Bremsstrahlung imaging with the gamma camera

A conventional gamma camera is used for the external imaging of bremsstrahlung generated from pure beta-emitters such as phosphorous-32 (32P). Tomographic images of a cylindrical phantom filled with water and containing four cylindrical sources of varying diameter are recorded using two collimators with symmetrical aperture configuration but different bore-lengths. The resolution of the system is comparable to single photon emitters for both collimaters; FWHM approximately 1.8 cm and FWTM approximately 2.9 cm. An effective linear attenuation coefficient of 0.14 cm-1 for 32P, calculated from isolated spherical sources in water, is used with the post-reconstruction Chang algorithm to correct the tomographic images. The use of a broad energy window and the symmetric apertures of the collimators yields an approximately radially symmetric, shift invariant, and stationary point-spread-function with distance from the collimator face as required for the use of image restoration filters. A new filter is proposed which shares the advantages of both neural network for deconvolution and advanced nonlinear filtering for noise removal and edge enhancement. The new filter compares favorably with the Wiener for image restoration and improves the conditions for quantitative measurements with the gamma camera. In addition, its application for image restoration does not require the knowledge of the object and noise power spectra and the serious problems (ring effects and noise overriding) associated with the inverse operation encountered in the Wiener filter are avoided.