Performance of a novel wafer scale CMOS active pixel sensor for bio-medical imaging

X-ray imaging: A potential enabler of automated particulate detection and cake-structure analysis in lyophilized products?

The presence of particulate matter in parenteral products is a major concern since it affects the patients' safety and is one of the main reasons for product recalls. Conventional quality control is based on a visual inspection, which is a labour-intensive task. Limited to clear solutions and the surface of lyophilised products, it cannot be applied to opaque containers. This study assesses the application of X-ray imaging for detecting the particulate matter in a pharmaceutical lyophilized product. The most common types of particulates (i.e., steel, glass, lyo stopper, polymers and organics in different size classes) were intentionally spiked in vials. After optimizing all relevant parameters of the X-ray set-up, all classes of particulates were detected. At the same time, due to contrast enhancement, the inherent structures of lyophilized cake became obvious. This work addresses the potential and limits of X-ray technology in that regard, paving the way for automated image-based particulate matter detection. Moreover, this paper discusses using this approach to predict critical quality attributes (CQAs) of the drug product based on the cake structure attributes.

Cascaded systems analysis of a-Se/a-Si and a-InGaZnO TFT passive and active pixel sensors for tomosynthesis

Medical imaging systems like full field digital mammography (FFDM) and digital breast tomosynthesis (DBT) commonly use amorphous selenium (a-Se) based passive pixel sensor (PPS) direct conversion x-ray detectors. On one hand, direct conversion detectors inherently offer better resolution characteristics in terms of a higher modulation transfer function (MTF), in comparison to the indirect CsI:Tl PPS x-ray imager. On the other hand, especially at lower doses, this superior performance of the direct imager is seldom retained in its detective quantum efficiency (DQE) curves. It is well known that a-Se PPS x-ray imagers suffer from high additive electronic noise originating from the from the amorphous silicon (a-Si) thin film transistor (TFT) array that is being used in the current back-plane technology. This degrades the noise power spectrum (NPS) and subsequently the overall DQE. To address this deficiency, we propose to replace the PPS back-plane by active pixel sensor (APS) back-plane technology, which has the potential to reduce the back-plane electronic noise by amplifying the input signal, especially at low doses. The proposed APS is based on amorphous In-Ga-Zn-O (a-IGZO) TFT technology, which can offer high mobility (5-20 cm² V^-1 s^-1), low leakage current (<10^-13 A) and low flicker noise (Hooge's parameter α _H ~ 1.5 [Formula: see text] 10^-3), leading to better imager noise performance. To test our hypothesis, we used linear cascaded systems analysis to model the imaging performance (MTF, NPS and DQE) of the PPS and APS a-Se direct imagers. This model was first validated using experimentally measured data obtained for a 85 µm pixel pitch a-Se/a-Si TFT PPS imager. Using this model, we analyzed the noise performance of the direct a-Se and indirect CsI:Tl x-ray a-IGZO APS imagers at different dose and electronic noise levels. Obtained results clearly showed that lowering back-plane electronic noise can significantly improve the performance of the a-Se/a-IGZO TFT APS imager. Our simulated results showed that a higher DQE at lower radiation doses (maximum DQE of 0.6 can be achieved at an exposure level of 1 µGy) can be achieved with the a-Se detector, thereby making this combination a promising candidate for low dose applications like DBT.

Task-Based Modeling of a 5k Ultra-High-Resolution Medical Imaging System for Digital Breast Tomosynthesis

High-resolution, low-noise X-ray detectors based on CMOS active pixel sensor (APS) technology have demonstrated superior imaging performance for digital breast tomosynthesis (DBT). This paper presents a task-based model for a high-resolution medical imaging system to evaluate its ability to detect simulated microcalcifications and masses as lesions for breast cancer. A 3-D cascaded system analysis for a 50- [Formula: see text] pixel pitch CMOS APS X-ray detector was integrated with an object task function, a medical imaging display model, and the human eye contrast sensitivity function to calculate the detectability index and area under the ROC curve (AUC). It was demonstrated that the display pixel pitch and zoom factor should be optimized to improve the AUC for detecting small microcalcifications. In addition, detector electronic noise of smaller than 300 e^- and a high display maximum luminance (>1000 cd/cm ²) are desirable to distinguish microcalcifications of [Formula: see text] in size. For low contrast mass detection, a medical imaging display with a minimum of 12-bit gray levels is recommended to realize accurate luminance levels. A wide projection angle range of greater than ±30° in combination with the image gray level magnification could improve the mass detectability especially when the anatomical background noise is high. On the other hand, a narrower projection angle range below ±20° can improve the small, high contrast object detection. Due to the low mass contrast and luminance, the ambient luminance should be controlled below 5 cd/ [Formula: see text]. Task-based modeling provides important firsthand imaging performance of the high-resolution CMOS-based medical imaging system that is still at early stage development for DBT. The modeling results could guide the prototype design and clinical studies in the future.

CMOS Active Pixel Sensors as energy-range detectors for proton Computed Tomography

Since the first proof of concept in the early 70s, a number of technologies has been proposed to perform proton CT (pCT), as a means of mapping tissue stopping power for accurate treatment planning in proton therapy. Previous prototypes of energy-range detectors for pCT have been mainly based on the use of scintillator-based calorimeters, to measure proton residual energy after passing through the patient. However, such an approach is limited by the need for only a single proton passing through the energy-range detector in a read-out cycle. A novel approach to this problem could be the use of pixelated detectors, where the independent read-out of each pixel allows to measure simultaneously the residual energy of a number of protons in the same read-out cycle, facilitating a faster and more efficient pCT scan. This paper investigates the suitability of CMOS Active Pixel Sensors (APSs) to track individual protons as they go through a number of CMOS layers, forming an energy-range telescope. Measurements performed at the iThemba Laboratories will be presented and analysed in terms of correlation, to confirm capability of proton tracking for CMOS APSs.