6. Introduction to Medical Visualization systems
6. INTRODUCTION TO MEDICAL VISUALIZATIONSYSTEMS
DICOM
Digital Imagingand Commun icationsin Medicine
It is a standard developed by the American College of Radiology (ACR) and the National Electrical Manufacturers
Association (NEMA). The standard specifies how digital image data can be moved from system to system. In addi-
tion,Supplem ent 28 Part 14 specifies a function that relates pixel values to displayed Luminance levels and is called
Grayscale Display Function Standard.
Overview
• DICOM conformance
• Architecture of a typical medical visualization system
• Overview of Barco’sDICOM THEATRE®
• Introduction to MGP configuration

6.1 DICOM conformance

Need for standardization

A digital signal from an image can be reproduced objectively and accurately. However, the visual interpretation of that signal is
dependenton the characteristics of the systems displaying that image i.e. imagesproduced by the same signal may appear different
dependingon the display device. Inmedical imaging, it is important that there be a visual consistency in how a given image appears,
whetherviewed, for example, on the display monitor of a workstation, a projector or as a film on a light-box. In the absence of any
standardwhich regulates how these images are to be visually presented on anydevice, a digital image which has good diagnostic
value when viewed on one device could look very different and have greatly reduced diagnostic value when viewed on another
device.
Accordingly,PS 3.14 was developed to provide mapping of digital image values into a given range of Luminance. The mapping
or relationship between digital values and display Luminance produces better visual consistency in how that image appears on
diverse display devices. The relationship that PS 3.14 defines between digital image values and displayed Luminance is based
uponmeasurements and models of human perception over a wide range of Luminanceand thus independently of the nature of the
presentation device.
Itis also not d ependent upon user preferences but uses a DICOM Presentation Lookup Table.
Asystem is DICOM-compliant when it respects a predefinedrelationship (PS3.14) between digital input signal
values and display Luminance.

6.2 Architecture of a typical medical visualization system

LUT
LookUp Table. A table containing the displays output values (L uminance) in function of the input signal (amplitude)

System components

Basicallya m edical visualizationsystem may contain:
• Calibration/Control unit
• Feedback unit
• Display unit

System Principal

Aclosed loop system insures a stable control system by means of a feedback signal being the L uminance at display level, and gets
ridof possible drift (caused mainly by aging and external conditions) in the displayed Luminance value.
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