A triple-head SPECT system with parallel-hole collimators of different acceptance angles.

We proposed to use three different parallel-hole collimators for a triple-head SPECT system. One of the collimators had a small collimator acceptance angle to provide ultra-high spatial resolution and the other two had larger collimator acceptance angles to achieve high counts. A new 2D reconstruction algorithm that combined the data acquired from different collimators was derived to take advantages of both high resolution and high sensitivity. The algorithm was evaluated using a computer-simulated matrix of spherical sources. For noise-free data, the accuracy (mainly determined by spatial resolution) obtained from combination of the collimator acceptance angles of 1.35, 4.05 and 6.75 degrees (or 1.35, 5.40 and 9.45 degrees) was slightly inferior to that obtained from three same LEHR collimators (with a 2.70 degrees collimator acceptance angle). This is because the modulation transfer function (MTF) resulting from three different collimators decreases more quickly at low frequencies but becomes comparable at high frequencies as compared with the MTF of the 2.70 degrees collimator. With noisy data, however, the image quality obtained with three different collimators was better than that resulting from any combinations of three same collimators. The improvement was only achieved by using the derived algorithm, while the conventional FBP algorithm did not improve image quality even with the same collimator configuration.