title: A simple objective method of recognizing goitre during parathyroid scintigraphy.
abstract: The presence of diffuse or multinodular goitre can lead to a false negative study of 10 to 20% of parathyroid investigations when the thallium-pertechnetate subtraction technique is used. A simple quantitative index is described that aids recognition of scintiscans whose diagnostic value may be limited by goitre. The index, referred to as the thallium thyroid index (TTI), is obtained from the ratio of thyroidal thallium counts above background to the mean background count density (expressed as counts cm-2) measured in regions just above and below the thyroid image. It correlates linearly with thyroid mass over the range 7 to 50 g, and goitre is likely to adversely affect the diagnostic quality of parathyroid scintiscans for values of TTI greater than 30 cm2 (corresponding to thyroid masses exceeding 35 g). TTI is insensitive to the time of commencement of image acquisition for times between 2 to 30 min following injection of the patient, and its correlation with thyroid mass has been confirmed by independent series of scans in two centres.
mesh_terms: D000236:Adenoma / Q000000981:diagnostic imaging; D000328:Adult; D005260:Female; D006042:Goiter / Q000175:diagnosis / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010280:Parathyroid Glands / Q000000981:diagnostic imaging*; D010282:Parathyroid Neoplasms / Q000000981:diagnostic imaging; D011877:Radionuclide Imaging; D013670:Sodium Pertechnetate Tc 99m; D013793:Thallium
chemical_list: C027549:thallium chloride; D013670:Sodium Pertechnetate Tc 99m; D013793:Thallium