Spatial resolution reconstruction method

The X-ray microtomograph used was a "Skyscan-1074 X-ray scaimer" (Skyscan, Belgium). The X-ray source operates at 40 kV and 1 mA. The detector is a 2D, 768 x 576 pixels, 8-bit X-ray camera with a spatial resolution of 41 pm. The sample, whose maximum size was a few cm, can be either rotated in a horizontal plane or moved vertically in order to get 2D scans at different vertical positions. The minimum vertical distance between two scans is 41 pm. The reconstruction of two-dimensional slices from the object was achieved by a classical back projection method. 

Reconstruction method used Choice of filters with a selected cutoff frequency in the filtered backprojection reconstruction method may introduce additional degradation of the spatial resolution of the scanner. For example, a filter with a too high cutoff value introduces noise and thus degrades spatial resolution. An error (KT) due to the reconstruction technique is usually a factor of 1.2-1.5 depending on the method (Huesman, 1977). 

Wu T, Zhang J, Moore R, et al (2004) Digital tomosynthesis mammography using a parallel maximum-likelihood reconstruction method. Proc SPIE 5368 1-11 Yang K, Kwan AL, Boone JM (2007) Computer modeling of the spatial resolution properties of a dedicated breast CT system. Med Phys 34 2059-2069... 

More work is stiU necessary to identify optimal trade-offs between improved image quality and scanning times. Furthermore, an iterative approach to scan protocol development will have to take into consideration methods which can accommodate image reconstruction noise and increased or decreased spatial resolution. 

A poor spatial resolution is an inherent feature of electrical methods. This is due to the fact that the electrodes are of finite size as well as due to the so-called soft field effects present in the image reconstruction methods and described with reference to equation (2) and (3). It may be expected, however, that in future imaging speed could increase further thanks to better measurement electronics. Perhaps 1000 frames per second would be a reasonable expectation. 

A number of experimental parameters have to be optimized in order to obtain the best SPECT image. These include attenuation, scatter, linearity of detector response, spatial resolution of the collimator and camera, system sensitivity, minimization of mechanical movements, image slice thickness, reconstruction matrix size and filter methods, sampling intervals and system deadtime. In a hospital, calibrating and monitoring these functions are usually performed by a Certified Nuclear Medicine Technician or a medical physicist. 

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