Low dose breast imaging-comparative performance of MBI and BSGI systems

Objectives To compare the relative performance of a breast specific gamma imaging (BSGI) system and a molecular breast imaging (MBI) system for low dose imaging

Methods The BSGI system comprised a single-head multi-crystal NaI system (pixel size 3.2×3.2 mm) equipped with a hexagonal-hole (HH) lead collimator. The MBI system comprised a dual-head cadmium zinc telluride solid state detector system (pixel size 1.6×1.6 mm) equipped with either conventional HH lead collimators or registered tungsten (RT) collimators. System sensitivity, uniformity, energy and spatial resolution were measured using standard NEMA methods. A 6-cm thick contrast detail (CD) phantom with 48 hot spots (3-10 mm diameter) was used to assess contrast-noise-ratio (CNR) using background count densities equivalent to those observed in clinical studies at doses of 4mCi and 20mCi Tc-99m sestamibi

Results The BSGI and MBI systems had integral uniformities of 6.5% and 3.2% respectively. Significant energy peak drift with count rates above 5 kcps was observed with BSGI. Energy resolution for Tc-99m was 14.2% and 4.4% for the BSGI and MBI systems respectively. System sensitivity was 390 (BSGI), 334 (MBI-HH) and 968 cpm/uCi (MBI-RT). MBI was configured with RT collimators and energy window 110-154 keV for clinical studies. Sensitivity of the MBI-RT was 1216 cpm/uCi for the clinical setting. At distances of 1, 3 and 5 cm, resolution was measured at 4.1, 5.2 and 6.3 mm on the BSGI system and 3.8, 4.8 and 7.9 mm on the MBI-RT system. However with dual head, effective resolution at 5 cm dropped back to 3.8 mm on MBI-RT. Using the Rose criterion for lesion detection (CNR>3) results from the CD phantom revealed that for the BSGI system, 9 hot spots at 4mCi and 5 at 20mCi were undetectable. For the MBI-RT system, 5 hot spots at 4mCi and 3 at 20mCi were undetectable

Conclusions Over the range 0-6 cm, the MBI-RT system demonstrated comparable or better spatial resolution than BSGI while yielding a 3-fold greater sensitivity. This resulted in improved lesion detection at all doses and allows MBI to be utilized at significantly lower doses than BSGI