Entrance Air Kerma Research Articles

SU‐FF‐I‐114: Comparison of Digital Tomosynthesis Technology with Conventional Technology for Intravenous Pyeolgram (IVP) Studies

Purpose: Digital tomosynthesis is a new spin on an old idea. It has been extensively studied and developed, but is just beginning to find its way into the clinic. We seek to compare digital tomosynthesis to conventional tomography utilizing a computed radiography (CR) system. To this end, we have developed quantitative measures to compare image quality and dose between images acquired using digital tomosynthesis and those acquired using conventional tomography with CR. Materials and methods: “Standard” IVP studies were performed on uniform acrylic phantoms. Dose in terms of entrance air kerma (EAK) was measured for each of the studies. The uniform phantom images were also used to quantify non‐uniformities in the images both globally and locally. Also, images were evaluated for the presence of artifacts. Results: EAK values for a standard IVP study (3 scout images, 3 tomographic cuts during 3 phases) of a “medium” patient consisting of 6 inches of acrylic ranged from 3.54 mGy to 80.1 mGy, depending upon technique, for digital tomosynthesis studies to 51.2 mGy for the same CR study. Also, keep in mind that additional planes or slice thicknesses can be derived from the digital data at no extra dose cost to the patient. Uniformity measures varied significantly in processed images for digital tomosynthesis studies acquired at varying techniques. Uniformity was consistent throughout conventional tomographic studies. Processed digital tomosynthesis images also displayed artifacts, some which mimic pathologic anatomy. Conclusions: Digital tomosynthesis has the potential to significantly reduce patient doses in IVP studies. However, techniques must be chosen appropriately to maximize image quality and minimize the presence of artifacts.

Comparison between a built‐in “dual side” chest imaging device and a standard “single side” CR

An integrated readout computed radiography system (Fuji XU-D1) incorporating dual-side imaging plates (ST-55BD) was analyzed in terms of modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) for standard beam qualities RQA 9 and RQA 5. NPS and DQE were assessed using a detector entrance air kerma consistent with clinical practice for chest radiography. Similar investigation was performed on a standard reader (Fuji FCR 5000) using single-side imaging plates (ST-VI). Negligible differences were found between the MTFs of the two imaging systems for RQA 9, whereas for RQA 5 the single-side system exhibited slightly superior MTF. Regarding noise response, the dual-side system turned out to be better performing for both beam qualities over a wide range of frequencies. For RQA 9, at 8 microGy, the DQE of the dual-side system was moderately higher over the whole frequency range, whereas for RQA 5, at 10 microGy, significant improvement was found at low- and midrange frequencies. As an example, at 1 cycle/mm, the following improvements in the DQE of the dual-side system were observed: +22% (RQA 9, at 8 microGy), +50% (RQA 9, at 30 microGy), and +45% (RQA 5, at 10 microGy).

High-resolution imager for digital mammography: physical characterization of a prototype sensor

The physical performance characteristics of a high-resolution sensor module for digital mammography were investigated. The signal response of the imager was measured at various detector entrance air kerma and was found to be linear. The spatial resolution was determined by measuring the presampling modulation transfer function, MTF(f), of the system. The noise power spectra, NPS(f), of the system were estimated using 26 kVp: Mo/Mo, 28 kVp: Mo/Rh and 30 kVp: Rh/Rh, with polymethyl methacrylate (PMMA) ‘tissue equivalent material’ of thickness 20, 45 and 57 mm for each of three x-ray spectra at detector entrance air kerma in the range between ∼80.2 and 92.3 µGy. The noise equivalent quanta, NEQ(f), and detective quantum efficiencies, DQE(f), for the various spectral conditions were computed. In addition, dose dependence of NPS(f) and DQE(f) was studied at various detector entrance air kerma ranging from 9.4 to 169.7 µGy. A spatial resolution of about 10 cycles mm−1 was obtained at the 10% MTF(f) level. A small increase in NEQ(f)was observed under higher energy spectral conditions while the DQE(f) decreased marginally. For a given spectrum, increasing PMMA filtration produced negligible change in DQE(f). The estimated DQE values at zero frequency were in the range between 0.45 and 0.55 under the conditions investigated in this study.

SU‐DD‐A2‐02: Investigation of Patient Doses Using a Tomographic Model for Diagnostic Radiology

Purpose: In this study, the patient's doses from diagnostic radiology were calculated using the tomographic model and Monte Carlo simulation. The tomographic model offers a realistic replication of human anatomy, and more accurate dosimetric results Method and Materials: The tomographic model Korean Typical Man 2 (KTMAN‐2) was segmented from PET/CT images and has 2×2×5mm3 voxel resolution. Three diagnostic x‐ray examination procedures, abdomen AP, chest PA, and pelvis PA were considered in this study. Energy deposition within organs and entrance air kerma (EAK) were calculated using KTMAN‐2 and Monte Carlo simulation. Also, organ dose comparisons were made for procedures of both a stylized and a tomographic model Results: For the chest PA examination, the lung dose assessed for the KTMAN‐2 is 0.08mGy. The absorbed doses to the stomach, liver and thyroid in the KTMAN‐2 exceed those within the stylized model by 279%, 161% and 90%, respectively. In the case of the abdomen AP examination, gut region and bladder receive a larger absorbed dose than other organs in KTMAN‐2. The absorbed doses to upper large intestine and small intestine are higher than in the stylized model. But conversely, the absorbed doses to lower large intestine and bladder in stylized model are higher than in the KTMAN‐2. For the pelvis PA examination, absorbed doses to gut region in stylized model are higher than in the KTMAN‐2 Conclusion: The model's exterior trunk shape, shape and position of organs and shielding of bone are leading factors contributing to differences in organ dose. Due to the supine position during tomographic images acquisition, back of KTMAN‐2 was pressed down and the abdominal organs are slightly shifted towards the thorax and the lungs are compressed. Thus the organ location difference between lying and upright posture should be corrected.

Retrospective patient dose analysis of a digital radiography system in routine clinical use

The log files generated in the flat-panel detector based digital radiography systems (Philips Digital Diagnost) at 11 different hospitals were used to acquire data regarding the dose-area product (DAP) and the entrance air kerma (EAK) for all X-ray examinations performed in routine clinical use. A retrospective statistical analysis of the data with respect to the dose levels was performed for several examination types. The resulting average dose levels were compared with the diagnostic reference levels (DRLs). While for the same type of examination the median dose level at different hospitals could differ by up to a factor of 5, almost all the dose levels were found to be much below the published DRL. Only in one hospital for one type of examination (Thorax PA) the DRL for the DAP was slightly exceeded, while for the same site and examination the EAK was still below the DRL. In conclusion, examination log files can be used for retrospective dose analysis and correlation with DRLs.

Measurement of effective dose for paediatric scoliotic patients

Purpose Paediatric radiation dose from scoliosis X-ray examinations is of concern because of its routine nature. Few studies have calculated effective dose which is the primary indicator of radiation risk. This study reports on the use of a new flexible Monte Carlo software package PCXMC14 for such calculation from documented radiographic and patient data. Method Patient and radiographic data were collected from 54 patient examinations for both postero-anterior (PA) and lateral X-ray projections. A spreadsheet mainly based on radiographic calibration was used to process the raw data and compute entrance air kerma for input in the PCXMC program. A partitioning model was developed to more accurately estimate the effect of an aluminium wedge filter. Results Results showed the effective dose ranged from 81 to 123 μSv for the PA projection and 124 to 207 μSv for the lateral projection, with patient weights varying from 20 to 70 kg. Conclusions This study demonstrates the usefulness of the PCXMC program to evaluate the effective dose in paediatric scoliosis radiography.

Radiation doses in pediatric radiology: influence of regulations and standards

The benefits of x-ray examinations contribute to the quality of modern medicine; however the risk of using x-rays, a carcinogen, has always been a concern. This concern is heightened for pediatric patients, who have a much greater sensitivity to the carcinogenic effects of radiation than adults. The principle of as low as reasonably achievable, or ALARA, is essential for minimizing the radiation dose patients receive, especially for pediatric patients. In order to keep radiation doses ALARA, one must know the dose patients receive. The determination of radiation dose in a standard way is therefore necessary so that these doses can be compared with practice, and for meaningful comparison against voluntary standards. In extreme situations, where public health needs may require mandatory standards, or regulations, the quantitative measurement and calculation of radiation dose becomes essential. How some radiation dose metrics and standards have evolved, including the value of different metrics such as entrance air kerma, organ dose, and effective dose will be presented. Recent pediatric x-ray studies, whether or not dedicated pediatric equipment is necessary, and recent initiatives by the Food and Drug Administration for pediatric population will be discussed.

Dose Assessment for Medical Exposure from Diagnostic X-rays Using a Human Voxel Model

Korean voxel model, KORMAN, segmented from whole-body MR data of an adult male, was used to calculate organ equivalent doses and effective doses due to diagnostic X-ray examinations. Calculated doses were normalized to entrance airkerma and compared with those derived using a stylized mathematical model, MIRD5. General purposed Monte Carlo code, MCNPX 2.3 was used for simulation of X-ray procedure. Korean voxel model picked up 0.048 Sv/Gy of effective dose per unit air kerma from a single chest PA examination, and 0.277 Sv/Gy from abdomen AP examination. These calculated results are higher than those of MIRD5. The difference of effective doses between Korean voxel model and MIRD5 was within 32%, which were caused by significant discrepancies of organ equivalent doses between the two models. As MIRD5 is representing reference man, whereas KORMAN is segmented from specific individual MR data, it is recognized that variation among individuals could be significant for dose assessment in X-ray examination. Substantial differences in calculated doses between voxel and mathematical models suggested that existing mathematical models should be revised.

血管造影検査における術者の被曝線量評価と放射線防護用具による被曝低減

A study was performed to evaluate operator dose during diagnostic and interventional radiology procedures (IVR) and to establish methods of operator dose reduction with a radiation protective device. Operator dose was measured by glass dosimeters worn on the neck and on the abdomen outside the lead apron. In addition, the dose of the primary beam at the collimator surface was measured, which made it possible to define the correlation between the entrance air kerma, measured with Skin Dose Monitor, and operator dose exposed during the monitored procedure. IVR protectors were developed to decrease the amount of scatter radiation received by operators performing the procedures, and their effects were evaluated in abdominal and cardiac angiography procedures. The average effective dose and doses of the neck and abdomen outside the lead apron, estimated for individual procedures, were as follows: abdominal angiography procedures: effective dose, 0.07 mSv; neck area, 0.18 mSv; abdominal area, 0.51 mSv; cardiac angiography procedures: effective dose, 0.07 mSv; neck area, 0.13 mSv; abdominal area, 0.68 mSv. Operator doses were well correlated with exposure dose in abdominal angiography procedures (diagnostic procedure r=0.84, IVR r=0.77). It was found that 68.0% of the effective dose in abdominal angiography procedures and 43.0% of the effective dose in cardiac angiography procedures could be reduced by the use of IVR protectors. Operator and patient doses in interventional radiology were interdependent. The minimization of operator doses is particularly important during interventional radiology, and it is necessary to be aware of practical radiation protection procedures. Measures that reduce patient dose will also reduce occupational exposure. Moreover, operator dose could be substantially reduced by the use of IVR protectors in addition to wearing a protective lead apron during IVR. It was suggested that IVR protectors are effective radiation protective devices in interventional radiology procedures.

Patient dose in full-field digital mammography: an Italian survey.

The aim of this study was to compare performance and patient dose of full-field digital mammography units for clinical use. Measurements of linearity and automatic exposure control stability were performed on four units installed in as many Italian sites. The tube output was also obtained by the same ionization chamber, permitting to evaluate ratios mGy/mAs for each available spectrum. The entrance air-kerma was calculated over a sample of 800 cranio-caudal mammograms and the average glandular dose obtained, assuming two mean glandular compositions of 50 and 30%, respectively. Digital systems showed very good linearity and comparable responses. The stability of the automatic exposure control was better than 5% for all systems. Regarding doses, the two mammography units that work mainly in contrast mode deliver, respectively, 17 and 28% more dose compared with those working in standard mode. For the latter mode, the mean average glandular dose was in the range 1.25-1.37 mGy and 1.37-1.49 mGy for the 50 and 30% glandular composition, respectively. Results of this study were compared with those of other surveys, showing that full-field digital mammography allows a significant clinical dose reduction compared with screen/film mammography.

Evaluation of the imaging properties of two generations of a CCD-based system for digital chest radiography.

Two generations of a CCD-based detector system with lens-based optical coupling for digital chest radiography were evaluated in terms of presampling MTF, NPS, NEQ, DQE, linearity in response, and SNR over the detector area. Measurements were performed over a wide exposure range and at several different beam qualities. Neither the presampling MTF nor the DQE showed any general strong beam quality dependence, whereas the NPS and NEQ did when compared at specific entrance air kerma values. The exposure dependency for the DQE was found to be considerable, with the detectors showing low DQE at low exposures, and higher DQE at higher exposures. It was found that the second generation has been substantially improved compared to its predecessor regarding all the relevant parameters. The DQE(0) at an entrance air kerma of 5 microGy increased from 9% to 15%, mainly due to a better system gain (including optical coupling efficiency and matching of the energy of the emitted light photons to the sensitivity of the CCD camera). The first generation of detectors was found to have problems with bad peripheral resolution [MTF(muN/2) <0.1]. This problem was nonexistent for the second generation for which uniform resolution has been obtained [MTF(muN/2)=0.3]. A theoretical calculation of the DQE of two model systems similar to the ones evaluated was also performed, and the results were comparable to the experimentally determined data at high exposures. The model shows that both systems suffer from low optical coupling efficiency due to the large demagnification used. The main conclusion is that although the second generation has been improved, there is still a problem with low system gain leading to relatively modest DQE values, especially at low exposures.

Numerical models for comparing filter materials for diagnostic radiology

As a result of the differences in the attenuation properties, it is impossible for two different elemental filter material to transmit equal primary photon spectra with the same radiometric equivalence over the entire energy spectrum for the same incident spectrum. However, earlier work reported in the literature show that it is possible to approximately match the spectra shape of transmitted primary photons over a large range of energy spectrum. In this work, the relative differences in the cumulative transmitted primary photons of filter materials used in diagnostic radiology have been investigated using EGS4 Monte Carlo codes. The quantitative influence of these relative differences on parameters such as efficiency of filter, tube current, heat capacity, entrance air kerma and exposure are presented. Simple comparative theoretical models were derived for these differences.

Filters for Dose Reduction in Conventional X-Ray Examinations of Children

The effects of five filtrations on dose reduction and image quality in paediatric chest radiography with a high voltage technique are presented. The radiographs were performed using a Sieregraph unit (Siemens) with 3.5 mm Al of primary total filtration, and added: 1 mm Al + 0.1 mm Cu, 1 mm Al + 0.2 mm Cu, 4 mm Al, 4 mm Al + 0.1 mm Cu. The entrance air kerma (including backscatter) for each child examined was measured using TLD-100, and the parameters of exposure were recorded. The absorbed organ doses and effective doses were calculated using Monte Carlo simulation. The authors' computer code was used for this purpose. The children were divided into three groups according to weight and height, corresponding to the mathematical human phantoms representing 5 year, 10 year and 15 year children. Additional filtrations exceeding 4 mm Al allowed for significant reduction of doses (nearly 50%). Although the visualisation of the anatomical structures in the filter groups were slightly reduced, nevertheless the films were acceptable for the given clinical questions.

Calculation of Patient Doses Using a Human Voxel Phantom of Variable Diameter

The voxel phantom Golem was used for the dosimetric part of the EU research project 'Predictivity and Optimisation in Medical Radiation Protection'. A risk-related dose quantity, HGolem was evaluated using calculated organ equivalent dose conversion coefficients and entrance air kerma values measured during the clinical examinations. Two types of examinations were considered: chest PA examinations, which were performed in 16 groups involving different speed classes, mean optical densities, tube voltages and methods of scatter reduction; and lumbar spine AP examinations, for which four different combinations of speed class and tube voltage were used. For the chest examinations, the expected effects of different examination techniques are clearly mirrored by the dosimetric results. For the lumbar spine examinations, part of the expected results was concealed by the unwanted influence of the patient diameters on the doses, which could be partially eliminated by adapting the voxel phantom to different sizes.

Management of Patient Skin Dose in Fluoroscopically Guided Interventional Procedures

To simulate dose to the skin of a large patient for various operational fluoroscopic conditions and to delineate how to adjust operational conditions to maintain skin dose at acceptable levels. Patient entrance skin dose was estimated from measurement of entrance air kerma (dose to air) to a 280-mm water phantom for two angiographic fluoroscopes. Effects on dose for changes in machine floor kVp, source-to-skin distance, air gap, electronic magnification, fluoroscopic dose rate control settings, and fluorographic dose control settings were examined. Incremental changes in operational parameters are multiplicative and markedly affect total dose delivered to a patient's skin. For long procedures, differences in doses of 8 Gy or more are possible for some combinations of operational techniques. Effects on skin dose from changes in operational parameters are multiplicative, not additive. Doses in excess of known thresholds for injury can be exceeded under some operating conditions. Adjusting operational parameters appropriately will markedly reduce dose to a patient's skin. Above all other operational factors, variable pulsed fluoroscopy has the greatest potential for maintaining radiation exposure at low levels.

A search for improved technique factors in paediatric fluoroscopy

A Monte Carlo computational model of a fluoroscopic imaging chain was used for deriving optimal technique factors for paediatric fluoroscopy. The optimal technique was defined as the one that minimizes the absorbed dose (or dose rate) in the patient with a constraint of constant image quality. Image quality was assessed for the task of detecting a detail in the image of a patient-simulating phantom, and was expressed in terms of the ideal observer's signal-to-noise ratio (SNR) for static images and in terms of the accumulating rate of the square of SNR for dynamic imaging. The entrance air kerma (or air kerma rate) and the mean absorbed dose (or dose rate) in the phantom quantified radiation detriment. The calculations were made for homogeneous phantoms simulating newborn, 3-, 10- and 15-year-old patients, barium and iodine contrast material details, several x-ray spectra, and for imaging with or without an antiscatter grid. The image receptor was modelled as a CsI x-ray image intensifier (XRII). For the task of detecting low- or moderate-contrast iodine details, the optimal spectrum can be obtained by using an x-ray tube potential near 50 kV and filtering the x-ray beam heavily. The optimal tube potential is near 60 kV for low- or moderate-contrast barium details, and 80-100 kV for high-contrast details. The low-potential spectra above require a high tube load, but this should be acceptable in paediatric fluoroscopy. A reasonable choice of filtration is the use of an additional 0.25 mm Cu, or a suitable K-edge filter. No increase in the optimal tube potential was found as phantom thickness increased. With the constraint of constant low-contrast detail detectability, the mean absorbed doses obtained with the above spectra are approximately 50% lower than those obtained with the reference conditions of 70 kV and 2.7 mm Al filter. For the smallest patient and x-ray field size, not using a grid was slightly more dose-efficient than using a grid, but when the patient size and field size were increased a fibre interspaced grid resulted in lower doses than imaging without a grid. For a 15-year-old patient the mean absorbed doses were up to 40% lower with this grid than without the grid.

Nationwide survey of fluoroscopy: radiation dose and image quality.

To determine the average abdominal entrance air kerma, low-contrast sensitivity, and spatial resolution in upper gastrointestinal tract fluoroscopy in the United States. A random sample of fluoroscopic facilities was selected to be surveyed for the Nationwide Evaluation of X-ray Trends program. Measurements were performed by using a newly developed fluoroscopic phantom. The surveys were conducted by state radiation control personnel. Average air kerma rates 1 cm above the tabletop, free in air, were 43 mGy/min (n = 340). The rate increased to 64 mGy/min when a 1.6-mm-thick copper filter, which simulated the use of barium contrast medium, was added to increase attenuation. The average entrance air kerma, free in air, for radiographs was 3.4 mGy, and an average of 12 radiographs were obtained per examination. Of 352 facilities surveyed, 306 (87%) were able to resolve wire mesh with 20 or more lines per inch. Of 339 facilities for which percentage contrast could be calculated, 192 (57%) had minimum percentage contrast values of 4% or more. Spatial resolution for fluoroscopy is adequate for most of the facilities surveyed, but a substantial proportion of facilities could not visualize low-contrast test objects, which strongly suggests image quality problems.

An Investigation into Variations in the Estimation of Mean Glandular Dose in Mammography

The regular assessment of breast dose is an important part of a quality control programme in mammography. It is common practice in the United Kingdom to deduce the mean glandular dose from an estimate of air kerma at the entrance surface of a standard breast phantom manufactured from Perspex (ICI, Darwin) of nominal thickness 40 mm. Factors are used to deduce the mean glandular dose from the entrance air kerma. The objectives of this study were to assess the impact of variations in technique on the assessment of mean glandular dose and the implications for comparative surveys. It was deduced that it is possible to achieve consistent dosimetry measurements, provided standard Perspex blocks are used and tube output is measured at a specific position.

Update on the recommended viewing protocol for FAXIL threshold contrast detail detectability test objects used in television fluoroscopy.

The significance of varying the viewing conditions that may affect the perceived threshold contrast of X-ray television fluoroscopy systems has been investigated. Factors investigated include the ambient room lighting and the viewing distance. The purpose of this study is to find the optimum viewing protocol with which to measure the threshold detection index. This is a particular problem when trying to compare the image quality of television fluoroscopy systems in different input field sizes. The results show that the viewing distance makes a significant difference to the perceived threshold contrast, whereas the ambient light conditions make no significant difference. Experienced observers were found to be capable of finding the optimum viewing distance for detecting details of each size, in effect using a flexible viewing distance. This allows the results from different field sizes to be normalized to account for both the magnification and the entrance air kerma rate differences, which in turn allow for a direct comparison of performance in different field sizes.

The contrast-detail behaviour of a photostimulable phosphor based computed radiography system

Contrast-detail measurements were performed on a computed radiography imaging system as a function of detector entrance air kerma over the dose range from 0.743 mu Gy (0.085 mR) to 277 mu Gy (31.8 mR). A theoretical model of contrast-detail behaviour for a photostimulable phosphor computed radiography system has been derived, which is based on a modified version of the Rose theory of threshold detection. Included in the model are both system and X-ray quantum noise terms, as well as the response of the eye. The zero-frequency noise power of the computed film images was measured with a double-beam scanning microdensitometer. For a given detector dose, good agreement was found between the predicted and measured data when this measurement of system noise was included in the model. The contrast-detail results obtained for the computed radiography system were also compared with contrast-detail results for an image intensifier-TV based digital imaging system and a conventional film-screen system.