Limitations of craniocaudal thallium-201 and technetium-99m-sestamibi mammoscintigraphy.

Previous studies with 201 Tl and 99m Tc-sestamibi (MIBI) have used large field of view (LFOV) cameras not optimized for breast imaging. The purpose of this study was to compare these agents and to determine if a small field of view (SFOV) camera designed to minimize the camera-to-breast distance could improve tumor detection. Methods : A 28-cm (SFOV) camera was fitted with slant-hole and diverging collimators to perform craniocaudal scintigraphy for direct comparison with mammography. Of the 46 patients studied, 20 had 201 Tl imaging alone and 26 had combined 201 Tl and MIBI imaging. LFOV (40 cm) breast and axillary images also were obtained. Visual and quantitative analyses of tumor uptake were performed. Results : The SFOV camera with nonparallel collimation showed variable 201 Tl and MIBI normal breast activity. This was partly due to significant scatter from cardiac and abdominal activity. Overall, 201 Tl had a sensitivity of 53%, which was 67% for tumors ≥1.5 cm and 20% for tumors ≤ 1.5 cm. MIBI sensitivity was 90% (9/10) for lesions ≥ 1.5 cm. Specificity was 93% for 201 Tl and 83% for MIBI. There was no significant difference in 201 Tl (1.76 ± 0.55) and MIBI (1.82 ± 0.95) tumor uptake ratios (p = 0.75). Conclusion : Technetium-99m-MIBI was more sensitive than 201 Tl for imaging lesions ≥ 1.5 cm. Craniocaudal positioning minimized the camera-to-breast distance but did not increase 201 Tl detection of tumors <1.5 cm and increased background breast activity due to scatter.