[en] We characterized the spectral response of CdTe sensors with different pixel sizes – namely 75, 150 and 300 $\mathrm{\mu }$m – bonded to the latest generation IBEX single photon counting ASIC developed at DECTRIS, to detect monochromatic X-ray energy in the range 10–60 keV. We present a comparison of pulse height spectra recorded for several energies, showing the dependence on the pixel size of the non-trivial atomic fluorescence and charge sharing effects that affect the detector response. The extracted energy resolution, in terms of full width at half maximum or FWHM, ranges from 1.5 to 4 keV according to the pixel size and chip configuration. We devoted a careful analysis to the Quantum Efficiency and to the Spectral Efficiency — a newly-introduced measure that quantifies the impact of fluorescence and escape phenomena on the spectrum integrity in high-$Z$ material based detectors. We then investigated the influence of the photon flux on the aforementioned quantities up to $180\cdot 10$⁶ cts/s/mm² and $50\cdot 10$⁶ cts/s/mm² for the 150 $\mathrm{\mu }$m and 300 $\mathrm{\mu }$m pixel case, respectively. Finally, we complemented the experimental data with analytical and with Monte Carlo simulations – taking into account the stochastic nature of atomic fluorescence – with an excellent agreement.

[en] We have measured the tensor analyzing power of d-⁴He elastic scattering at θ_d=150 in the energy range from 30 to 52 MeV. In this region the analyzing power is large, and the process can be employed as a standard to calibrate the tensor polarization of deuteron beams. (orig.)

[en] PILATUS systems are well established as X-ray detectors at most synchrotrons. Their single photon counting capability ensures precise measurements, but introduces a short dead time after each hit, which becomes significant for photon rates above a million per second and pixel. The resulting loss in the number of counted photons can be corrected for by applying corresponding rate correction factors. This article presents a Monte-Carlo simulation, which computes the correction factors taking into account the detector settings as well as the time structure of the X-ray beam at the synchrotron. For the PILATUS2 detector series the simulation shows good agreement with experimentally determined correction factors for various detector settings at different synchrotrons. The application of more accurate rate correction factors will improve the X-ray data quality at high photon fluxes. Furthermore we report on the simulation of the rate correction factors for the new PILATUS3 systems. The successor of the PILATUS2 detector avoids the paralysation of the counter, and allows for measurements up to a rate of ten million photons per second and pixel. For fast detector settings the simulation is capable of reproducing the data within one to two percent at an incoming photon rate of one million per second and pixel.

[en] The recent growth of the applications of positron emission tomography modality has led to a drastic increase in the number of units installed in western countries, prompting public health authorities to define a strategy concerning acceptance and regular tests (i.e. status tests and stability tests) to be performed on these systems. In parallel, standards concerning the qualification of PET systems have been updated (introduction of body scan characterization conditions) and appeared to be useful to set legal requirements, in spite of the fact that this is not their goal. The aim of this study is first to choose a set of tests described in the standards to define measurements to be performed at the acceptance of the systems after the regular maintenance (at least once every six months) and for assuring the stability of the systems. To verify the feasibility from technical and time requirements points of view, the quality assurance programme proposed has been applied on PET systems (Philips Gemini and GE Discovery LS). This study will present the feasibility and time requirements of the quality assurance programme proposed based on measurements performed independently from manufacturers. Introduction. In its Ordinance related to the use of the unsealed radioactive sources (November 1997), the Swiss Public Health Authority requires the supplier to carry out an acceptance test on all imaging devices used in the field of nuclear medicine before they can be used on patients. Moreover, a maintenance procedure of the imaging device has to be performed at least every six months by properly trained staff. This maintenance has to be followed by a status test that assures the integrity of the system before it can be used for further clinical applications. Daily and weekly stability tests under the responsibility of the users of the system are also defined. According to this Ordinance, all the measurements required for the acceptance and status tests should follow the international standards set by either the NEMA (National Electrical Manufacturers Association) or IEC (International Electrotechnical Commission). In order to set the list of tests required to accept a PET unit to be used on patients and to assure its stability over time, a working group has been created by the Swiss Public Health Authority involving manufacturers and medical physicists. On the basis of the two standards recently published within the framework of the qualification of PET (NEMA-NU-2, 2001 and IEC 61675-1, 1998), this group has proposed a set of recommendations which will be presented in this paper. The results of the measurements performed on two PET systems (Philips Gemini and GE Discovery LS) will be reported. Content of the tests. The background documents of this work are the standards NEMA NU-1994 and NEMA NU- 2001. Table 1 summarizes the tests required in the framework of the acceptance and status tests (RT: acceptance (or reception) tests and ST: Status tests (six month frequency). Conclusion This introduction of the proposed protocol should allow an objective qualification of the systems. However, the main problem that remains to be solved is to decide whether (a) ¹⁸F has to be provided by the centre to the manufacturers staff, who should then perform NEMA type tests or (b) if these tests have to be performed by in site medical physicists

[en] Like in the field of radiology, digital systems are also becoming the standard in the field of nuclear medicine. This offers not only the possibility to process, transmit and archive data from patients more easily but also to introduce quantitative measurements for quality controls. In this framework standards concerning the qualification of gamma camera systems have been updated and appeared to be useful to set legal requirements, in spite of the fact that this is not their goal. The aim of this study was first to choose a set of tests described in standards to define measurements to be performed at the acceptance of the systems, after the regular maintenances (at least once every six months; status test) and for assuring the stability of the systems. To verify the feasibility, from the point of view of technical and a time requirements, the quality assurance programme proposed has been applied on three gamma camera systems. The results of this study show that, based on international standards, new requirements concerning the quality assurance of the gamma camera of the Swiss Public Health Authority make it necessary to slightly modify some procedures to reduce the time required for the acceptance and status tests. In the Ordinance related to the use of unsealed radioactive sources (November 1997) the Swiss Public Health Authority requires the supplier to carry out a reception test on all imaging devices used in the field of nuclear medicine before they can be used on patients. Moreover, a maintenance procedure of the imaging device has to be performed at least every six months by properly trained staff. This maintenance has to be followed by a status test that assures the integrity of the system before it can be used for further clinical applications. Daily and weekly stability tests, under the responsibility of the users of the system, are also defined. According to the Swiss Ordinance, all the measurements required for the acceptance and status tests should follow International standards set by either the National Electrical Manufacturers Association (NEMA) or the International Electrotechnical Commission (IEC). In practice, it appeared that the standards available at that time were not sufficiently precise to allow the technical staff from the manufacturers to perform these tests. Thus, acceptance and status tests performed were manufacturer dependent and could not allow the comparison of performances of different systems. This study presents these recommendations, shows their feasibility, evaluates the time and the material required and proposes slight modifications to simplify a few measurements. The background document of this work is the standard NEMA NU-1. The tests required in the framework of reception and status test (RT: acceptance (or reception) test and ST: Status test (six month frequency) are summarized. These new requirements will permit a uniform qualification of the gamma camera systems. A set of minimal acceptance tests is now available and requires two and a half hour acquisition time per head. For status test, the acquisition time can be reduced to one hour and a half per head, taking into account that the longer test (intrinsic homogeneity) is often required in the process of the maintenance. The main problem encountered during this study is the manipulation of very high activities when dealing with the assessment of the counting rate behaviour. To reduce exposure, manufacturer staff should be properly trained and the strict respect of the standard (let the source decrease) should be preferred since this test is only required for reception of the unit where time constraint is less of a problem. Concerning stability tests, one should control the homogeneity at least weekly and should check the picking and contamination of the system on a daily basis

[en] The rapid technical advances in computed tomography have led to an increased number of clinical indications. Unfortunately, at the same time the radiation exposure to the population has also increased due to the increased total number of CT examinations. In the last few years various publications have demonstrated the feasibility of radiation dose reduction for CT examinations with no compromise in image quality and loss in interpretation accuracy. The majority of the proposed methods for dose optimization are easy to apply and are independent of the detector array configuration. This article reviews indication-dependent principles (e.g. application of reduced tube voltage for CT angiography, selection of the collimation and the pitch, reducing the total number of imaging series, lowering the tube voltage and tube current for non-contrast CT scans), manufacturer-dependent principles (e.g. accurate application of automatic modulation of tube current, use of adaptive image noise filter and use of iterative image reconstruction) and general principles (e.g. appropriate patient-centering in the gantry, avoiding over-ranging of the CT scan, lowering the tube voltage and tube current for survey CT scans) which lead to radiation dose reduction. (orig.)

[en] This work aims at establishing a set of diagnostic reference levels (DRLs) for various types of examinations performed in diagnostic and interventional radiology. The average doses for 257 types of radiological examinations were established during the 1998 nationwide survey on the exposure of the Swiss population by radiodiagnostics. They were calculated using appropriate dosimetric models and average technical parameters. The DRLs were derived from the average doses using a multiplying factor of 1.5. The DRLs obtained were rounded and compared to the data reported in the literature. The results are in most cases comparable to the DRLs determined by the 3.-quartile method. These discrepancies registered in some cases, particularly for complex examinations, can be explained by significant differences in the protocols and/or the technical parameters used. A set of DRLs is proposed for a large number of examinations to be used in Switzerland as temporary values until a national dosimetric database is set up. (authors)

[en] Diagnostic reference levels (DRLs) were established for 21 indication-based CT examinations for adults in Switzerland. One hundred and seventy-nine of 225 computed tomography (CT) scanners operated in hospitals and private radiology institutes were audited on-site and patient doses were collected. For each CT scanner, a correction factor was calculated expressing the deviation of the measured weighted computed tomography dose index (CTDI) to the nominal weighted CTDI as displayed on the workstation. Patient doses were corrected by this factor providing a realistic basis for establishing national DRLs. Results showed large variations in doses between different radiology departments in Switzerland, especially for examinations of the petrous bone, pelvis, lower limbs and heart. This indicates that the concept of DRLs has not yet been correctly applied for CT examinations in clinical routine. A close collaboration of all stakeholders is mandatory to assure an effective radiation protection of patients. On-site audits will be intensified to further establish the concept of DRLs in Switzerland. (authors)

[en] A Monte Carlo simulation is presented, which computes the rate correction factors taking into account the detector settings and the time structure of the X-ray beam. The results show good agreement with experimentally determined correction factors. The PILATUS detector system is widely used for X-ray experiments at third-generation synchrotrons. It is based on a hybrid technology combining a pixelated silicon sensor with a CMOS readout chip. Its single-photon-counting capability ensures precise and noise-free measurements. The counting mechanism introduces a short dead-time after each hit, which becomes significant for rates above 10"6 photons s"−"1 pixel"−"1. The resulting loss in the number of counted photons is corrected for by applying corresponding rate correction factors. This article presents the results of a Monte Carlo simulation which computes the correction factors taking into account the detector settings as well as the time structure of the X-ray beam at the synchrotron. The results of the simulation show good agreement with experimentally determined correction factors for various detector settings at different synchrotrons. The application of accurate rate correction factors improves the X-ray data quality acquired at high photon fluxes. Furthermore, it is shown that the use of fast detector settings in combination with an optimized time structure of the X-ray beam allows for measurements up to rates of 10"7 photons s"−"1 pixel"−"1

[en] An EU-funded project called DOSE DATAMED has been set up to develop mutually acceptable methods for future surveys of population exposure from medical x-rays, including issuing guidance on suitable patient dose quantities and dosimetry methods. The second report from the project group deals with guidance on how to conduct population dose surveys for medical exposures to improve the comparability of results from various countries. In order to assess population exposures from medical radiology in terms of the collective or per caput effective dose, it is necessary to estimate representative mean effective doses for each type of x-ray examination that makes a significant contribution to the collective dose in a country. Suitable practical dose quantities are entrance surface dose or the dose-area product for simple radiography, the total dose-area product for examinations including fluoroscopy, and the computed tomography dose index and the dose-length product for CT examinations. Factors for converting these practical dose quantities into effective doses are provided in the report. Guidance on assessing the frequency of x-ray examinations includes the definition of 225 specific x-ray examinations and 70 broader categories of examinations, and the identification of those 20 examinations most contributing to the collective effective dose. Information on the age and sex distribution of the patients undergoing these 20 important examinations is provided to assist in relating the collective doses to the collective detriment. Simple approaches for those countries that do not have resources to make comprehensive frequency or dose surveys are provided. The uncertainties involved in various survey methods are addressed. New approaches using dose data stored in the DICOM header and information in the radiological information system (RIS) are also discussed. (author)