Limited Module #5
total absorption of an xray photon by the atom of the body part is termed:
photoelectric effect
the principal means of controlling involuntary motion is to:
use shorter exposure time
controlling motion
use shortest exposure time possible
how does collimation affect fog?
when collimation is left open, there is more scatter radiation which produces fog
after an imaging plate is scanned by the CR reader unit, it is erased with:
white light
how do smaller pixels affect spatial resolution?
will produce greater spatial resolution
The erasure process will begin if a CR cassette is opened and the plate is exposed for:
15 seconds
What is the size of the flat panel detector inside the table of a DR system?
17 x 17
name the two quality control tests that are done regularly to check the collimator's light field size and central ray alignment
collimator and central ray alignment
what are the names of the two test tools used to perform a quality control check of the collimator and central ray alignment?
collimator template and beam alignment cylinder
_________________ should be used for body parts that have extreme differences in tissue density
compensating filters
what device should be used when imaging body parts that have widely different thicknesses of structures?
compensating filters
A "cassette based" digital xray system is termed:
computed radiography
barium fluorohalide with europium is used in which of digital radiography formats?
computer radiograph
when fog prevents specific details from being seen in the image, what type of image may be requested?
cone down image
name at least 6 pathologic conditions that would require an increase in exposure factors
congestive heart failure, pleural effusion, rheumatoid arthritis, paget's disease, cirrhosis of liver, edema
The difference in radiographic density between any two adjacent portions of the image is called:
contrast
which photographic factor makes the anatomy in the image visible?
contrast
ability of a digital system to distinguish anatomic structures that have a similar subject contrast is termed:
contrast resolution
If a CR plate is divided in half and used for two separate exposures the side not receiving the exposure must always be:
covered by lead shields
what is the purpose of a Potter-Bucky diagram?
reduce appearance of grid lines
the principal method of reducing involuntary motion is to:
reduce exposure time
if the radiographic image is too dark, which exposure factors would you change to solve the problem?
reduce mAs
name three things that will increase spatial resolution
reduce motion, use max SID, use shortest OID, and use small FSS
list at least five factors that will increase spatial resolution in the radiographic image
reduce patient motion, decrease OID, increase SID, small focal spot size, reduce quantum mottle
when the xray exposure is greater or less than what is needed to produce an image, automatic _____________ occurs
rescaling
the storage phosphors in CR plates are hypersensitive to:
scatter radiation
radiation produced by photoelectric effect is called:
secondary radiation
the advantages of using CR and DR over conventional radiography include:
see images very quickly, wide dynamic range is enabled, density and contrast can be easily adjusted
unequal magnification of a body part is referred to as:
shape distortion
define spatial resolution:
sharpness of image
the image management system used in a digital radiology department is called:
PACS
the management system used in digital imaging to store and view images is termed:
PACS
the system used to view and store digital xray images is called a ___________ system
PACS
which of the following is used in CR to store a digital image?
PSP plate
in DR environments, the abbreviation PACS stands for:
Picture Archiving and Communications System
one of the most important things a limited operator can do to control scatter radiation is to:
collimate
which factor is the primary controller of radiographic contrast?what is teh distance between the tube target and the IR called?
SID
name two ways in which an exposure technique cart can fail
generator may be out of calibration RT isnt using it but memorizing technique
a decrease in SID will result in:
increased magnification
correct exposure
-DR systems: depends on manufacture -CR systems: exposure indexes --carestream ---fixed index, 1400-1800 ---equivalent to 400 film/screen ---fixed system so it does not matter what body part you are doing the index should always be between 1400 and 1800 ---exposure errors: 2200 (4x ideal), 1900 (2x ideal), 1300 (50% of ideal), 1100 (25% of ideal) --FUJI ---variable exposure index ---equivalent to a 400 film/screen --- variable system which means it depends on body part as to what the correct exposure index should be ---indexes: chest (200-400), extremities (300-500)
grid conversions
-GCF = mAs with grid/ mAs without grid -ratio and conversion factor: --no grid - 1 --5:1 -2 --6:1 - 3 --8:1 - 4 --10:1 or 12:1 - 5 --16:1 - 6 -grid conversion formula --mAs1 / mAs2 = GCF1 /GCF2
poter bucky diagram
-Gustav Bucky and Hollis Potter -moves grid during exposure -reduces appearance of grid lines -Gustav Bucky actually invented the grid and Hollis Potter improved on the design by making the grid move
distance and intensity
-SID -as SID increases, xray intensity decrease -inverse square law --intensity of radiation at a given point source is inversely proportional to the square of the distance --every time your distance is doubled, the instensity at any given point receives 1/4 of the dose due to radiation having to spread over a larger area -- formula: I1/ I2 = D1^2/ D2^2
Picture Archiving and Communication System (PACS)
-acquisition -interpretation -storage -display system --CRT monitor: 2084x2084 resolution --microcomputer, subtraction, edge enhancement, windowing, highlighting -network: many computers are connected to interact with each other --nodes: each computer in a network is called a node ---PACS workstations, remote PACS workstations, departmental mainframe, hospital mainframe, teleradiology -storage system: arching, magnetic tape, optical discs (use for all storage) -information systems --Hospital information system (HIS) and Radiology information systems (RIS) --HIS has patient demographics and RIS has all radiology information -Digital imaging and communications in medicine (DICOM) --allows different types of imaging systems from different manufacturers to communicate with each other and allows images to be sent from one place to the other and look the same --standardizes a gray scale
beam restriction
-aperture diaphragm -cones/cylinders -collimators --set of lead shutters --infinite number of field sizes --shapes the radiation field --light source: shows positioning light, 45 degree mirror --if the light angle changes from 45 degrees it will make the light field and xray field not match; so if you think centered correctly and you have collimated using the light field, your actual image will be off centered and possibly larger or smaller than you intended -positive beam limitation devices: when a cassette is placed in the bucky, sensors will not allow collimators to be opened larger than the film size -ancillary devices: lead blockers and masks -affects on radiographic film: as field size increases, density increases and contrast decreases
subject contrast
-as kVp increases, subject contrast decreases -increasing kVp causes an increase in beam penetration which means less gets absorbed so everything looks grey or black -optimal kVp --kVps should be chosen based off of what body part is being radiographed -changing kVp -- general rule of thumb: make adjustments in increments of either 15% or 8% --level 30 (50kVp): 4-5% for visible change, # for change: 1-3 kVp --level 50 (90 kVp): 8-9% for visible change, # for visible change: 4-8 kVp --level 90 (130 kVp): 10-12% for visible change, # for change: 9-16 kVp - amount of irradiated material: as part thickness increases, subject contrast decreases --due to more scatter being produced which then makes everything look like the same shade of grey; "fogging" -type of irradiated material: subject contrast between bone and soft tissue is greater than subject contrast between adjacent soft tissue structures --differential absorption: air = higher density (black); fat; water; muscle; bone = lower density (white)
methods to control scatter
-beam restriction -grids -air gap --will have a larger OID --with larger OID, scattered photons will scatter away from IR; with small OID, scattered photons will have nowhere to go but onto IR --larger OID = less scatter reaching IR = increased contrast -kVp --decrease in kVp should be considered when other methods fail to provide sufficient contrast --decreasing kVp will increase contrast in two ways: narrows the scale of contrast, decrease energy of scatter radiation and decrease fog
computed radiography (CR)
-cassette based -film is not the IR -front of cassette must be radiolucent -photostimulable phosphor (PSP) -barium fluorohalide plate - 200-400 speed screen film -latent image is stored until processed -if you have a film system and speed is between 200 and 400, you do not need to change technique charts
direct capture radiography (DR)
-cassette less -electrical output is proportional to radiation intensity -2 approaches --indirect (2 steps: xrays to light to electrical signal) --direct (1 step: xrays to electrical signal) -amorphous selenium is a direct-direct radiography method which means there is only 1 step in converting xray information into electrical signal to be digitized -amorphous silicon must have a light source first which means it indirect process --cesium iodide glows when xray hits it which then that light is converted into an electrical signal by amorphous silicon -DR systems are light a puzzel with each of the small detects make up a piece of the puzzle, those small detectors are called DELs and correspond to 1 pixel of final image -DEL --detector element size --"pixel size" --smallest available 100 um, smaller the DEL the better the spatial resolution
grid cut off
-caused by primary beam being absorbed into grid lines -types: --off-level: when grid is tilted or when xray beam is angled across the grid --off-center: when xray beam is off center to one side of grid --off-focus: when SID is outside the focal range of grid --upside down: when grid is reversed
conditions requiring an exposure decrease because they are easy to penetrate
-chest conditions --COPD --pneumothorax -- active TB -conditions of bone --degenerative arthritis --gout --hyperparathyroidism --iytic metastasis --multiple myeloma --necrosis --active osteomyelitis --osteoporosis --sarcoma -abdomen --bowel obstruction --pneumoperitoneum -generalized conditions --advanced age --atrophy --emaciation
conditions requiring an exposure increase because they are harder to penetrate
-chest conditions --atelectasis --bronchiectasis --cardiomegaly --CHF --edema --empyema --hemothorax --hydropnemothorax --metastases --pleural effusion --pneumoconiosis diseases --pneumonia --TB -conditions of bone --acromegaly --rheumatoid arthrisis --osteochondroma --healed osteomylelitis -- osteopetrosis --paget disease -abdomen --ascites --cirrhosis of liver -soft tissue: edema -generalized conditions --heavy musculature and large bones
coherent scattering
-classical scatter -unmodified scatter -occurs at very low xray energies -types: Thompson, Rayleigh -xray photon causes electrons to vibrate =release a photon with the same energy and wavelength -moves away from the atom in a different direction than the original xray photon -atom is not ionized -little significance to diagnostic imaging
compensating filters
-compensating filters can be placed between radiographic tube and IR to compensate for variations in tissue density -most often placed between tube and patient in the xray beam
spatial resolution
-dependent of the size of pixels/matrix --larger the matrix = smaller pixel size = better spatial resolution -signal to noise ratio (SNR or S/N) -geometric factors: OID, SID, FSS -conventional radiography: 8 lp/mm, has slightly better spatial resolution -computed radiography: 6 lp/mm -direct radiography: 4 lp/mm
grids
-device used to improve radiographic: contrast on film and spatial resolution on digital radiography -thin lead strips that absorb scatter -if using grids with DR then the amount of noise will be decreased -scatter increases as patient thickness increases and with larger field size, lower atomic number of tissue, and higher kVp -use a grid when body part thickness exceeds 10 cm and kVp is above 50 -types of grids --parallel: have grid lines that are parallel to each other --focused: designed to match angle of beam divergences so center grid lines are parallel but then they start to angle as you work your way towards the outside of the grid that have more of an angle -grid patterns: linear (lines only in 1 direction), criss-cross/cross-hatched (have lines in both directions like a tic tact toe board -grid quality: amount of lead --as lead content of a grid increases, the ability of grid to remove scatter and improve contrast increases --affected by grid ratio and grid frequency
contrast
-differences between adjacent densities -number of black, white, and gray tones -controlled by kVp -high contrast. (short scale): very few grays, very black and white, increases contrast, low kVp -low contrast (long scale): many grays, decreased contrast, high kVp
contrast resolution
-dynamic range -range of values over which a system can respond -corresponds to numerical range of each pixel --number of bits (1 byte = 256 different shades of gray) -number of shades of gray --8 bits (1 byte) = 256 grays -- 9 bits = 512 grays --10 bits = 1042 grays --11 bits = 2048 grays --12 bits = 4096 grays --16 bits = 65,535 grays -most modern digital systems are running on 12 or 16 bit systems -contrast to noise ratio -dynamic ranges --black and white : 2 --human eye: 32 --xray beam: 1024 --screen film radiography = 1,000 --CR and DR = 16,384 --the greater the dynamic range the higher the contrast resolution and better the image; singe our eyes can only see 32 different shades of grays, when we get up into the thousands it confuses our brains and makes the image look sharper even though it really isnt
exposure principles
-exposure: mAs and kVp -controlling noise (scatter): collimation, grids, scatter shields --grids: grid frequency vs scanning frequency ---grid frequency must be higher than scanning frequency, moire effect -basic principles that are the same as with film/screen: receptor exposure (signal strength), subject contrast (signal differences), over exposure is common (exposure factors creep) --some techs will bump their techniques up because they know that the computer will make the pictures all look the same no matter what technical factors you use (automatic rescaling) so they are creeping up the exposures which will just increase patient dose
types of systems
-fixed kVp systems -variable kVp systems
Photostimulable phosphor (PSP)
-imaging plate -layers from top to bottom : protective layer, phosphor layer, support layer, conductor layer, light shield layer
fixed kVp systems
-kVp held constant -mAs is varied to achieve appropriate image density -advantages --uses optimal kVps ---optimum kVp: use the highest kVp setting that will produce sufficient contrast for image quality --decrease patient dose --uniform radiographic contrast (film) --lengthened exposure latitude --extends tube life --reduces voluntary motion -disadvantages --lower overall film contrast --more scatter --small incremental changes may not be possible -extrapolate techniques --15-20% mAs change per cm --for every 4-5 cm increase in part thickness, double mAs; for every decrease in part thickness, cut mAs in half
variable kVp systems
-kVp to be used for a particular projection is varied depending on measured body part thickness -advantage: permits small incremental changes in exposure -disadvantage: inconsistent radiographic contrast and may increase patient exposure
technique charges
-listing of various radiographic examinations performed in facility -provides exposure for each body part according to its thickness -xrays machines that use AEC or APR systems must have a technique chart -unique to each machine and facility -patient/phantom testing: use 2 kVp/cm rule and radiograph patients/phantoms of varying thickness evaluate radiographs to determine kVp range
mAs reciprocity
-mA --measurement of the current --# of electrons crossing from cathode to anode per second --1 mA = 6.3 x 10^15 electrons per second --m A is directly proportional to tube current and directly proportional to number of xrays produced -seconds --exposure time; amount of time the electrons are allowed to pass from cathode to anode -mAs = mA x seconds -mAs --xray quantity --primary control of IR exposure: directly proportionate --need at least 25-30% change in mAs to notice a visible difference in picture -law of reciprocity --no matter what combination of mA and time settings are used as long as the mAs is the same, the IR exposure should not change
signal to noise ratio
-measure of signal strength relative to background noise --signal strength is determined by radiation amount so if you increase kvp or mAs you will increase signal strength --increasing kVp will also potentially increase noise level since increasing kVp will increase scatter -the higher the SNR, the better the spatial resolution -SNR of an xray imaging system is directly related to number of photons per unit and per unit time, incident on detector -major source of noise in any system comes from xray source itself -scatter is major source of noise -want to keep distance between signal and noise as far apart as possible; when they start getting close together due to either a decrease in signal or increase in noise, then images will become very grainy -how to increase signal? --increase radiation output, increase kVp (decreases patient exposure and could reduce image quality), increase mAs (increases patient does and maintains image quality) -how to decrease noise? --remove/reduce scatter reaching IR (collimation, optimal kVp, scatter shields, girds) -- direct DR rather than indirect DR
AEC
-measures the amount of radiation reaching the film -terminates the exposure time when the appropriate amount of radiation is reached -most important: posiitioning and collimation -advantage: more consistent exposure -disadvantage: very little positioning latitude -technical considerations --kVp: if kVp is changed, the AEC will adjust time accordingly (if kVp is increased, exposure time is decreased) --mA: if mA is changes, AEC will adjust time accordingly (if mA is increased, exposure time is decreased)
distortion
-misrepresentation of the true size or shape of the image as compared to the object -affected by tube angle and distances -Size --OID, SID, SOD --SOD = SID - OID --magnification ---SID: greater SID, less magnification ---OID: greater OID, more magnification -Shape --Alignment: proper alignment of tube, part, IR , and central ray ---central ray: beam divergency, farther away an object is from central ray, the greater the distortion --angulation: direction and degree ---direction: usually longitudinal, when patient is reverse from normal position, reverse tube direction ---degree: states as the angles between Cr and IR from standard reference point perpendicularity, changes SID --shape distortion causes either elongation or foreshortening ---elongation: makes part look longer than it really is; caused be tube or IR being improperly aligned ---foreshortening: makes part look shorter than it is; only when part is improperly aligned
patient measurement
-must measure body part accurately to select correct exposure technique -caliper: tool used for body part measurement --both jaws of caliper must be firmly in contact with body part
digital image
-new terms: spatial resolution and contrast resolution -pixel vs voxel
grid frequency
-number of grid lines per inch or centimeter -60-196 pines/inch
mAs and kVp relationship
-optimum kVp: kVp is the controlling factor of the quality of beam --penetrability of beam: higher the kVp = more penetrating and shorter wave length -kVp: controls quality, penetrability, subject contrast, amount of scatter, greatest effect on exposure latitude -15% rule -- if kVp is increased by 15%, density will be doubled so in order to maintain exposure you need to cut mAs in half --uses: contrast, density, motion -if using 60-90 kVp, a change of +- kVp will be sufficient --add or subtract 10 from kVp and double or half mAs accordingly
density
-overall blackness of an image -controlled by quantity of x-rays -mAs --does not control density on digital radiography
overexposure vs underexposure
-overexposure: increase in patient dose and image contrast is reduced -underexposure: objectionable mottle, decrease in SNR and spatial resolution -density does not change
xray interactions
-photoelectric absorption -coherent scattering -Compton scattering -pair production -photodisintegration -only photoelectric absorption, coherent scattering, and Compton scattering are associated with diagnostic xrays
pixel vs voxel
-pixel is 2 dimensional and voxel is 3 dimensional -we image voxels but display the information in pixels -collection of pixels or voxels in rows and columns = a matrix -depending on how much radiation hits a specific DEL then that pixel will be assigned a number. the higher the radiation amount the higher the HU number, the darker the pixel -matrix sizes --512x512 (262,144 pixels) --1024x1024 (1,048,576 pixels) --2000x2000 (4,000,000 pixels) -modality and matrix size --mammo: 4,000x4,000 --digital radiography : DR=2000 x 2000, CR = 3250x4280 --digital fluoro: 1000x1000 --CT: 512x512 or 1024x1024 --ultrasound: 512x512 or 1024x1024 --MRI: 512x512 or 1024x1024 --nuc med: 64x64 -14x17 cassette will equal approximately 2048x2500 matrix size which would be about 5.8 pixels per mm and would require approximately 11.5 MB of disk space to store image
processing CR image
-plate is placed into a scanner -high intensity laser beam scans plate -then causes trapped electrons to return to valence band -blue light is emitted (optically stimulated luminescence) -light strikes photomultiplier tube -photomultiplier converts light energy into electrical energy -electrical energy is digitized and sent to the computer -CR cassettes can be processed 10,000 times before they start losing ability to hold image
viewing digital image
-postprocessing --annotation --windowing ---manipulating the CT gray scale, adjusts the contrast and brightness ---window width: contrast, higher the window width: more shades of grays ---window level: brightness; higher window level=darker the image ---windowing takes place of changing mAs to change density and changing our kVp to change contrast with plain film, now it is done electronically after image is taken --magnification --image flip --image inversion --subtraction --pixel shift --region of interest -all done in PACS
grid movement
-reciprocating: motor driven, moves back and forth during exposure, we now use this type -oscillating: powerful electromagnet, moves in circular fashion
differences between screen-film and digital exposure principles
-screen film --exposure (mAs): changes optical density --differences in exposure (kVp): changes subject contrast --processing: tends to degrade contrast --recorded detail: geometric factors -digital --exposure (mAs): no change in density --differences in exposure (kVp): little change in subject contrast --processing: changes density and subject contrast --spatial resolution: geometric factors, SNR, pixel/matrix size
recorded detail
-sharpness of the lines of the image -distances, patient, film/screen combinations is what controls is -can be called *spatial resolution*, definition, sharpness, resolution, detail -lines pairs per millimeter -factors affecting detail --geometry: focal spot (as focal spot decreases, recorded detail increases), distance (as SID increases, recorded detail increases, as OID decreases, recording detail increases) --penumbra vs umbra ---umbra: distinctly sharp area of shadow or region of complete shadow --penumbra: imperfect, unsharp shadow surrounding the umbra --motion: voluntary (can control if choose, requires communication, reduce exposure time, possible immobilization), involuntary (patient has no control over movement, reduce exposure time, positioning sponges), equipment motion
digital image vs screen/film
-spatial resolution is less than conventional radiography -contrast resolution is better than conventional radiography -exceptional latitude (room for error) when compared to conventional radiography -processing of images is must faster than conventional radiography -techniques do not need to be as precise as they do for film
grid ratio
-the ratio of the height of the lead strips to the distance between them -grid ratio = h/D
adjustments of techniques
-variations in patient/part size: as thickness increases, density will decrease unless adjusts are made in exposure which are normally done with change in mAs -pediatric techniques: tissues of children are more sensitive to radiation damage, techniques need to be more precise -obese patient techniques: kVp must be increased -alteration of density: minimum change necessary to cause a visible change in density is 30% of mAs -alteration of contrast levels: 15% rule -variations in SID: mAs1 / mAs2 = D1^2 / D2 ^2 -certain conditions require an exposure increase and some require an exposure decrease
photoelectric absorption
-xray photon hits an inner shell electron -electron is ejected from the atom (ionized atom and photoelectron) -xray photon energy is absorbed in its place -photoelectron then travels a short distance -characteristic radiation is then produced -since an inner shell electron was ejected, there is a domino effect as the electrons from outer shells drop inward to fill the empty space; as those do so, it must release energy and that energy is released as characteristic radiation
Compton scattering
-xray photon interacts with a loosely bound outer shell electron: Compton or recoil electron, Compton scattered photon -compton effect -backscatter radiation -electron that is ejected from outer shell is termed a Compton and recoil electron; the xray photon which is scattered and goes in a different direction is the compton scattered photon -serious impact on image quality -possess an energy high enough to create a radiation hazard -primary cause of occupational radiation exposure -this is what causes fog on film or noise on digital images
the central ray alignment quality control test must show that the alignment is within ___________ of perpendicular
1
What factors need to be considered when selecting the mA station? 1. exposure time 2. FSS 3 thickness of part
1 and 2
the factors that affect the quantity of xrays in the xray beam are: 1. mAs 2. kVp 3 APR
1 and 2
which of the following modalities in radiology produces digital images that can be sent through a computer network? 1. CT 2. MRI 3. conventional radiography
1 and 2
which of the following factors will affect the quantity of scattered radiation fog on a radiograph? 1.kVp 2. CR plate 3. field size
1 and 3
the control limit for the xray tube beam alignment is that the beam must be within:
1 degree of perpendicular
a technique chart provides the following information 1. mA 2. kVp 3. SID
1, 2, and 3
scattered radiation affects the radiographic image by causing 1. fog 2. reduced contrast 3. reduced recorded detail
1, 2, and 3
which of the following will result in increased radiographic density? 1. increased mA 2. increased exposure time 3. decreased SID
1, 2, and 3
match the following terms with their descriptions 1. analog to digital converter (ADC) 2. dead pixels 3. rescaling 4. smoothing 5. edge enhancement 6. dynamic range A. a processing technique in which each pixels frequency is averaged with the surrounding tissues pixel values, done to remove noise which can be bothersome to radiologist B. takes the stored charge from the detector and converts it into a digital value C. when xray exposure is greater or less than what is needed to produce an image, this processing system is engaged, it is designed to display all the pixels for the area of interest with uniform density and contrast D. response of detector to different levels of radiation exposure E. occurs when there may be a defect in a component of the computer screen matrix, may cause a loss of patient information F. processing technique in which images can be made sharper and have greatly increased contrast; however, it does introduce some noise and loss of detail
1. ADC - B 2. dead pixels - E 3. rescaling - C 4. smoothing - A 5. edge enhancement - F 6. dynamic range - D
fill in the blanks with T or F to indicate whether each statement is true or false 1. an exposure technique chart is not necessary when using digital imaging systems 2. with direct conversion DR, the xray energy is converted directly into an electrical signal 3. subtraction and contrast enhancement are postprocessing techniques 4. CR imaging plates should never be split to enable two separate exposures on one plate 5. CR imaging plates are more sensitive to scatter radiation both before and after exposure to xrays 6. when there is a high signal to noise ratio, the least amount of information is captured
1. F 2. T 3. T 4. F 5. T 6. T
Match the following terms with corresponding definitions: 1. OID 2. penumbra 3. inverse square law 4. SID 5. size distortion 6. elongation 7. shape distortion 8. foreshortening 9. dnesity 10. long scale contrast 11. contrast 12. short scale contrast 13. quantum mottle A.source-image receptor distance B. intensity is inversely proportional to the square of distance C. object-image receptor distance D. result of unequal magnification E. overall blackness on image F. magnification of a part G. unsharp edges H. difference in density between adjacent structures I. object appears shorter J. object appears longer K. produced by low kVp L. produced by high kVp M. grainy or mottled image
1. OID - C 2. Penumbra - G 3. inverse square law - B 4. SID - A 5. size distortion - F 6. elongation - J 7. shape distortion - D 8. foreshortening - I 9. density - E 10. long scale contrast - L 11. contrast - H 12. short scale contrast - K 13. quantum mottle - M
fill in the blanks with T or F 1. higher kVp results in more scattered radiation 2. quality control test of collimator field and xray field must show that the two fields are within 2% of the SID 3. as the kVp is increased, the Compton effect is decreased 4. as the kVp is increased, the photoelectric effect is increased 5. the production of scatter results in fog on the radiograph 6. as collimation is increased, or made larger, scatter radiation fog is decreased 7. the atomic number of the body part influences the quantity of scatter radiation fog 8. increase thickness = more interactions = increase scatter = increased fog 9. the patient is the principal source of scattered radiation in radiography 10. a grid is placed between patient and IR 11. compton scatter travels in a forward direction only 12. scatter radiation fog reduces the visibility of detail 13. standard control limit for the xray tube's central ray alignment is that the tube must be mounted so that the beam is within 1 degree of perpendicular 14. the collimator and beam alignment must be checked using two separate quality control tests
1. T 2. T 3. F 4. F 5. T 6. F 7. T 8. T 9. T 10. T 11. F 12. T 13. T 14. F
match the following terms with their descriptions 1. brightness 2. contrast resolution 3. quantum mottle 4. matrix 5. pixel 6. spatial resolution 7. window level 8. window width A. describes images that are grainy or mottled, caused when not enough photons reach detector B. ability to distinguish anatomic structures of similar subject contrast C. a control that adjusts the density in image D. series of thoughts of small squares that make up the viewing monitors active are E. control that adjusts the contrast in the image F. amount of detail or sharpness of an image as seen on the viewing monitor G. used in place of density in digital imaging H. an individual square or picture element in monitors active area
1. brightness - G 2. contrast resolution - B 3. quantum mottle - A 4. matrix - D 5. pixel - H 6. spatial resolution - F 7. window level - C 8. window width - E
match the following terms with their descriptions: 1.digital imaging 2. computed radiography (CR) 3. photostimulable storage phosphor (PSP) 4. digital radiography (DR) 5. indirect conversion 6. direct conversion 7. postprocessing A. a cassette less digital xray systems B. a cassette based digital xray system C. means for adjusting any image of a body part with computer software D. process in which detectors convert xray energy directly into an electrical signal E. general term fro the process of acquiring images of the body using xrays, displaying them digitally, and viewing and storing F. two step process in which xray energy is converted to light and then to an electrical signal G. stores the image of body part
1. digital imaging -E 2. computed radiography - B 3. photostimulable storage phosphor - G 4. digital radiography - A 5. indirect conversion - F 6. direct conversion - D 7. postprocessing - C
label the following to indicate if they need an increased technique or decreased technique 1. paget's disease 2. edema 3. bowel obstruction 4. sarcoma 5. hemothorax 6. pneumothorax 7. bronchiectasis 8. advanced age 9. d.egenerative arthritis 10. gout 11. atelectasis 12. COPD 13. metastases 14. pleural effusion
1. paget's disease - increased 2. edema - increased 3. bowel obstruction - decreased 4. sarcoma - decreased 5. hemothorax - increased 6. pneumothorax - decreased 7. bronchiectasis - increased 8. advanced age - decreased 9. degenerative arthritis - decreased 10. gout - decreased 11. atelectasis - increased 12. COPD - decreased 13. metastases - increased 14. pleural effusion - increased
fog on the radiograph becomes objectionable when the body part size is larger than
10 or greater
the phosphor plate inside the CR cassette can be used _____________ times before it needs to be replaced
10,000
a grid is used when body part becomes larger than:
10-12 cm
a grid should be used if the body part measures at least:
10-12 cm
when a radiograph needs to be repeated because the original image was too dark or too light, what is the minimum change in mAs that should be made in each case?
100% if to light, 50% if too dark
a general rule of thumb for mAs changes when an image is too light or too dark is to make adjustments in increments of:
100% if too light, 50% if too dark
When using DR systems, indirect conversion of x-ray energy requires how many steps?
2
with DR indirect conversion, _______________ steps are required to process the image
2
When a large OID is used spatial resolution can be improved by: 1. decreasing the SID 2. increasing SID 3. maintaining the small focal spot
2 and 3
the advantages of using a variable kVp technique chart are: 1. lower image contrast 2. improved visibility of detail 3. ability to make small incremental changes in exposure technique
2 and 3
which of the following is/are necessary to process a CR image? 1. darkroom 2. Cr reader unit 3. computer system
2 and 3
which of the following methods is an effective way to obtain a technique chart? 1. have each xray operator write down the techniques for 1 week 2. request assistance from imaging manufacturer's technical representative 3. hire a consultant who is an expert in technique chart preparation
2 and 3
how many pixels are there in a 1650x1800 viewing monitor?
2,970,000
Which mA station can be used for most average size patients to take advantage of the small focal spot?
200
the ma should be kept below what level in order to use small focal spot size and obtain better detail?
200 mA
the small focal spot can only be used at which mA settings?
200 mA
Which matrix below will provide the greatest spatial resolution?
2000 x 2500
when using a CR plate, how much of the energy of the latent image is lost if the plate is not processed within 8 hours?
25%
with CR imaging plates, how much of the energy of the xray image in the phosphor is lost in 8 hours?
25%
1 byte = ____________ shades of grays
256
with CR and DR, images can be processed and seen in:
3-5 seconds
By how much do the mAs have to be changes in order to see a visible shift in image density?
30%
to see a noticeable difference in IR exposure on your radiograph, you must change the mAs by at least:
30%
what is the minimum change in mAs that will prompt a visible change in image density?
30%
a doubling in kVp will result in how many more photons being emitted?
4 times more
the typical SIDs used in radiology today are:
40 and 48
in general, an increase of 15% in kVp will necessitate a ________% decrease in mAs to maintain the same IR exposure
50
a grid should be used when the kVp is greater than:
60
if an exposure is made using 300 mA, 0.3 sec, 85 kVp, 40 in SID, what is the value of the mAs?
90 mAs
name at least four body parts or projections for which a compensating filter will help obtain a radiograph of more even density
AP t-spine AP should Axiolateral hip AP scoliosis spien
an exposure technique chart may not need to be posted for the ___________ type of exposure control system
APR
name at least 6 pathologic conditions that would require a decrease in exposure facotrs
COPD, active TB, gout, degenerative arthritis, bowel obstruction, advanced age
imaging plates from digital CR are processed in an:
CR reader
in the diagnostic range of kVp settings (50-100), the majority of scattered radiation will be from which interaction with matter?
Compton effect
what is the name of the processing technique that allows xray images to be produced with uniform density and contrast, regardless of the amount of exposure?
automatic rescaling
digital radiography
can be either computed radiography (CR) or direct capture radiography (DR)
the universally accepted standard for exchanging medical images is termed:
DICOM
the method for calibrating a particular display system for the purpose of presenting images consistently on different viewing monitors and printers is called the:
DICOM grayscale function
the phosphor that absorbs the xray energy in a ______________ system is called a flat panel detector
DR
defective pixels are caused by
Dust scratches and interactions between materials
how doe the following affect geometric sharpness? FSS SID OID
FSS: magnification decreases SID: magnification increases OID: magnification decreases
How does each of the following affect distortion appearing on a radiograph? Focal spot size Tube angulation OID
FSS: not affected Tube angulation: angle will produce distortion OID: As OID is increased, distortion will occur
T/F the function of the grid is to reduce the amount of scatter produced in the patient
False: absorb scatter from patient before it hits IR
T/F positive beam limitation is another term utilized in reference to automatic technique selection
False: automatic collimation
T/F the kVp for a specific body part that is sufficient to adequately penetrate the part regardless of size and provide a diagnostic level of contrast without excess exposure to the patient is called ideal kVp
False: optimum kVp
fill in the missing information: High Contrast: ________ shades of gray _________ contrast __________ kVp _________ scale Low Contrast: ___________ shades of gray ___________ contrast ___________ kVp ___________ scale
High contrast: few shades of gray; increased contrast; low kVp; short scale Low contrast: more shades of gray; decreased contrast; high kVp; long scale
what is the relationship between SID and the following? IR exposure contrast recorded detail size distortion shape distortion
IR exposure: indirect contrast: none recorded detail: direct size distortion: indirect shape distortion: non
the majority of photons that are scattered will scatter in which direction?
In a more forward direction
The official organization that accredits hospitals and clinics and requires technique charts is?
Joint Commission
list the five factors that will affect distortion
SID, OID, CR angle, part position, IR position
How do the following affect IR exposure? SID kVp mAs
SID: inversely proportional (as SID increases, exposure decreases) kVp: directly proportional (as kVp increases, exposure increases) mAs: directly proportional (higher mAs results in greater exposure)
What affect if any does the following have on magnification? SOD OID SID FSS
SOD: no affect OID: as OID is increased, there is more magnification SID: increased SID equals little magnification FSS: no affect
how many times can a CR imaging plate be used?
at least 10,000
which of the following is a true statement regarding the use of collimation with digital systems?
at least two sides of collimation should be seen on the image
a major advantage of CR and DR digital imaging systems is:
ability to see images very fast
name at least two major advantages of using CR and DR systems
ability to see images very fast, wide dynamic range is enabled, density and contrast can be easily adjusted
what types of images from a radiology department are stored in a PACS system?
all digital images (CT, MRI, ultrasound, nuc med, and xrays)
Compton scatter leaves the body in what direction?
all directions
the photoconductor used in DR flat panel detectors is:
amorphous selenium and silicon
what material is used as a conductor in a direct conversion flat panel detector system?
amphorous selenium
With direct-conversion DR, the x-ray energy is directly converted to:
an electrical signal
what is teh name of the device that takes the stored charge in the detector and converts it into digital values?
analog to digital converter (ADC)
which of the following takes the stored charge in the flat panel detector and converts it into digital value?
analog to digital converter (ADC)
technique charts are based on patient part measurements obtained using xray calipers and are expressed in __________________
centimeters
what causes the fogged image artifact in the digital image?
background or scattered radiation
the PSP in the CR imaging plate is:
barium fluorohalide with europium
the phosphor used in the Cr imaging plate is:
barium fluorohalide with europium
the higher the SNR, the ____________ the spatial resolution
better
where are compensating filters placed?
between tube and IR
motion of the patient, tube, or IR during the exposure results in:
blurring and less spatial resolution
the photoelectric process is an interaction between an xray photon and a __________ electron
body
what is the optimum relationship between the central ray, body part of interest, and the IR in order to produce minimal shape distortion on a radiograph?
body part is parallel to IR and CR is perpendicular to both
which of the following projections can benefit from use of compensating filters?
both AP spine and axiolateral hip
the digital imaging term for density is:
brightness
what is the term used to describe density in the digital envrionment?
brightness
a moving grid may be part of a radiographic table or upright unit and is called a
bucky grid
which tool and which units are used to measure body part thickeness?
calipers and cm
what should you do if motion is anticipated in advance of making the exposure?
decrease exposure time
list at least three meausres that should be taken to prevent voluntary motion during radiography
decrease exposure time, communication, and place them in comfortable/stable positions
according to the inverse square law, if the SID is doubled, the intensity or quantity of xrays will
decrease to 1/4 of the original intensity
when a body part is dense, or has a greater atomic number, scatter radiation is:
decreased
when kVp is increased, the photoelectric effect is:
decreased
Fog affects radiographic quality by causing
decreased contrast
how does a decrease or increase in kVp affect contrast?
decreased kVp = increased contrast increased kVp = reduced contrast
collimation of the xray beam ___________ IR exposure and ___________ the amount of scatter radiation produced
decreases; decreases
the primary function of mAs during a radiographic exposure is to regulate:
density
photographic properties
density and contrast
when "windowing", the level will determine ______________ while the width determines the ____________ of the image
density; contrast
Motion of the patient, either voluntary or involuntary, during the exposure will result in decreased:
detail
define distortion:
differences between actual subject and its image
define contrast:
differences in density between adjacent portions of image
a misrepresentation in the size or shape of the structure being examined is called:
distortion
If the mA, exposure time, or mAs doubles, the dose to the patient will:
double
if mA, exposure time, or mAs doubles, the number of photons will:
double
if the mAs is doubled, the dose to the patient will:
double
as a general rule of thumb, if your radiograph's Exposure Index is too low, how should you adjust your exposure factors?
double mAs
when using the 15% rule, a 15% change in kVp will produce approximately the same changes in radiographic density as:
doubling or halving mAs
you use the 15% rule to maintain IR exposure, so as you cut your mAs in half, patient dose goes __________ exposure latitude _________________ exposure times _______________
down; increase; decrease
response of the detector to different levels of radiation exposure is termed:
dynamic range
the number of gray shades that an imaging system can produce is termed:
dynamic range
what is the name of the processing technique in which images can be made sharper and have greatly increased contrast?
edge enhancement
what is the name of the processing technique in which xray images can be made sharper and have greatly increased contrast?
edge enhancement
assume that your xray control panel has the following mA settings: 50, 100, 200, and 300. which might you use for radiography of elbow, lumbar spine, and chest?
elbow: 100 mA l-spine: 200 mA chest: 300 mA
how is the energy of the xray beam affected when the kVp is adjusted?
energy increases when kVp increases, and vice versa
what happens to the energy of the photon when it is scattered?
energy is decreased
what are two ways to minimize shape distortion?
ensure body is parallel to IR and CR is perpendicular to IR
if a digital image appears on the viewing monitor as overexposed or underexposed, what should be checked?
exposure indicator number
T/F if the SID is increased or decreased, the density on the image is not changed
false
T/F increased quantum mottle will result in increased spatial resolution
false
T/F the contrast on the viewing monitor is adjusted by controlling the window level
false
T/F the xray interaction with matter that is responsible for the majority of scattered radiation reaching the IR is photoelectric absorption
false: Compton
T/F quantum mottle occurs in digital images if there is too many photons reaching the IR
false: not enough
T/F compton scattering is likely to occur when the x-ray photon interacts with an inner shell electron
false: outer shell
T/F grid cut off occurs when scattered radiation is absorbed by the grid
false: useful radiation
what are two major types of technique charts?
fixed and variable
the kVp can be determined for a technique chart using what two types of kVp settings?
fixed or variable
which one of the following could you use to control spatial resolution?
focal spot
Generalized unwanted exposure on the image is called:
fog
the production of scatter radiation during an exposure results in what effect on the xray image?
fog
unwanted exposure in the radiographic image is called:
fog
what are the two terms used to describe shape distortion?
foreshortening and elongation
the number of grid lines in an inch defines grid:
frequency
as the distance from a radiation source increases, the object receives less radiation. this occurs principally because xray photons: what law does this describe?
get farther apart as they get farther from the target; inverse square law
the first step in avoiding motion is to use:
good communication skills to make sure patient understands what is expected and is willing to cooperate
an increase in the OID will result in:
greater magnification and less recorded detail
the larger the matrix the ______________ the spatial resolution and the _______________________ the pixel size
greater; smaller
on a radiograph, the appearance of decreased density on the side of the image is most likely caused by the
grid cutoff
what causes the moire pattern artifact in the digital image?
grid lines are not aligned with laser scanning frequency of CR reader
compton scattering is likely to occur when the irradiated tissue has a _____________ atomic number
high
the storage phosphors in the CR plate are hypersensitive to _____________ levels of scatter radiation exposure
high
low kVp produces an image with what type of contrast?
high (short scale)
compton scattering is likely to occur when the x-ray photons have _____________ energy
higher
the higher the dynamic range the _____________ the contrast resolution
higher
when there is a likelihood of motion, how should the mA and exposure time be set?
higher mA with lower exposure time
what does "optimal kVp" mean>
highest kVp setting that will produce sufficient contrast for acceptable image quality
what does the 15% rule mean?
if you increase or decrease kVp by 15%, mAs must be doubled or halved
what causes the quantum mottle artifact in the digital image?
inadequate exposure technique
the major limitation in imaging obese patient is:
inadequate penetration of body part
what causes the phantom or ghost image artifact in the digital image?
incomplete IR erasure
a grid should be used when an ______________ in contrast is desired when using film
increase
if you increase OID what should you do to help maintain image size?
increase SID
If a large OID produces an unacceptable loss of spatial resolution what other factors can be changed to improve the image?
increase SID or decrease FSS
How should exposure factors be adjusted when there is the likelihood of motion?
increase mA and decrease exposure time
list two pathologic conditions that require an exposure increase and two that require a decrease
increase: pleural effusion and rheumatoid arthritis decrease: COPD and sarcoma
when kVp is increased, the Compton scatter is:
increased
when kVp is increased, will the quantity of secondary radiation fog be increased or decreased?
increased
what does decreasing collimation do to the contrast in the image?
increases contrast
what is the most important technical factor adjustment that should be made when imaging obese patients?
increasing kVp
what type of light source is used to erase the stored image in a CR imaging plate?
intense white light
the inverse square law tells us the relationship between which two factors?
intensity and distance
if the SID is doubled, what will happen to xray intensity or quantity?
intensity will decrease to 1/4 of original intensity
If the SID is reduced by 50%, what will happen to x-ray intensity or quantity?
intensity will increase by 4 times
what happens to the xray photon during the photoelectric effect?
interacts with an atom in the body rather than an electron interacting with the anode
what happens to the xray photon when the Compton effect is occurring?
interacts with an outer orbital electron removing it from the atom
patient motion can be categorized in what two ways?
involuntary and voluntary
what is the difference between involuntary motion and voluntary motion?
involuntary motion is motion you can't control and you can control voluntary motion
as the kVp is increased, the photoelectric effect:
is decreased
as kVp is increased, the Compton effect:
is increased
how is scatter affected when a body part is very dense or has a high atomic number?
it is decreased
what is the effect of increased kVp on scatter radiation fog?
it is increased
Why should the small focal spot be used as much as possible?
it provides better image sharpness
because of the wider dynamic range of digital systems, a slightly higher ____________ setting may be acceptable for radiography projections done using a grid or bucky
kVp
of all of the exposure factors _____________ has the greatest effect on beam quality, attenuation, and exposure latitude
kVp
one of the most important aspects of setting the exposure technique when using digital imaging systems is to ensure that which of the following is correctly set on the generator?
kVp
the primary factor controlling radiographic contrast and xray penetration is:
kVp
what is the primary exposure factor used to control subject contrast?
kVp
which of the following will affect the quality of xray beam?
kVp
which factors affect xray quality?
kVp and filtration
list two possible causes when a radiographic image appears gray and flat
kVp is to high, and fog
name several technique factors that must be included on an exposure technique chart
kVp, mA, SID
list at least three factors that will affect radiographic contrast
kVp, subject contrast, collimation
which two factors affect the subject contrast?
kVp, tissue density
what causes an image to have grainy appearance?
lack of photons
When a CR plate is inserted into the reader for processing, the phosphor is scanned with a:
laser
with CR digital systems, the imaging plate is scanned with a ____________ after being inserted into the reader device
laser beam
what type of light source is used in the CR reader unit to release the stored xray energy?
laser light
changing from the small to the large focal spot results in:
less recorded detail
the smaller the effective focal spot, the __________ the penumbra, and the __________ the spatial resolution
less, greater
a _____________ grid has lead lines running in only one direction
linear
When the goal is to differentiate between tissues that have very similar densities is a long or short scale of contrast most desirable? Why?
long scale because more gray tones will show
low contrast can also be called
long scale contrast
high kVp produces an image with what type of contrast?
low (long scale)
the unit used to indicate the total quantity of xrays in an exposure is:
mA
Which of the prime factors of exposure are directly proportional to the quantity of exposure?
mA, exposure time
which technique factors, if adjusted upward, will increase density?
mA, exposure time, mAs, kVp
which factors affect xray quantity?
mA, kVp, and filtration
name the four prime factors of radiographic exposure
mA, kVp, exposure time, SID
the dose a patient receives during a diagnostic exposure is directly proportional to the:
mAs
the primary controller of radiographic density is:
mAs
what unit is used to indicate the total quantity of exposure?
mAs
quantum mottle occurs when:
mAs or kVp is set too low
prime factors that affect xray emission
mAs, kVp, SID
what do each of the following stand for? mAs kVp SID OID
mAs: milliamperage-seconds kVp: kilovoltage SID: source-image distance OID: object-image distance
what is the relationship of the following set of factors with recorded detail mAs kVp FSS
mAs: none kVp: none FSS: indirect
name three reasons why an exposure technique chart may not work properly
machine isnt calibrated, digital processor may not be working properly, RT may not be referring to it and instead just memorizing the technique
another name for size distortion is:
magnification
size distortion can be controlled by keeping _______ as low as possible
magnification
distance and quality
magnification, recorded detail, contrast
a technique chart that requires every factor to be set individual is called a
manual chart
tissue density refers to:
mass density of part
The viewing monitors active area is made up of thousands of small squares called the:
matrix
on a digital viewing monitor, the active area of the monitor is called the
matrix
how does a greater electrical signal in a digital imaging system affect noise and image quality?
more information is captured which means greater spatial resolution
what are the five factors that affect spatial resolution?
motion, OID, SID, FSS, quantum mottle
what causes extraneous line pattern artifacts in digital image?
noise
what type of body part will require compensating filters?
one that has 2 widely varying thicknesses that have to be included in one image
The kVp that is sufficient to penetrate the body part adequately without excess exposure to the patient is called?
optimum kVp
most of the photons that scatter will scatter in which specific direction?
outside of body
define density:
overall blackness of image
the term used to describe a dark image is:
overexposure
define elongation:
part appears longer than it is
define foreshortening:
part appears shorter than it is
the principal source of scatter radiation is the:
patient
what types of information must be included on every digital image?
patients name, date of birth, date of exam, name and location of xray facility
specialty exposure technique charts must be provided for which two diverse groups of patients?
pediatric and obese
what is the name of the tool that is used to stimulate different densities on a radiograph?
penetrometer
having unsharp or fuzzy edges of structures in an image is called:
penumbra
the "fuzzy" unsharpness at the edges of structures or body parts is called:
penumbra
which type of radiation interaction produces scattered radiation that is characteristic of subject irradiated?
photoelectric
how will a larger matrix affect the pixels
pixels will be smalleer
one means of controlling distortion is by controlling the:
poart posiiton
contrast is influenced by
presence of fog and collimation
______________ will occur in digital systems if there are too few photons reaching the IR
quantum mottle
a term used to describe a grainy or mottled image is:
quantum mottle
in digital imaging, unwanted graininess in the image is called:
quantum mottle
noise in the digital image is referred as:
quantum mottle
the technical term for a grainy or spotty image is:
quantum mottle
which of the following will be seen in the xray image if either the kVp or the mA is set to low for the projection?
quantum mottle
name at least six artifact patterns seen in digital imaging
quantum mottle, moire pattern, light spots, scratches or tears, fogging, extraneous lines
which type of Potter-Bucky diagram is operated by a motor which drives the grid back and forth during the exposure?
reciprocating grid
geometric properties
recorded detail and distortion
When an overall radiographic image appears blurred what aspect of image quality is affected? Which exposure factor might be changed to solve this problem?
sharpness or spatial resolution; shorter exposure time
describe short scale and long scale contrast
short scale = high differences, few differences; long scale = low contrast, more gray tones
High contrast produced by low kVp results in an image with
short scale contrast
high contrast can also be called
short scale contrast
if an xray image is blurred or has motion, which exposure factors are used to correct this?
shorter exposure time
the ability of a digital system to convert the xray input electrical signal into a useful radiographic image is termed the
signal to noise ratio
the ability of a digital system to convert the xray input electrical signal into a useful image is term
signal to noise ratio (SNR)
radiographic distortion can be categorized in which two ways?
size and shape
what technical exposure adjustment can be made to reduce radiation exposure to patient?
slightly increase kVp
when selecting a low mA station (100 mA), you should use:
small focal spot
the technique that can be useful in viewing very small structures and the fine details of bone is called
smoothing
what is the name of the technique in which each pixel's frequency is averaged with the surrounding tissue's pixel values in an effort to reduce noise in the image?
smoothing
what is a penetromter?
solid piece of aluminum with steps of varying thicnkess
what two entities require that exposure technique charts be placed in every radiography room?
state laws and Joint Commission
the densities of the tissues within the patient are referred to as:
subject contrast
Two postprocessing techniques are
subtraction, contrast enhancement
a listing of the exams and exposure factors used for those exams that must be placed in every room is called the:
technique chart
one advantage of using a fixed exposure technique chart is that:
the exposures will have more latitude for exposure error
how is scatter affected when the body part is thicker or larger?
the greater the scatter
why is there less scatter radiation with a body part that is more dense or has a higher atomic number?
there is more photoelectric effect
what effect does a thicker or larger body part have on scattered radiation?
there will be greater scatter
list two factors that affect volume of tissue irradiated
thickness of the subject and size of radiation field
Manual technique charts are based on patient part measurements obtained using an x-ray caliper. These measurements are expressed as:
thickness, in cm
the mass density of the body part is referred to as:
tissue density
T/F a doubling in kVp would result in four times more xrays being emitted from the tube
true
T/F a patient with large abdomen would produce more scattered radiation than a patient with a small abdomen
true
T/F if the SID is reduced in half, the intensity or quantity of xrays will increase by four times
true
T/F technique charts are unique to each xray machine and facility
true
T/F the sharpness in the radiographic image is referred to as spatial resolution
true
T/F using optimum kVp to formulate exposure techniques results in minimal patient exosure and wide exposure latitude
true
the term used to describe a light image is:
underexposure
describe the term fog
unwanted exposure to image
name three strategies that can be used to reduce scatter radiation fog
use a grid for body parts over 10 cm, reduce field size, reduce kVp
the most effective method of reducing scattered radiation fog on a radiograph is to:
use a grid or bucky
breathing technique
use long exposure times to blur out unwanted information
which of the following will reduce scatter radiation?
using a smaller field size
which type of technique chart has a specific mAs value for each projection and uses changes in kVp to compensate for variances in patient or part size?
variable kVp
how does scatter radiation affect CR imaging plate?
very sensitive to scatter radiation and must be protected before and after
primary scatter consideration is the:
volume of tissue irradiated
state the four factors that directly affect the quantity of scatter radiation fog
volume of tissue, kVp, density of matter, field size
the brightness of the viewing monitor in digital imaging is adjust by the:
window level
what adjustment controls the density or brightness of the digital image on the viewing monitor and printed image?
window level
what adjustment controls the contrast of the digital image on the viewing monitor and printed image?
window width
the control limit for the collimator on the xray tube is that it must be maintained within a range of:
±2 of SID
the control limit for the collimator's light field and the actual radiation field must be within:
±2% of SID
