Performance characteristics of a new pixelated portable gamma camera

Objectives To characterize the performance characteristics of Ergo (Digirad, Poway, CA), a new commercially available pixelated portable gamma camera system.

Methods The Digirad Ergo consists of 11,520 elements of 3 mm x 3 mm CsI(Tl) crystals with a thickness of 6 mm that are coupled to silicon photodiodes. The detector has a pixel size of 3.31x3.24 mm and was evaluated with LEAP and LEHR collimators. The flood-field uniformity for Tc-99m and Tl-201was assessed with fillable flood phantoms. Energy spectra were acquired for Tc-99m, In-111, Tl-201 and Ga-67 to evaluate energy linearity and energy resolution. Spectral fits were performed to calculate the energy photopeaks and resolutions. The pixel size and multiple-energy spatial registration was evaluated by measuring mixed Tc-99m/Tl-201 point sources placed at known distances apart. The system sensitivity was measured according to the NEMA NU1-2007 standard for both LEAP and LEHR collimators at 10 cm from the surface of the collimators. The system resolution without scatter was measured for both LEAP and LEHR using Tc 99m filled capillary tubes located at 0, 2, 4, 6, 10, and 12 cm away from the surface of the collimator. Line profiles across the Tc-99m line sources were fitted to a Gaussian function to estimate the spatial resolution (mm-FWHM).

Results All isotope-collimator pairs demonstrate good flood field uniformity with integral uniformity ≤ 4.9% and differential uniformity ≤ 3.1% for all pairs. The system demonstrated energy linearity with <1% and an energy resolution of 8.0% at 140 keV. The pixel sizes were measured to be 3.23x3.18 mm and multiple-energy spatial registration was measured to be within 3.3 mm (or 1 pixel). The system sensitivity at 10 cm was measured to be 231.3 cpm/µCi for LEAP and 128.5 cpm/µCi for LEHR. The system resolution was observed to vary linearly with distance away from the collimator and was measured to be 8.3 mm and 9.8 mm at 10 cm for LEHR and LEAP, respectively.

Conclusions The performance characteristics of the Digirad Ergo system suggest excellent imaging capabilities for a portable general purpose gamma camera system