Fundamental Imaging Research Articles

An ultra-low noise optical head for liquid environment atomic force microscopy.

The design considerations and eventual performance of a new, ultra-low noise optical head for dynamic atomic force microscopy (AFM) are presented. The head, designed specifically for the study of hydration layers and ion organization next to solid surfaces and biomolecules, displays an integrated tip-sample distance noise below 3 pm. The sensitivity of the optical beam deflection sensor, operating at frequencies up to 8.6 MHz (3 dB roll-off), is typically below 10 fm/√Hz, enabling utilization of high frequency cantilevers of low thermal noise for fundamental and higher mode imaging. Exceptional signal stability and low optical noise are achieved by replacing the commonly used laser diode with a helium-neon laser. An integral photothermal excitation of the cantilever produces pure harmonic oscillations, minimizing the generation of higher cantilever modes and deleterious sound waves characterizing the commonly used excitation by a piezoelectric crystal. The optical head is designed to fit on top of the widespread Multimode(®) (Bruker) piezo-tube and accommodate its commercial liquid cell. The performance of the new AFM head is demonstrated by atomic resolution imaging of a muscovite mica surface in aqueous solution.

Improving Cardiac Phase Extraction in IVUS Studies by Integration of Gating Methods.

Coronary intravascular ultrasound (IVUS) is a fundamental imaging technique for atherosclerotic plaque assessment. However, volume-based data retrieved from IVUS studies can be misleading due to the artifacts generated by the cardiac motion, hindering diagnostic, and visualization of the vessel condition. Then, we propose an image-based gating method that improves the performance of the preexisting methods, delivering a gating in an appropriate time for clinical practice. We propose a fully automatic method to synergically integrate motion signals from different gating methods to improve the cardiac phase estimation. Additionally, we present a local extrema identification method that provides a more accurate extraction of a cardiac phase and, also, a scheme for multiple phase extraction mandatory for elastography-type studies. A comparison with three state-of-the-art methods is performed over 61 in-vivo IVUS studies including a wide range of physiological situations. The results show that the proposed strategy offers: 1) a more accurate cardiac phase extraction; 2) a lower frame oversampling and/or omission in the extracted phase data (error of 1.492 ±0.977 heartbeats per study, mean ± SD); 3) a more accurate and robust heartbeat period detection with a Bland-Altman coefficient of reproducibility (RPC) of 0.23 s, while the second closest method presents an RPC of 0.36 s. The integration of motion signals performed by our method shown an improvement of the gating accuracy and reliability.

The three-dimensional inverse-scattering and inverse-source problems with a planar aperture.

When signals are recorded on a planar aperture with point emitters/detectors, from either a three-dimensional (3D) scattering potential or from a 3D spatially-incoherent source distribution, an integral equation arises containing the product of two Green's functions in the weak scattering limit (the Born approximation). This fundamental imaging equation for scatterers or sources is derived and solved analytically.

Endoscopic ultrasonography using new functions for pancreatobiliary diseases: current status and future perspectives.

A new endoscopic ultrasound processor (EU-ME2 Premier Plus) has recently been developed. It improves fundamental imaging and enables three new functions; namely, tissue harmonic echo (THE), elastography, and contrast harmonic endoscopic ultrasonography (CH-EUS). However, many aspects regarding the usefulness of these three functions in the diagnosis of pancreatobiliary diseases remain unknown. In connection with and prior to the convening of Endoscopy Forum Japan 2014, endoscopic ultrasonography using EU-ME2 Premier Plus was carried out for pancreatic, bile duct, and gallbladder cases at 12 participating institutions (Japan [n = 10]; other Asian countries [n = 2]). A questionnaire survey was conducted regarding the usefulness of EU-ME2 Premier Plus for each EUS case. In addition, participants' views were surveyed by asking them to vote as to whether or not the three functions of EU-ME2 Premier Plus were useful for several items under pancreatic, bile duct, and gallbladder indications. According to the participants' views, THE (particularly THE-P mode) is essential for the diagnosis of cystic lesions. Many participants viewed elastography as useful in only extremely limited cases. Although CH-EUS was not considered useful for all cases, its indications covered a broad range. Additional studies are warranted to clarify the functions of EU-ME2 Premier Plus in more detail.

Acoustic enhancement with fundamental imaging and CPS imaging: comparison between nano-scale PFOB lipidic particles and C3F8 lipidic microbubbles,a vitro experimental study

Objective To prepare two kinds of nano-scale ultrasound contrast agents, perfluorooctyl bromide(PFOB) lipidic particles and perfluoropropane(C3F8) lipidic microbubbles, and compare their characteristics of acoustic enhancement with fundamental imaging and contrast pulse sequence(CPS) imaging in vitro. Methods Physico-chemical properties of PFOB lipidic particles and C3F8 lipidic microbubbles were measured, including morphous, size distribution, Zeta potential, concentration and stability. PFOB lipidic particles with and without biotin, C3F8 lipidic microbubbles with and without biotin were prepared, respectively. Size distribution of four contrast agents were measured, before and after adding avidin. Then, four kinds of ultrasound contrast agents were imaged with both fundamental and CPS imaging before and after avidin was added. Signal intensities were compared using METLAB software. Results ①Addition of avidin had no effect on particle diameters of control lipidic particles/microbubbles. However, the particle diameters of biotinylated lipidic particles and microbubbles were both enlarged with the addition of avidin (P<0.05). ②With fundamental imaging, neither control nor biotinylated PFOB particles were visible before adding avidin. After avidin was added, significant signal enhancement from biotinylated PFOB particles was detected (P<0.05); while control PFOB particles were still unvisible.However, with fundamental imaging, both control and biotinylated C3F8 microbubbles manifested ultrasonic backscatter before and after adding avidin, without significant difference between their signal intensity. ③CPS imaging couldn′t detect nonlinear signal from biotinylated PFOB particles neither before nor after the addition of avidin. However, CPS imaging could detect nonlinear signal from biotinylated C3F8 microbubbles both before and after adding avidin, without significant difference in their signal intensity. Conclusions Compared to C3F8 microbubbles, PFOB particles have better particle size controllability, and higher signal-to-noise (target to nontarget signal) ratio, thus are more suitable for targeted contrast ultrasound imaging. Key words: Ultrasonography; Microbubbles; Liposomes; Perfluorooctyl bromide

Subharmonic, Non-linear Fundamental and Ultraharmonic Imaging of Microbubble Contrast at High Frequencies

There is increasing use of ultrasound contrast agent in high-frequency ultrasound imaging. However, conventional contrast detection methods perform poorly at high frequencies. We performed systematic in vitro comparisons of subharmonic, non-linear fundamental and ultraharmonic imaging for different depths and ultrasound contrast agent concentrations (Vevo 2100 system with MS250 probe and MicroMarker ultrasound contrast agent, VisualSonics, Toronto, ON, Canada). We investigated 4-, 6- and 10-cycle bursts at three power levels with the following pulse sequences: B-mode, amplitude modulation, pulse inversion and combined pulse inversion/amplitude modulation. The contrast-to-tissue (CTR) and contrast-to-artifact (CAR) ratios were calculated. At a depth of 8 mm, subharmonic pulse-inversion imaging performed the best (CTR = 26 dB, CAR = 18 dB) and at 16 mm, non-linear amplitude modulation imaging was the best contrast imaging method (CTR = 10 dB). Ultraharmonic imaging did not result in acceptable CTRs and CARs. The best candidates from the in vitro study were tested in vivo in chicken embryo and mouse models, and the results were in a good agreement with the in vitro findings.

Image Quality Analysis of Various Gastrointestinal Endoscopes: Why Image Quality Is a Prerequisite for Proper Diagnostic and Therapeutic Endoscopy.

Arising from human curiosity in terms of the desire to look within the human body, endoscopy has undergone significant advances in modern medicine. Direct visualization of the gastrointestinal (GI) tract by traditional endoscopy was first introduced over 50 years ago, after which fairly rapid advancement from rigid esophagogastric scopes to flexible scopes and high definition videoscopes has occurred. In an effort towards early detection of precancerous lesions in the GI tract, several high-technology imaging scopes have been developed, including narrow band imaging, autofocus imaging, magnified endoscopy, and confocal microendoscopy. However, these modern developments have resulted in fundamental imaging technology being skewed towards red-green-blue and this technology has obscured the advantages of other endoscope techniques. In this review article, we have described the importance of image quality analysis using a survey to consider the diversity of endoscope system selection in order to better achieve diagnostic and therapeutic goals. The ultimate aims can be achieved through the adoption of modern endoscopy systems that obtain high image quality.

Observation of vortex domain structures in multiferroic hexagonal manganites RMnO3by transmission electron microscopy

Multiferroic hexagonal manganite RMnO3 (R = rare-earth elements) shows improper ferroelectricity accompanied by tilting of MnO5 hexahedra as the primary order parameter. The ferroelectricity is originated from displacements of rare-earth ions along c-axis triggered by the MnO5 hexahedra tilting. Although coupling between ferroelectric and antiferromagnetic domains below the magnetic transition temperature of ∼90 K has been reported from previous work[1], the relationship between the ferroelectric domains and structural domains due to the MnO5 hexahedra tilting has not been well-studied. In this talk, we will report our studies on unique patterns of ferroelectric antiphase domains with a vorticity in hexagonal RMnO3, obtained from the results of transmission electron microscopy [2].The electron diffraction patterns obtained at room temperature exhibit superlattice reflection spots due to the MnO5 hexahedra tilting and displacements of rare-earth ions along c-axis, in addition to the fundamental reflections associated with the high symmetry structure with the space group of P63/mmc. Unique antiphase/ferroelectric "cloverleaf-like" domain patterns are clearly observed in dark-field images taken using superlattice spots. The fundamental and superlattice dark-field imaging combined with high-resolution imaging clearly demonstrates that in the cloverleaf-like domain patterns the antiphase and ferroelectric domains arrange periodically with certain rotation direction. In addition, there exist two types of cloverleaf-like domain patterns with the opposite rotations next to each other in the superlattice dark-field images. These results indicate that the cloverleaf-like domain patterns can be considered as the aggregation of vortices and antivortices consisting of ferroelectric and antiphase domains.

Computed Tomography Perfusion Imaging for the Assessment of Brain Tumors

he radiographic characterization of intra-axial brain tumors is a critical component in the clinical management of paT tients. Magnetic resonance (MR) and computed tomography (CT) imaging are fundamental imaging techniques used in the initial diagnosis and subsequent surveillance during/after treatment. On the basis of diagnostic imaging (often after the development of symptoms/signs), surgical intervention often is performed that frequently is followed by adjuvant chemotherapy or radiation. Serial imaging, typicallyMR imaging, is used to assess the response to adjuvant therapy and to monitor for recurrence or progression. Currently, CT imaging (nonperfusion) often is reserved for acute neurologic decline that results from hemorrhage, hydrocephalus, or other mass lesions.

Modeling the optical transfer function in the imaging chain

Modeling the imaging chain has become a critical design tool to understand the relationship between design trades and image quality in camera systems. The mathematical models for the fundamental components of an imaging chain are well understood and have been validated using working camera systems. However, the complexity of camera designs continues to grow as the technology advances to drive higher performance using different approaches. The fundamental imaging chain models do not always meet the needs of the new imaging system designs, thus requiring the models to advance in complexity as well. Of particular interest to the optical designers is the development of mathematical models that enable more complex modeling of the wavefront errors for the optical transfer functions (OTF) in the image chain models. A tutorial on the imaging chain is given followed by an innovative approach using an η matrix for modeling the OTF in the imaging chain.

In vivo application of short-lag spatial coherence and harmonic spatial coherence imaging in fetal ultrasound.

Fetal scanning is one of the most common applications of ultrasound imaging and serves as a source of vital information about maternal and fetal health. Visualization of clinically relevant structures, however, can be severely compromised in difficult-to-image patients due to poor resolution and the presence of high levels of acoustical noise or clutter. We have developed novel coherence-based beamforming methods called Short-Lag Spatial Coherence (SLSC) imaging and Harmonic Spatial Coherence imaging (HSCI), and applied them to suppress the effects of clutter in fetal imaging. This method is used to create images of the spatial coherence of the backscattered ultrasound as opposed to images of echo magnitude. We present the results of a patient study to assess the benefits of coherence-based beamforming in the context of first trimester fetal exams. Matched fundamental B-mode, SLSC, harmonic B-mode, and HSCI images were generated using raw radio frequency data collected on 11 volunteers in the first trimester of pregnancy. The images were compared for qualitative differences in image texture and target conspicuity as well as using quantitative imaging metrics such as signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and contrast. SLSC and HSCI showed statistically significant improvements across all imaging metrics compared with B-mode and harmonic B-mode, respectively. These improvements were greatest for poor quality B-mode images where contrast of anechoic targets was improved from 15 dB in fundamental B-mode to 27 dB in SLSC and 17 dB in harmonic B-mode to 30 dB in HSCI. CNR improved from 1.4 to 2.5 in the fundamental images and 1.4 to 3.1 in the harmonic case. These results exhibit the potential of coherence-based beamforming to improve image quality and target detectability, especially in high noise environments.

Which Technique Is Better for Detection of Right‐to‐Left Shunt in Patients with Patent Foramen Ovale: Comparing Contrast Transthoracic Echocardiography with Contrast Transesophageal Echocardiography

At present there is no consensus on which technique is more suitable for the detection of right-to-left shunt (RLS) in patients with patent foramen ovale (PFO). The aim of study was to compare the efficacy of contrast transthoracic echocardiography (cTTE) and contrast transesophageal echocardiography (cTEE) in the detection of RLS. A prospective study was undertaken in 29 patients with PFO. Both cTTE with harmonic imaging modality and cTEE with fundamental imaging modality were performed for all the patients. The severity of RLS were semiquantitatively assessed with a four-level grade system by scaling the numbers of microbubbles (MBs) in the left atrium after complete opacification of the right atrium within the first 3 cardiac cycles. Level 1 represents no MBs, indicating no RLS. Level 2, ≤10 MBs, indicating mild RLS. Level 3, 11-30 MBs, indicating moderate RLS and Level 4, >30 MBs, indicating severe RLS. Contrast TTE demonstrated significantly higher sensitivity for detection of RLS than cTEE (86% vs. 56%, P<0.05). For cTTE, there were 4, 1, 5, and 19 cases determined at levels 1, 2, 3, and 4, respectively, whereas for the same group of patients 13, 2, 6, and 7 cases were identified by cTEE at levels 1, 2, 3, and 4, respectively. The severity of RLS detected by cTTE was significantly greater than that by cTEE (P<0.01). Contrast TTE is more efficacious in the detection of RLS than cTEE. The former can be used as an alternative to the latter in clinical practice.

Multi-detector CT features of acute intestinal ischemia and their prognostic correlations.

Acute intestinal ischemia is an abdominal emergency occurring in nearly 1% of patients presenting with acute abdomen. The causes can be occlusive or non occlusive. Early diagnosis is important to improve survival rates. In most cases of late or missed diagnosis, the mortality rate from intestinal infarction is very high, with a reported value ranging from 60% to 90%. Multi-detector computed tomography (MDCT) is a fundamental imaging technique that must be promptly performed in all patients with suspected bowel ischemia. Thanks to the new dedicated reconstruction program, its diagnostic potential is much improved compared to the past and currently it is superior to that of any other noninvasive technique. The increased spatial and temporal resolution, high-quality multi-planar reconstructions, maximum intensity projections, vessel probe, surface-shaded volume rending and tissue transition projections make MDCT the gold standard for the diagnosis of intestinal ischemia, with reported sensitivity, specificity, positive and negative predictive values of 64%-93%, 92%-100%, 90%-100% and 94%-98%, respectively. MDCT contributes to appropriate treatment planning and provides important prognostic information thanks to its ability to define the nature and extent of the disease. The purpose of this review is to examine the diagnostic and prognostic role of MDCT in bowel ischemia with special regard to the state of art new reconstruction software.

Editor's Note

It is my pleasure once again to be able to present an exciting issue of Ultrasound in Obstetrics & Gynecology (UOG) to mark the start of a new year. Leading the issue is an insightful and balanced Editorial1 by the Founding Editor, Stuart Campbell. In this article, Professor Campbell convincingly challenges the conventional doctrine, which is supported by various international Colleges, that avoids ultrasound screening and surgical intervention for fetal macrosomia. Other highlights of the issue include a meta-analysis by Khalil et al.2, which demonstrates the unexpected burden of neurodevelopmental delay in children born with major congenital cardiac defects, and another by Martins et al.3, analyzing only randomized controlled trials, which reports that ultrasound monitoring alone for controlled ovarian stimulation is as effective as using ultrasound with serial hormone assessment. This time last year we set ourselves the challenging task of improving the academic quality of the Journal and, as a reflection of this goal, I am delighted to announce that we have managed to increase the Impact Factor (IF) of UOG to 3.557 – the highest in the history of the Journal. This would not have been possible without the hard work, dedication and determination of our reviewers, editors and editorial staff. UOG is now ranked eighth out of 78 reproductive health journals, with an IF that is practically indistinguishable from those of the British and American Journals of Obstetrics and Gyn(a)ecology, which have a much wider spectrum of subjects to cover. Last year we also announced a focus on promoting the submission and publication of articles relating to non-invasive prenatal testing (NIPT) and array comparative genomic hybridization (CGH). This initiative appears to be gathering momentum, as anticipated from a technology that is expected to result in a paradigm shift in the care provided in early pregnancy. Articles on NIPT and array CGH accounted for about 10% of those published in 2013 and were amongst the most downloaded and cited4-8. In view of this success, UOG will continue to make every effort to attract and publish work on these topics for the benefit of our readers. Their inclusion has not been at the expense of other clinically relevant topics, with articles on soft-marker screening for Down syndrome, prevention of adverse perinatal outcome using low-dose aspirin and a summary of the International Ovarian Tumor Analysis (IOTA) studies also being downloaded over 3000 times each since publication9-11. It therefore seems that not only is UOG achieving academic success with an increasing IF, but also that it is having a valuable clinical impact; this is evidenced by the magnitude of downloads of articles with practice-changing messages as well as those of clinical guidelines12, 13. With this in mind, it is reassuring to note that the seminal series of articles published in 2011 on the topic of accurate diagnosis of miscarriage continues to have a significant influence on both national guidelines and consensus statements14, 15. The Journal issues have continued to include our new article types: Referee Commentaries, to add context and counterpoint to selected papers, and ‘How To’ articles on fundamental imaging techniques. Feedback received on Referee Commentaries has been positive, so it is my intention to continue their publication for the foreseeable future. The ‘How To’ format has also had its successes16, but, as for all recent initiatives, I would value your comments to help determine whether this type of Journal output should be maintained. Looking to the future, we aim to keep the Journal focused on current topics of research and debate, to continue to provide a fast and effective editorial service and to remain responsive to authors and accessible to readers. I am confident that, with the support of my fellow editors and the office staff, UOG will continue to improve and progress and to provide a home for ground-breaking publications in our field. I would like to thank you, as readers and authors, for your continued loyalty to the Journal.

Implementation of parallel transmit beamforming using orthogonal frequency division multiplexing-achievable resolution and interbeam interference

The speed of sound in the human body limits the achievable data acquisition rate of pulsed ultrasound scanners. To overcome this limitation, parallel beamforming techniques are used in ultrasound 2-D and 3-D imaging systems. Different parallel beamforming approaches have been proposed. They may be grouped into two major categories: parallel beamforming in reception and parallel beamforming in transmission. The first category is not optimal for harmonic imaging; the second category may be more easily applied to harmonic imaging. However, inter-beam interference represents an issue. To overcome these shortcomings and exploit the benefit of combining harmonic imaging and high data acquisition rate, a new approach has been recently presented which relies on orthogonal frequency division multiplexing (OFDM) to perform parallel beamforming in transmission. In this paper, parallel transmit beamforming using OFDM is implemented for the first time on an ultrasound scanner. An advanced open platform for ultrasound research is used to investigate the axial resolution and interbeam interference achievable with parallel transmit beamforming using OFDM. Both fundamental and second-harmonic imaging modalities have been considered. Results show that, for fundamental imaging, axial resolution in the order of 2 mm can be achieved in combination with interbeam interference in the order of -30 dB. For second-harmonic imaging, axial resolution in the order of 1 mm can be achieved in combination with interbeam interference in the order of -35 dB.

Robust shear wave motion tracking using ultrasound harmonic imaging

Robust shear-wave motion detection is essential for producing reliable shear elasticity measurements for ultrasound shear-wave elastography (SWE). However, because shear-wave motion is extracted from radiofrequency signals which can be heavily contaminated by noise, shear-wave motion detection can be very challenging, especially for in vivo applications. This study investigated the implementation of harmonic imaging (HI) to facilitate more robust shear-wave tracking based on HI’s effectiveness in suppressing imaging noise associated with ultrasound reverberation, phase aberration, and clutter noise. A HI shear-wave tracking sequence was developed combining the pulse-inversion HI method with the plane wave imaging technique to transmit phase-inverted pulses at a high frame rate of several kilohertz. The backscattered ultrasound signals from phase-inverted pulses were added to suppress the fundamental and enhance the second harmonic component, from which the shear-wave motion was extracted. A pork belly phantom experiment showed that HI could significantly improve shear-wave motion detection by producing almost three-fold less underestimation of shear-wave motion and over ten-fold more precision for shear-wave speed measurements than fundamental imaging. An in vivo transthoracic case study of a human heart showed that HI substantially improved the success rate of shear-wave motion detection and could provide consistent estimates of the left ventricle myocardium stiffness.

Harmonic tracking of acoustic radiation force-induced displacements

Ultrasound-based elasticity imaging methods rely upon accurate estimates of tissue deformation to characterize the mechanical properties of soft tissues. These methods are corrupted by clutter, which can bias and/or increase variance in displacement estimates. Harmonic imaging methods are routinely used for clutter suppression and improved image quality in conventional B-mode ultrasound, but have not been utilized in ultrasound-based elasticity imaging methods. We introduce a novel, fully-sampled pulse-inversion harmonic method for tracking tissue displacements that corrects the loss in temporal sampling frequency associated with conventional pulse-inversion techniques. The method is implemented with acoustic radiation force impulse (ARFI) imaging to monitor the displacements induced by an impulsive acoustic radiation force excitation. Custom pulse sequences were implemented on a diagnostic ultrasound scanner to collect spatially-matched fundamental and harmonic information within a single acquisition. B-mode and ARFI images created from fundamental data collected at 4 MHz and 8 MHz are compared with 8-MHz harmonic images created using a band-pass filter approach and the fully sampled pulse-inversion method. In homogeneous, tissue-mimicking phantoms, where no visible clutter was observed, there was little difference in the axial displacements, estimated jitter, and normalized cross-correlation among the fundamental and harmonic tracking methods. The similarity of the lower- and higher-frequency methods suggests that any improvement resulting from the increased frequency of the harmonic components is negligible. The harmonic tracking methods demonstrated a marked improvement in B-mode and ARFI image quality of in vivo carotid arteries. Improved feature detection and decreased variance in estimated displacements were observed in the arterial walls of harmonic ARFI images, especially in the pulse-inversion harmonic ARFI images. Within the lumen, the harmonic tracking methods improved the discrimination of the blood–vessel interface, making it easier to visualize plaque boundaries. Improvements in harmonic ARFI images in vivo were consistent with suppressed clutter supported by improved contrast and contrast-to-noise ratio (CNR) in the matched harmonic B-mode images compared with the fundamental B-mode images. These results suggest that harmonic tracking methods can improve the clinical utility and diagnostic accuracy of ultrasound-based elasticity imaging methods.

Understanding Scanning Tunneling Microscopy Contrast Mechanisms on Metal Oxides: A Case Study

A comprehensive analysis of contrast formation mechanisms in scanning tunneling microscopy (STM) experiments on a metal oxide surface is presented with the oxygen-induced (2√2×√2)R45° missing row reconstruction of the Cu(100) surface as a model system. Density functional theory and electronic transport calculations were combined to simulate the STM imaging behavior of pure and oxygen-contaminated metal tips with structurally and chemically different apexes while systematically varying bias voltage and tip-sample distance. The resulting multiparameter database of computed images was used to conduct an extensive comparison with experimental data. Excellent agreement was attained for a large number of cases, suggesting that the assumed model tips reproduce most of the commonly encountered contrast-determining effects. Specifically, we find that depending on the bias voltage polarity, copper-terminated tips allow selective imaging of two structurally distinct surface Cu sites, while oxygen-terminated tips show complex contrasts with pronounced asymmetry and tip-sample distance dependence. Considering the structural and chemical stability of the tips reveals that the copper-terminated apexes tend to react with surface oxygen at small tip-sample distances. In contrast, oxygen-terminated tips are considerably more stable, allowing exclusive surface oxygen imaging at small tip-sample distances. Our results provide a conclusive understanding of fundamental STM imaging mechanisms, thereby providing guidelines for experimentalists to achieve chemically selective imaging by properly selecting imaging parameters.

Role of EUS in Diagnosis of Autoimmune Pancreatitis

Context The diagnosis of autoimmune pancreatitis (AIP) is based on a combination of pancreatic histology, imaging, serology, other organ involvement, and response to steroids. In this setting, endoscopic ultrasound (EUS) is considered the procedure of choice to obtain pancreatic tissue in order to establish the diagnosis and/or to exclude malignancy. However, negative cytology or histology obtained by EUS-FNA does not exclude AIP. In order to further investigate these subgroups of patients, there are two promising imaging tools: real-time EUS elastography of the pancreas and contrast-enhanced EUS. Objective and methods To evaluate the diagnostic yield of EUS in detection of AIP by comparing EUS findings with standard radiological imaging (CT and/or MRI) in patients with suspected autoimmune disease referred to our tertiary center. Results Thirty-two patients with radiological suspicious of AIP underwent EUS. Focal enlargement of pancreatic parenchyma and focal narrowing of main pancreatic duct (MPD) were detected in the same way by MRI and EUS, being both techniques better that CT (12/21, 12/32, and 7/19, respectively). Diffuse pancreatic parenchyma enlargement and detection of multiple stricture of MPD were better identified by EUS (8/19 with CT, 3/21 with RMN, 12/32 with EUS; 1/19 with CT, 1/21 with RMN, 6/32 with EUS, respectively). Focal and diffuse AIP presented hypervascularization pattern after contrast agent injection in the majority of patients (10/13). At elastography, focal AIP presented with a pattern of small spotted mainly blue colour signals that are evenly spread, showing a different pattern from pancreatic cancer. In addition, when targeted masses were unclear on fundamental B-mode EUS imaging, elastography was useful to find the targeted area to biopsy. Conclusion We believe that EUS elastography and contrast-enhanced EUS alone or in combination are promising tools in the diagnostic approach of focal AIP. It seems that in the near future their use might be integrated in the diagnostic algorithms of AIP.

Improved Shear Wave Motion Detection Using Pulse-Inversion Harmonic Imaging With a Phased Array Transducer

Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the shear wave motion and give consistent shear wave speed measurements of the left ventricular myocardium while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve shear wave motion tracking and thus potentially facilitate more robust assessment of tissue elasticity by SWE.