Enrico Dolazza

Optimization of operational conditions for direct digital mammography detectors for digital tomosynthesis

Amorphous selenium (a-Se) flat-panel digital mammography detectors are being investigated for tomosynthesis, which poses tremendously challenges on the detector temporal and low dose performance. Our previous investigation has demonstrated that a-Se detectors provide adequate temporal performance (lag and ghosting) for tomosynthesis, however its detective quantum efficiency (DQE) at 1 mR (1/10 of average exposure in screening mammography) was only ~1/3 of the value at 10 mR due to electronic noise. Before engineering methods can be developed to overcome this problem, optimization of imaging parameters, such as x-ray spectrum and anti-scatter grid, can greatly improve the detector performance at the low dose used in tomosynthesis. The purpose of this paper is to determine the optimal x-ray spectrum and whether an anti-scatter grid is beneficial in tomosynthesis. The SNR of a 200 μm microcalcification within the breast was calculated as a function of x-ray spectra. Two target materials (Mo and W) were used. The density and thickness of the breast were varied. The scatter to primary ratio behind the breast with and without grid was calculated. The detector performance of a state-of-the-art a-Se digital mammography detector with 85 micron pixel size was incorporated in the calculation of SNR. The total breast dose was kept constant at 1.6 mGy. Our results showed that for tomosynthesis with 11 acquisition views, the optimal kVp is at least 2-3 kVp higher than the optimum for screening mammography. In the extreme case of an 8 cm dense breast, the optimal spectrum was 39 kVp (W/Rh), which was 9 kVp higher than the optimal kVp when detector noise is negligible. W/Rh was found to be the optimal target filter combination for all breast thicknesses (2-8 cm). Our results also showed that grid has no clear advantage even for breast thickness of 8 cm.

Ultrasound beam softening compensation system

The disclosed ultrasound system processes ultrasound signals having centroid frequencies that decrease as a function of time. The system includes transducers for receiving the ultrasound signals and generating electrical signals representative thereof. The system further includes data samplers for sampling the electrical signals with a sampling frequency. A controller controls the sampling frequency so that it decreases according to a function of time and the centroid frequency.

Optimal Quantization Of Noisy Signals

Physical signals acquired, quantized and processed in imaging systems are inherently noisy. Considering the source signal and noise statistics when designing a quantizing and processing system leads to a number of general and practical results. The theory and application of these techniques leads to an optimal bit-efficient quantization format with a number of interesting properties. Applying these can have beneficial effects on hardware costs arithmetic processing and data compression.

NEW TRENDS IN X-RAY CT IMAGING

Remarkably fast evolution of the diagnostic X-ray Computed Tomography (CT) in the past decade from single slice axial scanning to 64- slice helical imaging was driven by achievements in the areas of X-ray generation and detection, and data processing. We analyze in detail how the new imaging requirements translate into performance improvements of the Data Measuring System (DMS) of a CT scanner. This includes the x-ray detector, and the associated front-end electronics. Specifically, the paper enters in the requirements for the scintillator materials (crystalline, and ceramic), as well as for the photodetectors, including the new application of the back-illuminated silicon photodiodes. This paper also presents the new trends in data acquisition electronics, and high density optoelectronic packaging used in modern multislice DMS. Finally, the authors attempt to predict the future development of medical X-ray CT imaging, based on their professional experience, and imagination.

Feasibility of Amorphous Selenium Based Photon Counting Detectors for Digital Breast Tomosynthesis

Amorphous selenium (a-Se) has been incorporated successfully in direct conversion flat panel x-ray detectors, and has demonstrated superior image quality in screening mammography and digital breast tomosynthesis (DBT) under energy integration mode. The present work explores the potential of a-Se for photon counting detectors in DBT. We investigated major factors contributing to the variation in the charge collected by a pixel upon absorption of each x-ray photon. These factors included x-ray photon interaction, detector geometry, charge transport, and the pulse shaping and noise properties of the photon counting readout circuit. Experimental measurements were performed on a linear array test structure constructed by evaporating an a-Se layer onto an array of 100 μm pitch strip electrodes, which are connected to a 32 channel low noise photon counting integrated circuit. The measured pulse height spectrum (PHS) under polychromatic xray exposure was interpreted quantitatively using the factors identified. Based on the understanding of a-Se photon counting performance, design parameters were proposed for a 2D detector with high quantum efficiency and count rate that could meet the requirements of photon counting detector for DBT.

The Bell-Spline, A Digital Filtering / Interpolation Algorithm

The paper describes and analyzes the Bell-Spline, a new algorithm that performs combined filtering and interpolation of a digital data set. In Digital Image Processing, the Bell-Spline algorithm can be effectively used to magnify or demagnify images of any integer or non-integer factor. Because of its inherent capability to filter the spatial frequencies of the image being interpolated, the algorithm can be tuned so as to prevent apparent loss of dynamic contrast of highly magnified images, or so as to minimize spatial aliasing of images that are demagnified or magnified by a small non-integer factor. The Bell-Spline algorithm performs the combined filtering and interpolation of an original two-dimensional pixel array with few operations per interpolated pixel. It is therefore suitable, and in fact has been used, for real-time image processing applications.

Advanced X-ray Detectors for Volumetric CT

The rapid evolution of X-ray computed tomography (CT) in the past decade, from single slice axial scanning to 256-slice helical imaging, was driven by remarkable progress in X-ray generation and detection and by continuously lower cost of high speed computation. In this paper, we present the characteristics of the X-ray detectors required for todays multi-slice CT scanners suitable for cardiac applications. In particular, the parametric requirements for isotropic, solid-state, scintillator based, X-ray detectors and their associated electronics used in volumetric CT imaging are described.