[Radiography] Technique - Exposure Factors. KVP = Energy of x-rays = higher penetrability, it moves through tissue. The energy determines the QUALITY.

[Radiography] Technique - [Radiography] Technique - Exposure FactorsExposure Factors

KVP = Energy of x-rays = higher KVP = Energy of x-rays = higher penetrability, it moves through tissue.penetrability, it moves through tissue.

The energy determines the QUALITY of x-The energy determines the QUALITY of x-ray produced.ray produced.1. increase in KVP = electrons gain high 1. increase in KVP = electrons gain high energyenergy2. higher the energy of electrons = greater 2. higher the energy of electrons = greater quality of x-raysquality of x-rays3. greater quality = greater penetrability 3. greater quality = greater penetrability KVP = QUANTITY = increased kVp = KVP = QUANTITY = increased kVp = more x-rays produced. more x-rays produced.

MA = tube current = number of electrons MA = tube current = number of electrons and quantity of x-rays produced.and quantity of x-rays produced.MA does not affect quality of x-rays MA does not affect quality of x-rays produced.produced.

KVP = quality & quantityKVP = quality & quantityMA = quantityMA = quantityTime = quantity Time = quantity

Purpose of using GridsPurpose of using Grids1.) Increases contrast1.) Increases contrast2.) Reduces density2.) Reduces density3.) Must use more MAS with a grid.3.) Must use more MAS with a grid.

The choice to use a grid depends on:The choice to use a grid depends on:1.) KVP used1.) KVP used2.) thickness of part2.) thickness of partParts 10 cm or larger with a KVP higher Parts 10 cm or larger with a KVP higher than 60 produce enough scatter to than 60 produce enough scatter to necessitate the use of a grid.necessitate the use of a grid.

Air Gap TechniqueAir Gap Technique::This is like a grid. This is like a grid.

Less scatter on film but less detail also. Less scatter on film but less detail also. You can increase SID to help with detail. You can increase SID to help with detail.

The greater the gap the less scatter The greater the gap the less scatter reaches film.reaches film.

10 inch air gap = 15:1 grid (small body 10 inch air gap = 15:1 grid (small body part 10cm) part 10cm)

Need proper balance of density and contrastNeed proper balance of density and contrastDensity = overall blacknessDensity = overall blackness

Primary controlling factor for density is MASPrimary controlling factor for density is MAS

TTo make a visible change in densityo make a visible change in density::Requires a minimum 30% change in MAS or Requires a minimum 30% change in MAS or doubledouble

KVP affects density - alters amount and KVP affects density - alters amount and penetrating ability of x-ray beam, so, increasing penetrating ability of x-ray beam, so, increasing penetration of x-ray beam results in more penetration of x-ray beam results in more radiation – results into more density on x-ray. radiation – results into more density on x-ray.

^ KVP = ^ quantity of radiation & ^ density^ KVP = ^ quantity of radiation & ^ density

Changes in KVp is not equal throughout the Changes in KVp is not equal throughout the ranges of KV (low med. & high)ranges of KV (low med. & high)

A greater change is required at a higher KVp A greater change is required at a higher KVp (greater than 90) compared with a lower KVP (greater than 90) compared with a lower KVP (less than 70)(less than 70)

KVP affects density and other aspects - so, KVP KVP affects density and other aspects - so, KVP is not primary factor for changes in density.is not primary factor for changes in density.example: 50 kVp increase 10 kVp very dark example: 50 kVp increase 10 kVp very dark greater changegreater change90 kVp increase 10 kVp slightly darker smaller 90 kVp increase 10 kVp slightly darker smaller change change

To maintain density with KVp use the 15% To maintain density with KVp use the 15% rule:rule:change KVP by 15% and you will have the change KVP by 15% and you will have the same effect on density as doubling MASsame effect on density as doubling MAS

example: KVP 82 change to 94 (15%)example: KVP 82 change to 94 (15%)same assame asMAS 10 change to 20 (double)MAS 10 change to 20 (double)

Patient thicknessPatient thicknessIn general, for every 4cm of thickness of patient, In general, for every 4cm of thickness of patient, you need to adjust MAS by ayou need to adjust MAS by afactor of 2factor of 2

example: example: thin pt. 18 cm use 40 MASthin pt. 18 cm use 40 MAS

thicker pt. 22 cm use 80 MAS to maintain thicker pt. 22 cm use 80 MAS to maintain densitydensity40 X 2 = 80 for the additional 4cm of thickness40 X 2 = 80 for the additional 4cm of thickness

KVP (penetrating power) is the controlling factor KVP (penetrating power) is the controlling factor for contrast.for contrast.

High KV = more densities but fewer differences High KV = more densities but fewer differences = low contrast= low contrastLow KV = fewer densities but greater differences Low KV = fewer densities but greater differences = high contrast= high contrastKV also affects amount of scatterKV also affects amount of scatterHigh KV = increase in scatter - only adds High KV = increase in scatter - only adds unwanted density (fog) on film. So, increasing unwanted density (fog) on film. So, increasing fog always decreases contrast.fog always decreases contrast.Low KV = decreases scatter - reduces fog, so, Low KV = decreases scatter - reduces fog, so, increases contrast. increases contrast.

Influencing Factors of ContrastInfluencing Factors of ContrastThe most influencing factor for contrast is The most influencing factor for contrast is controlling the amount of scatter.controlling the amount of scatter.less scatter (fog) = increases contrastless scatter (fog) = increases contrast

1.) Grids - absorption of scatter that exits patient1.) Grids - absorption of scatter that exits patient2.) Collimation - wider field = more scatter = less 2.) Collimation - wider field = more scatter = less contrastcontrastsmaller field = reduces scatter = greater contrastsmaller field = reduces scatter = greater contrast

3.) Air Gap - distance between patient and film - 3.) Air Gap - distance between patient and film - this prevents scatter from getting to film.this prevents scatter from getting to film.So, when amount of scatter is reduced = higher So, when amount of scatter is reduced = higher contrast contrast

4.) Body Part - composition, thickness, 4.) Body Part - composition, thickness, compactness. compactness.

These differences make the range of densities These differences make the range of densities (contrast)(contrast)Tissues with higher atomic number absorb more Tissues with higher atomic number absorb more radiation - bone, contrast radiation - bone, contrast Tissues with lower atomic number absorb less Tissues with lower atomic number absorb less radiation - airradiation - air

Wide range of tissue composition = high contrastWide range of tissue composition = high contrastsimilar types of tissue = low contrastsimilar types of tissue = low contrastThicker tissue = more scatter = less contrastThicker tissue = more scatter = less contrast

USING A HIGHER KV FOR A THICKER USING A HIGHER KV FOR A THICKER PART ONLY ADDS TO THE INCREASE PART ONLY ADDS TO THE INCREASE IN SCATTER.IN SCATTER.This degrades the quality of film. This This degrades the quality of film. This creates fog which decreases the contrast.creates fog which decreases the contrast.

Skinny person - good contrastSkinny person - good contrast

Heavy person - fog, one density, not a lot Heavy person - fog, one density, not a lot of contrast on film of contrast on film

Exposure ModificationsExposure Modifications::Pediatric chest = use fast exposure times Pediatric chest = use fast exposure times to stop motion.to stop motion.Minimum KVP to Penetrate Chest in Minimum KVP to Penetrate Chest in ChildrenChildrenPremature 50 KVPremature 50 KVInfant 55 KVInfant 55 KVChild 60 KVChild 60 KV

Pediatric patients skull - younger than 6 Pediatric patients skull - younger than 6 years old - use 15% less KVP years old - use 15% less KVP

Adapting exposure factors for children Adapting exposure factors for children based on exposure factors for adults, based on exposure factors for adults, excluding chest and skull examsexcluding chest and skull exams

Age Exposure factor adaptationAge Exposure factor adaptation0-5 years ; 25% of MAS that is indicated 0-5 years ; 25% of MAS that is indicated for adultsfor adults6-12 ; 50% of MAS that is indicated for 6-12 ; 50% of MAS that is indicated for adults adults

Casts can be made of fiberglass or Casts can be made of fiberglass or plaster. plaster.

Fiberglass generally requires no change in Fiberglass generally requires no change in exposure factors. exposure factors.

Plaster require an increase in exposure, Plaster require an increase in exposure, this depends on whether the cast is still this depends on whether the cast is still wet or whether it is dry.wet or whether it is dry.

Dry cast - increase of 2 times the MASDry cast - increase of 2 times the MASWet cast - increase of 3 times the MAS Wet cast - increase of 3 times the MAS

Pathology: If changes are needed to Pathology: If changes are needed to compensate for diseases it is (generally) best to compensate for diseases it is (generally) best to adjust the KVP because this affects the adjust the KVP because this affects the penetrating ability. (minimun of 15% rule)penetrating ability. (minimun of 15% rule)

Additive conditions - may need to add KVPAdditive conditions - may need to add KVPAbdomen - aortic aneurysm, ascites, cirrhosis, Abdomen - aortic aneurysm, ascites, cirrhosis, hypertrophy of some organs (splenomegaly)hypertrophy of some organs (splenomegaly)Chest - atelectasis, congestive heart failure, Chest - atelectasis, congestive heart failure, malignancy, pleural effusion, pneumoniamalignancy, pleural effusion, pneumoniaSkeleton - hydrocephalus, metastases, Skeleton - hydrocephalus, metastases, osteochondeoma, Paget's disease (late stage)osteochondeoma, Paget's disease (late stage)Etc. - abscess, edema, sclerosis Etc. - abscess, edema, sclerosis

Destructive conditions - may need to Destructive conditions - may need to decrease KVPdecrease KVPAbdomen - bowel obstruction, free airAbdomen - bowel obstruction, free airChest - emphysema, pneumothoraxChest - emphysema, pneumothoraxSkeleton - gout, metastases, multiple Skeleton - gout, metastases, multiple myeloma, Paget's disease (early stage) myeloma, Paget's disease (early stage) osteoporosisosteoporosisEtc. - atrophy, emaciation, malnutrition Etc. - atrophy, emaciation, malnutrition

Soft TissueSoft Tissue::Objects in soft tissue: if less density is Objects in soft tissue: if less density is required - MAS should be decreasedrequired - MAS should be decreasedImportant to know whether contrast should Important to know whether contrast should be increased or decreasedbe increased or decreasede.g. airway for soft tissue neck - contrast e.g. airway for soft tissue neck - contrast should be increasedshould be increasedForeign body - decrease contrast to Foreign body - decrease contrast to visualize both bone and soft tissuevisualize both bone and soft tissueSoft tissues that require a decrease in Soft tissues that require a decrease in density should use a decreased MASdensity should use a decreased MASSoft tissues that require a higher or lower Soft tissues that require a higher or lower contrast should use a change in KVP contrast should use a change in KVP

Variables and their effect on the photographic Variables and their effect on the photographic properties of the x-ray imageproperties of the x-ray image::

Radiographic variablesRadiographic variables Density Density ContrastContrast

Increase MAS Increase MAS increase increase no changeno changeDecrease MAS Decrease MAS decrease decrease no changeno changeincrease KVP increase KVP increase increase decreasedecreasedecrease KVP decrease KVP decrease decrease increaseincreaseincrease SID increase SID decrease decrease no changeno changedecrease SID decrease SID increase increase no changeno changeincrease OIDincrease OID decrease decrease increaseincrease

Radiographic variablesRadiographic variables Density Density ContrastContrast

decrease OID decrease OID increase decrease increase decreaseincrease Grid ratio decrease increaseincrease Grid ratio decrease increasedecrease grid ratio increase decrease grid ratio increase decrease decreaseincrease film-screen increase no change increase film-screen increase no change speedspeed

decrease film-screen decrease film-screen decrease no decrease no change speedchange speed

Radiographic variablesRadiographic variables Density Density ContrastContrast

increase collimation increase collimation decrease decrease increase increasedecrease collimation decrease collimation increase increase decrease decreaseincrease focal spot no change no changeincrease focal spot no change no change size size

decrease focal spot no change no changedecrease focal spot no change no change size size

increase central ray decrease no change increase central ray decrease no change

angleangle

Using 100 mA(small focal spot) station for Using 100 mA(small focal spot) station for extremity has better detail thanextremity has better detail thanUsing the same mAs and same kV with higher Using the same mAs and same kV with higher ma stationma station

Scatter radiation is detrimental to the quality of Scatter radiation is detrimental to the quality of film and adds unwanted density to the film film and adds unwanted density to the film without adding any patient information.without adding any patient information.

Scatter decreases contrast and using grids Scatter decreases contrast and using grids increase the contrast.increase the contrast.

Beam restricting devices and grids are used to Beam restricting devices and grids are used to limit scatter radiation.limit scatter radiation.

Two major factors that affect the amount of Two major factors that affect the amount of scatter radiation - KVP and the volume of tissue scatter radiation - KVP and the volume of tissue irradiated (opening collimation and larger irradiated (opening collimation and larger patient).patient).

1.) Using higher KVP produce more scatter as 1.) Using higher KVP produce more scatter as compared with a lower KVP.compared with a lower KVP.

2.) Larger field size and the thicker the patient 2.) Larger field size and the thicker the patient the greater amount of scatter produced from the the greater amount of scatter produced from the patient.patient.You should use appropriate KVP and limit x-ray You should use appropriate KVP and limit x-ray beam to limit scatter. beam to limit scatter.

Beam restriction serves two purposes - Beam restriction serves two purposes - this increases contrast, alsothis increases contrast, also1.) limits patients exposure1.) limits patients exposure2.) reduces scatter2.) reduces scatter

Because collimation decreases x-ray field, Because collimation decreases x-ray field, less scatter is produced within theless scatter is produced within thepatient, so, less scatter and contrast patient, so, less scatter and contrast increases. increases.

Exposure factors may need to be changed when Exposure factors may need to be changed when increasing collimation. (less density) So, as increasing collimation. (less density) So, as collimation increases (smaller area), density collimation increases (smaller area), density decreases, as collimation decreases (larger decreases, as collimation decreases (larger area), density increases.area), density increases.When collimating a lot you must increase When collimating a lot you must increase exposure to compensate for loss of density. The exposure to compensate for loss of density. The KVP should not be increased because it results KVP should not be increased because it results in decreased contrast. To change density only, in decreased contrast. To change density only, MAS should be changed.MAS should be changed.It is recommended with a lot of collimation It is recommended with a lot of collimation requires an increase in as much as 30% to 50% requires an increase in as much as 30% to 50% of the MAS to compensate for the loss of of the MAS to compensate for the loss of density.density.

Increases Factor:Increases Factor: Effect Effect

Collimation - Collimation - Patient dose decreases Patient dose decreases scatter decreases scatter decreases contrast increases contrast increases density decreases density decreasesField Size - Field Size - Patient dose increases Patient dose increases scatter increases scatter increases contrast decreases contrast decreases density increases density increases

Purpose of using grids:Purpose of using grids:1.) increases contrast1.) increases contrast2.) reduces density2.) reduces density3.) must use more MAS with a grid3.) must use more MAS with a grid

The choice to use a grid depends on:The choice to use a grid depends on:1.) KVP used1.) KVP used2.) thickness of part2.) thickness of part

Grids Grids --Improve contrast, using a grid requires additional Improve contrast, using a grid requires additional MAS resulting in a higher patient dose.MAS resulting in a higher patient dose.Grids are typically used only when the patient Grids are typically used only when the patient part is 10 cm (adult knee size)or greater and part is 10 cm (adult knee size)or greater and when using more than 60 KVP. when using more than 60 KVP.

Air gap technique:Air gap technique:

This is like using a grid. Less scatter on This is like using a grid. Less scatter on film but also less detail. You can increase film but also less detail. You can increase SID to help with the detail. The greater the SID to help with the detail. The greater the gap the less scatter.gap the less scatter.Using an increases OID is necessary for Using an increases OID is necessary for the air gap tech. However, this decreases the air gap tech. However, this decreases quality. To decrease unsharpness and quality. To decrease unsharpness and increase detail, you must increase SID. increase detail, you must increase SID.

Accurate measurement of part thickness is Accurate measurement of part thickness is critical to the effective use of exposure critical to the effective use of exposure technique chartstechnique charts..

Two types of technique charts:Two types of technique charts: 1.) Variable KVP/fixed MAS 1.) Variable KVP/fixed MAS 2.) Fixed KVP/variable MAS 2.) Fixed KVP/variable MAS

1.) Variable KVP/fixed MAS: (Best with small 1.) Variable KVP/fixed MAS: (Best with small extremities)extremities)KVP increases as part size increases. Baseline KVP increases as part size increases. Baseline KVP is increased by 2 for every 1cm increase in KVP is increased by 2 for every 1cm increase in part thickness, and MAS stays the same.part thickness, and MAS stays the same.

Accurate measurement of part thickness is critical Accurate measurement of part thickness is critical to use this type of chart.to use this type of chart.In general changing the KVP for variations in part In general changing the KVP for variations in part thickness is ineffective throughout the entire range thickness is ineffective throughout the entire range of x-rays. This kind of chart is most effective with of x-rays. This kind of chart is most effective with small extremities such as hands and feet. At low small extremities such as hands and feet. At low KVP levels, small changes in KVP may be more KVP levels, small changes in KVP may be more effective than changing the MAS. effective than changing the MAS.

Contrast will vary and these types of charts tend to Contrast will vary and these types of charts tend to be less accurate for part size extremes. Adequate be less accurate for part size extremes. Adequate penetration of the part is not assured, and the x-ray penetration of the part is not assured, and the x-ray produced with the use of this type of chart tend to produced with the use of this type of chart tend to have higher contrast have higher contrast

2.) Fixed KVP/variable MAS2.) Fixed KVP/variable MAS

This uses an Optimal KVP which is the This uses an Optimal KVP which is the KVP value that is high enough to ensure KVP value that is high enough to ensure penetration of the part but not too high to penetration of the part but not too high to diminish x-ray contrast. Then the MAS is diminish x-ray contrast. Then the MAS is varied to the part thickness. varied to the part thickness.

In general, for every 4-5 cm change in part In general, for every 4-5 cm change in part thickness, the MAS should be adjusted by thickness, the MAS should be adjusted by a factor of 2. (double MAS)a factor of 2. (double MAS)

Accurate measurement of part thickness is Accurate measurement of part thickness is important but less critical compared with important but less critical compared with variable KVP.variable KVP.

An advantage of using this chart is that An advantage of using this chart is that patient groups can be formed around 4-5 patient groups can be formed around 4-5 cm changes. You can use patient cm changes. You can use patient thickness groups. It is easierthickness groups. It is easierto use, more consistency on films, to use, more consistency on films, standardization of contrast.standardization of contrast.

(15% rule) 100 KV up to 115 KV = (15% rule) 100 KV up to 115 KV = doubling MASdoubling MASTo make a visible change in density it To make a visible change in density it requires at least 30% change in MAS or requires at least 30% change in MAS or 50%.50%.Changes in KV differ at high and low Changes in KV differ at high and low levels. greater change is needed with 90 levels. greater change is needed with 90 KV compared to 50 KVKV compared to 50 KV

90 KV and increase 10 KVP = slightly 90 KV and increase 10 KVP = slightly darkerdarker50 KV and increase 10 KVP = very dark50 KV and increase 10 KVP = very dark

To maintain density with KVP use 15% To maintain density with KVP use 15% rule rule

so 15% increase in KVP = doubling MAS so 15% increase in KVP = doubling MAS maintains densitymaintains densityKVP 82 change to 94 (15%) is same as KVP 82 change to 94 (15%) is same as MAS 10 change to 20 (double)MAS 10 change to 20 (double)

For each additional 4cm thickness you For each additional 4cm thickness you need to double MAS to maintain density.need to double MAS to maintain density.

15% rule15% rule

60 = 69 60 = 69 62 =71.362 =71.365 = 74.7565 = 74.7568 = 78.268 = 78.270 = 80.570 = 80.572 = 82.8 72 = 82.8 75 = 86.2575 = 86.25