Comparison of 99mTc-methoxyisobutyl isonitrile and 201T1 scintigraphy in visualization of suppressed thyroid tissue.
Both (201)TI and (99m)Tc-methoxyisobutyl isonitrile (MIBI) have been used in the visualization of suppressed thyroid tissue in patients with autonomously functioning thyroid nodules (AFTNs). It has been suggested that thyroid-stimulating hormone (TSH) control is not a major determinant of both tracers. However, the mechanism of thyroid uptake of these agents is controversial. In this study, we compared (201)TI and MIBI in the visualization of suppressed thyroid tissue in patients with a solitary toxic AFTN.


METHODS
Thirty-two patients (13 triiodothyronine [T3] and 19 T3 + levorotatory thyroxine [T4] hyperthyroid patients) with toxic AFTNs visualized on (99m)Tc-pertechnetate scanning were included in the study. All patients underwent MIBI and (201)TI thyroid scintigraphy within a 3-d interval. The scintigrams were analyzed both visually and semiquantitatively. For the semiquantitative analysis, regions of interest (ROIs) were generated over the nodule (N) and contralateral normal lobe (E), and the mean counts in each ROI were calculated.


RESULTS
The N/E uptakes (mean +/- SD) for pertechnetate, MIBI, and (201)TI were 11.37 +/- 4.53, 4.76 +/- 1.38, and 1.63 +/- 0.15, respectively, in T3 + T4 hyperthyroid patients and 9.46 +/- 3.64, 2.73 +/- 0.63, and 1.57 +/- 0.23, respectively, in T3 hyperthyroid patients. Our results showed that (201)TI uptake of suppressed thyroid tissue compared with AFTN was more prominent and significantly higher than that of MIBI for both groups of patients (P = 1.08E-05 for T3 and 6.15E-09 for T3 + T4 hyperthyroidism). There was no significant difference for either pertechnetate or (201)TI (P > 0.05) when the N/E uptakes of both groups of patients were compared. However, the N/E uptake of MIBI in T3 + T4 hyperthyroid patients was significantly higher than that in T3 hyperthyroid patients (P = 6.69E-06).


CONCLUSIONS
Clear visualization of suppressed thyroid tissue with both (201)TI and MIBI in patients with low serum concentrations of TSH suggests that TSH is not a major factor in the thyroid uptake of either agent. (201)TI is superior to MIBI in the visualization of suppressed thyroid tissue in patients with a toxic thyroid nodule. An increased rate of metabolism in the follicular cells of AFTNs in T3 + T4 hyperthyroid patients compared with that in T3 hyperthyroid patients might be responsible for the higher N/E for MIBI compared with that for (201)TI.
Department of Nuclear Medicine, Marmara University School of Medicine, Istanbul, Turkey.
T Y
TY
Erdil
C
C
Onsel
B
B
Kanmaz
B
B
Caner
K
K
Sönmezoğlu
I
I
Ciftçi
T
T
Turoğlu
L
L
Kabasakal
H B
HB
Sayman
I
I
Uslu
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000209:etiology; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D013670:Sodium Pertechnetate Tc 99m; D017256:Technetium Tc 99m Sestamibi; D013794:Thallium Radioisotopes; D013961:Thyroid Gland / Q000000981:diagnostic imaging*; D016606:Thyroid Nodule / Q000150:complications / Q000000981:diagnostic imaging*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D019275:Radiopharmaceuticals; D013794:Thallium Radioisotopes; D014284:Triiodothyronine; D013972:Thyrotropin; D017256:Technetium Tc 99m Sestamibi; D013670:Sodium Pertechnetate Tc 99m; D013974:Thyroxine