Diagnostic Imaging Module 6

Density

Film blackening in area increases with exposer

Intensity

Amount of light in area increases with exposure

Contrast

Difference between structures in area

Latitude

Range of contrast in images

Sharpness

Abruptness in boundary between two structures

Detail visibility

Ability to discern between two small objects depends on contrast and sharpness

resolution  

quantitate measure of detail visibility 

INCREASING KV INCREASES

QUALITY AND
QUANTITY

KV affects

Density, Contrast

INCREASING MA and TIME CAUSES AN INCREASE IN

QUANTITY

mA and Time affects

Density

CHANGING MA CAN AFFECT IMAGE SHARPNESS DUE TO

FOCAL SPOT BLOOMING

TIME CAN AFFECT IMAGE SHARPNESS DUE TO

BLURRING CAUSED BY MOTION

GENERATOR EFFICIENCY REFERS TO THE AMOUNT OF RIPPLE ON

KV waveform

SINGLE PHASE TWO PULSE RIPPLE general efficiency

100%

SIX PULSE RIPPLE general efficiency

13.5%

TWELVE PULSE RIPPLE

3.4%

VOLTAGE RIPPLE AFFECTS THE KINETIC ENERGY OF THE ELECTRONS
CROSSING

the tube

WHEN LOW ENERGY ELECTRONS STRIKE THE TARGET THEIR ENERGY IS

converted to heat

SINGLE PHASE SYSTEMS PRODUCE MORE LOW ENERGY ELECTRONS THAN

Three phase systems

IN THREE PHASE SYSTEMS THE AVERAGE PHOTON ENERGY IS MUCH
GREATER THAN

Single phase systems

Heel Effect

THE BEAM ENTERING THE PATIENT DOES NOT HAVE AN UNIFORM DENSITY

NON-UNIFORMITY

THE PHOTONS ON THE TARGET SIDE ARE
MORE LIKELY ABSORBED BY THE TARGET THAN THE PHOTONS ON
THE CATHODE SIDE OF THE BEAM

The heel effect causes

NON-Uniformity

Technicians can use NON-UNIFORMITY  by

PLACING THICKER BODY PART UNDER CATHODE SIDE, THE IMAGE
CAN COME OUT MORE UNIFORM

Focal spot size affects

sharpness

Area of un sharpness

Penumbra or partial shadow

SID

Source to Image Distance

Properties of image affected by SID

Quality, Density, Sharpness, SIZE OF
RADIOGRAPHIC IMAGE

AS SID increases  

X Ray beams decrease, sharpness improves, IMAGE MAGNIFICATION DECREASES

AN INCREASE IN SID REQUIRES

LONGER EXPOSURES
DUE TO THE INVERSE SQUARE LAW

INCREASED EXPOSURE TIME INCREASES THE CHANCE
OF

Motion

OID

Object to Image Distance

As OID is
decreased

magnification is ALSO decreased

Alignment

Image plane being perpendicular to central ray

Improper alignment causes

distortion

Object motion causes

blurry images

Beam Limiting device

Modify primary beam size and shape

Filtration

Removal of low energy x ray photons

Inherent filtration

Glass or insulation oil

Added filtraiton

Sheets of aluminum

Inherent filtration increases with

age and tungsten deposits of tube

Half Value Layer

Amount of 1100 Aluminum required to reduce beam density to half

Subject

The region and thickness of anatomy being irridated

Contrast media

Vary absorption characteristics of organ or cavity

Compression

Reduce density, increases contrast, and increases sharpness

GRID

Alternating strips of lead and a radio translucent substance

Grids are used
to reduce

scatter radiation created by object
interaction

Intensifying Screens

Reduce amount of exposure necessary to get a density

Hurter and driffield curve

express characteristics of film

film is exposed to a

sensiometer