SPECT imaging with off-set detector system: comparison of sampling angles 2, 4 and 6 degrees

We evaluated an off set reconstruction method for single photon emission computed tomography (SPECT), and compared it with the conventional on set reconstruction method, using sampling angles of 2, 4, and 6 degrees.

A triple-detector system was used. In the off-set acquisition, sampling angles of the opposite detector were shifted 1/2 of the sampling angles of 2, 4, and 6 degrees. For example, when projection data were acquired every 6-degrees (sampling angle = 6 degrees), the projection angles were at 0 degrees, 6 degrees, 12 degrees, and 174 degrees with one detector, and 177 degrees, 183 degrees, 189 degrees, and 357 degrees with the other, opposite, detector. The conventional on set reconstruction images were compared with an off set reconstruction for a pool phantom of uniform concentration, a hot rods phantom, a myocardial phantom, and a human study.

The off set reconstruction method was better at all three sampling angles. FWHM (mm) were 11.02 at off-set versus 11.17 at on-set (sampling angle 2 degrees), 11.13 at off-set versus 11.48 at on-set (sampling angle 4 degrees), and 11.24 at off-set versus 11.64 at on-set (sampling angle 6 degrees), respectively. In human myocardium SPECT, visualization of the interventricular septum and cardiac cavity was improved.

Off set reconstruction by means of filtered back projection will be an efficient sampling mode, having a larger number of effective projection angles.