Calculation and usage of the thyroid to background ratio on the pertechnetate thyroid scan.
Feline hyperthyroidism is a common endocrine disorder. A single dose of 148MBq (4mCi) 131I is 95-98% effective for the treatment of hyperthyroidism in cats; however, the cause for treatment failures has not been determined. In a series of 113 hyperthyroid cats having pertechnetate thyroid scintigraphy before treatment using a standard 148MBq (4mCi) 131I dose, the thyroid to salivary gland (T:S) ratio and the thyroid to background (T:B) ratio were calculated. Results in 107 (95%) cats successfully treated were compared with results in six (5%) cats that remained hyperthyroid after treatment. T:B ratio was significantly higher for cats that had treatment failure (median 13.0, range 3.6-73.0) than for cats successfully treated (median 4.4, range 1.2-69.0) (P = 0.02), whereas there was no significant difference in their T:S ratios (P = 0.2). The T:B ratio is a new approach to evaluating the thyroid pertechnetate scan with the intent of identifying which hyperthyroid cats may fail treatment using a standard 148 MBq (4 mCi) 131 dose and which, therefore, require a higher dose.
Wallack
Seth
S
VICSD, Radiology, 7522 Clairemont Mesa Blvd., San Diego, CA 92111, USA. seth@vicsd.com
Metcalf
Michelle
M
Skidmore
Angela
A
Lamb
Christopher R
CR
D000818:Animals; D002371:Cat Diseases / Q000000981:diagnostic imaging*; D002415:Cats; D006980:Hyperthyroidism / Q000000981:diagnostic imaging / Q000662:veterinary*; D007275:Injections, Intravenous / Q000662:veterinary; D007279:Injections, Subcutaneous / Q000662:veterinary; D011877:Radionuclide Imaging; D012189:Retrospective Studies; D013670:Sodium Pertechnetate Tc 99m / Q000008:administration & dosage; D013961:Thyroid Gland / Q000000981:diagnostic imaging*; D017211:Treatment Failure; D016896:Treatment Outcome
D013670:Sodium Pertechnetate Tc 99m