Ch 7 Principles Of Exposure And Image Quality

Front 1

X-ray beam Quantity Factors

Back 1

1. mA

2. Exposure time

3. mAs*

4. kVp *

5. SID*

6. Filtration*

* indicates prime factor

Front 2

X-ray beam quality factors

Back 2

1. kVp

2. Filtration

Front 3

4 prime factors of radiographic exposure:

Back 3

1. Milliamperage (mA)

2. Exposure time

3. kVp

4. SID (source image receptor distance)

Front 4

Exposure

Back 4

A broad term used to describe the x-rays that the patient is exposed to, the amount of xrays in the primary beam, and also the amount of xrays that reach the image receptor.

Front 5

Miliamperage

Back 5

1. Controls radiographic density

2. Controls quantity of xrays produced (rate of exposure is photons produced per second)

3. Controlled by adjusting the filament heat.

4. Quantity of exposure is directly proportional to mA.

Front 6

Exposure Time

Back 6

1. Controls radiographic density.

2. Controls quantity of x-rays produced.

3. Controlled by adjusting the timer in x-ray circuit.

4. Controls duration of exposure.

5. Quantity of exposure is directly proportional to exposure time.

Front 7

Primary controller of radiographic density

Back 7

mAs

Front 8

Primary controller of the penetrating of xrays

Back 8

kVp

Front 9

Kilovoltspeak kVp

Back 9

1. Controls radiographic contrast.

2. Controls xray penetrating

3. Controls the quantity AND quality of the x-ray beam.

4. Increased kVp results in increased quantity of photons.

5. Increased kVp results in increased penetration of the body part.

Front 10

Primary controller of radiographic contrast

Back 10

kVp

Front 11

Source - image receptor distance (SID)

Back 11

1. Affects the density and intensity of the x-ray beam.

2. Quantity of the exposure is inversely proportional to the square of the distance. (More distance = less exposure).

3. Each dimension of the radiation field is proportional to the square of the SID. Therefore, the field area is proportional to the square of the SID and the radiation intensity is inversely proportional to the square of the SID. (Size of field bigger as distance increases, intensity lower as distance increases).

Front 12

Inverse square law

Back 12

Original intensity ÷ new intensity = new distance squared ÷ original distance squared

***intensity or quantity of xrays is reduced 4X when SID doubles and is increased 4X when SID is halved.

Front 13

Common SID

Back 13

40 inches for everything except lateral and oblique cervical and chest which are 72 inches

Front 14

4 primary factors that directly affect how the xray image looks:

Back 14

1. density

2. Contrast

3. Distortion

4. Spatial resolution

**density and contrast are considered photographic properties.

**distortion and recorded detail are considered geometric properties

Front 15

Density

Back 15

A photographic property that refers to the overall blackness or darkness of the radiographic image. Density affects the visibility of detail.

Front 16

Overexposed

Back 16

An image that is too dark.

Front 17

Underexposed

Back 17

An image that is too light. (Not enough mAs).

Front 18

Primary control for varying density:

Back 18

mAs

Front 19

Tissue density

Back 19

The mass density or atomic number of the body part being xrayed. Lower density body parts are darker (fat) and higher density body parts appear lighter (bone)

Front 20

Radiographic Density vs Tissue Density

Back 20

Inversely related, more dense tissues will appear lighter on the image.

Front 21

Brightness

Back 21

The term used in digital imaging in place of density.

Front 22

Contrast

Back 22

A photographic property defined as the difference in radiographic density between adjacent portions of the image.

Too much contrast makes the image too black and white (short scale). Too little contrast creates a flat grey appearance making it difficult to differentiate.

Front 23

Visibility of detail is controlled by

Back 23

Density and contrast

Front 24

Optimal Contrast

Back 24

Varies depending on the body part. Contrast is primarily controlled by the kVp.

Front 25

Subject Contrast

Back 25

The range of differences in the intensity of the xray beam after it has been attenuated by the patient. It is affected by kVp and tissue density.

* long scales of contrast (high kVp 100 to 120) are desired for structures with high subject Contrast like the chest

**short scales (low kVp 75 to 90)of contrast are desirable when the subject Contrast is low (ie the abdomen with many structures of similar density)

Front 26

Contrast is directly influenced by:

Back 26

1. Subject Contrast

2. Fog (decreases contrast)

3. Collimation (too wide increases scatter producing fog and decreasing contrast).

Front 27

Radiographic Distortion

Back 27

A geometric property referring to differences between the actual subject and it's radiographic image. Can be either size distortion or shape distortion.

Front 28

Size distortion

Back 28

When the part is magnified as a result of the relationship between the SID (source - image receptor distance) and the OID (object-image receptor distance).

* controlled by positioning the body part as close to the IR as possible and using the longest SID practical.

* Larger SID'S are needed for greater OID's

Front 29

Radiographic images can never be smaller than the actual body size

Back 29

True because the body part is always slightly above the IR and magnified slightly.

Front 30

Shape Distortion

Back 30

The result of unequal magnification.

The least shape distortion occurs when the plane of the subject is parallel to the plane of the IR. Only the central ray is truly perpindicular so the least distortion is at the center of the image.

Front 31

Foreshortening

Back 31

Projects the body part so it appears shorter than it really is. This usually occurs when the body part is not correctly aligned.

Front 32

Elongation

Back 32

Projects the object so it appears longer than it really is. This distortion occurs when either the IR or the xray tube is not aligned with the body part.

Front 33

Spatial Resolution

Back 33

Previously called recorded detail is a geometric property that refers to the sharpness of the image. Also sometimes called: resolution, sharpness, definition, or detail. In Optimum resolution, the edge sharpness of structures in the image are crisp and accurately rendered. Poor resolution tends to appear fuzzy.

Front 34

Factors that affect spatial resolution:

Back 34

1. Patient motion

2. OID

3. SID

4. Focal spot size

*the last 3 are geometric factors

Front 35

Factors Affecting Size Distortion

Back 35

1. OID

2. SID

Front 36

Factors Affecting Shape Distortion

Back 36

1. Alignment of

a. Central ray

b. Body part

c. Image receptor

And

2. CR angular ion

A. Direction

B. Degree

Front 37

Umbra

Back 37

The actual anatomic area, body part, or structure shown in the radiographic image.

Front 38

Penumbra

Back 38

Describes the "unsharp edges" of the umbra, or body part. Also known as "blur" or "geometric unsharpness". The goal is to reduce the penumbra as much as possible

Front 39

Effects of Image Geometry on Recorded Detail

Back 39

Decreased OID = Decreased penumbra = greater recorded detail.

Increased SID = decreased penumbra = greater recorded detail.

Smaller focal spot have smaller penumbra and greater recorded detail.

Magnification results in image unsharpness.

Front 40

Quantum mottle

Back 40

A grainy or mottled image appearance caused by insufficient photons from a kVp or mAs that was set too low.

Front 41

Ch 7 summary

Back 41

Part 1

Front 42

Ch 7 summary 2

Back 42

Part 2