As kVp increaseso Increase speed of electron flowo Decrease beam wavelengtho Increase beam frequencyo More penetrationo Less attenuation (photoelectric)o Higher beam qualityo More scatter (Compton effect)

Photoelectric- what is absorbed in the body Compton and photoelectric are inversely proportional

o Less contrast (long scale) o Lower patient dose

Quality control test for kVp accuracyo Performed annuallyo Acceptance parameter= +/- 5% of the tested kVp

Anode heel effecto Radiation produced at the target and as

part of the primary beam is not uniform in intensity along its axis

o A greater intensity of the primary beam occurs towards the cathode end of the tube

o Cathode is always on the right in the USA

o % of central ray intensity is higher at the cathode so you could put thicker anatomy on that side

Use it to your advantageo Take the heel effect into account when

imaging anatomy that is thicker at one end than the othero Primarily long bone radiographyo Very relevant in analog, relevant in CR, irrelevant in DR= have specific

algorithm to give consistent brightness Selected anatomy for application of anode heel effect:

o Forearmo Humeruso Footo Tibia/fibula (put patient’s head to the right) o Femuro Thoracic spine

Source to Image Distance (SID)o Affects intensity of radiationo Affects density & “S”/”EI” number

o 200 = optimalo Within ±70 still goodo Lower number = overexposureo Higher number = underexposure

What SID affects?o Affects magnification (size distortion)o Affects recorded detail (resolution)o Affects size of the radiation field w/o collimationo Affects patient dose

*Think of a flashlight against a wallo Asking same amount of light to cover a larger field, so the amount of

exposure that reaches the IR goes down Inverse vs. Direct Square Law Inverse square law : used to measure new dose rates (mR, etc), or intensity,

when distance to, or from a radiation source, is changed Affects DOSE

EXAMPLE: An RT(R), standing 100 cm from a fluoro unit, receives an expose dose of 50 mR/hour. If the RT moves to 150 cm, what is the new dose?

(50mR x 100cm)/(150cm2) = (50 x 10,000) / (22,500)ANS: 22.2 mR/hour

Direct square law : use when asked to maintain radiographic density when distance is changed

o Affects DENSITYo Increase SID = decrease magnification = increase resolutiono Decrease SID = increase magnification = decrease resolution

EXAMPLE: If 20 mAs produces an acceptable @ 40” SID, what new mAs will produce the same density @ 50” SID?

(20 x 502)/(402) = (20 x 250)/(1600)ANS: 31 mAs

Radiographic Distortiono SIZE: magnification

-OID (object image distance)-SID (source image distance)-SOD (source object distance)

SID – OID = SOD

o SHAPE: elongation or foreshorteningo Angle on CRo Angle on body parto Angled IR

OIDo Relates to the distance of the object to the IRo Primarily affects magnificationo INCREASE OID = INCREASE magnification and DECREASE resolutiono Try to keep OID as short as possibleo Dramatic affect on magnification

Resolutiono Focal spot (smaller focal spot = better resolution)o SIDo OIDo Analog IR speed (RSI)o Quantum mottle (noise) – DR

Produced w/ high S/EI numberso Artifactso Motiono Distortiono Ranking (greatest effect to least effect)

1. Motion2. RSI (analog only)

o Changing speed of analog IR will have a dramatic effect but it won’t be “repeat worthy”

3. OID4. Artifacts (includes noise)5. Focal spot6. SID

Analong image receptor terminologyo Photoemission - ability of a phosphor to emit light when exposed to

radiationo Spectral emission - the color spectrum of light emitted by the PSP

when exposed to radiationo Conversion efficiency - the amount of light emitted when exposed to a

quantity of radiation. Increase efficiency= increase # of light photons produced with

less radiation exposureo Latent image - invisible image acquired on the film, before chemical

processingo Manifest image - visible image after chemical processing

Analog image receptors

o 95% of screen- film image is produced by light (photo and spectral emission) from rare earth PSP’s

o In radiography, dual intensifying screens used with dual emulsion film Both screens give of light and light transferred to adjacent

emulsion of the film o Modern receptor fronts made of carbon fiber to reduce patient doseo Back of receptor contains a thin sheet of aluminum to reduce

“backscatter”o Light tight and air tight holder for radiographic film

To maintain integrity of the film and make sure there is good screen contact

More screen film contact will always result in less resolution o Primary function is to decrease patient doseo Type is determined by procedure and speed

How fast they can convert radiation to light o Reflecting/ absorbing layer of screen that when if light photons want

to go in a different direction this prevents this Want light going to phosphor layer Reflective layer is titanium dioxide or magnesium oxide

depends on manufacturer In analog mammography- uses single screen with single emulsion to improve

detail (eliminates crossover effect) Relative speed index

o Determined by the following (just for analog) Conversion efficiency of phosphor

If less efficient, it cannot produce enough light= slower speed

# of phosphor crystals used Thickness of phosphor layer

Don’t typically do Increase thickness= increase speed

Amount of reflective later Be able to ID these:

o Rare earth phosphors- analog ONLY Yttrium tanlate Gadolinium Lanthanum oxybromide Barium lead sulfate Terbium

o CR image plate Barium fluorohalide and europium Cesium bromide and europium

Europium is an activator without these you would not have an image

No europium no image

Typical RSI values 400 rs 200 rs 100 rs 50 rs CR IP= 200- 300 rs

o RSI increases the speed of the receptor, result in less recorded detail (more radiographic blur). Advantage is that higher RSI values decrease patient does

o Also produces more density without compensation Intensification factor= exposure required w/o screens divided by

exposure required with screens Spectral matching

o For the greatest efficiency of the system, the color sensitivity of the film must match the spectral emission of the screen’s phosphor crystal

o If not, there is a loss of ½ the expected RSI of the system Quantum mottle

o Classified as a radiographic “artifact”o Aka radiographic noiseo Always caused by underexposureo Results from insufficient # of photons reaching the phosphor to

produce required density Increase S #

o Possible with higher RSI receptors, including CR and image intensification @ lower mA or mAs values

o Increase mAs reduces quantum mottle o S # of 600 to drop it from 600 to 300 you double the mAs

They are directly proportional o Image receptor variability- you will not get the same exact S number if

you do the same image twice Terms

o Fluorescence- ability of phosphors to emit visible light ONLY when exposed to x-ray with no afterglow

o Phosphorescence- the continued emission of light after the x-ray source has terminated. This causes unwanted exposure to the film

The phosphorescence is called screen lag or afterglow This means that something is wrong with the receptor if it

occurs in analog Screen- film contact

o Image receptors are subjected to rough handling, dropping, etco Could lead to warping of screens resulting in “poor screen-film

contact”

o Exhibited by loss of recorded detail and areas of increased density when viewed @6

o QC testing consisting of the “wire mesh test” should be performed annually

When you suspect that it is not air or light tight Look at mesh to see if there is an area that is darker or it is

more blurryo Want air tight so the emulsion of the film is in direct contact from the

light Anatomy that is in the light from the screen to get to the

emulsion of the film o Light tight so the film doesn’t get fogged

The CR imaging plateo Similar to a conventional receptor expect it does not need to be light

tight This is because there is not film in it

o Has 1 screen so you don’t have the double construction IP Comparisons

o Conventional Carbon fiber front Polyester base Adhesive layer Phosphor layer Reflective layer Protective layer Aluminum/lead foil for backscatter

o CR Carbon fiber front Polyethylene terephtalate (PET) base Blue tinted antihalo and reflective layer BaFx: Eu2+ or CsBr: Eu2+

Barium fluoride or cesium bromide Barium fluorhalo is a powder Cesium bromide is needle filaments Cesium bromide is more condensed which means there

is better resolution which means they don’t diffuse light as much as powder would

CsBr= always has better resolution Lead foil for backscatter

o Put plate in CR read, once it’s in it pulls the plate out (slow scan). Neon helium laser (gives off red light) will scan plate as it moves through the system in a left to right scanning pattern (raster) then top to bottom every time the laser hits the phosphor it gives off the image it captured, giving off reddish color and you don’t want it go to through

the reflective layer which is what the antihalo layer does they are made to metastable atoms, 50% useless 50% useful

Image acquisition and readouto A latent image is formed when exit radiation is absorbed by the PSP

and the europium creates metastable electrons, causing these electrons to excitate to a higher energy level, where they become stored

o Antihalo is there for protection of the reflective layer against the red light

o During this process, approximately 50% of the PSP’s storage energy in “F” centers, while the rest will emit non-diagnostic light

F center- active part that stores radiation/ where anatomical info is

50% of PSP are useless o Stored radiation energies will be

released during the readout phase when exposed to a neon-helium laser

Line focus principleo Principle by which an anode target

is constructed in order to produce a smaller effective focal spot

o Outer edge of radiation beam- penumbra- blurriness in the outer part of the beam

o Effective focal spot is what is giving you the resolution o By angling the anode you can redirect the photons down toward the

patient o Large focal spot will make more heat o Smaller the number the better the resolution o Manufacturer tells you the size of the effective focal spot

Test manually every year Test for focal spot blooming- increases in effective focal spot

Gridso Used for all procedures requiring increased exposure or kVp due to

part thicknesso IT DOES NOT REDUCE SCATTER PRODUCTIONo Located in radiographic table and uprighto Primary functions

Absorb scatter Coming from patient

Increase contrast More scatter=less contrast

When do you use a grid?o If part thickness exceeds 10-12 cm

o If kVp exceeds 70o For portable, stretcher, wheelchair chests, if thickness is > 26 cmo Why is the thickness more when for a chest?

Due to air in the lungs/radiolucentness in the lungs Grid frequency- the # of Pb strips/inch or cm (40/cm-103/in) Grid ratio- height of the Pb strips in relation to the distance between strips

o R=h/d o More important than grid frequency! o What is the ratio of a grid that possess 4mm lead strips and

interspacing of 0.5 mm? 4.0/0.5= 8 Grid ratio is identified as 8:1

Effects of density/radiographic exposureo Anything that results in less scatter being produced, or absorbs

more scatter, results in more contrast, but less densityo As grid ratio increases, its scatter absorption efficiency increases, but

density decreases w/o compensationo More scatter=more contrast=less density

Types of Gridso Parallel

Not in common practice Least efficient All lead strips parallel to each other Get advantage because it can give you an unlimited SID without

having grid cut off because of beam divergence More primary gets absorbed by the parallel beam Density goes down significantly Minimal use in modern radiology departments Primary advantage= unlimited SID use Disadvantage=not as efficient as other grids

o Focused Primarily in practice Are most efficient than parallel due to canted Pb strips that

coincide with the divergent beam Used in all modern radiographic tables and uprights Found in every radiographic table and upright unit Grid radius, focal range, convergence point

Where they all meet in space which means there is a restriction of the SID

You cannot use a focused grid beyond its grid radius Exceeding grid radius will produce grid cut off

Grid cutoff is recognized by a loss of density at both lateral edges of the image (distance decentering)

o Crossed Designed by placing 2 parallel grids at 90 degrees

Crossed grids are most efficient design Cannot angle the central ray in any direction Require significant increases in mAs, and result in excessive

patient dose Recommended with high kVp techniques only Might see them in a dedicated chest room but nothing else The more lead strips= the more primary beam your loosing

Other grid problemso Other technologist errors can result in evidence of grid cut-off

Off level grid Lateral decentering- not centered to center of the grid Not detenting the tube

More gridso Recommended that 8:1 grids be used @ kVp ranges of 80o kVp ranges > 100 require the use of 16:1

Grid and density o As grid ratio increases, density decreaseso Approx. 80% of scatter is absorbed BUTo Approx. 40% of primary beam is also absorbed in the Pb stripso Proper density compensations are determined by the specific ratio

Grid compensationso 16:1 grids produce the most contrast, but the least densityo 5 6:1 grid is mostly in mammography o From non-grid to grid

6:1= 3x> mAs 8:1= 4x> mAs 10:1 or 12:1= 5x> mAs 16:1= 6x> mAs

Grids increase pt dose Changing mAs between ratios

o To find new mAso mAs 1x new grid’s mAs factor/old grid’s mAs factoro ex. Changing from 8:1 using 20 mAs to 16:1

20x6/4= 30 mAs Contrast improvement factor

o Best measure of determining the efficiency of a grid K or CIF= contrast with a grid/ contrast without a grid K or CIF- contrast improvement

Air Gapo Use of a viable “air-gap” technique will achieve the same level of

efficiency as the use of a grido Intentional use of 6”+ OID to re-direct scatter away from the IPo SID must be increased to reduce magnification

o You are going to have distortion which is why you have to increase the SID

o You do this if you do not have a grid Rules of Air Gap

o A 6” air- gap requires a 72” SID provides an efficiency similar to an 8:1 grid

o Anything under 6” doesn’t require an air gap but increase the magnification and decrease resolution

o A 10” air-gap requires a 10 foot/120 inches SID and provides an efficiency similar to a 16:1 grid

Best for chest radiography @ 100-120 kVpo Not recommended for use on hyperthenic/obese patients

200 mA- 10 (s)- 65 kvp- 40” SID- 400 RSI (NON-GRID)250 mA- ___ (s) - 75 kvp- 50” SID- 200 RSI (12:1 grid).64 seconds

grid always wins with contrastRSI always wins for resolution