RECORDED DETAIL

Geometry, Image Receptor, Motion

Factors affecting Recorded Detail

Focal Spot Size, Distance

Geometric Factors

Focal Spot Size

Major controller of image resolution

Does not affect x-ray quantity or quality

Controlled by the line focus

principle

Controls penumbra

Most X-ray Tube

equipped with two focal-spot sizes

Small and Large

Sizes of FSS

Microfocus Tubes

Tube that has a very small focal

spot

Specifically designed for imaging very small microcalcifications at relatively short SID

Used in mammography

Umbra

The distinctly sharp area or area of complete shadow

Receives essentially no photons

Penumbra

Edge gradient, focal spot blur, focal spot blooming

The imperfect, unsharp shadow surrounding the umbra

Receives more photons

Important factor for determining spatial resolution

Line Focus Principle

Angling the target

Minimize EFS

To improve resolution

Maximize AFS

to absorb heat

Anode heel effect

consequence for line focus principle

Large Focal Spot Size

Used for general imaging

Used to image thick or dense body parts

Provides for a shorter exposure time

Minimizes motion blur

More capacity to produced x-rays

Higher anode heat capacity

Small Focal Spot Size

Used for fine-detail imaging

Used to image thin or less dense body parts

Used for extremity radiography

Less capacity to produce x-rays

Always used for magnification radiography

Lower anode heat capacity

Blooms more

at higher mA

Rare

It is ___ for blooming to cause a visible film density

difference

If perceived, replacement of the tube is indicated

Distance

Affects magnification

For magnified image:

Short OID, Long OID

Long SID, Short OID

Sharpest Image Detail

Tube-Object Film Alignment

Arrowhead: near the source

• Size of penumbra > effective

focal spot size

• Arrowhead: away from the

source

• Size of penumbra <

effective focal spot size

Intensifying Screen Speed, Non-screen Holder, Film Screen Holder, Target-Object-Film-Alignment

Image Receptor

Film Screen Combination

Mostly classified by speed

• Inversely proportional to the image resolution

IS: poorer resolution than film

line per square millimeter

lp/mm

100 lp/mm

Radiographic film

7 lp/mm

Very Fast Screen

15 lp/mm

Fine-detail screen

50 lp/mm

Non-Screen/ Direct exposure film

10 lp/mm

Unaided eye

1200 RSV

Very fast

300 RSV

Ultra high or hi-plus

200 RSV

High or fast

100 RSV

Standard

50 RSV

Detail, slow, high resolution

25 RSV

Ultra detail

Slow Screen (IS)

For examination that requires

higher resolution

For extremity examination

Higher patient dose

Fast Screen (IS)

Use to reduce patient dose

For examination that do not

require higher resolution

Size, thickness, concentration

Resolving power depends on phosphor what?

Film-Screen Contact

IS and film are sandwiched together

Pressure Pad

keep them in direct contact with one another

Wire-Mesh Test

Used to check for screenfilm contact

Poor contact:

• Darker areas of blurring

• Increased penumbra

• Poor detail

Adjustment:

• Repair the cassette

• Discard the cassette

Voluntary, Involuntary, Equipment

Motion Blur

Voluntary Motion

Under the direct control of the patient

Patient communication

Involuntary Motion

Not under the direct control of the patient

Decrease exposure time

Equipment Motion

Difficult to detect

May cause vibration of the cassette in the Bucky tray

Motion Blur

Affects recorded detail

Blurring of an image that

results from

• Movement of the patient during exposure

• Movement of the x-ray tube during exposure

• Not a problem

Results in loss of radiographic quality

Results in repeated radiographs

Motion Reduction

Carefully instructing the patient

Immobilization

Short exposure time

Large SID and small OID

Same relation as to focal-spot blur

Low ripple power

High-speed image receptor

Moving Grid Mechanism

An auxiliary equipment that causes the table or restraining devices to move

Factors that Improves Resolution

REDUCE FOCAL SPOT SIZE

REDUCE OID

INCREASE SID

ELIMINATE MOTION

REDUCE INTENSIFYING

SCREEN PHOSPHOR SIZE AND LAYER THICKNESS

INCREASE PHOSPHOR

CONCENTRATION