Cadmium Zinc Telluride (CZT) photon counting detector Characterisation for soft tissue imaging

The use of photon counting detection technology has resulted in significant X-ray imaging research interest in recent years. Computed Tomography (CT) scanners can benefit from photon-counting detectors, which are new technology with the potential to overcome key limitations of conventional CT detectors. Researchers are still studying the effectiveness and sensitivity of semiconductor detector materials in photon counting detectors for detecting soft tissue contrasts. This study aimed to characterize the performance of the Cadmium Zinc Telluride photon counting detector in identifying various tissues. An optimal frame rate per second (FPS) of CZT detector was evaluated by setting the X-ray tube voltage and current at 25 keV, 35 keV and 0.5 mA, 1.0 mA respectively by keeping the optimum FPS fixed, the detector energy thresholds were set in small steps from 15 keV to 35 keV and the Currents were set for X-ray tubes in ranges of 0.1 mA to 1.0 mA to find the relationship between voltage and current of the X-ray source and counts per second (CPS). The samples i.e., fat, liver, muscles, paraffin wax, and contrast media were stacked at six different thickness levels in a stair-step chamber made from Plexi-glass. X-ray transmission at six different thicknesses of tissue samples was also examined for five different energy (regions) thresholds (21 keV, 25 keV, 29 keV, 31 keV, and 45 keV) to determine the effect on count per second (CPS). In this study, 12 frames per second is found to be the optimum frame rate per second (FPS) based on the spectral response of an X-ray source and CPS has a linear relationship with X-ray tube current as well. It was also noted that A sample's thickness also affects its X-ray transmission at different energy thresholds. A high sensitivity and linearity of the detectors make them suitable for use in both preclinical and medical applications.

Positron Emission Tomography (PET) image enhancement using a gradient vector orientation based nonlinear diffusion filter (GVOF) for accurate quantitation of radioactivity concentration

To accurately quantify in vivo radiotracer uptake using Positron Emission Tomography (PET) is a challenging task due to low signal-to-noise ratio (SNR) and poor spatial resolution of PET camera along with the finite image sampling constraint. Furthermore, inter lesion variations of the SNR and contrast along with the variations in size of the lesion make the quantitation even more difficult. One of the ways to improve the quantitation is via post reconstruction filtering with Gaussian Filter (GF). Edge preserving Bilateral Filter (BF) and Nonlinear Diffusion Filter (NDF) are the alternatives to GF that can improve the SNR without degrading the image resolution. However, the performance of these edge preserving methods are only optimum for high count and low noise cases. A novel parameter free gradient vector orientation based nonlinear diffusion filter (GVOF) is proposed in this paper that is insensitive to statistical fluctuations (e. g., SNR, contrast, size etc.). GVOF method applied on the PET images collected with the NEMA phantom with varying levels of contrast and noise reveals that the GVOF method provides the highest SNR, CNR (contrast-to-noise ratio) and resolution compared to the original and other filtered images. The percentage bias in estimating the maximum activity representing SUVmax (Maximum Standardized Uptake Value) for the spheres with diameter > 2cm where the partial volume effects (PVE) is negligible is the lowest for the GVOF method. The GVOF method also improves the maximum intensity reproducibility. Robustness of the GVOF against variation in sizes, contrast levels and SNR makes it a suitable post filtering method for both accurate diagnosis and response assessment. Furthermore, its capability to provide accurate quantitative measurements irrespective of the SNR, it can also be effective in reduction of radioactivity dose.