LAUSR

For certain radionuclides that decay through emitting two or more gamma photons consecutively within a short time interval - called cascade gamma-rays, the location where a radiopharmaceutical molecule emits cascade gamma-rays can be identified through coincidence detection of the photons. If each cascade photon is detected through a collimation mechanism, the location of the molecule can be inferred from the intersection of the back-projections of the two photons. In this work, we report the design and evaluation of a 3-dimensional stationary imager based on this concept for imaging distributions of cascade-emitting radionuclides in radiopharmaceutical therapy. The imager was composed of two gamma-ray cameras assembled in an L-shape. Both cameras were NaI(Tl) scintillator based, one with a multi-slit collimator, the other with a multi-pinhole collimator. The field of view (FOV) was 100 mm (Ø) × 100 mm (L). We evaluated the performance of the imager through simulated and experimental studies, with radionuclide 177Lu (cascade photon emitter). The imager's coincidence detection efficiency at the center of field-of-view was 3.85×10-6, and spatial resolution was 6.65 mm. Simulated hot-rod and experimental cardiac phantom studies demonstrate expected 3-dimensional imaging capability.