BACKGROUND: The aim of this study was to determine which of
the most popular colour scales used in the Xeleris processing system
(GE) should preferably be used during a clinical interpretation
of myocardial perfusion images, and to find out whether a colour
scale saturation level affects the diagnostic efficacy of the study.
MATERIAL AND METHODS: From among 100 patients in whom
a myocardial perfusion scintigraphy had been performed, a subgroup
of people referred for coronary angiography, with neither
prior history nor ECG signs of a myocardial infarction has been
selected retrospectively. This group consisted of 41 patients (14
females) in the age group 46 to 76 years. All patients underwent
two-day myocardial perfusion SPECT imaging using 99mTc-MIBI
as a radiopharmaceutical.
Reconstructed slices were interpreted in 3 colour scales:
white-red-yellow-green-blue-black with computer-assigned
thresholds (French 100%), the same French scale but without
a white colour (image maximum set manually to a border value between red and white — French w.w.), and a white-yellow-violet-
pink-blue-black scale (GEcolor), by consensus of two
experienced nuclear medicine specialists. A semiquantitative
method for evaluation of perfusion images was applied, based
on myocardium segmentation. Perfusion in each segment was
scored using a five-point system. Study interpretation (normal/
abnormal perfusion) was based on summed stress scores
(SSS), being equal/above or below a given threshold value. The
choice of optimal SSS threshold value was based on sensitivity
and specificity of the study in detection of perfusion defects
resulting from critical stenoses of main coronary arteries
RESULTS: SSS values differed among colour scales
(p < 0.00001). The lowest values were obtained for a French
100% scale (mean value = 5.0, SD = 8.0), the highest for
French w.w. (mean values = 8.1, SD = 8.7), and for GE colour
scale — mean value — 5.6, SD — 7.9. A French 100% scale
gave high sensitivity (88%), as well as specificity (83%), but
only when a low SSS threshold value of 2, hardly acceptable
for study interpreters, was used. When higher threshold values
were applied, they compromised the sensitivity of the study.
A French w.w. scale with SSS threshold values lower than
3 provided a slightly higher sensitivity (94%), but with a significant
reduction in specificity (to values below 50%). Only a threshold
value of 4 provided acceptable, but still low specificity (63%) with
preserved high sensitivity (88%). At the same time, the scale GE colour
provided indices of diagnostic efficacy with the SSS threshold
value of 3 as high as a scale French 100% with threshold value of 2.
CONCLUSIONS: A French scale (Xeleris, GE) is not the scale
of choice for the interpretation of myocardial perfusion SPECT
images. It seems that a GE colour scale is better suited for this
purpose. SSS threshold values accepted as diagnostic criteria
for the detection of myocardial perfusion abnormalities should
be suited separately for every translation table. The choice of optimal
value should be verified by results of coronary angiography.
Nuclear Med Rev 2010; 13, 2: 64–6
