Incident Air Kerma Research Articles

Dose evaluation in paediatric patients undergoing skull examinations

The purpose of this study was to estimate the kerma-area product (KAP) and incident air kerma of radiographic skull examinations in a large paediatric hospital in Brazil. In addition, the influence of thickness on patient parameters and radiographic technique was verified. A total of 125 paediatric patients (69 males and 56 females) were evaluated, and 294 radiographs (125 projections in anteroposterior/posteroanterior and 123 in lateral, and 46 in Towne) were performed. To analyse the results, the patients were divided into age groups: 0–1 year, 1–5 years, 5–10 years, and 10–15 years. Anthropometric data of the patient (weight, height and thickness) and radiographic technique data (voltage, product current time and focus skin distance) were collected. The analysis of patients' thicknesses and other characteristics which can be used to determine radiographic protocols showed that thickness can be estimated from the patient's age, height, or weight with an uncertainty higher than 15%. The age groups, which are usually used to compare radiographic techniques, are not appropriate for data-oriented decisions. For practical purposes, we suggest the following groups with fixed radiographic protocols; age: <0.5 year, 0.5–1 year, and >1 year; height: 40–60 cm, 60–80 cm, and >80 cm; weight: <5 kg, 5–10 kg and >10 kg. There was a very small correlation between the patient dose and thickness, with a difference of up to 20-fold in dose for patients of the same thickness. If radiological protocols were to be standardized, it should be possible to keep the dose below ∼0.9 mGy. The correlation between the KAP and the patient's thickness is clearer; however, the dispersion of the KAP values is even greater, especially for anteroposterior/posteroanterior projection.

Radiation doses in mammography exams: Effects of oncological treatments

IntroductionBreast cancer treatments cause breast changes that are detectable in subsequent mammography exams. This work investigates if these changes are perceived as differences in breast composition by automatic exposure systems, and if such differences are high enough to have impact in exam doses. MethodsData was obtained for 226 patients treated with unilateral conservative surgery followed by radiotherapy (S&RT) of the left (114) or right (112) breast, who had mammographic exams in direct digital GE units, Senographe DS (SenoDS) or Senographe Essential (Essential). The relevant data was extracted from Digital Imaging and Communications in Medicine (DICOM) images, and the Mean Glandular Dose (MGD) was calculated using the model of Dance. ResultsCompression force and area were 15–30% lower for treated breasts (S&RT) relative to untreated, while compressed breast thickness (CBT), incident air kerma (Ki) and MGD were 14–17%, 22–28% and 10–18% higher, respectively. The variation of MGD and Ki with CBT is similar for treated and untreated breasts. High values of Ki, MGD and CBT occur for some treated breasts with relatively small areas, probably as a result of less compressible breast tissue. Equipment-determined composition was found to be similar for treated and untreated breasts. ConclusionTreated breasts are imaged with slightly higher doses as a result of higher CBT, but the dependence of Ki and MGD on CBT remains unchanged. There is no need to separate data for treated and untreated breasts in large-scale analysis of exam doses.

Tantalum-specific contrast-to-noise ratio or conventional detector dose-driven exposure control in angiography: radiation dose and image quality evaluation in a porcine model

BackgroundThe aim of this animal study was to compare the fluoroscopic image quality (IQ) and radiation dose between a tantalum (Ta)-specific contrast-to-noise ratio-driven exposure control (Ta-CEC) and a detector dose-driven exposure control (DEC) in abdominal angiography.MethodsNine angiography scenarios were created in seven anaesthetised pigs using Ta-based embolisation material during percutaneous liver and kidney intervention. Fluoroscopic images were acquired using three DEC protocols with different dose levels and Ta-CEC protocols with different IQ levels, sampled in small steps. Polymethyl-methacrylate and aluminium plates were used to simulate attenuation of three water equivalent thicknesses (WET). Three blinded readers evaluated the IQ of DEC and dose equivalent Ta images and selected the Ta-IQ equivalent image corresponding to the DEC image.ResultsInterobserver agreement for the IQ assessment was 0.43 for DEC, 0.56 for Ta-CEC and for the assessment of incident air kerma at the interventional reference point (Ka,r) for the Ta-IQ equivalent image 0.73. The average IQ of the dose equivalent Ta images was superior compared to the DEC images (p < 0.001) and also for every WET (26, 31, or 36 cm) and dose level (p ≤ 0.022). The average Ka,r for the Ta-IQ equivalent images was 59 ± 16% (mean ± standard deviation) lower compared to the DEC images (p < 0.001).ConclusionsCompared to DEC, Ta-CEC significantly improved the fluoroscopic depiction of Ta, while maintaining the Ka,r. Alternatively, the Ka,r can be significantly reduced by using Ta-CEC instead of DEC, while maintaining equivalent IQ.

Evaluation of the Accuracy of the Displayed Average Glandular Dose in Mammography

We aimed to clarify the error of displayed value against the measured value of the average glandular dose (AGD) in two-dimensional (2D) mammography and digital breast tomosynthesis (DBT) and evaluate the accuracy of the displayed AGD as an index to estimate AGD. Polymethyl methacrylate (PMMA) phantoms with thicknesses varying from 20 to 80 mm were imaged, and the values displayed on the mammography system were used as the displayed AGD. The incident air kerma and the half-valued layer were measured, and the measured AGD in 2D mammography was calculated using the equation by Dance et al. On the other hand, the measured AGD in DBT was calculated by correcting for different projection angles. The relative error to the PMMA thickness was evaluated by assessing the relative error of the displayed AGD against the measured AGD. The maximum relative error of the displayed AGD against the measured AGD was 17.3% in 2D mammography, 19.1% in the standard (ST) mode, and 19.8% in the high-resolution (HR) mode. The relative error of the displayed AGD against the measured AGD tended to increase with increase in PMMA thickness. This tendency was especially noticeable for PMMA with thicknesses of 70 and 80 mm in DBT.

From the use of exposure index in quality control testing to the use of exposure index for quality control of clinical images

AimThe exposure index (EI) is used in routine quality control (QC) tests performed in the radiographic equipment installed in our hospitals. This study aimed at investigating the factors affecting the calculation of EI in QC and clinical images, and the implementation of target EI (EIT) and deviation index (DI) in clinical practice. MethodsThe EI is 100 times the incident air kerma (IAK) in μGy on the image receptor, using the RQA-5 X-ray beam quality. Conformance to this relationship was investigated in QC images and clinical images acquired using anthropomorphic phantom body parts and different examination protocols, tube potential settings and radiation field sizes. Furthermore, a survey on EIT and DI data from clinical images was performed. ResultsThough automatic exposure control (AEC) systems have been adjusted for an IAK of 2.5 μGy, for most anthropomorphic phantom images the EIs were far from 250, depending on the manufacturer, the anatomy imaged, and the examination protocol. Regarding the survey results, DI calculation was feasible in only 38 % of the systems, since for the rest EIT values have not been set. However, the rationale based on which EIT have been selected is unclear. Some systems use only one while others many different EIT values. ConclusionBefore using EI for quality control of clinical images image all receptors and AEC systems should be properly calibrated. Then, the methodology of selecting appropriate EIT should be refined, since the EI calculation may vary, depending on the manufacturer, the anatomy imaged, and the examination protocol.

Accuracy Evaluation of Air Kerma-area Product of Over-couch-type X-ray Fluoroscopic System

The purpose of this study was to evaluate the accuracy of incident air kerma (Ka,r) and air kerma-area product (PKA) displayed on over-couch-type X-ray fluoroscopic systems by comparing them with the measured values. An ionizing chamber was placed at the patient entrance reference point to measure the Ka,r. The PKA was calculated by multiplying the Ka,r by the irradiation area. These measured values were compared with the displayed values. The differences between measured and displayed Ka,r and PKA were less than ±35%, which was the criteria of the Japanese Industrial Standards (JIS). However, the accuracy of the displayed values differed depending on the manufacturer and the device. Although no error exceeding the JIS criteria was observed, it is necessary to understand the characteristics of the X-ray fluoroscopic systems related to displayed dose and to manage the systems by performing dose measurements periodically.

Assessment of Regional Diagnostic Reference Levels in Dental Radiography in Tamil Nadu.

Aim:The aim of this article is to assess Tamil Nadu adult diagnostic reference levels (DRLs) by collecting radiation dose data from the four different dental modalities.Materials and Methods:The study was carried out using routine adult exposure settings in 131 intraoral, 75 panoramic, 35 cephalometric, and 10 dental cone beam computed tomography (CBCT) X-ray devices. DRLs were assessed for intraoral and extraoral (panoramic, cephalometric, and CBCT) examinations in terms of incident air kerma (Ka, i) and kerma area product (PKA), respectively. Air kerma measurements, for all dental units, were made using calibrated RTI black Piranha 557 dosimeter (RTI Electronics AB, Sweden). The dosimeter was kept at the exit cone of the X-ray tube and on the detector side of the X-ray unit for intraoral and extraoral air kerma measurements, respectively. The obtained air kerma in extraoral modalities is multiplied with the beam area to evaluate PKA.Results:The third quartile values calculated from the median for adult intraoral (mandibular molar), panoramic, cephalometric, and CBCT were 1.5 mGy, 116 mGycm2, 40 mGycm2, and 532 mGycm2, respectively. The proposed DRL in the present study was comparable to those reported in Germany, Greece, the UK, Japan, and Korea.Conclusion:This study revealed the need for dose management and radiation dose optimization, in various dental facilities in the state. It was also found that dental facilities employed with the digital type of detector are not always related to lower exposure.

Mean Glandular Dose Measurement in Three Mammography Centers in Kashan: An approach to Provide a Local DRL

Purpose: Mammography is the most important diagnostic modality for early detection of breast cancer, however, concerns related to the side effects induced by ionizing radiation are still present. In the current study, the Mean Glandular Dose (MGD) values for mammography examinations as well as a local Diagnostic Reference Level (DRL) were obtained for mammography centers in Kashan, Iran. Materials and Methods: Three mammography devices from three radiology centers were selected to obtain the MGD values of mammography examinations. To assess the MGD values, the technical parameters for patients’ imaging at these three radiology centers were extracted. Then, the incident air kerma (in mGy) value received by each patient was measured by a UNIDOS E electrometer (PTW, Germany) along with a SFD mammography ionization chamber (PTW, Germany). Finally, the incident air kerma values were converted to the MGD values by specific conversion factors. Based on the obtained MGD values, a local DRL was also established for mammography examinations. Results: Mean MGD values per exposure were obtained 2.39 ± 1.46 mGy for Right Craniocaudal (RCC), 2.64 ± 1.67 mGy for Left Craniocaudal (LCC), 2.82 ± 1.89 mGy for Right Mediolateral Oblique (RMLO), and 3.09 ± 1.90 mGy for left mediolateral oblique views. Moreover, a local DRL obtained from mammography examinations, which was established as the overall median of MGD value, was 1.72 mGy (1.91 mGy for digital and 1.32 mGy for analog mammography). Conclusion: The MGD values for different views obtained in this study are in the range of previously reported values. Considering the European guidelines for quality assurance in breast cancer screening and diagnosis, it can be mentioned that the obtained DRL was less than the recommended dose level (2.0 mGy).

Comparison of a contrast-to-noise ratio-driven exposure control and a regular detector dose-driven exposure control in abdominal imaging in a clinical angiography system.

The first purpose of this phantom study was to verify whether a contrast-to-noise ratio (CNR)-driven exposure control (CEC) can maintain target CNR in angiography more precisely compared to a conventional detector dose-driven exposure control (DEC). The second purpose was to estimate the difference between incident air kerma produced by CEC and DEC when both exposure controls reach the same CNR. A standardized 3D-printed phantom with an iron foil and a cavity, filled with iodinated contrast material, was developed to measure CNR using different image acquisition settings. This phantom was placed into a stack of polymethylmethacrylate and aluminum plates, simulating a patient equivalent thickness (PET) of 2.5-40cm. Images were acquired using fluoroscopy and digital radiography modes with CEC using one image quality level and four image quality gradients and DEC having three different detector dose levels. The spatial frequency weighted CNR and incident air kerma were determined. The differences in incident air kerma between DEC and CEC were estimated. When using DEC, CNR decreased continuously with increasing attenuation, while CEC within physical limits maintained a predefined CNR level. Furthermore, CEC could be parameterized to deliver the CNR as a predefined function of PET. To provide a given CNR level, CEC used equal or lower air kerma than DEC. The mean estimated incident air kerma of CEC compared to DEC was between 3% (PET 20cm) and 40% (PET 27.5cm) lower in fluoroscopy and between 1% (PET 20cm) and 55% (PET 2.5cm) lower in digital radiography while maintaining CNR. Within physical and legislative limits, the CEC allows for a flexible adjustment of the CNR as a function of PET. Thus, the CEC enables task-dependent examination protocols with predefined image quality in order to easier achieve the as low as reasonably achievable principle. CEC required equal or lower incident air kerma than DEC to provide similar CNR, which allows for a substantial reduction of skin radiation dose in these situations.

Effect of equalization filters on measurements with kerma-area product meter in a cardiovascular angiography system.

PurposeThis study aimed to evaluate the effect of equalization filters (EFs) on the kerma‐area product (KAPQKM) and incident air‐kerma (Ka,i,QKM) using a kerma‐area product (KAP) meter. In addition, potential underestimations of the Ka,i,QKM values by EFs were identified.Materials and methodsA portable flat‐panel detector (FPD) was placed to measure the X‐ray beam area (A) and EFs dimension at patient entrance reference point (PERP). Afterward, a 6‐cm3 external ionization chamber was placed to measure incident air‐kerma (Ka,i,Qext) at PERP instead of the portable FPD. KAP reading and Ka,i,Qext were simultaneously measured at several X‐ray beam qualities with and without EFs. The X‐ray beam quality correction factor by KAP meter (kQ,Q0KM) was calculated by A, Ka,i,Qext and KAP reading to acquire the KAPQKM and Ka,i,QKM. Upon completion of the measurements, KAPQKM, Ka,i,QKM, and Ka,i,Qext were plotted as functions of tube potential, spectral filter, and EFs dimension. Moreover, Ka,i,QKM/Ka,i,Qext values were calculated to evaluate the Ka,i,QKM underestimation.ResultsThe kQ,Q0KM values increased with an increase in the X‐ray tube potential and spectral filter, and the maximum kQ,Q0KM was 1.18. KAPQKM and Ka,i,QKM decreased as functions of EFs dimension, whereas Ka,i,Qext was almost constant. Ka,i,QKM/Ka,i,Qext decreased with an increase in EFs dimension but increased with an increase in tube potential and spectral filter, and the range was 0.55–1.01.Conclusions Ka,i,QKM value was up to approximately two times lower than the Ka,i,Qext values by EFs. When using the Ka,i,QKM value, the potential Ka,i,QKM underestimation with EFs should be considered.

X-Rays through the Looking Glass: Mobile Imaging Dosimetry and Image Quality of Suspected COVID-19 Patients

Background: This paper aims to evaluate the clinical utility and radiation dosimetry, for the mobile X-ray imaging of patients with known or suspected infectious diseases, through the window of an isolation room. The suitability of this technique for imaging coronavirus disease 2019 (COVID-19) patients is of particular focus here, although it is expected to have equal relevance to many infectious respiratory disease outbreaks.Materials and Methods: Two exposure levels were examined, a “typical” mobile exposure of 100 kVp/1.6 mAs and a “high” exposure of 120 kVp/5 mAs. Exposures of an anthropomorphic phantom were made, with and without a glass window present in the beam. The resultant phantom images were provided to experienced radiographers for image quality evaluation, using a Likert scale to rate the anatomical structure visibility.Results and Discussion: The incident air kerma doubled using the high exposure technique, from 29.47 μGy to 67.82 μGy and scattered radiation inside and outside the room increased. Despite an increase in beam energy, high exposure technique images received higher image quality scores than images acquired using lower exposure settings.Conclusion: Increased scattered radiation was very low and can be further mitigated by ensuring surrounding staff are appropriately distanced from both the patient and X-ray tube. Although an increase in incident air kerma was observed, practical advantages in infection control and personal protective equipment conservation were identified. Sites are encouraged to consider the use of this technique where appropriate, following the completion of standard justification practices.

Real-time estimation of surface dose based on incident air kerma in diagnostic radiology.

To estimate the surface dose in diagnostic radiology in real time based on the relationship between the incident air kerma and the surface dose. The air kerma for 20 X-ray beams with tube voltages of 50-140kV and a half-value layer (HVL) of 2.27-9.65mm Al was measured using an ionization chamber. The beam quality was classified based on the quality indexes (QIs) of 0.4, 0.5, and 0.6, which are defined as the ratio of the effective energy to the maximum energy corresponding to the tube potential. The surface dose for 20 X-ray beams was evaluated based on the measured air kerma, backscatter factor, and ratio of the mass-energy absorption coefficients of water to air, which were calculated using the Monte Carlo method. Finally, the relationship between the air kerma and the surface dose was investigated for X-ray beams with the specific QI values. The surface dose at a water phantom was represented by a linear approximation of R2>0.98, with the air kerma, regardless of the X-ray beam quality. The surface dose estimated based on a linear approximation with the air kerma indicated an agreement within 8% with that evaluated by the chamber measurements at HVL>3.4mm Al. It is possible to estimate the surface dose in real time using the linear relationship between the incident air kerma and the surface dose regardless of the X-ray beam quality by accepting ±10% uncertainty in the surface dose estimation.

The empirical formula for calculating the incident air Kerma in intraoral radiographic imaging.

The aim of this paper is to determine the empirical formula for calculating the incident air kerma (Ki), used as a patient dose descriptor in the intraoral radiographic imaging. The data for the formula were collected during the regular annual inspection of intraoral dental X-ray units in 2018, 2019 and early 2020. The measurement data of 50 X-ray units were processed to develop the formula. Exposure factors for imaging molars of the upper jaw of an average patient in a clinical setting were used in the measurement. The formula validity was statistically evaluated using coefficient of correlation, standard error of the fitted function and the mean relative percentage deviation. The measurement values of the radiation doses and calculated values obtained by using the final formula showed good agreement - the mean relative percentage deviation values less than ±15%. Although there are differences in X-ray units, voltages, manufacturers and device architectures (single-phase and high-frequency), the measurement data comply well with computed ones in all cases.

Backscatter factors calculation for intraoral dental radiology

The dosimetry of intraoral radiography procedures is of great interest since dental examinations are among the most numerous radiological procedures. Usually, the surveys are performed using measurements free in air. The entrance surface air kerma (K e ) can be estimated from measurements of incident air kerma and the use of backscatter factors (BSF). The purpose of this work is to calculate BSF values suitable for intraoral radiography. In addition to specific intraoral radiography, a comprehensive reassessment of internationally recommended BSF values was performed through Monte Carlo simulations. Moreover, the K e was estimated using the calculated BSF values for a sample of 44 intraoral radiography systems. The interpolation of intraoral radiography BSF values from reference data can lead to an overestimation of up to 10% and 6% in comparison with the values calculated in this work for monoenergetic photons and x-ray spectra, respectively. Such discrepancy may be relevant when defining diagnostic reference levels (DRLs) or performing quality control tests. The calculations for a sample of 44 intraoral radiography systems showed that the majority of the equipment operates with an entrance surface air kerma higher than 3.5 mGy. In the case of adopting a single value to estimate K e , the use of BSF equal to 1.2 results in less dispersion compared to calculated values in this work and the use of 1.1 can underestimate K e values up to 12%.

Impact of photoelectric cross section data on systematic uncertainties for Monte Carlo breast dosimetry in mammography

Monte Carlo (MC) simulations are employed extensively in breast dosimetry studies. In the energy interval of interest in mammography energy deposition is predominantly caused by the photoelectric effect, and the corresponding cross sections used by the MC codes to model this interaction process have a direct influence on the simulation results. The present work compares two photoelectric cross section databases in order to estimate the systematic uncertainty, related to breast dosimetry, introduced by the choice of cross sections for photoabsorption. The databases with and without the so-called normalization screening correction are denoted as ‘renormalized’ or ‘un-normalized’, respectively. The simulations were performed with the PENELOPE/penEasy code system, for a geometry resembling a mammography examination. The mean glandular dose (MGD), incident air kerma (K air), normalized glandular dose (DgN) and glandular depth-dose (GDD(z)) were scored, for homogeneous breast phantoms, using both databases. The AAPM Report TG-195 case 3 was replicated, and the results were included. Moreover, cases with heterogeneous and anthropomorphic breast phantoms were also addressed. The results simulated with the un-normalized cross sections are in better overall agreement with the TG-195 data than those from the renormalized cross sections; for MGD the largest discrepancies are 0.13(6)% and 0.74(5)%, respectively. The MGD, K air and DgN values simulated with the two databases show differences that diminish from approximately 10%/3%/6.8% at 8.25 keV down to 1.5%/1.7%/0.4% at 48.75 keV, respectively. For polyenergetic spectra, deviations up to 2.5% were observed. The disagreement between the GDDs simulated with the analyzed databases increases with depth, ranging from −1% near the breast entrance to 4% near the bottom. Thus, the choice of photoelectric cross section database affects the MC simulation results of breast dosimetry and adds a non-negligible systematic uncertainty to the dosimetric quantities used in mammography.

Surgivisio® and O-arm®O2 cone beam CT mobile systems for guidance of lumbar spine surgery: Comparison of patient radiation dose.

To compare patient radiation doses in cone beam computed tomography (CBCT) of two mobile systems used for navigation-assisted mini-invasive orthopedic surgery: O-arm®O2 and Surgivisio®. The study focused on imaging of the spine. Thermoluminescent dosimeters were used to measure organs and effective doses (ED) during CBCT. An ionization-chamber and a solid-state sensor were used to measure the incident air-kerma (Ki) at the center of the CBCT field-of-view and Ki during 2D-imaging, respectively. The PCXMC software was used to calculate patient ED in 2D and CBCT configurations. The image quality in CBCT was evaluated with the CATPHAN phantom. The experimental ED estimate for the low-dose 3D-modes was 2.41 and 0.35mSv with O-arm®O2 (Low Dose 3D-small-abdomen) and Surgivisio® (3DSU-91 images), respectively. PCXMC results were consistent: 1.54 and 0.30mSv. Organ doses were 5 to 12 times lower with Surgivisio®. Ki at patient skin were comparable on lateral 2D-imaging (0.5mGy), but lower with O-arm®O2 on anteroposterior (0.3 versus 0.9mGy). Both systems show poor low contrast resolution and similar high contrast spatial resolution (7 line-pairs/cm). This study is the first to evaluate patient ED and organ doses with Surgivisio®. A significant difference in organs doses was observed between the CBCT systems. The study demonstrates that Surgivisio® used on spine delivers approximately five to six times less patient ED, compared to O-arm®O2, in low dose 3D-modes. Doses in 2D-mode preceding CBCT were higher with Surgivisio®, but negligible compared to CBCT doses under the experimental conditions tested.

Optmization of exposure parameters in digital mammography (CR) using figure of merit

A high diagnostic standard associated with the lowest radiation dose possible for the patient is the aim for a quality examination in mammography, this can be achieved through the Figure of Merit which is a parameter used for optimization in digital mammography. The objective of this work is to determine the optimized radiographic technique (kV and anode / filter combination) for the CR detection system (Computerized Radiography), using the parameter of the figure of merit (FOM), from the contrast noise Ratio (CNR) and the average glandular dose (AGD), with two breast simulators (PMMA and CIRS) and perform a comparison between them. The optimization process was performed on the Siemens Mammomat 3000 Nova Mammograph and the Kodak Direct View CR 850 System CR scanning system using two breast, PMMA and CIRS simulators in the following thicknesses: 2, 4.5 and 7 cm. In order to calculate the AGD, the incident air kerma (Ka,i) was measured and the X-ray beam characteristic factors were applied, according to the technical parameters used for each exposure performed in the simulators. With the values of AGD and CNR associated with each image, the technique optimized for the mammograph-CR set was calculated using the figure of merit. Both simulators presented similar FOM for the conditions tested, but should not be considered equivalent. The following X-ray spectra were selected (anode / filter combination): 2 cm thick (Mo / Mo), 4.5 cm thick (W / Rh) and 7 cm (W / Rh). The estimated doses referring to the optimized techniques found in this work respected the acceptable reference levels in international protocols for quality control in mammography.

Impact of a contrast-to-noise ratio driven and material specific exposure control on image quality and radiation exposure in angiography

Conventional detector-dose driven exposure controls (DEC) do not consider the contrasting material of interest in angiography. Considering the latter when choosing the acquisition parameters should allow for optimization of x-ray quality and consecutively lead to a substantial reduction of radiation exposure. Therefore, the impact of a material-specific, contrast-to-noise ratio (CNR) driven exposure control (CEC) compared to DEC on radiation exposure was investigated. A 3D-printed phantom containing iron, tantalum, and platinum foils and cavities, filled with iodine, barium, and gas (carbon dioxide), was developed to measure the CNR. This phantom was placed within a stack of polymethylmethacrylate and aluminum plates simulating a patient equivalent thickness (PET) of 2.5–40 cm. Fluoroscopy and digital radiography (DR) were conducted applying either CEC or three, regular DEC protocols with parameter settings used in abdominal interventions. CEC protocols where chosen to achieve material-specific CNR values similar to those of DEC. Incident air kerma at the reference point(Ka,r), using either CEC or DEC, was assessed and possible Ka,r reduction for similar CNR was estimated. We show that CEC provided similar CNR as DEC at the same or lower Ka,r. When imaging barium, iron, and iodine Ka,r was substantially reduced below a PET of 20 cm and between 25 cm and 30 cm for fluoroscopy and Dr When imaging platinum and tantalum using fluoroscopy and DR and gas using DR, the Ka,r reduction was substantially higher. We estimate the Ka,r reduction for these materials between 15% and 84% for fluoroscopy and DR between 15% and 93% depending on the PET. The results of this study demonstrate a high potential for skin dose reduction in abdominal radiology when using a material-specific CEC compared to DEC. This effect is substantial in imaging materials with higher energy K-edges, which is beneficial, for example, in long-lasting embolization procedures with tantalum-based embolization material in young patients with arterio-venous malformations.

Normalized glandular dose coefficients for digital breast tomosynthesis systems with a homogeneous breast model

This work aims at calculating and releasing tabulated values of dose conversion coefficients, DgNDBT, for mean glandular dose (MGD) estimates in digital breast tomosynthesis (DBT). The DgNDBT coefficients are proposed as unique conversion coefficients for MGD estimates, in place of dose conversion coefficients in mammography (DgNDM or c, g, s triad as proposed in worldwide quality assurance protocols) used together with the T correction factor. DgNDBT is the MGD per unit incident air kerma measured at the breast surface for a 0° projection and the entire tube load used for the scan. The dataset of polyenergetic DgNDBT coefficients was derived via a Monte Carlo software based on the Geant4 toolkit. Dose coefficients were calculated for a grid of values of breast characteristics (breast thickness in the range 20–90 mm and glandular fraction by mass of 1%, 25%, 50%, 75%, 100%) and the simulated geometries, scan protocols, irradiation geometries and typical spectral qualities replicated those of six commercial DBT systems (GE SenoClaire, Hologic Selenia Dimensions, GE Senographe Pristina, Fujifilm Amulet Innovality, Siemens Mammomat Inspiration and IMS Giotto Class). For given breast characteristics, target/filter combination, tube voltage and half value layer (HVL), two spectra with two HVL values have been simulated in order to permit MGD estimates from experimental HVL values via mathematical interpolation from tabulated values. The adopted breast model assumes homogenous composition of glandular and adipose tissues; it includes a 1.45 mm thick skin envelope in place of the 4–5 mm envelope commonly adopted in dosimetry protocols. The simulation code was validated versus AAPM Task group 195 Monte Carlo reference data sets (absolute differences not higher than 1.1%) and by comparison to relative dosimetry measurements with radiochromic film in a PMMA test object (differences within the maximum experimental uncertainty of 11%). The calculated coefficients show maximum relative deviations of −17.6% and +6.1% from those provided by the DBT dose coefficients adopted in the EUREF protocol and of 1.5%, on average, from data in the AAPM TG223 report. A spreadsheet is provided for interpolating the tabulated DgNDBT coefficients for arbitrary values of HVL, compressed breast thickness and glandular fraction, in the corresponding investigated ranges, for each DBT unit modeled in this work.

Evaluation of image quality and patient exposure in fluoroscopy using a phantom: Is there any clinical relevance?

ObjectiveTo investigate the impact of X-ray preset acquisition protocol settings on fluoroscopy image quality (IQ) and radiation exposure. Materials & MethodsA quality control (QC) phantom was imaged with a modern digital C-arm system, using various preset fluoroscopy protocols. IQ was assessed using human observers and in-house software for automated evaluation, based on contrast-to-noise ratios of details and their background. Patient radiation exposure was evaluated using the displayed Incident Air-Kerma and Kerma-Area Product values. ResultsProtocol selection affects radiation exposure by a factor of about 3. IQ evaluation showed that acquisition protocols produce images with quite different characteristics. The visual IQ evaluation method was time consuming and cumbersome. The automated method, utilized the visual IQ evaluation results for calibration of detection thresholds. However, it failed to reproduce these results for all images and details types. In some images, digital image processing created artifacts which affected the pixel value distributions around details in a way that could be handled only by the human vision. ConclusionManufacturers provide many preset protocols designated for specific clinical uses, which have large impact on IQ characteristics and radiation exposure. However, protocol settings’ selection rationale is essentially a “black box” for the end user. Though QC phantoms are currently used for IQ evaluation, they are not appropriate for drawing firm conclusions concerning the expected performance of each protocol in clinical practice. Currently, there is no consensus on the optimum technical characteristics of preset protocols for specific procedures. More work is needed in this area.