Collimatorless Coincidence Imaging

Several radionuclides used in nuclear medicine emit multiple photons per decay in near coincidence. Other researchers have explored combining electronics which can detect these coincident arrivds with various collimator designs and with time-of-flight information. However, our computer simulations indicate that coincidence detection alone may be sufficient. The coincidence detector was modelled as a square 10x10 array of 2x2x4m.m CdTe crystals without collimators. Monte Carlo methods were used to shulate data sets that would be generated by continuous objects embedded in uniform backgrounds. Least-squares minimization was used to reconstruct images from this data. Results indicate that both low-contrast objects and low-count images can be reconstructed. Since the coincidence count rate from distant sources is small, background from such sources is effectively suppressed. Several additional geometries which incorporate t!! concept of collimatorless coincidence imaging are included.