LIMITATIONS OF CRANIOCAUDAL TL-201 AND TECHNETIUM-99M-SESTAMIBI MAMMOSCINTIGRAPHY

Previous studies with Tl-201 and Tc-99m-sestamibi (MIBI) have used lar ge 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 perfo rm craniocaudal scintigraphy for direct comparison with mammography. O f the 46 patients studied, 20 had Tl-201 imaging alone and 26 had comb ined Tl-201 and MIBI imaging. LFOV (40 cm) breast and axillary images also were obtained. Visual and quantitative analyses of tumor uptake w ere performed. Results: The SFOV camera with nonparallel collimation s howed variable Tl-201 and MIBI normal breast activity. This was partly due to significant scatter from cardiac and abdominal activity. Overa ll, Tl-201 had a sensitivity of 53%, which was 67% for tumors greater than or equal to 1.5 cm and 20% for tumors less than or equal to 1.5 c m. MIBI sensitivity was 90% (9/10) for lesions greater than or equal t o 1.5 cm. Specificity was 93% for Tl-201 and 83% for MIBI. There was n o significant difference in Tl-201 (1.76 +/- 0.55) and MIBI (1.82 +/- 0.95) tumor uptake ratios (p = 0.75). Conclusion: Technetium-99m-MIBI was more sensitive than Tl-201 for imaging lesions > 1.5 cm. Craniocau dal positioning minimized the camera-to-breast distance but did not in crease Tl-201 detection of tumors <1.5 cm and increased background bre ast activity due to scatter.