Unit 5 (Fluoroscopy)
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. What would you like to do?
who invented fluoroscopy and when?
name some basic components of the image receptor of the earliest fluoroscopy unit:
- fluoroscopic screen
- image intensification
- video camera and monitor
name two functional studies that utilize fluoroscopy:
- GI tract studies
describe our ethical guidelines when it comes to using fluoroscopy for patient positioning:
the unneccessary radiation exposure caused by using fluoro for positioning is unethical because technologists have been trained in positioning.
what is the mA range in fluoroscopic x-ray tubes?
.5 to 5.0 mA
what is the minimum SOD in fixed fluoroscopic equipment?
describe viewing early fluoroscopic screens:
- very dim
- required "dark adapted" viewing
- low visual acuity
- uses scotopic vision (rods)
the rods of the eyse utilize _________ vision, and the cones of the eyes utilize _________ vision.
when was the image intensifier first introduced, and what did it offer?
- higher visual acuity
- uses photopic vision (cones)
use the labeling of this picture to describe what happens in the image intensifier:
- A. entrance x-ray photon
- B. light photons: converted from the x-ray photons after passing through input fluorescent screen
- C. photocathode and input fluorescent screen: where conversions take place
- D. photoelectrons: converted from light photons after passing through photocathode
- E. electron stream
- F. electrostatic lenses: negatively charged, therefore pushing electrons toward center as they travel
- G. glass house
- H. anode: positively charged point where electrons are drawn. electron stream is flipped when passing through (focal spot)
- I. output fluorescent screen: converts electrons back to light
- J. exiting light photons
what is the main function of the image intensifier?
to reduce patient dose by amplification
what is another name for the fluorescent screen?
how do you determine the total brightness gain?
minification screen x flux gain = total brightness gain
what is the input screen of the image intensifier composed of and what is its function?
- .1 to .2 mm layer of sodium activated CsI (cesium iodide)
- converts intercepted x-ray beam to light
what is the function of the photocathode of the image intensifier?
emits electrons when struck by light photons emitted by input screen
what is the function of the electrostatic lenses in the image intensifier?
they accelerate and focus the electron pattern across the tube to the anode
what is the primary source of brightness gain?
the electrostatic lenses
what is the function of the magnification tubes of the image intensifier?
they give greater voltage to the electrostatic lenses which allows them to increase the acceleration of electrons and shift the focal point away from the anode
the smaller the area of the input screen, the _______________ magnification on the output screen.
what is a dual focus magnification tube?
- offers more than one size area that can be interacted with
- ex. 23/15
describe the anode of the image intensifier:
it is positively charged, 25kVp, with a hole in the center that allows electrons to pass through to the output screen
where does the cross-over point of the focal spot take place?
at the anode (unless magnification pushes it toward the input screen)
what is the output screen of the image intensifier composed of and what is its function?
- glass fluorescent screen composed of zinc-cadmium sulfide
- emits light when struck by electrons
how do you determine minification gain?
minification gain = (input screen diameter2)/(output screen diameter2)
in determining minification gain, what are the general ranges of screen diameters?
- input screen ranges from 15 to 30 cm
- output screen is around 2.5 cm
- therefore, the big number will always be on top when determining minification gain
the measurement of conversion efficiency of the output screen:
give an example of how flux gain is determined:
if one electron strikes the output screen and 50 light photons are emitted, then the flux gain is 50.
what is a modern term used to represent an increase in brightness, or brightness gain?
who recommend the use of the conversion factor to quantify the increase in brightness created by an image intensifier?
the ICRU (International Commission of Radiation Units and Measurements)
pay attention to slide number 27 of the power point as an example for working formulas to calculate minification gain and total brightness gain.
an expression of the ability of an image intensifier to convert x-ray energy into light energy and increase brightness in the process:
brightness gain (now called conversion factor)
an expression of the luminance at the output phosphor divided by the input exposure rate:
conversion factor (formerly called the brightness gain)
as the tube ages the exposure rate ___________. therefore, the exposure rate needs to be ____________ to maintain brightness.
how do you determine the conversion factor?
conversion factor = luminance at output phosphor / input exposure rate
what is the unit of measurement in figuring the conversion factor?
- candela per square meter per milliroentgen per second
the numeric version of the conversion factor is approximately ________ of the brightness gain value.
the higher the conversion factor or brightness gain value, the _________ the efficiency of the image intensifier.
what is ABC and what does it do?
- automatic brightness control
- makes automatic adjustments to equipment exposure factors
- maintains contrast and density by adjusting kVp and/or mA
amplifies video signal rather than adjusting exposure factors:
automatic gain control
what is the difference between automatic gain control and automatic brightness control?
- automatic gain control amplifies video signal
- automatic brightness control (ABC) adjusts exposure factors
name four main factors that affect image quality:
- quantom mottle
in fluoroscopy, what is contrast controlled by and what is it affected by?
- controlled by amplitude of video signal
- affected by scattered ionizing radiation and penumbral light scatter
in fluoroscopy, the resolution of video viewing is limited by:
the 525 line raster pattern of the monitor
how do raster patterns affect resolution?
the greater the number of lines in the raster pattern, the greater the resolution of the video signal
what is the primary cause of size distortion and how can it be combated?
- combated by bringing image intensifier as close to patient as possible (thereby decreasing OID)
name two common shape distortions caused by the shape of the input screen:
- pin cushion effect
____________ shape of the input screen helps to minimize _________________, but does not remove it all.
what is quantom motte, its cause, and how it is most commonly remedied?
- blotchy, grainy appearance
- caused by too little exposure
- remedied by increasing mA
name two types of video viewing systems:
- closed circuit television
- video camera tube
a video viewing system in which there is a video camera coupled to an output screen and monitor:
closed circuit television
two types of video viewing systems in which a video camera tube is used:
- Vidicon or Plumbicon tube
how are Vidicon and Plumbicon tubes different?
- they have different target materials
- Plumbicon has a faster response time than Vidicon
in video camera tubes, there is a __________ signal going in, and a __________ signal going out.
in a video camera tube, the cathode is the:
- A. cathode
- B. control grid
- C. focusing coil
- D. deflecting coil
- E. electron beam
- F. glass face plate
- G. signal plate
- H. target
- I. video signal
- J. anode
name three parts that make up the anode of the video camera tube:
- face plate
- signal plate
name two parts of the cathode of the video camera tube and their functions:
- heating assembly: has an electron gun that controls thermionic emission
- control grid: shapes the electron beam
describe the target of the video camera tube:
- a thin insulating mica
- a matrix of globules of photoconductive material
give the target materials of the two video camera tube types:
- Vidicon: antimony trisulfide
- Plumbicon: lead oxide (faster)
what is the function of the raster pattern?
accelerates the electron beam across the TV camera tube to the anode
what slows the raster pattern at the anode?
wire mesh in front of the target
in the video camera tube, shapes the electron stream into a single point:
electromagnetic focusing coils
in the video camera tube, causes the electron stream to scan the target in the raster pattern:
name two components of the video camera tube that contribute to the formation of the raster pattern:
- electromagnetic focusing coils
- deflecting coils
in the video camera tube, a positively charged thin film of graphite:
the signal plate of the anode
what is the function of the anode target in the video camera tube?
it changes the light pattern to the electronic signal that is sent to the video system
list the forms of energy as they travel through the cathode ray tube:
from electrical, to electron, to light (which will be viewed at the monitor)
- A. iron trap
- B. electron gun
- C. control grid
- D. focus coil
- E. deflecting coil
- F. electron beam
- G. anode
- H. fluorescent screen
- I. light photons
a semiconducting device that emits electrons in proportion to the amount of light striking the photoelectric cathode:
video camera charged coupled device (CCD)
what does the CCD's fast discharge achieve?
it eliminates lag
name two advantages of the CCD over the video tube:
- it operates at lower voltages
- it is more durable
here are the notes i jotted down in class from the youtube video on CCDs we watched from the powerpoint. decipher and go over them at your own risk!!
- CCDs made of silicon
- the human eye is more sensitive to green light (closer to middle of light spectrum)
- x-ray interacts, receptor receives the interaction, CCD receives it. With every x-ray interaction, releases negative charge (electrons)…capacitors in CCDs get more intensity (like from tissues, ligaments, etc), stores charge, then you’ve got the whole grid of reception with the CCD (the whole finished picture).
- the areas with greater electrical charge have greater intensity. we want it to be changed to a digital form so we can see it.
in digital fluoroscopy, the image intensifier output screen is coupled to:
TFTs (thin film transistors)
in digital fluoroscopy, TFT photodiodes are connected to:
each pixel element
in digital fluoroscopy, resolution is limited out of concerns for
TFTs improve ___________________ and are used to display images on _______________.
- image quality/contrast
- an LCD screen
name four ways of recording the fluoroscopic image:
- dynamic systems
- cine film systems
- videotape recording
- static spot filming systems
when recording the fluoroscopic image, what is a film size of note in digital fluoroscopy?
105mm chip film
name two types of dynamic systems used in recording the fluoroscopic image:
give measurements and rates specific to cine film systems for when the movie camera intercepts the image:
- 16mm and 35mm formats
- records series of static exposures at high speeds
- 30-60 frames per second
what do cine film systems offer as compared to dynamic systems?
increased resolution (at the cost of increased patient dose)
list some common advantages and disadvantages of videotape recording:
- (VHS and VHS-S)
- often used today with the speech pathologist
- allows playback in real-time after the procedure
- limited storage space is a disadvantage
in static spot filming systems, what changes in mA are necessary in comparing fluoro and radiography modes?
- fluoro mode: 2 to 5 mA
- radiography mode: 100 to 1200 mA
in static spot filming systems, which mode increases the dose to the patient and personnel in the fluoroscopy room?
radiographic mode increases dose as compared to fluoro mode
where is the film located in static spot filming systems?
stored in a lead compartment until an exposure is ready to be made
in static spot filming systems, what size film is utilized, and how can it be divided for exposures?
- 9x9 film size
- divides into 1 on 1; 2 on 1; 4 on 1; and 6 on 1
in static spot filming, what allows the film to be exposed photographically?
a beam-splitting mirror during the exposure
in static spot filming, since the process is photographic, how must it be developed?
in a wet processor in a darkroom
in static spot filming, how many frames per second can be taken?
up to 12 frames per second
taking an image using the image intensifier causes _________ dose to the patient as compared to the spot film.
describe digital fluoroscopy with the use of a CCD:
- uses the CCD to generate an electrical signal
- the signal is sent to an ADC
- allows for post processing and electronic storage and distribution
name the three pillars of radiation protection and who they are meant to protect
- time, distance, shielding
- patient, radiologists and technologists, others
in patient protection, list the minimum SSDs (source to skin distances) for both mobile and stationary equipment:
- mobile equipment: 12" minimum SSD
- stationary equipment: 15" minimum SSD
for patient protection, when do audible alarms sound in the use of fluoroscopy?
at 5 minutes
what is the maximum exposure rate of the x-ray beam at tabletop that is deemed acceptable by the FDA?
- maximum of 10 R/min: for units with automatic brightness stabilization (ABS)
- maximum of 5 R/min: for units without automatic brightness stabilization (ABS)
- (typically 1-3 R/min is used)
give typical exposure rates for cinefluoroscopy, cassettes, and 105 mm film:
- cinefluoroscopy: 7.2 R/min
- cassettes: 30 mR/exposure
- 105 mm film: 10 mR/exposure
the minimum required shielding required for lead gloves and thyroid shields:
.25 mm lead equivalency(by the NCRP No. 102)
the minimum required shielding required for lead aprons:
.5 mm lead equivalency (by the NCRP No. 102)
describe the angle and level of most scatter radiation in the fluoro room:
- 90° angle to the incident beam
- the level of the radiologist's/technologist's gonad area
the minumum required shielding for the primary barrier of the fluoro tower's image intensifier:
2.0mm of lead equivalency (by the FDA)
the minimum required shielding for the protective curtain:
.25 mm lead equivalency (by the NCRP No. 102)
the minimum required shielding for the bucky slot cover:
.5 mm lead (Pb) equivalency
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