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
Cathode: ↑
Anode Heel Effect *In theory the N/A unless film
Anode: ↓ anode heel effect screen technology
does cause a is involved
change in density
but this is not
evident in digital
imaging

Contrast Chart
Variable Effect Contrast Relationship
↑↓ ↓↑
kVp inverse
Ø Ø
mAs none
Ø Ø
SID none
↑↓ ↑↓
OID direct
↑↓ ↓↑
Filtration inverse
↑↓ ↑↓
Collimation direct
↑↓ ↓↑
Tissue Thickness inverse
↑
Contrast Media + direct
↑↓ ↑↓
Grid ratio direct
Ø Ø
Focal spot size none
↓ Always ↓ contrast
Film Processing *+/- developing
time and temp
beyond optimal

Detail Chart
Variable Effect Detail Relationship
↑↓ ↑↓
SID direct
↑↓ ↓↑
OID inverse
↑↓ ↓↑
Tissue Thickness inverse
↑↓ ↓↑
Focal Spot Size inverse
↑↓ ↓↑
Motion inverse