Resolution Ultrasound Imaging Research Articles

Ultrasound image resolution influences analysis of skeletal muscle composition.

Analysis of muscle composition using ultrasound requires standardization of several equipment settings (i.e. gain). However, the influence of image resolution, which is altered by imaging depth, on measures of muscle composition is unknown. We analysed rectus femoris muscle composition using ultrasound images captured from 32 males and females (aged 28±5years) at depths of 9.0, 7.3, 5.9 and 4.7cm. The transducer's orientation was fixed using a clamp during image acquisition to minimize movement. Across each image resolution, a region of interest encompassing the same anatomical area within the muscle was used for muscle composition analysis. Muscle composition was analysed using a combination of first-, second- and higher-order texture features. Muscle composition agreement across image resolutions was evaluated using a one-way ANOVA and intraclass correlation coefficients (ICC). Most muscle composition features displayed differences due to image resolution (p<.05). ICCs demonstrated poor-to-good agreement across different image resolutions. In general, higher resolution images (i.e. shallower imaging depth) demonstrated better agreement (ICC>0.90) compared to lower resolution images. Ultrasound image resolution influences muscle composition analysis. Image resolution should be fixed within and between individuals when evaluating muscle composition using ultrasound.

Deep Learning for Ultrasound Localization Microscopy.

By localizing microbubbles (MBs) in the vasculature, ultrasound localization microscopy (ULM) has recently been proposed, which greatly improves the spatial resolution of ultrasound (US) imaging and will be helpful for clinical diagnosis. Nevertheless, several challenges remain in fast ULM imaging. The main problems are that current localization methods used to implement fast ULM imaging, e.g., a previously reported localization method based on sparse recovery (CS-ULM), suffer from long data-processing time and exhaustive parameter tuning (optimization). To address these problems, in this paper, we propose a ULM method based on deep learning, which is achieved by using a modified sub-pixel convolutional neural network (CNN), termed as mSPCN-ULM. Simulations and in vivo experiments are performed to evaluate the performance of mSPCN-ULM. Simulation results show that even if under high-density condition (6.4 MBs/mm2), a high localization precision ( [Formula: see text] in the lateral direction and [Formula: see text] in the axial direction) and a high localization reliability (Jaccard index of 0.66) can be obtained by mSPCN-ULM, compared to CS-ULM. The in vivo experimental results indicate that with plane wave scan at a transmit center frequency of 15.625 MHz, microvessels with diameters of [Formula: see text] can be detected and adjacent microvessels with a distance of [Formula: see text] can be separated. Furthermore, when using GPU acceleration, the data-processing time of mSPCN-ULM can be shortened to ~6 sec/frame in the simulations and ~23 sec/frame in the in vivo experiments, which is 3-4 orders of magnitude faster than CS-ULM. Finally, once the network is trained, mSPCN-ULM does not need parameter tuning to implement ULM. As a result, mSPCN-ULM opens the door to implement ULM with fast data-processing speed, high imaging accuracy, short data-acquisition time, and high flexibility (robustness to parameters) characteristics.

Thermoacoustic imaging based on noise suppression of multi-channel amplifier and additive circuit

&lt;sec&gt;Thermoacoustic imaging (TAI) is an emerging biomedical imaging method in which microwave is used as an excitation source to generate acoustic signals. The TAI possesses the advantages of high contrast of microwave imaging and high resolution of ultrasound imaging, which is also noninvasive. While the signal-to-noise ratio (SNR) of TAI is often very low. It is usually required by averaging the thermoacoustic signal many times to improve the SNR. However, averaging the signal to improve the SNR can significantly reduce the TAI’s time resolution, which hinders the development of rapid TAI. Here in this paper, we propose to reduce the cost and improve the time resolution of TAI based on multi-channel amplifier and additive circuit. The received thermoacoustic signals are divided into 4 channels and then entered into 4 amplifiers simultaneously.&lt;/sec&gt;&lt;sec&gt;After being amplified, the signals are added and collected by the data acquisition system for reconstructing the image. The phantom results indicate that the time resolution of TAI increases 5 times and the SNR rises from 6 dB to 12 dB, with the multi-channel amplifier and additive circuit adopted. The method proposed in this paper is helpful in promoting the development and clinical application of TAI, especially it has a great significance for developing the ultra-fast TAI.&lt;/sec&gt;

A novel transcranial ultrasound imaging method with diverging wave transmission and deep learning approach

Real time brain transcranial ultrasound imaging is extremely intriguing because of its numerous applications. However, the skull causes phase distortion and amplitude attenuation of ultrasound signals due to its density: the speed of sound is significantly different in bone tissue than in soft tissue. In this study, we propose an ultrafast transcranial ultrasound imaging technique with diverging wave (DW) transmission and a deep learning approach to achieve large field-of-view with high resolution and real time brain ultrasound imaging. DW transmission provides a frame rate of several kiloHz and a large field of view that is suitable for human brain imaging via a small acoustic window. However, it suffers from poor image quality because the diverging waves are all unfocused. Here, we adopted adaptive beamforming algorithms to improve both the image contrast and the lateral resolution. Both simulated and in situ experiments with a human skull resulted in significant image improvements. However, the skull still introduces a wavefront offset and distortion, which degrades the image quality even when adaptive beamforming methods are used. Thus, we also employed a U-Net neural network to detect the contour and position of the skull directly from the acquired RF signal matrix. This approach avoids the need for beamforming, image reconstruction, and image segmentation, making it more suitable for clinical use.

Quantitative, real-time in vivo tracking of magnetic nanoparticles using multispectral optoacoustic tomography (MSOT) imaging

The goal of this work was to demonstrate real-time tracking of in vivo nanoparticle concentrations utilizing multispectral optoacoustic tomography (MSOT). Combining the high contrast of optical imaging with the high resolution of ultrasound imaging, MSOT was utilized for non-invasive, real-time tomographic imaging of particles in mice and the results calibrated against analysis of tissue samples with electron paramagnetic resonance (EPR) spectroscopy. In a longitudinal study, the pharmacokinetics (pK) and biodistribution of Cyanine-7 (Cy7) conjugated superparamagnetic iron oxide nanoparticles (Cy7-SPIONs) were monitored after intravenous administration into the tail vein of healthy B6-albino mice. Concentrations of Cy7-SPIONs determined by MSOT image analysis of the liver, spleen, and kidneys showed excellent agreement with EPR data obtained on tissue samples ‒ validating MSOT’s ability to quantify SPION concentrations with high spatial resolution. Both methods of analysis indicated highest accumulation of Cy7-SPIONs in the liver followed by the spleen, and negligible accumulation in the kidneys; SPION accumulation in organs with high concentrations of mononuclear phagocytic system macrophages is typical. Additionally, our study observed that particles modified with a 2 kDa polyethylene glycol (PEG) demonstrated significantly prolonged half-life in circulation compared to particles with 5 kDa PEG. The study demonstrates the potential of Cy7-SPIONs and MSOT for quantitative localization of magnetic nanoparticles in vivo, which can potentially be used to study their toxicity, quantify the efficacy of targeted drug delivery (e.g. within tumors), and their use as a multi-modal diagnostic agent to monitor disease progression.

Soft tissue deformation tracking by means of an optimized fiducial marker layout with application to cancer tumors.

Interventional radiology methods have been adopted for intraoperative control of the surgical region of interest (ROI) in a wide range of minimally invasive procedures. One major obstacle that hinders the success of procedures using interventional radiology methods is the preoperative and intraoperative deformation of the ROI. While fiducial markers (FM) tracing has been shown to be promising in tracking such deformations, determining the optimal placement of the FM in the ROI remains a significant challenge. The current study proposes a computational framework to address this problem by preoperatively optimizing the layout of FM, thereby enabling an accurate tracking of the ROI deformations. The proposed approach includes three main components: (1) creation of virtual deformation benchmarks, (2) method of predicting intraoperative tissue deformation based on FM registration, and (3) FM layout optimization. To account for the large variety of potential ROI deformations, virtual benchmarks are created by applying a multitude of random force fields on the tumor surface in physically based simulations. The ROI deformation prediction is carried out by solving the inverse problem of finding the smoothest force field that leads to the observed FM displacements. Based on this formulation, a simulated annealing approach is employed to optimize the FM layout that produces the best prediction accuracy. The proposed approach is capable of finding an FM layout that outperforms the rationally chosen layouts by 40% in terms of ROI prediction accuracy. For a maximum induced displacement of 20mm on the tumor surface, the average maximum error between the benchmarks and our FM-optimized predictions is about 1.72mm, which falls within the typical resolution of ultrasound imaging. The proposed framework can optimize FM layout to effectively reduce the errors in the intraoperative deformation prediction process, thus bridging the gap between preoperative imaging and intraoperative tissue deformation.

Piezocomposite transducer design and performance for high resolution ultrasound imaging transducers

Piezocomposite design for dedicated ultrasonic imaging applications requires precise homogenization models for predicting the electromechanical characteristics of the new material. Thus, several homogenization models have been developed. As part of this work, we applied several analytical homogenization models for piezocomposite of 2–2 and 1–3 connectivities. To validate these analytical models, a comparative study was made between various models and experimental measurements. As a result, these homogenized electromechanical properties are effectively used for the calculation and comparison of electroacoustic response for typical transducers aimed at ultrasound imaging applications. An optimal design of transducer aimed at ultrasound imaging applications is proposed as a dedicated imaging performance index, elaborated through a trade-off between sensitivity and bandwidth.

Application of multi-wavelength technique for photoacoustic imaging to delineate tumor margins during maximum-safe resection of glioma: A preliminary simulation study

Accurate margin delineation and safe maximal resection of glioma is one of the most challenging problems of neurosurgery, due to its close resemblance to normal brain parenchyma. However, different intraoperative visualization methods have been used for real-time intraoperative investigation of the borders of the resection cavity, each having advantages and limitations. This preliminary study was designed to simulate multi-wavelength photoacoustic imaging for brain tumor margin delineation for maximum safe resection of glioma. Since the photoacoustic signal is directly related to the amount of optical energy absorption by the endogenous tissue chromophores such as hemoglobin; it may be able to illustrate the critical structures such as tumor vessels during surgery. The simulation of the optical and acoustic part was done by using Monte-Carlo and k-wave toolbox, respectively. As our simulation results proved, at different wavelengths and depths, the amount of optical absorption for the blood layer is significantly different from others such as normal and tumoral tissues. Furthermore, experimental validation of our approach confirms that, by using multi-wavelengths proportional to the depth of the tumor margin during surgery, tumor margin can be differented using photoacoustic imaging at various depths. Photoacoustic imaging may be considered as a promising imaging modality which combines the spectral contrast of optical imaging as well as the spatial resolution of ultrasound imaging, and may be able to delineate the vascular-rich glioma margins at different depths of the resection cavity during surgery.

High Resolution Minimum Variance Beamformer With Low Complexity in Medical Ultrasound Imaging

Although the minimum variance beamformer (MVB) shows a significant improvement in resolution and contrast in medical ultrasound imaging, its high computational complexity is a major problem in a real-time imaging system. Therefore, it seems necessary to propose a new method with a lower computational complexity that preserves the advantages of the MVB. In this paper, the MVB was implemented with a partial generalized sidelobe canceler (GSC) with a blocking matrix based on our previous study, which projected the incoming signals to a lower dimensional space. The partial GSC separated the weight vector into one fixed and one adaptive weight, whereby the optimization could be performed with lower complexity on the adaptive part. In addition, this dimension reduction allowed us to increase the length of the subarray when using a spatial smoothing method, which was used to decorrelate the incoming signals. The subarray length was limited to half the length of the full array size in the ordinary MVB, while the proposed beamformer could cross over this limitation. The results demonstrated that the point spread function of the proposed beamformer was about 6.3 times narrower than the classic MVB, while the contrast was almost saved. These results were achieved with linear computational complexity by the proposed method, while it was cubic for the MVB. For a sample scenario, the proposed method needed only 1.8% of the required ops of the MVB.

Diagnosis of Fetal Abnormalities during the First Trimester.

The quality of prenatal diagnosis of fetal abnormalities has advanced with improved resolution of ultrasound imaging and cytogenetic/molecular analysis. In this article, we briefly review the history of diagnosing fetal abnormalities and the current status of prenatal diagnosis during the first trimester (up to the first 14 weeks' gestation), focusing especially on fetal malformations and chromosomal abnormalities. As for detectable morphological abnormalities, roughly half of all major structural anomalies including those in the central nervous system, cardiovascular system and gastrointestinal system can be detected, if not definitely diagnosed. For screening of chromosomal abnormalities, especially for trisomy 21, ultrasound soft markers such as increased nuchal translucency, maternal serum markers and their combinations have been implemented. More recently, non-invasive prenatal testing, by analyzing cell-free DNA in maternal serum, is now available to detect chromosomal abnormalities with higher predictability. Although invasive chorionic villus sampling offers definite diagnosis for chromosomal abnormalities during the first trimester, non-invasive diagnostic techniques are patient-friendly and promising in the future perspectives on prenatal diagnosis for chromosomal abnormalities.

Differentiation of Vascular Characteristics Using Contrast-Enhanced Ultrasound Imaging

Ultrasound contrast imaging has been used to assess tumour growth and regression by assessing the flow through the macro- and micro-vasculature. Our aim was to differentiate the blood kinetics of vessels such as veins, arteries and microvasculature within the limits of the spatial resolution of contrast-enhanced ultrasound imaging. The highly vascularised ovine ovary was used as a biological model. Perfusion of the ovary with SonoVue was recorded with a Philips iU22 scanner in contrast imaging mode. One ewe was treated with prostaglandin to induce vascular regression. Time-intensity curves (TIC) for different regions of interest were obtained, a lognormal model was fitted and flow parameters calculated. Parametric maps of the whole imaging plane were generated for 2 × 2 pixel regions of interest. Further analysis of TICs from selected locations helped specify parameters associated with differentiation into four categories of vessels (arteries, veins, medium-sized vessels and micro-vessels). Time-dependent parameters were associated with large veins, whereas intensity-dependent parameters were associated with large arteries. Further development may enable automation of the technique as an efficient way of monitoring vessel distributions in a clinical setting using currently available scanners.

High resolution ultrasonic imaging based on frequency sweep in both of transducer element domain and imaging line domain

We developed the super resolution FM-chirp correlation method (SCM) and its high frame rate version called synthetic aperture-SCM (SA-SCM) based on frequency sweep in order to improve the range resolution in ultrasound imaging. However, in these methods, discontinuities in the lateral direction tend to occur, because the SCM processing is performed line by line in the image. In addition, in array transducers, grating lobes are more likely to occur when the spatial resolution is increased using high-frequencies. Therefore, another version called SCM-weighted SA was proposed. In the SCM-weighted SA, in order to avoid the lateral discontinuities, first the SCM processing is performed on each echo received by each transducer element, and then the obtained SCM result is used as a weight for SA processing. The SCM-weighted SA can generate multiple B-mode images each of which corresponds to each carrier frequency, and the appropriate low frequency images among them have no grating lobes. While this plurality of B-mode images can be used as multi-frequency images, it can also be integrated as one high SNR image. In the present study, we propose a method to generate the integrated one B-mode image by applying SCM again in the line direction of the obtained multi-frequency images, which is called SCM-weighted SA-SCM. This method can further improve the range resolution.

An IEEE Single Precision Floating Point Arithmetic-Based Apodization Architecture for Portable Ultrasound Imaging System

Portable ultrasound systems are useful in point-of-care diagnostic. Improving the image contrast and spatial resolution over a large range of imaging depths while maintaining the minimum area and power are the desiderata in case of ultrasound systems. Adaptive apodization is used for obtaining high contrast and spatial resolution ultrasound images; however, the implementation of adaptive apodization in hardware consumes large area and power. In this paper, an adaptive algorithm is presented for obtaining good image contrast and resolution using low computational complexity. In the proposed apodization algorithm, minimum and maximum variance criteria and normalized cross-correlation are used to enhance the image contrast and spatial resolution over a large range of imaging depths. A resource optimized, IEEE single precision arithmetic-based architecture of the proposed method is also presented in this paper. Field II toolbox and the experimental data taken from the plane-wave imaging challenge in medical ultrasound are used for evaluating the performance of the proposed methods. Simulation and experimental results demonstrate that the proposed method provides better resolution coupled with the improved contrast performance than conventional dual apodization with cross-correlation methods. The architecture of the proposed method consumes 358.66-mW dynamic power and 1122.1 k NAND-2 equivalent gates are found to be in UMC 90-nm CMOS standard cell library. Implementation of the proposed method requires the calculation of inverse square root. A quadratic approximation-based inverse square root calculation method and its datapath to support IEEE single precision arithmetic are also presented. The datapath of the inverse square root calculator reduces the memory requirement up to 70% which need to be adopted in pursuit of higher performances.

Improvement of Performance Degradation in Synthetic Aperture Extension of Enhanced Axial Resolution Ultrasound Imaging Based on Frequency Sweep.

We are studying a method based on the carrier frequency sweep for axial high resolution ultrasonic imaging to provide the range resolution that corresponds to the carrier wavelength. The first proposal for this type of method was based on the focused pulse transmission. Then, to improve the frame rate, the method was extended to a synthetic aperture-type method that transmits divergent pulses. While the method is effective in terms of the frame rate, degradation of the enhanced axial resolution performance is a concern. Therefore, using finite element method simulations and simple experiments, the performance of the synthetic aperture method with high axial resolution is evaluated via comparison with the original method using focused pulses. The evaluation confirmed that the performance degradation of the synthetic aperture method is caused by weakness in the transmitted wave intensity and deterioration of the phase coherence in the reception beamforming. Based on this result, we propose a method that is less affected by the latter cause and show its effectiveness.

Unilateral Foot Drop by Bilateral Ganglion Cysts: An Imaging Approach to Diagnosis

Ganglion cysts are pseudocysts with no epithelial lining of their own. These are non- neoplastic lesions filled with gelatinous material and originate from tendon sheath, ligament, bursa, joint capsule or subchondral bone. Rarely, they may present in an intramuscular location, away from the joint with no synovial communication. Upper limb involvement is more common and such lesions are usually found on the hand, wrist and ankle. Despite their common occurrence, peripheral nerve compression due to these cysts is rare with cases of ulnar and median nerve compressions infrequently reported in the literature. In lower limb, dorsal surface of the foot is reported to be the most common site. Occurrence of ganglion cysts in lower limb causing compressive neuropathy is an even rarer combination. We report a case with unilateral common peroneal nerve palsy with incidentally detected bilateral intramuscular ganglion cysts. Even an extensive literature search did not reveal any such case report. The patient underwent high resolution ultrasound imaging for the possible cause of compression of common peroneal nerve. Incidentally, cystic lesions were identified in the intramuscular plane causing nerve compression in the right leg with similar lesions at the same location in the left leg. On the left side, patient was free of neuropathic symptoms as the nerve was seen passing between the cystic lesions, not getting compressed. The patient then underwent MR imaging with contrast and intramuscular ganglion was kept as the provisional diagnosis of the cystic lesion. Operative management was planned to relieve the compressive neuropathy and excision biopsy of the lesion proved it to be a ganglion cyst.

Early Ultrasound Fetal Parameters as a Predictor for Pregnancy Outcome: A Prospective Observational Cohort Study

Background Ongoing technological advancements have allowed the resolution of ultrasound imaging in the first trimester to evolve to a level at which early fetal development can be assessed and monitored in detail. Objective To find a relation between first-trimester ultrasound fetal measurements and adverse pregnancy outcomes. Subjects and Methods A prospective observational cohort study conducted on 500 pregnant women at 1st trimester attending ANC clinic of obs&amp; gyne. department of Al-Azhar university hospital (Assiut -Egypt). Ultrasound measurements of early fetal parameter GSD, CRL and YSD at 5-12 weeks of gestation were done. Results of measurements were classified into three classes, class A&lt;10th centile, class B 10th-90th centile and Class C&gt;90th centile. Patients were followed up throughout pregnancy to determine normal and abnormal outcomes in each class. Comparison between different classes was made to show association with abnormal pregnancy outcomes. Results Early fetal ultrasonographic parameters class A &amp; C were significantly associated with 1st, 2nd-trimester abortions, IUFD, APH and PROM (p&lt;0.001) with no significant association between these parameters and other pregnancy outcomes (p&gt;0.05). Conclusion Our study emphasizes the role of early ultrasound in predicting abnormal pregnancy outcomes it could be useful to obstetricians to anticipate adverse outcomes and being warned to manage prenatal care and delivery more appropriately. Recommendation Early fetal ultrasound should be used as a tool to predict pregnancy outcome so as to manage prenatal care and delivery more efficiently

Investigation of ultrasonic absorption in the MHz frequency range by silicon substrates with a built-in porous silicon layer

The present study is focused on the development and characterization of an innovative substrate to optimize the axial resolution of ultrasonic transducers on a silicon substrate that is dedicated to ultrasound imaging. The substrate must efficiently dampen wave propagation to avoid degradation of the axial resolution of ultrasound images. In this study, the proposed approach implements a silicon substrate with a built-in acoustic damping layer composed of porous silicon. Porous silicon layers with thicknesses of less than 100 µm and porosities varying from 27% to 62% were fabricated, and their substrate resonances were characterized. The experimental results obtained in the frequency range from 6 MHz to 10 MHz show that the substrate acoustic damping is controlled by adjusting the characteristics of the porous silicon layer; a significant damping of 70% is demonstrated with only 70 µm of porous silicon.

Developing gold nanotubes as photoacoustic contrast agents

Photoacoustic imaging (PAI) combines the spectral selectivity of laser excitation with the high resolution of ultrasound imaging, representing a noninvasive modality that holds remarkable potential for clinical translation. In particular, multispectral optoacoustic tomography has emerged has an innovative PAI technology, which enables high detection specificity by resolving multiple spectral signatures through tissues and accurately decomposing the biodistribution of relevant molecules from non-specific background contributions. Key criteria for developing PAI contrast agents include strong absorbance in the near-infrared (NIR) tissue transparent region and low toxicity. In this study, we have fabricated gold nanotubes (Au NTs) with controlled length and NIR absorption for the application as in vivo MSOT contrast agents. The length control relies on the synthesis of silver nanorod template under certain growth conditions. The Au NTs were coated with a layer of biocompatible polymer, poly(sodium 4-styrenesulfonate) (PSS), to ensure colloidal stability and low cytotoxicity. The PSS-Au NTs have shown excellent MSOT signal enhancement on tissue-mimicking phantom and in vivo, demonstrating the potential for further development towards a theranostic nanoplatform integrating PAI capability and therapeutic functions.

Increasing dielectric loss of a graphene oxide nanoparticle to enhance the microwave thermoacoustic imaging contrast of breast tumor.

Microwave-induced thermoacoustic imaging (MTAI) utilizes the high dielectric contrast of tissues in the microwave range, and, combined with the high resolution of ultrasound imaging, can noninvasively obtain anatomical and functional structure information. However, adequate contrast in certain indications (e.g., breast tumor in their early stages) can be difficult to achieve due to the minimal dielectric difference in the target tissues. A tumor specific targeting nanoparticle with high dielectric loss would enhance MTAI contrast in such applications. In this work, we propose a physics-principle-based technique that increases the dielectric loss of a nanoparticle by increasing its atomic defect to generate an amplified thermoacoustic signal. In principle, bovine serum albumin loaded on graphene oxide (GO) serves as a reductant to create additional vacancies in GO to produce more electric dipoles. Upon pulsed microwave irradiation, the defect dipoles are polarized repeatedly, causing transient heating and thermoelastic expansion, and ultimately generating an amplified acoustic wave. This hypothesis was tested in vitro and in vivo with a breast tumor animal model. The results demonstrate that the nanoparticle can effectively enhance the MTAI contrast of breast tumors. The physics-principle-based technique is likely to contribute to early breast tumor imaging.

Usefulness of Comprehensive High - Resolution Ultrasound Imaging in Dermatologic Field: Epidermal Cyst

Dermatologic ultrasound (US) has been growing rapidly in line with the development of more potent machines and high-frequency probes. The minimum frequency recommended for performing dermatologic examinations was 15 MHz...