  Using coded aperture, for localization of radioactive hot-spots, results in
enhanced efficiency and under certain configurations wide Field of View (FOV).
We present a coded aperture assembly technique which can be restructured
easily, as well as the reduction of the intrinsic noise of coded apertures
constructed with this technique, when they localize spatially extended
{\gamma}-emitters. Specifically, Modified-Uniformly-Redundant-Array (MURA)
coded apertures are structured by embedding lead spheres in a matrix of
positions machined inside a transparent medium such as acrylic glass, resulting
in an advantageous transparent to opaque area ratio and thus an improved
detection efficiency. This configuration also induces a systematic,
element-wise, noise on the Point-Spread-Function (PSF) of the correlation
matrix. When imaging with these apertures extended hot-spots, a penumbra
phenomenon occurrs and reduces this intrinsic noise, in the way a kernel filter
does. Fast-Fourier-Transform (FFT) is used to analyze the effect of this
phenomenon on the correlation matrix and to explain the maximization of its
Signal-to-Noise Ratio (SNR) for certain extent of the hot-spots. Simulations
have been used for the detailed study of the SNR dependence on the dimensions
of the hot-spot, while experiments with two 99mTc cylindrical sources with 11mm
and 24mm diameter, respectively and 1.5 MBq activity each, confirm the
reduction of the intrinsic noise. The results define the way of optimization of
the imaging setup for the detection of extended hot-spots. Such an optimization
could be useful for example in the case of lymph nodes or thyroid remnant
imaging in nuclear medicine. Finally, we propose a kernel filter, derived by
the Auto-Correlation-Function (ACF), to be applied on PSFs with high intrinsic
noise, in order to eliminate it.
