IMAGE VIEWING CONDITIONS

7.5. IMAGE VIEWING CONDITIONS

7.5.1. Luminance and homogeneity of the viewboxes

7.5.1.1. Scope — Objective: To verify that the viewboxes provide adequate viewing conditions for mammography;

— References [3, 4, 15]; — Minimum frequency: At acceptance, annually, and after changes.

7.5.1.2. Instrumentation

Light meter (photometer) to measure luminance (range: 100–7000 cd/m 2 ).

7.5.1.3. Methodology (1) Assess the need for replacing defective fluorescent tubes, noting lack of cleanliness, colour of the tubes and

the viewbox screens, vibrations, etc. 23 (2) Record the information on the data collection sheet. (3) Select five measurement points (one point should be centrally located and the other four should be located

towards the corners of the viewbox), at least 50 mm away from the edges. (4) Place the light meter in contact with the surface of the viewbox at each selected point. (5) Measure the luminance at each point. Record the values on the data collection sheet. (6) Repeat for each viewbox in use.

7.5.1.4. Calculation procedure In a single viewbox or single panel of a viewbox bank, select the central luminance value (L c ) and the most

discrepant reading recorded (L disc ). Apply the following equation:

Maximum deviation (%) = 100 disc

(1) For viewboxes consisting of several panels or for viewboxes adjacent to one another: the maximum deviation between the central luminance value of any panel, L cx , and the calculated mean of the central luminance of all panels, L mean , is found using the equation:

Maximum deviation (%) L = 100 cx - L mean (5)

L mean

7.5.1.5. Interpretation of results and conclusions Tolerances: (1) Luminance:

Acceptable: Maximum luminance for each panel: >3000 cd/m 2 (nit);

23 It is recommended that an inventory of the viewboxes in the institution be maintained, noting their location and age.

(2) Luminance uniformity: Acceptable: <30% maximum deviation for different areas of a single viewbox or single panel in a viewbox bank and <15% maximum deviation between central luminance of panels in a viewbox bank or between adjacent viewboxes.

7.5.1.6. Recommendations and corrective actions (1) In case of detecting abnormalities during the visual inspection, contact the person in charge of the

maintenance service. (2) If the luminance level is below the required level or a lack of uniformity exists that surpasses the tolerance, replace the fluorescent tubes in the poorly performing viewboxes as soon as possible. (3) Triphosphor or quadphosphor tubes are recommended because of their increased luminance output. If possible, all tubes should be replaced in a viewbox or viewbox bank at the same time to ensure uniformity. It is advisable to purchase fluorescent tubes in one batch to ensure that the colour matches between the tubes.

7.5.2. Interpretation room ambient illumination

7.5.2.1. Scope

— Objective: To verify that the interpretation room has adequate viewing conditions for mammography; — References [3, 4]; — Minimum frequency: At acceptance, annually, and after changes.

7.5.2.2. Instrumentation Light meter (photometer) to measure illuminance (range: 1–1000 lx).

7.5.2.3. Methodology (1) Place the photometer at a distance of 0.5 m from the previously turned off viewbox 24 , directed towards the

environmental lights, and measure the background light levels. (2) Record the value on the data collection sheet.

7.5.2.4. Interpretation of results and conclusions Tolerances: Room illuminance:

Achievable: 10 lx; Acceptable: 50 lx.

7.5.2.5. Recommendations and corrective actions If the area illumination conditions are greater than the recommended values, contact the person in charge

of the maintenance service to modify the illumination of the area.

24 If there is more than one viewbox, check that all of them are turned off.