Low-dose digital radiographic device “Siberia” based on a multistrip ionization chamber was developed in Budker Institute of Nuclear Physics. Originally, the detector was filled with Xe gas under 10bar pressure, however, the latest study showed that Kr filled detector at 20bar has higher signal-to-noise ratio (SNR) than Xe one. The main factor affecting SNR is amplitude fluctuation of detected signal. Kr has lower value of K-shell binding energy and less K-shell fluorescence yield than Xe gas. It leads to less distortion of registered X-ray spectra and better energy localization. As a result the detector has better channel shape and higher DQE value.

The new effective one-dimensional detector for digital scanning radiography is presented. The progress in the design of low-noise electronics allowed the Multistrip Ionization Chamber to be used as the X-ray detector. The detector has been designed for use in the Low-dose Digital Radiographic Device “Siberia” instead of a multiwire proportional chamber. The working gas is Xe under 12atm pressure. The main detector parameters are as follows: total number of channels, −1024; channel size, −0.4×0.4mm2; space resolution, −1.25lp/mm; contrast sensitivity, −1%; dynamic range, −480; surface dose for chest image, −3 to 5mR.

Two types of one-dimensional X-ray detectors for scanning radiography are presented. One of them is a fast Multi Wire Proportional Chamber (MWPC) operating in direct photon-counting mode. The MWPC parameters: efficiency - 30%, width of channel - 0.6 mm, total number of channels - 640, maximum counting rate per chamber - 3 x 10(8) counts/s. Patient irradiation effective dose from lung radiography is 7 mu Sv. Since 1997, the radiographic device based on MWPC went into mass production and 60 devices were in operation in Russian hospitals to the end of 1999. However, progress in design of the low noise electronics allowed to use the Multistrip Ionisation Chamber (MIC) instead of MWPC. The MIC parameters: efficiency close to 80%, width of channel - 0.4 min, total number of channels - 1024. Application of MIC has some advantages over MWPC. MIC has higher counting rate, higher spatial resolution, low sensitivity to gas impurity and lower cost. The electronics noise is equivalent to signal from 4 photons. (C) 2001 Elsevier Science B.V. All rights reserved.

A detector with an angular aperture of 160° based on multi-wire proportion chamber is presented. The detector can work either in full-aperture mode or in scanning mode with restricted aperture. In the first one, which is used for the investigation of fast-running processes, angular resolution is 0.05°. In the other mode for high resolution powder diffraction, angular resolution is 0.002°. The count rate is 1MHz per channel. The detector operates in the “movies” mode with as many as 8000 frames and a minimum frame time of 10μs.

Вениамин Александрович Сидоров (к семидесятилетию со дня рождения), Балакин В.Е., Барков Л.М., Диканский Н.С., Кругляков Э.П., Кулипанов Г.Н., Онучин А.П., Пархомчук В.В., Скринский А.Н., Тихонов Ю.А., Хабахпашев А.Г., Хриплович И.Б., Чириков Б.В.

We describe a digital x-ray imaging device with a one-dimensional multiwire proportional chamber used as the detector. The device works in direct counting mode. In combination with high quantum efficiency, zero intrinsic background and pixel size of 0.6 mm it allows significantly lower irradiation doses and improved image quality for some types of radiographic study. At present the device is officially certificated for medical use in Russia. It is produced industrially in Russia, and several tens of such installations are already operating in

In this paper we consider two types of gaseous detectors for radiography. The first one, the Multiwire Proportional Chamber, is used at present as a part of the digital radiographic system. It works in counting mode, has a quantum efficiency of 30% and a spatial resolution of 0.6 mm. Our new detector, the Multistrip Ionisation Chamber, is filled with Xe at 10 atm., has a quantum efficiency up to 70% and a spatial resolution of 0.4 mm. This method with integration of collected charge allows to avoid the problems of counting rate and gas ageing and considerably reduces the cost of electronics.

We describe a digital x-ray imaging device with a one-dimensional multiwire proportional chamber used as the detector. The device works in direct counting mode. In combination with high quantum efficiency, zero intrinsic background and pixel size of 0.6 mm it allows significantly lower irradiation doses and improved image quality for some types of radiographic study. At present the device is officially certificated for medical use in Russia. It is produced industrially in Russia, and several tens of such installations are already operating in hospitals.

The multiwire proportional chamber (MWPC), operating in a direct photon-counting mode, is used as the basis of 1D and 2D X-ray detectors. The 1D detector used in our scanning radiographic systems is serially produced. Its counting rate is about 200 MHz, its spatial resolution 0.6 mm, the number of channels is 640. The 2D detector, designed for diffraction structural researches on synchrotron radiation at the storage ring VEPP-3, is being commissioned now. Its characteristics are: 5 MHz, 1.5 mm, 65536 channels. The second 1D detector (10 MHz, 75 μm, 3300 channels, σ = 150 μm) is made for the same purposes. A third 1D detector with a registration angle of 60° (500 MHz, 0.6 mm, 1900 channels) is under development. All the detectors operate in a frame-by-frame mode and are free (except 2D) of parallax error.

The paper outlines a digital radiographic device which records radiation by scanning with a one-dimensional multiwire proportional chamber connected on-line to a computer. The device drastically reduces a dosage load on patients, improves the diagnostic potentialities of projectional radiography, yields quantitative diagnostic information, creates special diagnostic programmes, has fast-access and fire-safe archives. The device may be used for general-purpose radiographic examinations and it has advantages when used instead of conventional fluorographs.

Application of MultiWire Proportional Chambers (MWPC) and MicroStrip Gas Chambers (MSGC) in medical radiography is discussed. These detectors are capable of detecting X-rays in counting mode with high efficiency, thus giving essential dose reduction compared to film/screen techniques. This was demonstrated on several Digital Radiographic Devices (DRD) with one-dimensional MWPC and scanning in the orthogonal direction. Effective pixel sizes of 1 mm and 0.5 mm for different devices with highly parallel readout systems has been achieved. The counting rate capability of DRDs is similar to 500 kHz/pixel, which is enough to get high statistics of X-rays with a short exposure. Dose saving factors from 1 to 2 orders of magnitude for several common examinations were demonstrated.Further development of this approach can be made with MSGC which reproduce operation of MWPC in a much smaller scale. First tests of prototype chambers with 200 mu m pitch of strips at high pressure have shown the possibility to reach a gain of similar to 10(4) in a 6 bar Xe mixture. A proper choice of substrate material permits one to avoid charging problems at high fluxes. These features allow, one to build a counting device with 0.2 mm pixels for the detection of X-rays of 20-60 keV.

We present results from an evaluation of a significantly improved version of the Siberian Digital Radiographic Device (SDRD). The SDRD is already in clinical use in Novosibirsk and Moscow where it produces images of high diagnostic value at considerably lower doses than conventional film-screen combinations. It uses a fast multiwire proportional chamber with highly parallel readout as a detector. Improvements in the readout system have given a reduction by a factor of two in the pixel size. We have used well established methods to compare imaging performance of the new SDRD with the old version as well as with a film-screen combination used in routine clinical practice in the UK. At the same level of exposure the threshold contrast for objects of the order of the pixel size is two times better for the new SDRD than for the old one, and the minimum size of objects visible in the image is two times smaller (0.25 mm) for the new system than for the old SDRD (0.5 mm).

The Siberian digital radiographic device (SDRD) is in clinical use in Novosibirsk and Moscow where it produces images of high diagnostic value at considerably lower dose levels than conventional film-screen combinations. The authors have made contrast-detail measurements to compare its imaging performance with film-screen systems used in clinical practice in the UK. They have also compared clinical doses for Russian SDRD examinations with doses for the equivalent examinations in the UK. The SDRD performs better than the UK film-screen systems for large low-contrast objects at all exposure levels, and requires lower doses, by up to two orders of magnitude, when compared for a range of common examinations.