Validation of calibration schemes with sealed sources for quantitative bone SPECT/CT

Objectives Quantitative bone SPECT for clinical applications has recently advanced and accurate cross-calibration is needed. Several calibration schemes have been presented to define quantitative values using different sources under various geometric conditions. Differences in source and geometric conditions can decrease the accuracy of cross-calibration factors (CCF). The present study aimed to validate the effect of various calibration schemes using sealed 57Co and 99mTc sources.

Methods We used standard point, self-produced point-like and disk sources. Temporal variations were compared according to CCF using ^99mTc and ⁵⁷Co point sources. Variations in source shape and geometric conditions were also analyzed. We investigated the effects of the geometric conditions of the source-to-camera distance (SCD) and lateral distance on the CCF by moving the camera or source away from the origin. The CCF calculated using the simulation tool incorporated into the SPECT/CT device (Symbia, Intevo, Siemens^®) was defined as reference values.

Results /b> Temporal variation in CCF caused by the ^99mTc point source reached a maximum of > 7%. The difference between measured values and the reference value for the ⁵⁷Co point source was stable and remained within 2%. Variations in source shape indicated that the ⁵⁷Co standard point source was the most stable. The ratio (%) of deviation from the reference value increased according to the shape of disk sources, reaching a maximum of 7%. Both SCD and lateral distance decreased as a function of distance from the origin. Conclusions: Standard ⁵⁷Co point sources helped to maintain the quality of quantitative SPECT/CT imaging data. Different calibration schemes influence the reliability of quantitative values. The method of calibration for quantitative SPECT should be immediately standardized to eliminate uncertainty.

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