Tc-99m DTPA renal scintigraphy using deconvolution analysis with six functional images of the mean time to evaluate acute pyelonephritis.

In 38 children with proved P-fimbriated Escherichia coli acute pyelonephritis, Tc-99m DTPA dynamic renal scintigraphy in the zoom mode using deconvolution analysis was performed, and the results were compared with those of Tc-99m DMSA scans. From the dynamic study, six functional images of the mean time were generated. Each functional image was analyzed separately to search for focal areas of increased mean time within the kidney contour, especially over the kidney parenchyma. Time-activity curves from these areas were generated and analyzed. Tc-99m DMSA scintigraphy showed generalized or focal decreased uptake in 32 (41.8%) kidneys, and deconvolution analysis of Tc-99m DTPA scintigraphy revealed pathologic renographic curves in 58 (77.6%) kidneys. Prolonged whole-kidney and normal renal parenchymal transit times (dilatation without obstruction) were found in 38 (50%) kidneys, whereas prolonged whole-kidney and renal parenchymal transit times (dilatation with obstruction) were observed in 20 (27.6%) kidneys. Separate analysis of each of the six functional images of the mean time showed focal areas of increased mean time in the kidney parenchyma of 11 kidneys. In five cases, time-activity curves from these areas showed a sharp increase of activity on the descending part of the curve, which might reflect the return of urine from the collecting system into kidney cortex (i.e., intrarenal reflux). These results showed that in a urinary tract with acute pyelonephritis, urodynamic changes may lead to obstructive nephropathy and intrarenal reflux. Tc-99m DTPA renal scintigraphy in the zoom mode using deconvolution analysis with six functional images of the mean time has proved to be a valuable method to evaluate acute pyelonephritis, thus allowing dynamic and morphologic analysis of the urinary tract at the same time.

Determination of small objects from pinhole scintigrams.

This study assessed the possibility of measuring the linear dimensions of small structures using pinhole scintigraphy. A number of glass objects were made with a spherical, cylindrical or conical shape. Their maximum dimensions (diameters and heights) were 3.5-22.5 mm. These glass objects were filled with 131I, placed inside a plastic neck phantom and imaged using a gamma camera equipped with a pinhole collimator. The source-to-collimator distance was varied from 2 to 12 cm. An algorithm for image segmentation (threshold selection) was used to divide the image into object and background. On the segmented image, the number of non-zero pixels in the direction of the principal axes was multiplied by the appropriate calibration factor to obtain the linear dimensions of the object. Spatial resolution of the pinhole collimator, expressed as the full-width at half-maximum (FWHM), varied from 8 to 10 mm for the range of source-to-collimator distances examined. We found that, for dimensions up to 1.5 x FWHM, finite spatial resolution affects the accuracy of measurement. Non-linear correlation between true and calculated dimensions was used to take the latter into account. Our results are now being used to improve quantitation of remnant thyroid tissue masses for the calculation of radioiodine ablation doses.

Radioiodine uptake in thyroid cancer patients after diagnostic application of low-dose 131I.

The aim of this study was to investigate the influence of the diagnostic administration of 74 MBq 131I on subsequent uptake of therapeutic radioiodine in thyroid cancer patients. Retention measurements were performed using a whole-body counter in 24 patients 6 weeks after total thyroidectomy. Profile scans were performed 2, 24, 48 and 72 h after the administration of the diagnostic dose and 72 h after the administration of the ablation-therapeutic dose (4.4 GBq). The mean ( +/- S.D.) effective half-life of the diagnostic dose in thyroid remnants was 40.3 +/- 23.0 h. The uptake in the thyroid remnants of the subsequent ablation dose 72 h after administration was 30.4 +/- 19.8% of that predicted from the diagnostic study. The greater reduction in uptake was associated with the longer half-life of iodine and higher uptake in the thyroid remnants at 24 h, with a longer interval between surgery and administration of the diagnostic dose and a shorter period between administration of the diagnostic and ablation doses. Our results show that a diagnostic dose of 74 MBq 131I markedly reduces thyroid uptake of an ablation dose of 131I. This should be taken into account during radiation dose planning whenever a quantitative dosimetric study is to be performed.