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Display and printing devices

Introduction

Display and printing devices are critical parts of the medical imaging system for digital modalities including CR and DR, digital mammography, CT, MRI, ultrasound, and nuclear medicine. It is critical that the appropriate displays be used, that these be calibrated using a photometer and the appropriate test patterns, and that they be located in an area with controlled, low ambient illumination. Film, or hard-copy, images must be an accurate representation of the image on the display.

Important Principles

The primary concern regarding displays is that both the resolution and gray scale be adequate to present the information in the image to the physician. This means that most computer-based displays are inadequate for this purpose. Displays specifically designed as medical image displays must be used. Such displays have sufficient resolution (number of pixels) and the ability to display appropriate gray scale.

Printing devices are also critical and must be designed for this purpose. Paper printing devices are not acceptable in that the gray scale reproduction is inadequate for the proper display of medical images. The key to an appropriate film image is that printing device-film combination can display the same gray scale information as the electronic display. This must be evaluated as part of acceptance testing, and periodically as part of the display and printing device quality control program.

The SMPTE test pattern was developed in 1985 for this purpose and is still in use today (see Gray, et al., below). The AAPM also provides test patterns (see AAPM TG 18 Report, below) including a comprehensive TG18 pattern.

Introduction to References

The primary reference for displays is the AAPM Task Group 18 report entitled "Assessment of Display Performance for Medical Imaging Systems" and includes downloadable test patterns. In Quality Control References, Gray, in the paper entitled "Multiformat Video and Laser Camera Acceptance Testing (and Quality Control)" provides information on acceptance testing and quality control of printing devices.