Air-tissue Interface Research Articles

Dosimetric Impact of Prescription Point Placement in Heterogeneous Medium for Conformal Radiotherapy Dose Calculation with Various Algorithms

Objective: The aim of the study is to compare the accuracy of dose calculation for different dose calculation algorithms with different prescription points (air, tissue, air–tissue interface in carcinoma lung patients and bone, tissue, and bone–tissue interface in carcinoma buccal Mucosa tumors). Materials and Methods: Forty-one patients with carcinoma lung and buccal mucosa were retrospectively selected for this study. A three-dimensional conformal radiotherapy reference plan was created using the prescription point in the tissue with Monte Carlo (MC) algorithms for both the groups of patients. The reference plan was modified by changing the prescription point and algorithms in the tissue, air, air–tissue interface for lung patients and tissue, bone, and bone–tissue interface for buccal mucosa patients. The dose received by the target volume and other organs at risk (OAR) structures was compared. To find out the statistical difference between different prescription points and algorithms, the statistical tests were performed with repeated measures ANOVA. Results: The target volume receiving 95% dose coverage in lung patients decreased to −3.08%, −5.75%, and −1.87% in the dose prescription point at the air–tissue interface with the dose calculation algorithms like MC, collapsed cone (CC), and pencil beam (PB), respectively, compared to that of the MC tissue. Spinal cord dose was increased in the CC and PB algorithms in all prescription points in patients with lung and buccal mucosa. OAR dose calculated by PB in all prescription points showed a significant deviation compared to MC tissue prescription point. Conclusion: This study will help demonstrate the accuracy of dose calculation for the different dose prescription points with the different treatment algorithms in radiotherapy treatment planning.

The chick chorioallantoic membrane assay as an in vivo model for colon tumor analysis with optical coherence tomography

Optical coherence tomography (OCT) has emerged as a promising imaging modality for biomedical research. In this paper, a commercial OCT system was used to differentiate two colon cell lines implanted in a chick embryo chorioallantoic membrane (CAM) model, using the attenuation coefficient of light. Malignant and non-malignant tumors were developed from RKO and NCM460 cell lines, respectively. OCT B-scan images were collected from 30 CAM models, 15 with RKO-cells and 15 with NCM460-cells. A support vector machine (SVM) classifier was trained and tested using features obtained from two different bands of interest in the depth-resolved attenuation coefficient images. Quantitative analysis revealed that the non-malignant tumors present a higher attenuation coefficient than the malignant tumors immediately after the air-tissue interface. On the other side, at a depth of 206 µm, malignant tumors exhibit higher attenuation coefficient values. Using the features median, interquartile range, and maximum of the A-scans attenuation coefficient values for two adjacent bands in-depth, the SVM nested cross-validation presents an accuracy, recall, precision, and AUC of 1.0, which gives evidence that non-malignant and malignant tumors can be distinguished with high accuracy. This work represents an important step toward the use of OCT imaging for real-time biopsy of colorectal tissues.

An Analysis of Positron Emission Tomography Maximum Standard Uptake Value Among Patients With Head and Neck Cancer Receiving Photon and Proton Radiation

IntroOne main advantage of proton therapy versus photon therapy is its precise radiation delivery to targets without exit dose, resulting in lower dose to surrounding healthy tissues. This is critical given the proximity of head and neck tumors to normal structures. However, proton planning requires careful consideration of factors including air-tissue interface, anatomical uncertainties, surgical artifacts, weight fluctuations, rapid tumor response, and daily variations in setup and anatomy, as these heterogeneities can lead to inaccuracies in targeting and creating unwarranted hotspots to a greater extent than photon radiation. Additionally, the elevated relative biological effectiveness (RBE) at the Bragg peak's distal end can also increase hot spots within and outside the target area. Purpose/MethodsThe purpose of this study was to evaluate for a difference in PET SUV uptake following definitive treatment, between IMPT or IMRT. Additionally, we compared the biologic dose between PET areas of high and low uptake within the CTV-primary of patients treated with IMPT. This work is assuming that the higher SUV uptake may potentially result in higher toxicities. For the purposes of this short communication, we are strictly focusing on the SUV uptake, and do not have correlation with toxicity outcomes. To accomplish this, we compared the 3- and 6-month post-treatment FDG PET scans for 100 matched oropharyngeal cancer patients treated definitively without surgery using either IMPT (n=50) or IMRT (n=50). ResultsOur study found a significant difference in biologic dose between the high and low-uptake regions on 3-month post-treatment scans of IMPT. However, this difference did not translate to a significant difference in PET uptake in the CTV-primary at 3 and 6-months follow-up between IMPT and IMRT patients. ConclusionStudies propose proton's higher RBE at the Bragg peak could lead to tissue inflammation. Our study did not corroborate these findings. This study's conclusion underscores the need for further investigations with ultimate correlation with clinical toxicity outcomes.

Bacterial vesicles block viral replication in macrophages via TLR4-TRIF-axis

Gram-negative bacteria naturally secrete nano-sized outer membrane vesicles (OMVs), which are important mediators of communication and pathogenesis. OMV uptake by host cells activates TLR signalling via transported PAMPs. As important resident immune cells, alveolar macrophages are located at the air-tissue interface where they comprise the first line of defence against inhaled microorganisms and particles. To date, little is known about the interplay between alveolar macrophages and OMVs from pathogenic bacteria. The immune response to OMVs and underlying mechanisms are still elusive. Here, we investigated the response of primary human macrophages to bacterial vesicles (Legionella pneumophila, Klebsiella pneumoniae, Escherichia coli, Salmonella enterica, Streptococcus pneumoniae) and observed comparable NF-κB activation across all tested vesicles. In contrast, we describe differential type I IFN signalling with prolonged STAT1 phosphorylation and strong Mx1 induction, blocking influenza A virus replication only for Klebsiella, E.coli and Salmonella OMVs. OMV-induced antiviral effects were less pronounced for endotoxin-free Clear coli OMVs and Polymyxin-treated OMVs. LPS stimulation could not mimic this antiviral status, while TRIF knockout abrogated it. Importantly, supernatant from OMV-treated macrophages induced an antiviral response in alveolar epithelial cells (AEC), suggesting OMV-induced intercellular communication. Finally, results were validated in an ex vivo infection model with primary human lung tissue. In conclusion, Klebsiella, E.coli and Salmonella OMVs induce antiviral immunity in macrophages via TLR4-TRIF-signaling to reduce viral replication in macrophages, AECs and lung tissue. These gram-negative bacteria induce antiviral immunity in the lung through OMVs, with a potential decisive and tremendous impact on bacterial and viral coinfection outcome.7FMb6rvPxRFWumGrBQKEMqVideo

Best Practice Recommendations for the Safe use of Lung Ultrasound.

Die Sicherheit des Ultraschalls ist bei der Untersuchung der Lunge von besonderer Bedeutung, da spezifische Wechselwirkungsmechanismen an der alveolaren Luft-Gewebegrenze auftreten. Lungengewebe ist dabei deutlich empfindlicher als solides Gewebe gegenüber mechanischen Kräften. Die ursächlichen biologischen Effekte basierend auf Totalreflektion von Schallwellen sind zudem nur unzureichend untersucht. Andererseits ist der klinische Nutzen des Lungenultraschalls beträchtlich und hat Aufgrund der Pandemiesituation erheblichen Stellenwert dazugewonnen. Dabei erweist sich dieser bisweilen dem anderer radiologischer Bildgebungsverfahren ebenbürtig. Deshalb widmet sich diese Arbeit, basierend auf derzeit verfügbaren Literaturquellen, dem Einfluss von Schalleffekten auf das Lungenparenchym und evaluiert bestehende Empfehlungen zur Schalldruckreduzierung bei der Durchführung der Lungensonographie. Es wird ein Vorgehen empfohlen, um klinisch relevante Bilder zu erhalten und gleichzeitig die Ultraschallsicherheit zu gewährleisten. Ein besonderes Augenmerk liegt auf der Sicherheit neuer Ultraschall Modalitäten, welche zum Zeitpunkt früherer Empfehlungen noch nicht berücksichtigt waren. Abschließend werden notwendige Forschungs- und Ausbildungsschritte empfohlen, um Wissenslücken auf dem Gebiet des Lungenultraschalls in Zukunft schließen zu können. Diese Empfehlungen für die Praxis wurden von ECMUS, dem Sicherheitskommittee der EFSUMB, unter Mitwirkung von international Experten auf dem Gebiet der Lungensonographie und biologischer Ultraschallwechselwirkung erstellt. The safety of ultrasound is of particular importance when examining the lungs, due to specific bioeffects occurring at the alveolar air-tissue interface. Lung is significantly more sensitive than solid tissue to mechanical stress. The causal biological effects due to the total reflection of sound waves have also not been investigated comprehensively. On the other hand, the clinical benefit of lung ultrasound is outstanding. It has gained considerable importance during the pandemic situation, showing comparable diagnostic value with other radiological imaging modalities. Therefore, based on currently available literature, this work was dedicated determining possible ultrasound effects on the lung parenchyma and evaluating existing recommendations for acoustic output power limits when performing lung sonography. This work recommends a stepwise approach to obtain clinically relevant images while ensuring lung ultrasound safety. A special focus was set on the safety of new ultrasound modalities, which had not yet been introduced at the time of previous recommendations. Finally, necessary research and training steps are recommended in order to close knowledge gaps in the field of lung ultrasound safety in the future. These recommendations for practice were prepared by ECMUS, the safety committee of the EFSUMB, with participation of international experts in the field of lung sonography and ultrasound bioeffects.

Numerical simulations for characterization of missing articulatory information in ultrasound imaging of speech

The air–tissue interface at the tongue surface allows submental (below the chin) B-mode ultrasound images to depict the shape of the tongue in real time, useful for measuring and understanding typical and disordered tongue articulation during speech production. However, parts of the tongue are obscured; depending on an individual speaker's anatomy and tongue movement patterns, the anterior tongue tip may be shadowed by the mandible bone and the sublingual airspace. To characterize this missing information about the tongue tip in ultrasound images, midsagittal ultrasound images were numericallysimulated. Three-dimensional anatomic models were constructed using magnetic resonance imaging (MRI) data to map tongue tissue, surrounding air, and an estimated position of the mandible. Pulse-echo ultrasound images were then numerically simulated using the open-source k-Wave toolbox. Acoustic properties of the medium and an imaging array model are identified that allow simulations to replicate features in ultrasound images recorded from the same speakers as the MRI data, while maintaining computational efficiency. The potential to recover missing information on the tongue tip position from reverberation artifacts is assessed.

The vulnerable air-tissue interface: Summary of ultrasound related bioeffects on lung and their implications for the use of different imaging modes and applications beyond

Introduction: Lung tissue is sensitive to mechanical stress. Animal studies showed induction of pulmonary capillary hemorrhage (PCH) in lung in the diagnostic regime at intensities. Therefore, this work summarizes novel findings regarding the interaction of ultrasound at the alveolar epithelium-gas interface. Method: Literature research related to ultrasound bio-effects on lung was carried out. Furthermore, recent studies reporting thresholds of PCH induction depending on imaging mode and duration will be discussed. Results: Ventilated lung tissue is more vulnerable to mechanical forces than solid tissue. From peak negative pressure below 1.5 MPa the likelihood of PCH induction increases with exposure time. Such PCH is asymptomatic but can falsify the diagnostic outcome. The causes remain still unknown but is not related to cavitation or thermal effects. The extent of PCH in lung is depending of physiological beside acoustic parameters. The extend of PCH is, therefore, not entirely predictable. In addition, observational studies on humans could not confirm the findings as investigated on pathological level on animal models. Conclusion: The vulnerability of lung should become aware in the lung ultrasound community. Current recommendations for output limitations given by AIUM and EFSUMB should be followed and only increased for diagnostics needs.

Abstract P1-10-11: Optical stimulated luminescence dosimeters for skin dose measurements during accelerated partial breast brachytherapy: In vivo dosimetric validation and clinical outcomes

Abstract BACKGROUND: The role of multi-lumen catheter devices in the delivery of high dose rate (HDR) brachytherapy for adjuvant accelerated partial breast irradiation (APBI) for women with DCIS or early-stage breast cancer has been well established. In vivo dosimetry (IVD) using optically stimulating luminescence dosimeters (OSLD) is a feasible way to detect applicator instability that may cause translational and rotational inaccuracies during HDR brachytherapy delivery. Herein, we evaluate the accuracy and effectiveness of IVD to improve patient outcomes following APBI brachytherapy using the Strut Adjusted Volume Irradiation (SAVI) device. METHODS: Single-institution cohort study piloting the use of OSLD on the patient’s skin during HDR brachytherapy APBI to assess the estimated maximum skin dose (skin Dmax) and the achievable accuracy of OSLD for skin Dmax measurements. Women treated with SAVI-based APBI between November 1, 2018 and October 1, 2021 were eligible to enroll in our study. All patients met the American Society for Radiation Oncology “suitable” or “cautionary” criteria and were treated according to the American Brachytherapy Society consensus treatment planning guidelines. A SAVI preplan was created to estimate the probable point of skin Dmax. During CT simulation, a radiopaque marker was placed on the skin for visualization during treatment planning. Correction factors were applied to account for the OSLD tissue-air interface that is not present in the TG-43 expected dose calculations. Measured and calculated IVD doses were analyzed to assess agreement and cause for discrepancies found. Breast phantom IVD measurements repeated seven times with two independent dose points were analyzed to assess the best accuracy achievable under ideal conditions. RESULTS: We enrolled 41 patients with an average age of 68 years. Table 1 details the brachytherapy treatment delivery and dosimetry data. Higher skin Dmax as a percentage of the radiation prescription was associated with the occurrence of breast volume loss noted on subsequent clinical breast exams (OR 1.84 per each 5% increase in skin Dmax; 95% CI 1.21 – 3.32; p=0.016). The graphically estimated skin Dmax threshold was 80% with all cases of noted breast volume loss occurring above this threshold. The overall level of achievable IVD accuracy was ±3.32% based on breast phantom measurements. Under ideal conditions, all measurements were in the ±7% range. Three of 14 phantom measurement exceeded the 6% discrepancy range. Clinical IVD measurements detected 5 true positive cases (12.2% of cohort) that required intervention due to rotations in the SAVI applicator. For a ±7% tolerance criteria, 90.2% of the patients tested passed IVD. Of the eight patients that failed at the 7% level, IVD detected 3 OSLD placement errors, 2 rotational discrepancy cases, and 1 large air-gap at the point of measurement. CONCLUSIONS: Accuracy and reproducibility are imperative tenets of HDR brachytherapy APBI. IVD utilizing OSLD is an effective method for detecting treatment set-up and delivery errors for patients receiving SAVI-based APBI with dose accuracy within ±3.32%. Errors requiring intervention due to SAVI device rotation were detected in 12.2% of our cohort, and these errors would have likely gone undetected without IVD. Using OSLD as IVD to measure skin Dmax doses that may increase the risk of breast cosmetic defects should be investigated further. Table 1. Brachytherapy treatment delivery and dosimetry data. *PTV-Eval is a uniform 10 mm expansion on the CTV with exclusion of PTV within 5 mm of skin or chest wall. +Percent dose discrepancy refers to difference in dose between APBI plan calculations and IVD measurements. Citation Format: Tyler Gutschenritter, Afua Yorke, Nayak Polissar, Nirnaya Miljacic, Janice Kim, Lori Young. Optical stimulated luminescence dosimeters for skin dose measurements during accelerated partial breast brachytherapy: In vivo dosimetric validation and clinical outcomes [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-11.

HALO: A software tool for real-time head alignment in the MR scanner.

MRI studies in human subjects often require multiple scanning sessions/visits. Changes in a subject's head position across sessions result in different alignment between brain tissues and the magnetic field which leads to changes in magnetic susceptibility. These changes can have considerable impacts on acquired signals. Head ALignment Optimization (HALO), a software tool was developed by the authors for active head alignment between sessions. HALO provides real-time visual feedback of a subject's current head position relative to the position in a previous session. The tool was evaluated in a pilot sample of seven healthy human subjects. HALO was shown to enable subjects to actively align their head positions to the desired position of their initial sessions. The subjects were able to improve their head alignment significantly using HALO and achieved good alignment with their first session meeting stringent criteria similar to that used for within-run head motion (less than 2 mm translation or 2 degrees rotation in any direction from the desired position). Moreover, we found a negative correlation between the post-alignment rotation and similarity in inter-session BOLD patterns around the air-tissue interface near sinus which further highlighted the impact of tissue-field alignment on BOLD data quality. Utilization of HALO in longitudinal studies may help to improve data quality by ensuring the consistency of susceptibility gradients in brain tissues across sessions. HALO has been made publicly available.

Considerations for CT Number Calibration and Imaging Parameter Selection for Adaptive Planning on a Novel On-Board Helical kVCT System

<h3>Purpose/Objective(s)</h3> To evaluate the impact of CT number calibration and imaging parameters on adaptive dose calculation accuracy relative to the CT planning process for an on-board helical kVCT imaging system used in helical tomotherapy treatments. <h3>Materials/Methods</h3> Helical kVCT calibrations were performed with thorax protocols at 120 kVp for <i>Fine</i> and <i>Normal</i> imaging modes using a standard electron density phantom. For this system, <i>Mode</i> determines the longitudinal beam width at isocenter, couch speed, and views per rotation, which impact the scatter signal, scan time, and patient dose, respectively, and offers <i>Fine</i> (50 mm beam width, long relative scan time, high relative mAs/rotation), <i>Normal</i> (100 mm, moderate scan time, moderate mAs/rotation), and <i>Coarse</i> (∼140 mm, short scan time, low mAs/rotation) mode options. An SBRT treatment plan was simulated for CT simulation scans of an anthropomorphic lung phantom and transferred to on-board helical kVCT scans with varying imaging and calibration protocols, and clinically relevant DVH metrics and dose-difference maps were used to compare the calculated dose distributions. <h3>Results</h3> Use of <i>Fine</i> mode for helical kVCT calibration resulted in smaller dose-volume deviations relative to the planning CT, with the magnitude of these deviations dependent on the mode used to acquire the scan of the lung phantom. For scans acquired under <i>Fine</i> mode, use of <i>Fine</i> mode calibration showed average differences in target volume DVH metrics of ± 1.0% (-1.7% max difference) compared to ± 2.5% (-3.6% max difference) with application of <i>Normal</i> mode calibration for the same images. Likewise, for phantom scans acquired under <i>Normal</i> mode, these differences were ± 1.2% (+ 2.1%) for <i>Fine</i> calibration compared to ± 1.4% (-2.1%) for <i>Normal</i> calibration, while for phantom scans acquired under <i>Coarse</i> mode, differences were ± 2.0% (-4.1%) and ± 3.3% (-6.2%), respectively. Dose-difference maps confirmed the greatest deviations in the calculated dose distributions occurred in the high-dose, target volume region, though some differences were also observed at the tissue-air interface of the chest wall. Visual differences relative to the planning CT were lessened with use of <i>Fine</i> mode acquisitions of both the calibration and lung phantoms. <h3>Conclusion</h3> Use of <i>Fine</i> mode for helical kVCT number calibration and image acquisition resulted in dose calculations most consistent with those calculated on diagnostic-quality CT images. If excess patient dose from additional imaging is a concern, <i>Normal</i> or <i>Coarse</i> mode image acquisitions with application of <i>Fine</i> mode calibration provided dose calculation accuracies within a reasonable tolerance as well. Also, while <i>Fine</i> mode increases scan times relative to other modes, this additional time is still significantly lessened compared to on-board CBCT or MVCT systems currently used for CT-based online adaptive planning.

Mechanical damage thresholds for hematomas near gas-containing bodies in pulsed HIFU fields

Objective. Boiling histotripsy (BH) is a novel high intensity focused ultrasound (HIFU) application currently being developed for non-invasive mechanical fractionation of soft tissues and large hematomas. In the context of development of BH treatment planning approaches for ablating targets adjacent to gas-containing organs, this study aimed at investigation of the ultrasound pressure thresholds of atomization-induced damage to the tissue-air interface and correlation of the danger zone dimensions with spatial structure of nonlinear HIFU field parameters. Approach. A flat interface with air of freshly clotted bovine blood was used as an ex vivo model due to its homogenous structure and higher susceptibility to ultrasound-induced mechanical damage compared to soft tissues. Three 1.5 MHz transducers of different F-numbers (0.77, 1 and 1.5) were focused at various distances before or beyond a flat clot surface, and a BH exposure was delivered either at constant, high-amplitude output level, or at gradually increasing level until a visible damage to the clot surface occurred. The HIFU pressure field parameters at the clot surface were determined through a combination of hydrophone measurements in water, forward wave propagation simulation using ‘HIFU beam’ software and an image source method to account for the wave reflection from the clot surface and formation of a standing wave. The iso-levels of peak negative pressure in the resulting HIFU field were correlated to the outlines of surface erosion to identify the danger zone around the BH focus. Main results. The outline of the danger zone was shown to differ from that of a typical BH lesion produced in a volume of clot material. In the prefocal area, the zone was confined within the 4 MPa contour of the incident peak-to-peak pressure; within the main focal lobe it was determined by the maximum BH lesion width, and in the postfocal area—by the transverse size of the focal lobe and position of the first postfocal pressure axial null. Significance. The incident HIFU pressure-based danger zone boundaries were outlined around the BH focus and can be superimposed onto in-treatment ultrasound image to avoid damage to adjacent gas-containing bodies.

Near-Reflectionless Wireless Transmission Into the Body With Cascaded Metasurfaces

The ability to transmit wireless signals into the body is important for medical communication, sensing, and powering technologies. However, the efficiency of signal transmission is limited by the large reflection encountered at the interface between air and biological tissue. Here, we demonstrate an approach to overcome this reflection using cascaded metasurfaces (MSs) with deeply subwavelength thickness to transform the wave impedance at the air–tissue interface. We develop a procedure to systematically synthesize these MSs using a multilayer tissue model that can account for different body compositions. Using this procedure, we design a three-layer MS operating at 2.45 GHz with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /24.5$ </tex-math></inline-formula> thickness. Full-wave simulations in a computational human body model show that the MS provides transmission equivalent to replacing the background with a tissue-matched medium, while experimental measurements demonstrate 12.1 dB enhancement of transmission into a multilayer tissue phantom.

Optical clearing and testing of lung tissue using inhalation aerosols: prospects for monitoring the action of viral infections.

Optical clearing of the lung tissue aims to make it more transparent to light by minimizing light scattering, thus allowing reconstruction of the three-dimensional structure of the tissue with a much better resolution. This is of great importance for monitoring of viral infection impact on the alveolar structure of the tissue and oxygen transport. Optical clearing agents (OCAs) can provide not only lesser light scattering of tissue components but also may influence the molecular transport function of the alveolar membrane. Air-filled lungs present significant challenges for optical imaging including optical coherence tomography (OCT), confocal and two-photon microscopy, and Raman spectroscopy, because of the large refractive-index mismatch between alveoli walls and the enclosed air-filled region. During OCT imaging, the light is strongly backscattered at each air–tissue interface, such that image reconstruction is typically limited to a single alveolus. At the same time, the filling of these cavities with an OCA, to which water (physiological solution) can also be attributed since its refractive index is much higher than that of air will lead to much better tissue optical transmittance. This review presents general principles and advances in the field of tissue optical clearing (TOC) technology, OCA delivery mechanisms in lung tissue, studies of the impact of microbial and viral infections on tissue response, and antimicrobial and antiviral photodynamic therapies using methylene blue (MB) and indocyanine green (ICG) dyes as photosensitizers.

Physical limits to human brain B0 shimming with spherical harmonics, engineering implications thereof.

As the MRI main magnetic field rises for improved signal-to-noise ratio, susceptibility-induced B0-inhomogeneity increases proportionally, aggravating related artifacts. Considering only susceptibility disparities between air and biological tissue, we explore the topological conditions for which perfect shimming could be performed in a Region of Interest (ROI) such as the human brain or part thereof. After theoretical considerations for perfect shimming, spherical harmonic (SH) shimming simulations of very high degree are performed, based on a 100-subject database of 1.7-mm-resolved brain fieldmaps acquired at 3T . In addition to the whole brain, shimmed ROIs include slabs targeting the prefrontal cortex, both or single temporal lobes, or spheres in the frontal brain above the nasal sinus. We show "perfect" SH shimming is possible only if the ROI can be contained in a sphere that does not enclose sources of magnetic field inhomogeneity, which are gathered at the air-tissue interface. We establish a [Formula: see text]Hz inhomogeneity hard shim limit at 7T for whole brain SH shimming, that can only be attained at shimming degree higher than 90. On the other hand, under limited power and SH degree resources, 3D region-specific shimming is shown to greatly improve homogeneity in critical zones such as the prefrontal cortex and around ear canals.

Quantitative susceptibility-weighted imaging in presence of strong susceptibility sources: Application to hemorrhage

PurposeTo optimize quantitative susceptibility-weighted imaging also known as true susceptibility-weighted imaging (tSWI) for strong susceptibility sources like hemorrhage and compare to standard susceptibility-weighted imaging (SWI) and quantitative susceptibility mapping (QSM). MethodsTen patients with known intracerebral hemorrhage (ICH) were scanned using a 3D SWI sequence. The magnitude and phase images were utilized to compute QSM, tSWI and SWI images. tSWI parameters including the upper threshold for creating susceptibility-weighted masks and the multiplication factor were optimized for hemorrhage depiction. Combined tSWI was also computed with independent optimized parameters for both veins and hemorrhagic regions. tSWI results were compared to SWI and QSM utilizing region-of-interest measurements, Pearson's correlation and Kruskal-Wallis test. ResultsFifteen hemorrhages were found, with mean susceptibility 0.81 ± 0.37 ppm. Unlike SWI which utilizes a phase mask, tSWI uses a mask computed from QSM. In tSWI, the weighted mask required an extended upper threshold far beyond the standard level for more effective visualization of hemorrhage texture. The upper threshold was set to the mean maximum susceptibility in the hemorrhagic region (3.24 ppm) with a multiplication factor of 2. The blooming effect, seen in SWI, was observed to be larger in hemorrhages with higher susceptibility values (r = 0.78, p < 0.001) with reduced blooming on tSWI. On SWI, 4 out of 15 hemorrhages showed phase wrap artifacts in the hemorrhagic region and all patients showed some phase wraps in the air-tissue interface near the auditory and frontal sinuses. These phase wrap artifacts were absent on tSWI. In hemorrhagic regions, a higher correlation was observed between the actual susceptibility values and mean gray value for tSWI (r = −0.93, p < 0.001) than SWI (r = −0.87, p < 0.001). ConclusionIn hemorrhage, tSWI minimizes both blooming effects and phase wrap artifacts observed in SWI. However, unlike SWI, tSWI requires an altered upper threshold for best hemorrhage depiction that greatly differs from the standard value. tSWI can be used as a complementary technique for visualizing hemorrhage along with SWI.

Accuracy Evaluation of Collapsed Cone Convolution Superposition Algorithms for the Nasopharynx Interface in the Early Stage of Nasopharyngeal Carcinoma.

This study combined the use of radiation dosimeteric measurements and a custom-made anthropomorphic phantom in order to evaluate the accuracy of therapeutic dose calculations at the nasopharyngeal air-tissue interface. The doses at the nasopharyngeal air-tissue interface obtained utilizing the Pinnacle and TomoTherapy TPS, which are based on collapsed cone convolution superposition (CCCS) algorithms, were evaluated and measured under single 10 × 10 cm2, 2 × 2 cm2, two parallel opposed 2 × 2 cm2 and clinical fields for early stage of nasopharyngeal carcinoma by using EBT3, GR-200F, and TLD 100. At the air-tissue interface under a 10 × 10 cm2 field, the TPS dose calculation values were in good agreement with the dosimeter measurement with all differences within 3.5%. When measured the single field 2 × 2 cm2, the differences between the average dose were measured at the distal interface for EBT3, GR-200F, and TLD-100 and the calculation values were -15.8%, -16.4%, and -4.9%, respectively. When using the clinical techniques such as IMRT, VMAT, and tomotherapy, the measurement results at the interface for all three techniques did not imply under dose. Small-field sizes will lead to dose overestimation at the nasopharyngeal air-tissue interface due to electronic disequilibrium when using CCCS algorithms. However, under clinical applications of multiangle irradiation, the dose errors caused by this effect were not significant.

Ultrasound at the pulmonary air-tissue interface: Mechanism of haemorrhage induction and implications for safe use of diagnostic and therapeutic lung ultrasound applications

Despite the high-diagnostic value of sonographic lung imaging, providing substantial patient benefit, clinician should be aware that ultrasound exposure on lung is not absolutely without risk of harm. As shown in animal models, lung ultrasound (LUS) even in the diagnostic regime can induce pulmonary capillary haemorrhage (PCH) at the alveolar epithelium-gas interface. Acoustic peak negative pressure in the range of 1.0–1.5 MPa correlates well with PCH threshold. However, in retrospective human studies, adverse events could not be demonstrated following LUS examination, which is evidence of symptomatic PCH after therapeutic ultrasound ablation in proximity of lung exists. Therefore, this subject remains controversial. This work summarizes the underlying physical causes and consequences of ultrasound induced PCH. The complexity of PCH thresholds depending on imaging modes, pathological lung conditions including ventilation parameters will be presented. In addition, current recommendations for the safe use of LUS based on Safety Indices given by AIUM and EFSUMB guidelines and the impact of LUS specific settings, available on modern scanners, will be discussed.

3D printed transwell-integrated nose-on-chip model to evaluate effects of air flow-induced mechanical stresses on mucous secretion.

While there are many chip models that simulate the air-tissue interface of the respiratory system, only a few represent the upper respiratory system. These chips are restricted to unidirectional flow patterns that are not comparable to the highly dynamic and variable flow patterns found in the native nasal cavity. Here we describe the development of a tunable nose-on-chip device that mimics the air-mucosa interface and is coupled to an air delivery system that simulates natural breathing patterns through the generation of bi-directional air flow. Additionally, we employ computational modeling to demonstrate how the device design can be tuned to replicate desired mechanical characteristics within specific regions of the human nasal cavity. We also demonstrate how to culture human nasal epithelial cell line RPMI 2650 within the lab-on-chip (LOC) device. Lastly, Alcian Blue histological staining was performed to label mucin proteins, which play important roles in mucous secretion. Our results revealed that dynamic flow conditions can increase mucous secretion for RPMI 2650 cells, when compared to no flow, or stationary, conditions.

Dosimetric Comparison in Malignant Glioma Patients Clinically Treated on Hybrid Magnetic Resonance Imaging (MRI)-Linac (MRL) vs. Conventional Linac

The Magnetic Resonance Imaging (MRI)-Linac (MRL) is a hybrid machine integrating a high field strength 1.5T MRI with a linear accelerator, providing superior soft tissue visualization of tumors and organs-at-risk (OARs) during treatment delivery. A special consideration for MRL radiotherapy is accounting for interactions of secondary electrons generated within the magnetic field, which can alter dose deposition at air-tissue interfaces. We evaluated dosimetric outcomes in clinically treated malignant glioma patients who received at least one fraction of radiotherapy on both the MRL and a conventional Linac.Thirty-seven glioma patients treated on both the MRL and a conventional Linac for adjuvant chemoradiotherapy between July 2019 and February 2021 were analyzed. Planning was completed on treatment planning systems (TPS) using a Monte-Carlo algorithm that accounts for magnetic field effects (Monaco v5.40) for the MRL, and a convolution-superposition algorithm (Pinnacle v9.8) for the conventional Linac. Dosimetric parameters of interest from the target, OARs, and air-tissue interface volumes for each patients' clinical treatment plans were extracted and compared. For 10 representative patients, in vivo skin doses during a single fraction of MRL and conventional Linac treatment were obtained using an Optically Stimulated Luminescent Dosimeter (OSLD) placed in a defined location on the patient's skin near the Planning Target Volume (PTV). Student's t-test and Wilcoxon signed-rank test were used to compare parameters between Monaco and Pinnacle. Spearman's correlation was used to assess the relationship between in vivo OSLD measurements and TPS skin dose. Threshold for statistical significance was P < 0.05.Most patients were treated for high grade glioma (76% Grade III or IV, 24% Grade II), and median PTV was 257.4 cm3 (range, 37.1-570.3 cm3). MRL and conventional Linac had similar V100, V95, D98, and D95 for PTV, and D3cc for optic chiasm, optic nerves, and each cochlea (P = NS). However, clinically delivered Monaco plans had significantly greater doses within air cavities (mean Dmean higher by 1.3 Gy, P < 0.0001) and skin (mean Dmean higher by 1.9 Gy, P < 0.0001; mean D2cc higher by 8.1 Gy, P < 0.0001; mean V20 Gy higher by 7.2 cm3, P < 0.0001), compared to clinically delivered Pinnacle plans. In vivo OSLD skin readings were 14.5% greater for treatments delivered on the MRL (P = 0.0027), and were more accurately predicted by Monaco (r = 0.95, P < 0.0001) vs. Pinnacle (r = 0.80, P = 0.0096).In this prospective study of clinically treated glioma patients on both MRL and conventional Linac, the dosimetric impact of the magnetic field was minimal for the target and standard OARs. However, higher doses to skin and air cavities were observed. In vivo correlation of dose to skin was more accurately predicted with Monaco. Future MRL planning processes are being designed to account for skin dosimetry and treatment delivery.

Slot-scan dual-energy bone densitometry using motorized X-ray systems.

We investigate the feasibility of slot-scan dual-energy (DE) bone densitometry on motorized radiographic equipment. This approach will enable fast quantitative measurements of areal bone mineral density (aBMD) for opportunistic evaluation of osteoporosis. We investigated DE slot-scan protocols to obtain aBMD measurements at the lumbar spine (L-spine) and hip using a motorized x-ray platform capable of synchronized translation of the x-ray source and flat-panel detector (FPD). The slot dimension was 5 × 20 cm2 . The DE slot views were processed as follows: (1) convolution kernel-based scatter correction, (2) unfiltered backprojection to tile the slots into long-length radiographs, and (3) projection-domain DE decomposition, consisting of an initial adipose-water decomposition in a bone-free region followed by water-CaHA decomposition with adjustment for adipose content. The accuracy and reproducibility of slot-scan aBMD measurements were investigated using a high-fidelity simulator of a robotic x-ray system (Siemens Multitom Rax) in a total of 48 body phantom realizations: four average bone density settings (cortical bone mass fraction: 10-40%), four body sizes (waist circumference, WC=70-106cm), and three lateral shifts of the body within the slot field of view (FOV) (centered and ±1cm off-center). Experimental validations included: (1) x-ray test-bench feasibility study of adipose-water decomposition and (2) initial demonstration of slot-scan DE bone densitometry on the robotic x-ray system using the European Spine Phantom (ESP) with added attenuation (polymethyl methacrylate [PMMA] slabs) ranging 2 to 6cm thick. For the L-spine, the mean aBMD error across all WC settings ranged from 0.08g/cm2 for phantoms with average cortical bone fraction wcortical =10% to ∼0.01g/cm2 for phantoms with wcortical =40%. The L-spine aBMD measurements were fairly robust to changes in body size and positioning, e.g., coefficient of variation (CV) for L1 with wcortical =30% was ∼0.034 for various WC and ∼0.02 for an obese patient (WC=106cm) changing lateral shift. For the hip, the mean aBMD error across all phantom configurations was about 0.07g/cm2 for a centered patient. The reproducibility of hip aBMD was slightly worse than in the L-spine (e.g., in the femoral neck, the CV with respect to changing WC was ∼0.13 for phantom realizations with wcortical =30%) due to more challenging scatter estimation in the presence of an air-tissue interface within the slot FOV. The aBMD of the hip was therefore sensitive to lateral positioning of the patient, especially for obese patients: e.g., the CV with respect to patient lateral shift for femoral neck with WC=106cm and wcortical =30% was 0.14. Empirical evaluations confirmed substantial reduction in aBMD errors with the proposed adipose estimation procedure and demonstrated robust aBMD measurements on the robotic x-ray system, with aBMD errors of ∼0.1g/cm2 across all three simulated ESP vertebrae and all added PMMA attenuator settings. We demonstrated that accurate aBMD measurements can be obtained on a motorized FPD-based x-ray system using DE slot-scans with kernel-based scatter correction, backprojection-based slot view tiling, and DE decomposition with adipose correction.