Fundamental Imaging Research Articles

Simulation of a new hybrid MPGD with improved time resolution and decreased discharge probabilities using Garfield++

In this work, a new hybrid MPGD consisting of two GEM foils and a metallic mesh was proposed. Based on the simulation studies, this design can significantly reduce the rise time of signal and has a better performance in respect of particle identification compared with the triple GEM design. The gain with various voltages setting was computed in order to provide us references for future experiment. The simulation results also show that the time and space resolution compared to the triple GEM detector are also improved. The time and space resolution of hybrid detector with \(\hbox {Ar/CO}_2\)(70/30) and Ar/isobutane(95/5) were investigated for various drift electric field intensities. This new hybrid detector shows excellent potential for both fundamental research and imaging applications.

Conventional Modalities and Novel, Emerging Imaging Techniques for Musculoskeletal Tumors.

Imaging of musculoskeletal tumors requires a multimodality approach and includes radiography, computed tomography (CT), and magnetic resonance imaging (MRI). Topics related to primary bone and soft-tissue tumors are reviewed. The fundamental imaging principles are discussed as well as the applications of emerging imaging modalities. MRI is the preferred technique for the evaluation of musculoskeletal tumors, whereas other imaging modalities play a complementary role. Radiography is indicated as the first-line imaging modality in bone and soft-tissue tumors, whereas CT is the preferred modality for evaluating cortical osseous lesions or calcifications and in patients with contraindications to MRI. Positron emission tomography (PET)/CT and PET/MRI are helpful in identifying the glucose metabolism of the lesion. Ultrasonography is the most useful for biopsy guidance and can aid in differentiating cystic from solid masses and identifying vascularity. Novel modalities, such as diffusion-weighted imaging, spectroscopy, and habitat imaging, show promise in increasing diagnostic accuracy and affecting treatment strategies. Conventional modalities and emerging, novel imaging techniques can provide noninvasive methods to diagnose and evaluate musculoskeletal tumors.

Motion-Extended Array Synthesis—Part III: An Offset Imaging System Perspective

Motion-extended array synthesis (MXAS) is a concept for the realization of a 1-D or 2-D synthetic array, accomplished specifically without recourse to a reference waveform. The essential idea is that the relative motion between a minimum of two collection platforms with different velocity vectors can be exploited to create a virtual array, the size of the virtual array being the space swept out by the relative motion of the collectors. From fundamental imaging theory, the process is properly described as an offset imaging system (OIS) for which the range of baselines engendered is similar to that for a real aperture of the same size, but is offset by some potentially very large distance. For a far-field scenario, this may be equivalently described in terms of spatial frequencies, with the real and virtual imaging systems differing by the presence (in the latter) of an offset spatial frequency. We show that the MXAS construct is properly understood as an OIS, the MXAS processing method yields a form of the principal solution for an OIS, and the MXAS method is advantageous relative to conventional aperture synthesis processing measures, for an OIS. We consider imaging performance implications due to the offset nature of the imaging system, for spatially coherent and incoherent scenarios, and conclude that for many applications of interest, the process introduces no appreciable degradation.

Postpartum Woman With Seizures

A 27-year-old woman, postpartum day 9, presented with sudden onset of headache, vomiting, visual blurring, and 3 episodes of generalized tonic-clonic seizures. She had had an uneventful cesarean delivery 9 days previously and was discharged home. Her antenatal period was uneventful, and she did not have gestational hypertension. On examination, she was alert, oriented, and afebrile. Her blood pressure was 150/100 mm Hg, which had increased from her mean antenatal recording of 130/80 mm Hg. Fundus examination result was normal, and there were no focal neurologic deficits. Magnetic resonance imaging (MRI) of the brain showed T2 and T2 fluid-attenuated inversion recovery (FLAIR) hyperintense signals in bilateral parietooccipital lobes (Figures 1 and 2) and bilateral cerebellar hemispheres (Figure 3), without any diffusion restriction. She was treated with intravenous labetalol, nifedipine, and fosphenytoin. Her blood pressure normalized and her symptoms subsided, and she was later discharged.Figure 2Axial MRI showing T2 FLAIR hyperintensity of bilateral parietal lobes (arrows).View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3Axial MRI showing T2 FLAIR hyperintensity of bilateral cerebellar hemispheres (arrows).View Large Image Figure ViewerDownload Hi-res image Download (PPT) Posterior reversible encephalopathy syndrome. Posterior reversible encephalopathy syndrome is a clinicoradiologic entity, characterized by the clinical triad of headache, visual blurring, and seizures. The classic neuroimaging feature is parietooccipital lobe edema, observed as T2 hyperintense lesions in the MRI.1Bartynski W.S. Posterior reversible encephalopathy syndrome, part 1: fundamental imaging and clinical features.AJNR Am J Neuroradiol. 2008; 29: 1036-1042Crossref PubMed Scopus (796) Google Scholar Cerebellar involvement as observed in this case is much rarer, and such atypical presentations are also possible.2McKinney A.M. Short J. Truwit C.L. et al.Posterior reversible encephalopathy syndrome: incidence of atypical regions of involvement and imaging findings.AJR Am J Roentgenol. 2007; 189: 904-912Crossref PubMed Scopus (519) Google Scholar Posterior reversible encephalopathy syndrome is usually accompanied by hypertension. Other causes include chronic kidney disease and immunosuppressive therapy.3Garg R.K. Posterior leukoencephalopathy syndrome.Postgrad Med J. 2001; 77: 24-28Crossref PubMed Scopus (236) Google Scholar Patients with blood pressure fluctuations in the antepartum and postpartum period are particularly vulnerable for the syndrome. In the setting of postpartum seizures, the differential diagnosis includes postpartum eclampsia, cerebral venous thrombosis, and intracerebral hemorrhage.

Anisotropic contrast optical microscope.

An optical microscope is described that reveals contrast in the Mueller matrix images of a thin, transparent, or semi-transparent specimen located within an anisotropic object plane (anisotropic filter). The specimen changes the anisotropy of the filter and thereby produces contrast within the Mueller matrix images. Here we use an anisotropic filter composed of a semi-transparent, nanostructured thin film with sub-wavelength thickness placed within the object plane. The sample is illuminated as in common optical microscopy but the light is modulated in its polarization using combinations of linear polarizers and phase plate (compensator) to control and analyze the state of polarization. Direct generalized ellipsometry data analysis approaches permit extraction of fundamental Mueller matrix object plane images dispensing with the need of Fourier expansion methods. Generalized ellipsometry model approaches are used for quantitative image analyses. These images are obtained from sets of multiple images obtained under various polarizer, analyzer, and compensator settings. Up to 16 independent Mueller matrix images can be obtained, while our current setup is limited to 11 images normalized by the unpolarized intensity. We demonstrate the anisotropic contrast optical microscope by measuring lithographically defined micro-patterned anisotropic filters, and we quantify the adsorption of an organic self-assembled monolayer film onto the anisotropic filter. Comparison with an isotropic glass slide demonstrates the image enhancement obtained by our method over microscopy without the use of an anisotropic filter. In our current instrument, we estimate the limit of detection for organic volumetric mass within the object plane of ≈49 fg within ≈7 × 7 μm2 object surface area. Compared to a quartz crystal microbalance with dissipation instrumentation, where contemporary limits require a total load of ≈500 pg for detection, the instrumentation demonstrated here improves sensitivity to a total mass required for detection by 4 orders of magnitude. We detail the design and operation principles of the anisotropic contrast optical microscope, and we present further applications to the detection of nanoparticles, to novel approaches for imaging chromatography and to new contrast modalities for observations on living cells.

Superharmonic Imaging for Medical Ultrasound: a Review.

Ultrasound with harmonics has emerged as an exceptional alternative to competitively low resolution fundamental ultrasound imaging. The use of second harmonic is already a trend now but higher harmonics are also being seen as even better option due to its improved resolution. The resolution improved with frequency but achieves penetration of reduced energy. The cumulative addition of higher harmonics during propagation yields higher harmonics giving better resolution with adequate penetration. This paper summarizes the progress of such similar decade old harmonic ultrasound imaging technique i.e., superharmonic imaging (SHI) geared towards medical field. It comprises of harmonics higher than second harmonic preferably up to 5th harmonic. We conclude that SHI can be an advanced ultrasound imaging with comprehensive high resolution and adequate penetration depth on sole and coded modes.

How to improve detectability of crack size in nonlinear sub-harmonic imaging

Crack growth is regarded as an important monitoring parameter for structural degradation. To precisely estimate crack size, therefore, has been highly demanded to monitor structural healthiness and to assess residual life of various structures from small components to huge plants. Conventional non-destructive inspections have been successfully detected cracks, but some deficiencies for accuracy still remain. Nonlinear sub-harmonic generation was well proved to detect closed cracks that could cause underestimation of crack size. Moreover, sub-harmonic phased array (PA) imaging was proposed to visualize where the closed cracks are. The sub-harmonic PA images, however, has lower spatial resolution than the fundamental frequency PA images due to its longer wavelength, which often prevents from clearly observing closed cracks. Many of signal processing techniques have been developed to improve spatial resolution of images for more than half a century, and some resolution enhancing techniques such as deconvolutions and an eigen-analysis based technique are employed to make the resolution of sub-harmonic imaging better. Point spread function issues for deconvolution have been also investigated theoretically and experimentally. In addition, some experiments with CT specimens have been done to prove closed-crack localization by improving spatial resolution of sub-harmonic imaging.

Endoscopic ultrasound of pancreatic lesions.

Endoscopic ultrasound (EUS) is a well-established tool for the evaluation of pancreatic lesions. Due to the closer proximity of EUS to the pancreas, EUS offers a high sensitivity for detection of small pancreatic mass and is the preferred modality for obtaining tissue for diagnosis of pancreatic mass. Contrast-enhanced EUS and/or elastography provide additional information to the fundamental B-mode ultrasound images, leading to more accurate diagnosis. The aim of this video-article is to show the different steps in performing EUS on pancreatic lesions and to provide some tips and tricks to improve and facilitate the execution of EUS on pancreatic lesions.

Hybrid Strategy to Simulate 3-D Nonlinear Radio-Frequency Ultrasound Using a Variant Spatial PSF

There are several simulators for medical ultrasound (US) applications that can fully compute the nonlinear propagation on the transmitted pulse and the corresponding radio-frequency (RF) images. Creanuis is one recent model used to generate nonlinear RF images; however, the time requirements are long compared with linear models using a convolution strategy. In this paper, we describe an approach using convolution coupled with nonlinear information to create a pseudoacoustic tool that is able to quickly generate realistic US images. Several point-spread functions (PSFs) are computed with Creanuis. These PSFs are extracted at different depths in order to take into account variation in the resolution and apparition of harmonics during propagation. One convolution is then conducted for each PSF to generate a set of nonlinear raw RF images. The final image is obtained by merging these raw images using a PSF-weighting function. This hybrid Creanuis strategy was extended to 2-D, 2-D +t , 3-D, and 3-D +t images for both linear and phased-array geometries. We validated h-Creanuis using the mean deviation between the proposed images and those created using Creanuis and examined their statistical distributions. The mean deviations of Creanuis and h-Creanuis are below 2.5% for fundamental and second-harmonic images. The 3-D +t images obtained demonstrate the correct motion characteristics for speckle in sequences of both fundamental and second-harmonic images.

Optimal Acquisition Settings for Speckle Tracking Echocardiography–Derived Strains in Infants: An In Vitro Study

The purpose of this study was to investigate the effect of frame rate and probe frequency on the accuracy of speckle tracking echocardiography–derived strain measurements in infants. An infant-sized left ventricle phantom with sonomicrometer crystals was made from polyvinyl alcohol. The examined stroke rates were 60, 120 and 180 strokes per min (SPM). Longitudinal strain and circumferential strain measurements were analyzed from a total of 1860 cine loops. These cine loops were acquired using two pediatric probes of different frequencies at both fundamental and harmonic imaging modes. Both probes were examined at different settings (in total, 30 different frame rate–frequency combinations). At optimal settings, both longitudinal and circumferential strain displayed high accuracy. Frequency settings did not have a consistent effect on accuracy, while low frame rates led to less accurate measurements. We recommend a frame rate/heart ratio >1 frame per second/beats per min, especially for circumferential strain.

Initially Asymmetrical Function on MAG3 Renography Increases Incidence of Adverse Outcomes

To discriminate pathological from physiological hydronephrosis (99m)Tc-mercaptoacetyltriglycine (MAG3) diuretic renography is a fundamental imaging modality. Initial asymmetrical differential function or decreasing function on serial MAG3 scans is a classic surgical indication. However, prognostic evidence supporting this is limited. Therefore, we examined the association between initial function and outcomes. We hypothesized that patients with initially asymmetrical function would have higher odds of functional decline, and experience symptoms and surgical intervention compared to patients with initially symmetrical scans. We retrospectively reviewed the charts of 1,124 pediatric patients with hydronephrosis seen at Stollery Children's Hospital from 2000 to 2014. A total of 387 cases of unilateral ureteropelvic junction obstruction were grouped by initial postnatal differential function with asymmetrical defined as a greater than 10% difference in relative function. Postnatal surveillance, followup MAG3 results, pyeloplasty rates and post-pyeloplasty outcomes were compared. Of 387 patients 143 (37%) had initially asymmetrical function. Of those undergoing MAG3 scan surveillance 17% experienced a 10% or greater decline in ipsilateral differential function vs a 6% rate of function loss in the initially symmetrical group (OR 3.2, 95% CI 1.6-6.4, p = 0.0008). The overall pyeloplasty rate in patients with asymmetrical and symmetrical function was 27% and 16%, respectively (OR 1.9, 95% CI 1.1-3.2, p = 0.013). Patients with initially asymmetrical function had an increased rate of pyeloplasty secondary to symptoms compared to those with initially symmetrical function (16% vs 8%, OR 2.1, 95% CI 1.1-4.0, p = 0.019). Mean time to functional decline and pyeloplasty was 19and 17 months, respectively. Patients with initially asymmetrical differential function had increased ORs for subsequent renal decline, symptom onset and pyeloplasty.

Improvement of Shear Wave Motion Detection Using Harmonic Imaging in Healthy Human Liver

Quantification of liver elasticity is a major application of shear wave elasticity imaging (SWEI) to non-invasive assessment of liver fibrosis stages. SWEI measurements can be highly affected by ultrasound image quality. Ultrasound harmonic imaging has exhibited a significant improvement in ultrasound image quality as well as for SWEI measurements. This was previously illustrated in cardiac SWEI. The purpose of this study was to evaluate liver shear wave particle displacement detection and shear wave velocity (SWV) measurements with fundamental and filter-based harmonic ultrasound imaging. In a cohort of 17 patients with no history of liver disease, a 2.9-fold increase in maximum shear wave displacement, a 0.11 m/s decrease in the overall interquartile range and median SWV and a 17.6% increase in the success rate of SWV measurements were obtained when filter-based harmonic imaging was used instead of fundamental imaging.

Native Myocardial T1 Mapping, Are We There Yet?

T1 or longitudinal relaxation time is one of the very fundamental magnetic resonance imaging (MRI) time constants and a tissue characterizing parameter. Only during the last decade did it become possible to quantify T1 values of the myocardium through T1 mapping. Evolving from only region of interest analysis and long acquisition times to the pixel-based parametric mapping and short breath-hold sequences, T1 mapping is reaching maturity among cardiac magnetic resonance (CMR) techniques. Both inversion recovery methods such as MOdified Look-Locker Inversion (MOL-LI) and Shortened MOLLI (ShMOLLI) and saturation recovery methods such as Saturation recovery Single-Shot Acquisition (SASHA) are available for T1 quantification with variable degrees of accuracy, precision, and reproducibility. Native (non-contrast) T1 values increase with edema, amyloid deposition, and fibrosis, while they decrease in fat or iron deposition in the myocardium. These features enabled significant expansion of the clinical applications of native T1 mapping where it provides high sensitivity and specificity and even acts as a disease biomarker or a predictor of prognosis. It is of particular usefulness in diffuse myocardial diseases where conventional CMR techniques might be deceiving. A brighter future for the technique is expected if certain challenges are to be faced, examples of which are the need for standardization of normal values, acquisition techniques, and improving analysis tools.

Design, Fabrication, and Characterization of a Bifrequency Colinear Array.

Ultrasound imaging with high resolution and large penetration depth has been increasingly adopted in medical diagnosis, surgery guidance, and treatment assessment. Conventional ultrasound works at a particular frequency, with a [Formula: see text] fractional bandwidth of [Formula: see text], limiting the imaging resolution or depth of field. In this paper, a bifrequency colinear array with resonant frequencies of 8 and 20 MHz was investigated to meet the requirements of resolution and penetration depth for a broad range of ultrasound imaging applications. Specifically, a 32-element bifrequency colinear array was designed and fabricated, followed by element characterization and real-time sectorial scan (S-scan) phantom imaging using a Verasonics system. The bifrequency colinear array was tested in four different modes by switching between low and high frequencies on transmit and receive. The four modes included the following: 1) transmit low, receive low; 2) transmit low, receive high; 3) transmit high, receive low; and 4) transmit high, receive high. After testing, the axial and lateral resolutions of all modes were calculated and compared. The results of this study suggest that bifrequency colinear arrays are potential aids for wideband fundamental imaging and harmonic/subharmonic imaging.

Submolecular Imaging by Noncontact Atomic Force Microscopy with an Oxygen Atom Rigidly Connected to a Metallic Probe.

In scanning probe microscopy, the imaging characteristics in the various interaction channels crucially depend on the chemical termination of the probe tip. Here we analyze the contrast signatures of an oxygen-terminated copper tip with a tetrahedral configuration of the covalently bound terminal O atom. Supported by first-principles calculations we show how this tip termination can be identified by contrast analysis in noncontact atomic force and scanning tunneling microscopy (NC-AFM, STM) on a partially oxidized Cu(110) surface. After controlled tip functionalization by soft indentations of only a few angstroms in an oxide nanodomain, we demonstrate that this tip allows imaging an organic molecule adsorbed on Cu(110) by constant-height NC-AFM in the repulsive force regime, revealing its internal bond structure. In established tip functionalization approaches where, for example, CO or Xe is deliberately picked up from a surface, these probe particles are only weakly bound to the metallic tip, leading to lateral deflections during scanning. Therefore, the contrast mechanism is subject to image distortions, artifacts, and related controversies. In contrast, our simulations for the O-terminated Cu tip show that lateral deflections of the terminating O atom are negligible. This allows a detailed discussion of the fundamental imaging mechanisms in high-resolution NC-AFM experiments. With its structural rigidity, its chemically passivated state, and a high electron density at the apex, we identify the main characteristics of the O-terminated Cu tip, making it a highly attractive complementary probe for the characterization of organic nanostructures on surfaces.

A model and regularization scheme for ultrasonic beamforming clutter reduction

Acoustic clutter produced by off-axis and multipath scattering is known to cause image degradation, and in some cases these sources may be the prime determinants of in vivo image quality. We have previously shown some success addressing these sources of image degradation by modeling the aperture domain signal from different sources of clutter, and then decomposing aperture domain data using the modeled sources. Our previous model had some shortcomings including model mismatch and failure to recover B-Mode speckle statistics. These shortcomings are addressed here by developing a better model and by using a general regularization approach appropriate for the model and data. We present results with L1 (lasso), L2 (ridge), and L1/L2 combined (elastic-net) regularization methods. We call our new method aperture domain model image reconstruction (ADMIRE). Our results demonstrate that ADMIRE with L1 regularization, or weighted toward L1 in the case of elastic-net regularization, have improved image quality. L1 by itself works well, but additional improvements are seen with elastic-net regularization over the pure L1 constraint. On in vivo example cases, L1 regularization showed mean contrast improvements of 4.6 and 6.8 dB on fundamental and harmonic images, respectively. Elastic net regularization (α = 0.9) showed mean contrast improvements of 17.8 dB on fundamental images and 11.8 dB on harmonic images. We also demonstrate that in uncluttered Field II simulations the decluttering algorithm produces the same contrast, contrast-tonoise ratio, and speckle SNR as normal B-mode imaging, demonstrating that ADMIRE preserves typical image features.

A Primer on the Physical Principles of Tissue Harmonic Imaging.

Tissue harmonic imaging (THI) is a routinely used component of diagnostic ultrasonography (US). In this method, higher-frequency harmonic waves produced by nonlinear fundamental US wave propagation are used to generate images that contain fewer artifacts than those seen on conventional fundamental wave US tissue imaging. Harmonic frequencies are integer multiples of the fundamental frequency. The majority of current clinical US systems use second harmonic echoes for THI image formation. Image processing techniques (ie, bandwidth receive filtering, pulse inversion, side-by-side phase cancellation, and pulse-coded harmonics) are used to eliminate the fundamental frequency echoes, and the remaining harmonic frequency data are used to generate the diagnostic image. Advantages of THI include improved signal-to-noise ratio and reduced artifacts produced by side lobes, grating lobes, and reverberation. THI has been accepted in US practice, and variations of the technology are available on most US systems typically used for diagnostic imaging in radiologic practice. Differential THI is a further improvement that combines the advantages of THI, including superior tissue definition and reduced speckle artifact, with the greater penetration of lower frequency US, which permits high-quality harmonic imaging at greater depth than could previously be performed with conventional THI.

Spectral and color prediction for arbitrary halftone patterns: a drop-by-drop, WYSIWYG, “ink on display” print preview

Accurately previewing the appearance of a print job can make the difference between producing saleable output and wasting expensive materials and is a challenge to which a host of solutions already exist. However, what the majority of these have in common is that they base their predictions on the inputs to a printing system (e.g., continuous-tone data in ink channels) instead of its outputs (i.e., the halftone data that is then printed) and that they are only valid for a given set of choices already made in the printing system (e.g., color separation and halftoning). Alternatively, attempting to make appearance predictions using general-purpose models such as Kubelka Munk, Yule Nielsen and Neugebauer results in limited performance on systems whose behavior diverges from these models' assumptions, such as inkjet printing. As a result of such constraints, the resulting previews either work only under limited conditions or fail to predict some artifacts while erroneously predicting others that do not materialize in print. The approach presented here takes advantage of the flexibility of the HANS framework and the insights into spectral correlation to deliver a print preview solution that can be applied to any printing system, that allows for the variation of fundamental imaging choices without the need for re-computing model parameters and that delivers ICC-profile-level accuracy.

The Celestial Imagination: Proclus the Philosopher on Theurgy

This paper focuses on Proclus’s On the hieratic art of the Greeks – considered as a contemporary philosophical problem – exploring some of its fundamental concepts and images, thus delineating Proclus’s notion of theurgy, which he primarily conceived as divine action manifesting in the union between a god and the theurgist, and only secondarily as a technique. These aesthetic experiments of thought or philosophical performances, by means of which a divine self is created, had deep metaphysical, cosmological, psychological, ethical, linguistic and even political and religious implications for Late Antiquity Platonism, and had a profound impact on the development of Renaissance philosophy and magic. Such practices are meant to be understood in the context of the philosophical paideia of which it represents its final stage and consummation; they are developed by intricate hermeneutics of a poetic theology operated by very sophisticated conceptions of symbol, analogy and the imagination, all of which are at the base of the celestial-terrestrial correspondences used by theurgists in their hymn singing.

Airborne ultraviolet imaging system for oil slick surveillance: oil-seawater contrast, imaging concept, signal-to-noise ratio, optical design, and optomechanical model.

The airborne ultraviolet imaging system, which assesses oil slick areas better than visible and infrared optical systems, was designed to monitor and track oil slicks in coastal regions. A model was built to achieve the upwelling radiance distribution of oil-covered sea and clean seawater, based on the radiance transfer software. With this model, the oil-seawater contrast, which affects the detection of oil-covered coastal areas, was obtained. The oil-seawater contrast, fundamental imaging concept, analog calculation of SNR, optical design, and optomechanical configuration of the airborne ultraviolet imaging system are illustrated in this paper. The study of an airborne ultraviolet imaging system with F-number 3.4 and a 40° field of view (FOV) in near ultraviolet channel (0.32-0.38μm) was illustrated and better imaging quality was achieved. The ground sample distance (GSD) is from 0.35 to 0.7m with flight height ranges from 0.5 to 1km. Comparisons of detailed characteristics of the airborne ultraviolet imaging system with the corresponding characteristics of previous ultraviolet systems were tabulated, and these comparisons showed that this system can achieve a wide FOV and a relative high SNR. A virtual mechanical prototype and tolerances analysis are illustrated in this paper to verify the performance of fabrication and assembly of the ultraviolet system.