Conventional B-mode Imaging Research Articles

Role of high-frame-rate imaging for monitoring high-intensity focused ultrasound treatment

During high-intensity focused ultrasound (HIFU) treatment, tissue change, and acoustic cavitation as its precursor, should be monitored both in and outside the HIFU focal zone, to ensure the intended therapeutic effect and to prevent potential adverse effects, respectively. Unlike boiling-induced bubbles, cavitation-generated microbubbles are difficult to detect with conventional B-mode imaging because their life is significantly shorter than the typical image repetition period. An image repetition period less than a few milliseconds is required to detect them. This can only be accomplished by high-frame-rate imaging with plane or diverging waves. In-vivo as well as ex-vivo experimental results evidencing the effectiveness of such imaging to detect cavitation-generated microbubbles will be shown in this paper. A number of researches are underway to ultrasonically detect HIFU-induced tissue change, which occurs at much lower temperature than boiling. During echo data acquisition for detecting such tissue change, HIFU exposure is typically intermitted. High frame-rate-imaging also has a significant advantage there because the tissue motion by being released from the radiation force by HIFU can be ignored if the intermission is within a few milliseconds. Ex-vivo experimental results evidencing the effectiveness to detect HIFU-induced tissue change by high-frame rate imaging will also be shown.

Assessing the Stability of Aortic Aneurysms with Pulse Wave Imaging.

Purpose To assess whether the stability of murine aortic aneurysms is associated with the homogeneity of pulse wave propagation within the saccular wall. Materials and Methods All animal procedures were approved by the institutional Animal Care and Use Committee. Apolipoprotein E and tissue inhibitor of metalloproteinases-1 knockout mice (n = 26) were infused with angiotensin II by using subcutaneously implanted osmotic pumps, with an additional control mouse used for histologic examination (n = 1). Pulse wave imaging (PWI) was performed just before infusion and 15 days after infusion by using 40-MHz ultrasonography at 8000 frames per second (with electrocardiographic gating). Aneurysm appearance on B-mode images was monitored every 2-3 days for 30 days. On the basis of B-mode images obtained after 30 days, aneurysms were deemed to have been unstable if they had ruptured; otherwise, they were deemed stable. Statistical significance was assessed by using two-tailed t tests. Results In normal aortas, the pulse waves propagated at relatively constant velocities (mean ± standard deviation, 2.8 m/sec ± 0.9). Fifteen days after infusion, all mice had developed aneurysms, with significant (P < .001/12) changes in maximum anterior-posterior diameter (increase of 54.9% ± 2.5) and pulse wave velocity (PWV) (decrease of 1.3 m/sec ± 0.8). While there was no significant difference in these parameters (P = .45 for diameter and P = .55 for PWV) between stable aneurysms (n = 12) and unstable aneurysms (n = 14), the standard deviation of the high-resolution PWV was significantly higher (P < .001/12) in unstable aneurysms (5.7 m/sec ± 1.6) than in stable ones (3.2 m/sec ± 0.9). Conclusion High-resolution PWI was used to measure the local homogeneity of pulse wave propagation within the saccular wall, which is lower in unstable aneurysms than in stable ones. Hence, if proven to add additional information beyond size and appearance in human studies, PWI could potentially be used to assess the stability of aneurysms by providing information that is complementary to the anatomic data obtained with conventional B-mode imaging. © RSNA, 2016 Online supplemental material is available for this article.

Assessment for diagnosis of lymph node metastasis in esophageal cancer using endoscopic ultrasound elastography.

BackgroundWe performed endoscopic ultrasound real-time tissue elastography to more accurately diagnose lymph node metastasis of esophageal cancer. The aim of this study was to evaluate the ability of EUS elastography to distinguish benign from malignant lymph nodes in esophageal cancer patients.MethodsThe present study had two steps. As the first step (study 1), we developed diagnostic criteria for metastatic lymph nodes using elastography and verified the validity of the criteria. Three hundred and twenty-two lymph nodes from 35 patients treated by surgical resection were included in the study. As the second step (study 2), we preoperatively examined the lymph nodes of esophageal cancer patients with EUS elastography and compared its diagnostic performance with that of the conventional B-mode EUS images. A total of 115 lymph nodes from 31 patients were included.ResultsIn study 1, lymph nodes were considered malignant if 50 % or more of the node appeared blue, or if the peripheral part of the lesion was blue and the central part was red/yellow/green. The sensitivity and specificity of the elastography were 79.7 and 97.6 % with an accuracy of 93.8 %, which was significantly higher than the values for conventional B-mode imaging. In study 2, the sensitivity and specificity of the EUS elastography were 91.2 and 94.5 % with an accuracy of 93.9 %, which was also significantly higher than the values for conventional B-mode EUS imaging.ConclusionsThe present study demonstrated that EUS elastography is useful for diagnosing lymph node metastasis of esophageal cancer.

Review of Quantitative Ultrasound: Envelope Statistics and Backscatter Coefficient Imaging and Contributions to Diagnostic Ultrasound.

Conventional medical imaging technologies, including ultrasound, have continued to improve over the years. For example, in oncology, medical imaging is characterized by high sensitivity, i.e., the ability to detect anomalous tissue features, but the ability to classify these tissue features from images often lacks specificity. As a result, a large number of biopsies of tissues with suspicious image findings are performed each year with a vast majority of these biopsies resulting in a negative finding. To improve specificity of cancer imaging, quantitative imaging techniques can play an important role. Conventional ultrasound B-mode imaging is mainly qualitative in nature. However, quantitative ultrasound (QUS) imaging can provide specific numbers related to tissue features that can increase the specificity of image findings leading to improvements in diagnostic ultrasound. QUS imaging can encompass a wide variety of techniques including spectral-based parameterization, elastography, shear wave imaging, flow estimation, and envelope statistics. Currently, spectral-based parameterization and envelope statistics are not available on most conventional clinical ultrasound machines. However, in recent years, QUS techniques involving spectral-based parameterization and envelope statistics have demonstrated success in many applications, providing additional diagnostic capabilities. Spectral-based techniques include the estimation of the backscatter coefficient (BSC), estimation of attenuation, and estimation of scatterer properties such as the correlation length associated with an effective scatterer diameter (ESD) and the effective acoustic concentration (EAC) of scatterers. Envelope statistics include the estimation of the number density of scatterers and quantification of coherent to incoherent signals produced from the tissue. Challenges for clinical application include correctly accounting for attenuation effects and transmission losses and implementation of QUS on clinical devices. Successful clinical and preclinical applications demonstrating the ability of QUS to improve medical diagnostics include characterization of the myocardium during the cardiac cycle, cancer detection, classification of solid tumors and lymph nodes, detection and quantification of fatty liver disease, and monitoring and assessment of therapy.

Quantitative Ultrasound for Staging of Hepatic Steatosis in Patients on Home Parenteral Nutrition Validated with Magnetic Resonance Spectroscopy: A Feasibility Study

Patients on home parenteral nutrition are at risk for developing liver dysfunction, which is due partly to the accumulation of lipids in the liver (steatosis) and may progress to end-stage liver disease with overt liver failure. Therefore, a timely diagnosis with easy access to repeated assessment of the degree of liver steatosis is of great importance. A pilot study was performed in 14 patients on long-term home parenteral nutrition using the computer-aided ultrasound method. Ultrasound radio frequency data were acquired using a phased array transducer and were converted into conventional B-mode images. All patients were subjected to proton magnetic resonance spectroscopy measurement of liver fat content for reference. Computer-aided ultrasound parameters similar to those in a previous validation study in cows revealed significant correlations with fat content measured by magnetic resonance spectroscopy. The most significant parameters were the residual attenuation coefficient (R = 0.95, p < 0.001) and the lateral speckle size (R = 0.77, p = 0.021). These findings indicate the potential usefulness of computer-aided ultrasound for staging of hepatic steatosis.

Performance of novel tissue harmonic echo imaging using endoscopic ultrasound for pancreatic diseases.

Background and study aims: Recently, tissue harmonic echo (THE) imaging has advanced with the development of a new endoscopic ultrasound (EUS) monitor/processing unit. With this new technology, penetration (THE-P) and resolution (THE-R) images can be obtained. The aim of this study was to investigate the performance of this novel THE imaging using a new processing unit for pancreatic diseases. Patients and methods: Fifty patients with pancreatic lesions (38 cystic, 12 solid) were retrospectively analyzed. At each examination, 3 EUS images of the same pancreatic lesion were obtained using B-mode, THE-P mode, and THE-R mode imaging. Each set of EUS images was randomly arranged and evaluated independently by 4 physicians blinded to the imaging technique. Images were compared using a Likert scale 5-point grading system for each parameter. Results: For cystic lesions, THE-P mode images were significantly superior to conventional B-mode images for visualizing the boundary, septum, nodules, and total image quality (P < 0.05). THE-R mode images were significantly superior to conventional B-mode images for visualizing the boundary, septum, and total image quality (P < 0.05). However, for solid lesions, there was no significant difference in all the evaluation points between THE-P and conventional B-mode images. THE-R mode images were inferior to conventional B-mode images for visualizing the boundary, internal structure, and total image quality (P < 0.05). Conclusions: For pancreatic cystic lesions, THE mode images provided better lesion characterization than conventional B-mode images. Further research is required to determine if this improvement will result in improved EUS diagnostics.

Determining temperature distribution in tissue in the focal plane of the high (>100 W/cm2) intensity focused ultrasound beam using phase shift of ultrasound echoes

In therapeutic applications of High Intensity Focused Ultrasound (HIFU) the guidance of the HIFU beam and especially its focal plane is of crucial importance. This guidance is needed to appropriately target the focal plane and hence the whole focal volume inside the tumor tissue prior to thermo-ablative treatment and beginning of tissue necrosis. This is currently done using Magnetic Resonance Imaging that is relatively expensive. In this study an ultrasound method, which calculates the variations of speed of sound in the locally heated tissue volume by analyzing the phase shifts of echo-signals received by an ultrasound scanner from this very volume is presented. To improve spatial resolution of B-mode imaging and minimize the uncertainty of temperature estimation the acoustic signals were transmitted and received by 8MHz linear phased array employing Synthetic Transmit Aperture (STA) technique. Initially, the validity of the algorithm developed was verified experimentally in a tissue-mimicking phantom heated from 20.6 to 48.6°C. Subsequently, the method was tested using a pork loin sample heated locally by a 2MHz pulsed HIFU beam with focal intensity ISATA of 129W/cm2. The temperature calibration of 2D maps of changes in the sound velocity induced by heating was performed by comparison of the algorithm-determined changes in the sound velocity with the temperatures measured by thermocouples located in the heated tissue volume. The method developed enabled ultrasound temperature imaging of the heated tissue volume from the very inception of heating with the contrast-to-noise ratio of 3.5–12dB in the temperature range 21–56°C. Concurrently performed, conventional B-mode imaging revealed CNR close to zero dB until the temperature reached 50°C causing necrosis. The data presented suggest that the proposed method could offer an alternative to MRI-guided temperature imaging for prediction of the location and extent of the thermal lesion prior to applying the final HIFU treatment.

Bimodal Multiparameter-Based Approach for Benign–Malignant Classification of Breast Tumors

Proposed here is a breast tumor classification technique using conventional ultrasound B-mode imaging and a new elasticity imaging-based bimodal multiparameter index. A set of conventional ultrasound (US) and ultrasound elastography (UE) parameters are studied, and among those, the effective ones whose independent as well as combined performance is found satisfactory are selected. To improve the combined US performance, two new US parameters are proposed: edge diffusivity, which assesses edge blurriness to differentiate malignant from benign lesions, and the shape asymmetry factor, which quantifies tumor shape irregularity by comparing the tumor boundary with an ellipse fitted to the lesion. Then a new bimodal multiparameter characterization index is defined to discriminate 201 pathologically confirmed breast tumors of which 56 are malignant lesions, 79 are fibroadenomas, 42 are cysts and 24 are inflammatory lesions. The weights of the multiparameter bimodal index are optimally computed using a genetic algorithm (GA). To evaluate the performance variation of the index on different data sets, the tumors are categorized into three classes: malignant lesion versus fibroadenoma, malignant lesion versus fibroadenoma and cyst and malignant lesion versus fibroadenoma, cyst and inflammation. The test results reveal that the proposed bimodal index achieves satisfactory quality metrics (e.g., 94.64%–98.21% sensitivity, 97.24%–100.00% specificity and 96.52%–99.44% accuracy) for classification of the aforementioned three classes of breast tumors. Its performance is also observed to be better in totality of the quality metrics sensitivity, specificity, accuracy, positive predictive value and negative predictive value as compared with that of a conventional bimodal index as well as unimodal multiparameter indices based on US or UE. It is suggested that the proposed simple bimodal linear classifier may assist radiologists in better diagnosis of breast tumors and help reduce the number of unnecessary biopsies.

Advances in Lower Extremity Ultrasound

Diagnostic ultrasound techniques used in the evaluation of the musculoskeletal system are rapidly evolving. Conventional B-mode and Doppler ultrasound imaging methods are workhorses in the diagnosis and treatment decision making for traumatic and pathologic conditions of joints, tendons, muscles, ligaments, and peripheral nerves. Recently developed sonoelastography techniques enable the qualitative and quantitative evaluation of the material properties of musculoskeletal tissues . The recent availability of sonoelastography on clinical machines will facilitate its progressive utilization in routine clinical practice. Exciting new developments in ultrasound imaging enable real-time fusion with imported magnetic resonance or computed tomography images, facilitating ultrasound-guided interventional procedures and teaching of ultrasound anatomy to trainees. In this review article, the authors discuss new advances in sonoelastography of the lower extremity with emphasis on shear wave imaging and briefly the exciting features of ultrasound fusion imaging with computed tomography and magnetic resonance imaging.

Spatial coherence in human tissue: implications for imaging and measurement.

The spatial coherence properties of the signal backscattered by human tissue and measured by an ultrasound transducer array are investigated. Fourier acoustics are used to describe the propagation of ultrasound through a model of tissue that includes reverberation and random scattering in the imaging plane. The theoretical development describes how the near-field tissue layer, transducer aperture properties, and reflectivity function at the focus reduce the spatial coherence of the imaging wave measured at the transducer surface. Simulations are used to propagate the acoustic field through a histologically characterized sample of the human abdomen and to validate the theoretical predictions. In vivo measurements performed with a diagnostic ultrasound scanner demonstrate that simulations and theory closely match the measured spatial coherence characteristics in the human body across the transducer array's entire spatial extent. The theoretical framework and simulations are then used to describe the physics of spatial coherence imaging, a type of ultrasound imaging that measures coherence properties instead of echo brightness. The same echo data from an F/2 transducer was used to generate B-mode and short lag spatial coherence images. For an anechoic lesion at the focus, the contrast-to-noise ratio is 1.21 for conventional B-mode imaging and 1.95 for spatial coherence imaging. It is shown that the contrast in spatial coherence imaging depends on the properties of the near-field tissue layer and the backscattering function in the focal plane.

Improved Detection of Kidney Stones Using an Optimized Doppler Imaging Sequence.

Kidney stones have been shown to exhibit a "twinkling artifact" (TA) under Color-Doppler ultrasound. Although this technique has better specificity than conventional Bmode imaging, it has lower sensitivity. To improve the overall performance of using TA as a diagnostic tool, Doppler output parameters were optimized in-vitro. The collected data supports a previous hypothesis that TA is caused by random oscillations of micron sized bubbles trapped in the cracks and crevices of kidney stones. A set of optimized parameters were implemented such that that the MI & TI remained within the FDA approved limits. Several clinical kidney scans were performed with the optimized settings and were able to detect stones with improved SNR relative to the default settings.

Stabilization technique for real-time high-resolution vascular ultrasound using frequency domain interferometry.

We have proposed an ultrasound imaging method based on frequency domain interferometry (FDI) with an adaptive beamforming technique to depict real-time high-resolution images of human carotid artery. Our previous study has investigated the performance of the proposed imaging method under an ideal condition with a high signal-to-noise ratio (SNR). In the present study, we propose a technique that has the potential to improve accuracy in estimating echo intensity using the FDI imaging method. We investigated the performance of the proposed technique in a simulation study that two flat interfaces were located at depths of 15.0 and 15.2 mm and white noise was added. Because the -6 dB bandwidth of the signal used in this simulation study is 2.6 MHz, the conventional B-mode imaging method failed to depict the two interfaces. Both the conventional and proposed FDI imaging methods succeeded to depict the two interfaces when the SNR ranged from 15 to 30 dB. However, the average error of the estimated echo intensity at the interfaces using the conventional FDI imaging method ranged from 7.2 to 10.5 dB. In contrast, that using the FDI imaging method with the proposed technique ranged from 2.0 to 2.2 dB. The present study demonstrates the potential of the FDI imaging method in depicting robust and high-range-resolution ultrasound images of arterial wall, indicating the possibility to improve the diagnosis of atherosclerosis in early stages.

Short-lag spatial coherence imaging on matrix arrays, part 1: Beamforming methods and simulation studies.

Short-lag spatial coherence (SLSC) imaging is a beamforming technique that has demonstrated improved imaging performance compared with conventional B-mode imaging in previous studies. Thus far, the use of 1-D arrays has limited coherence measurements and SLSC imaging to a single dimension. Here, the SLSC algorithm is extended for use on 2-D matrix array transducers and applied in a simulation study examining imaging performance as a function of subaperture configuration and of incoherent channel noise. SLSC images generated with a 2-D array yielded superior contrast-to-noise ratio (CNR) and texture SNR measurements over SLSC images made on a corresponding 1-D array and over B-mode imaging. SLSC images generated with square subapertures were found to be superior to SLSC images generated with subapertures of equal surface area that spanned the whole array in one dimension. Subaperture beamforming was found to have little effect on SLSC imaging performance for subapertures up to 8 x 8 elements in size on a 64 × 64 element transducer. Additionally, the use of 8 x 8, 4 x 4, and 2 x 2 element subapertures provided 8, 4, and 2 times improvement in channel SNR along with 2640-, 328-, and 25-fold reduction in computation time, respectively. These results indicate that volumetric SLSC imaging is readily applicable to existing 2-D arrays that employ subaperture beamforming.

Improvement of accuracy in ultrasonic measurement of luminal surface roughness of carotid arterial wall by deconvolution filtering

The diagnosis of early-stage atherosclerosis is important for preventing cardiovascular diseases such as a stroke or a heart attack. The main cause of such diseases is atherosclerosis. In early-stage atherosclerosis, the luminal surface of the arterial wall becomes rough because of the detachment of endothelial cells and the degeneration of the internal elastic layer. Therefore, it would be useful if the minute luminal surface roughness of the carotid arterial wall observed in the early stage of atherosclerosis can be measured noninvasively by ultrasonography. In conventional ultrasonography, the axial resolution of a B-mode image depends on the ultrasonic pulse length of 150 µm (at 10 MHz) because a B-mode image is constructed using the amplitude of the RF echo. However, the thickness of an endothelial cell covering the luminal surface is 10–20 µm. Therefore, a minute surface roughness cannot be measured from a conventional B-mode image. We have realized the transcutaneous measurement of such a minute surface roughness of about 10 µm using the phased-tracking method. However, the lateral spatial resolution degrades owing to the point spread function (PSF) because the diameter of an ultrasonic beam is finite. In the present study, we proposed a method of improving the lateral spatial resolution in the estimation of surface roughness using a Wiener filter to suppress the effect of the PSF of the ultrasound system employed. The proposed method was validated using a phantom and then applied to the in vivo measurement of carotid arteries.

Sonoelastography of the Liver

: In general population, chronic liver disease is a great public health problem. Liver fibrosis, a common pattern in the usual causes of chronic liver disease, involves the gathering of collagen and other macromolecules inside the extracellular matrix. Fibrosis tends to proceed, leading to liver dysfunction, portal hypertension, and eventually cirrhosis. Liver biopsy is the gold standard for the diagnosing of liver fibrosis, and unfortunately it is invasive, expensive, with sampling variability and probable complications (mortality rate is procedure-related: one in 10,00012,000). For patients with chronic liver disease, it is important to delineate the degree and grading of fibrosis progression. Ultrasonography (US) provides ideal noninvasive assessment for diffuse liver disease because of its low cost and wide availability. Conventional B-mode US is good for the diagnosis of advanced cirrhosis, but is insensitive for fibrosis. Elastography may be employed as a substitute diagnostic technique for fibrosis. The METAVIR scoring system assigns fibrosis to five stages of F0: no fibrosis, F1: portal and periportal fibrosis with no septum, F2: portal and periportal fibrosis with rare septa, F3: portal and periportal fibrosis with many septa, F4: cirrhosis). In elastography, a mechanical force (compression or vibration) is applied to the soft tissues, and a conventional imaging technique such as US or MR imaging is used to create a map of soft-tissue deformation. There are two types of elastography: static and dynamic elastography. Static elastography is now a more common type of elastographic imaging. In this method, a single and very small compressive force is used by pressing with the ultrasound probe, typically and then the displacement of tissue is calculated. Static elastography has been widely used with superficial organs. It is more difficult to apply in deeper organs, and also the qualitative figures have not been displayed to have value for detection of liver fibrosis by using a vibratory stimulus to produce shear waves (which slowly pass through tissues) to be tracked by ultrasound. The spreading rate of shear waves depends upon the shear modulus of tissues, which is usually proportional to the Youngs modulus directly. Hence, quantifying tissue stiffness is possible by using this method. The first ultrasound system to apply this method is the Fibroscan (by Echosens) which can evaluate liver fibrosis. Shear waves are sent into the liver by a piston at the center of the probe, and the shear waves velocity is used to assess the shear modulus. This tool has proved feasible for the noninvasive diagnosis of moderate and severe fibrosis, but mild changes are not detected. Development of other systems to apply acoustic radiation force imaging (ARFI) (such as the Siemens S2000) by pushing on organs with a high-powered ultrasound pulse is under way. Currently, there are three main techniques to evaluate liver stiffness: transient elastography (FibroScan by Echosens), acoustic radiation force impulse (ARFI) imaging, and shear-wave (SW) elastography . Among these methods, transient elastography offers the capacity to estimate mean tissue stiffness noninvasively. Several recent studies have proved that the measurements of liver stiffness with transient elastography are well correlated with the METAVIR stages of fibrosis. In addition, transient elastography is helpful as it can be performed repeatedly. However, it is not a real-time technique because the sonographic images are not visible during the measurement. In patients with hepatosteatosis and increased body mass index (BMI), the reproducibility of transient elastography is substantially reduced as the modality of ultrasonography itself has restrictions for visualizing the liver clearly in these patients. Real-time sonoelastography is another method for the evaluation of tissue elasticity. It uses a B-mode ultrasound, combining with elastography with the conventional US scanner. This device estimates the relative hardness of the organs and displays this data as real-time color images. It can show tissue elasticity images and conventional B-mode images at the same time. There are many reports and approaches to evaluate liver stiffness without liver biopsy. Among them, the FibroScan appears useful.

Contrast in intracardiac acoustic radiation force impulse images of radiofrequency ablation lesions.

We have previously shown that intracardiac acoustic radiation force impulse (ARFI) imaging visualizes tissue stiffness changes caused by radiofrequency ablation (RFA). The objectives of this in vivo study were to (1) quantify measured ARFI-induced displacements in RFA lesion and unablated myocardium and (2) calculate the lesion contrast (C) and contrast-to-noise ratio (CNR) in two-dimensional ARFI and conventional intracardiac echo images. In eight canine subjects, an ARFI imaging-electroanatomical mapping system was used to map right atrial ablation lesion sites and guide the acquisition of ARFI images at these sites before and after ablation. Readers of the ARFI images identified lesion sites with high sensitivity (90.2%) and specificity (94.3%) and the average measured ARFI-induced displacements were higher at unablated sites (11.23 ± 1.71 µm) than at ablated sites (6.06 ± 0.94 µm). The average lesion C (0.29 ± 0.33) and CNR (1.83 ± 1.75) were significantly higher for ARFI images than for spatially registered conventional B-mode images (C = -0.03 ± 0.28, CNR = 0.74 ± 0.68).

Real-Time Elastography for the Detection of Prostate Cancer

The lack of reliable imaging tools in detecting prostate cancer makes a random biopsy still the standard of care to detect prostate cancer. To reduce the number of cores during a biopsy and therefore the risk of biopsy-related complications, an imaging tool which provides reliable guided biopsies is required. Transrectal real-time elastography has shown to have the ability to visualize prostate cancer foci to some extent. In addition to the conventional B-mode image of transrectal ultrasound, it adds information about the stiffness of the prostate tissue. This review highlights the most important studies on elastography to follow the improvements in techniques and to outline the ability to detect prostate cancer and guide biopsies.

Synthetic aperture focusing for short-lag spatial coherence imaging.

It has been demonstrated that short-lag spatial coherence (SLSC) ultrasound imaging can provide improved speckle SNR and lesion CNR compared with conventional Bmode images, especially in the presence of noise and clutter. Application of the van Cittert-Zernike theorem predicts that coherence among the ultrasound echoes received across an array is reduced significantly away from the transmit focal depth, leading to a limited axial depth of field in SLSC images. Transmit focus throughout the field of view can be achieved using synthetic aperture methods to combine multiple transmit events into a single final image. A synthetic aperture can be formed with either focused or diverging transmit beams. We explore the application of these methods to form synthetically focused channel data to create SLSC images with an extended axial depth of field. An analytical expression of SLSC image brightness through depth is derived for the dynamic receive focus case. Experimental results in a phantom and in vivo are presented and compared with dynamic receive focused SLSC images, demonstrating improved SNR and CNR away from the transmit focus and an axial depth of field four to five times longer.

Expressiveness of temperature-induced changes in backscattered energy in conventional B-mode images

Changes on conventional B-mode images have been correlated with temperature, aiming to develop a reliable method for noninvasive temperature estimation. The assumption is that temperature variations induce wave propagation changes that modify the backscattered ultrasound signal and these changes have an expression in ultrasonographic images. One of the main effects is the change on the image intensity that is mainly caused by temperature-related changes in backscattered energy (CBE) from tissue inhomogeneities. It is reported that CBE is dependent on medium speed-of-sound and density, behaving in different ways for lipid or aqueous scatterers. In this paper, we demonstrate that CBE has an expression on B-mode images recorded from conventional ultrasound scanners. We observed that different regions have positive, negative, or undefined correlations with temperature, and that this behavior is due to the dependence of CBE with scatterers type. This differentiated behavior enables the segmentation of different structures inside the same tissue. Our experimental setup consisted in the temperature elevation from 36 to 44 °C (hyperthermia range) of ex-vivo tissue samples. We considered bovine muscle and porcine muscle and fat. For both samples, we observed coherent segmentations of the different structures, pointing for a potential clinical application of the proposed analysis.

Pocket ultrasound devices to perform EchoScopy

Recently a new category of handheld device has burgeoned with its advantages of the increased portability and affordability. These devices are smaller than usual portable models, which are often the size of a laptop computer. Currently, the smallest available handheld device is the Vscan™ (GE Healthcare), a pocket size ultrasound device, providing conventional B-mode and colour Doppler imaging (CDI) but does not possess the function of pulsed wave Doppler imaging. With a compact size, it is possible to retain it in a white coat pocket, like a stethoscope, and to use it as adjunctive tool for patient physical examination. Further ultrasound devices from other companies also exist; these are also hand-held or at most brought to the bedside with the support of a shoulder band or a small wheel car, working with batteries and without the need to be connected to a mains electrical socket. EFSUMB is currently striving to identify the level of clinical conditions in a non-cardiac setting that can be resolved by handheld or pocket size ultrasound scanners, primarily by physicians who have limited patient information but need to establish a clinical diagnosis e.g. in primary care. This basic ultrasound approach has been defined by EFSUMB as „EchoScopy”, to distinguish this use of basic ultrasound from conventional sonographic examination of abdominal organs. We are currently investigating the use of EchoScopy in daily routine use under strictly defined clinical conditions. Vscan™, as well other extremely portable ultrasound scanners, can in fact be applied at the bedside as part of the initial physical clinical examination of patients. The use can be separated into clinical divisions to screen for vascular, cardiac, thoracic and abdominal diseases, though it should not replace the usual echography when there are more complex clinical questions. The technique will not compete with the FAST concept (Focused Assessment with Sonography in Trauma (FAST)) but will find its eventual place as an extension of the routine physical examination [www.esfumb.org].