Components of
Image Quality
Radiographic Artifacts

Radiologic Technology A

Spring 2009

X-ray Exposure Factors

Radiographic Density & Contrast

Components of
Image Quality

Radiographic Artifacts

Review Chapter 7

Primary radiation exits the tube

Interacts with various densities in the body

Photons may be absorbed

Scattered

Passed through without any interference to the cassette or image receptor (IR)

How well we can see something on the image

Image detail
is affected by:
Photographic properties
and
Geometric properties

Photographic Properties

–______

–______

X-ray Exposure Factors

TECHNIQUE SELECTION:

Radiographer selects the

Kilovoltage peak (kVp)

Milliamperage (mA) & time (s)

Milliamperage x time = mAs

(milliamperage multiplied by a set time measured in seconds)

Kilovoltage Peak

kVp

One kilovolt = 1000 volts

The amount of ______selected for the x-ray tube.

Range 30 to 150 kVp

kVp controls ______?

Milliamperage

One milliampere (mA) = one thousandth of an ampere.

The amount of ______supplied to the x-ray tube

How ______x-rays will be produced

Range 10 to 1200 mA

Time

In seconds

How long x-rays will be produced

0.001 to 6 seconds

Milliampere Seconds

Technologists think in terms of mAs

Calculated by mA x seconds

Ex: 100mA X 0.2s = 20 mAs

How many x-rays will be produced and for how long.

Modern x-ray machines only allow control of

mAs controls ______?

Factors Affecting Density

Primary control factor

–mA

–Time (seconds)

Influencing factors

–kVp

–Grids

–Beam restriction

–Body structures (size of pt, pathology

–Processing

–SID & OID

–Film Screen combinations

Primary Controlling Factor of Density

mAs

mA = ______of electrons sent across the tube combined with TIME (S) = mAs

mAs controls ______on radiograph

primary function of mAs is DENSITY

Imagine this…

If the mA station is changed from 200 to 400 mA, twice as many electrons will flow from the cathode to the anode.

From 10 mA to 1000 mA = 100 x more

mA controls how manyelectrons are coming at the target

mAs is a combination of how many and for how long(seconds)

Changing Mas – Changes Density
+ 25 % + 50 % mas

Influencing Factor
on Density:
kVp

 kVp more energy = more photons passing though tissue & striking the image

15% kVp = doubling of exposure to the film

 15% kVp = halving of exposure to the film

15% rule will also change the contrast of the image because kV is the primary method of changing image contrast.

Remember :

15% change ( ) KVP has the same effect as doubling or ½ the MAS on density

Change in kVp

kVp controls the energy level of the electrons and subsequently the energy of the x-ray photons.

A change from 72 kVp will produce

x-rays with a lower energy than at

82 kVp

Difference between a ball traveling 72 mph and 82 mph (how much energy did it take to throw the ball at the rates?)

+ 15% kvp - 15% kvp

Radiolucent vs. Radiopaque

______ materials allow x-ray photons to pass through easily (soft tissue).

______materials are not easily penetrated by x-rays (bones)

Creating the Image

______

–no interaction

–Responsible for dark areas

______

 (grays) – produces no diagnostic info

______

(photoelectric effect)

–Responsible for light areas

Images

______= THE AMOUNT OF BLACKENING “DARKNESS” ON THE RADIOGRAPH (mAs)

______– THE DIFFERENCES BETWEEN THE BLACKS TO THE WHITES (kVp)

Why you see what you see…

The films or images have different levels of density – different shades of gray

X-rays show different features of the body in various shades of gray.

The gray is darkest in those areas that do not absorb X-rays well – and allow it to pass through

The images are lighter in dense areas (like bones) that absorb more of the X-rays.

Image Production

______ – The beam of photons, B4 it interacts with the pt’s body.

______ – The resulting beam that is able to exit from the patient.

______ – Radiation that interacts with matter & only continues in a different direction – not useful for image production.

______ – Primary radiation that is changed (partially absorbed) as it travels through the pt.

Patient Body Size
and
Pathology

3 Different Body Habitus
Hypersthenic Sthenic Hyposthenic

PATHOLOGY

Pleural

Effusion

Excessive fluid in lung

More dense than air

pneumonia

LUNG
Cancer

LUNG CANCER

Density and Images

Goal: Producing optimal radiographs
DENSITY

Controlling Factor of
Contrast

Controlling Factor of Contrast

Kilovolts to anode side – kVp

Kilovolts controls ______the electrons are sent across the tube

kVp – controls ______on images

Scale of Contrast?
Which one is “better”
How does the kVp affect these images?

Short Scale vs. Long Scale

Beam Restriction
and
Grids

Scatter

–Creates fog

–Lowers contrast (more grays)

Increases as

–kV increases

–Field size increases

–Thickness of part increases

Effects of collimation (beam restriction) on scatter

Collimate to area of interest -reduces scatter and radiation dose to the patient

Grids

A device with lead strips that is placed between the patient and the cassette

Used on larger body parts to reduce the number of scattering photons from reaching the image

GRID NO GRID
CONTROLS CONTRAST

Basic Grid Construction

•Radiopaque lead strips

•Separated by radiolucent interspace material - Typically aluminum

Allow primary radiation to reach the image receptor (IR)

Absorb most scattered radiation

Primary disadvantage of grid use

–Grid lines on film

GRIDS

Grid is placed
between patient (behind table or upright bucky) & cassette

Grids absorb scatter –
prevents it from reaching the image

GRIDS
CAN
LEAVE
LINES
ON THE
IMAGE

GEOMETRIC Properties

Recorded Detail

DISTORTION

–______distortion

Magnification

–______distortion

Elongation

Foreshortening

RECORDED DETAIL

RECORDED DETAIL

The degree of sharpness in an object’s borders and structural details.

How “clear” the object looks on the radiograph

Recorded Detail

The degree of sharpness in an object’s borders and structural details.

Other names:

-sharpness of detail

-definition

-resolution

-degree of noise

Factors that affect
Recorded Detail

Geometric unsharpness

OID SID SIZE SHAPE

Motion unsharpness (blurring)

Intensifying Screens

Film Speed / Composition

Film – Screen contact

Kvp & Mas (density / visibility)

MOTION
AKA
Blurring

Motion

Can be voluntary or involuntary

Best controlled by short exposure times

Use of careful instructions to the pt.

Suspension of pt. respiration

Immobilization devices

Decrease Motion Unsharpness

Instruct patient not to move or breath

Use Immobilization devices

Use Short exposure times

Lock equipment in place

Object Unsharpness

Main problem is trying to image a 3-D object on a 2-D film.

Human body is not straight edges and sharp angles.

We must compensate for object unsharpness with factors we can control: focal spot size, SID & OID

SID
Source to Image Distance

The greater the source X-ray tube) to image (cassette) distance, the greater the image sharpness.

Standard distance = 40 in. most exams

Exception = Chest radiography 72 in.

SID

Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy”

-On a radiograph called Penumbra

Penumbra (fuzziness) obscures true border – umbra

Farther the flashlight from object = sharper borders. Same with radiography.

OID
Object to Image Distance

The closer the object to the film, the sharper the detail.

OID , penumbra , sharpness 

OID , penumbra , sharpness 

Structures located deep in the body, radiographer must know how to position to get the object closest to the film.

Distortion

Misrepresentation of the true size or shape of an object

–MAGNIFICATION

–size distortion

–TRUE DISTORTION

–shape distortion

MAGNIFICATION

TUBE CLOSE TO THE PART (SID)

PART FAR FROM THE CASSETTE (OID)

Size Distortion & OID

If source is kept constant, OID will affect magnification

As OID , magnification 

The farther the object is from the film, the more magnification

Size Distortion & SID

Major influences: SID & OID

As SID , magnification 

Standardized SID’s allow radiologist to assume certain amt. of magnification factors are present

Must note deviations from standard SID

40” SID VS 72” SID

SHAPE DISTORTION
Elongation
and
Foreshortening

Shape Distortion

Misrepresentation of the shape of an object

Controlled by alignment of the beam, part (object), & image receptor

Influences: Central ray angulation & body part rotation

A = good
B & C = shape distortion
(elongation of part)

D & E =
shape distortion
(foreshortening of part)

Image Distortion

When the part to be imaged – does not lay parallel with the IR (cassette)

If the Central Ray is not perpendicular to the part

–CR should be at right angle with the cassette

Central Ray Angulation

Body parts are not always 90 degrees from one another

Central ray angulation is used to demonstrate certain details that can be hidden by superimposed body parts.

Body part rotation or obliquing the body can also help visualize superimposed anatomy.

Central Ray

Radiation beam diverges from the tube in a pyramid shape.

Photons in the center travel along a straight line – central ray

Photons along the beam’s periphery travel at an angle

When central ray in angled, image shape is distorted.

Elongation Foreshortened Normal

Focal Spot Size

Smaller x-ray beam width will produce a sharper image.

Fine detail = small focal spot (i.e. small bones)

General radiography uses large focal spot

Beam from penlight size flashlight vs. flood light beam

FOCAL SPOT ANGLE

ARTIFACTS:
AN UNWANTED DENSITY
ON THE FILM

Artifacts - Types

Processing Artifacts

Exposure Artifacts

Handling & Storage Artifacts

Processing Artifacts

Emulsion pickoff

Chemical fog

Guide-shoe marks

Water marks

Chemical spots

Guide-shoe & roller scratches

Exposure Artifacts

Motion

Improper patient position

Wrong screen-film match

Poor film/screen contact

Double exposure

Warped cassette

Improper grid position

Artifact

PATIENT ARTIFACT - JEWERLY

Handling & Storage Artifacts

Light fog

Radiation fog

Static

Kink marks

Scratches

Dirty cassettes

Crimping /cresent mark

cast

POOR SCREEN CONTACT

Patient motion

motion

Double
exposure
Child

Poor
screen
contact

Double exposure

?

?

PATHOLOGY NOT ARTIFACT

Name &
cause
of this?

Dust in imaging plate can cause white marks on image

Both in film/screen and computed radiography

Evaluating Images

What do you think?

Does this show good detail?

Is all of the anatomy present?

How is the density / contrast?

Does this show good detail?

–YES

Is all of the anatomy present?

–No (part of the little finger is not seen)

How is the density / contrast?

 Density – a little “light” underexposed

 Contrast is good

See anything
wrong
with
this
image?

Contrast? What influences this? (kVp in f/s)

Collimation – reducing the size of beam
helps to improve the image, and reduce the dose to the patient