Exposure of the Swiss population by radiodiagnostics: 2003 review.

A nationwide investigation was conducted in Switzerland to establish the exposure of the population by medical x rays and update the results of the 1998 survey. Both the frequency and the dose variations were studied in order to determine the change in the collective dose. The frequency study addressed 206 general practitioners (GPs), 30 hospitals, and 10 private radiology institutes. Except for the latter, the response rate was very satisfactory. The dose study relied on the assessment of the speed class of the screen-film combinations used by the GPs as well as the results of two separate studies dedicated to fluoroscopy and CT. The investigation showed that the total number of all medical x-ray examinations performed by GPs registered a 1% decrease between 1998 and 2003, and that the sensitivities of the film-screen combinations registered a shift towards higher values, leading to a reduction of the dose delivered by a GP of the order of 20%. The study indicated also that the total number of all x-ray examinations performed in hospitals increased by 4%, with a slight increase of radiographies by 1% but significant decrease of examinations involving fluoroscopy (39%), and a 70% increase for CT examinations. Concerning the doses, the investigation of a selection of examinations involving fluoroscopy showed a significant increase of the kerma-area product (KAP) per procedure. For CT the study showed an increase of the dose-length product (DLP) per procedure for skull and abdomen examinations, and a decrease for chest examination. Both changes in the frequency and the effective dose per examination led to a 20% increase in the total collective dose.

How to set up and apply reference levels in fluoroscopy at a national level.

A nationwide survey was launched to investigate the use of fluoroscopy and establish national reference levels (RL) for dose-intensive procedures. The 2-year investigation covered five radiology and nine cardiology departments in public hospitals and private clinics, and focused on 12 examination types: 6 diagnostic and 6 interventional. A total of 1,000 examinations was registered. Information including the fluoroscopy time (T), the number of frames (N) and the dose-area product (DAP) was provided. The data set was used to establish the distributions of T, N and the DAP and the associated RL values. The examinations were pooled to improve the statistics. A wide variation in dose and image quality in fixed geometry was observed. As an example, the skin dose rate for abdominal examinations varied in the range of 10 to 45 mGy/min for comparable image quality. A wide variability was found for several types of examinations, mainly complex ones. DAP RLs of 210, 125, 80, 240, 440 and 110 Gy cm2 were established for lower limb and iliac angiography, cerebral angiography, coronary angiography, biliary drainage and stenting, cerebral embolization and PTCA, respectively. The RL values established are compared to the data published in the literature.

Number of X-ray examinations performed on paediatric and geriatric patients compared with adult patients.

The age of the patient is of prime importance when assessing the radiological risk to patients due to medical X-ray exposures and the total detriment to the population due to radiodiagnostics. In order to take into account the age-specific radiosensitivity, three age groups are considered: children, adults and the elderly. In this work, the relative number of examinations carried out on paediatric and geriatric patients is established, compared with adult patients, for radiodiagnostics as a whole, for dental and medical radiology, for 8 radiological modalities as well as for 40 types of X-ray examinations. The relative numbers of X-ray examinations are determined based on the corresponding age distributions of patients and that of the general population. Two broad groups of X-ray examinations may be defined. Group A comprises conventional radiography, fluoroscopy and computed tomography; for this group a paediatric patient undergoes half the number of examinations as that of an adult, and a geriatric patient undergoes 2.5 times more. Group B comprises angiography and interventional procedures; for this group a paediatric patient undergoes a one-fourth of the number of examinations carried out on an adult, and a geriatric patient undergoes five times more.

[CT utilisation in Switzerland: frequency and secular trends]. / Pratique du scanner en Suisse: fréquence et évolution temporelle.

PURPOSE: This study analyzes CT examinations in Switzerland. MATERIALS AND METHODS: Using different sources (administrative data on the equipment, a 1998 nationwide inquiry into practices, and data provided by the Swiss University Hospitals of Basel, Zurich, and Lausanne), we determined the frequency of CT examinations (hospitals and private radiologists) in 1998 according to different descriptive variables and studied the progression in CT use over time. RESULTS: CT scanners increased by 7% between 1998 and 2004. The average annual number of CT examinations in 1998 was 46.3/1000 population, 3.4% of all radiological examinations in Switzerland in 1997-1998. The most frequent examination was CT of the skull (24%), while private radiology institutes perform more CTs of the spine. More CT examinations were performed for men than for women (sex ratio M/F=1.17). The average annual increase in CT in Swiss hospitals varied from 8% for Basel to 18% for Lausanne. Finally, the proportion of pediatric examinations was 5%; their numbers appear to be stabilizing. CONCLUSION: There is a significant increase in CT examinations. It is hoped that our study will heighten awareness among doctors of CT examinations in order to optimize their use.

90Sr in deciduous teeth from 1950 to 2002: the Swiss experience.

Switzerland has recorded the level of activity of 90Sr in the milk teeth of children from different regions of the country since the first atomic explosions in the atmosphere. Activity peaked at 0.421 Bq g-1 Ca at the beginning of the sixties, coinciding with the detonation of many large nuclear devices. Following the Nuclear Test Ban Treaty that ended atmospheric nuclear weapon tests, a steady and significant decrease in 90Sr activity in milk teeth has been observed-down to a value of 0.03 Bq g-1 Ca for children born in 1994. The apparent half-life of 90Sr in milk teeth is 9.8+/-3 years. With the exception of the period from 1962 to 1964, there is no correlation between the activity in the teeth of children born in a given year and the year of extraction. Between 1953 and 1992, the milk teeth of children born in Zürich county showed 16% less activity than teeth from children born in Vaud county. Dairy consumption habits might be responsible for this trend. The effect of the 90Sr deposition from Chernobyl is barely measurable in milk teeth, and no effect is seen from the five Swiss nuclear reactors. This paper emphasizes the necessity of a very high purity chemical separation of 90Sr or 90Y to determine 90Sr activity in milk teeth or other samples.

A strategy to qualify the performance of radiographic monitors.

The purpose of this work was to compare standard desktop display systems with dedicated medical display systems. The set of image tests proposed by the American Association of Physicists in Medicine (AAPM TG18) was used to assess a Philips 107S desktop display system and a Siemens medical display. Three observers performed the subjective assessment, in a non-concerted manner. The objective assessment was performed using a CCD camera according to the AAPM TG18 procedure. The results clearly demonstrate the inadequacy of standard desktop display systems in the framework of diagnostic radiology. Moreover, a good correlation between the subjective and objective assessment methods was obtained.

A comparison of the performance of modern screen-film and digital mammography systems.

This work compares the detector performance and image quality of the new Kodak Min-R EV mammography screen-film system with the Fuji CR Profect detector and with other current mammography screen-film systems from Agfa, Fuji and Kodak. Basic image quality parameters (MTF, NPS, NEQ and DQE) were evaluated for a 28 kV Mo/Mo (HVL = 0.646 mm Al) beam using different mAs exposure settings. Compared with other screen-film systems, the new Kodak Min-R EV detector has the highest contrast and a low intrinsic noise level, giving better NEQ and DQE results, especially at high optical density. Thus, the properties of the new mammography film approach those of a fine mammography detector, especially at low frequency range. Screen-film systems provide the best resolution. The presampling MTF of the digital detector has a value of 15% at the Nyquist frequency and, due to the spread size of the laser beam, the use of a smaller pixel size would not permit a significant improvement of the detector resolution. The dual collection reading technology increases significantly the low frequency DQE of the Fuji CR system that can at present compete with the most efficient mammography screen-film systems.

Performance comparison of an active matrix flat panel imager, computed radiography system, and a screen-film system at four standard radiation qualities.

Four standard radiation qualities (from RQA 3 to RQA 9) were used to compare the imaging performance of a computed radiography (CR) system (general purpose and high resolution phosphor plates of a Kodak CR 9000 system), a selenium-based direct flat panel detector (Kodak Direct View DR 9000), and a conventional screen-film system (Kodak T-MAT L/RA film with a 3M Trimax Regular screen of speed 400) in conventional radiography. Reference exposure levels were chosen according to the manufacturer's recommendations to be representative of clinical practice (exposure index of 1700 for digital systems and a film optical density of 1.4). With the exception of the RQA 3 beam quality, the exposure levels needed to produce a mean digital signal of 1700 were higher than those needed to obtain a mean film optical density of 1.4. In spite of intense developments in the field of digital detectors, screen-film systems are still very efficient detectors for most of the beam qualities used in radiology. An important outcome of this study is the behavior of the detective quantum efficiency of the digital radiography (DR) system as a function of beam energy. The practice of users to increase beam energy when switching from a screen-film system to a CR system, in order to improve the compromise between patient dose and image quality, might not be appropriate when switching from screen-film to selenium-based DR systems.

Radiation exposure in dental radiology: a 1998 nationwide survey in Switzerland.

OBJECTIVES: To measure the frequencies of dental radiological examinations in Switzerland and to determine the associated collective radiation doses. METHODS: To evaluate the frequencies, a sample of 376 dental practitioners and other institutions performing dental radiology were requested to fill in questionnaires designed to measure, amongst others, frequencies of dental radiodiagnoses according to type of examination, patient age and gender, dental specialty and type of surgery. The associated collective radiation doses were determined by multiplying the relevant frequencies with dose estimates obtained from recent measurements and calculations. RESULTS: The total number of dental examinations performed in Switzerland in 1998 was 4.1 million (581 per 1000 population). Periapical, bitewing and panoramic radiographs were the most frequent types of dental examinations. The collective dose associated with dental radiology was 71 person.Sv. This amounts to an annual average effective dose to the population of 10 muSv per caput, which is in agreement with the figures reported for countries of similar healthcare level. Various features such as the age distribution of the radiographed patients, the forms of collimators used, film consumption and the use of digital imaging systems are presented. CONCLUSIONS: Several recommendations for dose reduction are made. These include the re-evaluation of the patterns and justification for prescribing some particular types of dental examinations as well as the avoidance of unnecessary irradiation by the use of rectangular collimation and high sensitivity F-speed films.

Calibration and testing of a TLD dosemeter for area monitoring.

The response of a TLD-600/TLD-700 area dosemeter has been characterized in neutron fields around the 590 MeV cyclotron ring at the Paul Scherrer Institute (PSI). The dosemeter is based on a cylindrical paraffin moderator with three of each type of TLD chip at the centre, and is intended to use for area monitoring around accelerator facilities. The dosemeter is calibrated in terms of ambient dose equivalent using a non-moderated 252Cf neutron source. The ambient dose equivalent response has been tested in five locations where the neutron fields and dose rates have been well characterized by Bonner sphere spectrometer and active neutron monitor measurements. The different spectrum shapes and dose rates in the five locations permit the comparison of the behavior of the active and passive dosemeters in these neutron fields.

Influence of detector collimation on SNR in four different MDCT scanners using a reconstructed slice thickness of 5 mm.

The purpose of this paper is to compare the influence of detector collimation on the signal-to-noise ratio (SNR) for a 5.0 mm reconstructed slice thickness for four multi-detector row CT (MDCT) units. SNRs were measured on Catphan test phantom images from four MDCT units: a GE LightSpeed QX/I, a Marconi MX 8000, a Toshiba Aquilion and a Siemens Volume Zoom. Five-millimetre-thick reconstructed slices were obtained from acquisitions performed using detector collimations of 2.0-2.5 mm and 5.0 mm, 120 kV, a 360 degrees tube rotation time of 0.5 s, a wide range of mA and pitch values in the range of 0.75-0.85 and 1.25-1.5. For each set of acquisition parameters, a Wiener spectrum was also calculated. Statistical differences in SNR for the different acquisition parameters were evaluated using a Student's t-test (P<0.05). The influence of detector collimation on the SNR for a 5.0-mm reconstructed slice thickness is different for different MDCT scanners. At pitch values lower than unity, the use of a small detector collimation to produce 5.0-mm thick slices is beneficial for one unit and detrimental for another. At pitch values higher than unity, using a small detector collimation is beneficial for two units. One manufacturer uses different reconstruction filters when switching from a 2.5- to a 5.0-mm detector collimation. For a comparable reconstructed slice thickness, using a smaller detector collimation does not always reduce image noise. Thus, the impact of the detector collimation on image noise should be determined by standard deviation calculations, and also by assessing the power spectra of the noise.

Adult reference levels in diagnostic and interventional radiology for temporary use in Switzerland.

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 3rd-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.

Radiation exposure by radio-diagnostics in Switzerland: a pilot patient-oriented survey.

A patient-oriented survey was conducted in Switzerland with the aim to establishing the distribution of medical X-ray examinations among the population. A sample of 1235 people aged between 15 and 74 y (589 males and 637 females) was contacted. The participants were asked to give the number of medical X-ray examinations performed during the previous 12 months. Three-fourths of the sample did not undergo any medical X-ray examination during a 12 month-period, and 10% of the population underwent more than 1 medical X-ray examination in a year. These results were independent of the geographic region. The age distributions of the participants who did not undergo any medical X-ray examination and those who underwent one medical X-ray examination were similar. On the other hand, the age distribution of the participants who underwent more than one medical X-ray examination was characterised by a higher contribution from the elderly.

Quantitative characterization of edge enhancement in phase contrast x-ray imaging.

The aim of this study was to model the edge enhancement effect in in-line holography phase contrast imaging. A simple analytical approach was used to quantify refraction and interference contrasts in terms of beam energy and imaging geometry. The model was applied to predict the peak intensity and frequency of the edge enhancement for images of cylindrical fibers. The calculations were compared with measurements, and the relationship between the spatial resolution of the detector and the amplitude of the phase contrast signal was investigated. Calculations using the analytical model were in good agreement with experimental results for nylon, aluminum and copper wires of 50 to 240 microm diameter, and with numerical simulations based on Fresnel-Kirchhoff theory. A relationship between the defocusing distance and the pixel size of the image detector was established. This analytical model is a useful tool for optimizing imaging parameters in phase contrast in-line holography, including defocusing distance, detector resolution and beam energy.

90Sr, 238U, 234U, 137Cs, 40K and 239/240Pu in Emmental type cheese produced in different regions of Western Europe.

A method is presented for the determination of (90)Sr and uranium in Emmental type cheese collected in dairy plants from different European countries. Results display a significant correlation (r = 0.708 Student t-test = 6.02) between the (90)Sr content of the cheese and the altitude of grazing. The highest (90)Sr activity is 1.13 Bq kg(-1) of cheese and the lowest is 0.29 Bq kg(-1). Uranium activity is very low with a highest (238)U value of 27 mBq kg(-1). In addition, (234)U/(238)U ratio shows a large enrichment in (234)U for every location. Without any significant indication of the geographic origin of the cheese, this enrichment is believed to be due to the geological features of the pasture, soil and underground water. These results tend to prove that the contamination of milk by uranium originates principally from the water that the cows drink instead of the forage. This finding may have a great importance in models dealing with dairy food contamination by radionuclides following a nuclear accident. Also, the (90)Sr content and to a lesser extent the (234)U/(238)U ratio could be used to trace the authenticity of the origin of the cheese. (137)Cs activity is lower than the detection limit of 0.1 Bq kg(-1) in all the samples collected (n = 20). Based on natural (40)K activity in cheese (15-21 Bq kg(-1)), the decontamination factor for the alkaline cations from milk to cheese is about 20. Plutonium activity stays below the detection limit of 0.3 mBq kg(-1).

X-ray imaging of the chest in Switzerland in 1998: a nationwide survey.

The use in Switzerland of three chest X-ray imaging modalities is studied. The frequency and dosimetric aspects associated with chest radiography, chest CT, and photofluorography are investigated and the Swiss figures are compared with those of other countries. The frequencies are established by means of a nationwide survey performed in 1998, whereas the doses are determined by modelling, based on the technical parameters of the examinations. The annual frequencies of chest radiography, chest CT, and photofluorography are 201, 7, and 7 per thousand population, respectively. The standard effective doses related to these three types of examinations are 0.057, 9, and 0.13 mSv, respectively. The collective dose associated with chest X-ray imaging amounts to 606 man.Sv, representing 8.5% of the total collective dose due to diagnostic and interventional radiology. The geographic and seasonal variations, as well as the distribution with the medical specialty and with the age of the patient, are established. The Swiss results compare well with the average data published in the literature for other countries of similar health care level. Chest radiography shows a significant decrease with time. It dropped by a factor of 2 in 20 years. The conformity of the indication of chest X-ray modalities with referral guidelines is also investigated.

Dosimetric aspects of a national survey of diagnostic and interventional radiology in Switzerland.

The effective dose delivered to the patient was determined, by modeling, for 257 types of examinations covering the different modalities of diagnostic and interventional radiology. The basic operational dosimetric quantities considered were obtained from the parameters of the examinations on the basis of dosimetric models. These models required a precise characterization of each examination. The operational dosimetric quantities were converted into doses to organs and effective doses using appropriate conversion factors. The determination of the collective effective dose to the Swiss population requires a number of corrections to account for the variability of several parameters: sensitivity of the detection system, age, gender, and build of the patient. The use of various dosimetric models is illustrated in this paper for a limited number of examination types covering the different radiological modalities, for which the established typical effective doses are given. With regard to individual doses, the study indicated that the average effective doses per type of examination can be classified into three levels: (a) the weakly irradiating examinations (less than 0.1 mSv), which represent 78% of the examinations and 4% of the collective dose, (b) the moderately irradiating examinations (between 0.1 mSv and 10 mSv), which represent 21% of the examinations and 72% of the collective dose, (c) the strongly irradiating examinations (more than 10 mSv), which represent 1% of the examinations and 24% of the collective dose.

Nation-wide survey on radiation doses in diagnostic and interventional radiology in Switzerland in 1998.

A nation-wide survey on radiation doses in diagnostic and interventional radiology was conducted in Switzerland in 1998 aiming at establishing their collective radiological impact on the Swiss population. The study consisted on the one hand of surveying the frequency of more than 250 types of examinations, covering conventional radiology, mammography, fluoroscopy, angiography, interventional radiology, CT, bone densitometry, conventional tomography and dental radiology. On the other hand, for each type of examination the associated patient dose was established by modeling. The results of this study show that about 9.5 million diagnostic and interventional examinations are performed annually in Switzerland (1.34 per caput) and that the associated annual collective dose is of the order of 7100 person.Sv (1.0 mSv per caput). Switzerland is similar to other European countries in terms of the frequency of examinations and the collective dose.

Calibration of ionization chambers in air kerma length.

Pencil ionization chambers are employed for the direct determination of the computed tomography dose index (CTDI), which is used for patient dosimetry in CT examinations. The chambers are calibrated in air kerma length in a reference x-ray field. The precision of calibration is influenced by several factors which are investigated in the present work. It is shown that the best irradiation length is 50% of the chamber rated length. The reading must be corrected for a residual signal due to the irradiation of the sensitive chamber volume by scattered radiation. The origin of this radiation is identified mainly at the edges of the diaphragm limiting the useful field. The residual signal is determined by a linear fit of measurements performed at minimum of three diaphragm apertures. The optimum geometric conditions are also discussed.

Using 80 kVp versus 120 kVp in perfusion CT measurement of regional cerebral blood flow.

Perfusion CT studies of regional cerebral blood flow (rCBF), involving sequential acquisition of cerebral CT sections during IV contrast material administration, have classically been reported to be achieved at 120 kVp. We hypothesized that using 80 kVp should result in the same image quality while significantly lowering the patient's radiation dose, and we evaluated this assumption. In five patients undergoing cerebral CT survey, one section level was imaged at 120 kVp and 80 kVp, before and after IV administration of iodinated contrast material. These four cerebral CT sections obtained in each patient were analyzed with special interest to contrast, noise, and radiation dose. Contrast enhancement at 80 kVp is significantly increased (P < .001), as well as contrast between gray matter and white matter after contrast enhancement (P < .001). Mean noise at 80 kVp is not statistically different (P = .042). Finally, performance of perfusion CT studies at 80 kVp, keeping mAs constant, lowers the radiation dose by a factor of 2.8. We, thus, conclude that 80 kVp acquisition of perfusion CT studies of rCBF will result in increased contrast enhancement and should improve rCBF analysis, with a reduced patient's irradiation.