National inventory of authorized diagnostic imaging equipment in Ghana: data as of September 2020.

Introduction: to address the challenge of inadequate and non-equitable distribution of diagnostic imaging equipment, countries are encouraged to evaluate the distribution of installed systems and undertake adequate monitoring to ensure equitability. Ghana´s medical imaging resources have been analyzed in this study and evaluated against the status in other countries. Methods: data on registered medical imaging equipment were retrieved from the database of the Nuclear Regulatory Authority and analyzed. The equipment/population ratio was mapped out graphically for the 16 regions of Ghana. Comparison of the equipment/population ratio was made with the situation in other countries. Results: six hundred and seventy-four diagnostic imaging equipment units from 266 medical imaging facilities (2.5 units/facility), comprising computed tomography (CT), general X-ray, dental X-ray, single-photon emission computed tomography (SPECT) gamma camera, fluoroscopy, mammography and magnetic resonance imaging (MRI) were surveyed nationally. None of the imaging systems measured above the Organization for Economic Co-operation and Development (OECD) average imaging units per million populations (u/mp). The overall equipment/population ratio estimated nationally was 21.4 u/mp. Majority of the imaging systems were general X-ray, installed in the Greater Accra and Ashanti regions. The regional estimates of equipment/population ratios were Greater Accra (49.6 u/mp), Ashanti (22.4 u/mp), Western (21.4 u/mp), Eastern (20.6 u/mp), Bono East (20.0 u/mp), Bono (19.2 u/mp), Volta (17.9 u/mp), Upper West (16.7 u/mp), Oti (12.5 u/mp), Central (11.9 u/mp), Northern (8.9 u/mp), Ahafo (8.9 u/mp), Upper East (6.9 u/mp), Western North (6.7 u/mp), Savannah (5.5 u/mp) and North-East (1.7 u/mp). Conclusion: medical imaging equipment shortfall exist across all imaging modalities in Ghana. A wide inter-regional disparity in the distribution of medical imaging equipment exists contrary to WHO´s recommendation for equitable distribution. A concerted national plan will be needed to address the disparity.

In Vivo Transcutaneous Monitoring of Hemoglobin Derivatives Using a Red-Green-Blue Camera-Based Spectral Imaging Technique.

Cyanosis is a pathological condition that is characterized by a bluish discoloration of the skin or mucous membranes. It may result from a number of medical conditions, including disorders of the respiratory system and central nervous system, cardiovascular diseases, peripheral vascular diseases, deep vein thrombosis, and regional ischemia. Cyanosis can also be elicited from methemoglobin. Therefore, a simple, rapid, and simultaneous monitoring of changes in oxygenated hemoglobin and deoxygenated hemoglobin is useful for protective strategies against organ ischemic injury. We previously developed a red-green-blue camera-based spectral imaging method for the measurements of melanin concentration, oxygenated hemoglobin concentration (CHbO), deoxygenated hemoglobin concentration (CHbR), total hemoglobin concentration (CHbT) and tissue oxygen saturation (StO2) in skin tissues. We leveraged this approach in this study and extended it to the simultaneous quantifications of methemoglobin concentration (CmetHb), CHbO, CHbR, and StO2. The aim of the study was to confirm the feasibility of the method to monitor CmetHb, CHbO, CHbR, CHbT, and StO2. We performed in vivo experiments using rat dorsal skin during methemoglobinemia induced by the administration of sodium nitrite (NaNO2) and changing the fraction of inspired oxygen (FiO2), including normoxia, hypoxia, and anoxia. Spectral diffuse reflectance images were estimated from an RGB image by the Wiener estimation method. Multiple regression analysis based on Monte Carlo simulations of light transport was used to estimate CHbO, CHbR, CmetHb, CHbT, and StO2. CmetHb rapidly increased with a half-maximum time of less than 30 min and reached maximal values nearly 60 min after the administration of NaNO2, whereas StO2 dramatically dropped after the administration of NaNO2, indicating the temporary production of methemoglobin and severe hypoxemia during methemoglobinemia. Time courses of CHbT and StO2, while changing the FiO2, coincided with well-known physiological responses to hyperoxia, normoxia, and hypoxia. The results indicated the potential of this method to evaluate changes in skin hemodynamics due to loss of tissue viability and vitality.

Machine Learning: The Next Paradigm Shift in Medical Education.

Machine learning (ML) algorithms are powerful prediction tools with immense potential in the clinical setting. There are a number of existing clinical tools that use ML, and many more are in development. Physicians are important stakeholders in the health care system, but most are not equipped to make informed decisions regarding deployment and application of ML technologies in patient care. It is of paramount importance that ML concepts are integrated into medical curricula to position physicians to become informed consumers of the emerging tools employing ML. This paradigm shift is similar to the evidence-based medicine (EBM) movement of the 1990s. At that time, EBM was a novel concept; now, EBM is considered an essential component of medical curricula and critical to the provision of high-quality patient care. ML has the potential to have a similar, if not greater, impact on the practice of medicine. As this technology continues its inexorable march forward, educators must continue to evaluate medical curricula to ensure that physicians are trained to be informed stakeholders in the health care of tomorrow.

Wound Size Imaging: Ready for Smart Assessment and Monitoring.

Significance: We introduce and evaluate emerging devices and modalities for wound size imaging and also promising image processing tools for smart wound assessment and monitoring. Recent Advances: Some commercial devices are available for optical wound assessment but with limited possibilities compared to the power of multimodal imaging. With new low-cost devices and machine learning, wound assessment has become more robust and accurate. Wound size imaging not only provides area and volume but also the proportion of each tissue on the wound bed. Near-infrared and thermal spectral bands also enhance the classical visual assessment. Critical Issues: The ability to embed advanced imaging technology in portable devices such as smartphones and tablets with tissue analysis software tools will significantly improve wound care. As wound care and measurement are performed by nurses, the equipment needs to remain user-friendly, enable quick measurements, provide advanced monitoring, and be connected to the patient data management system. Future Directions: Combining several image modalities and machine learning, optical wound assessment will be smart enough to enable real wound monitoring, to provide clinicians with relevant indications to adapt the treatments and to improve healing rates and speed. Sharing the wound care histories of a number of patients on databases and through telemedicine practice could induce a better knowledge of the healing process and thus a better efficiency when the recorded clinical experience has been converted into knowledge through deep learning.

Body morphometry appropriate computational phantoms for dose and risk optimization in pediatric renal imaging with Tc-99m DMSA and Tc-99m MAG3.

Current guidelines for administered activity (AA) in pediatric nuclear medicine imaging studies are based on a 2016 harmonization of the 2010 North American Consensus guidelines and the 2007 European Association of Nuclear Medicine pediatric dosage card. These guidelines assign AA scaled to patient body mass, with further constraints on maximum and minimum values of radiopharmaceutical activity. These guidelines, however, are not formulated based upon a rigor-ous evaluation of diagnostic image quality. In a recent study of the renal cortex imaging agent 99mTc-DMSA (Li Y et al 2019), body mass-based dosing guidelines were shown to not give the same level of image quality for patients of differing body mass. Their data suggest that patient girth at the level of the kidneys may be a better morphometric parameter to consider when selecting AA for renal nuclear medicine imaging. The objective of the present work was thus to develop a dedicated series of computational phantoms to support image quality and organ dose studies in pediatric renal imaging using 99mTc-DMSA or 99mTc-MAG3. The final library consists of 50 male and female phantoms of ages 0 to 15 years, with percentile variations (5th to 95th) in waist circumference (WC) at each age. For each phantom, nominal values of kidney volume, length, and depth were incorporated into the phantom design. Organ absorbed doses, detriment-weighted doses, and stochastic risks were assessed using ICRP reference biokinetic models for both agents. In Monte Carlo radiation transport simulations, organ doses for these agents yielded detriment-weighted dose coefficients (mSv/MBq) that were in general larger than current ICRP values of the effective dose coefficients (age and WC-averaged ratios of eDW/e were 1.40 for the male phantoms and 1.49 for the female phantoms). Values of risk index (ratio of radiation-induced to natural background cancer incidence risk x 100) varied between 0.062 (newborns) to 0.108 (15-year-olds) for 99mTc-DMSA and between 0.026 (newborns) to 0.122 (15-year-olds) for 99mTc-MAG3. Using tallies of photon exit fluence as a rough surrogate for uniform image quality, our study demonstrated that through body region-of-interest optimization of AA, there is the potential for further dose and risk reductions of between factors of 1.5 to 3.0 beyond simple weight-based dosing guidance.

An audit of licenced Zambian diagnostic imaging equipment and personnel.

INTRODUCTION: Estimates indicate that two-thirds of the world's population lack adequate access to basic medical imaging services integral to universal health coverage (UHC). Furthermore, sparse country-level radiological resource statistics exist and there is scant appreciation of how such data reflect healthcare access. The World Health Organisation posits that one X-ray and ultrasound unit for every 50,000 people will meet 90% of global imaging demands. This study aimed to conduct a comprehensive review of licensed Zambian radiological equipment and human resources. METHODS: An audit of licensed imaging resources, using the national updated Radiation Protection Authority and Health Professions Council of Zambia databases. Resources were quantified as units or personnel per million people, stratified by imaging modality, profession, province and healthcare sector, then compared with published Southern African data. RESULTS: Over half of all equipment (153/283 units, 54%) and almost two thirds of all radiation workers (556/913, 61%) are in two of ten provinces, serving one third of the population (5.49/16.4, 33.5%). Three-quarters of the national equipment inventory (212/283 units, 75%) and nearly ninety percent of registered radiation workers (800/913, 88%) are in the public sector, serving 96% of the population. Southern African country-level public-sector imaging resources principally reflect national per capita healthcare spending. CONCLUSION: To achieve equitable imaging access pivotal for UHC, Zambia will need a more homogeneous distribution of specialised radiological resources tailored to remedy disparities between healthcare sectors and provincial regions. Analyses of licenced radiology resources at country level can serve as a benchmark for medium-term radiological planning.

In vivo assessment of inflammation in carotid atherosclerosis by noninvasive photoacoustic imaging.

Objectives: The objective of this study was to demonstrate the feasibility of using noninvasive photoacoustic imaging technology along with novel semiconducting polymer nanoparticles for in vivo identifying inflammatory components in carotid atherosclerosis and assessing the severity of inflammation using mouse models. Methods and Results: Healthy carotid arteries and atherosclerotic carotid arteries were imaged in vivo by the noninvasive photoacoustic imaging system. Molecular probes PBD-CD36 were used to label the inflammatory cells to show the inflammation information by photoacoustic imaging. In in vivo imaging experiments, we observed the maximum photoacoustic signal enhancement of 4.3, 5.2, 8 and 16.3 times between 24 h post probe injection and that before probe injection in four carotid arteries belonging to three atherosclerotic mice models. In the corresponding carotid arteries stained with CD36, the ratio of 0.043, 0.061, 0.082 and 0.113 was found between CD36 positive (CD36(+)) expression area and intima-media area (P < 0.05). For the CD36(+) expression less than 0.008 in eight arteries, no photoacoustic signal enhancement was found due to the limited system sensitivity. The photoacoustic signal reflects CD36(+) expression in plaques, which shows the feasibility of using photoacoustic imaging for in vivo assessment of carotid atherosclerosis. Conclusion: This research demonstrates a semiconducting polymer nanoparticle along with photoacoustic technology for noninvasive imaging and assessment of inflammation of carotid atherosclerotic plaques in vivo.

Bayesian assessment of diagnostic accuracy of a commercial borescope and of trimming chute exams for diagnosing digital dermatitis in dairy cows.

Digital dermatitis (DD) is a worldwide infectious disease of cattle that causes lameness, discomfort, and economic losses. The reference standard test to diagnose DD is visual observation in a trimming chute, which cannot be practically performed daily on dairy farms. Moreover, some lesion misclassification may occur using this standard diagnostic method. The possibility of misclassification makes the use of a trimming chute debatable as a perfect reference standard test. The objective of this study was, therefore, to assess the diagnostic accuracy of a commercial borescope and trimming chute exam. The accuracy (sensitivity and specificity) of the tests and DD prevalence were investigated using Bayesian latent class analyses. Our hypothesis was that a commercial borescope can be routinely used to diagnose DD in a milking parlor without previous feet cleaning. A cross-sectional study was performed in a freestall facility. The lesions were scored (M0, M1, M2, M3, M4, M4.1) in the milking parlor with a borescope, followed by an examination in the trimming chute 48 to 72 h after the borescope exam. A total of 870 hind feet were scored during 2 sessions of trimming chute exams and borescope exams in the milking parlor. The data were analyzed in 2 ways. First, data were dichotomized into DD lesions (M1, M2, M3, M4, M4.1) and absence of DD lesions (M0). Second, data were dichotomized into active DD lesions (M1, M2, M4.1) and inactive lesions (M0, M3, M4). A Bayesian latent class model allowing for conditional dependence between tests was used to estimate tests' accuracy, likelihood ratio, and DD prevalence. When the data were dichotomized into DD lesions (M1-M4.1) versus absence of DD (M0) lesions, the sensitivity and specificity of the borescope was 55% [95% credible interval (CrI) 40-71%] and 81% (95% CrI 75-88%). The sensitivity of trimming chute exams was 79% (95% CrI 68-88%), and specificity was 80% (95% CrI 71-89%). When the data were dichotomized into active lesions (M1, M2, M4.1) versus inactive lesions or absence of lesions (M3, M4, M0), the sensitivity and specificity of the borescope were, respectively, 32% (95% CrI 13-58%) and 91% (95% CrI 88-95%). The sensitivity and specificity of trimming chute exams were 91% (95% CrI 81-97%) and 81% (95% CrI 75-89%), respectively. In conclusion, it is possible to use the borescope in the milking parlor without cleaning the feet to monitor prevalence of DD lesions. However, an isolated borescope examination, especially for diagnosing active DD lesions, has low sensitivity for use as a surveillance method. For such use, the sensitivity could be improved by repeating the borescope exam on a regular basis.

The Impact of Positron Range on PET Resolution, Evaluated with Phantoms and PHITS Monte Carlo Simulations for Conventional and Non-conventional Radionuclides.

PURPOSE: The increasing interest and availability of non-standard positron-emitting radionuclides has heightened the relevance of radionuclide choice in the development and optimization of new positron emission tomography (PET) imaging procedures, both in preclinical research and clinical practice. Differences in achievable resolution arising from positron range can largely influence application suitability of each radionuclide, especially in small-ring preclinical PET where system blurring factors due to annihilation photon acollinearity and detector geometry are less significant. Some resolution degradation can be mitigated with appropriate range corrections implemented during image reconstruction, the quality of which is contingent on an accurate characterization of positron range. PROCEDURES: To address this need, we have characterized the positron range of several standard and non-standard PET radionuclides (As-72, F-18, Ga-68, Mn-52, Y-86, and Zr-89) through imaging of small-animal quality control phantoms on a benchmark preclinical PET scanner. Further, the Particle and Heavy Ion Transport code System (PHITS v3.02) code was utilized for Monte Carlo modeling of positron range-dependent blurring effects. RESULTS: Positron range kernels for each radionuclide were derived from simulation of point sources in ICRP reference tissues. PET resolution and quantitative accuracy afforded by various radionuclides in practicable imaging scenarios were characterized using a convolution-based method based on positron annihilation distributions obtained from PHITS. Our imaging and simulation results demonstrate the degradation of small animal PET resolution, and quantitative accuracy correlates with increasing positron energy; however, for a specific "benchmark" preclinical PET scanner and reconstruction workflow, these differences were observed to be minimal given radionuclides with average positron energies below ~ 400 keV. CONCLUSION: Our measurements and simulations of the influence of positron range on PET resolution compare well with previous efforts documented in the literature and provide new data for several radionuclides in increasing clinical and preclinical use. The results will support current and future improvements in methods for positron range corrections in PET imaging.

Diagnosis and management of surgical disease at Ethiopian health centres: cross-sectional survey of resources and barriers to care.

OBJECTIVES: The aim of this study was to characterise the resources and challenges for surgical care and referrals at health centres (HCs) in South Wollo Zone, Ethiopia. SETTING: Eight primary HCs in South Wollo Zone, Ethiopia. PARTICIPANTS: Eight health officers and nurses staffing eight HCs completed a survey. DESIGN: The study was a survey-based, cross-sectional assessment of HCs in South Wollo Zone, Ethiopia and data were collected over a 30-day period from November 2014 to January 2015. PRIMARY AND SECONDARY OUTCOME MEASURES: Survey assessed human and material resources, diagnostic capabilities and challenges and patient-reported barriers to care. RESULTS: Eight HCs had an average of 18 providers each, the majority of which were nurses (62.2%) and health officers (20.7%). HCs had intermittent availability of clean water, nasogastric tubes, rectal tubes and suturing materials, none of them had any form of imaging. A total of 168 surgical patients were seen at the 8 HCs; 58% were referred for surgery. Most common diagnoses were trauma/burns (42%) and need for caesarean section (9%). Of those who did not receive surgery, 32 patients reported specific barriers to obtaining care (91.4%). The most common specific barriers were patients not being decision makers to have surgery, lack of family/social support and inability to afford hospital fees. CONCLUSIONS: HCs in South Wollo Zone, Ethiopia are well-staffed with nurses and health officers, however they face a number of diagnostic and treatment challenges due to lack of material resources. Many patients requiring surgery receive initial diagnosis and care at HCs; sociocultural and financial factors commonly prohibit these patients from receiving surgery. Further study is needed to determine how such delays may impact patient outcomes. Improving material resources at HCs and exploring community and family perceptions of surgery may enable more streamlined access to surgical care and prevent delays.

Prevalence of Musculoskeletal Disorders Symptoms Among Czech Dental Students. Part 2: The Predictive Value of Digital Assessment.

This article is the second part of an evaluation of musculoskeletal disorders (MSDs) prevalence among dental students. As the majority of complaints are in the back region, there is an endeavor to analyze objectively the disorders in this region. One of the non-invasive and non-radiation methods is the spinal curve mapping using the Spinal Mouse® device (Idiag AG, Fehraltorf, Switzerland). The aim of this study was to determine a correlation between subjectively described complaints and the results of an objective examination of the spine using the Spinal Mouse® device. Information about the participants is given in the first part of the article. All the participants were examined with the Spinal Mouse® device in several body positions. Further, the Matthiass test was performed to evaluate neuromuscular stabilization of the axial skeleton in static conditions. Musculoskeletal pain occurred more often in students who had a higher range of motion (ROM) and had worse static stabilization of spine. Other assessed factors or measured parameters did not have any influence on musculoskeletal pain. Some of the parameters measured with the Spinal Mouse® device showed a correlation with the prevalence of musculoskeletal.

A novel method for fast image simulation of flat panel detectors.

We have developed a novel method for fast image simulation of flat panel detectors, based on the photon energy deposition efficiency and the optical spread function (OSF). The proposed method, FastEPID, determines the photon detection using photon energy deposition and replaces particle transport within the detector with precalculated OSFs. The FastEPID results are validated against experimental measurement and conventional Monte Carlo simulation in terms of modulation transfer function (MTF), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), contrast, and relative difference of pixel value, obtained with a slanted slit image, Las Vegas phantom, and anthropomorphic pelvis phantom. Excellent agreement is observed between simulation and measurement in all cases. Without degrading image quality, the FastEPID method is capable of reducing simulation time up to a factor of 150. Multiple applications, such as imager design optimization for planar and volumetric imaging, are expected to benefit from the implementation of the FastEPID method.

Current approaches to instrumental assessment of swallowing in children.

PURPOSE OF THE REVIEW: This article reviews recent developments in the instrumental assessment of swallowing in children with a specific focus on research published between January 2017 and June 2018. RECENT FINDINGS: Instrumental swallowing assessments reported in the time period included: videofluoroscopic study of swallowing, digital cervical auscultation, dynamic ultrasound, high-resolution impedance manometry, nasal airflow thermistry and respiratory inductance plethysmography. Several studies were found exploring tools to objectively quantify videofluoroscopic study of swallowing data; swallowing from the mouth through to stomach was addressed including approaches to analysing mastication as well as evaluating oesophageal motility disorders. SUMMARY: Even though a vast range of instrumentation were studied, lack of clarity on clinical feasibility and objective measures that facilitate medical decision-making in practice mean further research is required to provide guidance on implementation. Promising novel approaches to aid the quantification of swallowing physiology from the mouth, pharynx and through to the oesophagus are emerging.

In vivo characterization of light scattering properties of human skin in the 475- to 850-nm wavelength range in a Swedish cohort.

We have determined in vivo optical scattering properties of normal human skin in 1734 subjects, mostly with fair skin type, within the Swedish CArdioPulmonary bioImage Study. The measurements were performed with a noninvasive system, integrating spatially resolved diffuse reflectance spectroscopy and laser Doppler flowmetry. Data were analyzed with an inverse Monte Carlo algorithm, accounting for both scattering, geometrical, and absorbing properties of the tissue. The reduced scattering coefficient was found to decrease from 3.16 ± 0.72 to 1.13 ± 0.27 mm-1 (mean ± SD) in the 475- to 850-nm wavelength range. There was a negative correlation between the reduced scattering coefficient and age, and a significant difference between men and women in the reduced scattering coefficient as well as in the fraction of small scattering particles. This large study on tissue scattering with mean values and normal variation can serve as a reference when designing diagnostic techniques or when evaluating the effect of therapeutic optical systems.

Automated Risk Control in Medical Imaging Equipment Management Using Cloud Application.

Medical imaging equipment (MIE) is the baseline of providing patient diagnosis in healthcare facilities. However, that type of equipment poses high risk for patients, operators, and environment in terms of technology and application. Considering risk management in MIE management is rarely covered in literature. The study proposes a methodology that controls risks associated with MIE management. The methodology is based on proposing a set of key performance indicators (KPIs) that lead to identify a set of undesired events (UDEs), and through a risk matrix, a risk level is evaluated. By using cloud computing software, risks could be controlled to be manageable. The methodology was verified by using a data set of 204 pieces of MIE along 104 hospitals, which belong to Egyptian Ministry of Health. Results point to appropriateness of proposed KPIs and UDEs in risk evaluation and control. Thus, the study reveals that optimizing risks taking into account the costs has an impact on risk control of MIE management.

Chirp phantom for MTF calculations. A study of its precision in noisy environments.

Bar pattern phantoms are used to determine the maximum number of line-pairs per mm that an imaging system can resolve. In some cases, a numerical determination of the modulation transfer function (MTF) can also be carried out. However, calculations can only be performed in a relatively small number of frequencies because of the small number of bar groups in the phantom. In this work, a new bar pattern phantom has been simulated. This phantom consists of 66 pairs of lines of different periods and these periods vary exponentially with spatial position, like in a chirp wave. An oversampling procedure has been implemented to obtain the pre-sampled MTF of the system and the results obtained have been compared with those obtained with the edge method, recommended by the IEC. Monte Carlo simulations were carried out for three different levels of noise aimed at investigating the effect of noise on the uncertainties of the MTF determination. In addition, using the analytic expressions for the MTF calculation, statistical fluctuations of noise in phantom images were propagated to MTF values. Despite the smaller size of the chirp phantom, uncertainties in the chirp method are smaller than those of the edge method. For the edge image, the standard deviation of the MTF is proportional to the frequency f, whereas for the chirp method it is proportional to its square root. It is shown that applying an oversampling method allows the use of a single line pair per period without compromising the precision in noisy environments.

Multi-layer imager design for mega-voltage spectral imaging.

The architecture of multi-layer imagers (MLIs) can be exploited to provide megavoltage spectral imaging (MVSPI) for specific imaging tasks. In the current work, we investigated bone suppression and gold fiducial contrast enhancement as two clinical tasks which could be improved with spectral imaging. A method based on analytical calculations that enables rapid investigation of MLI component materials and thicknesses was developed and validated against Monte Carlo computations. The figure of merit for task-specific imaging performance was the contrast-to-noise ratio (CNR) of the gold fiducial when the CNR of bone was equal to zero after a weighted subtraction of the signals obtained from each MLI layer. Results demonstrated a sharp increase in the CNR of gold when the build-up component or scintillation materials and thicknesses were modified. The potential for low-cost, prompt implementation of specific modifications (e.g. composition of the build-up component) could accelerate clinical translation of MVSPI.

Spectral imaging using clinical megavoltage beams and a novel multi-layer imager.

We assess the feasibility of clinical megavoltage (MV) spectral imaging for material and bone separation with a novel multi-layer imager (MLI) prototype. The MLI provides higher detective quantum efficiency and lower noise than conventional electronic portal imagers. Simulated experiments were performed using a validated Monte Carlo model of the MLI to estimate energy absorption and energy separation between the MLI components. Material separation was evaluated experimentally using solid water and aluminum (Al), copper (Cu) and gold (Au) for 2.5 MV, 6 MV and 6 MV flattening filter free (FFF) clinical photon beams. An anthropomorphic phantom with implanted gold fiducials was utilized to further demonstrate bone/gold separation. Weighted subtraction imaging was employed for material and bone separation. The weighting factor (w) was iteratively estimated, with the optimal w value determined by minimization of the relative signal difference ([Formula: see text]) and signal-difference-to-noise ratio (SDNR) between material (or bone) and the background. Energy separation between layers of the MLI was mainly the result of beam hardening between components with an average energy separation between 34 and 47 keV depending on the x-ray beam energy. The minimum average energy of the detected spectrum in the phosphor layer was 123 keV in the top layer of the MLI with the 2.5 MV beam. The w values that minimized [Formula: see text] and SDNR for Al, Cu and Au were 0.89, 0.76 and 0.64 for 2.5 MV; for 6 MV FFF, w was 0.98, 0.93 and 0.77 respectively. Bone suppression in the anthropomorphic phantom resulted in improved visibility of the gold fiducials with the 2.5 MV beam. Optimization of the MLI design is required to achieve optimal separation at clinical MV beam energies.

The assessment and characterization of the built-in internal photometer of primary diagnostic monitors.

The purpose of this work was to perform the initial evaluation of primary diagnostic monitor (PDM) characteristics following the implementation of New York City quality assurance (NYC QA) regulations on January 1, 2016, and compare the results of the QA measurements performed by an external photometer and the PDM manufacturer's built-in photometer. TG-18 and Society of Motion Picture and Television Engineers test patterns were used to evaluate monitor performance. Overall, 79 PDMs were included in the analysis. The verification of grayscale standard display function (GSDF) calibration, using a built-in photometer, showed that only 2 out of 79 PDMs failed calibration. However, the same measurements performed by the external luminance meter showed that 15 out of 79 monitors had failed GSDF calibration. Measurements of the PDMs maximum luminance (Lmax ), using an external photometer showed that 10 out of 53 PDMs calibrated for Lmax = 400 cd/m2 and 17 out of 26 PDMs calibrated for Lmax = 500 cd/m2 do not meet the manufacturer's recommended 10% tolerance limit for the target Lmax calibration. Two PDMs did not pass the Lmax ≥ 350 cd/m2 NYC QA regulations with Lmax = 331 cd/m2 and Lmax = 340 cd/m2 . All tested PDMs exceeded the minimum luminance ratio (LR) of 250:1 as required by NYC QA regulations. Measurements taken of Lmax and LR performed by a built-in photometer showed that none of the PDMs had failed the NYC QA regulations. All PDMs passed the luminance uniformity test with a maximum nonuniformity of 17% (according to NYC regulations it must be less than 30%). The luminance uniformity test could only be performed using an external photometer. The evaluation of 79 PDMs of various ages and models demonstrated up to 18% disagreement between luminance measurements performed by the manufacturer's built-in photometer when compared with those performed by an externally calibrated luminance meter. These disagreements were larger for older PDMs.