Sub-millimeter Resolution Research Articles

Effect of motion, cortical orientation and spatial resolution on quantitative imaging of cortical R2* and magnetic susceptibility at 0.3 mm in-plane resolution at 7 T

MR images of the effective relaxation rate R2* and magnetic susceptibility χ derived from multi-echo T2*-weighted (T2*w) MRI can provide insight into iron and myelin distributions in the brain, with the potential of providing biomarkers for neurological disorders. Quantification of R2* and χ at submillimeter resolution in the cortex in vivo has been difficult because of challenges such as head motion, limited signal to noise ratio, long scan time, and motion related magnetic field fluctuations. This work aimed to improve the robustness for quantifying intracortical R2* and χ and analyze the effects from motion, spatial resolution, and cortical orientation. T2*w data was acquired with a spatial resolution of 0.3 × 0.3 × 0.4 mm3 at 7 T and downsampled to various lower resolutions. A combined correction for motion and B0 changes was deployed using volumetric navigators. Such correction improved the T2*w image quality rated by experienced image readers and test-retest reliability of R2* and χ quantification with reduced median inter-scan differences up to 10 s−1 and 5 ppb, respectively. R2* and χ near the line of Gennari, a cortical layer high in iron and myelin, were as much as 10 s−1 and 10 ppb higher than the region at adjacent cortical depth. In addition, a significant effect due to the cortical orientation relative to the static field (B0) was observed in χ with a peak-to-peak amplitude of about 17 ppb. In retrospectively downsampled data, the capability to distinguish different cortical depth regions based on R2* or χ contrast remained up to isotropic 0.5 mm resolution. This study highlights the unique characteristics of R2* and χ along the cortical depth at submillimeter resolution and the need for motion and B0 corrections for their robust quantification in vivo.

Quantum Dot Patterning and Encapsulation by Maskless Lithography for Display Technologies.

For their unique optical properties, quantum dots (QDs) have been extensively used as light emitters in a number of photonic and optoelectronic applications. They even met commercialization success through their implementation in high-end displays with unmatched brightness and color rendering. For such applications, however, QDs must be shielded from oxygen and water vapor, which are known to degrade their optical properties over time. Even with highly qualitative QDs, this can only be achieved through their encapsulation between barrier layers. With the emergence of mini- and microLED for higher contrast and miniaturized displays, new strategies must be found for the concomitant patterning and encapsulation of QDs, with sub-millimeter resolution. To this end, we developed a new approach for the direct patterning of QDs through maskless lithography. By combining QDs in photopolymerizable resins with digital light processing (DLP) projectors, we developed a versatile and massively parallel fabrication process for the additive manufacturing of functional structures that we refer to as QD pockets. These 3D heterostructures are designed to provide isotropic encapsulation of the QDs, and hence prevent edge ingress from the lateral sides of QD films, which remains a shortcoming of the current technologies.

Forward modelling of [formula omitted] camera view in ST40 informed by experimental data

Embedding diagnostics in future pilot plants will be a challenging task, because of space- and irradiation-related concerns. Relying on high-fidelity synthetic diagnostics would then be valuable.The 3D Monte-Carlo ray-tracing code CHERAB allows the development of numerous synthetic spectroscopic diagnostics. Focus of the present work is the introduction of new CHERAB models. The forward modelling of a synthetic Dα camera in ST40, the privately funded, high-field spherical tokamak, owned and operated by Tokamak Energy Ltd, and the comparison against experimental data is chosen as a testbed for quality assessment. Main output of the study then consists of estimates of the neutral particle densities throughout the chamber, of crucial relevance within edge plasma studies.Starting from simple analytical models, a 2D Dα source in the poloidal plane is generated. However, the centre column limited plasmas in ST40 display an intrinsically-3D Dα emission, mostly localised around the discrete poloidal limiters on the centre column, not captured by any axisymmetric source model. Hence, a novel methodology is introduced in CHERAB to approximate the 3D non-toroidally-symmetric pattern via a piece-wise emission distribution.Irrespective of the geometry of the emission and size of the tokamak, the pronounced non-homogeneity in the edge plasma emission requires sub-millimetric (∼ power fall-off length) spatial resolution to guarantee an accurate estimate of the peak emission. Minimising the associated burden via implementation of a non-uniform source sampling algorithm, which is a modification of the standard CHERAB uniform sampling, results in a >10-fold reduction of the computational cost.The significantly-shortened simulation time also makes the inclusion of more sophisticated models affordable. Of potential appeal in view of highly-detached divertors, the approximation of optically thin plasma is dropped, and photon-plasma interactions are accounted for. Brand-new CHERAB models able to take into account phenomena of photon absorption and scattering are so introduced.

Single pulse protoacoustic range verification using a clinical synchrocyclotron

Objective. Proton therapy as the next generation radiation-based cancer therapy offers dominant advantages over conventional radiation therapy due to the utilization of the Bragg peak; however, range uncertainty in beam delivery substantially mitigates the advantages of proton therapy. This work reports using protoacoustic measurements to determine the location of proton Bragg peak deposition within a water phantom in real time during beam delivery. Approach. In protoacoustics, proton beams have a definitive range, depositing a majority of the dose at the Bragg peak; this dose is then converted to heat. The resulting thermoelastic expansion generates a 3D acoustic wave, which can be detected by acoustic detectors to localize the Bragg peak. Main results. Protoacoustic measurements were performed with a synchrocyclotron proton machine over the exhaustive energy range from 45.5 to 227.15 MeV in clinic. It was found that the amplitude of the acoustic waves is proportional to proton dose deposition, and therefore encodes dosimetric information. With the guidance of protoacoustics, each individual proton beam (7 pC/pulse) can be directly visualized with sub-millimeter (<0.7 mm) resolution using single beam pulse for the first time. Significance. The ability to localize the Bragg peak in real-time and obtain acoustic signals proportional to dose within tumors could enable precision proton therapy and hope to progress towards in vivo measurements.

Ultrasonic and Impact-Echo Testing for the Detection of Scaling in Geothermal Pipelines

The efficiency and longevity of components in geothermal plants are significantly reduced by mineral deposition in pipes, also known as scaling [1]. A number of methods are used to monitor fouling (a broader term for all types of organic and inorganic deposition) in other industries, such as the oil, gas and food industries. These include direct and indirect, offline, in-situ and online, as well as inline methods, each of which have pros and cons [2, 3]. An effective monitoring solution specific to the high temperature conditions in geothermal plants, which optimises maintenance and cleaning measures in dependency of scaling, has yet to be developed. In this paper, two non-destructive testing techniques: contact ultrasonic testing (UT) and impact-echo (IE) testing are investigated in their viability as methods to detect scaling growth in geothermal plants. A descaling measurement was conducted on a heavily scaled segment of an obsolete pipeline from the production well of the geothermal power plant in Sauerlach, Germany. The pipeline segment was inserted in a test rig and the scaling was gradually etched away using an acidic solution. At regular time intervals, the scaling thickness was measured mechanically and contact UT as well as IE measurements were carried out. The testing apparatus was designed to withstand high temperatures ({140},^{circ }{text {C}} at the inlet pipe surface) and to be easy to install whilst being cost-efficient. Both techniques yielded usable results with submillimeter resolution. The advantages and limitations of the two methods are discussed. Impact-echo testing, in particular, can be automated and presents a simple and cost-efficient scaling monitoring option.

High-frequency quantitative ultrasound for the assessment of the acoustic properties of engineered tissues in vitro.

Acoustic properties of biomaterials and engineered tissues reflect their structure and cellularity. High-frequency ultrasound (US) can non-invasively characterize and monitor these properties with sub-millimetre resolution. We present an approach to estimate the speed of sound, acoustic impedance, and acoustic attenuation of cell-laden hydrogels that accounts for frequency-dependent effects of attenuation in coupling media, hydrogel thickness, and interfacial transmission/reflection coefficients of US waves, all of which can bias attenuation estimates. Cell-seeded fibrin hydrogel disks were raster-scanned using a 40 MHz US transducer. Thickness, speed of sound, acoustic impedance, and acoustic attenuation coefficients were determined from the difference in the time-of-flight and ratios of the magnitudes of US signals, interfacial transmission/reflection coefficients, and acoustic properties of the coupling media. With this approach, hydrogel thickness was accurately measured by US, with agreement to confocal microscopy (r2 = 0.97). Accurate thickness measurement enabled acoustic property measurements that were independent of hydrogel thickness, despite up to 60% reduction in thickness due to cell-mediated contraction. Notably, acoustic attenuation coefficients increased with increasing cell concentration (p<0.001), reflecting hydrogel cellularity independent of contracted hydrogel thickness. This approach enables accurate measurement of the intrinsic acoustic properties of biomaterials and engineered tissues to provide new insights into their structure and cellularity. STATEMENT OF SIGNIFICANCE: High-frequency ultrasound can measure the acoustic properties of engineered tissues non-invasively and non-destructively with µm-scale resolution. Acoustic properties, including acoustic attenuation, are related to intrinsic material properties, such as scatterer density. We developed an analytical approach to estimate the acoustic properties of cell-laden hydrogels that accounts for the frequency-dependent effects of attenuation in coupling media, the reflection/transmission of ultrasound waves at the coupling interfaces, and the dependency of measurements on hydrogel thickness. Despite up to 60% reduction in hydrogel thickness due to cell-mediated contraction, our approach enabled measurements of acoustic properties that were substantially independent of thickness. Acoustic attenuation increased significantly with increasing cell concentration (p<0.001), demonstrating the ability of acoustic attenuation to reflect intrinsic physical properties of engineered tissues.

Evaluation of the distribution and mobility of labile phosphorus in sediment profiles of Lake Nansi, the largest eutrophic freshwater lake in northern China

Understanding various biogeochemical processes, especially in eutrophic sediments, necessitates fine-scale phosphorus (P) measurements in pore waters. To the best of our knowledge, the fine-scale distributions of P across the sediment profiles of Lake Nansi have rarely been investigated. Herein we evaluated the dynamic distributions of labile P and Fe across the sediment-water interface (SWI) of Lake Nansi at two-dimensional (2D) and sub-millimeter resolution, using well-established colorimetric diffusive gradients in thin films (DGT) methodology. The concentrations of labile P in all investigated sediment profiles exhibited strong spatial variations, ranging from 0 to 1.50 mg/L with a considerable number of hotspots. Lake Nanyang (0.55 ± 0.21 mg/L) had the highest mean concentration of labile P, followed by Lake Dushan (0.38 ± 0.19 mg/L), Lake Weishan (0.28 ± 0.21 mg/L), and Lake Zhaoyang (0.18 ± 0.09 mg/L). The highest concentrations of labile P were always detected in Lake Dushan, which had been subjected to excessive exogenous P pollution. The co-distributions of labile P and Fe in the majority of the sediment of Lake Nansi confirmed highly positive correlations (P < 0.01), suggesting that the mobility of labile P throughout the SWI was likely governed by iron redox processes. The apparent diffusion fluxes of P across the SWI ranged from −7.7 to 33.6 μg/m2·d, with a mean value of 5.26 ± 7.80 μg/m2·d. Positive apparent fluxes for labile P were recorded in most sediment cores, demonstrating the strong upward mobility of P from the sediment to the overlying water. Our results provided accurate and extensive information regarding the micro-distribution and dynamic exchange of labile P across the SWI. This allows for a better understanding of eutrophication processes and the implementation of P management strategies in Lake Nansi.

Magnetic fields enable precise spatial control over electrospun fiber alignment for fabricating complex gradient materials.

Musculoskeletal interfacial tissues consist of complex gradients in structure, cell phenotype, and biochemical signaling that are important for function. Designing tissue engineering strategies to mimic these types of gradients is an ongoing challenge. In particular, new fabrication techniques that enable precise spatial control over fiber alignment are needed to better mimic the structural gradients present in interfacial tissues, such as the tendon-bone interface. Here, we report a modular approach to spatially controlling fiber alignment using magnetically-assisted electrospinning. Electrospun fibers were highly aligned in the presence of a magnetic field and smoothly transitioned to randomly aligned fibers away from the magnetic field. Importantly, magnetically-assisted electrospinning allows for spatial control over fiber alignment at sub-millimeter resolution along the length of the fibrous scaffold similar to the native structural gradient present in many interfacial tissues. The versatility of this approach was further demonstrated using multiple electrospinning polymers and different magnet configurations to fabricate complex fiber alignment gradients. As expected, cells seeded onto gradient fibrous scaffolds were elongated and aligned on the aligned fibers and did not show a preferential alignment on the randomly aligned fibers. Overall, this fabrication approach represents an important step forward in creating gradient fibrous materials, where such materials are promising as tissue-engineered scaffolds for regenerating functional musculoskeletal interfacial tissues.

A multimodal imaging-guided software for access to primate brains

BackgroundImaging-guided access to the brain has become a routine procedure for various research and clinical applications, including drug administration, neurophysiological recording, and sampling tissue. Therefore, open-source software is required to handle such datasets in these specific applications. New methodsHere, we proposed an open-source tool utilizing different imaging modalities for automating the steps to access the brain. This tool provides means for easily calculating the coordination of the area of interest concerning a specific point of entry. The source and documentation are available at this link. ResultsWe have used this software for three different applications: electrophysiological recording, drug infusion in the nonhuman primate brain, and guided biopsy procedure in the human brain. We performed a neural recording of two monkeys' prefrontal cortex and inferior temporal cortex using this software in submillimeter resolution. We also applied our procedure for infusion in the putamen and caudate nuclei in both hemispheres of another group of rhesus monkeys with histological proof in one animal. More so, we validated this software in the human subjects that underwent biopsy surgery with the commercial software used in human biopsy surgery. Comparison with existing methodsOur software uses different imaging modalities by co-registering them. This will provide structural details of the skull and brain tissue. We can calculate each brain region’s coordination at the point of entry by re-slicing the images. Atlas-based image segmentation were implemented in our software. Three mentioned applications of our software in neuroscience will be further discussed in this paper. ConclusionIn our procedure, working with different imaging modalities provides a precise estimation of the specific region in the brain related to the location of implants or stereotaxic frames. There is no limitation to using metal implants in this procedure.

Simulation study of a brain PET scanner using TOF-DOI detectors equipped with first interaction position detection

Objective. The aim of this study is to evaluate the performance characteristics of a brain positron emission tomography (PET) scanner composed of four-layer independent read-out time-of-flight depth-of-interaction (TOF-DOI) detectors capable of first interaction position (FIP) detection, using Geant4 application for tomographic emission(GATE). This includes the spatial resolution, sensitivity, count rate capability, and reconstructed image quality. Approach. The proposed TOF-DOI PET detector comprises four layers of a 50 × 50 cerium-doped lutetium–yttrium oxyorthosilicate (LYSO:Ce) scintillator array with 1 mm pitch size, coupled to a 16 × 16 multi-pixel photon counter array with 3.0 mm × 3.0 mm photosensitive segments. Along the direction distant from the center field-of-view (FOV), the scintillator thickness of the four layers is 2.5, 3, 4, and 6 mm. The four layers were simulated with a 150 ps coincidence time resolution and the independent readout make the FIP detection capable. The spatial resolution and imaging performance were compared among the true-FIP, winner-takes-all (WTA) and front-layer FIP (FL-FIP) methods (FL-FIP selects the interaction position located on the front-most interaction layer in all the interaction layers). The National Electrical Manufacturers Association NU 2-2018 procedure was referred and modified to evaluate the performance of proposed scanner. Main results. In detector evaluation, the intrinsic spatial resolutions were 0.52 and 0.76 mm full width at half-maximum (FWHM) at 0° and 30° incident γ-rays in the first layer pair, respectively. The reconstructed spatial resolution by the filter backprojection (FBP) achieved sub-millimeter FWHM on average over the whole FOV. The maximum true count rate was 207.6 kcps at 15 kBq ml−1 and the noise equivalent count rate (NECR_2R) was 54.7 kcps at 6.0 kBq ml−1. Total sensitivity was 45.2 cps kBq−1 and 48.4 cps kBq−1 at the center and 10 cm off-center FOV, respectively. The TOF and DOI reconstructions significantly improved the image quality in the phantom studies. Moreover, the FL-FIP outperformed the conventional WTA method in terms of the spatial resolution and image quality. Significance. The proposed brain PET scanner could achieve sub-millimeter spatial resolution and high image quality with TOF and DOI reconstruction, which is meaningful to the clinical oncology research. Meanwhile, the comparison among the three positioning methods indicated that the FL-FIP decreased the image degradation caused by Compton scatter more than WTA.

Improved Selectivity in 7 T Digit Mapping Using VASO-CBV

Functional magnetic resonance imaging (fMRI) at Ultra-high field (UHF, ≥ 7 T) benefits from significant gains in the BOLD contrast-to-noise ratio (CNR) and temporal signal-to-noise ratio (tSNR) compared to conventional field strengths (3 T). Although these improvements enabled researchers to study the human brain to unprecedented spatial resolution, the blood pooling effect reduces the spatial specificity of the widely-used gradient-echo BOLD acquisitions. In this context, vascular space occupancy (VASO-CBV) imaging may be advantageous since it is proposed to have a higher spatial specificity than BOLD. We hypothesized that the assumed higher specificity of VASO-CBV imaging would translate to reduced overlap in fine-scale digit representation maps compared to BOLD-based digit maps. We used sub-millimeter resolution VASO fMRI at 7 T to map VASO-CBV and BOLD responses simultaneously in the motor and somatosensory cortices during individual finger movement tasks. We assessed the cortical overlap in different ways, first by calculating similarity coefficient metrics (DICE and Jaccard) and second by calculating selectivity measures. In addition, we demonstrate a consistent topographical organization of the targeted digit representations (thumb-index-little finger) in the motor areas. We show that the VASO-CBV responses yielded less overlap between the digit clusters than BOLD, and other selectivity measures were higher for VASO-CBV too. In summary, these results were consistent across metrics and participants, confirming the higher spatial specificity of VASO-CBV compared to BOLD.

Three-dimensional Whole-Heart Cardiac MRI Sequence for Measuring Trabeculation in Left Ventricular Noncompaction.

To compare three-dimensional (3D) whole-heart MRI with isotropic submillimeter resolution with standard two-dimensional (2D) cine MRI in measuring the bilayered myocardium in left ventricular noncompaction (LVNC). Twenty-four patients with LVNC (mean age, 42 years ± 16 [SD]) were retrospectively enrolled between October 2011 and July 2020. Compacted myocardium (CM) and noncompacted myocardium (NCM) were measured in long axis (Petersen approach) and short axis (Jacquier approach) at 3D whole-heart and 2D cine MRI by two independent readers. Image quality (1 = excellent, 2 = adequate, 3 = nondiagnostic), considering discrimination between NCM and CM and CM and adjacent tissue, was evaluated. Pearson, Spearman, and intraclass correlation tests were used as statistical tests. In long-axis measurements, the correlation between both sequences was moderate to strong for CM (Pearson, 0.66-0.79; Spearman, 0.61-0.68) and strong to very strong for NCM (Pearson, 0.90-0.97; Spearman, 0.77-0.91). Intraclass correlation coefficient (ICC) in 3D whole-heart MRI was 0.90 (95% CI: 0.78, 0.95) for CM and 0.94 (95% CI: 0.84, 0.97) for NCM, while ICC in 2D cine MRI was 0.77 (95% CI: 0.55, 0.89) for CM and 0.87 (95% CI: 0.72, 0.94) for NCM. Short-axis CM and NCM measurements had a strong to very strong correlation between both sequences (Pearson, 0.86-0.98; Spearman, 0.82-0.98). ICC in 3D whole-heart MRI was 0.96 (95% CI: 0.94, 0.99) for CM and 0.98 (95% CI: 0.97, 0.99) for NCM, while ICC in 2D cine MRI was 0.82 (95% CI: 0.63, 0.92) for CM and 0.87 (95% CI: 0.72, 0.94) for NCM. 3D whole-heart MRI demonstrated higher image quality than did 2D cine MRI (P < .001). 3D whole-heart MRI revealed higher image quality, with better structure discrimination and interobserver agreement in LVNC measurements, compared with standard 2D cine images.Keywords: MR Imaging, Cardiac, Cardiovascular Magnetic Resonance, Left Ventricular Noncompaction, Free-breathing Imaging Technique Supplemental material is available for this article. © RSNA, 2022See also the commentary by Jensen and Petersen in this issue.

Robotic large‐area optical biopsy imaging for automated detection of gastrointestinal cancers tested in tissue phantoms and ex vivo porcine bowel

AbstractGastrointestinal endoscopy is a subjective procedure that frequently requires tissue samples for diagnosis. Contact optical biopsy (OB) techniques have the aim of providing direct diagnosis of endoscopic areas without excising tissue samples but lack the wide‐area coverage required for locating and resecting lesions. This article presents a large‐area robotically deployed OB imaging platform for endoscopic detection of colorectal cancer as an add‐on for conventional endoscopes. In vitro, in silicon colon phantoms, the platform achieves an optical resolution of 0.5 line pairs per millimeter, while resolving simulated cancer lesions down to 0.75 mm diameter across large‐area images (55‐103 cm2). Large‐area OB images were generated in an ex vivo porcine colon. The platform allows centimeter‐sized large‐area OB imaging in vitro and ex vivo with submillimeter resolution, including automatic data segmentation of simulated cancer areas. The ability for robotic actuation and spectrum collection is also shown for ex vivo animal colon. If successful, this technology could widen access to user‐independent high‐quality endoscopy and early detection of gastrointestinal cancers.

Reactive two-step additive manufacturing of ultra-high temperature carbide ceramics

Ultra-high-temperature ceramics (UHTCs) are candidate structural materials for applications that require resiliency to extreme temperatures (>2000 °C), high mechanical loads, or aggressive oxidizing environments. Processing UHTC transition metal carbides as standalone materials using additive manufacturing (AM) methods has not been fully realized due to their extremely slow atomic diffusivities that impede sintering and large volume changes during indirect AM that can induce defect structures. In this work, a two-step, reactive AM approach was studied for the formation of the ultra-high temperature ceramic TiCx. Readily available equipment including a polymer powder bed fusion AM machine and a traditional tube furnace were used to produce UHTC cubes and lattice structures with sub-millimeter resolution. This processing scheme incorporated, (1) selective laser sintering of a Ti precursor mixed with a phenolic binder for green body shaping, and (2) ex-situ, isothermal gas-solid conversion of the green body in CH4 to form TiCx structures. Reactive post-processing in CH4 resulted in up to 98.2 wt. % TiC0.90 product yield and a reduction in net-shrinkage during consolidation due to the volume expansion associated with the conversion of Ti to TiC. Results indicated that reaction bonding associated with the Gibbs free energy release associated with TiC formation produced interparticle adhesion at low furnace processing temperatures. The ability to bond highly refractory materials through this type of process resulted in structures that were crack-free and resisted fracture during thermal shock testing. Broadly, the additive manufacturing approach presented could be useful for the production of many UHTC carbides that might otherwise be incompatible with prevailing AM techniques that do not include reaction synthesis.

Near-infrared 3D imaging with upconversion detection

We demonstrate a photon-sensitive, three-dimensional (3D) camera by active near-infrared illumination and fast time-of-flight gating. It uses picosecond pump pulses to selectively upconvert the backscattered photons according to their spatiotemporal modes via sum-frequency generation in a χ 2 nonlinear crystal, which are then detected by an electron-multiplying CCD with photon sensitive detection. As such, it achieves sub-millimeter depth resolution, exceptional noise suppression, and high detection sensitivity. Our results show that it can accurately reconstruct the surface profiles of occluded targets placed behind highly scattering and lossy obscurants of 14 optical depth (round trip), using only milliwatt illumination power. This technique may find applications in biomedical imaging, environmental monitoring, and wide-field light detection and ranging.

MR-self Noise2Noise: self-supervised deep learning-based image quality improvement of submillimeter resolution 3D MR images.

The study aimed to develop a deep neural network (DNN)-based noise reduction and image quality improvement by only using routine clinical scans and evaluate its performance in 3D high-resolution MRI. This retrospective study included T1-weighted magnetization-prepared rapid gradient-echo (MP-RAGE) images from 185 clinical scans: 135 for DNN training, 11 for DNN validation, 20 for qualitative evaluation, and 19 for quantitative evaluation. Additionally, 18 vessel wall imaging (VWI) data were included to evaluate generalization. In each scan of the DNN training set, two noise-independent images were generated from the k-space data, resulting in an input-label pair. 2.5D U-net architecture was utilized for the DNN model. Qualitative evaluation between conventional MP-RAGE and DNN-based MP-RAGE was performed by two radiologists in image quality, fine structure delineation, and lesion conspicuity. Quantitative evaluation was performed with full sampled data as a reference by measuring quantitative error metrics and volumetry at 7 different simulated noise levels. DNN application on VWI was evaluated by two radiologists in image quality. Our DNN-based MP-RAGE outperformed conventional MP-RAGE in all image quality parameters (average scores = 3.7 vs. 4.9, p < 0.001). In the quantitative evaluation, DNN showed better error metrics (p < 0.001) and comparable (p > 0.09) or better (p < 0.02) volumetry results than conventional MP-RAGE. DNN application to VWI also revealed improved image quality (3.5 vs. 4.6, p < 0.001). The proposed DNN model successfully denoises 3D MR image and improves its image quality by using routine clinical scans only. • Our deep learning framework successfully improved conventional 3D high-resolution MRI in all image quality parameters, fine structure delineation, and lesion conspicuity. • Compared to conventional MRI, the proposed deep neural network-based MRI revealed better quantitative error metrics and comparable or better volumetry results. • Deep neural network application to 3D MRI whose pulse sequences and parameters were different from the training data showed improvement in image quality, revealing the potential to generalize on various clinical MRI.

Intrinsic Temporal Performance of the RF Receive Coil in Magnetic Resonance Imaging.

The functional magnetic resonance imaging (fMRI) at ultra-high field (UHF, [Formula: see text]) is a powerful temporal acquisition method which promises to capture neuronal activities at submillimeter scale. But high-spatial-resolution fMRI still remains difficult, as the nuisance temporal noise which also grows with the main magnetic field strength. For decades, mainstream solutions in reducing motion-induced temporal noise include motion-correction algorithms in image post-processing as well as MR acquisition schemes in RF pulse sequence designs, however hardware-related studies have been rarely reported over the RF receive coil. In this study, we have proposed the intrinsic temporal performance model, which is specifically used for measuring coil-related intrinsic temporal SNR (tSNR*), and the intrinsic sensitivity variability and thermal noise variability have been proposed as model parameters. The intrinsic temporal performance of single-channel loops and array coils were evaluated using numerical electromagnetic simulations, and phantom experiments were designed to investigate the intrinsic thermal noise variability. It was observed that the achievable intrinsic tSNR* can be greatly lowered by ~90% even with 2 mm translational motion in the normal direction, suggesting the effect of RF receive coils in producing temporal noise. The proposed model provides a new perspective in optimizing coil designs and array coil temporal combination methods, which may offer a feasible means in achieving submillimeter resolutions at UHF. Moreover, model parameters from the intrinsic temporal performance model can be directly calculated based on single MRI acquisition, offering a practical performance metric for manufactures and customers in quality and assurance checks of RF receive coil products.

In Vivo Cherenkov Imaging-Guided FLASH Radiotherapy

<h3>Purpose/Objective(s)</h3> A fast-imaging technique was developed for the first <i>in vivo</i> Cherenkov emission imaging from an ultra-high dose rate (UHDR) electron beam source at single pulse (360 Hz) and submillimeter resolution for beam characterization and real time monitoring during delivery. <h3>Materials/Methods</h3> A CMOS camera, gated to the UHDR LINAC, imaged the Cherenkov emission profiles pulse by pulse during the irradiation of murine limbs and intestinal region and a tissue equivalent phantom. An intensifier's effect on image quality was investigated considering signal to noise and spatial resolution. Pulse by pulse and cumulative Cherenkov emission profiles were quantified spatially and temporally. <h3>Results</h3> An intensifier improved the emission profile's signal to noise ratio from 15 to 280, with reduced spatial resolution (2.8 to 1.0 line pairs/mm). The profile extended beyond the treatment field edge due to the lateral scattering of the electrons and optical photons in tissue. The CMOS camera with an intensifier detected changes of ∼3mm in Cherenkov emission profiles due to expiration and inspiration during the murine respiratory cycle. The intensified camera's spatial resolution facilitated accurate detection of beam parameters as confirmed with radiochromic film (i.e., output, shift, full width half max, symmetry and flatness). The camera resolved the LINAC's ramp up in output during the first 4-6 pulses until stability was reached, agreeing with a photomultiplier tube detected Cherenkov emission during delivery. <h3>Conclusion</h3> This fast-imaging technique can be utilized for in vivo intrafraction monitoring of FLASH patient treatments at single pulse resolution. It can display delivery differences during respiration, and variability in the delivered treatment's surface profile, which may be perturbed from the intended UHDR treatment especially with pencil beam scanning systems. The technique may leverage the Cherenkov emission surface profile to gate the treatment under FLASH conditions while considering beam parameters such as per pulse output or beam steering consistency during delivery.

Recent Advances in Tracking Devices for Biomedical Ultrasound Imaging Applications.

With the rapid advancement of tracking technologies, the applications of tracking systems in ultrasound imaging have expanded across a wide range of fields. In this review article, we discuss the basic tracking principles, system components, performance analyses, as well as the main sources of error for popular tracking technologies that are utilized in ultrasound imaging. In light of the growing demand for object tracking, this article explores both the potential and challenges associated with different tracking technologies applied to various ultrasound imaging applications, including freehand 3D ultrasound imaging, ultrasound image fusion, ultrasound-guided intervention and treatment. Recent development in tracking technology has led to increased accuracy and intuitiveness of ultrasound imaging and navigation with less reliance on operator skills, thereby benefiting the medical diagnosis and treatment. Although commercially available tracking systems are capable of achieving sub-millimeter resolution for positional tracking and sub-degree resolution for orientational tracking, such systems are subject to a number of disadvantages, including high costs and time-consuming calibration procedures. While some emerging tracking technologies are still in the research stage, their potentials have been demonstrated in terms of the compactness, light weight, and easy integration with existing standard or portable ultrasound machines.

Multi-modal tomographic imaging system for poolside characterization of nuclear test fuels: Design considerations and studies

Testing and qualification of advanced nuclear fuels involve an iterative process of prototyping, in-pile irradiation testing, and in/ex situ examination. Fuel restructuring and fission product migration during burnup are among the most important aspects of fuel evolution and affect several important performance characteristics (e.g., heat removal, accident tolerance, and fission product retention). Poolside nondestructive characterization techniques provide fuel developers with tools to understand fuel evolution at different time points of burnup. A design for a compact, submersible, and multi-modal (transmission and emission) gamma-ray tomography system for imaging irradiated nuclear fuel is presented herein. Detector selection, collimator geometry and fabrication, mechanical design, imaging protocol, and acquisition protocol are discussed. Modeling calculations showed that sub-millimeter resolution could be achieved in a matter of hours in both transmission and emission tomography images. Several design compromises and fabrication challenges are discussed to further the development of future submersible gamma-ray tomography instruments.