Viewing the Digital Image

Bushong Ch. 29

Hard Copy vs Soft Copy

Photometry The science of the response of the

human eye to light

The basic unit of photometry is the lumen (lm).

Illuminance describes the intensity of light

incident on a surface Luminance intensity is a

property of the source of light, such as a viewbox or a digital

display device

Monitors Cathode ray tube (CRT)

Liquid crystal display (LCD)

Plasma screen

Soft copy viewingdigital cathode ray tube (CRT)

active matrix liquid crystal display (AMLCD)

Active matrix liquid crystal displays are superior to cathode ray tube displays. LCD design –

gives out more light,

reduces ambient light

Better contrast resolution

Less noise Less maintenance

Crystals can be aligned by an external electric field

Plasma Display The plasma displays are made up

of many small fluorescent lights that are illuminated to form the color of the image.

Pixel A pixel is an

individual controllable set of dot triads. A dot triad is a grouping of one red dot, one green dot, and one blue dot. The number of pixels on a display is known as its resolution.

Resolution The more pixels

in an image, the higher the resolution of the image and the more information that can be displayed.

Pixels are arranged in a matrix

Dot pitch Dot pitch is the measurement of

how close the dots are located to one another within a pixel

Spatial Resolution improves with the use of higher-

megapixel digital display devices

A 1-megapixel display will have a 1000×1000-pixel arrangement. A high-resolution monitor will have a 5-megapixel display, or a 2000×2500-pixel arrangement

Refresh rate The refresh rate is the measure

of how fast the monitor rewrites the screen or the number of times that the image is redrawn on the display each second. The refresh rate helps to control the flicker seen by the user; the higher the refresh rate, the less flicker.

Viewable area The viewable area is measured

diagonally from one corner of the display to the opposite corner.

Cosine Law Is important when one is

describing the luminous intensity of a digital display device. When a monitor is viewed straight on, the luminous intensity is maximum. When a monitor is viewed from an angle, the contrast and the luminous intensity are reduced.

When a digital display device is viewed from the side, illumination and image contrast are reduced.

LCD Disadvantage The principal disadvantage of an

AMLCD is the angular dependence of viewing

Ergonomic design of digital workstations is critical

Transmission of Images PACS - Picture Archiving &

Communications System DICOM - Digital Images &

Communication in Medicine TELERADIOGRAPHY -Remote

Transmission of Images

PACS

Internet VPN

Digital Images Archive

Databaseand Workflow Engine

Workstations

Remote Workstations

Remote Facilities

PACS/HIS/RIS/X-ray System HIS = Hospital information system

RIS = Radiology information system

X-ray machine patient folder

Archive Servers An archive server is the file room of the PACS

PACS Common Functions Navigation functions are used to

move through images, studies, and patients.

The worklist is used to navigate through patients. Most worklists are customizable for the user. One doctor or technologist may want to see only CT studies or all neurologic studies done that day regardless of the modality.

Most modern PACS software conforms to the Windows look and feel.

Questions? "The pessimist sees difficulty in every

opportunity. The optimist sees the opportunity in every difficulty."

Winston Churchill