核素显像法估测不同条件下甲状腺模型体积计算方法的探讨

目的 探讨在核素平面显像条件下,Allen法和椭球体法对估测不同体积、不同放射性活度甲状腺模型体积的影响.方法 向甲状腺气球模型内注入不同体积和不同放射性活度的99Tcm O4- 溶液,并置入有机玻璃制成的颈部模型中,内充稻米模拟甲状腺颈部软组织吸收,进行核素平面显像.用Allen法和椭球体法在不同本底扣除水平下计算甲状腺模型体积,并将其与实际体积相比较,计算误差.结果 在99TcmO4-溶液为7.4和18.5MBq条件下,当甲状腺模型体积为20～30 ml时,用Allen 法,本底扣除20％,测量值误差最小,其相对误差均值为10.04％,误差范围为-19.23％～11.25％；当模型体积为40～80 ml时,用椭球体法,本底扣除20％,测量值误差最小,其相对误差均值为13.06％,误差范围为-21.41％ ～39.45％；当模型体积为90～110 ml时,用Allen法,本底扣除20％,测量值误差最小,其相对误差均值为8.12％,误差范围为- 11.05％～ 6.66％.在37.0和74.0 MBq条件下,当甲状腺模型体积为20～30 ml时,用Allen法,本底扣除20％,测量值误差最小,其相对误差均值为5.30％,误差范围为-1.25％～-11.73％；当模型体积为40～80 ml时,用椭球体法,本底扣除20％,测量值误差最小,其相对误差均值为11.74％,误差范围为- 30.36％～9.23％；当体积为90～ 110 ml 时,用Allen法,本底扣除15％,测量值误差最小,其相对误差均值为7.21％,误差范围为- 13.76％～1.46％.结论 用核素平面显像估测甲状腺模型体积时,体积大于90 ml或小于40 ml时用Allen 法,本底扣除20％时(体积大于90 ml、活度为37.0和74.0 MBq时本底扣除15％),测得的体积误差较小；体积在40～ 80 ml时,利用椭球体法,本底扣除20％,测得的体积误差较小.

Evaluation of thyroid volume estimation methods using radionuclide imaging under different condi-tions

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. 99TcmO/ 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 the neck soft tissue, and then underwent planar SPECT scans. Thyroid volumes were calculated with background correc- tion and compared with the true value to determine the measurement error. Results When the thyroid radi- oactivity 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 measure- ment 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 de- duction. 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 ra- dioactivity 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.