An iterative technique for the removal of artifacts caused by the near field effects of a coded aperture imaging system is presented. The technique, which we call z-Clean, first locates high energy sources within a three dimensional field of view using a least squares method and then removes the artifacts using a method similar to that of the CLEAN algorithm used in radio astronomy, but instead operating in the detector shadowgram domain rather than the final image domain. Computer simulations were performed of observations of four point sources of different intensities and at different depths from the detector. Both a continuous detector of 1 cm FWHM detection capability and a pixellated detector with 0.2 cm square pixels were investigated using a Modified Uniformly Redundant Array coded aperture of element size 0.6 cm. The efficacy of the z-Clean technique for artifact removal is demonstrated for both detector types for the three strongest sources of 100kBq, 50kBq and 10kBq using plane separations of 2 cm, 1 cm, 0.5 cm and 0.1 cm, to leave only small ghosts lying up to around 2 cm from the reconstructed source depth. For twenty trials of each observation, the three strongest sources are reconstructed no further than 0.7 cm from the closest plane with many being from 0 cm to 0.5 cm for both detector types. The depth location for all three strongest sources using both detector types is no worse than 0.5 cm from the actual source depth and is in most cases much better, being closer than 0.1 cm for the strongest source at plane separations of 1 cm, 0.5 cm and 0.1 cm. z-Clean was not able to remove the artifacts nor determine accurately the depth of the weakest source of 5kBq and in general sources that experience a phasing error are less accurately located although still better than 0.5 cm from the actual source depth for all such cases. The artifact removal and very good depth location come at the expense of an impact on the signal to noise ratio (SNR) of the sources. For the strongest source and using the continuous detector the SNR increases unexpectedly to give values higher than that for observations made only in the critical plane due to the ghosting of this source in other planes at different depths. For all other cases there is a decrease in SNR which is more marked for finer plane separations and for weaker sources.

提出了一种用于消除由编码孔径成像系统的近场效应引起的伪像的迭代技术。这项技术，我们称为z-Clean，首先使用最小二乘法在三维视场中定位高能量源，然后使用类似于射电天文学中CLEAN算法的方法去除伪影，而是采用操作在探测器阴影图域中而不是最终图像域中。对距检测器不同深度和不同深度的四个点源的观测进行了计算机模拟。使用元素大小为0.6 cm的改良均匀冗余阵列编码孔径，研究了具有1 cm FWHM检测能力的连续检测器和具有0.2 cm正方形像素的像素化检测器。对于两种最强的100kBq，50kBq和10kBq信号源的两种探测器类型，使用2 cm，1 cm，0.5 cm和0.1 cm的平面间距证明了z-Clean技术去除伪影的功效。距重建源深度约2 cm。对于每个观测值的20个试验，从最接近的平面重建0.7个最强辐射源，对于两种检测器类型，大多数重建源从0 cm到0.5 cm。使用这两种探测器类型的所有三个最强光源的深度位置均不低于实际光源深度的0.5 cm，并且在大多数情况下要好得多，在平面间距为1 cm，0.5 cm和0.5 cm时，最强光源的深度位置要比0.1 cm小。 0.1厘米 z-Clean无法消除伪影，也无法准确确定5kBq最弱信号源的深度，通常，尽管在所有此类情况下，距实际信号源深度仍优于0.5 cm，但定位相位误差的信号源的准确度较低。去除伪影和非常好的深度位置会以对信号源的信噪比（SNR）的影响为代价。对于最强的源并使用连续检测器，由于该源在不同深度的其他平面上的重影，因此SNR意外地增加，从而得到的值比仅在关键平面中进行观测的值高。对于所有其他情况，SNR的降低对于更精细的平面间隔和更弱的信号源而言更为明显。