Ultrahigh-Resolution Photon-Counting Detector CT of the Lungs: Association of Reconstruction Kernel and Slice Thickness With Image Quality.

BACKGROUND. Prior work has shown improved image quality for photon-counting detector (PCD) CT of the lungs compared with energy-integrating detector CT. A paucity of the literature has compared PCD CT of the lungs using different reconstruction parameters. OBJECTIVE. The purpose of this study is to the compare the image quality of ultra-high-resolution (UHR) PCD CT image sets of the lungs that were reconstructed using different kernels and slice thicknesses. METHODS. This retrospective study included 29 patients (17 women and 12 men; median age, 56 years) who underwent noncontrast chest CT from February 15, 2022, to March 15, 2022, by use of a commercially available PCD CT scanner. All acquisitions used UHR mode (1024 × 1024 matrix). Nine image sets were reconstructed for all combinations of three sharp kernels (BI56, BI60, and BI64) and three slice thicknesses (0.2, 0.4, and 1.0 mm). Three radiologists independently reviewed reconstructions for measures of visualization of pulmonary anatomic structures and pathologies; reader assessments were pooled. Reconstructions were compared with the clinical reference reconstruction (obtained using the BI64 kernel and a 1.0-mm slice thickness [BI641.0-mm]). RESULTS. The median difference in the number of bronchial divisions identified versus the clinical reference reconstruction was higher for reconstructions with BI640.4-mm (0.5), BI600.4-mm (0.3), BI640.2-mm (0.5), and BI600.2-mm (0.2) (all p < .05). The median bronchial wall sharpness versus the clinical reference reconstruction was higher for reconstructions with BI640.4-mm (0.3) and BI640.2-mm (0.3) and was lower for BI561.0-mm (-0.7) and BI560.4-mm (-0.3) (all p < .05). Median pulmonary fissure sharpness versus the clinical reference reconstruction was higher for reconstructions with BI640.4-mm (0.3), BI600.4-mm (0.3), BI560.4-mm (0.5), BI640.2-mm (0.5), BI600.2-mm (0.5), and BI560.2-mm (0.3) (all p < .05). Median pulmonary vessel sharpness versus the clinical reference reconstruction was lower for reconstructions with BI561.0-mm (-0.3), BI600.4-mm (-0.3), BI560.4-mm (-0.7), BI640.2-mm (-0.7), BI600.2-mm (-0.7), and BI560.2-mm (-0.7). Median lung nodule conspicuity versus the clinical reference reconstruction was lower for reconstructions with BI561.0-mm (-0.3) and BI560.4-mm (-0.3) (both p < .05). Median conspicuity of all other pathologies versus the clinical reference reconstruction was lower for reconstructions with BI561.0 mm (-0.3), BI560.4-mm (-0.3), BI640.2-mm (-0.3), BI600.2-mm (-0.3), and BI560.2-mm (-0.3). Other comparisons among reconstructions were not significant (all p > .05). CONCLUSION. Only the reconstruction using BI640.4-mm yielded improved bronchial division identification and bronchial wall and pulmonary fissure sharpness without a loss in pulmonary vessel sharpness or conspicuity of nodules or other pathologies. CLINICAL IMPACT. The findings of this study may guide protocol optimization for UHR PCD CT of the lungs.

Determination of scattered radiation dose for radiological staff during portable chest examinations of COVID-19 patients.

The COVID-19 pandemic has resulted in a large increase in the number of patients admitted to hospitals. Radiological technologists (RTs) are often required to perform portable chest X-ray radiography on these patients. Normally, when performing a portable X-ray, radiation protection equipment is critical as it reduces the scatter radiation dose to hospital workers. However, during the pandemic, the use of a lead shield caused a heavy weight burden on workers who were responsible for a large number of patients. This study aimed to investigate scatter radiation doses received at various distances, directions, and positions. Radiation measurements were performed using the PBU-60 whole body phantom to determine scatter radiation doses at 100-200 cm and eight different angles around the phantom. The tests were conducted with and without lead shielding. Additionally, the doses were compared using the paired t test (p < 0.005) to determine suitable positions for workers who did not wear lead protection that adhered to radiation safety requirements. Scatter radiation doses of all 40 tests showed a highest and lowest value of 1285.5 nGy at 100 cm in the anteroposterior (AP) semi upright position and 134.7 nGy at 200 cm in the prone position, respectively. Correlation analysis between the dosimeter measurement and calculated inverse square law showed good correlation, with an R2 value of 0.99. Without lead shielding, RTs must stay at a distance greater than 200 cm from patients for both vertical and horizontal beams to minimize scatter exposure. This would allow for an alternative way of performing portable chest radiography for COVID-19 patients without requiring lead shielding.

The effectiveness of the Safety in Interventional Radiology (SIR) Shield in reducing droplet transmission and its effect on image quality and radiation dose.

OBJECTIVE: To evaluate the efficacy of a barrier shield in reducing droplet transmission and its effect on image quality and radiation dose in an interventional suite. METHODS: A human cough droplet visualisation model in a supine position was developed to assess efficacy of barrier shield in reducing environmental contamination. Its effect on image quality (resolution and contrast) was evaluated via image quality test phantom. Changes in the radiation dose to patient post-shield utilisation was measured. RESULTS: Use of the shield prevented escape of visible fluorescent cough droplets from the containment area. No subjective change in line-pair resolution was observed. No significant difference in contrast-to-noise ratio was measured. Radiation dosage to patient was increased; this is predominantly attributed to the increased air gap and not the physical properties of the shield. CONCLUSION: Use of the barrier shield provided an effective added layer of personal protection in the interventional radiology theatre for aerosol generating procedures. ADVANCES IN KNOWLEDGE: This is the first time a human supine cough droplet visualisation has been developed. While multiple types of barrier shields have been described, this is the first systematic practical evaluation of a barrier shield designed for use in the interventional radiology theatre.

Radiopaque Recreations of Lung Pathologies From Clinical Computed Tomography Images Using Potassium Iodide Inkjet 3-dimensional Printing: Proof of Concept.

PURPOSE: The purpose of this study was to develop a 3-dimensional (3D) printing method to create computed tomography (CT) realistic phantoms of lung cancer nodules and lung parenchymal disease from clinical CT images. MATERIALS AND METHODS: Low-density paper was used as substrate material for inkjet printing with potassium iodide solution to reproduce phantoms that mimic the CT attenuation of lung parenchyma. The relationship between grayscale values and the corresponding CT numbers of prints was first established through the derivation of exponential fitted equation from scanning data. Next, chest CTs from patients with early-stage lung cancer and coronavirus disease 2019 (COVID-19) pneumonia were chosen for 3D printing. CT images of original lung nodule and the 3D-printed nodule phantom were compared based on pixel-to-pixel correlation and radiomic features. RESULTS: CT images of part-solid lung cancer and 3D-printed nodule phantom showed both high visual similarity and quantitative correlation. R2 values from linear regressions of pixel-to-pixel correlations between 5 sets of patient and 3D-printed image pairs were 0.92, 0.94, 0.86, 0.85, and 0.83, respectively. Comparison of radiomic measures between clinical CT and printed models demonstrated 6.1% median difference, with 25th and 75th percentile range at 2.4% and 15.2% absolute difference, respectively. The densities and parenchymal morphologies from COVID-19 pneumonia CT images were well reproduced in the 3D-printed phantom scans. CONCLUSION: The 3D printing method presented in this work facilitates creation of CT-realistic reproductions of lung cancer and parenchymal disease from individual patient scans with microbiological and pathology confirmation.

Multi-institution consensus paper for acquisition of portable chest radiographs through glass barriers.

BACKGROUND: To conserve personal protective equipment (PPE) and reduce exposure to potentially infected COVID-19 patients, several Californian facilities independently implemented a method of acquiring portable chest radiographs through glass barriers that was originally developed by the University of Washington. METHODS: This work quantifies the transmission of radiation through a glass barrier using six radiographic systems at five facilities. Patient entrance air kerma (EAK) and effective dose were estimated both with and without the glass barrier. Beam penetrability and resulting exposure index (EI) and deviation index (DI) were measured and used to adjust the tube current-time product (mAs) for glass barriers. Because of beam hardening, the contrast-to-noise ratio (CNR) was measured with image quality phantoms to ensure diagnostic integrity. Finally, scatter surveys were performed to assess staff radiation exposure both inside and outside the exam room. RESULTS: The glass barriers attenuated a mean of 61% of the normal X-ray beams. When the mAs was increased to match EI values, there was no discernible degradation of image quality as determined by the CNR. This was corroborated with subjective assessments of image quality by chest radiologists. The glass-hardened beams acted as a filter for low energy X-rays, and some facilities observed slight changes in patient effective doses. There was scattering from both the phantoms and the glass barriers within the room. CONCLUSIONS: Glass barriers require an approximate 2.5 times increase in beam intensity, with all other technique factors held constant. Further refinements are necessary for increased source-to-image distance and beam quality in order to adequately match EI values. This does not result in a significant increase in the radiation dose delivered to the patient. The use of lead aprons, mobile shields, and increased distance from scattering sources should be employed where practicable in order to keep staff radiation doses as low as reasonably achievable.

A phantom study to optimise the automatic tube current modulation for chest CT in COVID-19.

On March 11, 2020, the World Health Organization declared the coronavirus disease 2019 (COVID-19) pandemic. The expert organisations recommend more cautious use of thoracic computed tomography (CT), opting for low-dose protocols. We aimed at determining a threshold value of automatic tube current modulation noise index below which there is a chance to miss an onset of ground-glass opacities (GGO) in COVID-19. A team of radiologists and medical physicists performed 25 phantom CT studies using different automatic tube current modulation settings (SUREExposure3D technology). We then conducted a retrospective evaluation of the chest CT images from 22 patients with COVID-19 and calculated the density difference between the GGO and unaffected tissue. Finally, the results were matched to the phantom study results to determine the minimum noise index threshold value. The minimum density difference at the onset of COVID-19 was 252 HU (p < 0.001). This was found to correspond to the SUREExposure 3D noise index of 36. We established the noise index threshold of 36 for the Canon scanner without iterative reconstructions, allowing for a decrease in the dose-length product by 80%. The proposed protocol needs to be validated in a prospective study.

Feasibility of lung imaging with a large field-of-view spectral photon-counting CT system.

PURPOSE: The purpose of this study was to characterize the technical capabilities and feasibility of a large field-of-view clinical spectral photon-counting computed tomography (SPCCT) prototype for high-resolution (HR) lung imaging. MATERIALS AND METHODS: Measurement of modulation transfer function (MTF) and acquisition of a line pairs phantom were performed. An anthropomorphic lung nodule phantom was scanned with standard (120kVp, 62mAs), low (120kVp, 11mAs), and ultra-low (80kVp, 3mAs) radiation doses. A human volunteer underwent standard (120kVp, 63mAs) and low (120kVp, 11mAs) dose scans after approval by the ethics committee. HR images were reconstructed with 1024 matrix, 300mm field of view and 0.25mm slice thickness using a filtered-back projection (FBP) and two levels of iterative reconstruction (iDose 5 and 9). The conspicuity and sharpness of various lung structures (distal airways, vessels, fissures and proximal bronchial wall), image noise, and overall image quality were independently analyzed by three radiologists and compared to a previous HR lung CT examination of the same volunteer performed with a conventional CT equipped with energy integrating detectors (120kVp, 10mAs, FBP). RESULTS: Ten percent MTF was measured at 22.3lp/cm with a cut-off at 31lp/cm. Up to 28lp/cm were depicted. While mixed and solid nodules were easily depicted on standard and low-dose phantom images, higher iDose levels and slice thicknesses (1mm) were needed to visualize ground-glass components on ultra-low-dose images. Standard dose SPCCT images of in vivo lung structures were of greater conspicuity and sharpness, with greater overall image quality, and similar image noise (despite a flux reduction of 23%) to conventional CT images. Low-dose SPCCT images were of greater or similar conspicuity and sharpness, similar overall image quality, and lower but acceptable image noise (despite a flux reduction of 89%). CONCLUSIONS: A large field-of-view SPCCT prototype demonstrates HR technical capabilities and high image quality for high resolution lung CT in human.

Proof of Concept: Phantom Study to Ensure Quality and Safety of Portable Chest Radiography Through Glass During the COVID-19 Pandemic.

BACKGROUND: Chest radiography is often used to detect lung involvement in patients with suspected pneumonia. Chest radiography through glass walls of an isolation room is a technique that could be immensely useful in the current COVID-19 pandemic. PURPOSE: The purpose of this study was to ensure quality and radiation safety while acquiring portable chest radiographs through the glass doors of isolation rooms using an adult anthropomorphic thorax phantom. MATERIALS AND METHODS: Sixteen chest radiographs were acquired utilizing different exposure factors without glass, through the smart glass, and through regular glass. Images were scored independently by 2 radiologists for quantum mottle and sharpness of anatomical structures using a 5-point Likert scale. Statistically significant differences in Likert scale scores and entrance surface dose (ESD) between images acquired without glass and through the smart and regular glass were tested. Interreader reliability was also evaluated. RESULTS: Compared with conventional radiography, equal or higher mean image quality scores (mottle and anatomical structures) were observed with the smart glass using 100 kVp at 12 mAs and 20 mAs and 125 kVp at 6.3 mAs (100 kVp at 2 mAs and 125 kVp at 3.2 mAs were used for conventional radiography observations). There was no statistically significant difference in the Likert scale scores for image quality and the entrance surface dose for radiographs acquired without glass, through the smart glass, and through regular glass. Backscatter from the smart glass was minimal at a distance of 3 m and was recorded as zero at a distance of 4 m from the x-ray tube outside an isolation room. CONCLUSIONS: Good-quality portable chest radiographs can be obtained safely through the smart glass doors of the isolation room. However, this technique does result in minor backscatter radiation. Modifications in the exposure factors (such as increasing milliampere seconds) may be required to optimize image quality while using this technique.

A Programmable Platform for Accelerating the Development of Smart Ultrasound Transducer Probe.

During the COVID-19 pandemic, an ultraportable ultrasound smart probe has proven to be one of the few practical diagnostic and monitoring tools for doctors who are fully covered with personal protective equipment. The real-time, safety, ease of sanitization, and ultraportability features of an ultrasound smart probe make it extremely suitable for diagnosing COVID-19. In this article, we discuss the implementation of a smart probe designed according to the classic architecture of ultrasound scanners. The design balanced both performance and power consumption. This programmable platform for an ultrasound smart probe supports a 64-channel full digital beamformer. The platform's size is smaller than 10 cm ×5 cm. It achieves a 60-dBFS signal-to-noise ratio (SNR) and an average power consumption of ~4 W with 80% power efficiency. The platform is capable of achieving triplex B-mode, M-mode, color, pulsed-wave Doppler mode imaging in real time. The hardware design files are available for researchers and engineers for further study, improvement or rapid commercialization of ultrasound smart probes to fight COVID-19.

Early extrapulmonary prognostic features in chest computed tomography in COVID-19 pneumonia: Bone mineral density is a relevant predictor for the clinical outcome - A multicenter feasibility study.

BACKGROUND: Besides throat-nose swab polymerase chain reaction (PCR), unenhanced chest computed tomography (CT) is a recommended diagnostic tool for early detection and quantification of pulmonary changes in COVID-19 pneumonia caused by the novel corona virus. Demographic factors, especially age and comorbidities, are major determinants of the outcome in COVID-19 infection. This study examines the extra pulmonary parameter of bone mineral density (BMD) from an initial chest computed tomography as an associated variable of pre-existing comorbidities like chronic lung disease or demographic factors to determine the later patient's outcome, in particular whether treatment on an intensive care unit (ICU) was necessary in infected patients. METHODS: We analyzed 58 PCR-confirmed COVID-19 infections that received an unenhanced CT at admission at one of the included centers. In addition to the extent of pulmonary involvement, we performed a phantomless assessment of bone mineral density of thoracic vertebra 9-12. RESULTS: In a univariate regression analysis BMD was found to be a significant predictor of the necessity for intensive care unit treatment of COVID-19 patients. In the subgroup requiring intensive care treatment within the follow-up period a significantly lower BMD was found. In a multivariate logistic regression model considering gender, age and CT measurements of bone mineral density, BMD was eliminated from the regression analysis as a significant predictor. CONCLUSION: Phantomless assessed BMD provides prognostic information on the necessity for ICU treatment in course of COVID-19 pneumonia. We recommend using the measurement of BMD in an initial CT image to facilitate a potentially better prediction of severe patient outcomes within the 22 days after an initial CT scan. Consequently, in the present sample, additional bone density analysis did not result in a prognostic advantage over simply considering age. Significantly larger patient cohorts with a more homogenous patient age should be performed in the future to illustrate potential effects. CLINICAL RELEVANCE: While clinical capacities such as ICU beds and ventilators are more crucial than ever to help manage the current global corona pandemic, this work introduces an approach that can be used in a cost-effective way to help determine the amount of these rare clinical resources required in the near future.

Low dose radiation therapy for COVID-19: Effective dose and estimation of cancer risk.

BACKGROUND AND PURPOSE: The objective of this work is to evaluate the risk of carcinogenesis of low dose ionizing radiation therapy (LDRT), for treatment of immune-related pneumonia following COVID-19 infection, through the estimation of effective dose and the lifetime attributable risk of cancer (LAR). MATERIAL AND METHODS: LDRT treatment was planned in male and female computational phantoms. Equivalent doses in organs were estimated using both treatment planning system calculations and a peripheral dose model (based on ionization chamber measurements). Skin dose was estimated using radiochromic films. Later, effective dose and LAR were calculated following radiation protection procedures. RESULTS: Equivalent doses to organs per unit of prescription dose range from 10 mSv/cGy to 0.0051 mSv/cGy. Effective doses range from 204 mSv to 426 mSv, for prescription doses ranging from 50 cGy to 100 cGy. Total LAR for a prescription dose of 50 cGy ranges from 1.7 to 0.29% for male and from 4.9 to 0.54% for female, for ages ranging from 20 to 80 years old. CONCLUSIONS: The organs that mainly contribute to risk are lung and breast. Risk for out-of-field organs is low, less than 0.06 cases per 10000. Female LAR is on average 2.2 times that of a male of the same age. Effective doses are of the same order of magnitude as the higher-dose interventional radiology techniques. For a 60 year-old male, LAR is 8 times that from a cardiac CT, when prescription dose is 50 cGy.

Three-Tesla Magnetic Resonance Imaging of Patients With Deep Brain Stimulators: Results From a Phantom Study and a Pilot Study in Patients.

BACKGROUND: Deep brain stimulation (DBS) is a standard of care treatment for multiple neurologic disorders. Although 3-tesla (3T) magnetic resonance imaging (MRI) has become the gold-standard modality for structural and functional imaging, most centers refrain from 3T imaging in patients with DBS devices in place because of safety concerns. 3T MRI could be used not only for structural imaging, but also for functional MRI to study the effects of DBS on neurocircuitry and optimize programming. OBJECTIVE: To use an anthropomorphic phantom design to perform temperature and voltage safety testing on an activated DBS device during 3T imaging. METHODS: An anthropomorphic 3D-printed human phantom was constructed and used to perform temperature and voltage testing on a DBS device during 3T MRI. Based on the phantom assessment, a cohort study was conducted in which 6 human patients underwent MRI with their DBS device in an activated (ON) state. RESULTS: During the phantom study, temperature rises were under 2°C during all sequences, with the DBS in both the deactivated and activated states. Radiofrequency pulses from the MRI appeared to modulate the electrical discharge from the DBS, resulting in slight fluctuations of voltage amplitude. Six human subjects underwent MRI with their DBS in an activated state without any serious adverse events. One patient experienced stimulation-related side effects during T1-MPRAGE scanning with the DBS in an ON state because of radiofrequency-induced modulation of voltage amplitude. CONCLUSION: Following careful phantom-based safety testing, 3T structural and functional MRI can be safely performed in subjects with activated deep brain stimulators.

Modifications to mobile chest radiography technique during the COVID-19 pandemic - implications of X-raying through side room windows.

INTRODUCTION: Modifications to common radiographic techniques have resulted from the challenges presented by the COVID-19 pandemic. Reports exist regarding the potential benefits of undertaking mobile radiography through side room windows. The aim of this study was to evaluate the impact on image quality and exposure factors when undertaking such examinations. METHODS: A phantom based study was undertaken using a digital X-ray room. Control acquisitions, using a commercially available image quality test tool, were performed using standard mobile chest radiography acquisition factors. Image quality (physical and visual), incidence surface air kerma (ISAK), Exposure Index (EI) and Deviation Index (DI) were recorded. Image quality and radiation dose were further assessed for two additional (experimental) scenarios, where a side room window was located immediately adjacent to the exit port of the light beam diaphragm. The goal of experimental scenario one was to modify exposure factors to maintain the control ISAK. The goal of experimental scenario two was to modify exposure factors to maintain the control EI and DI. Dose and image quality data were compared between the three scenarios. RESULTS: To maintain the pre-window (control) ISAK (76 µGy), tube output needed a three-fold increase (90 kV/4 mAs versus 90 kV/11.25 mAs). To maintain EI/DI a more modest increase in tube output was required (90 kV/8 mAs/ISAK 54 µGy). Physical and visual assessments of spatial resolution and signal-to-noise ratio were indifferent between the three scenarios. There was a slight statistically significant reduction in contrast-to-noise ratio when imaging through the glass window (2.3 versus 1.4 and 1.2; P = 0.005). CONCLUSION: Undertaking mobile X-ray examinations through side room windows is potentially feasible but does require an increase in tube output and is likely to be limited by minor reductions in image quality. IMPLICATIONS FOR PRACTICE: Mobile examinations performed through side room windows should only be used in limited circumstances and future clinical evaluation of this technique is warranted.

Initial data from an experiment to implement a safe procedure to perform PA erect chest radiographs for COVID-19 patients with a mobile radiographic system in a "clean" zone of the hospital ward.

INTRODUCTION: With the current Covid-19 pandemic, general wards have been converted into cohort wards for Covid-19 patients who are stable and ambulant. A 2-radiographer mobile radiography team is required to perform bedside Chest X-rays (CXR) for these patients. Hospital guidelines require both radiographers to be in full Personal Protective Equipment (PPE) throughout the image acquisition process and the mobile radiographic unit needs to be disinfected twice after each case. This affects the efficiency of the procedure and an increase usage of limited PPE resources. This study aims to explore the feasibility of performing mobile chest radiography with the mobile radiographic unit in a "clean" zone of the hospital ward. METHODS: An anthropomorphic body phantom was used during the test. With the mobile radiographic unit placed in a "clean" zone, the phantom and the mobile radiographic unit was segregated by the room door with a clear glass panel. The test was carried out with the room door open and closed. Integrated radiation level and patient dose were measured. A consultant radiologist was invited to review and score all the images acquired using a Barco Medical Grade workstation. The Absolute Visual Grading Analysis (VGA) scoring system was used to score these images. RESULTS: A VGA score of 4 was given to all the 40 test images, suggesting that there is no significant differences in the image quality of the images acquired using the 2 different methods. Radiation exposure received by the patient at the highest kV setting through the glass is comparable to the regular CXR on patient without glass panel at 90 kV, suggesting that there is no significant increase in patient dose. CONCLUSION: The result suggests that acquiring CXR with the X-ray beam attenuating through a glass panel is a safe and feasible way of performing CXR for COVID-19 patients in the newly converted COVID wards. This will allow the mobile radiographic unit as well as one radiographer to be completely segregated from the patient. IMPLICATIONS FOR PRACTICE: This new method of acquiring CXR in an isolation facility set up requires a 2-Radiographer mobile radiography team, and is applicable only for patients who are generally well and not presented with any mobility issues. It is also important to note that a clear glass panel must be present in the barriers set up for segregation between the "clean" zone and patient zone in order to use this new method of acquiring CXR.