Impact of calibration methods for color medical displays on interpreting brain SPECT images

Color images are visualized on medical monitors that are adjusted by a grayscale standard display function (GSDF) or γ2.2. Although the GSDF is visually displayed as a linear graded grayscale, it does not specify how color medical images should be presented. On the other hand, the usual gamma setting for color images is γ2.2, but it has not been standardized. The color standard display function (CSDF) has recently been proposed as a standardized gamma setting for color medical monitors. However, the influence of various gamma settings on image characteristics should be determined. The present study aimed to identify differences in color-scale characteristics on nuclear medicine images displayed on medical monitors adjusted by CSDF, GSDF, and γ2.2.

Transverse normal (n = 1) and abnormal (n = 5) brain perfusion images were generated using a mathematical digital phantom. Transverse phantom and clinical brain images are shown using the clinically applied eight-color scale. Five nuclear medicine experts visually assessed phantom and clinical images using a defect severity scale that ranged from zero (no defect) to four (defect). Receiver operating characteristic curves were created and areas under the curves (AUCs) were analyzed. Defect scores for the clinical study were evaluated in the nine segments on basal ganglia slice, and defect scores were summed for each patient.

The average defect score for color A significantly differed in multiple comparison tests, but not in post hoc tests. The ranges of AUC for CSDF, GSDF, and γ2.2 were 0.86-0.94, 0.82-0.94, and 0.88-0.97, respectively. The AUCs of CSDF in all color scales did not significantly differ from other gamma settings. The summed defect scores of CSDF were similar to those of other gamma settings.

Nuclear medicine images were equally valid when adjusted by CSDF even at various gamma settings. Nuclear medicine images can be evaluated equally using any gamma setting. Nonetheless, the color gamma setting for medical monitors should be standardized.