Unit 6 - MI 237

thomas edison

who invented the fluoroscope?

dynamic imaging

real time images

allows motion w/in images

john coltman

who invented the image intensifer?

greatly improved image brightness by converting x-ray photons into light photons

what is the main purpose of the image intensifer?

modern fluoroscopy

used to see internal structures & their functions

diagnosing pathologies of soft tissues

x-ray tube, II, recording system, viewing system

what are the components of modern fluoroscopy?

fluoroscopic x-ray tube

requires longer exposures to capture motion

operates at lower mA then diagnostic tube

0.5 - 5

what is the range for fluoroscopic x-ray tube mA?

50 - 12,000

what is the range of normal diagnostic x-ray tube mA?

image intensifer

vacuum tube that converts the latent image from x-ray photons into light

increases birghtness of image

glass envelope

protective enclosure which maintains a vacuum seal

large, cruved input window & much smaller flat output

2 mm of lead

what is the glass envelope surrounded by?

input phosphor

curved surface

coverts x-ray photons to light photons

maintains distance of electrons hitting input phosphor

what is the point of the curve in the input phosphor?

6 - 23.3’’

what is the range in diamete of teh input phosphor layer?

cesium iodide

what material is the input phosphor made of?

66%

how much of the primary beam does the input phosphor absorb?

photocathode

bonded to input phosphor

converts light photons to electrons

cesium & antimony compounds

what is the photocathode made of?

photoemission

how does the photocathode convert light photons to electrons?

electrostatic lenses

negatively charged lenses line the periphery of the glass envelope that focuses & acclerates electrons TOWARDS anode

ensures every electron travels an equal distance from photocathode to anode

increase speed amplifies birghtness/intensity of electrons

when teh electrostatic lenses acclerate the electrons, what is happening?

anode

positively charged layer of aluminum w/ a hole in the center

attracts electron from the photocathode

output phosphor

small fluorescent screen

converts electrons back into light photons

increases brightness

the latent image information

what does the exiting light carry after going through the output phosphor?

silver-activated cadmium sulfide

what is the output phosphor made of?

magnification

smaller mode = more mag → increases resolution = increase pt dose → smaller FOV = increase mA

smaller diameter of input phosphor being used

focal point will shift closer to input phosphor

more voltage = more repelled electrons

what does increasing the voltage of the electrostatic lenses cause?

input phosphor diameter / input phosphor diameter w/ mag mode

what is the equation for finding the magnification factor?

dual, tri, & quad field

what are the availble different FOV options for magnification?

fewer electrons reaching the output phosphor = quantum noise

requires more photons = higher pt dose

uses geometric mag → OID, SID

causes excessive heat in tube → due to small focal spot

what are the main concerns when using mag mode causing the reduction of minification gain?

minification gain

ratio of input phosphor size compared to output phosphor size

compression of electrons from large diameter of input to small diameter of output

6 - 16’’

what is the range diameter size of the input phosphor?

1’’

what is the average diameter size of the output phosphor?

input diameter² / output diameter²

what is the formula for finding the minification gain?

flux gain

increasing brightness from input to output

represents tube’s conversion efficiency

decrease image quality/sharpness while increasing the brightness

what does flux gain do to an image?

from the accerlation of electrons traveling across intensifer

how does flux gain increase brightness from input to output?

number of light photons from output / number of x-ray photons striking input

what is the formula to find the flux gain?

total brightness gain

overall increase in image brightness achieved by II

by 10%

roughly, how much does the total brightness gain decrease over each year?

flux gain X minification gain

what is the formula to find the total brightness gain?

conversion factor

new unit for describing the output (total brightness gain) of the II

candela

how is the conversion factor for the total brightness gain expressed?

equal to approx. 1% of brightness gain

what is the conversion factor for total brightness gain?

coupling

takes light from II to next component (CCD or CMOS) in imaging chain to be converted into a useful format

light goes into one direction & can’t attach/be used for anything else

what is the disadvantage of coupling?

charged-coupled device

light sensitive semi-conductor w/ fiber optics mounted to II

uses higher DQE & SNR = increase resolution = lower pt dose

continous detection surface

what is an advantage of using a charged-coupld deivce rather than DEL?

automatic brightness control (ABC)

maintains image brightness (contrast) while moving over varying subject densities or contrast agents

monitors the electrical current between photocathode & anode of the II

kVp, mA or both

technique auto increasing = increase pt dose

what does ABC modifity to decrease noise, increase contrast resolution & birghtness?

continous fluoro

x-ray beam is continuously on

acquired & displayed at 30 frames/sec

can have high, normal or low doses

33 msec or 1/30 sec

how much time does each frame require?

0.5 - 4

what is the typically mA range for continuous fluoro?

low dose w/in continuous fluoro

halves mA selected by AERC

manually turned on/off

saves pt dose w/ minimal noise visual

high dose

used for increase penetration need for thicker pt → increase pt dose

pulse rate

30, 15, 7, 5, 3, or 2 pulses/sec

pulse width

exposure length of each pulse/beam (in msec) ON time

pulse interbal

beam OFF time

pulse height

mA value set by AERC/ABC

frame rate

number of images obtained/sec

decrease pt dose

if you decrease pulses/sec, what happens?

higher pulse

what kind of pulse is needed if you need to capture a fast motion?

temporal resolution

relates to the duration of time for aquistion of a single frame of dynamic process (cine imaging)

increasing frame rate

what would increase the temporal resolution?

sharper images

what type of image would a narrower pulse width create?

half pulse rate

what type of pulse rate would decrease the pt dose by 15%?

contrast

x-ray photons passing through input phosphor w/out being absorbed

multiple factors in the intensifier that cause a base fog

reduces visibility

spatial resolution

detail

improves in mag mode

4 to 6 lp/mm

what is the most common spatial resolution monitors have?

size distortion

primarily cause by OID

shape distortion

caused by geometric problems in the shape of II (curve)

pincusion, vignetting

what are examples of shape distortion?

pincushion distortion

borders/edge of a fluoro image are inherently magnified

due to inaccurate focusing electrons released from the periphery of the photocathode

electron minification is less periphery

what causes pincushion distortion?

vignetting

reduction of brightness at the edges of a fluoro image

result of off-focus electrons from the periphery of II photocathode

what causes vignetting distortion?

quantum mottle (noise)

blotchy/grainy appearance caused by insufficent radiation to create uniform image

static image controlled by mAs, but in fluoro is mA

fluoro units operate w/ minimal number of photons as possible to activate fluoro screen

static images

still images

spot image, photospot camera

what are the types of static images?

spot image

recorded at diagnostic mA levels

image is captured from radiation before it reachs intensifier

photospot camera

records a series of static images

takes up to 12 images/second

uses lower mA vaules = lowers pt dose

what is an advantage using the photospot camera?

cine (dynamic)

moive

capable of 15, 30, 60, & 90 acquisitions/second

fast enough to look like motion to the human eye

radiation pulse = decrease pt dose

what is an advantage of using cine images?

digital fluoro

any fluoro system can be made “digitial”

CCDs improve image quality & reduced pt dose

flat panel detectors (FPD) are used in place of II

w/ the addition of ADC & a computer

how can a fluoro unit become digitial?

small AMA & dual AMA

what are the types of dynamic FPD DEL options?

small AMA

larger DELs

typically used in diagnostic FPD

dual AMA

performs diagnostic imaging w/ normal AMA sizes can combine DELs by rows or forming larger “effective DELs/pixel for fluoro

binning

 is the process of combining the electric charge from adjacent CMOS or CCD sensor pixels into one super-pixel

to reduce noise by increasing the signal-to-noise ratio

what is the main purpose of binning?

digital fluoro FPD

reduces the risk of ghosting artifacts by utilizing a bakclighting system of LEDs diode array below AMA

enitre AMA recieves a quick flash of light after every exposure → light photons remove any residual charges

operates w/ normal mA values → increases contrast & spatial resolution

uses pulse imaging = decrease pt dose

what are the main points of using a FPD?

spatial resolution

when using a FPD in fluoro, what does NOT change when using mag mode?

laerger FOV size

less image distortion

improves contrast resolution

improved viewing & recording options

what are the benefits of using FPD in fluoro?

digital subtraction

mask image is then subtracted pixel by pixel from the contrast-filled image, resulting in the subtraction of the anatomical background

allows physician to concentrate on the pt vascular anatomy alone

roadmapping

a digital subtraction sequence is performed & the frame w/ maximum vessel opacfiication (map)

pt protection

higher kVp = higher engery beam & lower pt dose

mA should be as low as possible w/out unwanted levels of quantum noise

virtual collimation

faint lines on the last image hold indicate the position of the collimator plates