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OBJECTIVE - To estimate effective dose of kidney-ureter-bladder (KUB) radiographs in a contemporary population of patients with urolithiasis.
METHODS - A retrospective review was performed to identify patients visiting a urology clinic for urolithiasis where a KUB was obtained and whom had a recent computed tomography (CT). Effective dose for KUBs was estimated using a Monte Carlo based simulation program and for CT utilizing the reported dose-length-product. Age, gender, body mass index, and abdominal diameter were analyzed for association with effective dose. KUBs performed at outside facilities in referred patient were compared to those obtained locally when available.
RESULTS - Fifty-four patients were identified meeting criteria. The majority (92.6%) of KUBs contained multiple radiographs. Mean effective dose was 2.15 mSv ± 1.67 mSv. Only 26% of examinations effective dose was under 1 mSv. Body mass index, abdominal thickness, and image count were all associated with an increase in dose (P < .01 each). Similar to local KUBs, 88% of outside examinations contained multiple images.
CONCLUSION - KUB examinations in this contemporary setting are associated with a 2-fold higher effective dose then is often referenced. Increased effective dose is associated with increased patient size and number of images acquired. Nearly 1 in 5 patient's KUB effective dose was similar to a low-dose CT. KUBs role should be re-examined given its limited sensitivity, specificity, associated radiation, and other available imaging options.
Copyright © 2018. Published by Elsevier Inc.
PURPOSE - To develop and investigate a set of biophysical models based on a mechanically coupled reaction-diffusion model of the spatiotemporal evolution of tumor growth after radiation therapy.
METHODS AND MATERIALS - Post-radiation therapy response is modeled using a cell death model (M), a reduced proliferation rate model (M), and cell death and reduced proliferation model (M). To evaluate each model, rats (n = 12) with C6 gliomas were imaged with diffusion-weighted magnetic resonance imaging (MRI) and contrast-enhanced MRI at 7 time points over 2 weeks. Rats received either 20 or 40 Gy between the third and fourth imaging time point. Diffusion-weighted MRI was used to estimate tumor cell number within enhancing regions in contrast-enhanced MRI data. Each model was fit to the spatiotemporal evolution of tumor cell number from time point 1 to time point 5 to estimate model parameters. The estimated model parameters were then used to predict tumor growth at the final 2 imaging time points. The model prediction was evaluated by calculating the error in tumor volume estimates, average surface distance, and voxel-based cell number.
RESULTS - For both the rats treated with either 20 or 40 Gy, significantly lower error in tumor volume, average surface distance, and voxel-based cell number was observed for the M and M models compared with the M model. The M model fit, however, had significantly lower sum squared error compared with the M and M models.
CONCLUSIONS - The results of this study indicate that for both doses, the M and M models result in accurate predictions of tumor growth, whereas the M model poorly describes response to radiation therapy.
Copyright © 2017 Elsevier Inc. All rights reserved.
With the increasing use of coronary artery calcium (CAC) scoring to risk stratify asymptomatic patients for future cardiovascular events, there have been concerns raised regarding the theoretical risk of radiation exposure to this potentially large patient population. Newer CT protocols have sought to reduce radiation exposure without compromising image quality, but the reported radiation exposures in the literature remains widely variable (0.7-10.5 mSv). In this study, we report the radiation exposure of calcium scoring from our MESA cohort across several modern CT scanners with the aim of clarifying the radiation exposure of this imaging modality. To evaluate the mean effective doses of radiation, using dose length product, utilized for coronary artery calcium scoring in the MESA cohort, in an effort to understand estimated population quantity effective dose using individual measurements of scanner radiation output using current CT scanners. We reviewed effective dose in milliSieverts (mSv) for 3442 participants from the MESA cohort undergoing coronary artery calcium scoring, divided over six sites with four different modern CT scanners (Siemens64, Siemens Somatom Definition, GE64, and Toshiba 320). For effective dose calculation (milliSieverts, mSv), we multiplied the dose length product by conversion factor k (0.014). The mean effective dose amongst all participants was 1.05 mSv, a median dose of 0.95 mSV. The mean effective dose ranged from 0.74 to 1.26 across the six centers involved with the MESA cohort. The Siemens Somatom Definition scanner had effective dose of 0.53 (n = 123), Siemens 64 with 0.97 (n = 1684), GE 64 with 1.16 (n = 1219), and Toshiba 320 with 1.26 mSv (n = 416). Subgroup analysis by BMI, age, and gender showed no variability between scanners, gender, ages 45-74 years old, or BMI less than 30 kg/m(2). Subjects over age 75 yo had a mean effective dose of 1.29 ± 0.31 mSv, while the <75 yo subgroup was 0.78 ± 0.09 mSv (p < 0.05). Effective doses in subjects with BMI > 40 kg/m(2) was significantly greater than other subgroups, with mean dose of 1.47 ± 0.51 mSv (p < 0.01). Using contemporary CT scanners and protocols, the effective dose for coronary artery calcium is approximately 1 mSv, an estimate which is consistently lower than previously reported for CAC scanning, regardless of age, gender, and body mass index.
BACKGROUND - The high value of the specific absorption rate (SAR) of radio-frequency (RF) energy arising from the series of RF refocusing pulses in T2-weighted (T2-w) turbo spin echo (TSE) MRI hampers its clinical application at 7.0 Tesla (7T). T2-w gradient and spin echo (GRASE) uses the speed from gradient refocusing in combination with the chemical-shift/static magnetic field (B0) inhomogeneity insensitivity from spin-echo refocusing to acquire T2-w images with a limited number of refocusing RF pulses, thus reducing SAR.
OBJECTIVES - To investigate whether low SAR T2-w GRASE could replace T2-w TSE in detecting white matter (WM) disease in MS patients imaged at 7T.
METHODS - The .7 mm3 isotropic T2-w TSE and T2-w GRASE images with variable echo times (TEs) and echo planar imaging (EPI) factors were obtained on a 7T scanner from postmortem samples of MS brains. These samples were derived from brains of 3 female MS patients. WM lesions (WM-Ls) and normal-appearing WM (NAWM) signal intensity, WM-Ls/NAWM contrast-to-noise ratio (CNR) and MRI/myelin staining sections comparisons were obtained.
RESULTS - GRASE sequences with EPI factor/TE = 3/50 and 3/75 ms were comparable to the SE technique for measures of CNR in WM-Ls and NAWM and for detection of WM-Ls. In all sequences, however, identification of areas with remyelination, Wallerian degeneration, and gray matter demyelination, as depicted by myelin staining, was not possible.
CONCLUSIONS - T2-w GRASE images may replace T2-w TSE for clinical use. However, even at 7T, both sequences fail in detecting and characterizing MS disease beyond visible WM-Ls.
Copyright © 2015 by the American Society of Neuroimaging.
The authors have created a radiation transport code using the GEANT4 Monte Carlo toolkit to simulate pediatric patients undergoing CT examinations. The focus of this paper is to validate their simulation with real-world physical dosimetry measurements using two independent techniques. Exposure measurements were made with a standard 100-mm CT pencil ionization chamber, and absorbed doses were also measured using optically stimulated luminescent (OSL) dosimeters. Measurements were made in air with a standard 16-cm acrylic head phantom and with a standard 32-cm acrylic body phantom. Physical dose measurements determined from the ionization chamber in air for 100 and 120 kVp beam energies were used to derive photon-fluence calibration factors. Both ion chamber and OSL measurement results provide useful comparisons in the validation of the Monte Carlo simulations. It was found that simulated and measured CTDI values were within an overall average of 6% of each other.
Education, justification, and optimization are the cornerstones to enhancing the radiation safety of medical imaging. Education regarding the benefits and risks of imaging and the principles of radiation safety is required for all clinicians in order for them to be able to use imaging optimally. Empowering patients with knowledge of the benefits and risks of imaging will facilitate their meaningful participation in decisions related to their health care, which is necessary to achieve patient-centered care. Limiting the use of imaging to appropriate clinical indications can ensure that the benefits of imaging outweigh any potential risks. Finally, the continually expanding repertoire of techniques that allow high-quality imaging with lower radiation exposure should be used when available to achieve safer imaging. The implementation of these strategies in practice is necessary to achieve high-quality, patient-centered imaging and will require a shared effort and investment by all stakeholders, including physicians, patients, national scientific and educational organizations, politicians, and industry.
Nuclear spin hyperpolarization overcomes the sensitivity limitations of traditional NMR and MRI, but the most general method demonstrated to date (dynamic nuclear polarization) has significant limitations in scalability, cost, and complex apparatus design. As an alternative, signal amplification by reversible exchange (SABRE) of parahydrogen on transition metal catalysts can hyperpolarize a variety of substrates, but to date this scheme has required transfer of the sample to low magnetic field or very strong RF irradiation. Here we demonstrate "Low-Irradiation Generation of High Tesla-SABRE" (LIGHT-SABRE) which works with simple pulse sequences and low power deposition; it should be usable at any magnetic field and for hyperpolarization of many different nuclei. This approach could drastically reduce the cost and complexity of producing hyperpolarized molecules.
Copyright © 2014 Elsevier Inc. All rights reserved.
The current paper details the recommendations arising from an NIH-NHLBI/NCI-sponsored symposium held in November 2012, aiming to identify key components of a radiation accountability framework fostering patient-centered imaging and shared decision-making in cardiac imaging. Symposium participants, working in 3 tracks, identified key components of a framework to target critical radiation safety issues for the patient, the laboratory, and the larger population of patients with known or suspected cardiovascular disease. The use of ionizing radiation during an imaging procedure should be disclosed to all patients by the ordering provider at the time of ordering, and reinforced by the performing provider team. An imaging protocol with effective dose ≤3 mSv is considered very low risk, not warranting extensive discussion or written informed consent. However, a protocol effective dose >20 mSv was proposed as a level requiring particular attention in terms of shared decision-making and either formal discussion or written informed consent. Laboratory reporting of radiation dosimetry is a critical component of creating a quality laboratory fostering a patient-centered environment with transparent procedural methodology. Efforts should be directed to avoiding testing involving radiation, in patients with inappropriate indications. Standardized reporting and diagnostic reference levels for computed tomography and nuclear cardiology are important for the goal of public reporting of laboratory radiation dose levels in conjunction with diagnostic performance. The development of cardiac imaging technologies revolutionized cardiology practice by allowing routine, noninvasive assessment of myocardial perfusion and anatomy. It is now incumbent upon the imaging community to create an accountability framework to safely drive appropriate imaging utilization.
Copyright © 2014 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.
OBJECTIVE - To investigate and characterize the association between fluoroscopy radiation dose rate and various patient size metrics during ureteroscopy.
MATERIALS AND METHODS - Fluoroscopy data were collected from 100 patients undergoing ureteroscopy for stone disease. Radiation dose rates were determined from fluoroscopy dose and time. Estimated entrance skin dose was calculated from air kerma (AK) by applying correction factors. Effective dose (ED) was estimated with Monte Carlo-based simulation software. Patient size metrics included body mass index (BMI), anterior-posterior (AP) midline distance, AP transrenal thickness, and region of interest (ROI) pixel value magnitude on computed tomography scout. Univariate and multivariate regression analyses were performed to determine the association between AK dose rate and patient size metrics, adjusting for laterality and stone location.
RESULTS - Obese patients (>30 kg/m(2)) comprised 46% of the cohort. Mean fluoroscopy time, displayed AK, entrance skin dose, and ED were 4.2 ± 6.0 second, 1.2 ± 2.1 mGy, 1.2 ± 2.2 mGy, and 0.08 ± 0.15 mSv, respectively. Mean AK dose rate and ED dose rates were 0.30 ± 0.23 mGy/second and 0.021 ± 0.016 mSv/second, respectively. Compared with the nonobese category, the highest BMI category (≥35 kg/m(2)) had over a 3-fold higher mean AK rate (0.50 vs 0.16 mGy/second). On univariate and multivariate analysis, BMI, AP midline distance, AP transrenal thickness, and computed tomography scout region of interest pixel value magnitude were each significantly associated with dose rate.
CONCLUSION - Larger patients experience higher radiation dose rates under fluoroscopy. Severely obese patients receive 3-fold higher dose rates compared with nonobese patients. Given the higher incidence of stone disease in obese patients, all attempts should be made to minimize radiation exposure during ureteroscopy.
Copyright © 2013 Elsevier Inc. All rights reserved.
The information for the present discussion on the uncertainties associated with estimation of radiation risks and probability of disease causation was assembled for the recently published NCRP Report No. 171 on this topic. This memorandum provides a timely overview of the topic, given that quantitative uncertainty analysis is the state of the art in health risk assessment and given its potential importance to developments in radiation protection. Over the past decade the increasing volume of epidemiology data and the supporting radiobiology findings have aided in the reduction of uncertainty in the risk estimates derived. However, it is equally apparent that there remain significant uncertainties related to dose assessment, low dose and low dose-rate extrapolation approaches (e.g. the selection of an appropriate dose and dose-rate effectiveness factor), the biological effectiveness where considerations of the health effects of high-LET and lower-energy low-LET radiations are required and the transfer of risks from a population for which health effects data are available to one for which such data are not available. The impact of radiation on human health has focused in recent years on cancer, although there has been a decided increase in the data for noncancer effects together with more reliable estimates of the risk following radiation exposure, even at relatively low doses (notably for cataracts and cardiovascular disease). New approaches for the estimation of hereditary risk have been developed with the use of human data whenever feasible, although the current estimates of heritable radiation effects still are based on mouse data because of an absence of effects in human studies. Uncertainties associated with estimation of these different types of health effects are discussed in a qualitative and semi-quantitative manner as appropriate. The way forward would seem to require additional epidemiological studies, especially studies of low dose and low dose-rate occupational and perhaps environmental exposures and for exposures to x rays and high-LET radiations used in medicine. The development of models for more reliably combining the epidemiology data with experimental laboratory animal and cellular data can enhance the overall risk assessment approach by providing biologically refined data to strengthen the estimation of effects at low doses as opposed to the sole use of mathematical models of epidemiological data that are primarily driven by medium/high doses. NASA's approach to radiation protection for astronauts, although a unique occupational group, indicates the possible applicability of estimates of risk and their uncertainty in a broader context for developing recommendations on: (1) dose limits for occupational exposure and exposure of members of the public; (2) criteria to limit exposures of workers and members of the public to radon and its short-lived decay products; and (3) the dosimetric quantity (effective dose) used in radiation protection.