Preface:

Until now, transparent iatrical image photograph is still the iatrical image transferring method with most extensive medium and highest frequency. This kind of photograph is being read via even ray penetrating through, and diagnosis information is acquired in this way. Unfortunately, it’s not been paid enough attention to the performance of the photograph viewer, as well as requirements to the viewing environment. In fact, the performance of the photograph viewer and requirements to the viewing environment are officially required to be checked by the World Health Organization (WHO). This article provides some relative information and opinion for reference.

The impact on the diagnosis information transfer by the performance of photograph viewer and viewing environment

Cao Houde

Mr. Cao Houde, author of this article, medical image technology professor, is vice director committeeman of Chinese Society of Medical Image Technology, and deputy director of “Chinese Radiology Magazine? He has taken image technology work for years, and specialized in image technology quality control and medical equipment. He enjoy special allowance issued by the State Council since 1993.

一.Current Situation of domestic film viewer

Lightness of the viewer is an important performance parameter. According to the regulation of Ministry of Health, WS2-308+83, lightness of center of the screen should be no less than 1350cd/ m2. However, during actual operation, since the daylight lamp’s lightening performance descending and the screen getting old, the lightness decrease badly. According to survey to 35 viewer in 3 medical organizations, the lightness are all less than 500 cd/m2.

二.Discussion

⑴

Under typical viewing environment, the function relation between the least recognizable density discrepancy and image surrounding density is shown in figure 1.
The abscissa is image surrounding density (Ds), and ordinate is the least recognizable density discrepancy (ΔD). When Ds increase, ΔD decrease. When Ds is about 3.0, ΔD is 0.2, and when Ds is about 2.0, ΔD is 0.08. In another word, the image contrast when Ds is 3.0 is only 1/25 of the image contrast when Ds is 2.0. therefore, high lightness viewer will no-doubt decrease the image density, and enhance the image’s contrast, and increase the efficiency of image information transition.

⑵

As of lightness, the minimum visable diameter or contrast on the imgae is around 100cd/m2.
Therefore, lightness of the viewer is required to be certainly high, to meet viewing requirement. For instance, in radiation diagnose, when the density D is 0.25-2, it is called serviceable density. In fact, for most of viewer, in the area that density is higher than 2, viewer could provide enough lightness. For the area that density is higher than 2, the lightness of the viewer should be 10000 cd/m2, normal fluorescence lamp can’t reach this level, extensive lightness fluorescence lamp with 4000-6000 cd/m2 or above is required to aid. To be pointed out, when lightness reach that level, there should be some necessary shield tools, to prevent strong light from shining into eyes. Ideal viewer’s lightness should be adjustable.

⑶Since medical image expert chronically work in front of film viewer light, they are subject to eyes fatigue, and their eyes will be hurt after years of work. Especially under 50 Hz frequency, there are 100 times light-dark shift per second for the fluorescence lamp, the stroboflash hurts eyes badly. In this case, recently, more 50 KHz high frequency viewer light was putting into use, these lights could increase diagnostic detecting percentage and reduce eyes’ fatigue.

Lumination instance for different fluorescence lamp

A.50 Hz per second, light-dark shift 100 times, stroboflash is serious.

B.5000 Hz per second, light-dark shift 100 million times, lumination is stable, no stroboflash.

⑷

Besides the above-mentioned requirements to the film viewer, there are some certain requirements to the viewing environment. For instance, lighting source of the viewing room should be white or azury. Luminosity of where film viewer locates should be 50-100Lux. There should be window curtain to shield strong sunshine from out of window.