(left) Schematic view of the pinhole imaging geometry: A point source is placed in plane B at lateral position from the center. The rays enter the pinhole (with half opening angle ) at the angle and travel to the detector. (right) Illustration of the parallax effect: A ray enters the detector at the angle and is stopped in the detector material after traveling the distance . An event is recorded at a lateral displacement compared to a ray which enters the detector at an angle .
(left) Cross section of the imaging system. The FOV with diameter is depicted as the most inner gray circle. The tungsten collimator and the arrangement of the 24 detector modules are shown in the image. The FOV of a single pinhole reveals a partial view of the object which is magnified onto the detector module. (right) Side view of the imaging system. Nine detector rings are shown and the FOV of each detector ring is depicted. Pinholes in the tungsten collimator are angulated to create an area of high detection efficiency along the approximately axial extend of the object.
Detailed view of the cross section of the tungsten collimator. All 24 pinholes are shown with the FOV of the single pinholes. These FOV overlap in the center of the collimator and form an area of high detection efficiency. Detection efficiency is lowest in dark gray areas and highest in white areas. The FOV of the entire system which has a diameter of has been highlighted in the figure.
The figure shows one of the 10 tungsten cylinders which will constitute the pinhole collimator. Pinholes are obtained by machining grooves in the cylinder.
Comparison of point spread functions obtained with a round (A, C) and a square (B, D) pinhole. A and B are shown in three fold higher detector resolution than C and D which represents the detector resolution of the PSAPD.
Detection efficiency for a dual-headed SPECT system and the multipinhole PSAPD system as function of distance from the isocenter.
(A) Digital hot rod phantom with hot rods from 0.7 to . (B) Reconstruction of projection data simulated with the multipinhole PSAPD imaging system. (C) Reconstruction of projection data simulated with the dual-headed SPECT system.
Reconstructed image of the uniformity phantom (A) using the multipinhole PSAPD imaging system and (B) using the dual-headed SPECT system. (C) Standard deviation of the central volume versus number of iterations. The arrows show the minimum values of the standard deviation which is reached for multipinhole system after 15 iterations and for the dual-headed system after 17 iterations. Images (A) and (B) are reconstruction with 15 and 17 iterations, respectively.
(A) Slice through the myocardium of the MOBY mouse phantom. Same slice reconstructed from projection data simulated with (B) the multipinhole PSAPD system, and (C) the dual-headed microSPECT system.
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