3-D Contrast-Detail Analysis for Dedicated Emission Mammotomography

An observer based 3D contrast-detail study is performed in an effort to evaluate the limits of object detectability for a dedicated CZT-based SPECT mammotomography imaging system under various imaging conditions. A novel, geometric contrast-resolution phantom was developed that can be used for both positive ("hot") and negative contrasts ("cold"). The 3 cm long tillable tubes are arranged in six sectors having equal inner diameters ranging from 1 mm to 6 mm with plastic wall thicknesses of <0.25 mm, on a pitch of twice their inner diameters. Scans using simple circular trajectories are first obtained of the activity filled tubes in a uniform water filled cylinder, first with no background activity, and then varying the rod:background concentration ratios from 10:1 to 1:10. The rod phantom is then placed inside a non-uniformly shaped breast phantom and scans are again acquired using both simple and complex 3D trajectories for similarly varying contrasts. Scan times are adjusted to account for radioactive decay, and both low and high noise data is obtained. An iterative OSEM reconstruction algorithm is used to reconstruct the data. Images are evaluated by six independent readers, identifying smallest distinguishable rod for each concentration and experimental setup. Results indicate that, using the SPECT camera having 2.5 mm intrinsic pixels, the mean detectable size was ~3.1 mm at 10:1 ratio, degrading to ~5.5 mm with the 2.5:1 concentration ratio. Furthermore, there was little statistically significant difference (p < 0.05) between cylinder vs. breast, simple vs. complex trajectories, or whether the rods appeared hot (10:1) or cold (1:10), indicating that data acquisition with the mammotomography system is quite robust.