document: Angular disparity in ETACT scintimammography Emission tuned aperture computed tomography -LRB- ETACT -RRB- has been previously shown to have the potential for the detection of small tumors -LRB- < 1 cm -RRB- in scintimammography . However , the optimal approach to the application of ETACT in the clinic has yet to be determined . Therefore , we sought to determine the effect of the angular disparity between the ETACT projections on image quality through the use of a computer simulation . A small , spherical tumor of variable size -LRB- 5 , 7.5 or 10 mm -RRB- was placed at the center of a hemispherical breast -LRB- 15 cm diameter -RRB- . The tumor to nontumor ratio was either 5:1 or 10:1 . The detector was modeled to be a gamma camera fitted with a 4-mm-diam pinhole collimator . The pinhole-to-detector and the pinhole-to-tumor distances were 25 and 15 cm , respectively . A ray tracing technique was used to generate three sets of projections -LRB- 10 degrees , 15 degrees , and 20 degrees , angular disparity -RRB- . These data were blurred to a resolution consistent with the 4 mm pinhole . The TACT reconstruction method was used to reconstruct these three image sets . The tumor contrast and the axial spatial resolution was measured . Smaller angular disparity led to an improvement in image contrast but at a cost of degraded axial spatial resolution . The improvement in contrast is due to a slight improvement in the in-plane spatial resolution . Since improved contrast should lead to better tumor detectability , smaller angular disparity should be used . However , the difference in contrast between 10 degrees and 15 degrees was very slight and therefore a reasonable clinical choice for angular disparity is 15 degrees
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extractive_keyphrases: angular disparity small tumors image quality computer simulation spherical tumor hemispherical breast gamma camera pinhole collimator ray tracing technique image sets axial spatial resolution clinical choice
abstractive_keyphrases: emission tuned aperture computed tomography scintimammography pinhole-to-detector distances pinhole-to-tumor distances tuned aperture computed tomography reconstruction method in-plane spatial resolution