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Creating an image of diagnostic quality requires making the appropriate:
- Technical choices to create an image that has the visibility and sharpness of all the AOI
- Procedural skills to position the AOI per Merrill's atlas.

Critiquing an image of diagnostic quality encompasses the broadest and most complete analysis of an image. A critique of both the technical aspect (visibility & sharpness of all AOI) and procedural aspect (radiographic positioning of the AOI)
What factor do we assess first pertaining to density/IR exposure?Patient factors - thickness of body part & opacity of tissues - determines the different degrees of attenuation occurring per different tissue types. - pathology or trauma may affect attenuationDefine prime factors, and what are they?controlled by the radiographer: mA, kVp, time, distanceWhat are the four steps for film processing?1) developing 2) fixing 3) washing 4) dryingList the CF and IF for Density/IR exposure. 1st photographic property for visibilityCF: mAs IF: Patient factors - kVp 15% Rule - SID / inverse square law - anode heel effect - processor - orthopedic casting materialsCF: mAs influence on density/ IR exposurechoose mAs to give proper density/ IR exposure - directly proportional to density/ IR exposure ↓↑ mA = ↓↑density IR exposure ↓↑ exposure time = ↓↑ densityIR exposureIF: Patient factors influence on density/ IR exposurethickness of body part & opacity of tissues determine different degrees of attenuation. pathology/ trauma affect attenuation. emphysema and osteoporosis -- decrease mAsIF: kVp influence on density/ IR exposurepenetrability of beam affects how much remnant radiation exposes the IR. - choose kVp appropriate to penetrate AOI & produce a desired range of contrast 15% Rule ↓ mAs 50% if you ↑ kVp 15% to maintain density/ IR exp. Background info ⬆ kVp 15% to double density/ IR exposure most accurate w/ mid kVp range 66-80IF: SID influence on density/ IR exposureInverse square law shows that distance has an affect on the quantity of exposure reaching the IR. use Density Maintenance Formula in order to account for distance changes mAs 2 = mAs 1 x D2 ^2 / D1 ^2IF: Anode Heel Effect influence on density/ IR exposureDue to angulation of the anode, the cathode side of the tube produces more x-ray photons than the anode side. The drop off of the beam intensity is under the anode side, we want the thinner part of AOI under the anode side... Requirements: - only affects the outer margin of the AOI, meaning there must be a big difference in subject density. ex: femur, thoracic spine - AOI must be at least 12 inches longIF: Processing influence on density/ IR exposureneeds to be checked first bcus radiographer can do everything correctly and if processor isn't working, density can be affected. ⬆ time, temp & replenishing rate= ⬆ density/ IR exposure ⬇time, temp & replenishing rate= ⬇ density/ IR exposureIF: Orthopedic Casting Materials influence on density/ IR exposureWet plaster stays wet for 48 hours - measure other arm / leg to get thickness of AOI ⬆ kVp 10% & double mAs Dry plaster double mAs only , same kVp Fiberglass - use same technique as if there was no castName the four properties that must be assessed in order to determine if a radiograph is of radiograph quality:Proper density/IR exposure Sufficient contrast Maximum detail Minimal distortionOf all the major properties used to access radiographic quality, density/ IR exposure is a major property and probably the most important give reason for your answers:Without proper density/IR exposure you will not be able to access sufficient contrast, or have maximum detail or minimal distortion.The prime factors that relate to the quality of an x-ray exposure are:kVpDescribe how the inverse square law and the Exposure Maintenance Formula differ from one anotherThe inverse square law explains as the distance increases, the intensity of the beam emitted decreases. While, the exposure maintenance formula uses this concept (inverse square law) to adjust mAs so you maintain proper density/IR exposure no matter what change of SID is used.List the following tissue densities, muscle, air, fat, bone-in order of least tissue dense to most tissue dense. And which would have the least density/IR exposure to the most.-Air, Most density/IR exposure -fat -muscle -bone; Least density/IR exposureWhy are Quality assurance and control important?Quality assurance and control are important because it identifies the problem, monitors it, and identifies ways to fix the problem. Quality control is an aspect of quality assurance that monitors the problem. They are both important because we need the x-ray generator to be functioning properly for patient safety as well as the production of images for diagnostic qualityWhat are quality control tests?the aspect of quality assurance that monitors technical equipment to maintain quality standards. -helps stabilize equipment components of the radiographic imaging chainList the controlling factors for radiographic density/IR exposure. Secondly, list the influencing factors we have discussed in class.CF - mAs IF-Patient factors/part thickness, kVp, SID, Processor, Anode heel effect, casting materialsWhat is the 15% rule, and how will this guideline assist the radiographer to produce a radiographic image?The 15% rule is when mAs can be decreased by 50% & kVp is increased by 15%. This rule works best in the mid kVp range (66-80kVp) This helps to produce a diagnostic image because by increasing the kVp by 15% you can shorten the exposure time or mAs by halfIf the body part is 17" long and the thickness of the part varies considerably from one end to the other, what might you do to try to produce a radiographic image of uniform density/IR exposure?You can take advantage of the anode heel effect by placing the thinner part thickness of the AOI on the Anode side of the tube and thicker portion of the AOI under the Cathode side. The anode side has a drop off of intensity of the x-ray beam due to angulation of he anode.Ankle series done on a pt. 2mAs 62kVp 40"SID, the same pt returns 1 HOUR later with a PLASTER cast. New technique?Double mAs = 4 mAs, increased kVp by 10% =68.2 kVp and 40" SID remains the sameList the controlling factors and influencing factors for radiographic contrast.CF-kVp IF-subject contrast, film contrast, radiographic fogwhat is sufficient contrastwhen there are enough differences in adjacent radiographic densities to differentiate the structures of the AOI.What are four quality assurance/control tests for the x-ray machine? p.473 ?1. kVp accuracy 2. timer accuracy 3. mA linearity 4. exposure reproducibilityWhy is it important to have sufficient contrast in a Diagnostic Image?to have differences in radiographic densities so you are able to see differences in densities of adjacent tissues in the AOI.What terminology is used to describe a radiographic image that demonstrates short changes within densities.?short scale contrast / high contrast / increased contrast There are fewer, but more distinctive changes between steps of contrast. Useful in pointing out the big differences in an image. Associated with a decrease in kVp.Low contrast is also known as:Long scale or decreased contrast There are more overall steps with less distinctive changes between them (more shades of grey). Useful in showing a lot of AOI detail. Associated with an increase in kVp.CA state law accuracy collimationA collimator device may not be used if there is an error + or - 2% of the SID, in any direction that the x-ray beam is collimated.Define the term subject contrast and how does it affect radiographic contrastSubject contrast is the range of tissue densities in the part of interest and how the part of interest influences the differences in radiographic densities. kVp is a prime factor that controls subject contrast. kVp affects the radiographic contrast because it gives us the photon energy required to give us a scale of contrast. kVp will allow us to have high contrast with bigger differences in adjacent densities. Or kVp can give us the photon energy to produce low contrast, with little differences to adjacent densities.Use the 15% rule to come up with a new technique 100 mA .01 sec 70 kVp100 mA .005 sec 80.5 kVpUse the 15% rule to come up with a new technique 200 mA .025 sec 66 kVp200 mA .0125 sec 75.9 kVpWhy did we keep the same mA for the 15% rule?The reciprocity law. For the 15% rule to be considered we have had to "max out" our mA. In order to half our mAs we will shorten the exposure time. ?Radiographic fog is an influencing factor of radiographic contrast. Does the presence of Radiographic fog increase or decrease the diagnostic quality of the image. Give reasons.The presence of radiographic fog decreases the diagnostic quality because it is a veil of unwanted density on the image. With the presence of radiographic fog the ability to access contrast will decrease. This will decrease the overall visibility of all the anatomy of interest therefore present an image with decreased diagnostic quality.Define the term grid ratioGrid ratio is the ratio of the height of the lead strips inside the grid to the distance between the lead strips.2 specific criteria for as to when a radiographer should use a gridWhen part thickness is 10-12cm or more When 70kvp or more must be usedEasy Method for Grid conversionGrid Ratio GCF non-grid 1 5:1 , 6:1 2 8:1 3 10:1 4 12:1 5 16:1 6A diagnostic Lateral lumbar spine image is produced using 12:1 grid at 80mAs 86 kVp 40" SID Second image is requested using 8:1 grid. Utilize the easy methodmAs1/mAs2=GCR1/Gcf2 80mAs/x=5/3 (80mAs)(3)=5x 240mAs=5x 48mAs2=xName the factors that affect radiographic detailMotion- voluntary and involuntary Materials- R/S film speed Geometric factors- focal spot size, SID, OIDIn order to increase maximum detail on your radiograph what specific choices would you make to eliminate factors that affect radiographic details?Minimize motion as much as possible Shorten the exposure time using reciprocity law Use the 15% rule Decrease OID as much as possible Increase SID Use a small focal spot Use a faster film speed/intensifying screenName four methods which can be used to reduce the possibility of involuntary motion. Give reasons.- To reduce involuntary motion, you can decrease exposure time. To decrease the exposure time, you can use the reciprocity law to maintain mAs by doubling mA, and decreasing the exposure time in half. - You can use the 15% rule. If you increase your kVp by 15%, you can decrease your mAs 50% by reducing the exposure time by half - Decrease SID. Use the exposure maintenance formula. By decreasing SID you will decrease mAs to maintain density/IR exposure. When you decrease mAs you can decrease the exposure time - Use A faster film speed, and decrease the exposure time.Digital imaging systems use a more specific term for spatial resolution. Spatial resolution is determined by ______________________ Spatial resolution is measured in _____________________determined by Matrix size and the number of pixels measured in lines per centimeterDescribe what the relationship should be between the central ray, anatomical part, image receptor- in order to minimize shape distortion.body part parallel to the IR CR perpendicular to the body part CR perpendicular to IRHow does SID and OID affect size distortion?increase SID to minimize size distortion decrease OID to minimize size distortionList the CF and IF for contrast 2nd photographic property for visibilityCF: kVp IF: - subject contrast - film contrast - radiographic fogCF: kVp influence on contrastneed to choose kVp appropriate to penetrate the part of interest & produce the scale of contrast you desire in order to increase visibility of the AOI. kVp is needed to penetrate the body part & create contrast for visibilityIF: subject contrast influence on contrastSubject contrast is the range of tissue densities in the part of interest and how the part of interest influences the differences in radiographic densities.IF: film contrast influence on contrast- range of densities the film is capable of recording. D log E curve shows that the curve is closer to the Y-axis for faster filmsIF: radiographic fog influence on contrast- a veil of unwanted density -visibility reduced and affects ability to assess contrast. 4 Sources of radiographic fog: 1. Scatter Radiation (only one to consider for non-film IR) 2. Light 3. Chemicals 4. Film AgeList the IF for detail (maximum) 1st geometric property for sharpnessmotion materials geometric factorsIF: motion influence on detail#1 cause of loss of detail voluntary motion - direct control of the patient reduced by: 1) communication & clear instructions 2) immobilization devices if necessary involuntary motion- not in direct control of pt,.. peristalsis, heartbeat... reduced by: - decrease exposure time using reciprocity law - 15% rule when maxed out of reciprocity law, -decrease mAs 50% by decreasing exposure time only, when increase kVp 15% - decrease SID, decrease mAs by decreasing exposure time. - use faster R/S film/screen combo and decrease exp. timeIF: materials influence on detailfilm/ screen cominations intensifying screens make film respond faster so pt. dose is decreased. increased speed = decreased detail speed of screen determined by size, thickness, concentration of phosphor layer. ( increase these, speed increases) increase film speed = decreased detail speed of film increased by size and concentration of silver halide crystals, and thickness of the emulsionIF: geometric factors influence on detailfocal spot size - small focal spot size gives better detail OID - smaller OID give better detail, why we try to position the body part closer to the IR SID - increasing SID gives better detailList the IF for distortion (minimum) 2nd geometric property for sharpnesssize distortion (magnification) shape distortionsize distortionaka magnification OID minimized to reduce size distortion SID maximized to reduce size distortionshape distortion-results in foreshortening & elongation minimize by having: CR perpendicular to AOI CR perpendicular to IR AOI perpendicular to IR5 Rules of Thumb for kVp selection Rule 1 When patient thickness varies within Low range 55-65 kVpfor every increase of 1cm in thickness, increase by 2 kVp5 Rules of Thumb for kVp selection Rule 2 Under penetrated radiograph, can't see bony trabeculae and you need to repeatlow part of the low range 55- 59 kVp - increase 2 kVp to see visible change high part of the low range 60- 65 kVp - increase 4 kVp to see visible change5 Rules of Thumb for kVp selection Rule 3 15% ruleapplies to the mid-range 66- 80 kVp increase kVp 15% & decrease mAs 50% in order to maintain proper density purpose is to decrease pt dose & create a longer scale of contrast while maintaining proper density/IR exp.5 Rules of Thumb for kVp selection Rule 4 Mid range rule 66- 80 kVp6 kVp change is the minimum requirement to see a visible change5 Rules of Thumb for kVp selection Rule 5 High range rule 81- 120 (140) kVp10 kVp change is the minimum requirement to see a visible changelong scale contrast / low contrast / decreased contrast how kVp influences subject contrastresults from: ⬆kVp-⬇wavelength-⬆penetration-⬇attenuation-⬆remnant rad-⬆density/IR exposure - more shades of grey - useful in showing a lot of detail in AOIshort scale contrast / high contrast / increased contrast how kVp influences subject contrastresults from: ⬇kVp-⬆wavelength-⬇penetration-⬆attenuation-⬇remnant rad-⬇density/IR exposure - fewer, but more distinctive changes between steps of contrast.. - useful in pointing out big differenceskVp rangeslow = 55-65 mid = 66-80 high = 81- 120 / 140kVp upper ribslow- mid 60 - 70 grid when above 70kVp Hip -AP66 -76 mid range grid when above 70kVp abdomen pelvis lower ribs spine - AP lumbar spine - cervical spine - thoracic70 - 80 mid range gridkVp skull / facial bones/ sinus76- 86 mid- high range gridkVp spine- oblique lumbar70 - 80' mid- high range gridkVp hip - lateral76- 86 mid - high gridkVp spine - lateral lumbar80- 90 mid - high range gridkVp chest120 - 140 high range gridkVp fingers / toes52- 54 low rangekVp foot/ hand56- 62 low rangekVp ankle/ wrist58- 64 low rangekVp elbow/ forearm tib/ fib62- 68 low- mid rangekVp knee shoulder64- 74 low- mid range grid when above 70kVp femur70-76 mid range grid8 Pathological conditions that causes an Increase in Attenuation - increase kVp 5- 15%abscess edema CHF (congestive heart failure) empyema pleural effusions pneumonia ascites paget's disease7 Pathological conditions that cause a Decrease in Attenuation - decrease mAs 25 - 50%atrophy emphysema pneumothorax bowel obstruction carcinoma degenerative arthritis osteoporosisabscess multiple sitesan encapsulated infection increases tissue thickness & may alter composition particularly in the lungsedema multiple sitesswelling causes an increase in tissue thickness & may alter composition if it occurs in the lungsCHF - congestive heart failure chestwhen heart is failing, cardiac output is diminished. this results in backward failure or increased venous congestion in the lungs lung tissue density is increased & heart becomes enlargedempyema chestpus in the thoracic cavity causes an increase in tissue densitypleural effusions - hemothorax & hydrothorax in chestwhen pleural cavity fills with either blood or serous fluid, it displaces normal lung tissue. this results in an increase tissue density within the thoracic cavitypneumonia chestinflammation of the lung tissues cause fluid to fill in the alveolar spaces fluid has much greater tissue density that the air normally presentascites abdomenfluid accumulation within the peritoneal cavity causes an increase in tissue thickness. the free fluid has a unique "ground glass" appearance radiographicallyPaget's disease extremities & skullan increase occurs in bone cell activity, which leads to new bone growth. the result is increased bone thickness, with the pelvis, spine and skull most often affected.atrophy multiple siteswasting away of body tissue with diminished cell proliferation, resulting in reduced thickness of a specific part or the entire bodyemphysema chestoverdistension of the lung tissues by air will result in a decrease in lung tissue densitypneumothorax chestfree air in the pleural cavity displaces normal lung tissue and results in decreased density within the thoracic cavitybowel obstruction abdomenresults in abnormal accumulation of air & fluid in the bowel if a large amount of air is trapped in the bowel, the overall density of tissues is decreasedcarcinoma extremities & skullmalignancies in bone can cause a osteolytic process, resulting in decreased thickness and composition of the partdegenerative arthritis extremities & skullinflammation of the joints in a destruction of adjoining bone tissue, which decreases the composition of the partosteoporosis extremities & skulla defect in bone production due to failure of osteoblasts to lay down bone matrix results in decreased composition of the affected bonerepeat ratethe # of repeat exposures out of the total amount taken. -evaluated daily the processor is capable of counting the amount of films it develops. repeats are put in a separate pile for evaluation - the images in the repeat pile are all those that are not considered diagnosticreject analysesstudies the rejected films in an effort to determine why they were unacceptable. -for quality assurance they try to determine why they were discarded so they an develop a strategy to correct the mistakes. -they analyze, find the problem, and develop a way to fix it. the films are put into different piles based on why they were repeated .... technical vs. procedural reasons -majority of errors are underexposed filmswhat percentage of "repeats" are due to exposure error?eastman says 52% winkler says 68% technologist is the major source of the problem because more than half are exposure errors due to not assessing patient factors correctlywhat percentage of "repeats" are considered to have a perfect rating?a repeat ratio of 4% or less is considered a perfect rating. this means that 96% needs to be optimalmany factors may contribute to an increase in a department's repeat rate, but eastman sees one culprit. describe this culpritthe culprit is the failure to formulate x-ray technique charts or failure to use them accuratelywhat other aspects of an overall quality assurance program are discussed in this article?all x-ray equipment should be properly calibrated. tests to monitor calibration and processors must be checked regularly. sensitometry is necessary to ensure the processor is operating with acceptable limits. sensitometric strips are used to check the processorwhat is the first consideration to ensure successful use of technique charts?proper education is needed on how to use these charts. design specific charts for specific machines and rooms. -they should be posted and checked for accuracythere are two types of technique chart designs discussed in the article. what are the two types & what are some disadvantages associated with them?Fixed kVp - same kVp is used for all body parts of a particular exam regardless of size. - the variable factors are mA & exposure time - the drawback is that there is some trouble making incremental changes because many generators lack a sufficient # of timer stations. this leads to equipment calibration problems... for example, a darker image can occur at 400mA machine compared to 100mA machine Variable kVp - mAs is fixed & kVp is varied based on the thickness of body part. - the drawback is that changing the kVp alters the range, which affects the scale of contrast. the resulting range might be too wide or too narrow & the resulting contrast undesirablewhat reasons do radiographers give for not using technique charts? what solutions might you suggest, so as to encourage radiographers to utilize technique charts?reasons: - unavailability of charts - absences of equipment for calibration - not measuring body part w/ calipers - perception that charts are inaccurate / not up to date - no time to measure - lack of understanding the posted technique chart - no one assigned the job of technique chart administration - poor quality control creates variables within the exposure processing system so charts are innacurate solutions: - motivational speeches - encourage ethical & professional responsibility - legal & safety concerns - proper regular training, - incentives - reprimands at performance reviews - continuing educationmore on reject analysis-done to help reduce pt dose by limiting repeats rejects are separated into 2 piles: technical & procedural errors -- technical incorporates rad. quality technical is separated into 2 other piles: photographic properties (visibility- density&contrast) & geometric properties (sharpness- detail & distortion) biggest problem is density & underexposure analyze piles by looking at the CF's & IF's Many times the error is associated with incorrectly determining the patient factors. this can occur due to: 1) unknown pathologies , ...might be initial x-ray taken and the diagnosis was previously unknown. 2) not using the proper technique chartStep 1 Ask the broad questions1) Name of the radiographic exam 2) Name of the radiographic projectionStep 2 Narrow the search to the question:1) Narrowing technical aspect: -Photographic properties (visibility; density/IR exposure and contrast of AOI) -Geometric properties (sharpness; detail and distortion) 2) Narrow procedural aspect: -Correct positioning of the AOIStep 3 Evaluation process to critique the technical and procedural aspects of an image (which aspect(s) contributed to the resulting image and how so?)1) Technical Aspects: ~Primary Source: specific question that must be addressed after the image has been created ( is this an image of Dx. quality?) ~Secondary Source: framework for creating radiographic quality, in other words, how did you do it? 2) Procedural Aspect: ~Use "evaluation criteria" from Merrill's AtlasStep 4 Critique ConclusionWhich category does your image belong? ~ optimal diagnostic quality ~ acceptable diagnostic quality ~ unacceptable diagnostic qualityWhat is a Controlling Factor?The main determinant of a certain factor that contributes to radiographic quality.What are Influencing Factors?Other factors that contribute to radiographic quality as well.Keeping attenuation in mind, what is actually responsible for film exposure?Remnant radiation; That is, radiation which has not been attenuated by patient.The 25% - 30% rule of thumb refers to?The amount of increase or decrease in mAs needed to see a a visible change in density.What are the two steps of the archiving process?washing & dryingOur goal is to always produce images of Dx. quality, but sub-optimal images are often accepted for diagnosis. True or False?trueWhen is an image determined to be outside acceptance limits?When all relevant structures required to make diagnoses cannot be clearly seen.Why is Radiographic Contrast considered the second photographic property for visibility?we need to have adequate density before we can assess the contrast of a radiographic image.When is contrast appreciated on an image?When the AOI (1) consists of more than one tissue density, (2) varies in thickness, (3) or a combination of both.3 steps in evaluation of Contrast:1) Determine if proper density/IR exposure is present 2) Are there adequate differences in radiographic densities representing different tissue densities. 3) Are all AOI tissue densities visible on the radiograph.What is Radiographic Contrast?The result of all the different attenuations caused by the tissue densities of AOI which allows us to observe differences between adjacent densities on image.Adequate radiographic contrast means?Ability to see differences between densities of adjacent anatomical structures in AOI.We have Sufficient contrast when we've...Created enough differences in the adjacent radiographic densities to differentiate the anatomical structures of the AOI.3 Ranges of kVp used in Diagnostic Radiology:Low Range: 55 - 65 (extremities) Mid Range: 66 - 80 High Range: 81 - 120+ (140)kV adjustments for the various ranges:Low range (55 - 65) = 2 Mid range (66 - 80) = 6 High range (81 - 120+) = 10How do we choose which kVP setting to use?Choose the kVp that's appropriate to penetrate the part of interest and produce the scale of contrast you desire to increase visibility of the AOI.Why is contrast more subjective than density?Because there's no device for measuring it (e.g., densitometer)How is the speed of the film represented?The closer the DlogE curve is to the Y-axis, the faster the film. & patient dose is less.Relate speed and patient dose:⬆ film speed = ⬇ patient dose = ⬇detail of AOI ⬇ film speed =⬆ patient dose =⬆ detail of AOIHow is the latitude of the film represented?The steeper the DlogE curve, the smaller the range of densities that can be produced and the narrower the latitude. A more gradual curve produces a larger range of densities and therefore a wider latitude.Define latitude:The ability to accommodate a range of techniques while producing acceptable radiographs.What is the biggest source of radiographic fog and where is it created?scatter radiation, created in the patientWhat are the two main causes of scatter radiation?1. thick body part 2. high kVp (at a certain point, about 110+, the higher kVp will actually reduce scatter rad.)List the two methods of reducing radiographic fog/ scatter radiation1. Beam Restriction Devices 2. GridsReasons for using BRD's (beam restricting devices):1. Reduces patient dose by limiting the area of the primary beam that reaches patient. -More collimation=less tissue exposure & less dose -Less tissue=less potential to create scatter and cause fog 2. Scatter radiation production is reduced b/c the primary beam is reduced.Examples of BRD's:- Apertures/Diaphragms - Cylinder Cones - CollimatorsCylinder Cone:These produce less penumbra as they sit farther from the focal spot and are useful in focusing in on a specific part. Device reduces scatter and therefore density goes down so we must compensate by increasing mAs: -Using in collapsed position = increase mAs by 40% -Using in extended position = increase mAs by 60%What is the purpose of using a grid?To reduce the effects of scatter radiation by absorbing it before it reaches the IR. *note: It does not reduce scatter as scatter is created inside the patient and has already occurred.When is it appropriate to use a grid?-part thickness is 10 ⬆cm or 12 ⬆cm -a kVp of 70⬆Why is it important that the CR be centered to the grid?to avoid grid cut offWhat must we consider when selecting a specific grid ratio?Higher GR's require more mAs and thus a higher patient dose. Also centering CR to grid can be difficult.Why are lower GR's more ideal for portable exams or exams requiring a greater SID?They offer more wiggle room when centering the CR to the grid. This is important b/c we can no longer rely on the detent setting.Can we use the same exposure values as used with the table/bucky for non table/bucky exams that don't require a grid?No; The bucky has a much higher grid ratio because we can rely on detent for accurate centering of our CR. Thus our non-grid exam will need less mAs.Another characteristic of a grid is Grid Type. Explain...2 types- -Linear (strips parallel): Can use at any SID and w/ beam angulation. Scatter absorption is less efficient -Focus (strips angled): Specific to certain focal ranges and SID's. More efficient at absorbing scatter, but is more expensive.Another characteristic of a grid is the Lines per inch/cm (AKA Strip Density, Grid Density, or Grid Frequency). Explain the influence on scatter absorption efficiency...The higher the lines/inch or strip density, the more efficient the grid will be at absorbing scatter rad.Explain the Air Gap Technique...Increased OID creates an air gap which will reduce the amount of scatter rad. that reaches IR as it's absorbed in air. An example of this is the Lat. C-spine.