Radioprotection issues in uraniferous minerals collections with reference to an actual case.

Our work investigated the radioprotection implications associated with the possession of a collection of uraniferous minerals. Considering different scenarios, we developed (and applied to an actual collection) specific formulas for radiation doses evaluation. We discussed the shielding necessary to reduce the gamma irradiation down to the required values. A mathematical model was developed to estimate the minimum air flow rate to reduce the radon air concentration below the reference values. The radiation risks associated to the handling of single specimens was also addressed, including hand skin irradiation and shielding capabilities of surgical lead gloves. Finally, we discussed the radiation risks associated to the exhibition of a single specimen. The results, compared to the safety standards of the EU Directive 13/59, show that the exhibition of uraniferous samples with activity of a few MBq do not need specific radioprotection requirements nor for the involved personnel nor for visitors.

UNet and MobileNet CNN-based model observers for CT protocol optimization: comparative performance evaluation by means of phantom CT images.

Purpose: The aim of this work is the development and characterization of a model observer (MO) based on convolutional neural networks (CNNs), trained to mimic human observers in image evaluation in terms of detection and localization of low-contrast objects in CT scans acquired on a reference phantom. The final goal is automatic image quality evaluation and CT protocol optimization to fulfill the ALARA principle. Approach: Preliminary work was carried out to collect localization confidence ratings of human observers for signal presence/absence from a dataset of 30,000 CT images acquired on a PolyMethyl MethAcrylate phantom containing inserts filled with iodinated contrast media at different concentrations. The collected data were used to generate the labels for the training of the artificial neural networks. We developed and compared two CNN architectures based respectively on Unet and MobileNetV2, specifically adapted to achieve the double tasks of classification and localization. The CNN evaluation was performed by computing the area under localization-ROC curve (LAUC) and accuracy metrics on the test dataset. Results: The mean of absolute percentage error between the LAUC of the human observer and MO was found to be below 5% for the most significative test data subsets. An elevated inter-rater agreement was achieved in terms of S-statistics and other common statistical indices. Conclusions: Very good agreement was measured between the human observer and MO, as well as between the performance of the two algorithms. Therefore, this work is highly supportive of the feasibility of employing CNN-MO combined with a specifically designed phantom for CT protocol optimization programs.

ACTIVITY ESTIMATION WHEN DEALING WITH COLLECTIONS OF URANIFEROUS MINERALS.

The activity estimation of hand-size specimens of uraniferous minerals is not a trivial issue due to the manipulation difficulty caused by the emitted ionising radiation and the dependence of radiometric quantities from several parameters. Sample modelling requires approximations, leading to large uncertainty in the evaluation of the activity. In this work, a new procedure to evaluate uraniferous specimens activity, including a detailed description of measured parameters, the instrumentation and the mathematical formulation of the process, is presented. The proposed methodology takes into consideration sample size, ore composition and measured radiation. The procedure was used to measure the activity of a group of uraniferous mineral specimens belonging to Natural History Museum of the University of Florence, Italy. The experimental set-up was designed to reduce the measurement uncertainty. The aim of this work is to propose a methodology that can be easily applied to the specimens manipulation, conservation and exhibition.

On the dependence of quantitative diffusion-weighted imaging on scanner system characteristics and acquisition parameters: A large multicenter and multiparametric phantom study with unsupervised clustering analysis.

PURPOSE: The purpose of this multicenter phantom study was to exploit an innovative approach, based on an extensive acquisition protocol and unsupervised clustering analysis, in order to assess any potential bias in apparent diffusion coefficient (ADC) estimation due to different scanner characteristics. Moreover, we aimed at assessing, for the first time, any effect of acquisition plan/phase encoding direction on ADC estimation. METHODS: Water phantom acquisitions were carried out on 39 scanners. DWI acquisitions (b-value = 0-200-400-600-800-1000 s/mm2) with different acquisition plans (axial, coronal, sagittal) and phase encoding directions (anterior/posterior and right/left, for the axial acquisition plan), for 3 orthogonal diffusion weighting gradient directions, were performed. For each acquisition setup, ADC values were measured in-center and off-center (6 different positions), resulting in an entire dataset of 84 × 39 = 3276 ADC values. Spatial uniformity of ADC maps was assessed by means of the percentage difference between off-center and in-center ADC values (Δ). RESULTS: No significant dependence of in-center ADC values on acquisition plan/phase encoding direction was found. Ward unsupervised clustering analysis showed 3 distinct clusters of scanners and an association between Δ-values and manufacturer/model, whereas no association between Δ-values and maximum gradient strength, slew rate or static magnetic field strength was revealed. Several acquisition setups showed significant differences among groups, indicating the introduction of different biases in ADC estimation. CONCLUSIONS: Unsupervised clustering analysis of DWI data, obtained from several scanners using an extensive acquisition protocol, allows to reveal an association between measured ADC values and manufacturer/model of scanner, as well as to identify suboptimal DWI acquisition setups for accurate ADC estimation.

Addressing signal alterations induced in CT images by deep learning processing: A preliminary phantom study.

PURPOSE: We investigate, by an extensive quality evaluation approach, performances and potential side effects introduced in Computed Tomography (CT) images by Deep Learning (DL) processing. METHOD: We selected two relevant processing steps, denoise and segmentation, implemented by two Convolutional Neural Networks (CNNs) models based on autoencoder architecture (encoder-decoder and UNet) and trained for the two tasks. In order to limit the number of uncontrolled variables, we designed a phantom containing cylindrical inserts of different sizes, filled with iodinated contrast media. A large CT image dataset was collected at different acquisition settings and two reconstruction algorithms. We characterized the CNNs behavior using metrics from the signal detection theory, radiological and conventional image quality parameters, and finally unconventional radiomic features analysis. RESULTS: The UNet, due to the deeper architecture complexity, outperformed the shallower encoder-decoder in terms of conventional quality parameters and preserved spatial resolution. We also studied how the CNNs modify the noise texture by using radiomic analysis, identifying sensitive and insensitive features to the denoise processing. CONCLUSIONS: The proposed evaluation approach proved effective to accurately analyze and quantify the differences in CNNs behavior, in particular with regard to the alterations introduced in the processed images. Our results suggest that even a deeper and more complex network, which achieves good performances, is not necessarily a better network because it can modify texture features in an unwanted way.

Surgeon eye lens dose monitoring in catheterization lab: A multi-center survey: Invited for ECMP 2018 Focus Issue.

PURPOSE: To perform a multi-centre survey on the eye lens equivalent dose absorbed by primary interventionalist during catheterization procedures, using a personal dosimeter placed close to the eye lens. METHODS: 15 different cardiologists working in 3 different centers, for a total of 5 operating rooms were enrolled. All of them were provided with a single thermoluminescent dosimeter positioned on the inner side of the temples of eyeglasses. The dose monitoring, performed on a two-months basis, started in 2016 and is still running. All dose measurements were performed by a ISO 17025 standard accredited dosimetry service thus providing certified uncertainties as well. Correlation of eye lens and wrist dose with KAP was also investigated. RESULTS: A total number of 101 eye lens measurements were performed. Annual eye lens dose estimation was obtained for all 15 surgeons (mean, mode, range, standard deviation: 10.8, 8, 4.9-27.3, 5.6  mSv, respectively). Uncertainties on annual eye lens dose estimations ranged between 10% and 20%. No significant correlation was found between eye lens dose and KAP. CONCLUSIONS: Cardiologists involved in catheterization procedures may receive annual eye lens doses close to the ICRP 118 dose limit and thus individual monitoring with a dedicated dosimeter should be carried out. Uncertainty assessment play a relevant role in eye lens equivalent dose estimation to ensure not to exceed dose limit.

Pre and post operative radiation protection in Ru-106 brachytherapy ophthalmic plaque surgery and related material shielding properties.

Pre and post-operative exposure levels of medical staff and people from public in intra-operative Ru-106 ophthalmic brachytherapy are reported, together with attenuation properties of selected shielding materials. In particular radiation exposure of workers during plaque transportation and during medical assistance of implanted plaque patient was measured. Taking into account dose rates and considering standard assistance procedure of hospitalized patients, the exposure of medical staff and people of the public were evaluated for a given workload. In order to provide tools to optimize radiation protection, considering social and economic aspects due to possible hospital discharge or hospital stay, the attenuation properties of common shielding materials (lead, concrete, red brick, PMMA and gypsum) were measured, considering both narrow and broad beam setups. The eye was simulated using a water equivalent phantom and plaque was fixed on it. All measurements were performed with calibrated survey meters. Results were compared with numerical simulation of bremsstrahlung X-ray radiation spectra emitted from patient eye. Exposure levels measured at 1 m distance in front of the implanted eye are 0.05 µSv/h/MBq, at 10 cm from patient head, 0.44 µSv/h/MBq (plaque side), 0.4 µSv/h/MBq (front), 0.25 µSv/h/MBq (lateral, opposed to plaque), 0.2 µSv/h/MBq (back). Average exposure levels, under conservative assumptions, for medical staff is 17 µSv/patient and less than 23 µSv/patient for careers and comforters. TVLs in lead and concrete are about 1.6 cm and 11.5 cm respectively.

Dependence of apparent diffusion coefficient measurement on diffusion gradient direction and spatial position - A quality assurance intercomparison study of forty-four scanners for quantitative diffusion-weighted imaging.

PURPOSE: To propose an MRI quality assurance procedure that can be used for routine controls and multi-centre comparison of different MR-scanners for quantitative diffusion-weighted imaging (DWI). MATERIALS AND METHODS: 44 MR-scanners with different field strengths (1 T, 1.5 T and 3 T) were included in the study. DWI acquisitions (b-value range 0-1000 s/mm2), with three different orthogonal diffusion gradient directions, were performed for each MR-scanner. All DWI acquisitions were performed by using a standard spherical plastic doped water phantom. Phantom solution ADC value and its dependence with temperature was measured using a DOSY sequence on a 600 MHz NMR spectrometer. Apparent diffusion coefficient (ADC) along each diffusion gradient direction and mean ADC were estimated, both at magnet isocentre and in six different position 50 mm away from isocentre, along positive and negative AP, RL and HF directions. RESULTS: A good agreement was found between the nominal and measured mean ADC at isocentre: more than 90% of mean ADC measurements were within 5% from the nominal value, and the highest deviation was 11.3%. Away from isocentre, the effect of the diffusion gradient direction on ADC estimation was larger than 5% in 47% of included scanners and a spatial non uniformity larger than 5% was reported in 13% of centres. CONCLUSION: ADC accuracy and spatial uniformity can vary appreciably depending on MR scanner model, sequence implementation (i.e. gradient diffusion direction) and hardware characteristics. The DWI quality assurance protocol proposed in this study can be employed in order to assess the accuracy and spatial uniformity of estimated ADC values, in single- as well as multi-centre studies.

A straightforward multiparametric quality control protocol for proton magnetic resonance spectroscopy: Validation and comparison of various 1.5 T and 3 T clinical scanner systems.

PURPOSE: The aim of this study was to propose and validate across various clinical scanner systems a straightforward multiparametric quality assurance procedure for proton magnetic resonance spectroscopy (MRS). METHODS: Eighteen clinical 1.5 T and 3 T scanner systems for MRS, from 16 centres and 3 different manufacturers, were enrolled in the study. A standard spherical water phantom was employed by all centres. The acquisition protocol included 3 sets of single (isotropic) voxel (size 20 mm) PRESS acquisitions with unsuppressed water signal and acquisition voxel position at isocenter as well as off-center, repeated 4/5 times within approximately 2 months. Water peak linewidth (LW) and area under the water peak (AP) were estimated. RESULTS: LW values [mean (standard deviation)] were 1.4 (1.0) Hz and 0.8 (0.3) Hz for 3 T and 1.5 T scanners, respectively. The mean (standard deviation) (across all scanners) coefficient of variation of LW and AP for different spatial positions of acquisition voxel were 43% (20%) and 11% (11%), respectively. The mean (standard deviation) phantom T2values were 1145 (50) ms and 1010 (95) ms for 1.5 T and 3 T scanners, respectively. The mean (standard deviation) (across all scanners) coefficients of variation for repeated measurements of LW, AP and T2 were 25% (20%), 10% (14%) and 5% (2%), respectively. CONCLUSIONS: We proposed a straightforward multiparametric and not time consuming quality control protocol for MRS, which can be included in routine and periodic quality assurance procedures. The protocol has been validated and proven to be feasible in a multicentre comparison study of a fairly large number of clinical 1.5 T and 3 T scanner systems.

Quality assurance multicenter comparison of different MR scanners for quantitative diffusion-weighted imaging.

PURPOSE: To propose a magnetic resonance imaging (MRI) quality assurance procedure that can be used for multicenter comparison of different MR scanners for quantitative diffusion-weighted imaging (DWI). MATERIALS AND METHODS: Twenty-six centers (35 MR scanners with field strengths: 1T, 1.5T, and 3T) were enrolled in the study. Two different DWI acquisition series (b-value ranges 0-1000 and 0-3000 s/mm(2) , respectively) were performed for each MR scanner. All DWI acquisitions were performed by using a cylindrical doped water phantom. Mean apparent diffusion coefficient (ADC) values as well as ADC values along each of the three main orthogonal directions of the diffusion gradients (x, y, and z) were calculated. Short-term repeatability of ADC measurement was evaluated for 26 MR scanners. RESULTS: A good agreement was found between the nominal and measured mean ADC over all the centers. More than 80% of mean ADC measurements were within 5% from the nominal value, and the highest deviation and overall standard deviation were 9.3% and 3.5%, respectively. Short-term repeatability of ADC measurement was found <2.5% for all MR scanners. CONCLUSION: A specific and widely accepted protocol for quality controls in DWI is still lacking. The DWI quality assurance protocol proposed in this study can be applied in order to assess the reliability of DWI-derived indices before tackling single- as well as multicenter studies.

Considerations on the practical application of the size-specific dose estimation (SSDE) method of AAPM Report 204.

Computed tomography (CT) is responsible for much of the radiation exposure to the population for medical purposes. The technique requires high doses that vary widely from center to center, and for different scanners and radiologists as well. In order to monitor doses to patients, the American Association of Physicists in Medicine has developed the size-specific dose estimate (SSDE), which consists of the determination of patient size dependent coefficients for converting the standard dosimetric index, CTDIvol, into an estimate of the dose actually absorbed by the patient. The present work deals with issues concerning the use of SSDE in the clinical practice. First the issue regarding how much SSDE varies when, for a given CT protocol, the scan covers slightly different volumes is addressed. Then, the differences among SSDE values derived from different patient size descriptors are investigated. For these purposes, data from a clinical archive are analyzed by an automatic procedure specifically developed for SSDE.

Diffusion-weighted signal models in healthy and cancerous peripheral prostate tissues: comparison of outcomes obtained at different b-values.

PURPOSE: To evaluate the dependence on the b-values adopted of apparent diffusion coefficient (ADC), perfusion fraction (PF), slow and fast diffusion coefficient (Dslow, Dfast), corrected diffusion coefficient (D) and kurtosis (K), in healthy peripheral (HP) and peripheral cancerous (PCa) prostate tissues. MATERIALS AND METHODS: Patients who underwent multiparametric prostate MR examination were retrospectively evaluated for possible inclusion. ADC, PF, Dslow, Dfast, D, and K were estimated both in HP and PCa tissues, using three different ranges of b-values: 0-2300, 0-1800, 0-800 s/mm2 (group A, B and C, respectively). Analysis of variance (ANOVA) and receiver operating characteristic (ROC) analysis were performed, to establish differences among groups and to evaluate sensitivity and specificity of every parameter in distinguishing HP and PCa tissues when calculated with different b-values. RESULTS: In all, 57 patients were included. ANOVA showed significant differences of all parameters between group A-B vs. C, both in HP and PCa tissues. In ROC analysis K showed the best area under the curve (AUC) when calculated in groups A and B (0.87 and 0.86), while it was comparable with the ADC one in group C (both 0.82). CONCLUSION: A significant dependence on the adopted b-values of DWI parameters is shown. The best performance in distinguishing HP from PCa tissues was obtained by K, calculated using a high b-value sequence.

Curriculum for education and training of medical physicists in nuclear medicine: recommendations from the EANM Physics Committee, the EANM Dosimetry Committee and EFOMP.

PURPOSE: To provide a guideline curriculum covering theoretical and practical aspects of education and training for Medical Physicists in Nuclear Medicine within Europe. MATERIAL AND METHODS: National training programmes of Medical Physics, Radiation Physics and Nuclear Medicine physics from a range of European countries and from North America were reviewed and elements of best practice identified. An independent panel of experts was used to achieve consensus regarding the content of the curriculum. RESULTS: Guidelines have been developed for the specialist theoretical knowledge and practical experience required to practice as a Medical Physicist in Nuclear Medicine in Europe. It is assumed that the precondition for the beginning of the training is a good initial degree in Medical Physics at master level (or equivalent). The Learning Outcomes are categorised using the Knowledge, Skill and Competence approach along the lines recommended by the European Qualifications Framework. The minimum level expected in each topic in the theoretical knowledge and practical experience sections is intended to bring trainees up to the requirements expected of a Medical Physicist entering the field of Nuclear Medicine. CONCLUSIONS: This new joint EANM/EFOMP European guideline curriculum is a further step to harmonise specialist training of Medical Physicists in Nuclear Medicine within Europe. It provides a common framework for national Medical Physics societies to develop or benchmark their own curricula. The responsibility for the implementation and accreditation of these standards and guidelines resides within national training and regulatory bodies.

Cancer risk from professional exposure in staff working in cardiac catheterization laboratory: insights from the National Research Council's Biological Effects of Ionizing Radiation VII Report.

BACKGROUND: Occupational doses from fluoroscopy-guided interventional procedures are the highest ones registered among medical staff using x-rays. The aim of the present study was to evaluate the order of magnitude of cancer risk caused by professional radiation exposure in modern invasive cardiology practice. METHODS: From the dosimetric Tuscany Health Physics data bank of 2006, we selected dosimetric data of the 26 (7 women, 19 men; age 46 +/- 9 years) workers of the cardiovascular catheterization laboratory with effective dose >2 mSv. Effective dose (E) was expressed in milliSievert, calculated from personal dose equivalent registered by the thermoluminescent dosimeter, at waist or chest, under the apron, according to the recommendations of National Council of Radiation Protection. Lifetime attributable risk of cancer was estimated using the approach of Biological Effects of Ionizing Radiation 2006 report VII. RESULTS: Cardiac catheterization laboratory staff represented 67% of the 6 workers with yearly exposure >6 mSv. Of the 26 workers with 2006 exposure >2 mSv, 15 of them had complete records of at least 10 (up to 25) consecutive years. For these 15 subjects having a more complete lifetime dosimetric history, the median individual effective dose was 46 mSv (interquartile range = 24-64). The median risk of (fatal and nonfatal) cancer (Biological Effects of Ionizing Radiation 2006) was 1 in 192 (interquartile range = 1 in 137-1 in 370). CONCLUSIONS: Cumulative professional radiological exposure is associated with a non-negligible Lifetime attributable risk of cancer for the most exposed contemporary cardiac catheterization laboratory staff.