Joerg Kaercher

A large area X-ray imager with online linearization and noise suppression

A new large area imager for X-ray crystallography is described based on active pixel sensor technology. In order to meet the demanding requirements for crystallography the detector is designed with real time correction for reset noise, nonlinearity, spatial uniformity and bad pixels. The design of the detector is described along with its operating characteristics including noise, DQE and quantum gain. We describe new techniques to rapidly calibrate and characterize the X-ray imager.

Indirect-detection single-photon-counting x-ray detector for breast tomosynthesis

X-ray mammography is a crucial screening tool for early identification of breast cancer. However, the overlap of anatomical features present in projection images often complicates the task of correctly identifying suspicious masses. As a result, there has been increasing interest in acquisition of volumetric information through digital breast tomosynthesis (DBT) which, compared to mammography, offers the advantage of depth information. Since DBT requires acquisition of many projection images, it is desirable that the noise in each projection image be dominated by the statistical noise of the incident x-ray quanta and not by the additive noise of the imaging system (referred to as quantum-limited imaging) and that the cumulative dose be as low as possible (e.g., no more than for a mammogram). Unfortunately, the electronic noise (~2000 electrons) present in current DBT systems based on active matrix, flat-panel imagers (AMFPIs) is still relatively high compared with modest x-ray gain of the a-Se and CsI:Tl x-ray converters often used. To overcome the modest signal-to-noise ratio (SNR) limitations of current DBT systems, we have developed a large-area x-ray imaging detector with the combination of an extremely low noise (~20 electrons) active-pixel CMOS and a specially designed high resolution scintillator. The high sensitivity and low noise of such system provides better SNR by at least an order of magnitude than current state-of-art AMFPI systems and enables x-ray indirect-detection single photon counting (SPC) at mammographic energies with the potential of dose reduction.

A photon-counting large-area detector – PHOTON III

The appearance of significantly stronger third generation synchrotron sources at large scale facilities and microfocus technology using in-house sources has led to the replacement of imaging plates by CCD, CMOS and HPAD detectors. Current state-of-the-art CPAD detectors, such as the PHOTON II, deliver impressive results and have allowed the collection of the first in-house GPCR structure only a few months ago

Processing Twinned-Modulated and Composite Structures from CCD / CMOS Images

The Bruker APEX2 [1] software suite includes a full set of crystallographic programs for the solution and refinement of routine crystal structures. In addition to the standard tools required for routine problems, a number of advanced tools are also provided for analysis of non-merohedral twins and modulated structures. These tools include the CELL_NOW [2], SADABS [2] and TWINABS [2] programs and a Reciprocal Lattice Viewer with a q-vector analysis option. The Bruker SAINT [2] program is routinely used for the integration of image data collected with Bruker CCD (APEX II) or CMOS (PHOTON 100) two-dimensional detectors as part of the APEX2 software suite. SAINT has many advanced features for the processing of non-routine datasets. For example, a variety of new options have been implemented to facilitate the simultaneous integration of multiple domains for twinned and composite structures. Higher dimensional crystallography may be used to integrate modulated structures with up to three q-vectors. The output data for modulated structures may be output in either HKL5 or HKLF6 format suitable for input into the JANA2006[3] program. We will present results for one twinned-modulated structure and one composite structure to illustrate the use of the respective advanced options in SAINT to integrate images and JANA2006 to refine the structures.