Increasing film-focus distance (FFD) reduces radiation dose for x-ray examinations

Increasing film-focus distance (FFD) from the traditional 100 cm has been shown to be an effective method of reducing dose whilst maintaining image quality. In particular, previous work increasing the FFD from 100 to 130 cm for lumbar spine examinations demonstrated an effective dose reduction of 44%. Objective. The current study continues on from this work by investigating the dose-reducing efficacy of this FFD change for pelvis X-ray examinations. Materials and methods. Dose measurements at 100 and 130 cm using thermoluminescent dosemeters were undertaken using an anthropomorphic phantom and patients. Image quality was assessed using CEC anatomical criteria and psychophysical tests. Results. The results showed that increasing the FFD results in a reduction in effective dose of 33%, with no change in image quality. The data provided in this and previous studies demonstrate the need for rapid implementation of this simple cost-effective procedure across imaging departments, leading to an important reduction in collective dose. Conclusion. The CEC recommendation of using 115 cm FFD for a number of procedures, although useful compared with 100 cm, undervalues by a factor between 2 and 3 the potential of this dose-reducing tool.     

Patient dose, image quality and radiographic techniques for common X ray examinations in two Greek hospitals and comparison with European guidelines

The radiographic technique factors and the quality of each radiographic image for three common examinations (chest PA, pelvis AP and lumbar spine LAT) were compared with the European criteria and entrance surface dose (ESD) was measured for each radiograph in two Greek hospitals. The measurements were carried out using calibrated LiF thermoluminescence dosemeters. The patients were selected so that their weight was close to 70 +/- 10 kg and their height to 170 +/- 10 cm. Effective dose values were calculated using a PC-based Monte Carlo program. All four X ray rooms in the survey achieved mean doses well below the European reference doses. However the mean doses in the X ray rooms differed by a factor of about 3.     

Patient dose measurements in diagnostic radiology procedures in Montenegro

It was the aim of the study presented here to estimate for the first time patient dose levels in conventional diagnostic radiology in Montenegro. Measurements of patient dose in terms of entrance surface air kerma (ESAK) and kerma-area product (KAP) were performed on at least 10 patients for each examination type, in each of five randomly selected health institutions in Montenegro, so that a total of 872 patients for 16 different examination categories were included in the survey (817 patients for 1049 radiographies and 55 fluoroscopy patients). Exposure settings and individual data were recorded for each patient. Mean, median and third quartile values ESAK of patient doses are reported. The estimated mean ESAK values obtained are as follows: 4.7 mGy for pelvis anteroposterior (AP), 4.5 mGy for lumbar spine AP, 7.8 mGy for lumbar spine lateral (LAT), 3.1 mGy for thoracic spine AP and 4.3 mGy for thoracic spine LAT. When compared with the European diagnostic reference values, the mean ESAK for all studied examination types are found to be below the reference levels, except in chest radiography. Mean ESAK values for chest radiography are 0.9 mGy for posteroanterior (PA) projection and 2.0 mGy for LAT. The results exhibit a wide range of variation. For fluoroscopy examinations, the total KAP was measured. The mean KAP value per procedure for barium meal is found to be 22 Gy cm(2), 41 Gy cm(2) for barium enema and 19 Gy cm(2) for intravenous urography. Broad dose ranges for the same types of examinations indicate the necessity of applying practice optimisation in diagnostic radiology and establishment of national diagnostic reference levels.     

Estimation of patient doses for common diagnostic X-ray examinations in Latvian hospitals, analysis of radiographic techniques and comparison with European guidelines

This article deals with the estimation of doses received by patients undergoing radiological examinations in order to establish dose reference levels (DRLs) in Latvia. Several large hospitals, small hospitals and private practices were selected for patient dose measurements. The measurements were carried out using calibrated thermoluminiscence dosemeters attached to the patient's skin. Exposure parameters and patient's data were recorded. The entrance surface doses (ESDs) to patients undergoing several common X-ray examinations (chest AP/PA, chest LAT, lumbar spine AP/PA, lumbar spine LAT and pelvis) were measured. Data concerning the kV(p) settings, used type of films, focus-film distance and the ESD values were analysed and compared with those recommended by the European Community (EC). Among the different hospitals and private practices, discrepancies in the patient doses and techniques used for the examination were found, where the doses exceeded the EC recommended values owing to a very low kV(p) and a very low sensitivity of the screen film combinations used.     

The potential for reduction of radiation doses to patients undergoing some common X ray examinations in Tanzania

The potential for patient dose reduction in diagnostic radiology was investigated in five major Tanzanian hospitals. The aim of this study was to follow up previously reported suggestions for improved practices to achieve dose reductions. The suggestions were implemented and entrance surface dose measurement repeated by using well-calibrated LiF thermoluminescence dosemeters. The results show that dose reductions in chest PA X ray examinations ranged from 15% to 50%. For abdomen AP and pelvis AP X ray examinations, the dose reductions ranged from 24% to 73% and from 25% to 72%, respectively. The respective dose reductions for lumbar spine AP and LAT projections ranged from 4% to 58% and from 16% to 77%. Interestingly, the majority of radiographs obtained after the implementation of dose reduction measures were useful for intended diagnosis according to the opinion of radiologists. It is concluded that significant dose reductions can be achieved in the country without loss of diagnostic information. Such dose reductions also predict reductions of radiation risk to patients.     

Optimisation of image plate radiography with respect to tube voltage

PURPOSE: To find the tube voltage that results in the highest image quality per effective dose unit for chest and pelvis radiography, respectively, using image plates. METHODS: Two anthropomorphic phantoms (chest and pelvis) were imaged with several different tube voltages. The mA s settings were chosen so that the effective dose to the phantom was the same, regardless of the tube voltage, for the two examinations, respectively. The quality of the images was evaluated by six experienced radiologists using visual grading analysis. RESULTS: For both the chest and the pelvis examinations, the image quality increased when the tube voltage was reduced compared with the standard settings (125 and 70 kV for chest and pelvis, respectively), which were used for screen-film radiography previously. CONCLUSIONS: The image quality of image plate radiography can be increased by lowering the tube voltage compared with the one that was used for screen-film radiography.     

Entrance surface, organ and effective doses for some of the patients undergoing different types of X ray procedures in Bangladesh

Entrance surface doses (ESDs) were measured for the most common types of X ray procedures, such as chest PA, lumber spine AP, lumber spine lateral, skull AP, skull lateral and pelvis AP in four major hospitals of Dhaka, the capital city of Bangladesh. Organ/tissue doses for 29 organs/tissues and effective doses for the patients were also calculated using the entrance surface dose as the input quantity. Organ/tissue doses and effective doses were calculated by using XDOSE software based on the Monte Carlo computation method. It was observed that the fluctuation of the entrance surface dose was too large. The ratio of maximum and minimum ESD values ranged from 4.8 to 35.9. Consequently, variation of organ doses was large even in the same type of X ray examination and in the same facility. Mean effective doses for the above mentioned X ray procedures were also determined and compared with the effective doses of some other countries. In most cases effective doses measured for the different types of X ray procedures were found to be lower than the effective doses of some other countries.     

Patient dose in digital projection radiography

In projection radiography, two types of digital imaging systems are currently available, computed radiography (CR) and direct radiography (DR): a difference between them can be stated in terms of dose and image quality. In the Radiology Emergency Department of our hospital, a flat-panel DR equipment (Siemens Axiom Aristos FX) and two CR systems (Kodak CR-850) are employed. In 2006, five standard radiographic examinations (abdomen, chest, lumbar spine, pelvis, skull) were considered: doses delivered to patients in terms of both entrance skin dose (ESD) and effective dose (E) were calculated and compared in order to study the dosimetric discrepancies between CR and DR. Assessment of image quality is undertaken by Consultant Radiologists to ensure that the quality criteria for diagnostic radiographic images of the European guidelines were met. Results showed that both ESD and E in DR are lower than that in CR; all images met the criteria in the European Guidelines for both modalities and were used for reporting by the radiologists. Since the operators are the same and the image quality is comparable in both modalities, this study shows that in the considered examinations, DR can perform better than CR from a dosimetric point of view.     

Patient doses using multidetector computed tomography scanners in Kenya

Assessment of patient dose attributed to multislice computed tomography (CT) examination. A questionnaire method was developed and used in recording the patient dose and scanning parameters for the head, chest, abdomen and lumbar spine examinations. The patient doses due to brain, chest and abdomen examination were above the international diagnostic reference levels (DRLs) by factors of between one and four. The study demonstrated that the use of multislice CT elevates patient radiation dose, justifying the need for local optimised scanning protocols and the use of institutional DRL for dose management without affecting diagnostic image quality.     

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.     

Estimation of doses received by patients undergoing radiological examinations in Greece

This study deals with the estimation of doses received by patients undergoing radiological examinations in order to establish diagnostic reference levels (DRLs) within the process of optimisation of patients' exposure in Greece. Six large hospitals in Athens were selected and 385 patients made up the sample. The entrance surface doses (ESDs) to patients undertaking five common X ray examinations (chest, cervical spine, lumbar spine AP and LAT, pelvis) were estimated using both thermoluminescence dosemeters (TLDs) attached to the patient's skin and an ionisation chamber for air kerma measurements. Exposure settings and patient's data were recorded. Results concerning the kilovoltage and focus-to-film-distance (FFD) settings and the ESD values were analysed and compared to those recommended by the EU. Discrepancies in the patient doses and techniques used for the examinations studied were found among the different hospitals denoting the importance of establishing a national quality assurance programme and examination protocols to ensure patient doses are kept as low as possible. All the examinations studied fulfilled the EU recommendations except that for the chest where the doses were considerably higher due to the use of low kVP settings.     

Varied tube potential with constant effective dose at lumbar spine radiography using a flat-panel digital detector

The purpose of the study was to evaluate the image quality at different tube potential (kV) settings using anteroposterior lumbar spine radiography as a model. An Alderson phantom was used with a flat-panel detector. The tube potential varied between 48 and 125 kV while the tube charge (mAs) was adjusted to keep an effective dose of 0.11 mSv. Image quality was assessed with a visual grading analysis and with a CDRAD contrast-detail phantom together with a computer program. The VGA showed inferior image quality for the higher kV settings, > or =96 kVwith similar results for the contrast-detail phantom. When keeping the effective dose fixed, it seems beneficial to reduce kV to get the best image quality despite the fact that the mAs is not as high as with automatic exposure. However, this cannot be done with automatic exposure, which is set for a constant detector dose.     

Current status of patient radiation doses from computed tomography examinations in Tanzania

The aim of this study was to assess the magnitude of radiation dose imparted to patients undergoing CT (computed tomography) examinations in Tanzania. The effective doses to patients undergoing five common CT examinations were obtained from eight health centres. The doses to patients were estimated using measurements of CTDI, exposure-related parameters and the CTDOSE software based on NRPB conversion factors. The mean effective doses in Tanzania for CT examinations of head, lumbar spine, chest, abdomen and pelvis were 2.2+/-0.9, 5.4+/-2.3, 12.2+/-3.4, 15.3+/-6.0 and 13.4+/-7.3 mSv, respectively. The mean effective doses and the variations in dose between hospitals in Tanzania were mostly comparable with reported values in the literature for six different countries from Europe. The observed wide variation in mean effective dose for similar CT examination among hospitals was largely influenced by different CT scanning protocols employed among hospitals. In view of the observed causes of variation in patient doses, it was concluded that further studies are needed to investigate the methods that can reduce dose to patients without affecting image quality.     

Evaluation of image quality of lumbar spine images: a comparison between FFE and VGA

PURPOSE: The aim of the present study is to compare two different methods for evaluation of the quality of clinical X-ray images. METHODS: Based on fifteen lumbar spine radiographs, two new sets of images were created. A hybrid image set was created by adding two distributions of artificial lesions to each original image. The image quality parameters spatial resolution and noise were manipulated and a total of 210 hybrid images were created. A set of 105 disease-free images was created by applying the same combinations of spatial resolution and noise to the original images. The hybrid images were evaluated with the free-response forced error experiment (FFE) and the normal images with visual grading analysis (VGA) by nine experienced radiologists. RESULTS: In the VGA study, images with low noise were preferred over images with higher noise levels. The alteration of the MTF had a limited influence on the VGA score. For the FFE study, the visibility of the lesions was independent of the sharpness and the noise level. No correlation was found between the two image quality measures. CONCLUSIONS: FFE is a precise method for evaluation of image quality, but the results are only valid for the type of lesion used in the study, whereas VGA is a more general method for clinical image quality assessment. The results of the FFE study indicate that there might be a potential to lower the dose levels in lumbar spine radiography without losing important diagnostic information.     

The influence of patient thickness and imaging system on patient dose and physical image quality in digital chest imaging

The aim of this work was to study the influence of patient thickness, tube voltage and image detector on patient dose, contrast and ideal observer signal-to-noise ratio (SNR(I)), for pathological details positioned at different regions in the image in posterior-anterior (PA) chest radiology. A Monte Carlo computational model was used to compute measures of physical image quality (contrast, SNR(I)) and patient effective dose, E. Two metastasis-like details positioned in the central right lung and right lung near the spine, respectively, were studied. The tube voltage was varied between 100 and 150 kV and the patient thickness between 20 and 28 cm. Both, a computed radiography (CR) system and a direct radiography (DR) system, were investigated. The DR system provides both lower doses and better image quality compared with the CR system. The SNR(I)2/E is approximately 2.9 times higher for the DR system compared with the CR system.     

Comparison between 3-D and z-axis automatic tube current modulation technique in multidetector-row CT

In this study, the 3-D automatic tube current modulation (3-D ATCM) technique was compared with the z-axis ATCM technique on multidetector-row CT. Absorbed dose measurements were performed by inserting an ion chamber into the phantoms, and objective image noise shown as the standard deviation of CT value in Hounsfield units was measured on the obtained images. The ratio of absorbed doses with 3-D ATCM technique to z-axis ATCM technique was 94.7% using an elliptical cylinder phantom with an inner cylinder phantom and 96.3% using an elliptical cylinder phantom without an inner cylinder phantom. Differences in objective noise between the 3-D ATCM technique and z-axis ATCM technique were within a tolerable range compared with the setting noise index. Therefore, the 3-D ATCM technique effectively optimises the radiation dose, while maintaining an appropriate image quality compared with z-axis ATCM technique.     

Local diagnostic reference levels in standard X-ray examinations

The national diagnostic reference levels (NDRLs) form an efficient, concise and powerful standard for optimising radiation protection of a patient. However, in a large hospital, where many radiological departments are present, it is also possible to calculate and define lower dose values as local diagnostic reference levels (LDRLs). In our hospital there are eight radiological departments; in each of these, the entrance skin dose (ESD) distributions were determined for 10 standard projections (AP Abdomen, PA and LAT Chest, AP and LAT Lumbar Spine, LAT Lumbo-Sacral Joint, AP Pelvis, PA and LAT Skull and AP Urinary tract) and then the ESDs were compared with data previously published and with Italian NDRLs. All ESD values were below the corresponding NDRLs. The maximum/minimum ratio of ESDs ranged from 3.9 (LAT Skull) to 34.3 (AP Abdomen) for individual adult patients and from 2.1 (PA Skull) to 6.5 (Urinary tract) across the mean values of the radiological departments. Finally, it is shown how LDRLs can be proposed to obtain a more fully optimised radiation protection of patients.     

Comparison of patient radiation dose from chest and lumbar spine X-ray examinations in 10 hospitals in Ghana

This study estimated the patient dose in chest and lumbar spine radiographic examinations in 10 hospitals in Ghana. Dose estimations were done on 1045 patients (aged, 39.6 ± 10.6 y; range 18-85 y) involving 501 (47.9%) males and 544 (52.1%) females for a total of 1495 individual projections. The entrance surface dose (ESD) for the patients was assessed by an indirect method, using the patient's anatomical data and exposure parameters utilised for the specific examination and a Quality Assurance Dose Database software developed by Integrated Radiological Services Ltd in Liverpool, UK. The study showed variations in the ESDs for chest examinations with five of the hospitals having values above the internationally recommended levels. ESDs for lumbar spine anterior-posterior and lateral projections were within acceptable limits. Diagnostic reference levels proposed by the International Commission on Radiological Protection based on patient dose data are imperative to the current Ghanaian situation and will lead to a reduction of the radiation dose.     

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.