Image quality and patient dose in computed tomography examinations in Greece

The purpose of this study is to evaluate image quality of various computed tomography (CT) scanners installed in Greece, as well as to investigate patient doses from common CT examinations. An image quality survey was performed in 44 CT scanners countrywide. The imaging performance of the systems was evaluated by measurements of certain parameters, such as image noise, spatial uniformity, high- and low-contrast resolution and slice thickness accuracy. Moreover, preliminary results of patient dose survey are presented. Concerning image quality, 80 % of the scanners were found to be in compliance with the national legislation and relative international guidelines for all the examined parameters. Weighted CT dose index and dose-length product values for chest and abdomen routine examinations were generally below the dose reference levels (DRLs) suggested by the European Commission. However, some scanners were found to deliver significantly higher doses than the suggested DRL for head routine examinations. Finally, differences in the performance among scanners of the same type and similar age were observed, pointing out the importance of frequent calibration, routine quality control and proper maintenance.     

A survey on performance status of mammography machines: image quality and dosimetry studies using a standard mammography imaging phantom

It is essential to perform quality control (QC) tests on mammography equipment in order to produce an appropriate image quality at a lower radiation dose to patients. Imaging and dosimetric measurements on 15 mammography machines located at the busiest radiology centres of Mumbai, India were carried out using a standard CIRS breast imaging phantom in order to see the level of image quality and breast doses. The QC tests include evaluations of image quality and the mean glandular doses (MGD), which is derived from the breast entrance exposure, half-value layer (HVL), compressed breast thickness (CBT) and breast tissue compositions. At the majority of the centres, film-processing and darkroom conditions were not found to be maintained, which is required to meet the technical development specifications for the mammography film in use as recommended by the American College of Radiology (ACR). In most of the surveyed centres, the viewbox luminance and room illuminance conditions were not found to be in line with the mammography requirements recommended by the ACR. The measured HVL values of the machines were in the range of 0.27-0.39 mm aluminium (Al) with a mean value of 0.33±0.04 mm Al at 28 kV(p) following the recommendation provided by ACR. The measured MGDs were in the range of 0.14-3.80 mGy with a mean value of 1.34 mGy. The measured MGDs vary between centre to centre by a factor of 27.14. Referring to patient doses and image quality, it was observed that only one mammography centre has exceeded the recommended MGD, i.e. 3.0 mGy per view with the value of 3.80 mGy and at eight mammography centres the measured central background density (CBD) values for mammography phantom image are found to be less than the recommended CBD limit value of 1.2-2.0 optical density.     

Quality control of equipment used in digital and interventional radiology

Digital and interventional radiology are increasingly important areas of radiology. Quality control (QC) of such equipment is of particular importance to avoid unnecessary high doses and to help to achieve good image quality. Within the DIMOND III project, equipment requirements and specifications for digital and interventional radiology have been formulated. A protocol for QC tests has been drafted based on various national and international recommendations. Tests are included for various parts of the imaging chain, i.e. X-ray tube and generator, X-ray tube control system, laser printer and display station, and image quality and patient dose. Preliminary tolerance levels have been set for the various tests, after initial measurements. To check the suitability of QC tests and stated tolerance levels, measurements were made at the University Hospital Gasthuisberg in Leuven for equipment used for paediatric radiology and a unit used for chest examinations. The results of the various tests are reported.     

Results of a patient dose survey on diagnostic radiology in Lithuania

One of the most effective means towards optimisation of radiation protection for patients undergoing radiodiagnostic examinations are the diagnostic reference levels. In order to ensure the effective use of these levels, they have to be set properly. National characteristics, such as the conditions of the radiological equipments, the training of the staff, the availability of quality assurance systems, etc., have to be taken into account when these levels are established. Measurements under real conditions were considered as the best tools to achieve these reference levels. With an aim to establish the Lithuanian national diagnostic reference levels, the nationwide survey of entrance surface doses received by the patients during the most typical X-ray examinations has been performed. The most common types of examinations, such as chest PA, skull PA and LAT, abdomen AP, lumbar spine AP and LAT, thorax spine AP and LAT, and hip joint AP, were included in the list of procedures under consideration. Hospitals of different size and levels using different X-ray machines were represented in the survey. The standard thermoluminescence dosemeter techniques with pellets attached to the skin of the patient in the centre of radiation field were applied. The data were analysed statistically, and the averages and 75th percentile were calculated. The results show that the Lithuanian diagnostic reference levels might be rather close to the ones promoted by the International Atomic Energy Agency and the European Commission.     

A survey of 14 computed tomography scanners in Greece and 32 scanners in Italy. Examination frequencies,dose reference values,effective doses and doses to organs

A survey of examination frequencies, dose reference values, effective doses and doses to organs involving 14 scanners from Greece and 32 scanners from Italy was carried out for the years 1999 and 2000. Examination frequencies per scanner and per year were found to be 3590 for Greece and 4520 for Italy. For the types of examinations considered, CDTI(W) and DLP measurements were taken. Also scan lengths used for the same types of examinations were monitored. For the same types of examinations effective doses were calculated by two methods, and it was found that their mean values ranged from 13.1 mSv for thoracic spine to 1.6 mSv for the brain examinations. From the data of the 14 Greek laboratories, doses to organs were calculated and it was found that the thyroid receives 50.2 +/- 19.8 mGy during a cervical spine examination while the gonads receive 17.8 +/- 6.9 mGy during a routine pelvis examination.     

Patient doses in paediatric CT: feasibility of setting diagnostic reference levels

Despite the fact that doses to paediatric patients from computed tomography (CT) examinations are of special concern, only few data or studies for setting of paediatric diagnostic reference levels (DRLs) have been published. In this study, doses to children were estimated from chest and head CT, in order to study the feasibility of DRLs for these examinations. It is shown that for the DRLs, patient dose data from different CT scanners should be collected in age or weight groups, possibly for different indications. For practical reasons, the DRLs for paediatric chest CT should be given as a continuous DRL curve as a function of patient weight. For paediatric head CT, DRLs for a few age groups could be given. The users of the DRLs should be aware of the calibration phantom applied in the console calibration for different paediatric scanning protocols. The feasibility of DRLs should be re-evaluated every 2-3 y.     

The quality of dental radiography in the Czech Republic--results of a TLD and film postal audit

Since 2002, the postal audit in dental radiography has been supplementing standard quality control (QC) tools for dental intraoral X-ray machines. An aim of the audit is to check basic X-ray machine parameters (field size, exposure reproducibility), and a quality of the whole process of diagnostic imaging (entrance surface air-kerma measurement, a check of film processing and an image quality evaluation). The standard QC tests, performed by private companies, check mainly the X-ray unit. Conversely, the audit gives better information about the patient examination practices. During the period of January 2002 to May 2004 approximately 4000 audits were performed. The results confirmed that main problems in dental radiography are due to incorrect film processing, non-optimised setting of the exposure parameters and use of obsolete X-ray machines. Only approximately 30% of performed audits were satisfactory with respect to all checked parameters.     

Patient doses in CT examinations in Switzerland: implementation of national diagnostic reference levels

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.     

Evaluation of patient exposure in computerised tomogram in Poland

The increasing number of computerised tomography (CT) procedures performed in Poland in recent years has resulted in a growing contribution of these examinations to the whole exposure of the population to ionising radiation from medical sources. (The number of CT examinations in Poland was 170,000 in 1995 and 460,000 in 1999.) An evaluation is presented of doses to patients in CT examinations performed with different types of CT unit. To evaluate the exposure to patients dose linear product (DLP) was measured using a NOMEX dosemeter with a pencil chamber (PTW, Frieburg) and the cylindrical PMMA phantoms 'head' and 'body'. CTDI values were evaluated according to current methodology as described in European Guidelines (EUR 16262). The measurements were performed for seven types of CT unit made by different companies. The CTDI values were also compared to reference levels recommended by IAEA. In conclusion it was found that the value of collective effective dose (2200 man.Sv), has increased in Poland nearly 4 times in comparison to 1995, whereas the number of CT examinations increased nearly 3 times in this period. For most of the 'controlled' CT scanners the values of CTDI in head procedures are near to or higher than the IAEA Reference Level (50 mGy); this can result from the protocols, which are chosen without a dose analysis.     

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.     

Implementation of quality assurance in diagnostic radiology in Bosnia and Herzegovina (Republic of Srpska)

Application of a quality control (QC) programme is very important when optimisation of image quality and reduction of patient exposure is desired. QC surveys of diagnostics imaging equipment in Republic of Srpska (entity of Bosnia and Herzegovina) has been systematically performed since 2001. The presented results are mostly related to the QC test results of X-ray tubes and generators for diagnostic radiology units in 92 radiology departments. In addition, results include workplace monitoring and usage of personal protective devices for staff and patients. Presented results showed the improvements in the implementation of the QC programme within the period 2001--2005. Also, more attention is given to appropriate maintenance of imaging equipment, which was one of the main problems in the past. Implementation of a QC programme is a continuous and complex process. To achieve good performance of imaging equipment, additional tests are to be introduced, along with image quality assessment and patient dosimetry. Training is very important in order to achieve these goals.     

Evaluation of organ doses in CT examinations with an infant anthropomorphic phantom

The aim of this study is to evaluate organ doses in infant CT examinations with multi-detector row CT scanners. Radiation doses were measured with radiophotoluminescence glass dosemeters set in various organ positions within a 1-y-old child anthropomorphic phantom and organ doses were evaluated from the measurement values. Doses for tissues or organs within the scan range were 28-36 mGy in an infant head CT, 3-11 mGy in a chest CT, 5-11 mGy in an abdominal-pelvic CT and 2-14 mGy in a cardiac CT. The doses varied by the differences in the types of CT scanners and scan parameters used at each medical facility. Compared with those for children of various ages, the doses in an infant CT protocol were found to be similar to or slightly smaller than those in a paediatric CT for 5- or 6-y-old children.     

Organ and effective dose evaluation in diagnostic radiology based on in-phantom dose measurements with novel photodiode-dosemeters

Organ and the effective doses of patients undergoing clinical X ray examinations of chest and abdomen were evaluated with an anthropomorphic phantom and a new dosimetry system. The system was comprised of 34 pin photodiode dosemeters placed in/on particular tissues or organs of the anthropomorphic phantom, where the tissues and organs are defined by the International Commission on Radiological Protection (ICRP) to estimate the effective doses. Dosemeter signals were acquired on a personal computer directly, and converted into absorbed doses, from which the organ and the effective doses were evaluated on the computer. Our study showed that organ doses ranged from <0.01 to 0.72 mGy in routine X-ray radiography of chest and of abdomen and from 0.07 to 55.91 mGy in routine computed tomography (CT) examinations with current multi-slice CT scanners. The effective dose observed in the chest CT examination was approximately 300 times higher than that in chest radiography.     

Assessment of effective dose in paediatric CT examinations

Current concerns focus on the high doses encountered in computed tomography (CT) examinations as they are extending towards younger and more radiosensitive patients. Previous work produced conversion coefficients for effective dose (E) from dose-length product (DLP) for four anatomical body regions applicable to any patient size. This work aims to update the earlier work, incorporating the new ICRP 2007 tissue-weighting factors and testing the methodology on modern scanners. For each age and body region, E was determined relative to DLP. Measurements were carried out on a 64-slice scanner to test this methodology. The conversion coefficients show exponential decrease with patient size. Conversion factors for the pelvis region are lower than before (30-40 %), those for the chest increased (by up to 25 %) whereas those for the head and abdomen remained fairly similar. Application of the coefficients to modern scanners verified the results, so that this methodology can be applied for a wide range of paediatric CT examinations.     

Effective dose evaluation for chest and abdomen X-ray tests

The radiation doses resulting from diagnostic X-ray examinations are routinely measured in terms of entrance skin exposure (ESE). In this study, for the purpose of radiation protection, the radiation doses received from chest and abdomen X-ray tests were evaluated in terms of equivalent dose and effective dose. The dose calculations were conducted by using the MCNP Monte Carlo code and an adult hermaphrodite mathematical phantom. The effects of both operating high voltage and projection geometry on the effective dose were investigated. The absolute values of the effective doses may be provided from the national average ESE.     

Patient-size-dependent radiation dose optimisation technique for abdominal CT examinations

Since patient doses from computed tomography (CT) are relatively high, risk-benefit analysis requires dose to patients and image quality be optimised. The aim of this study was to develop a patient-dependent optimisation technique that uses patient diameter to select a combination of CT scanning parameters that minimise dose delivered to patients undergoing abdominal CT examinations. The study was performed using cylindrical phantoms of diameters ranging from 16 to 40 cm in order to establish the relationship between image degradation, CT scanning techniques, patient dose and patient size from two CT scanners. These relationships were established by scanning the phantoms using standard scanning technique followed by selected combinations of scanning parameters. The image noises through phantom images were determined using region of interest software available in both scanners. The energy depositions to the X-ray detector through phantoms were determined from measurements of CT dose index in air corrected for attenuation of the phantom materials. The results demonstrate that exposure settings (milliampere seconds) could be reduced by up to 82 % for smaller phantom relative to standard milliampere seconds, while detector signal could be reduced by up to 93 % for smaller phantom relative to energy depositions required when scanned using standard scanning protocols. It was further revealed that the use of the object-specific scanning parameters on studies performed with phantom of different diameters could reduce the incident radiation to small size object by up to 86 % to obtain the same image quality required for standard adult object. In view of the earlier mentioned fact, substantial dose saving from small-sized adults and children patients undergoing abdomen CT examinations could be achieved through optimal adjustment of CT scanning technique based on the patient transverse diameter.     

Volume computed tomography air kerma index and image quality evaluation in Brazil

The aim of this study was to evaluate the image quality of 29 computed tomography (CT) scanners in Brazil and to perform estimations of patient dose and image quality of common CT examinations at these equipment. The volume CT air kerma indexes (C(VOL)) were estimated, using normalised weighted air kerma indexes, supplied by the ImPACT group. The image quality tests were performed using the phantom and accreditation protocol from the American College of Radiology (ACR). The C(VOL) values for head scans varied between 8.7 and 108 mGy. The Hi-res chest examinations presented C(VOL) values varying from 0.4 to 32 mGy. For abdominal scans, the estimated C(VOL) values varied between 4.1 and 94 mGy. This wide variation of air kerma between different centres is related to the scanner type and also to the scanning parameters. The results also showed that the image quality did not attend all ACR CT accreditation requirements.     

Acceptance testing and routine quality control in general radiography: mobile units and film/screen fixed systems

This study presents the findings from acceptance testing and routine quality control (QC) of general radiographic X-ray equipment in Ireland during 2006 and early 2007, including mobile X-ray units and film/screen fixed systems. Acceptance testing and routine QC of the diagnostic X-ray imaging equipment are requirements of European and Irish legislation. One hundred general radiographic X-ray systems were tested within Ireland, 73% of them failed to meet the required QC guidelines, whereby one or more faults were identified. The majority of these failures were minor ones, requiring attention by the suppliers at the next routine service. Significant faults were only identified in seven systems. The suppliers were requested to investigate these issues as soon as possible and take the necessary corrective action. A review of the QC results highlights the need to perform comprehensive acceptance and routine testing of the systems.     

Patient dose estimation for multi-detector-row CT examinations

The spread of Multi-detector-row computed tomography (MDCT) has been remarkable. Here, various organ and tissue doses were evaluated with six types of MDCT scanners in common use in Japan; using thermoluminescence dosimeters and anthropomorphic phantoms under condition of routine clinical examinations of the chest in adult and child, of the head in child and of the abdomen-pelvis in adult. Estimated lung doses and averaged effective dose in chest examinations were 19.2 +/- 2.03 mGy and 9.54 +/- 0.90 mSv for the adult and 15.7 +/- 1.88 mGy and 7.42 +/- 0.82 mSv for the child phantom, respectively. The numerical difference between effective dose and organ or tissue doses was about 2-2.5 times. For the adult abdomen-pelvis examinations, averaged effective dose was 13.0 +/- 3.72 mSv. Averaged effective dose for the child head examinations was 2.6 +/- 1.32 mSv. In one case, the dose approached 80 mGy for the brain in the head examination, giving a difference from the effective dose of 10 times or more.     

Determination of ambient and personal dose equivalent for personnel and cargo security screening

In the past few years, imaging technology using ionising radiation has been gaining in importance for the screening of goods and persons for security reasons and in order to detect contraband. For radiation protection purposes it is extremely important to know that dose persons are exposed to when passing through a personnel scanner or, as a stowaway, in a cargo scanner, so as to remain within the prescribed dose limits. Within the scope of a research project, measurements were performed on different types of personnel X-ray scanners as well as cargo X-ray scanners, using the transmission and/or the backscattering method. All scanners investigated operate with a high dose rate and use short irradiation time. Owing to this method of scanning reliable values can only be determined for the personal and ambient dose equivalents, H(p)(10) and H(*)(10), by using a specially developed measuring system. The aim of this project was to determine the range of magnitudes of doses for representative personnel and cargo X-ray scanner systems. Depending on the type of scanner, the determined dose values for personnel scanners range from 0.07 microSv to 6 microSv. Measurements and instruments used in this study are described and the dose values obtained are discussed in detail.