Investigating focal spot position drift in a mobile imaging system equipped with a monobloc-based x-ray generator

BACKGROUND

Misalignment or double-contouring artifacts can appear in high-resolution 3D cone beam computed tomography (CBCT) images, potentially indicating geometric accuracy issues in the projection data. Such artifacts may go unnoticed in low-resolution images and could be associated with changes in the focal spot (FS) position.

PURPOSE

High-resolution 3D-CBCT imaging by a mobile imaging device with a large gantry clearance offers more versatility for clinical workflows in image-guided brachytherapy (IGBT), intraoperative radiation therapy (IORT), and spinal, as well as maxillofacial surgery. However, misalignment or double-contouring artifacts hinder workflow advancements in these domains. This paper introduces intrinsic calibration and geometrical correction methods as extensions to a well-established technique for addressing geometrical deviations resulting from factors such as gravity or mechanical inconsistencies. These extensions cover shifts and drifts of the FS depending on FS size selection, temperature, tube current, and tube potential. The proposed methods effectively mitigate artifacts in high-resolution CBCT images stemming from geometrical inaccuracies in projection data, without requiring additional equipment like a pinhole device.

METHODS

Geometrical offsets and drifts of the x-ray tube FS were characterized on a mobile multi-purpose imaging system, the ImagingRing-m. A pinhole-like experiment was simulated by adjusting the movable collimation unit to a small rectangular aperture within the FS size range. The influence of filament selection, that is, FS size, temperature, the relatively low tube currents, as well as tube potential settings have been studied on two different monobloc types sharing the same x-ray tube insert. The Catphan 504 and an Alderson head phantom were used to assess resulting image artifacts.

RESULTS

Switching the FS size to one different from what was used for geometrical (gravitation, mechanical variations) calibration induced the most notable position changes of the x-ray FS, resulting in double-contouring artifacts and blurring of high-resolution 3D-CBCT images. Incorporating these shifts into a geometrical correction method effectively minimized these artifacts. Thermal drifts exhibited the second largest geometrical changes, comparable to FS size shifts across the thermal operating conditions of the x-ray system. The proposed thermal drift compensation markedly reduced thermal drift effects. Tube current and potential had little impact within the range of available tube currents, eliminating the need for compensation in current applications.

CONCLUSIONS

Augmenting the geometrical calibration pipeline with proposed FS drift compensations yielded significant enhancements in image quality for high-resolution reconstructions. While compensation for thermal effects posed challenges, it proved achievable. The roles of tube current and potential were found to be negligible.

Routine Contrasted Chest CT Accurately Identifies Anatomic Variations of the Proximal Subscapular System

OBJECTIVE

The vascular anatomy of the proximal subscapular artery has been previously classified into 2 major types depending on the presence of a common subscapular trunk. The purpose of this study was to determine the utility, reliability, and cost of routine chest imaging to identify these anatomical variations.

METHODS

Data were collected retrospectively at a tertiary medical center for patients who were undergoing CT chest for various indications between October 2019 and October 2020. Two independent and blinded readers interpreted CT chest with contrast of 52 patients for a total 104 sides.

RESULTS

The proximal branching pattern of the subscapular system was identified to have a common trunk in 99 (95%) sides. The remaining five sides (5%) demonstrated two arterial pedicles; with one patient exhibiting the variant anatomy bilaterally.

CONCLUSION

Preoperative CT chest with contrast can accurately identify anatomic variation of the subscapular vascular system. For complex reconstruction requiring a single anastomosis in the vessel depleted neck, preoperative imaging can assure selection of a type I vascular anatomy of the proximal subscapular system. Preoperative imaging with contrasted CT has value in assessing this anatomy when planning for chimeric flaps involving circumflex scapular and thoracodorsal arteries.

LEVEL OF EVIDENCE

3 Laryngoscope, 134:684-687, 2024.

Multi-Scale Imaging of the Dynamic Organization of Chromatin

Chromatin is now regarded as a heterogeneous and dynamic structure occupying a non-random position within the cell nucleus, where it plays a key role in regulating various functions of the genome. This current view of chromatin has emerged thanks to high spatiotemporal resolution imaging, among other new technologies developed in the last decade. In addition to challenging early assumptions of chromatin being regular and static, high spatiotemporal resolution imaging made it possible to visualize and characterize different chromatin structures such as clutches, domains and compartments. More specifically, super-resolution microscopy facilitates the study of different cellular processes at a nucleosome scale, providing a multi-scale view of chromatin behavior within the nucleus in different environments. In this review, we describe recent imaging techniques to study the dynamic organization of chromatin at high spatiotemporal resolution. We also discuss recent findings, elucidated by these techniques, on the chromatin landscape during different cellular processes, with an emphasis on the DNA damage response.

Analysis of the relationship between LET, γH2AX foci volume and cell killing effect of carbon ions using high-resolution imaging technology

The strong cell killing effect of high linear energy transfer (LET) carbon ions is dependent on lethal DNA damage. Our recent studies suggest that induction of clusters of double-strand breaks (DSBs) in close proximity is one of the potential mechanisms. However, the relationship between LET, the degree of DSB clustering and the cell killing effect of carbon ions remains unclear. Here, we used high-resolution imaging technology to analyze the volume of γH2AX foci induced by monoenergetic carbon ions with a clinically-relevant range of LET (13-100 keV/μm). We obtained data from 3317 γH2AX foci and used a gaussian function to approximate the probability (p) that 1 Gy-carbon ions induce γH2AX foci of a given volume (vth) or greater per nucleus. Cell killing effects were assessed in clonogenic assays. The cell killing effect showed high concordance with p at vth = 0.7 μm3 across various LET values; the difference between the two was 4.7% ± 2.2%. This relationship was also true for clinical carbon ion beams harboring a mixed LET profile throughout a spread-out Bragg peak width (30-120 mm), with the difference at vth = 0.7 μm3 being 1.6% ± 1.2% when a Monte Carlo simulation-derived dose-averaged LET was used to calculate p. These data indicate that the cell killing effect of carbon ions is predictable by the ability of carbon ions to induce γH2AX foci containing clustered DSBs, which is linked to LET, providing the biological basis for LET modulation in the planning of carbon ion radiotherapy.

Highest resolution chemical imaging based on secondary ion mass spectrometry performed on the helium ion microscope

This paper is a review on the combination between Helium Ion Microscopy (HIM) and Secondary Ion Mass Spectrometry (SIMS), which is a recently developed technique that is of particular relevance in the context of the quest for high-resolution high-sensitivity nano-analytical solutions. We start by giving an overview on the HIM-SIMS concept and the underlying fundamental principles of both HIM and SIMS. We then present and discuss instrumental aspects of the HIM and SIMS techniques, highlighting the advantage of the integrated HIM-SIMS instrument. We give an overview on the performance characteristics of the HIM-SIMS technique, which is capable of producing elemental SIMS maps with lateral resolution below 20 nm, approaching the physical resolution limits, while maintaining a sub-nanometric resolution in the secondary electron microscopy mode. In addition, we showcase different strategies and methods allowing to take profit of both capabilities of the HIM-SIMS instrument (high-resolution imaging using secondary electrons and mass filtered secondary sons) in a correlative approach. Since its development HIM-SIMS has been successfully applied to a large variety of scientific and technological topics. Here, we will present and summarise recent applications of nanoscale imaging in materials research, life sciences and geology.

Artificial Compound Eye Systems and Their Application: A Review

The natural compound eye system has many outstanding properties, such as a more compact size, wider-angle view, better capacity to detect moving objects, and higher sensitivity to light intensity, compared to that of a single-aperture vision system. Thanks to the development of micro- and nano-fabrication techniques, many artificial compound eye imaging systems have been studied and fabricated to inherit fascinating optical features of the natural compound eye. This paper provides a review of artificial compound eye imaging systems. This review begins by introducing the principle of the natural compound eye, and then, the analysis of two types of artificial compound eye systems. We equally present the applications of the artificial compound eye imaging systems. Finally, we suggest our outlooks about the artificial compound eye imaging system.

Designing visible-light optical coherence tomography towards clinics

Background

The capabilities of visible-light optical coherence tomography (vis-OCT) in noninvasive anatomical and functional retinal imaging have been demonstrated by multiple groups in both rodents and healthy human subjects. Translating laboratory prototypes to an integrated clinical-environment-friendly system is required to explore the full potential of vis-OCT in disease management.

Methods

We developed and optimized a portable vis-OCT system for human retinal imaging in clinical settings. We acquired raster- and circular-scan images from both healthy and diseased human eyes.

Results

The new vis-OCT provided high-quality retinal images of both subjects without any known eye diseases and patients with various retinal diseases, including retinal occlusive disease and diabetic retinopathy (DR) over a broad range of ages.

Conclusions

A newly designed vis-OCT system is sufficiently optimized to be suited for routine patients' examinations in clinics. Vis-OCT has the potential to add new anatomical and functional imaging capabilities to ophthalmic clinical care.

Vessel-Wall Magnetic Resonance Imaging of Intracranial Atherosclerotic Plaque and Ischemic Stroke: A Systematic Review and Meta-Analysis

Introduction: Vessel-wall magnetic resonance imaging (MRI) has been suggested as a valuable tool for assessing intracranial arterial stenosis with additional diagnostic features. However, there is limited conclusive evidence on whether vessel-wall MR imaging of intracranial atherosclerotic plaques provides valuable information for predicting vulnerable lesions. We conducted this systematic review and meta-analysis to evaluate which characteristics of intracranial-plaque on vessel-wall MRI are markers of culprit lesions. Methods: The MEDLINE, EMBASE, and Cochrane Library of Clinical Trials databases were searched for studies reporting the association between vessel-wall MRI characteristics of intracranial plaque and corresponding stroke events. Odds ratios (ORs) for the prevalence of stroke with intracranial-plaque MRI characteristics were pooled in a meta-analysis using a random-effects model. Results: Twenty studies were included in this review. We found a significant association between plaque enhancement (OR, 10.09; 95% CI, 5.38-18.93), positive remodeling (OR, 6.19; 95% CI, 3.22-11.92), and plaque surface irregularity (OR, 3.94; 95% CI, 1.90-8.16) with stroke events. However, no significant difference was found for the presence of eccentricity (OR, 1.22; 95% CI, 0.51-2.91). Conclusion: Based on current evidence, intracranial plaque contrast enhancement, positive remodeling, and plaque irregularity on MRI are associated with increased risk of stroke events. Our findings support the design of future studies on intracranial-plaque MRI and decision making for the management of intracranial atherosclerotic plaques.

Novel Configurations of Ultrahigh Frequency (≤600 MHz) Analog Frontend for High Resolution Ultrasound Measurement

In this article, an approach to designing and developing an ultrahigh frequency (≤600 MHz) ultrasound analog frontend with Golay coded excitation sequence for high resolution imaging applications is presented. For the purpose of visualizing specific structures or measuring functional responses of micron-sized biological samples, a higher frequency ultrasound is needed to obtain a decent spatial resolution while it lowers the signal-to-noise ratio, the difference in decibels between the signal level and the background noise level, due to the higher attenuation coefficient. In order to enhance the signal-to-noise ratio, conventional approach was to increase the transmit voltage level. However, it may cause damaging the extremely thin piezoelectric material in the ultrahigh frequency range. In this paper, we present a novel design of ultrahigh frequency (≤600 MHz) frontend system capable of performing pseudo Golay coded excitation by configuring four independently operating pulse generators in parallel and the consecutive delayed transmission from each channel. Compared with the conventional monocycle pulse approach, the signal-to-noise ratio of the proposed approach was improved by 7⁻9 dB without compromising the spatial resolution. The measured axial and lateral resolutions of wire targets were 16.4 µm and 10.6 µm by using 156 MHz 4 bit pseudo Golay coded excitation, respectively and 4.5 µm and 7.7 µm by using 312 MHz 4 bit pseudo Golay coded excitation, respectively.

Development of an Ultra High Resolution PET Scanner for Imaging Rodent Paws: PawPET

A positron emission tomography (PET) scanner with submillimeter spatial resolution, capable of in vivo imaging of murine extremities was built based on two dual ended readout, hybrid depth of interaction (DOI) PET detectors. Each was composed of a 36 × 36 array of 0.43 mm × 0.43 mm × 8 mm unpolished lutetium oxyorthosilicate crystals separated by a 50 μm white diffuse reflector. The array was coupled to a position-sensing photomultiplier tube at one end and to an avalanche photodiode at the other end. The detector characterization included crystal identification accuracy, DOI, energy, and timing resolution measurements. The scanner was characterized in terms of its spatial resolution and its sensitivity and mouse images were acquired of a mouse paw injected with 18-F-NaF. Out of the 36 × 36 crystals only 33 × 33 crystals were identified. The coincidence timing, DOI, and energy resolution of the scanner was measured to be 2.8 ns, 1.4 mm, and 27%, respectively. The scanner's spatial resolution was measured with a line source and determined from an ordered subsets expectation maximization reconstruction to be 0.56 mm. The sensitivity of the scanner was measured to be 0.6% at the center of the field of view.

Cancer cell classification with coherent diffraction imaging using an extreme ultraviolet radiation source

In cancer treatment, it is highly desirable to classify single cancer cells in real time. The standard method is polymerase chain reaction requiring a substantial amount of resources and time. Here, we present an innovative approach for rapidly classifying different cell types: we measure the diffraction pattern of a single cell illuminated with coherent extreme ultraviolet (XUV) laser-generated radiation. These patterns allow distinguishing different breast cancer cell types in a subsequent step. Moreover, the morphology of the object can be retrieved from the diffraction pattern with submicron resolution. In a proof-of-principle experiment, we prepared single MCF7 and SKBR3 breast cancer cells on gold-coated silica slides. The output of a laser-driven XUV light source is focused onto a single unstained and unlabeled cancer cell. With the resulting diffraction pattern, we could clearly identify the different cell types. With an improved setup, it will not only be feasible to classify circulating tumor cells with a high throughput, but also to identify smaller objects such as bacteria or even viruses.

Enhanced phase regression with Savitzky-Golay filtering for high-resolution BOLD fMRI

Phase regression exploits the temporal evolution of phase in individual voxels to suppress blood oxygenation level dependent (BOLD) signal fluctuations caused by larger vessels and draining veins while preserving signal changes from microvascular effects. However, this process does not perform well when phase time series have low signal-to-noise ratios because of high levels of physiological noise. We demonstrate that Savitzky-Golay filters may be used to recover the underlying change in phase and completely restore the efficacy of phase regression. We do not make a priori assumptions regarding phase evolution and perform a data-driven exploration of parameter space to select the Savitzky-Golay filter parameters that minimize temporal variance in each voxel after phase regression. This approach is shown to work well on data acquired with single-shot and multi-shot pulse sequences, and should therefore be useful for both human and animal gradient-echo fMRI at high spatial resolutions at high fields. The ability to improve the spatial specificity of BOLD activation may be especially advantageous for clinical applications of fMRI that rely upon the accuracy of individual subject's activation maps to assist with presurgical planning and clinical decision-making. Enhanced phase regression with Savitzky-Golay filtering may also find other uses in analyses of resting state functional connectivity.

A microelectronic portal imaging device for image guided conformal microirradiation of murine cancer models

Image guided conformal small animal orthovoltage microirradiators are currently under development to perform radiobiological experiments with preclinical cancer models. An important component of these instruments is the treatment delivery image guidance system, a microelectronic portal imaging device (μEPID). Here, we present the design and implementation of a μEPID, specifically designed and constructed for small animal orthovoltage microirradiators. The μEPID can acquire images in the range of 60 kVp to 320 kVp x-ray photon energies and can endure high doses from orthovoltage beams without radiation damage. The μEPID can acquire 200 μm resolution images at a rate of 17 frames per second for online in vivo co-registration between irradiation beams and small animal anatomy. An exposure with less than 1% of a 2 Gy treatment field is required for imaging, which is an adequate ratio between imaging dose and treatment dose to avoid undesired irradiation of healthy tissue or alteration of the preclinical cancer model. The μEPID was calibrated for microdosimetry with a precision of 4.1% with respect to an ion chamber, used as a gold standard. To validate the in vivo device performance, irradiations of lung, brain, and xenograft breast cancer preclinical models were performed and analyzed.

Integration of ultra-high field MRI and histology for connectome based research of brain disorders

Ultra-high field magnetic resonance imaging (MRI) became increasingly relevant for in vivo neuroscientific research because of improved spatial resolutions. However, this is still the unchallenged domain of histological studies, which long played an important role in the investigation of neuropsychiatric disorders. While the field of biological psychiatry strongly advanced on macroscopic levels, current developments are rediscovering the richness of immunohistological information when attempting a multi-level systematic approach to brain function and dysfunction. For most studies, histology sections lost information on three-dimensional reconstructions. Translating histological sections to 3D-volumes would thus not only allow for multi-stain and multi-subject alignment in post mortem data, but also provide a crucial step in big data initiatives involving the network analyses currently performed with in vivo MRI. We therefore investigated potential pitfalls during integration of MR and histological information where no additional blockface information is available. We demonstrated that strengths and requirements from both methods can be effectively combined at a spatial resolution of 200 μm. However, the success of this approach is heavily dependent on choices of hardware, sequence and reconstruction. We provide a fully automated pipeline that optimizes histological 3D reconstructions, providing a potentially powerful solution not only for primary human post mortem research institutions in neuropsychiatric research, but also to help alleviate the massive workloads in neuroanatomical atlas initiatives. We further demonstrate (for the first time) the feasibility and quality of ultra-high spatial resolution (150 μm isotopic) imaging of the entire human brain MRI at 7T, offering new opportunities for analyses on MR-derived information.

Studying osteocytes within their environment

It is widely hypothesized that osteocytes are the mechano-sensors residing in the bone's mineralized matrix which control load induced bone adaptation. Owing to their inaccessibility it has proved challenging to generate quantitative in vivo experimental data which supports this hypothesis. Recent advances in in situ imaging, both in non-living and living specimens, have provided new insights into the role of osteocytes in the skeleton. Combined with the retrieval of biochemical information from mechanically stimulated osteocytes using in vivo models, quantitative experimental data is now becoming available which is leading to a more accurate understanding of osteocyte function. With this in mind, here we review i) state of the art ex vivo imaging modalities which are able to precisely capture osteocyte structure in 3D, ii) live cell imaging techniques which are able to track structural morphology and cellular differentiation in both space and time, and iii) in vivo models which when combined with the latest biochemical assays and microfluidic imaging techniques can provide further insight on the biological function of osteocytes.

Multimodal in vivo imaging exposes the voyage of nanoparticles in tumor microcirculation

Tumors present numerous biobarriers to the successful delivery of nanoparticles. Decreased blood flow and high interstitial pressure in tumors dictate the degree of resistance to extravasation of nanoparticles. To understand how a nanoparticle can overcome these biobarriers, we developed a multimodal in vivo imaging methodology, which enabled the noninvasive measurement of microvascular parameters and deposition of nanoparticles at the microscopic scale. To monitor the spatiotemporal progression of tumor vasculature and its vascular permeability to nanoparticles at the microcapillary level, we developed a quantitative in vivo imaging method using an iodinated liposomal contrast agent and a micro-CT. Following perfusion CT for quantitative assessment of blood flow, small animal fluorescence molecular tomography was used to image the in vivo fate of cocktails containing liposomes of different sizes labeled with different NIR fluorophores. The animal studies showed that the deposition of liposomes depended on local blood flow. Considering tumor regions of different blood flow, the deposition of liposomes followed a size-dependent pattern. In general, the larger liposomes effectively extravasated in fast flow regions, while smaller liposomes performed better in slow flow regions. We also evaluated whether the tumor retention of nanoparticles is dictated by targeting them to a receptor overexpressed by the cancer cells. Targeting of 100 nm liposomes showed no benefits at any flow rate. However, active targeting of 30 nm liposomes substantially increased their deposition in slow flow tumor regions (∼12-fold increase), which suggested that targeting prevented the washout of the smaller nanoparticles from the tumor interstitium back to blood circulation.

Increased imaging speed and force sensitivity for bio-applications with small cantilevers using a conventional AFM setup

In this study, we demonstrate the increased performance in speed and sensitivity achieved by the use of small AFM cantilevers on a standard AFM system. For this, small rectangular silicon oxynitride cantilevers were utilized to arrive at faster atomic force microscopy (AFM) imaging times and more sensitive molecular recognition force spectroscopy (MRFS) experiments. The cantilevers we used had lengths between 13 and 46 μm, a width of about 11 μm, and a thickness between 150 and 600 nm. They were coated with chromium and gold on the backside for a better laser reflection. We characterized these small cantilevers through their frequency spectrum and with electron microscopy. Due to their small size and high resonance frequency we were able to increase the imaging speed by a factor of 10 without any loss in resolution for images from several μm scansize down to the nanometer scale. This was shown on bacterial surface layers (s-layer) with tapping mode under aqueous, near physiological conditions and on nuclear membranes in contact mode in ambient environment. In addition, we showed that single molecular forces can be measured with an up to 5 times higher force sensitivity in comparison to conventional cantilevers with similar spring constants.

Layer-specific anatomical, physiological and functional MRI of the retina

Most retinal imaging has been performed using optical techniques. This paper reviews alternative retinal imaging methods based on MRI performed with spatial resolution sufficient to resolve multiple well-defined retinal layers. The development of these MRI technologies to study retinal anatomy, physiology (blood flow, blood volume, and oxygenation) and function, and their applications to the study of normal retinas, retinal degeneration and diabetic retinopathy in animal models are discussed. Although the spatiotemporal resolution of MRI is poorer than that of optical imaging techniques, it is unhampered by media opacity and can thus image all retinal and pararetinal structures, and has the potential to provide multiple unique clinically relevant data in a single setting and could thus complement existing retinal imaging techniques. In turn, the highly structured retina with well-defined layers is an excellent model for advancing emerging high-resolution anatomical, physiological and functional MRI technologies.