Density, Contrast, Distortion & Detail

Lab Test #3

Contrast and the 15% Rule

Objective: To demonstrate the influence of the 15% rule on contrast

1st exposure at recommended technique

Used as control

Contrast and the 15% rule

Apply the 15% rule twice and ↑ kVp ↓ mAs accordingly

All other factors stay the same

The math doesn’t quite add up on this one, so I think the images are from 2 different groups

Contrast and the 15% rule

Again, this image doesn’t match my lab sheet, I believe we lowered the kVp 15% and shot another on just for S&G

At this point, we should compare the 2 images to determine which has the longest scale of contrast

See next slide

Contrast and the 15% rule

Low kVp=High Contrast= Short scale High kVp=Low Contrast= Long scale

More B&W More Shades of Gray

Density- Control Image

Objective: To demonstrate the effect of select factors on density

Control image of knee phantom taken @ 5mAs, 60kVp, & 40” SID.

Density- Filter

With no change in tech factors, a copper sheet is taped to the face of the collimator

Filters have an inverse relationship on density thus:

↑ Filtration ↓ Density

Density- Grid

Copper filter removed No change in technical

factors Grid is introduced to IR Result: Adding a grid

decreases density this is an inverse relationship

(+) ↑ Grid ↓Density

Density- SID

Grid removed No change in technical

factors SID increased from 40”

to 60”

Density-Tissue Thickness

Grid is removed and hand phantom is substituted for knee

No change in technical factors

Overall, the hand the tissue thickness of the hand is much less than that of the knee

↑ tissue thickness ↓density

Density- Collimation-Control

Torso phantom is substituted for hand

14x17 collimation Use technique

recommended by console + 20 mAs

This image will be compared with the highly collimated image.

Density- Collimation

Collimation is increased to a 4x4 square.

Repeat exposure of torso with no change in technical factors

↑collimation ↓density

Density- Anode Heel Effect

Use a foot phantom and a 14x17 cassette

2 mAs, 60 kVp, 40” SID Leave collimation open

lengthwise to 17” Orient toes over the

anode side

Density- Anode Heel Effect

All technical factors remain the same

Foot is moved to opposite end of cassette to place toes on cathode side

In practice, the thickest tissue should be placed at the cathode end of tube

In theory, placed thicker tissue at anode end would effect density

A visible change in density would only be appreciated with film/screen

Size Distortion: Control

Objective: To demonstrate the various types of distortion

Control image of hand shot at 40” SID

Technique: Pre-programmed

Size Distortion: 6” OID

2nd image 6” OID is created with

sponges All other factors remain

the same Compare with control

image to note distortion (magnification)

Size Distortion: 12” OID

Image #3 OID is ↑ to 12” Collimation is exactly the

same No other factors have

been changed Note magnified

appearance of hand Such distortion can mask

pathology

Distortion: OID + SID

OID is ↓ to 6” SID is ↓ to 20” All remaining tech factors

are unchanged Result: Size distortion

(magnification in this case) can be caused by OID, SID or both

Shape Distortion: Control

Control exposure of knee phantom w/recommended tech factors

This image will be used for comparison with others

Shape Distortion: Angled Tube

2nd image of knee phantom

Tube is angled All tech factors remain

the same

Shape Distortion: Angled IR

3rd exposure of knee phantom

IR is angled All tech factors are

unchanged from control

Note closed joint spaces

Shape Distortion: Angled Anatomy

4th exposure of knee phantom

All tech factors remain constant except…

Phantom is angled Result: Shape distortion

can be caused by the angulation of tube, IR or anatomy being imaged.

Density & mAs

Objective is to demonstrate the effects of overexposure & underexposure on CR images

First image is made @ 60kVp, 10mAs w/40” SID

Density & mAs 2

mAs is ↑ 50 All other technical factors

remain the same LGM#’s of all images will be

compared with control LGM represents the # of

photons reaching IR to form the latent image

LGM is proportional to mAs

Density & mAs 3

↑ to 100 mAs No other technical factors

are changed At this stage, LGM#’s

appear to be ↑ as mAs is ↑ (a direct relationship).

Density & mAs 4

↑ to 200 mAs Remaining tech factors

unchanged LGM#’s increase with

each increase in mAs mAs is THE controlling

factor of density

Detail and Distortion: Motion

Objective: To demonstrate the effect of motion on detail

Technical factors: The programmed technique for a foot but ↓ mA

Decrease in mA is necessary to ↑ exposure time (applicable in next image)

1st image of top taken on 10x12 w/no motion

Detail and Distortion: Motion

2nd image- top is spinning while exposure is taken

Technical factors are unchanged

The lower mA ↑ exposure time, allowing the motion to be caught on film

Detail and Distortion: Motion

Additional image of this experiment

Compared to the 1st image (stationary), the lead letter attached to top is blurred.

Result: Increased motion decreases detail

Motion↑↓ Detail Although motion is generally a

detriment to good films, it can be used to the RT’s advantage

Ex: Using breathing technique to blur ribs

Quantum Mottle

Definition: a lack of sufficient incoming data to process an image; AKA quantum noise

No idea what this image has to do with anything, but that’s how it was labeled

That would be a cool name for a band though

Contrast- Control Image

Objective: To demonstrate how selected factors effect contrast

66kVp, 10 mAs, 40” SID on table top

Contrast 66kv

Skull phantom is replaced w/step wedge

Exposure taken with no changes in technical factors

Compare this image w/second exposure using a higher technique

Contrast: ↑kVp ↓mAs

↑ to 86kVp Compensate by ↓mAs to

¼ of its original value All other factors remain

the same

Contrast- 86kv

Again, step wedge takes the place of skull phantom

No change in technical factors

Compare shades of gray in adjacent densities

Comparison of Contrast

Low kVp High kVp

Contrast: +Grid

3rd image of skull Grid is introduced mAs ↑ 4x to

compensate All remaining factors

unchanged

Contrast: Scatter

4th image of skull Collimation open wide

to expose IR to scatter All remaining factors

unchanged Compare this series of

images to note differences in adjacent densities

Contrast Collimation

Skull is now positioned laterally

This exposure will use bucky instead of table top

100 kVp @ 20mAs

Contrast: Collimation

Repeat exposure of lateral skull

Collimated to 3”x3” area

All remaining factors are unchanged

Short vs Long Scale Contrast: kVp

Objective: To demonstrate short & long scale contrast

Elbow phantom @ 46kVp & 5mAs

Stepwedge 2 Contrast ????

I think this is supposed to be part of a contrast lab but I couldn’t match it up with anything

Also, it was posted twice in the images file…so there’s nothing to compare it to as far as I can tell

Short vs Long Scale Contrast; kVp

2nd image of elbow phantom

↑ to 70kVp ↓to 3mAs

Density Chart

Variables Effects Density Relationship

Filtration ↑↓ ↓↑ Inverse

Grid ↑↓ ↓↑ Inverse

Tissue Thickness ↑↓ ↓↑ Inverse

SID ↑↓ ↓↑ Inverse

Collimation ↑↓ ↓↑ Inverse

Anode Heel Effect Cathode: ↑Anode: ↓

*In theory the anode heel effect does cause a change in density but this is not evident in digital imaging

N/A unless film screen technology is involved

Contrast ChartVariable Effect Contrast Relationship

kVp ↑↓ ↓↑ inverse

mAs Ø Ø none

SID Ø Ø none

OID ↑↓ ↑↓ direct

Filtration ↑↓ ↓↑ inverse

Collimation ↑↓ ↑↓ direct

Tissue Thickness ↑↓ ↓↑ inverse

Contrast Media + ↑ direct

Grid ratio ↑↓ ↑↓ direct

Focal spot size Ø Ø none

Film Processing *+/- developing time and temp beyond optimal

↓ Always ↓ contrast

Detail Chart

Variable Effect Detail Relationship

SID ↑↓ ↑↓ direct

OID ↑↓ ↓↑ inverse

Tissue Thickness ↑↓ ↓↑ inverse

Focal Spot Size ↑↓ ↓↑ inverse

Motion ↑↓ ↓↑ inverse