engleski

Determination of small objects from pinhole scintigrams

This work investigates the possibilities of measuring the linear dimensions of small structures by pinhole scintigraphy. For this purpose a series of glass objects were made with spherical, cylindrical and conical shape. Their maximum chord lengths (diameters and heights) were from 3.5-22.5 mm. These glass objects were filled with 131-I activity, placed inside the plastic neck phantom and imaged by the gamma camera equipped with pinhole collimator. Source-to-collimator distance was varied from 2-12 cm. Algorithm for image segmentation (threshold selection) was used to divide image into object and background. In the segmented image, number of nonzero pixels in the direction of principal axes was multiplied with the appropriate calibration factor to obtain the linear dimensions of the object. Spatial resolution of the pinhole collimator, expressed as the full-width-half-maximum (FWHM), varied from 8-10 mm for the range of source-to-collimator distances examined. It was found that for dimensions up to 1.5xFWHM, finite spatial resolution affects the accuracy of measurements. Nonlinear correlation between true and calculated dimensions was used to take the latter into account. The results of this work are now being used to improve quantitation of remnant thyroid tissue mass in dosimetric calculation for radioiodine ablation.

pinhole scintigraphy; thyroid

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