Published Conversion Factors Research Articles

Duty of candour and clinically significant accidental or unintended exposures: revisiting the definition of moderate harm for patient safety incidents involving ionizing radiation.

To explore a quantitative interpretation of the term 'moderate harm' as applied to the triggering of the duty of candour associated with clinically significant accidental and unintended exposures to ionizing radiation. Current definitions of 'moderate harm' were matched to the lay descriptions of disease and injury states used in the calculation of detriment as disability-adjusted life years (DALY) by the World Health Organization, to obtain a value of detriment associated with 'moderate harm'. Published conversion factors between effective dose and DALY were used to calculate the effective dose associated with the same detriment. The DALY loss associated with a moderate harm incident is estimated as 0.0216 years. This corresponds to the detriment resulting from exposure to ionizing radiation of 21 mSv. An effective dose of 21 mSv relates to a probability of induced cancer of 0.0012. The results obtained closely match existing guidance although the method used is completely different. It is concluded that there is no evidence to change the existing guidance on the triggering of DoC in radiation incidents. An alternative approach to linking 'moderate harm' and radiation detriment has reinforced existing guidance.

Consumption of Pro Re Nata Inpatient Opioids Following Surgical Treatment of Severe Odontogenic Infections

<h3>Purpose</h3> The purpose of this study was to analyze the pro re nata (PRN) opioid consumption of patients with severe odontogenic infections following operating room incision and drainage using odontogenic infection severity scores. The null hypothesis was that no statistically significant difference in post-operative inpatient PRN opioid consumption exists between patients with infections of higher severity score and lower severity score. <h3>Methods</h3> This retrospective study reviewed consecutive charts of all patients admitted for severe odontogenic infections to the UTSW and Parkland Memorial hospital from January 2016 to December 2020. All patients admitted for greater than one hospital day and treated with surgical incision and drainage in the operating room with an American Society of Anesthesiologists (ASA) physical classification score of 1 or 2 as ranked by the anesthesia team prior to surgery were included. Patients with chronic pain conditions, history of substance abuse, or infections of non-odontogenic origin were excluded. Patients that required advanced airway post-surgery and intensive care unit stay or multiple operations were also excluded. Post-operative opioid doses were tabulated from the time the patient arrived on the floor as inpatient post-surgery until discharge using equianalgesic opioid tables and published conversion factors (1,2). Severity scores were assigned based on the risk to the airway and vital structures as described by Flynn et al (3). Patients with a severity score greater than or equal to five were designated as group A and less than five group B. The primary predictor variable was severity score, and the primary outcome variable was the amount of milligram morphine equivalents (MME) administered. Comparisons between Group A and Group B were conducted for age, ASA classification, hospital duration, severity score, and MME using t-tests. Values of p < 0.05 were considered statistically significant. <h3>Results</h3> A total of 93 subjects met the inclusion criteria. Group A included 40 subjects and group B included 53 subjects. The average age of subjects in group A was 38.28 years (SD=10.92), and in group B 38.03 years (SD=12.53). There was no significant difference between the groups in age (p = 0.93). The average hospital duration for patients in group A was 3.85 days (SD=1.17). Group B had an average hospital duration of 3.72 days (SD=1.08). There was no significant difference between the groups in hospital duration (p = 0.57). Group A consumed an average MME of 39.85, while group B consumed an average of 23.43. Group A consumed a significantly greater amount of PRN post-operative inpatient opioid medications (p = 0.02). <h3>Conclusion</h3> Patients with higher odontogenic infection severity scores consumed more post-operative PRN opioid analgesic medications. Given that odontogenic infections are largely preventable, it is imperative to prevent the progression of odontogenic infections to limit patient exposure to opioid medication.

Ultrasound determination of pediatric thyroid mass.

Radioiodine therapy for Graves disease can be achieved with dosing based on estimated thyroid gland mass. Thyroid mass can be estimated using linear ultrasound measurements, and conversion factors for volume and density. The choice of conversion factors could impact estimated thyroid mass and thus administered radioiodine dose. The objective of this study was to define the relationship between thyroid mass estimated by ultrasound and measured thyroid mass following thyroidectomy. This was a retrospective, exempt study that included patients < 18 years of age with < 6 months between thyroid ultrasound and thyroidectomy January 2010-June 2020. Thyroid dimensions by ultrasound, thyroid mass at thyroidectomy and histopathological diagnosis were collected. Published conversion factors were used to estimate thyroid volume with conversion to mass using a density of 1.05g/cm3. Pearson correlations and Bland-Altman difference analyses were used to define the relationship between estimated mass and specimen weight. Linear regression was used to calculate an optimal conversion factor for estimating thyroid mass. We included 86 patients, 67 female (78%), with a mean age of 14.5 ± 3.15 years. Mass estimated using all tested conversion factors had similar strong, positive correlation with specimen weight (r = 0.95). The mean difference between thyroid mass estimated by ultrasound and measured mass ranged from - 0.34g (conversion factor = 0.523) to 1.69g (conversion factor = 0.554). The optimal simplified factor for estimation of thyroid mass for the study sample was 0.537. All published conversion factors for estimating thyroid mass based on linear ultrasound measurements produce good estimates of thyroid mass. Errors in estimated mass are less than 2g on average.

Can the Third Part of Duodenum Behind SMA Be Detected With Confidence on CT as a Proposed Mechanism for Imaging Suspected Malrotation in Children? A Preliminary Proof of Concept Study

The aims of this study were to determine frequency and reliability of computed tomography (CT) detection of anatomic landmarks for imaging suspected midgut malrotation in infants and children, and to calculate an estimated effective dose of an upper abdominal CT scan in our patient population. Fifty consecutive pediatric patients who underwent a CT scan that included their upper abdomen between August 2016 and February 2018 were included. Four pediatric radiology consultants independently reviewed CT scans for detection of the third part of the duodenum and defined their confidence level of this through identification of continuity with the pyloric antrum, D1, D2, and D4 components of the duodenum, as well as the duodenojejunal flexure.Interobserver variability was assessed using Fleiss κ for agreement. A dose estimate, per scan, was calculated using the scanner dose-length product and published conversion factors by Deak. Thirty patients were boys. The average age was 7.5 ± 5.4 years (6 days to 16 years). The D3 segment was definitely identified in 70% of scans, with 68% to 73%, moderate agreement between the readers and a Fleiss κ of 0.47 to 0.52. The DJ flexure was definitely identified in only 30.5% cases, with 35%, poor agreement between readers (Fleiss κ of 0.03). The average estimated dose for a targeted CT scan of the abdomen was 0.9 mSv (0.04-2.4 mSv). The third part of the duodenum, which is integral in excluding malrotation on cross-sectional studies, was "definitely" identified in 70% of CT scans of children in our study, with 68% to 73% agreement between the readers and a Fleiss κ of 0.47 to 0.52.These preliminary proof of concept results demonstrating a combination of a comparable CT dose in relation to upper gastrointestinal contrast studies and an acceptable number of cases delineating the third part of the duodenum with moderate agreement are a first step in suggesting low-dose CT for an imaging diagnosis of malrotation. Malrotation can be excluded in cases where D3 is well demonstrated in the normal position, which negates the need to automatically refer children with bilious emesis to specialist centers for upper gastrointestinal contrast studies.

Dose quantities for measurement and comparison of doses to individual patients in computed tomography (CT)

The dose quantities displayed routinely on CT scanners, the volume averaged CT dose index (CTDIvol) and dose length product, provide measures of doses calculated for standard phantoms. The American Association of Medical Physics has published conversion factors for the adjustment of CTDIvol to take account of variations in patient size, the results being termed size-specific dose estimate (SSDE). However, CTDIvol and SSDE, while useful in comparing and optimising doses from a set procedure, do not provide risk-related information that takes account of the organs and tissues irradiated and associated cancer risks. A derivative of effective dose that takes account of differences in body and organ sizes and masses, referred to here as size-specific effective dose (SED), can provide such information. Data on organ doses from NCICT software that is based on Monte Carlo simulations of CT scans for 193 adult phantoms have been used to compute values of SED for CT examinations of the trunk and results compared with corresponding values of SSDE. Relationships within ±8% were observed between SED and SSDE for scans extending over similar regions for phantoms with a wide range of sizes. Coefficients have been derived from fits of the data to estimate SED values from SSDEs for different regions of the body for scans of standard lengths based on patient height. A method developed to take account of differences in scan length gave SED results within ±5% of values calculated using the NCI phantom library. This approach could potentially be used to estimate SED from SSDE values, allowing their display at the time a CT scan is performed.

Gelatinous and soft-bodied zooplankton in the Northeast Pacific Ocean: organic, elemental, and energy contents

Gelatinous and soft-bodied zooplankton (GZ) have long been considered to have low energetic value (‘trophic dead end hypothesis’) and be insufficient to sustain higher trophic levels. However, the nutritional composition and energy content of GZ are often poorly known for entire groups, ignoring species-, size-, and stage-specific differences. In this study, organic matter and elemental composition (carbon and nitrogen) were measured for &gt;1000 specimens from 34 GZ species collected from neritic and oceanic waters of the Northeast Pacific between 2014 and 2020. Species included 3 gastropods, 16 hydrozoans, 2 nude ctenophores, 6 scyphozoans, 3 tentaculate ctenophores, and 4 thaliaceans. Organic content and elemental composition were used to estimate energy content using published conversion factors and differed between and within taxonomic classes. Size-dependent variability was shown for several species. Differences in organic content and elemental composition by development stage were observed in a salp and scyphomedusa species, highlighting the need to consider life cycle stages separately. The relative energy values of GZ were generally low and highly variable, although some taxa were comparable to crustaceans. The findings of the present study emphasise the need for a more detailed consideration of GZ in marine food web models and time series analyses, to take into account their inter- and intraspecific variability.

Radiation Dose during Transarterial Radioembolization: A Dosimetric Comparison of Cone-Beam CT and Angio-CT Technologies

PurposeTo evaluate the radiation dose differences for intraprocedural computed tomography (CT) imaging between cone-beam CT and angio-CT acquired during transarterial radioembolization (TARE) therapies for hepatocellular carcinoma. Materials and MethodsA retrospective cohort of 22 patients who underwent 23 TARE procedures were selected. Patients were imaged in both cone-beam CT and angio-CT rooms as a part of their conventional treatment plan. Effective dose contributions from individual CT acquisitions as well as the cumulative dose contributions from procedural 3D imaging were evaluated. Angiography dose contributions were omitted. Cone-beam CT images were acquired on a C-arm Philips Allura system. Effective doses were evaluated by coupling previously published conversion factors (effective dose per dose-area product) to patient’s dose-area product meter readings after the procedure. Angio-CT images were acquired on a hybrid Canon Infinix-i Aquilion PRIME system. Effective doses from angio-CT scans were estimated using Radimetrics. Comparisons of a single patient’s dose differential between the 2 technologies were made. ResultsThe mean effective dose from a single CT scan was 6.42 mSv and 5.99 mSv in the cone-beam CT room and the angio-CT room, respectively (P = .3224), despite the greater field of view and average craniocaudal scan coverage in angio-CT. The mean effective dose summed across all CTs in a procedure was 12.89 mSv and 34.35 mSv in the cone-beam CT room and the angio-CT room, respectively (P = .0018). ConclusionsThe mean effective dose per CT scan is comparable between cone-beam CT and angio-CT when considered in direct comparison for a single patient.

P133 PRESCRIPTION OPIOID USE AMONG VETERANS WITH INFLAMMATORY BOWEL DISEASE

Abstract Background Opioids are commonly prescribed to manage pain in patients with IBD despite increasing evidence of harm associated with chronic use. The aim of the current study was to describe trends in opioid use among veterans with IBD. Methods This was a retrospective cohort study derived from the Veterans Affairs (VA) Health Care System. A unique patient identifier facilitated longitudinal evaluation of electronic databases that include medical diagnoses, surgical procedures, pharmaceuticals, labs, vital status information, dates of treatment, and radiology findings. Veterans were labeled as having IBD if there were at least 2 outpatient or 1 inpatient health care encounters with an ICD-9/10 diagnostic code consistent with IBD from fiscal years 2002 to 2016. Veterans without a minimum of 2 years of follow-up or who had a cancer diagnosis within 1 year before or after IBD diagnosis were excluded. In order to standardize the quantity of opioid exposure, morphine milligram equivalents (MME) for each prescription was calculated using published conversion factors. Individual prescriptions with missing quantity or day’s supply and prescriptions exceeding 1000 MME/day were excluded. Opioid exposure during the first year following the initial diagnosis date was determined as the average MME/day for those with at least one opioid prescription. Annual opioid prescribing rates per 100 IBD patients were calculated. Comorbidities were assessed using a modified Charlson Comorbidity Index (CCI), excluding cancer from the calculation. Results During the study period, 65,817 veterans with IBD were identified. The majority were males (92.1%), Caucasian (78.2%), and had a mean age of 58.2 years. In total, 1,471,019 individual opioid prescriptions were evaluated. The quantity and rate of opioid prescriptions peaked in 2012, with 115,774 unique prescriptions and 698.5 opioid prescriptions per 100 IBD patients, respectively. Twenty-seven percent (n=17,844) of IBD patients had at least one opioid prescription within the initial year of diagnosis. Mean opioid exposure during the initial year of diagnosis averaged 33.2 MME/day, and 12.2% had mean opioid exposure greater than 50 MME/day. Opioid exposure peaked in 2005 at 37.4 MME/day and consistently declined to 29.3 MME/day in 2016. Conclusion There has been a significant decline in opioid prescriptions, prescribing rate, and mean opioid exposure since peaking in 2012. These trends are similar to those seen in the non-veteran US population.

Measurements of pediatric radiation exposure during barium imaging procedures

Radiological imaging has been considered a vital tool in the diagnosis of gastrointestinal tract (GIT) disorders. Gastrointestinal radiography (GIR) has been a major and first-choice method for diagnosing GIT diseases with barium as contrast media since its emergence in 1910. Radiographic examination of children, especially neonates, attracts particular interest because of the increased opportunity for expression of delayed radiogenic cancers as a consequence of relative longer life expectancy. Barium studies are of particular interest because it constitutes 5% of the total number of radiological examinations and 17% of the collective doses. Although, the task is important, there are few data on radiation doses to infants and children undergoing barium procedures. The current study intends to evaluate the radiation dose to pediatric patients during barium studies and to estimate the effective doses and radiation risk of the aforementioned procedures. A total of 43 pediatric barium procedures were performed in this study. 21.7% of the sample was barium meal, 8.6% were undergone barium swallow while 69.5% of the sample were barium enemas. Entrance surface air kerma (ESAKs) were calculated from patient exposure parameters using DosCal software. Effective doses (E) were calculated using published conversion factors and methods recommended by the national Radiological Protection Board (NRPB). The mean film numbers was 12.4, 8.9 and 8 for barium meal, barium enema and barium swallow, respectively. The maximum number of X rays was obtained in barium meal (21 film per a single procedure). The mean patient doses per procedure were 2.1 ± 0.8 mGy, 3.0 ± 23 mGy and 1.2 ± 0.2 mGy for barium meal, swallow and enema, respectively. The mean effective doses were 0.3 mSv, 1.0 mSv and 0.2 mSv at the same order. The dose values in this study were higher than previous studies. The unnecessary radiation exposure can be reduced significantly by reducing the number of films and screening time. Diagnostic reference level is recommended to improve the practice. Disclosure Authors have nothing to disclose.

SU‐F‐T‐669: Commissioning of An Electronic Brachytherapy System for Targeted Mouse Irradiation

Purpose:The aim of this study was to commission the Xoft Axxent™ electronic brachytherapy (eBT) source and 10 mm diameter surface applicator with NIST traceability for targeted irradiations of mouse anal carcinomas.Methods:The Xoft Axxent™ electronic brachytherapy (eBT) and 10 mm diameter surface applicator was chosen by the collaborating physician as a radiation delivery mechanism for mouse anal carcinomas. The target dose was 2 Gy at a depth of 3 mm in tissue to be delivered in a single fraction. To implement an accurate and reliable irradiation plan, the system was commissioned by first determining the eBT source output and corresponding dose rate at a depth of 3 mm in tissue. This was determined through parallel‐plate ion chamber measurements and published conversion factors. Well‐type ionization chamber measurements were used to determine a transfer coefficient, which correlates the measured dose rate at 3 mm to the NIST‐traceable quantity, air‐kerma rate at 50 cm in air, for eBT sources. By correlating these two quantities, daily monitoring in the well chamber becomes an accurate and efficient quality assurance technique. Once the dose‐rate was determined, a treatment recipe was developed and confirmed with chamber measurements to deliver the requested dose. Radiochromic film was used to verify the dose distribution across the field.Results:Dose rates at 3 mm depth in tissue were determined for two different Xoft Axxent™ sources and correlated with NIST‐traceable well‐type ionization chamber measurements. Unique transfer coefficients were determined for each source and the treatment recipe was validated by measurements. Film profiles showed a uniform dose distribution across the field.Conclusion:A Xoft Axxent™ eBT system was successfully commissioned for use in the irradiation of mouse rectal tumors. Dose rates in tissue were determined as well as other pertinent parameters to ensure accurate delivery of dose to the target region.

Total Effective Radiation Dose Attributable to Medical Imaging in Patients With Acute Chest Pain: A Single-Center Comparison Study Between Dual-Source Coronary CT Angiography and Usual Care

Introduction: Coronary CT angiography (CCTA) can safely disposition low to intermediate risk chest pain (CP); however, there is conflicting data with respect to cumulative radiation exposure when compared with usual care over short follow-up intervals. Objectives: We report the effective radiation dose from index and downstream testing in low to intermediate risk symptomatic patients evaluated for chest pain in the ED with either CCTA or usual care to define various sources of patient radiation dose and quantify effective dose over a year and a half of follow-up. Patients and Methods: We evaluated radiation exposure from initial and downstream testing in a prospectively collected, matched cohort evaluated for CP in the emergency department (ED) with either CCTA compared with usual care over a median follow-up of 19.6 months. Effective radiation dose was calculated using published conversion factors. Results: Prospective, ECG-triggered acquisition using a 128-slice dual-source multidetector computed tomography (DSCT) scanner was performed in 92.9% of scans with a median effective dose from CCTA of 6.8 mSv (IQR 5.2, 9.1 mSv). CCTA cohort patients were more likely to undergo cardiac testing with exposure to radiation (P < 0.001); however, the median effective dose in patients exposed to radiation from cardiac testing was significantly lower in the CCTA cohort (7.1 mSv vs. 11.8 mSv, P < 0.001). Fewer patients in the CCTA cohort had additional non-cardiac thoracic imaging radiation exposure (40.8%) compared with usual care (92.8%). Total radiation exposure from any source was similar between the CCTA and usual care groups (100% vs 98.4%, P = 0.087), as was median total effective radiation dose (P = 0.105). Upfront CCTA was not associated with higher rates of incidental non-cardiac findings. Conclusions: Initial evaluation of acute chest pain in the ED with CCTA was not associated with an increase in total radiation exposure over a follow-up period of 19 months. CCTA offers a more comprehensive evaluation of multiple thoracic organ systems leading to reduced radiation exposure from non-cardiac thoracic testing and no increase in incidental imaging findings. This may represent an added benefit in this population of patients presenting acutely.

Greenhouse gas emissions from conventional and organic cropping systems in Spain. I. Herbaceous crops

AbstractAgriculture is a major driver of climate change, particularly when all indirect emission sources are accounted for. Mitigation options targeted on one process are often proposed, ignoring their secondary effects on the overall greenhouse gas balance. Integrative methodologies such as life cycle assessment (LCA) are often applied without adjusting emission factors to specific site characteristics. Here, we used LCA to calculate the global warming potential of 38 pairs of organic and conventional herbaceous cropping systems and products in Spain. Crop products included rainfed cereals and pulses, rice, open-air vegetables, and greenhouse vegetables. We used data from farmer interviews and published conversion factors. Our results show that the emission balances were dominated by fossil fuel use rather than by direct field emissions. Organic management reduced crop emissions by 36–65 %, with the exception of rice showing an increase of 8 % due to methane generation. Product-based emissions of organic crops were also lower by 30 % on average, except for rice.

A comparison of coronary CTA and stress testing using high-efficiency SPECT MPI for the evaluation of chest pain in the emergency department

BackgroundRecent studies have compared CTA to stress testing and MPI using older Na-I SPECT cameras and traditional rest-stress protocols, but are limited by often using optimized CTA protocols but suboptimal MPI methodology. We compared CTA to stress testing with modern SPECT MPI using high-efficiency CZT cameras and stress-first protocols in an ED population. MethodsIn a retrospective, non-randomized study, all patients who underwent CTA or stress testing (ETT or Tc-99m sestamibi SPECT MPI) as part of their ED assessment in 2010-2011 driven by ED attending preference and equipment availability were evaluated for their disposition from the ED (admission vs discharge, length of time to disposition), subsequent visits to the ED and diagnostic testing (within 3 months), and radiation exposure. CTA was performed using a 64-slice scanner (GE Lightspeed VCT) and MPI was performed using a CZT SPECT camera (GE Discovery 530c). Data were obtained from prospectively acquired electronic medical records and effective doses were calculated from published conversion factors. A propensity-matched analysis was also used to compare outcomes in the two groups. ResultsA total of 1,458 patients underwent testing in the ED with 192 CTAs and 1,266 stress tests (327 ETTs and 939 MPIs). The CTA patients were a lower-risk cohort based on age, risk factors, and known heart disease. A statistically similar proportion of patients was discharged directly from the ED in the stress testing group (82% vs 73%, P = .27), but their time to disposition was longer (11.0 ± 5 vs 20.5 ± 7 hours, P < .0001). There was no significant difference in cardiac return visits to the ED (5.7% CTA vs 4.3% stress testing, P = .50), but more patients had follow-up studies in the CTA cohort compared to stress testing (14% vs 7%, P = .001). The mean effective dose of 12.6 ± 8.6 mSv for the CTA group was higher (P < .0001) than 5.0 ± 4.1 mSv for the stress testing group (ETT and MPI). A propensity score-matched cohort showed similar results to the entire cohort. ConclusionsStress testing with ETT, high-efficiency SPECT MPI, and stress-only protocols had a significantly lower patient radiation dose and less follow-up diagnostic testing than CTA with similar cardiac return visits. CTA had a shorter time to disposition, but there was a trend toward more revascularization than with stress testing.

Conversion factors for determining organ doses received by paediatric patients in high-resolution single slice computed tomography with narrow collimation

Estimations of organ doses DT received during computed tomographic examinations are usually performed by applying conversion factors to basic dose indicators like the computed tomography dose index (CTDI) or the dose-length-product (DLP). In addition to the existing conversion factors for beam apertures of 5 mm or 10 mm, we present new DLP-DT conversion factors adapted to high-resolution CT (HRCT) examinations of infants and young children with beam apertures of the order of 1 mm and under consideration of bow tie filtration. Calculations are performed on mathematical MIRD phantoms for an age range from 0, 1, 5, 10, 15 up to (for comparison) 30 years by adapting PCXMC, a Monte Carlo algorithm originally developed by STUK (Helsinki, Finland) for dose reconstructions in projection radiography. For this purpose, each single slice CT examination is approximated by a series of corresponding virtual planar radiographies comprising all focus positions. The transformation of CT exposure parameters into exposure parameters of the series of corresponding planar radiographies is performed by a specially developed algorithm called XCT. The DLP values are evaluated using the EGSRay code. The new method is verified at a beam aperture of 10 mm by comparison with formerly published conversion factors. We show that the higher spatial resolution leads to an enhanced DLP-DT conversion factor if a small organ (e. g. thyroid gland, mammae, uterus, ovaries, testes) is exactly met by the chosen CT slice, while the conversion factor is drastically reduced if the chosen CT slice is positioned above or below the organ. This effect is utilized for dose-saving examinations with only a few single slices instead a full scan, which technique is applied in about 10% of all paediatric chest CT examinations.

Estimation of Cooling Rates During Close-Coupled Gas Atomization Using Secondary Dendrite Arm Spacing Measurement

Al-4 wt pct Cu alloy has been gas atomized using a commercial close-coupled gas-atomization system. The resulting metal powders have been sieved into six size fractions, and the SDAS has been determined using electron microscopy. Cooling rates for the powders have been estimated using a range of published conversion factors for Al-Cu alloy, with reasonable agreement being found between sources. We find that cooling rates are very low relative to those often quoted for gas-atomized powders, of the order of 104 K s−1 for sub-38 µm powders. We believe that a number of numerical studies of gas atomization have overestimated the cooling rate during solidification, probably as a consequence of overestimating the differential velocity between the gas and the particles. From the cooling rates measured in the current study, we estimate that such velocities are unlikely to exceed 20 m s−1.

Estimating the Effective Radiation Dose Imparted to Patients by Intraoperative Cone-Beam Computed Tomography in Thoracolumbar Spinal Surgery

Observational. To estimate the radiation dose imparted to patients during typical thoracolumbar spinal surgical scenarios. Minimally invasive techniques continue to become more common in spine surgery. Computer-assisted navigation systems coupled with intraoperative cone-beam computed tomography (CT) represent one such method used to aid in instrumented spinal procedures. Some studies indicate that cone-beam CT technology delivers a relatively low dose of radiation to patients compared with other x-ray-based imaging modalities. The goal of this study was to estimate the radiation exposure to the patient imparted during typical posterior thoracolumbar instrumented spinal procedures, using intraoperative cone-beam CT and to place these values in the context of standard CT doses. Cone-beam CT scans were obtained using Medtronic O-arm (Medtronic, Minneapolis, MN). Thermoluminescence dosimeters were placed in a linear array on a foam-plastic thoracolumbar spine model centered above the radiation source for O-arm presets of lumbar scans for small or large patients. In-air dosimeter measurements were converted to skin surface measurements, using published conversion factors. Dose-length product was calculated from these values. Effective dose was estimated using published effective dose to dose-length product conversion factors. Calculated dosages for many full-length procedures using the small-patient setting fell within the range of published effective doses of abdominal CT scans (1-31 mSv). Calculated dosages for many full-length procedures using the large-patient setting fell within the range of published effective doses of abdominal CT scans when the number of scans did not exceed 3. We have demonstrated that single cone-beam CT scans and most full-length posterior instrumented spinal procedures using O-arm in standard mode would likely impart a radiation dose within the range of those imparted by a single standard CT scan of the abdomen. Radiation dose increases with patient size, and the radiation dose received by larger patients as a result of more than 3 O-arm scans in standard mode may exceed the dose received during standard CT of the abdomen. Understanding radiation imparted to patients by cone-beam CT is important for assessing risks and benefits of this technology, especially when spinal surgical procedures require multiple intraoperative scans.

Variability of outdoor fine particulate (PM2.5) concentration in the Indian Subcontinent: A remote sensing approach

The rapid increase of aerosols over the Indian Subcontinent over the last decade has the potential for severe health implications. However, the lack of a dense network to measure PM2.5 (particles with aerodynamic diameter<2.5μm) hinders health risk assessments at regional scale. Here, we utilize Multiangle Imaging SpectroRadiometer (MISR)-retrieved columnar aerosol optical depths to estimate surface PM2.5 based on recently published conversion factors that account for the composition and vertical distribution of aerosols. We examine the space–time variability of bias-corrected (utilizing coincident in-situ observations) PM2.5 over the Indian Subcontinent for the period Mar 2000–Feb 2010. We show that 51% of the subcontinent's 1.4 billion people are exposed to pollution that exceed the World Health Organization's highest annual air quality threshold of 35μgm−3, while another 13% and 18% are exposed in the ranges 25–35 and 15–25μgm−3 respectively. Of the remaining population who breathe clean air, only 25% live in urban areas. In many regions, the high-levels of pollution are persistent rather than episodic. PM2.5 concentrations in the rural areas of the Indo-Gangetic Basin are higher than many urban centers in peninsular India. Five hotspots (where PM2.5 increases by >15μgm−3 over the ten-year period) are identified, which cover parts of the eleven Indian states and Bangladesh affecting ~23% of the population. Our results highlight the urgent need to carry out local cohort studies at these hotspots to better understand the health impacts under local conditions.

Anti-Mullerian hormone: poor assay reproducibility in a large cohort of subjects suggests sample instability

What is the variability of anti-Müllerian hormone (AMH) concentration in repeat samples from the same individual when using the Gen II assay and how do values compare to Gen I [Diagnostic Systems Ltd (DSL)] assay results? The Gen II AMH assay displayed appreciable variability, which can be explained by sample instability. AMH is the primary predictor of ovarian performance and is used to tailor gonadatrophin dosage in cycles of IVF/ICSI and in other routine clinical settings. Thus, a robust, reproducible and sensitive method for AMH analysis is of paramount importance. The Beckman Coulter Gen II ELISA for AMH was introduced to replace earlier DSL and Immunotech assays. The performance of the Gen II assay has not previously been studied in a clinical setting. We studied an unselected group of 5007 women referred for fertility problems between 1 September 2008 and 25 October 2011; AMH was measured initially using the DSL AMH ELISA and subsequently using the Gen II assay. AMH values in the two assays were compared using a regression model in log(AMH) with a quadratic adjustment for age. Additionally, women (n = 330) in whom AMH had been determined in different samples using both the DSL and Gen II assays (paired samples) identified and the difference in AMH levels between the DSL and Gen II assays was estimated using the age-adjusted regression analysis. A subset of 313 women had repeated AMH determinations (n = 646 samples) using the DSL assay and 87 women had repeated AMH determinations using the Gen II assay (n = 177 samples) were identified. A mixed effects model in log(AMH) was utilized to estimate the sample-to-sample (within-subject) coefficients of variation of AMH, adjusting for age. Laboratory experiments including sample stability at room temperature, linearity of dilution and storage conditions used anonymized samples. In clinical practice, Gen II AMH values were ∼20% lower than those generated using the DSL assay instead of the 40% increase predicted by the kit manufacturer. Both assays displayed high within-subject variability (Gen II assay CV = 59%, DSL assay CV = 32%). In the laboratory, AMH levels in serum from 48 subjects incubated at RT for up to 7 days increased progressively in the majority of samples (58% increase overall). Pre-dilution of serum prior to assay, gave AMH levels up to twice that found in the corresponding neat sample. Pre-mixing of serum with assay buffer prior to addition to the microtitre plate gave higher readings (72% overall) compared with sequential addition. Storage at -20°C for 5 days increased AMH levels by 23% compared with fresh samples. The statistical significance of results was assessed where appropriate. The analysis of AMH levels is a retrospective study and therefore we cannot entirely rule out the existence of differences in referral practices or changes in the two populations. Our data suggests that AMH may not be stable under some storage or assay conditions and this may be more pronounced with the Gen II assay. The published conversion factors between the Gen II and DSL assays appear to be inappropriate for routine clinical practice. Further studies are urgently required to confirm our observations and to determine the cause of the apparent instability. In the meantime, caution should be exercised in the interpretation of AMH levels in the clinical setting. S. Roberts is supported by the NIHR Manchester Biomedical Research Centre.

Multisection CT Protocols: Sex- and Age-specific Conversion Factors Used to Determine Effective Dose from Dose-Length Product

To determine conversion factors for the new International Commission on Radiological Protection (ICRP) publication 103 recommendations for adult and pediatric patients and to compare the effective doses derived from Monte Carlo calculations with those derived from dose-length product (DLP) for different body regions and computed tomographic (CT) scanning protocols. Effective dose values for the Oak Ridge National Laboratory phantom series, including phantoms for newborns; 1-, 5-, and 10-year-old children; and adults were determined by using Monte Carlo methods for a 64-section multidetector CT scanner. For each phantom, five anatomic regions (head, neck, chest, abdomen, and pelvis) were considered. Monte Carlo simulations were performed for spiral scanning protocols with different voltages. Effective dose was computed by using ICRP publication 60 and publication 103 recommendations. The calculated effective doses were compared with those derived from the DLP by using previously published conversion factors. In general, conversion factors determined on the basis of Monte Carlo calculations led to lower values for adults with both ICRP publications. Values up to 33% and 32% lower than previously published data were found for ICRP publication 60 and ICRP publication 103, respectively. For pediatric individuals, effective doses based on the Monte Carlo calculations were higher than those obtained from DLP and previously published conversion factors (eg, for chest CT scanning in 5-year-old children, an increase of about 76% would be expected). For children, a variation in conversion factors of up to 15% was observed when the tube voltage was varied. For adult individuals, no dependence on voltage was observed. Conversion factors from DLP to effective dose should be specified separately for both sexes and should reflect the new ICRP recommendations. For pediatric patients, new conversion factors specific for the spectrum used should be established.

A comparison of radiation doses between state-of-the-art multislice CT coronary angiography with iterative reconstruction, multislice CT coronary angiography with standard filtered back-projection and invasive diagnostic coronary angiography

ObjectiveTo accurately compare the radiation dose between prospectively gated cardiac multidetector CT (with and without iterative reconstruction) and diagnostic invasive coronary angiography using the latest International Commission on Radiological Protection...