Exam 3 Flashcards
Who invented Fluoroscopy
Thomas Edison
Unit for illumination level
lambert
Function of rods and cones
rods - dim vis
cones - bright vis
Photopic vision?
bright vis (cones)
Scotopic vision?
dim vis (rods)
What is visual acuity?
accuracy of vis.
Factors that affect the brightness of fluoroscopic images (4)
bright - kVp, mAs, anat. (Z, tissue density), pos. of anat.
Compare the mA of Fluoroscopy Vs Conventional x-ray
fluoro use less mA than conventional XR
Learn the components of Image intensifier, and the materials used and f(x)
- metal housing
- vacuumed glass/metal envelope
- input phosphor - cesium iodide crystals; change 1 XR energy photon into several vis. light photons 4. photocathode - cesium & antimony compounds; emits e-‘s when stimulated by light from input
phosphor (photoemission) - (neg. charged) electrostatic focusing lenses - focuses e- stream on the output phosphor
- anode - (pos. charged electrode) circular plate w hole to output phosphor; attracts e-‘s emitted by the neg. photocathode, w potential diff. of 25 kV across tube
- output phosphor - zinc cadmium sulfide; produce light photons of much greater intensity than input phosphor
flux gain?
ratio of # of light photons at output phosphor to # of XRs at input phosphor
minification gain ?
ratio of square of diameter of input phosphor to square of diameter of output phosphor
brightness gain ?
ability of I.I. to increase illumination level of image
calculate flux gain
flux gain = # output light photons / # input XR photons
calculate minification gain
minification gain = (diameter input phosphor)^2 / (diameter output phosphor)^2
calculate total brightness gain
total brightness gain = minification gain x flux gain
What is veiling glare?
reduction in contrast
What is vignetting?
reduction in brightness at periphery
What is a multi-field image intensifier?
can choose area of input phosphor that is exposed to rad
Which is the magnification mode (27 or 17 or12)?
12
Advantages of magnification mode
improved spatial & contrast res.
Which mode gives you more coverage of the anatomy? (27, 17, or 12)
27
what is focal point?
where the beam from the input phosphor to the output phosphor converge
What happens to the focal point as you change the mode from big(25) to small(12)?
the focal point moves closer to the input phosphor, and away from the output phosphor
How can you calculate the magnification factor of a multi-field image intensifier?
MF = initial diameter of input phosphor / new diameter of input phosphor
What is the disadvantage of the magnification mode?
increased dose (by ABC)
How the light from the output phosphor is converted to a visible image on the monitor?
camera tube changes output light to video signal
What is the function of television camera tube? Name the two common models.
to change output light into video signal; vidicon & plumbicon tube
Learn the components & f(x) of television camera tube
- cathode
- e- gun: heated filament, supplies constant e- current by thermionic emission
- control grids: converts e-‘s into e- beam
- electrostatic grids: accelerates/focuses e- beam
- steering coils: controls size/pos of e- beam; directs e-‘s (like focusing cup)
- target assembly (face plate/window, signal plate, target plate) changes e- beam into video signal
(intense light = greater signal)
Learn the three layers of the target assembly and their functions
face plate/window - thin part of glass envelope
signal plate - conduct video signal out of the tube into the external video circuit
target plate - photoconductive layer; swept by electron beam and conducts e-‘s in light and insulates when dark
What are the chemicals used in signal plate and target plate.
signal plate - thin layer of metal/graphite
target plate - antimony trisulfide
Which is the photoconductive layer of the television camera tube?
target plate
What are the two systems used to connect the television camera tube to the image intensifier? Advantages & Disadvantage of ea?
fiber optic system- disadvantage: old, cannot save img (can’t accommodate aux devices) & requires cassette loaded spot films; advantage: simplest, compact, easy to move I.I., can rough handle
lens system - advantage: do not need to re-expose to save img; disadvantage: lenses must be perfectly aligned
How many lines per frames are used in CRT monitors used in regular fluoroscopy?
525 lines/frames in CRT monitors
Learn the function of a photo spot camera. What is the advantage of using it?
receives images from output phosphor
provides adequate img quality w/o interruption of fluoro, provides up to 12 img’s/sec, requires less pt
exposure than cassette loaded system
Advantage of DF
- speed of img acquisition
2. ability to post process img to enhance contrast
What is the matrix size commonly used in DF?
1024x1024
What is a 1000 line system?
the img matrix in DF is sometimes described as a 1000-line system
2 Factors determining the spatial resolution of DF images
- img matrix
2. size of I.I.
Spatial resolution is pixel limited. Why?
pixel size = I.I. size / matrix
During DF the x-ray tube operates in the _________mode.
radiographic
What is a pulse progressive fluoroscopy? What is the advantage of pulse progressive fluoroscopy?
img’s obtained from DF are obtained by pulsing the XR beam; reduces pt dose
interrogation T ?
T required for XR tube to be switched on & reach selected kVp & mA
extinction T ?
T required for XR tube to be switched off
duty cycle?
fraction of T that the XR tube is energized (100 ms/s = 10% duty cycle)
How the digital image is formed in a CCD?
sensitive component of CCD is a layer of crystalline silicon, when it is illuminated, electrical charge is generated, which is then sampled, pixel by pixel, and manipulated to produce digi img. the CCD is mounted on the output phosphor of the I.I. tube and is coupled thru fiber optics or lens system
What are the advantages of CCD?
(principally) small size & ruggedness; high spatial/contrast res., low noise, high SNR, high DQE (greater sensitivity to light), no warm-up, no lag/blooming, no spatial distortion, unlimited life, no maintenance, unaffected by magnetic fields, linear response, lower pt dose
What is DQE stands for? High DQE means _____________?
Detective Quantum Efficiency; % of XRs absorbed by IR
What is image blooming?
if img is too bright, you cannot see the tissue behind it; it happens when excess light overflows
Spatial resolution of a CCD is ________________lp/mm
in a 1024 matrix system, 10 lp/mm
What are the 2 factors that determine the spatial resolution of a CCD?
its physical size & pixel count
What is “Pin cushion” or “barrel” artifact?
a spatial distortion that can be seen w TV camera tubes, does not occur in CCD
What are the advantage of the linear response of CCD ?.
particularly helpful for subtraction imaging and results in wider dynamic range & better contrast res. than conventional fluoro; it can be electronically manipulated
What are the advantages of FPIR?
(flat panel img receptor) smaller, lighter, & more easily manipulated than an I.I.; easy pt manipulation and tech movement, & no radiographic cassettes;
distortion-free, constant img qual. over entire img, improved contrast res., high DQE, rectangular img area similar to img monitor, unaffected by external magnetic fields (good for img-guided catheter navigation)
Explain image guided catheter navigation
magnetic wire tip introduced into pt vasculature and the catheter is remotely manipulated thru tortuous vessels by 2 large steering magnets on either side of pt; a new possible area of IV Rad bc FPIR is insensitive to external magnetic fields; advanced application in cardiovascular and neurovascular rad
Compare the SNR of conventional fluoroscopy and DF
SNR Conventional: 200:1
SNR DF: 1000:1 (much better signal)
What is the advantage of progressive mode of DF?
when vid signal read in progressive mode, the electron beam of TV camera tube sweeps the target assembly continuously from top to bottom in 33 ms —> no interlace of one field w another occurs —> sharper img w less flicker
Speed of image acquisition is determined by what factors? (3)
dynamic range of ea. pixel, # of pixels, method of storage
What is a hybrid subtraction?
temporal subtraction & energy subtraction combined —> enhanced img contrast bc of reduced pt motion btw subtracted img’s
What is a temporal subtraction?
refers to a # of computer-assisted techniques where an img obtained at one T is subtracted from an img obtained at a later T; most common type of subtraction used
What are the two methods used in temporal subtraction?
mask mode & time-interval difference mode (TID)
What is a mask image?
initial XR pulsed exposure is made and stored in primary memory and is displayed on video monitor
What is image integration?
T required for one video frame is 33 ms. bc it’s relatively slow to respond & noise may be high, several video frames (4-8) may be summed in memory to create one img
What is the advantage of re-masking?
blur from motion/improper technique may be replaced w later images as the mask image; gives better contrast by using a better subtraction img
Which mode of temporal subtraction is used in cardiac evaluation?
Time-Interval Difference Mode (TID) (subtracted img from progressive masks and following frames) —> convey flow of contrast dynamically
What is the cause of misregistration artifacts? How can you eliminate it?
pt motion btw mask img & subsequent img; can be eliminated by registration of the mask (shifting the mask by one more more pixels so that the superimposition of img’s again obtained —> remask)
What is road mapping?
special application of DSA (digi subtraction angio), where a mask img is acquired and stored, contrast is injected and subtraction img are acquired —> black guidewire/catheter in a white vessel
Principle advantages of DF exams?
img subtraction techniques possible, enhanced vis. of vasculature that result from venous injection of contrast material
Disadvantage of DF?
reduced img contrast bc of assoc. scatter rad. (but can be enhanced electronically)
the fluoroscope is used for exams of?
moving internal structures & fluids
what emits e-‘s when illuminated by the input phosphor?
photocathode
magnification mode results in what 3 things?
- better spatial res., 2. better contrast res., 3. higher pt dose
what converts the light signal from the output phosphor to an electronic signal?
TV camera tube or CCD
what is a change is a quantity or signal in response to another quantity or signal and is widely used in medical imaging
modulation
video monitoring uses a rate of ________?
30 frames/sec
for a 23-cm I.I., a 525-line TV system provides a spatial res. of what? a 1024-line system?
1 lp/mm; 2 lp/mm
the higher the bandpass, the better the _____________
horizontal res.
when the CCD is directly coupled to the I.I., the entire CCD signal is what?
sampled & drives the ABS system
DF w CCD results in what over conventional fluoro?
wider dynamic range & better contrast res.
3 primary advantages of flat panel monitors?
easier to view, easier to manipulate & provide better img’s
what 3 things determine the speed w which the img can be acquired, processed, & transferred to an output device?
dynamic range of ea pixel, # of pixels, & storage method
DF provides better contrast res. through what?
post processing of img subtraction
mask mode results in what?
successive subtraction images of contrast-filled vessels
TID produces subtracted images from what?
progressive masks & following frames
