title: EVALUATION OF THYROID TO BACKGROUND RATIOS AND COMPARISON OF VARIOUS SCINTIGRAPHIC MEASUREMENTS AND THEIR CORRELATION TO SERUM T4 IN HYPERTHYROID CATS.
abstract: Thyroid-to-salivary ratio and percent dose uptake are the most widely recognized scintigraphic measurements. Recently, the thyroid-to-background ratio has been proposed as an alternate method. However, this method has not been validated. The purpose of this observational, cross-sectional, prospective study was to determine the location of a background region of interest (ROI) that is most reflective of blood pool activity. We also hypothesized that the thyroid-to-background ratio using this background ROI would be a better predictor of thyroid function. Fifty-six cats presented to the Virginia-Maryland College of Veterinary Medicine seeking radioiodine therapy for hyperthyroidism were enrolled in this cross-sectional study to evaluating thyroid-to-background ratio. A blood sample for measuring plasma radioactivity was collected at the time of scintigraphy. The plasma radioactivity was compared to the background ROIs in eight anatomic regions. Scintigraphic measures of thyroid-to-background and thyroid-to-salivary ratios, and percent dose were then compared to serum T4 . The heart ROI was most closely correlated with plasma pertechnetate activity (r = 0.70). Percent dose uptake was most closely correlated with serum T4 (r = 0.74), followed by thyroid-to-salivary ratio (r = 0.66) and thyroid-to-background ratio using the heart ROI (r = 0.59). Thyroid-to-background ratio using the heart background ROI is a good predictor T4 but percent dose uptake and thyroid-to-salivary ratio proved to be better predictors of T4 than any of the thyroid-to-background ratios.
authors.affiliation: Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, 24061.
authors.forename: Ann
authors.initials: A
authors.lastname: Bettencourt
authors.affiliation: Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, 24061.
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Daniel
authors.affiliation: Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, 24061.
authors.forename: David
authors.initials: D
authors.lastname: Panciera
authors.affiliation: Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, 24061.
authors.forename: Marti
authors.initials: M
authors.lastname: Larson
authors.affiliation: Laboratory for Study Design and Statistical Analysis, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, 24061.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Werre
mesh_terms: D000818:Animals; D002415:Cats; D003430:Cross-Sectional Studies; D005260:Female; D006980:Hyperthyroidism / Q000532:radiotherapy / Q000662:veterinary*; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008297:Male; D011446:Prospective Studies; D011877:Radionuclide Imaging / Q000662:veterinary*; D013670:Sodium Pertechnetate Tc 99m / Q000378:metabolism; D013974:Thyroxine / Q000097:blood*
chemical_list: D007457:Iodine Radioisotopes; D013670:Sodium Pertechnetate Tc 99m; D013974:Thyroxine
keywords: feline; hyperthyroidism; pertechnetate; quantitative analysis; thyroid scintigraphy; thyroid-to-background ratio