[Radiography] Technique - Exposure Factors

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Radiography Technique Exposure Factors KVP Energy of x rays higherpenetrability it moves through tissue The energy determines the QUALITY of x .
ray produced 1 increase in KVP electrons gain high2 higher the energy of electrons greaterquality of x rays3 greater quality greater penetrability.
KVP QUANTITY increased kVp more x rays produced MA tube current number of electronsand quantity of x rays produced MA does not affect quality of x rays.
KVP quality quantityMA quantityTime quantity Purpose of using Grids1 Increases contrast.
2 Reduces density3 Must use more MAS with a grid The choice to use a grid depends on 1 KVP used2 thickness of part.
Parts 10 cm or larger with a KVP higherthan 60 produce enough scatter tonecessitate the use of a grid Air Gap Technique This is like a grid .
Less scatter on film but less detail also You can increase SID to help with detail The greater the gap the less scatterreaches film 10 inch air gap 15 1 grid small body part.
Need proper balance of density and contrastDensity overall blacknessPrimary controlling factor for density is MASTo make a visible change in density Requires a minimum 30 change in MAS or.
KVP affects density alters amount andpenetrating ability of x ray beam so increasingpenetration of x ray beam results in moreradiation results into more density on x ray KVP quantity of radiation density.
Changes in KVp is not equal throughout theranges of KV low med high A greater change is required at a higher KVp greater than 90 compared with a lower KVP less than 70 .
KVP affects density and other aspects so KVPis not primary factor for changes in density example 50 kVp increase 10 kVp very darkgreater change90 kVp increase 10 kVp slightly darker smaller.
To maintain density with KVp use the 15 change KVP by 15 and you will have thesame effect on density as doubling MASexample KVP 82 change to 94 15 MAS 10 change to 20 double .
Patient thicknessIn general for every 4cm of thickness of patient you need to adjust MAS by afactor of 2thin pt 18 cm use 40 MAS.
thicker pt 22 cm use 80 MAS to maintain40 X 2 80 for the additional 4cm of thickness KVP penetrating power is the controlling factorfor contrast High KV more densities but fewer differences.
low contrastLow KV fewer densities but greater differences high contrastKV also affects amount of scatterHigh KV increase in scatter only adds.
unwanted density fog on film So increasingfog always decreases contrast Low KV decreases scatter reduces fog so increases contrast Influencing Factors of Contrast.
The most influencing factor for contrast iscontrolling the amount of scatter less scatter fog increases contrast1 Grids absorption of scatter that exits patient2 Collimation wider field more scatter less.
smaller field reduces scatter greater contrast3 Air Gap distance between patient and film this prevents scatter from getting to film So when amount of scatter is reduced higher 4 Body Part composition thickness .
compactness These differences make the range of densities contrast Tissues with higher atomic number absorb moreradiation bone contrast.
Tissues with lower atomic number absorb lessradiation airWide range of tissue composition high contrastsimilar types of tissue low contrastThicker tissue more scatter less contrast.
USING A HIGHER KV FOR A THICKERPART ONLY ADDS TO THE INCREASEIN SCATTER This degrades the quality of film Thiscreates fog which decreases the contrast .
Skinny person good contrastHeavy person fog one density not a lotof contrast on film Exposure Modifications Pediatric chest use fast exposure times.
to stop motion Minimum KVP to Penetrate Chest inPremature 50 KVInfant 55 KVChild 60 KV.
Pediatric patients skull younger than 6years old use 15 less KVP Adapting exposure factors for childrenbased on exposure factors for adults excluding chest and skull exams.
Age Exposure factor adaptation0 5 years 25 of MAS that is indicatedfor adults6 12 50 of MAS that is indicated for Casts can be made of fiberglass or.
Fiberglass generally requires no change inexposure factors Plaster require an increase in exposure this depends on whether the cast is stillwet or whether it is dry .
Dry cast increase of 2 times the MASWet cast increase of 3 times the MAS Pathology If changes are needed tocompensate for diseases it is generally best toadjust the KVP because this affects the.
penetrating ability minimun of 15 rule Additive conditions may need to add KVPAbdomen aortic aneurysm ascites cirrhosis hypertrophy of some organs splenomegaly Chest atelectasis congestive heart failure .
malignancy pleural effusion pneumoniaSkeleton hydrocephalus metastases osteochondeoma Paget s disease late stage Etc abscess edema sclerosis Destructive conditions may need to.
decrease KVPAbdomen bowel obstruction free airChest emphysema pneumothoraxSkeleton gout metastases multiplemyeloma Paget s disease early stage .
osteoporosisEtc atrophy emaciation malnutrition Soft Tissue Objects in soft tissue if less density isrequired MAS should be decreased.
Important to know whether contrast shouldbe increased or decreasede g airway for soft tissue neck contrastshould be increasedForeign body decrease contrast to.
visualize both bone and soft tissueSoft tissues that require a decrease indensity should use a decreased MASSoft tissues that require a higher or lowercontrast should use a change in KVP.
Variables and their effect on the photographicproperties of the x ray image Radiographic variables Density ContrastIncrease MAS increase no changeDecrease MAS decrease no change.
increase KVP increase decreasedecrease KVP decrease increaseincrease SID decrease no changedecrease SID increase no changeincrease OID decrease increase.
Radiographic variables Density Contrastdecrease OID increase decreaseincrease Grid ratio decrease increasedecrease grid ratio increase decreaseincrease film screen increase no change.
decrease film screen decrease no change Radiographic variables Density Contrastincrease collimation decrease increasedecrease collimation increase decreaseincrease focal spot no change no change.
decrease focal spot no change no changeincrease central ray decrease no change Using 100 mA small focal spot station forextremity has better detail thanUsing the same mAs and same kV with higher.
ma stationScatter radiation is detrimental to the quality offilm and adds unwanted density to the filmwithout adding any patient information Scatter decreases contrast and using grids.
increase the contrast Beam restricting devices and grids are used tolimit scatter radiation Two major factors that affect the amount ofscatter radiation KVP and the volume of tissue.
irradiated opening collimation and larger1 Using higher KVP produce more scatter ascompared with a lower KVP 2 Larger field size and the thicker the patientthe greater amount of scatter produced from the.
You should use appropriate KVP and limit x raybeam to limit scatter Beam restriction serves two purposes this increases contrast also1 limits patients exposure.
2 reduces scatterBecause collimation decreases x ray field less scatter is produced within thepatient so less scatter and contrastincreases .
Exposure factors may need to be changed whenincreasing collimation less density So ascollimation increases smaller area densitydecreases as collimation decreases largerarea density increases .
When collimating a lot you must increaseexposure to compensate for loss of density TheKVP should not be increased because it resultsin decreased contrast To change density only MAS should be changed .
It is recommended with a lot of collimationrequires an increase in as much as 30 to 50 of the MAS to compensate for the loss of density Increases Factor EffectCollimation Patient dose decreases.
scatter decreasescontrast increasesdensity decreasesField Size Patient dose increasesscatter increases.
contrast decreasesdensity increases Purpose of using grids 1 increases contrast2 reduces density.
3 must use more MAS with a gridThe choice to use a grid depends on 1 KVP used2 thickness of partImprove contrast using a grid requires additional.
MAS resulting in a higher patient dose Grids are typically used only when the patientpart is 10 cm adult knee size or greater andwhen using more than 60 KVP Air gap technique .
This is like using a grid Less scatter onfilm but also less detail You can increaseSID to help with the detail The greater thegap the less scatter Using an increases OID is necessary for.
the air gap tech However this decreasesquality To decrease unsharpness andincrease detail you must increase SID Accurate measurement of part thickness iscritical to the effective use of exposure.
technique charts Two types of technique charts 1 Variable KVP fixed MAS2 Fixed KVP variable MAS1 Variable KVP fixed MAS Best with small.
extremities KVP increases as part size increases BaselineKVP is increased by 2 for every 1cm increase inpart thickness and MAS stays the same Accurate measurement of part thickness is critical.
to use this type of chart In general changing the KVP for variations in partthickness is ineffective throughout the entire rangeof x rays This kind of chart is most effective withsmall extremities such as hands and feet At low.
KVP levels small changes in KVP may be moreeffective than changing the MAS Contrast will vary and these types of charts tend tobe less accurate for part size extremes Adequatepenetration of the part is not assured and the x ray.
produced with the use of this type of chart tend tohave higher contrast 2 Fixed KVP variable MASThis uses an Optimal KVP which is theKVP value that is high enough to ensure.
penetration of the part but not too high todiminish x ray contrast Then the MAS isvaried to the part thickness In general for every 4 5 cm change in partthickness the MAS should be adjusted by.
a factor of 2 double MAS Accurate measurement of part thickness isimportant but less critical compared withvariable KVP An advantage of using this chart is that.
patient groups can be formed around 4 5cm changes You can use patientthickness groups It is easierto use more consistency on films standardization of contrast .
15 rule 100 KV up to 115 KV doubling MASTo make a visible change in density itrequires at least 30 change in MAS orChanges in KV differ at high and low.
levels greater change is needed with 90KV compared to 50 KV90 KV and increase 10 KVP slightly50 KV and increase 10 KVP very dark To maintain density with KVP use 15 .
so 15 increase in KVP doubling MASmaintains densityKVP 82 change to 94 15 is same asMAS 10 change to 20 double For each additional 4cm thickness you.
need to double MAS to maintain density 65 74 7575 86 25The choice to use a grid depends on: 1.) KVP used 2.) thickness of part Parts 10 cm or larger with a KVP higher than 60 produce enough scatter to necessitate the use of a grid. Air Gap Technique: This is like a grid. Less scatter on film but less detail also. You can increase SID to help with detail. The greater the gap the less scatter reaches ...

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