DICOM Calibration of Commercial Off-The-Shelf (COTS) display devices for use in radiotherapy

Abstract

In a modern, distributed radiotherapy environment image evaluation is becoming increasingly common at office desktop computers, many of which will be equipped with inexpensive Commercial Off-The-Shelf (COTS) display devices. To ensure consistency of image interpretation it is important to achieve consistency of display device performance. 15 displays (4 different models from 2 manufacturers) were characterised and the potential for their calibration against the DICOM Greyscale Standard Display Function (GSDF) explored. Each display’s luminance output was measured as a function of grey-level using a calibrated LXChroma photometer (IBA Dosimetry, Germany) with an automated sequence of greyscale images. A modification to the graphics card look-up table was calculated to adjust system performance to match the GSDF and the measurements were repeated. Prior to calibration there was considerable variation in performance across displays, including between those of the same model and manufacturer. The max luminance and max/min luminance ratio ranged from 94–401 cd/m2 (m = 213 cd/m2, sd = 95 cd/m2) and 85–1005 (m = 228, sd = 223) respectively. Initially, no display matched the GSDF to within the ‘secondary class’ limit of ±20% across all light levels, with the error being between 0.2 and 63.0%. Following calibration, all displays but one were within ±15% of the GSDF, with the outlier being +21% at a single measurement point. Care must be taken when deploying COTS displays because of initial variability in performance. However, performance can be successfully standardised through calibration against the GSDF. When appropriately calibrated, high quality yet relatively inexpensive COTS displays may offer a suitable alternative to traditional, expensive ‘medical grade’ display devices.