Quantitative Variation of Time-Activity Curve Derived Parameters with Regional Variation of Background Region of Interest, in Salivary Scintigraphy: A Retrospective Comparative Evaluation

ABSTRACT

Aim and Objective: Quantitative analysis of time-activity curve (TAC) derived from 99mTc-pertechnetate salivary glandscintigraphy, used in the evaluation of salivary gland function, is almost always corrected for background count. The objectiveof this study was to (a) Examine the effect of the alteration of anatomical position of the background region of interest (ROI) onthe (1) semi-quantitative parameters, i.e., upslope (Us) and stimulated downslope (Ds), derived from TAC and (2) on minimumand maximum pixel counts of pixel histogram of background ROI. (b) Examine the effect of minimum and the maximum pixelcounts of the background ROI on the values of Us and Ds.Materials and Methods: In this retrospective study, 16 patients were included who had undergone 99mTc-pertechnetatesalivary scintigraphy for various reasons but had normal salivary scintigraphy reports. Three different sets of background indifferent anatomical positions were chosen (i) A pair of supraclavicular background ROI, (ii) an isolated central rectangularbackground ROI in brain, and (iii) an isolated suprathyroid ROI. We then calculated two important semi quantitative parameters,i.e., Us and Ds from the TAC of the salivary glands. Individual TAC was generated against each set of the above-mentionedbackgrounds. Individual pixel histogram was also generated against each TAC. Minimum and maximum pixel count of thegenerated background pixel histograms was identified. Comparative studies were made among the afore-mentioned variables.Results and Conclusion: The values of Us and Ds derived from respective background corrected TAC matched well amongeach other irrespective of the altered anatomical positions of the background ROI. The minimum pixel counts per second (CPS)of the background pixel histogram varied with the change in anatomical position of the background ROI but it did not affect thevalues of Us and Ds. In contrast, the maximum pixel CPS of the background pixel histogram varied inversely with the valuesof Ds, although the value of Ds, showed no variation with the change in position of the background ROI.