Evaluation of thyroid volume estimation methods using radionuclide imaging under different conditions

Objective To optimize the estimation of thyroid volume using Allen's and ellipsoid methods under different conditions including thyroid volume and radioactivity dosage.Methods Four sets of thyroid gland models were created.Ten different volumes of saline were injected to 10 balloons in each set.99TcmO4- solutions with four different radioactivity doses were injected into each set of balloons.The thyroid models were placed into a plexiglasscontainer,which was filled with rice to simulate theneck soft tissue,and then underwent planar SPECT scans.Thyroid volumes were calculated with background correction and compared with the true value to determine the measurement error.Results When the thyroid radioactivity was 7.4 and 18.5 MBq,and the thyroid volume ranged from 20 to 30 ml,the measurement error was the smallest (range:- 19.23％ to 11.25％,mean:10.04％ ) using Allen's method with 20％ of background radioactivity deduction.When the thyroid volume was in the range of 40 to 80 ml,the measurement error was the smallest (range:-21.41％ to 39.45％,mean:13.06％ ) using ellipsoid method with 20％ of background radioactivity deduction.When the thyroid volume was in the range of 90 to 110 ml,the measurement error was the smallest (range:-11.05％ to 6.66％,mean:8.12％ ) using Allen's method with 20％ of background radioactivity deduction.When the thyroid radioactivity was 37.0 and 74.0 MBq,and the thyroid volume was in the range of 20 to 30 ml,the measurement error was smallest (range:- 1.25％ to - 11.73％,mean:5.30％ ) using Allen's method with 20％ of background radioactivity deduction.When the thyroid volume was in the range of 40 to 80 ml,.the measurement error was the smallest ( range:-30.36％ to 9.23％,mean:11.74％ ) using ellipsoid method with 20％ of background radioactivity deduction.When the thyroid volume was in the range of 90 to 110 ml,the measurement error was the smallest (range:-13.76％ to 1.46％,mean:7.21％ ) using Allen's method with 15％ of background radioactivity deduction.Conclusions To optimize the estimation of thyroid volume using radionuclide imaging,Allen's method can be applied at thyroid volumes greater than 90 ml or less than 40 ml with 20％ of background radioactivity deduction; ellipsoid method can be applied when the thyroid volume is in the range of 40 to 80 ml with 20％ of background radioactivity deduction. Key words: Thyroid gland;  Models, theoretical;  Radionuclide imaging;  Volume