E. Beuville

High resolution X-ray imaging using a silicon strip detector

The authors present the first images and an initial evaluation of a scanned-slot X-ray imaging system based on edge-on silicon strip detectors and high-speed low-noise parallel processing ASICs. The authors have demonstrated noiseless single photon counting above a minimal threshold of 7.2 keV. Edge scans show negligible cross talk between different channels in the ASIC. The Modulation Transfer Function (MTF) has been measured and found to agree with the ideal MTF for 100 /spl mu/m pixel size. The first images are obtained at very low exposures and show the high performance of the system. The authors also present a way of enhancing the X-ray flux to a slot by using a refractive X-ray lens. They believe this focusing device will significantly enhance the potential for scanned-slot X-ray imaging.

In application specific integrated circuit and data acquisition system for digital X-ray imaging

Abstract We have developed an Application Specific Integrated Circuit (ASIC) and data acquisition system for digital X-ray imaging. The chip consists of 16 parallel channels, each containing preamplifier, shaper, comparator and a 16 bit counter. We have demonstrated noiseless single-photon counting over a threshold of 7.2 keV using Silicon detectors and are presently capable of maximum counting rates of 2 MHz per channel. The ASIC is controlled by a personal computer through a commercial PCI card, which is also used for data acquisition. The content of the 16 bit counters are loaded into a shift register and transferred to the PC at any time at a rate of 20 MHz. The system is non-complicated, low cost and high performance and is optimised for digital X-ray imaging applications.

High-resolution scanned-slit x-ray imaging using a refractive lens for x-ray focusing

We are developing a slit-scanning digital mammography system with the goal of reducing radiation dose and improving dynamic range in comparison to conventional film-screen mammography. The system is based on a linear silicon detector connected to a fast parallel processing ASIC controlled from a PC. The detector system is configured from a silicon wafer such that the X-rays enter the wafer edge-on, resulting in a high efficiency over the entire range of diagnostic X-ray energies since the absorption length of the detector can be made large. An evaluation of the system gives an MTF close to that predicted theoretically for a 100-micrometer pitch pixel detector. We also propose to reduce tube-loading in the slit- scanning system with a refractive X-ray lens that can increase the incident photon flux by about 5-fold according to ray tracing simulations. Moreover the lens shapes the energy spectrum to obtain pseudo-monochromatic beam thus enhancing contrast sensitivity, for example in mammography. We estimate a scan time with the final system of the order of a few seconds for a full-field digital mammogram. Phantom images of microcalcifications and of tumor-like masses, and an initial evaluation of a scanned-slit photon-counting X-ray imaging system, are presented.

A retrospective on the LBNL PEM project.

We present a retrospective on the LBNL Positron Emission Mammography (PEM) project, looking back on our design and experiences. The LBNL PEM camera utilizes detector modules that are capable of measuring depth of interaction (DOI) and places them into 4 detector banks in a rectangular geometry. In order to build this camera, we had to develop the DOI detector module, LSO etching, Lumirror-epoxy reflector for the LSO array (to achieve optimal DOI), photodiode array, custom IC, rigid-flex readout board, packaging, DOI calibration and reconstruction algorithms for the rectangular camera geometry. We will discuss the high-lights (good and bad) of these developments.

High Resolution Mammography Using a Scanned Slit Silicon Strip Detector

It is generally believed that digital mammography is the most promising technique for early detection of breast-cancer[1]. However, there are many technological challenges associated with digital mammography. With the high resolution and low noise needed for detection of micro-calcifications and low contrast tumors, a tremendous amount of data has to be acquired and read out in a few seconds. This puts difficult constraints on electronics and the data-acquisiton system.

A digital pixel address generator for pixel array detectors

Abstract An 8×8 analog pixel array detector prototype has been constructed for characterizing a larger 50×50 digital pixel array detector (DPAD) that will be used for protein crystallography. Each detector readout element in the array consists of a preamplifier and shaper, with adjustable reset and shaping times. The readout array is bump-bonded to a Si pixel array detector and provides 64 independent analog output channels for data processing. This paper describes the digital processing electronics which is used for mapping the prototype pixel detector characteristics. The event driven digital encoding circuitry processes each photon hit by grouping each pixel into a column of 8 pixels and then grouping each column into an array of 8 columns forming an 8×8 pixel array. The logic is inexpensive and easy to implement. Results from these measurements were used as an aid in the design of the DPAD detector and DPAD ASIC.

Integrated gas microstrip and microgap chambers for a MicroTPC vertex detector

Readout devices are being developed for use in a gas based vertex detector called the MicroTPC. The readout devices will consist of either integrated microstrip or microgap detectors, These devices are unique in that they have the detector fabricated directly onto the silicon with the preamplifier and shaper electronics. This offers lower noise and higher channel density compared to conventional microstrip design, Both devices were fabricated at Hewlett Packard using a standard 0.8 /spl mu/m, 3 metal process. Integrated gas microstrip detectors have been tested and an energy resolution of 18% FWHM, an electronics noise of 80 e/sup -/ r.m.s. and a gas gain of 200 was achieved, Integrated gas microgap detectors have also been fabricated and tested but only limited success has been achieved in comparison to the microstrip detectors. These devices, in conjunction with a low mass, high resolution MicroTPC should make a vertex detector well suited for heavy-ion physics environments such as RHIC and the LHC.

New astrophysics mission for a low-energy gamma-ray burst observatory (LEGO)

We propose a new astrophysics space mission for a low energy gamma-ray-burst observatory (LEGO) that will fit the envelope of a small-explorer (SMEX) type mission. The LEGO instrument combines silicon pixel detectors with ultra-high energy resolution and a novel cost effective fine-pitch coded mask, to image the sky with sub-arcminute accuracy in the 0.3 - 30 keV range with a wide field-of-view. LEGO is well adapted to study hundreds of short transients such as gamma-ray bursts and soft gamma repeaters in the unexplored energy range below 5 keV. LEGO takes one of the next logical steps in GRB studies in the post-BeppoSAX era by attacking the astrophysics questions raised by recent discoveries of variable radio, optical, and x-ray counterparts to burst sources. In addition to monitoring the sky for gamma-ray bursts, LEGO would provide a first all-sky monitor in the 0.3 - 30 keV range. LEGO will be sensitive to all mCrab sources in the sky in a day and to 0.1 mCrab sources in a year, and thus, may provide daily light curves and sensitive spectral measurements on about 103 objects and yearly data on an order of magnitude more sources.