure time
4. cumulative manual-reset timer
5. light in fluoroscope room
6. image intensifier an image quality considerations
7. ancillary equipment (closed circuit TV system, cinefluorogrpahy, etc)
8. contrast media
9. accessories (shielding)
10. radio graphic or x-ray film and film processing
11. patient and patient positioning
12. ancillary factors (x-ray design, ABC)
what are the factors that influence patient fluoroscopic exposure?
patient to image intensifier distance
low absorption tabletop
primary protective barrier
bucky slot cover
protective curtains or drapes
x-ray tube and x-ray equipment that influence patient dose
allowable exposure rates
cumulative manual reset timer
light in the fluoroscopic room
what use of fluoroscopic exposure factors patient does
image and detector contrast
magnification (geometric and electronic)
what is included in image quality considerations?
target to panel distance (TPD)
patient to image intensifier distance
sensitivity of the image receptor
what factors DIRECTLY influence the exposure rate at the panel or tabletop and the patient/operator's patient dose?
collimating to are of interest only
using "last frame hold"
patient to detector/ patient to image intensifier distance short as possible
use HIGHEST kVP and LOWEST mA
pulsed fluoro, lower frame rates
use LARGEST image intensifier mode (non mag) w/ collimation
How to reduce patient exposure?
illumination or lighting in room
image receptor quality, image monitor adjustments (brightness/ contrast)
absorption of tabletop
factors that INDIRECTLY influence exposure rate by impacting use of technical factors
fluoroscopic tubes are often designed with smaller focal spot and operate for longer period of time at a much lower mA
difference between x-ray tubes and fluoroscopic x-ray tubes
energy conversion when a fast moving stream of electrons is suddenly decelerated in the "target" (anode)
how are x-rays produced?
0.5-5 mA (usually 1 to 3 mA)
what are the current of the x-ray tube in mA?
> 100 mA, short exposure time (100 msec or less)
what is the mA of a spot film?
x-ray out put and patient radiation dose
mA is directly proportional to what?
this is the tube voltage used determines the maximum photon energy or the peak value of x-ray beam produced
higher kVp values will increase transmission of the beam through the patient so less radiation is required
image contrast degrades as kVp is increased. therefor if image has low contrast objects then operate at lower kVp values
what is kVp
what is the most important action to avoid unnecessary patient exposure?
image quality is improved
when x-ray beam is reduced with collimation what happens to the image quality?
what kVps are x-rays tubes in fluoroscopy capable of operating at?
3 millimeters (mm) aluminum. necessary to protect patient's skin
what must the filtration be for the x-ray tubes?
what is the anode made of?
what should the target to panel distance be?
shall not be less than 12 inches and should be at least 18 inches
this is due to patient dose decreasing with increasing distance due to loss of low energy x-rays and energy intensity
what should the target to tabletop distance be?
INCREASES patient radiation
fewer x-rays are intercepted at image intensifier due to inverse square law losses
when moving the image intensifier away (increasing the patient to image intensifier distance) what does this do to patient dose?
terminates exposure when pressure is released
what is a dead man type switch?
the image intensifier assembly, must be at least 2 millimeter of lead for equipment capable of operating above 125 kVp
what is the primary protective barrier?
this is a cover that goes over the two inch wide opening at the fluoroscopist's gonad level when the bucky tray is moved to the end of the examination table
0.25 millimeter lead equivalent thick
what is the bucky slot cover and how thick must it be?
0.25 millimeter lead equivalent
use for over-table tower image intensifier, not required on C-arm systems)
how thick are the protective curtains (drapes or sliding panel)?
as high as 500 millirads per hour
how much scatter radiation comes form the patient at one foot (in millirads)?
may not exceeded 5 rads per minute
limit doe snot apply when using ABC (on larger patients)
what is the allowable exposure rate?
doubles the radiation dose
when exposure time is doubled, what happens to radiation dose to patient and operator?
assists in protection of patient
when does the cumulative manual reset timer audible signal occur?
excessive light decreases ability of eye to resolve detail on TV screen
cause fluoroscopist to change technical factors
increasing technical factors (mA, kVp) will increase patient radiation
what happens when you have excessive light in the fluoroscopy room?
the x-rays that penetrate and exit the patient strike the input phosphor
input phosphor converts energy into light photos
light photons are then absorbed by photocathode causing electrons to be given off
electrons are sped up by accelerating anode and focused by electrostatic lenses and go to the output phosphor
output phosphor (screen) abosrbs electrons and emits light photos, can be viewed or further processing by video system
how does an image intensifier work?
these are non-interacting and small angle scattered photons, carries the x-ray image
what are the ex-rays that penetrate and exit the patient called?
the ability of the image intensifier tube to increase the illumination level of the image
what does brightness gain mean?
as much as 10%
this is due to aging of input and output screens. done by measuring the conversion fractor
how much does brightness gain deteriorate/degrade each year?
this is the ratio of the intensity of the output phosphor to the input exposure rate to the input phosphor
(intensity of output phosphor measured in candelas or cd)/ (millirads/second)
how do you calculate conversion factor?
allows 10% of output phosphor light image to be scanned by vidicon, and 90% the output phosphor light to be projected towards the cine camera, photospot camera or direct viewing
what is a beam splitter mirror?
electronic (flux) gain x minification gain
what is the equation for total brightness gain of image intensifier?
(input screen diameter) squared / (output screen diameter) squared
this is the increase in brightness or intensity, NOT in quality or number of x-ray photons
what is minification gain?
how big are most output phosphors?
the output phosphor is thousand of times brighter due to its smaller size and additional energy given the electrons were accelerated through the image intensifier
how does brightness at output phosphor compare to brightness at the input phosphor?
measurement of the increase in light photons due to the conversion efficiency of the output screen (does NOT look at conversion efficiency of input screen)
varies from 50 to 150
what is flux gain? What does it vary from in terms of numbers?
when the number of absorbed photons is low, caused by statistical fluctuaion of absorbed x-ray photons.
happens more with HIGH resolution, HIGH contrast system
what is it called when the image is grainy or blotchy in appearance? why does this happen?
resolution, sensitivity, contrast
change exposure factors (kVp and mA)
increasing exposure increases number of available x-ray photos, which decreases statistical fluctuations
what factors determine the visibility of quantum mottle?
how do you adjust quantum mottle?
what mA is used in manual mode for adult abdominal fluorosocpy?
determined by the relative attenuation of the tissues dependent upon kVp
kVp (energy of the x-ray beam)
subject contrast is reduced with high kVp x-ray beams
what is Subject contrast determined by?
characteristics of image intensifier, type of TV camera target, the amplitude of output image brightness/video signal, brightness/contrast setting s of monitor to optimize the signal to noises ratio
ratio of brightness between two adjacent areas of fluoroscopy image
what determines Detector (intensifier) contrast?
525 horizontal lines
how man lines are on the monitor for resolution?
1000 line system
how many line system does a higher resolution video have to provide better resolution?
to differentiate small objects as separate images when they are close together
measured in line pairs per millimeter or in object size visible
as object becomes smaller (better resolution), the spatial frequency becomes higher
overall resolution of image system express in modulation transfer function (MTF)- "perfect" system would be a value of 1, but a "real" system is less than one at higher spatial frequencies
what is the definition of resolution?
1 to 2 line pairs per millimeter (lp/mm)
resolution of zinc-cadmium image tube is what?
about 4 lp/mm
resolution of cesium iodide image tube is what?
object to image distance
what causes size distortion?
geometric problems in the shape of the image intensification tube
what causes shape distortion?
a form of optical distortion in which straight lines along the edge of a screen or a lens bulge toward the center. effect reduced when magnification modes are used
can compromise 8-10% of image area (periphery)
input phosphor is curved but the output phosphor if flat
what is pincushion distortion?
takes certain amount of tie for the image to build up and decay on the Vidicon target
the blurring of the image as the camera is moved rapidly during an imaging procedure
why does lag occur? what is lag?
image intensity is greater at the center and less at the edges.
unequal magnification/ unequal illumination
peripheral image is displayed over a larger area of the output screen, cause brightness gain from minification is less than the center
what is it called when you have a fall off of brightness at the periphery of an image or image brightness loss at the edges of the image?
consequence of light scatter in the output window of the image intensifier. this adds to the background signal and reduces the contrast of the image
can be reduced by having an image intensifier with advanced output window designs
what is veiling glare?
everything connected by cables
what does closed circuit mean?
inexpensive and compact unit
bad thing is it has lag but this reduces quantum mottle
has a small electronic vacuum tube containing vidicon (photo conductive) target and electron gun
electron gun produces scanning electron beam, focused onto vidicon target to produce the television picture consisting of 525 lines of dots
light intensity makes the target conductive, this makes proportional electron charge to be generated
this charge is converted to proportional voltage that is sent to camera control unit--> synchronization timing pulses are attached to produce video signal
video signal sent to TV monitor
vidicon camera reduces contrast by 0.8 but then monitor enhances contrast by factor of 2
how does a vidicon camera work?
camera control unit
monitor/ TV tube
what are the three units of a closed circuit TV system?
contains power supply and control that regulate the camera
amplifies video signal, regulates focusing and synchronizes the video signal between the camera and monitor
what is a camera control unit?
contains the picture tube (cathode ray tube) and controls regulate brightness and contrast
scanned along 525 lines by a narrow electron beam 30 times per second
needs to be synchronized to avoid flicker (interlaced scanning)
Monitor/TV tube- how many lines and how many per second?
operation of camera shutters at same frequency as x-ray pulses
what does synchronization refer to?
division of 60 (7.5, 15, 30, 60, 90, 120)
HIGHER the frame rate sequence, the HIGHER dose will be applied to patient
frame frequency in cinefluorography
ability of lens to concentrate light on a given area of the cine film
HIGHER F number, means less light available to form image
what is F-number?
the HIGHER the framing frequency then the HIGHER the patient dose
framing frequency and patient radiation, how are they related?
95% dose reduction
how much reduction in patient dose is there when using video disk recording during fluoroscopy?
1. image is available for instant replay w/o intermediate processing system
2. patient's exposure to radiation is not increased
POOR image quality
has a fixed frame speed (30/ sec)
advantages/disadvantages of video tape recording
cassette positioned between patient and image intensifier
have BEST resolution due to higher mA (100 or more)
short exposure time to reduce patient motion
spot films with cassettes
thin, light tight x-ray film holder
contains intensifying screens (convert energy of the x-ray beam into visible light (fluorescence) which is then exposed on x-ray film to form an invisible "latent imae")
the front surface has to have low anatomic number--> carbon fiber, cardboard, bakelite, aluminum
what is a cassette? what is the front surface made of?
this is 1/2 to 1/3 the dose of film cassette spot films
use higher mA (not has high as cassette spot film) and short exposure, therefore results in substantial dose reduction when compared to when cassettes are used BUT the image quality is inferior
spot film cameras (photospot cameras)
barium or iodine
high atomic number to decrease transmission of x-rays
need to have optimal kVp to get good contrast
what is used for contrast media and why?
reduce the scattered radiation produced in the patient before it reaches image intensifier or x-ray film
usually placed prior to input layer of the image intensifier (ex 8:1)
what is the function of a radiographic grid?
16 or 35 mm
35 mm involves more patient exposure than 16 BUT gives higher quality image
it has high framing frequencies so it deliver about 10 times more dose than fluoroscopy for the same kVp
cine film sizes
needed for cine films or spot films w/ cassettes
darkroom, processor, processing techniques
tissue density (disease processes affect this)
elemental composition (anatomic number) of tissue--> higher number will adsorb more x-rays (calcium in bone, iodine and barium contrast)
what factors of the body affect attenuation and absorption?
5%. most x-rays are absorbed by the patient
these remaining photons or remnant x-rays go to the image intensifier
what percent of photons will emerge from the patient unaffected?
minimum is 12 inches (30 cm) for mobile fluoroscopic equipment
at least 18 inches (45 cm) for stationary fluoro equipment
source to skin distance
high kVp, large field size, thick body part
how is most scattered radiation produced? and what factors affect scattered radiation
relatively high mA available
high effective kVp
near constant potential
advantages of a three phase generator/ high frequency generator vs a one or two phase generator
1. x-ray tube (cathode and anode)
2. image intensifier
what are the two components of the fluoroscopy system?
convert an x-ray flux into a minified light image (electronically amplify the brightness of an image)
1. vaccuum bottle/glass envelope
2. input later (convert x-ray photons to electrons)
3. electronic lenses to focus electrons
4. output phosphor converts energy of electrons into visible light
what does the image intensifier do? and what are the components of it?
thoughs of times brighter due to the smaller size and additional energy when electrons are accelerated
is light at the input phosphor or the output phosphor brighter?
field size of the input phosphor is changed by applying an electronic principle
the higher the voltage on the electrostatic focusing lens, the more the electron beam is focused
can be done with 6 inch or 9 inch input phosphor mode
9 inch used when view large anatomic areas, when size unimportant then 6 inch mode is used due to better image quality
6 inch mode has reduced minification gain with fewer photoelectrons, dimmer image will results. will have ABC to increase mA to compensate for decreased brightness--> patient dose increases
what is a multifield (dual focus and trifocus) image?
(normal mode size) squared / (magnification mode size) squared
ratio of patient radiation dose
image quality of the image intensifier is affected by?
automatic brightness stabilization
keeps the light output of the image intensifier constant over variations of patient attenuation and system geometry
it adjusts the kVp and the mA in fast acting feedback loop
what is another name for automatic brightness control? what does this do?
kVp is set. therefore brightness sensor will automatically adjust the mA to get correct brightness of image
variable mA, preset kVp
varying mA and when it hits the upper limit and lower limit then the kVp will adjust as well
variable mA with kVp following
brightness sensor will control the kVp
will have previously selected mA values
low mA will have high kVp which is good for GI
high mA will have low kVp which is good for iodine based contrast
variable kVp with selected mA
difficult for operator to select what is best
variable kVp and variable mA
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