Tube Current-exposure Time Research Articles

Patient dose and associated exposure parameters in pelvic x-ray examinations: dependence on radiographic system.

Technological differences between computed radiography (CR) and digital radiography (DR) systems can influence patient doses and exposure parameters in pelvic x-ray examinations. The presence of radiosensitive organs in the pelvic region underscores the need to optimize these parameters for both CR and DR systems. This prospective study aimed to compare the patient doses and exposure parameters for adult patients undergoing pelvic x-ray examinations using CR and DR systems, based on data from Sri Lanka. The study included data from 56 x-ray examinations, with 25 using CR and 31 using DR. Patient demographic characteristics and exposure parameters (kVp: kilovoltage peak, mAs: tube current-exposure time product) were recorded, and patient doses were measured in terms of the kerma-area product (PKA) using a PKA meter. Despite similar mean weight and body mass index (BMI), the CR systems showed significantly higher mean kVp (7.4%), mAs (16.4%), and PKA (29.7%) than the DR systems (CR - kVp: 73.2, mAs: 37.8, PKA: 2.29Gy cm2; DR - kVp: 67.8, mAs: 31.6, PKA: 1.61Gy cm2). The Mann-Whitney U test revealed statistically significant differences in PKA and kVp between the CR and DR systems (p < 0.05). Furthermore, even with lower patient weight and BMI, the mean mAs and PKA in this study were substantially higher than those reported in the literature for both CR and DR systems. These results suggest the need to optimize current mAs settings for the studied hospitals and introduce radiographic system-specific exposure parameters and reference dose levels for pelvic x-ray examinations in order to enhance patient protection.

Towards the establishment of national diagnostic reference levels for abdomen, KUB, and lumbar spine x-ray examinations in Sri Lanka: a multi-centric study

Diagnostic reference levels (DRLs) and achievable doses (ADs) provide guidance to optimise radiation doses for patients undergoing medical imaging procedures. This multi-centre study aimed to compare institutional DRLs (IDRLs) across hospitals, propose ADs and multi-centric DRLs (MCDRLs) for four common x-ray examinations in Sri Lanka, and assess the potential for dose reduction. A prospective cross-sectional study of 894 adult patients referred for abdomen anteroposterior (AP), kidney-ureter-bladder (KUB) AP, lumbar spine AP, and lumbar spine lateral (LAT) x-ray examinations was conducted. Patient demographic information (age, sex, weight, BMI) and exposure parameters (tube voltage, tube current-exposure time product) were collected. Patient dose indicators were measured in terms of kerma-area product (PKA) using a PKA meter. IDRLs, ADs, and MCDRLs were calculated following the International Commission on Radiological Protection guidelines, with ADs and MCDRLs defined as the 50th and 75th percentiles of the median PKA distributions, respectively. IDRL ranges varied considerably across hospitals: 1.42–2.42 Gy cm2 for abdomen AP, 1.51–2.86 Gy cm2 for KUB AP, 0.83–1.65 Gy cm2 for lumbar spine AP, and 1.76–4.10 Gy cm2 for lumbar spine LAT. The proposed ADs were 1.82 Gy cm2 (abdomen AP), 2.03 Gy cm2 (KUB AP), 1.27 Gy cm2 (lumbar spine AP), and 2.21 Gy cm2 (lumbar spine LAT). MCDRLs were 2.24 Gy cm2 (abdomen AP), 2.40 Gy cm2 (KUB AP), 1.43 Gy cm2 (lumbar spine AP), and 2.38 Gy cm2 (lumbar spine LAT). Substantial intra- and inter-hospital variations in PKA were observed for all four examinations. Although ADs and MCDRLs in Sri Lanka were comparable to those in the existing literature, the identified intra- and inter-hospital variations underscore the need for dose reduction without compromising diagnostic information. Hospitals with high IDRLs are recommended to review and optimise their practices. These MCDRLs serve as preliminary national DRLs, guiding dose optimisation efforts by medical professionals and policymakers.

Comparison of Radiation Dose and Image Quality of Pediatric High-Resolution Chest CT Between Photon-Counting Detector CT and Energy-Integrated Detector CT: A Matched Study.

BACKGROUND. Photon-counting detector (PCD) CT has been shown to reduce radiation dose and improve image quality in adult chest CT examinations; its potential impact in pediatric CT is not well documented. OBJECTIVE. The purpose of our study was to compare radiation dose, objective image quality, and subjective image quality of PCD CT and energy-integrating detector (EID) CT in children undergoing high-resolution CT (HRCT) of the chest. METHODS. This retrospective study included 27 children (median age, 3.9 years; 10 girls, 17 boys) who underwent PCD CT between March 1, 2022, and August 31, 2022, and 27 children (median age, 4.0 years; 13 girls, 14 boys) who underwent EID CT between August 1, 2021, and January 31, 2022; all examinations comprised clinically indicated chest HRCT. The patients in the two groups were matched by age and water-equivalent diameter. Radiation dose parameters were recorded. One observer placed ROIs to measure objective parameters (lung attenuation, image noise, and SNR). Two radiologists independently assessed subjective measures (overall image quality and motion artifacts) using 5-point Likert scales (1 = highest quality). Groups were compared. RESULTS. PCD CT, in comparison with EID CT, showed lower median CTDIvol (0.41 vs 0.71 mGy, p < .001), DLP (10.2 vs 13.7 mGy × cm, p = .008), size-specific dose estimate (0.82 vs 1.34 mGy, p < .001), and tube current-exposure time product (48.0 vs 202.0 mAs, p < .001). PCD CT and EID CT showed no significant difference in right upper lobe (RUL) lung attenuation (mean, -793 vs -750 HU; p = .09), right lower lobe (RLL) lung attenuation (mean, -745 vs -716 HU; p = .23), RUL image noise (mean, 55 vs 51 HU; p = .27), RLL image noise (mean, 59 vs 57 HU; p = .48), RUL SNR (mean, -14.9 vs -15.8; p = .89), or RLL SNR (mean, -13.1 vs -13.6; p = .79). PCD CT and EID CT showed no significant difference in median overall image quality for reader 1 (1.0 vs 1.0, p = .28) or reader 2 (1.0 vs 1.0, p = .17) or median motion artifacts for reader 1 (1.0 vs 1.0, p = .07) or reader 2 (1.0 vs 1.0, p = .22). CONCLUSION. PCD CT showed significantly reduced dose levels without a significant difference in objective or subjective image quality compared with EID CT. CLINICAL IMPACT. These data expand understanding of the capabilities of PCD CT and support its routine use in children.

PHANTOM AND CLINICAL STUDIES ON LOW-DOSE CT PROTOCOL FOR APPLICATOR RECONSTRUCTION IN THREE-DIMENSIONAL BRACHYTHERAPY USING SIZE-SPECIFIC DOSE ESTIMATES BASED ON WATER EQUIVALENT DIAMETER.

To verify the feasibility of low-dose computed tomography (CT) protocol for applicator reconstruction in three-dimensional brachytherapy among patients of different sizes, using size-specific dose estimate based on water equivalent diameter (SSDEdw) in phantom and clinical studies. Pre-scans of a female pelvic phantom were followed by reconstruction of each image set with iDose4 levels 3-5. Imaging data from 64 cervical cancer patients were divided into low, standard and high weight groups. Among two to five CT scans required for applicator reconstruction, the first scan was adopted by routine-dose CT protocol (tube voltage = 120 kV, tube current-exposure time product = 320 mA.s) and the remaining by low-dose CT protocol (tube voltage = 120 kV, tube current-exposure time product = 80 mA.s). The SSDEdw and image quality parameters were compared among the groups, and correlations between SSDEdw and body mass index, area of reference plane (AreaROI3) and mean CT value of reference plane (CTROI3) were analyzed. According to the phantom test results, we determined tube voltage to 120 kV and tube current-exposure time product to 80 mA.s as the low-dose protocol. Clinical study revealed no statistically significant differences in signal-to-noise ratio (SNR) and contrast-noise-ratio (CNR) between low-dose and routine-dose CT in Groups A and B; in Group C, these were significantly lower in the former. The SSDEdw was significantly lower under low-dose than routine-dose protocol in all groups, with strong negative correlation with BMI and AreaROI3 in Groups A and B and moderate-to-strong negative correlation in Group C. Because of the characteristics of three-dimensional brachytherapy, in patients with BMI < 24.0 kg per m2, low-dose CT protocol can minimize radiation exposure and achieve precise, individualized treatment.

Assessment of subjective image quality, contrast to noise ratio and modulation transfer function in the middle ear using a novel full body cone beam computed tomography device

BackgroundMulti slice computed tomography (MSCT) is the most common used method in middle ear imaging. However, MSCT lacks the ability to distinguish the ossicular chain microstructures in detail resulting in poorer diagnostic outcomes. Novel cone beam computed tomography (CBCT) devices’ image resolution is, on the other hand, better than MSCT resolution. The aim of this study was to optimize imaging parameters of a novel full body CBCT device to obtain optimal contrast to noise ratio (CNR) with low effective dose, and to optimize its clinical usability.MethodsImaging of five anonymous excised human cadaver temporal bones, the acquisition of the effective doses and the CNR measurements were performed for images acquired on using Planmed XFI® full body CBCT device (Planmed Oy, Helsinki, Finland) with a voxel size of 75 µm. All images acquired from the specimens using 10 different imaging protocols varying from their tube current exposure time product (mAs) and tube voltage (kVp) were analyzed for eight anatomical landmarks and evaluated by three evaluators.ResultsWith the exception of protocol with 90 kVp 100 mAs, all other protocols used are competent to image the finest structures. With a moderate effective dose (86.5 µSv), protocol with 90 kV 450 mAs was chosen the best protocol used in this study. A significant correlation between CNR and clinical image quality of the protocols was observed in linear regression model. Using the optimized imaging parameters, we were able to distinguish even the most delicate middle ear structures in 2D images and produce accurate 3D reconstructions.ConclusionsIn this ex vivo experiment, the new Planmed XFI® full body CBCT device produced excellent 2D resolution and easily created 3D reconstructions in middle ear imaging with moderate effective doses. This device would be suitable for middle ear diagnostics and for e.g., preoperative planning. Furthermore, the results of this study can be used to optimize the effective dose by selecting appropriate exposure parameters depending on the diagnostic task.

Radiation Doses in Diagnostic Radiology and Method for Dose Reduction

Objective: The current research study aims to calculate entrance surface air kerma for skull, chest, cervical spine, lumbar spine, and pelvic X-ray examinations in interior posterior and posterior interior positions and generate a method for chest dose reduction to decrease radiation risk. Materials and Methods: The indirect dose measurement was used in the current research. The X-ray tube output was measured using RAD-CHECK Plus ionization chamber and the indirect entrance surface air kerma was calculated via applying physical acquisition parameters such as a focus on skin distance, tube current times exposure time (mAs), and applied tube voltage (kV), and applying a mathematical model. Results: The main findings were obtained from comparing the radiation doses with the reference levels of International organizations such as the American College of Radiology and the International Atomic Energy Authority. The mean entrance skin dose for the skull (AP), skull (PA), skull (LAT), cervical spine (PA), cervical spine (LAT), lumbar spine (AP), lumbar spine (LAT), pelvis (AP), and pelvis (LAT) of adult X-ray examinations was within the diagnostic reference dose level values obtained by ACR (2018) except for the ESD for chest (AP) which was 0.88 mGy. Conclusions: The results of the study concluded that by adjusting the applied tube voltage, kV, and tube current product time, mAs decreased the radiation dose to the chest X-ray by 58%.

Assessment of head CT protocol to reduce the radiation dose in eye lens in some selected hospital in Kaduna State, Nigeria

The lens of the eye are very sensitive to radiation and mostly exposed to scattered radiation during the Computed Tomography (CT) procedure. The study measures the absorbed doses to the lens of the eye and proposed a diagnostic reference level for head examination by comparing the current research result with the international standard. The incurred doses of 62 patients who undergone head and neck CT procedure were measure using thermoluminescent dosimeters (TLD-100), the protocols adopted in the study were brain (sequential and spiral), sinus (sequential and spiral), and neck-brain (spiral). The scanning parameters were CT dose index (CTDI), dose length product (DLP), tube current-exposure time product (mAs), kilovoltage peak (kVp), pitch factor, for each patient were recorded. The patients were divided into two age groups (½ to 17) years for Pediatric and >18 years for adult patient, TLD chips were placed on the patient's skin surface at two different locations to measure the absorbed dose of the lens of the eye. The mean dose and standard deviation to left and right eye lens for Hospital A, for Paediatrics Patients were (left 5.29 ± 7.32 mGy, right 5.73 ± 8.9O mGy), Adult Patients (left 5.74 ± 9.23 mGy, right 4.78 ± 6.11 mGy), Hospital B Paediatrics (left 5.08 ± 9.06 mGy, right 2.82 ± 2.67 mGy) Adult (left 0.26 ± 0.07 mGy, right 0.48 ± 0.08 mGy), Hospital C Paediatrics (left 8.95 ± 15.20 mGy, right 7.32 ± 6.14 mGy) Adult (left 6.41 ± 4.15 mGy, right 7.24 ± 5.69 mGy). Threshold recommended by International Commission on Radiological Protection (ICRP) for lens of the eye damage, it appears to be clinically safe. While CT scan remains a crucial tool, further dose reduction can be achieved by controlling different factors affecting patient doses.

Correlation between X-ray tube current exposure time and X-ray photon number in GATE.

X-ray image quality relies heavily on the emitted X-ray photon number which depends on X-ray tube current and exposure time. To accurately estimate the absorbed dose in an imaging protocol, it is better to simulate the X-ray imaging with a Monte Carlo platform such as GATE (Geant4 Application for Tomographic Emission). Although input of GATE is the X-ray photon number of the simulated X-ray tube, it lacks a good way to setup the photon number for a desired X-ray tube current setting. To provide a method to correlate the experimental X-ray tube current exposure time and the X-ray photon number in GATE. The accumulated radiation dose of a micro-computed tomography (CT) X-ray tube was recorded at different current exposure times with a general-purpose ion chamber. GATE was used to model the experimental microCT imaging system and calculate the total absorbed dose (cGy) in the sensitive volume of the ion chamber with different X-ray photon numbers. Linear regression models are used to establish a correlation between the estimated X-ray photon number and the X-ray tube settings. At first, one model establishes the relationship between the experimentally measured dose and the X-ray tube setting. Then, another model establishes a relationship between the simulated dose and the X-ray number in GATE. At last, by correlating these two models, a regression model to estimate the X-ray output number from an experimental X-ray tube setting (mAs) is obtained. For a typical micro-CT scan, the X-ray tube is operated at 50 kVp and 0.5 mA for a 500 ms exposure time per projection (0.25 mAs). For these X-ray imaging parameters, the X-ray number per projection is estimated to be 3.613×106 with 1.0 mm Al filter. The findings of this work provide an approach to correlate the experimental X-ray tube current exposure time to the X-ray photon number in the GATE simulation of the X-ray tube to more accurately determine radiation dose for an imaging protocol.

Comparative Test of the Effect of X-Ray Tube Current Analysis and Exposure Time on CR (Computed Radiography) Image Quality

The medical image system in the form of digital examination results using Computed Radiography (CR) needs to be analyzed, this can be done by knowing the quality of the image contrast resolution and the quality of its spatial resolution. This study conducted a comparative test between two methods of analyzing contrast resolution of medical images. Image quality on Computed Radiography can be determined using contrast resolution analysis, namely calculating the CNR value and PSNR value. The study was carried out using a phantom to represent the density of the bone. The voltages used are 50 kV, 60 kV, 70 kV and 81 kV, respectively. With each voltage, the tube current and exposure time (mAs) were varied 1.6 mAs, 2 mAs, 4 mAs, 8 mAs, 16 mAs, and 32 mAs. The higher the CNR value obtained, the better the image quality. While the PSNR value to get the optimal quality of medical image contrast, the current-time variation of 4 mAs and 16 mAs must be used. Due to the time-current variation, a high PSNR value is obtained, which indicates that the noise of the medical image is getting smaller so that a good contrast quality of the medical image is obtained. Both of these methods can be used to test the suitability of X-ray device, especially for quality control of medical images

Radiation risk for patients undergoing cardiac computed tomography examinations

The various technological advancements in computed tomography (CT) have resulted in remarkable growth in the use of CT imaging in clinical practice, not the least of which has been its establishment as the most valuable imaging examination for the assessment of cardiovascular system disorders. The objective of this study was to assess the effective radiation dose and radiation risk for patients during cardiac CT procedures, based on studies from four different hospitals equipped with 128 slice CT equipment. A total of eighty-three patients were investigated in this study with different clinical indications. Effective doses were also calculated using software based on Monte Carlo simulation. The mean patient age (years), weight (kg), and body mass index (BMI (kg/m2)) were 49 ± 11, 82 ± 12, and 31 ± 6, respectively. The results of the study revealed that the tube voltage (kVp) and tube current-exposure time product (mAs) ranged between 100 to 140 and 50 to 840 respectively. The overall average patient dose values for the volume CT dose index [(CTDIvol), in mGy)] and dose length product (DLP) (in mGy·cm) were 34.8 ± 15 (3.7–117.0) and 383.8 ± 354 (46.0–3277.0) respectively. The average effective dose (mSv) was 15.2 ± 8 (1.2–61.8). The radiation dose values showed wide variation between different hospitals and even within the same hospital. The results indicate the need to optimize radiation dose and to establish diagnostic reference levels (DRLs) for patients undergoing coronary computed tomography angiography (CCTA), also to harmonize the imaging protocols to ensure reduced radiation risk.

Highly reduced-dose CT of the lumbar spine in a human cadaver model.

PurposeFeasibility of a highly reduced-dose lumbar spine CT protocol using iterative reconstruction (IR) in a human cadaver model.Materials and methodsThe lumbar spine of 20 human cadavers was repeatedly examined using three different reduced-dose protocols (RDCT) with decreasing reference tube current-exposure time products (RDCT-1: 50 mAs; RDCT-2: 30 mAs; RDCT-3: 10 mAs) at a constant tube voltage of 140 kV. A clinical standard-dose protocol (SDCT) served as the reference (reference tube current–exposure time product: 70 mAs; tube voltage: 140 kV). Images were reconstructed using filtered back projection (FBP) and two increasing levels of IR: IRL4 and IRL6. A five-point scale was used by two observers to assess the diagnostic quality of anatomical structures (cortical and trabecular bone, intervertebral foramina, pedicles and intervertebral joints, spinous and transverse processes). Objective image noise (OIN) was measured. Results were interpreted using a linear mixed-effects regression model.ResultsRDCT-2 with IRL6 (1.2 ± 0.5mSv) was the lowest reduced-dose protocol which provided diagnostically acceptable and equivalent image quality compared to the SDCT (2.3 ± 1.1mSV) with FBP (p > 0.05). All RDCT protocols achieved a significant reduction of the mean (±SD) effective radiation doses (RDCT-1: 1.7±0.9mSv; RDCT-2: 1.2±0.5mSv; RDCT-3: 0.4±0.2mSv; p < 0.05) compared to SDCT. OIN was lower in all RDCT protocols with the application of IRL4 and IRL6, compared to the SDCT with FBP (p < 0.05).ConclusionHighly reduced-dose lumbar spine CT providing diagnostically acceptable image quality is feasible using IR in this cadaver model and may be transferred into a clinical setting.

Organ Doses from Chest Radiographs in Tuberculosis Patients in Canada and Their Uncertainties in Periods from 1930 to 1969

This paper describes a study to estimate absorbed doses to various organs from film-based chest radiographs and their uncertainties in the periods 1930 to 1948, 1949 to 1955, and 1956 to 1969. Estimated organ doses will be used in new analyses of risks of cancer and other diseases in tuberculosis patients in Canada who had chest fluoroscopic and radiographic examinations in those periods. In this paper, doses to lungs, female breast, active bone marrow, and heart from a single chest radiograph in adults and children of ages 1, 5, 10, and 15 y in the Canadian cohort and their uncertainties are estimated using (1) data on the tube voltage (kV), total filtration (mm Al), tube-current exposure-time product (mA s), and tube output (mR [mA s]−1) in each period; (2) assumptions about patient orientation, distance from the source to the skin of a patient, and film size; and (3) new calculations of sex- and age-specific organ dose conversion coefficients (organ doses per dose in air at skin entrance). Variations in estimated doses to each organ across the three periods are less than 20% in adults and up to about 30% at younger ages. Uncertainties in estimated organ doses are about a factor of 2 to 3 in adults and up to a factor of 4 at younger ages and are due mainly to uncertainties in the tube voltage and tube-current exposure-time product.

A study for tube current exposure time products and image quality in digital mammography

Objective To investigate the relationship between current-exposure time products (mAs) and image quality in digital mammography. Methods The CDMAM phantom of 2 to 7 cm thickness were exposed by manual exposure modes using Mo-Rh anode-filer combinations. The exposure parameters were set as follows: (2 cm, 27 kVp, 10 to 90 mAs); (3 cm, 29 kVp, 20 to 120 mAs); (4 cm, 29 kVp, 20 to 200 mAs); (5 cm, 30 kVp, 40 to 220 mAs); (6 cm, 31 kVp, 40 to 260 mAs); (7 cm, 32 kVp, 80 to 280 mAs). The image quality figure (IQF), contrast to noise ratio (CNR), figure of merit (FOM) and the average glandular dose (AGD) were obtained from images. The optimum filtration and kVp for each breast thickness was found from the calculated FOMs. The optimum mAs for each breast thickness were found from the calculated FOMs and IQFs. And the Pearson correlation analysis was used to analyze the correlations among AGD, CNR and IQF. Results With the increase of mAs, the average glandular dose were linearly increased, and the FOM first increased and then decreased or changed slowly. The AGD, CNR and IQF were significantly correlated when the compression thickness was less than 7 cm (r all>0.87, P<0.05). The optimized exposure parameters were list as follows (2 cm,27 kVp,20 to 30 mAs);(3 cm,29 kVp,30 to 50 mAs); (4 cm,29 kVp,80 to 100 mAs); (5 cm, 30 kVp, 80 to 120 mAs); (6 cm, 31 kVp, 100 to 140 mAs); (7 cm, 32 kVp, 80 to 120 mAs). Conclusion The optimum range of mAs can be confirmed with different breast compression thickness and the setting of automatic exposure parameters should be chosen in clinical practice. Key words: Mammography; Image quality; Radiation dosage

IAEA survey of dental cone beam computed tomography practice and related patient exposure in nine Central and Eastern European countries.

Cone beam CT (CBCT) in dentistry and maxillofacial surgery is a widely used imaging method for the assessment of various maxillofacial and dental pathological conditions. The objective of this study was to summarize the results of a multinational retrospective-prospective study that focused on patient exposure in this modality. The study included 27 CBCT units and 325 adult and paediatric patients, in total. Data on patients, clinical indications, technical parameters of exposure, patient dose indicator, or, alternatively, dose to phantom were collected. The dose indicator used was air kerma-area product, PKA. In most scanners operators are offered with a variety of options regarding technical parameters, especially the field of view size. The median and the third quartile value of PKA for adult patients in 14 different facilities were 820 mGy cm² and 1000 mGy cm² (interquartile range = 1058 mGy cm²), and 653 mGy cm² and 740 mGy cm² (interquartile range = 1179 mGy cm²) for children, as reported by four different institutions. Phantom dose data were reported from 15 institutions, and median PKA ranged from 125 mGy cm² to 1951 mGy cm². Median PKA values varied by more than a 10-fold between institutions, mainly due to differences in imaging protocol used, in particular field of view and tube current-exposure time product. The results emphasize the need for a cautious approach to using dental CBCT. Imaging only when the clinical indications are clear, accompanied with the appropriate radiographic techniques and the optimum imaging protocol, will help reduce radiation dose to patients.

Estimation of organ absorbed dose in pediatric chest X-ray examination: A phantom study

Children have a greater risk of developing lifetime cancer and other biological effects from ionizing radiation exposure than adults. The aim of this study was to measure the absorbed dose received by lungs and heart in pediatric chest X-ray examination using nanoDot optically stimulated luminescent dosimeter (OSLD). The X-ray system, Siemens Multix Top was used. A pediatric phantom developed by using beeswax and polyurethane foam was exposed at 50 kVp, 52 kVp, 55 kVp, 57 kVp and 60 kVp, with fixed tube current-exposure time (3 mAs), which is normally used in pediatric clinical chest X-ray examinations. The nanoDot OSLDs were placed in different parts in the thorax of the phantom according to the position of organs in the chest area, which are lungs and heart. For lungs, absorbed dose measurement nanoDot OSLDs were placed in the apex and base at three different depths. The phantom was exposed three times for each kVp value, and the absorbed doses were measured in mGy. The findings show that the measured absorbed dose to the heart increased with the increase in kVp. Overall, a 22% increase in absorbed dose to heart and a 29% increase in lungs with the increase in kVp was recorded. In addition, absorbed dose to the base of left and right lungs was recorded higher up to 9% as compared to the apex of lungs. In conclusion, the absorbed dosage increases with exposure, while the absorbed dose decreases with depth. It is necessary for the radiographer to select an appropriate exposure setting based on the physical characteristics of the pediatric patient.

Feasibility of Submillisievert CT of the Skeletal Pelvis Using Iterative Reconstruction: A Human Cadaver Study.

OBJECTIVE. The purpose of this study is to investigate the feasibility of submillisievert CT of the skeletal pelvis of human cadavers using a standard-dose protocol and four different reduced-dose protocols reconstructed with filtered back projection (FBP) and iterative reconstruction (IR). MATERIALS AND METHODS. The pelvis of 25 human cadavers was repeatedly examined using different reduced-dose CT (RDCT) protocols with decreasing reference tube current-exposure time products (RDCT protocol 1, 80 mAs; RDCT protocol 2, 60 mAs; RDCT protocol 3, 40 mAs; and RDCT protocol 4, 10 mAs) and a tube voltage of 120 kV. A standard-dose CT (SDCT) protocol (reference tube current-exposure time product, 100 mAs; tube voltage, 120 kV) used for the same cadavers served as the reference. Raw data were reconstructed using FBP and two increasing levels of IR (IR levels 4 and 6). The image quality and diagnostic acceptability of images of the anterior pelvic ring, acetabulum, and posterior pelvic ring including the sacroiliac joints were evaluated on a 5-point scale. A mixed-effects model for repeated measures was performed. RESULTS. The image quality of all anatomic structures was rated as diagnostically acceptable for all protocols reconstructed with IR, except for 11 cadavers that were imaged using RDCT protocol 4. For reconstructions with FBP, image quality was generally rated lower and was diagnostically acceptable only for images obtained using SDCT and RDCT protocol 1 and 2. RDCT protocol 3 with IR was the RDCT protocol with the largest reduced dose still allowing diagnostically acceptable image quality for all anatomic structures in all cadavers. Compared with SDCT, the RDCT protocols resulted in significantly reduced mean (± SD) effective radiation doses (SDCT, 2.0 ± 0.7 mSv; RDCT protocol 1, 1.6 ± 0.6 mSv; RDCT protocol 2, 1.2 ± 0.4 mSv; RDCT protocol 3, 0.8 ± 0.3 mSv; and RDCT protocol 4, 0.3 ± 0.1 mSv; p = 0.001). CONCLUSION. Diagnostically acceptable submillisievert CT of the skeletal pelvis is feasible using IR. To adhere to the ALARA (as low as reasonably achievable) principle, submillisievert pelvic CT protocols combined with IR should be implemented as part of routine clinical practice.

Evaluation of the dose reduction capabilities in digital radiography of the chest using contrast-detail phantom

Assessment of the quality of the images obtained using optimized (low-dose) protocols is the inherent part of the optimization in X-ray diagnostics. To perform the objective quantitative image quality assessment one can use dedicated test-objects, including several components for the simultaneous measurement of the different physical image characteristics (contrast and spatial resolution). The use of such test objects allows estimating and assessing the relations between the patient dose, parameter of the X-ray examination and image quality. That is especially important for the optimization of the digital radiographic examinations performed with automated exposure control. The aim of the current study was to evaluate the possibilities of the patient dose reduction using “contrast-detail” test-object for the digital radiography of the chest in posterior-anterior projection performed with automated exposure control. The study was performed in St-Petersburg Mariinsky hospital on a digital X-ray unit “ARC-Electron” with a flat-panel detector. The combination of a test-object and a tissue-equivalent phantom were imaged on a range of chest X-ray protocols: on a 60–150 kV tube voltage range with automated exposure control; and using fixed 90 kV tube voltage on a range of 2–100 mAs tube current-exposure time product. Dose-area product (cGy×cm2) was measured for each exposure; effective dose (mSv) was estimated for each exposure based on dose-area product. A dedicated software was developed for the automated image quality assessment. The results of the study indicate that the use of a high tube voltage (140–150 kV) with current automated exposure control settings would lead to 60% and 95% reduction of the dose-area product and effective dose, respectively, compared to the standard protocol. The adjustment of the current automated exposure control settings with the reduction of the tube current-exposure time product from 11,2 mAs to the 4,2 mAs for the tube voltage of 90 kV would lead to the reduction of both the dose-area product and effective dose up to a factor of three, compared to the standard protocol. For both scenarios image quality characteristics decreased by less than 15%. The proposed low-dose protocols are under the clinical approbation at Mariinsky hospital. The proposed method of image quality assessment and development of low-dose protocols is recommended for inclusion in the quality assurance program for the radiography examinations.

Internal breast dosimetry in mammography: Monte Carlo validation in homogeneous and anthropomorphic breast phantoms with a clinical mammography system.

PurposeTo validate Monte Carlo (MC)‐based breast dosimetry estimations using both a homogeneous and a 3D anthropomorphic breast phantom under polyenergetic irradiation for internal breast dosimetry purposes.MethodsExperimental measurements were performed with a clinical digital mammography system (Mammomat Inspiration, Siemens Healthcare), using the x‐ray spectrum selected by the automatic exposure control and a tube current‐exposure time product of 360 mAs. A homogeneous 50% glandular breast phantom and a 3D anthropomorphic breast phantom were used to investigate the dose at different depths (range 0–4 cm with 1 cm steps) for the homogeneous case and at a depth of 2.25 cm for the anthropomorphic case. Local dose deposition was measured using thermoluminescent dosimeters (TLD), metal oxide semiconductor field‐effect transistor dosimeters (MOSFET), and GafChromic™ films. A Geant4‐based MC simulation was modified to match the clinical experimental setup. Thirty sensitive volumes (3.2 × 3.2 × 0.38 mm3) on the axial‐phantom plane were included at each depth in the simulation to characterize the internal dose variation and compare it to the experimental TLD and MOSFET measurements. The experimental 2D dose maps obtained with the GafChromic™ films were compared to the simulated 2D dose distributions.ResultsDue to the energy dependence of the dosimeters and due to x‐ray beam hardening, dosimeters based on these three technologies have to be calibrated at each depth of the phantom. As expected, the dose was found to decrease with increasing phantom depth, with the reduction being ~93% after 4 cm for the homogeneous breast phantom. The 2D dose map showed nonuniformities in the dose distribution in the axial plane of the phantom. The mean combined standard uncertainty increased with phantom depth by up to 5.3% for TLD, 6.3% for MOSFET, and 9.6% for GafChromic™ film. In the case of a heterogeneous phantom, the dosimeters are able to detect local dose gradient variations. In particular, GafChromic™ film showed local dose variations of about 46% at the boundaries of two materials.ConclusionsResults showed a good agreement between experimental measurements (with TLD and MOSFET) and MC data for both homogeneous and anthropomorphic breast phantoms. Larger discrepancies are found when comparing the GafChromic™ dose values to the MC results due to the inherent less precise nature of the former.MC validations in a heterogeneous background at the level of local dose deposition and in absolute terms play a fundamental role in the development of an accurate method to estimate radiation dose. The potential introduction of a breast dosimetry model involving a nonhomogeneous glandular/adipose tissue composition makes the validation of internal dose distributions estimates crucial.

Body size and tube voltage-dependent guiding equations for optimal selection of image acquisition parameters in clinical X-ray imaging.

The purpose of this work was to present body size and tube voltage-dependent equations for optimal selection of image acquisition parameters in guiding clinical X-ray imaging. The dose output of X-ray tubes was expressed as a function of the image acquisition parameters of tube voltage (kVp), tube current-exposure time product (mAs), and body size (d). Dose power (n) to kVp was determined to be a linear function of body size in an earlier phantom study. Tube voltage-dependent attenuation coefficients of water were used to determine the kVp effect on the depth dose of X-rays from the body's entrance surface. The new expression for the dose output of X-ray tubes in patients was then employed for image quality and radiation dose optimization, assuming that image quality is a logistic function of the radiation dose to patients. For constant kVp, the percentage of mAs increase for a 1-cm increase in body size d is dependent on the kVp applied. For constant mAs, the percentage of kVp increase for a 1-cm increase in body size is dependent on both body size d and the kVp applied. For constant body size, the percentage of kVp increase should be a fraction of the percentage of decrease in the mAs, where the fraction is dependent on the body size. The improved body size and tube voltage-dependent governing equations for variations in X-ray imaging parameters should be more accurate in guiding optimal selection of the kVp and mAs image acquisition parameters in medical X-ray imaging.

A Projection Quality-Driven Tube Current Modulation Method in Cone-Beam CT for IGRT: Proof of Concept.

Purpose:To develop a projection quality-driven tube current modulation method in cone-beam computed tomography for image-guided radiotherapy based on the prior attenuation information obtained by the planning computed tomography and then evaluate its effect on a reduction in the imaging dose.Materials and Methods:The QCKV-1 phantom with different thicknesses (0-400 mm) of solid water upon it was used to simulate different attenuation (μ). Projections were acquired with a series of tube current–exposure time product (mAs) settings, and a 2-dimensional contrast to noise ratio was analyzed for each projection to create a lookup table of mAs versus 2-dimensional contrast to noise ratio, μ. Before a patient underwent computed tomography, the maximum attenuation within the 95% range of each projection angle (θ) was estimated according to the planning computed tomography images. Then, a desired 2-dimensional contrast to noise ratio value was selected, and the mAs setting at θ was calculated with the lookup table of mAs versus 2-dimensional contrast to noise ratio,. Three-dimensional cone-beam computed tomography images were reconstructed using the projections acquired with the selected mAs. The imaging dose was evaluated with a polymethyl methacrylate dosimetry phantom in terms of volume computed tomography dose index. Image quality was analyzed using a Catphan 503 phantom with an oval body annulus and a pelvis phantom.Results:For the Catphan 503 phantom, the cone-beam computed tomography image obtained by the projection quality-driven tube current modulation method had a similar quality to that of conventional cone-beam computed tomography . However, the proposed method could reduce the imaging dose by 16% to 33% to achieve an equivalent contrast to noise ratio value. For the pelvis phantom, the structural similarity index was 0.992 with a dose reduction of 39.7% for the projection quality-driven tube current modulation method.Conclusions:The proposed method could reduce the additional dose to the patient while not degrading the image quality for cone-beam computed tomography. The projection quality-driven tube current modulation method could be especially beneficial to patients who undergo cone-beam computed tomography frequently during a treatment course.