Current status and future technical advances of ultrasonic imaging

Lumen segmentation using a Mask R-CNN in carotid arteries with stenotic atherosclerotic plaque

In patients at high risk for ischemic stroke, clinical carotid ultrasound is often used to grade stenosis, determine plaque burden and assess stroke risk. Analysis currently requires a trained sonographer to manually identify vessel and plaque regions, which is time and labor intensive. We present a method for automatically determining bounding boxes and lumen segmentation using a Mask R-CNN network trained on sonographer assisted ground-truth carotid lumen segmentations. Automatic lumen segmentation also lays the groundwork for developing methods for accurate plaque segmentation, and wall thickness measurements in cases with no plaque. Different training schemes are used to identify the Mask R-CNN model with the highest accuracy. Utilizing a single-channel B-mode training input, our model produces a mean bounding box intersection over union (IoU) of 0.81 and a mean lumen segmentation IoU of 0.75. However, we encountered errors in prediction when the jugular vein is the most prominently visualized vessel in the B-mode image. This was due to the fact that our dataset has limited instances of B-mode images with both the jugular vein and carotid artery where the vein is dominantly visualized. Additional training datasets are anticipated to mitigate this issue.

The fractal derivative wave equation: Application to clinical amplitude/velocity reconstruction imaging

This paper proposes a dissipative acoustic wave equation in which the fractal derivative is employed to represent dissipation. The proposed model is derived from the viscoelastic constitutive relationship via the fractal derivative. It is noted that the fractal derivative is a local operator and avoids the expensive computational costs of non-local fractional derivative, which is popular in recent decades to describe frequency-dependent dissipation in acoustic wave propagation in soft materials. The proposed model is tested to simulate the clinical amplitude/velocity reconstruction imaging of breast tumors, where the reflecting plate is imaged as an elevated line in correspondence to tumor. Numerical experiments show that the present model is capable of indicating the size, position and quantity of tumors. The comparative study confirms that the fractal derivative acoustic wave equation has an advantage over the fractional derivative model regarding computational costs.

Stimuli-Responsive Soft Untethered Grippers for Drug Delivery and Robotic Surgery

Untethered microtools that can be precisely navigated into deep in vivo locations are important for clinical procedures pertinent to minimally invasive surgery and targeted drug delivery. In this mini-review, untethered soft grippers are discussed, with an emphasis on a class of autonomous stimuli-responsive gripping soft tools that can be used to excise tissues and release drugs in a controlled manner. The grippers are composed of polymers and hydrogels and are thus compliant to soft tissues. They can be navigated using magnetic fields and controlled by robotic path-planning strategies to carry out tasks like pick-and-place of microspheres and biological materials either with user assistance, or in a fully autonomous manner. It is envisioned that the use of these untethered soft grippers will translate from laboratory experiments to clinical scenarios and the challenges that need to be overcome to make this transition are discussed.

3D Reconstruction of Chick Embryo Vascular Geometries Using Non-invasive High-Frequency Ultrasound for Computational Fluid Dynamics Studies

Recent animal studies have provided evidence that prenatal blood flow fluid mechanics may play a role in the pathogenesis of congenital cardiovascular malformations. To further these researches, it is important to have an imaging technique for small animal embryos with sufficient resolution to support computational fluid dynamics studies, and that is also non-invasive and non-destructive to allow for subject-specific, longitudinal studies. In the current study, we developed such a technique, based on ultrasound biomicroscopy scans on chick embryos. Our technique included a motion cancelation algorithm to negate embryonic body motion, a temporal averaging algorithm to differentiate blood spaces from tissue spaces, and 3D reconstruction of blood volumes in the embryo. The accuracy of the reconstructed models was validated with direct stereoscopic measurements. A computational fluid dynamics simulation was performed to model fluid flow in the generated construct of a Hamburger-Hamilton (HH) stage 27 embryo. Simulation results showed that there were divergent streamlines and a low shear region at the carotid duct, which may be linked to the carotid duct's eventual regression and disappearance by HH stage 34. We show that our technique has sufficient resolution to produce accurate geometries for computational fluid dynamics simulations to quantify embryonic cardiovascular fluid mechanics.

High performance relaxor-based ferroelectric single crystals for ultrasonic transducer applications

Relaxor-based ferroelectric single crystals Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) have drawn much attention in the ferroelectric field because of their excellent piezoelectric properties and high electromechanical coupling coefficients (d₃₃∼2000 pC/N, kt∼60%) near the morphotropic phase boundary (MPB). Ternary Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PMN-PT) single crystals also possess outstanding performance comparable with PMN-PT single crystals, but have higher phase transition temperatures (rhombohedral to tetragonal T_rt, and tetragonal to cubic T_c) and larger coercive field E_c. Therefore, these relaxor-based single crystals have been extensively employed for ultrasonic transducer applications. In this paper, an overview of our work and perspectives on using PMN-PT and PIN-PMN-PT single crystals for ultrasonic transducer applications is presented. Various types of single-element ultrasonic transducers, including endoscopic transducers, intravascular transducers, high-frequency and high-temperature transducers fabricated using the PMN-PT and PIN-PMN-PT crystals and their 2-2 and 1-3 composites are reported. Besides, the fabrication and characterization of the array transducers, such as phased array, cylindrical shaped linear array, high-temperature linear array, radial endoscopic array, and annular array, are also addressed.

Modular Assembly Micro-Robots for Natural Orifice Transluminal Endoscopic Surgery

Surgical operations are progressively being performed using minimally invasive techniques. Natural Orifice Transluminal Endoscopic Surgery (NOTES) is a novel surgical technique that uses the natural orifices of the human body in order to approach the peritoneal cavity. There are two basic types of robotics for NOTES; the external robots that stay outside the patient but act inside the abdominal cavity, and the internal robots that stay and act in the abdomen. The internal robots could only be mini-robots. The development of modular assembling reconfigurable micro-robots is a revolutionary idea for the NOTES. Modular micro-robots consist of small subunits which could be assembled and construct a functional miniature robot. These surgical micro-robots may increase the possibility for true scarless tele-surgery. Although specific applications of intrabdominal surgical micro-robots are still in an early concept stage, the field is rapidly evolving. In the future, patients may be operated by specialized micro-robotic intrabdominal surgeons.

Ultrasound common carotid artery segmentation based on active shape model

Carotid atherosclerosis is a major reason of stroke, a leading cause of death and disability. In this paper, a segmentation method based on Active Shape Model (ASM) is developed and evaluated to outline common carotid artery (CCA) for carotid atherosclerosis computer-aided evaluation and diagnosis. The proposed method is used to segment both media-adventitia-boundary (MAB) and lumen-intima-boundary (LIB) on transverse views slices from three-dimensional ultrasound (3D US) images. The data set consists of sixty-eight, 17 × 2 × 2, 3D US volume data acquired from the left and right carotid arteries of seventeen patients (eight treated with 80 mg atorvastatin and nine with placebo), who had carotid stenosis of 60% or more, at baseline and after three months of treatment. Manually outlined boundaries by expert are adopted as the ground truth for evaluation. For the MAB and LIB segmentations, respectively, the algorithm yielded Dice Similarity Coefficient (DSC) of 94.4% ± 3.2% and 92.8% ± 3.3%, mean absolute distances (MAD) of 0.26 ± 0.18 mm and 0.33 ± 0.21 mm, and maximum absolute distances (MAXD) of 0.75 ± 0.46 mm and 0.84 ± 0.39 mm. It took 4.3 ± 0.5 mins to segment single 3D US images, while it took 11.7 ± 1.2 mins for manual segmentation. The method would promote the translation of carotid 3D US to clinical care for the monitoring of the atherosclerotic disease progression and regression.

Modular Assembly Micro-Robots for Natural Orifice Transluminal Endoscopic Surgery, the Future of Minimal Invasive Surgery

Surgical operations are progressively being performed using minimally invasive techniques. Natural Orifice Transluminal Endoscopic Surgery (NOTES) is a novel surgical technique that uses the natural orifices of the human body in order to approach the peritoneal cavity. There are two basic types of robotics for NOTES; the external robots that stay outside the patient but act inside the abdominal cavity, and the internal robots that stay and act in the abdomen. The internal robots could only be mini-robots. The development of modular assembling reconfigurable micro-robots is a revolutionary idea for the NOTES. Modular micro-robots consist of small subunits which could be assembled and construct a functional miniature robot. These surgical micro-robots may increase the possibility for true scarless tele-surgery. Although specific applications of intrabdominal surgical micro-robots are still in an early concept stage, the field is rapidly evolving. In the future, patients may be operated by specialized micro-robotic intrabdominal surgeons.

A review of localization systems for robotic endoscopic capsules

Obscure gastrointestinal (GI) bleeding, Crohn disease, Celiac disease, small bower tumors, and other disorders that occur in the GI tract have always been challenging to be diagnosed and treated due to the inevitable difficulty in accessing such a complex environment within the human body. With the invention of wireless capsule endoscope, the next generation of the traditional cabled endoscope, not only a dream has come true for the patients who have experienced a great discomfort and unpleasantness caused by the conventional endoscopic method, but also a new research field has been opened to develop a complete miniature robotic device that is swallowable and has full functions of diagnosis and treatment of the GI diseases. However, such an ideal device needs to be equipped with a highly accurate localization system to be able to exactly determine the location of lesions in the GI tract and provide essential feedback to an actuation mechanism controlling the device's movement. This paper presents a comprehensive overview of the localization systems for robotic endoscopic capsules, for which the motivation, challenges, and possible solutions of the proposed localization methods are also discussed.

Continuous wave ultrasonic Doppler tomography

In continuous wave ultrasonic Doppler tomography (DT), the ultrasonic beam moves relative to the scanned object to acquire Doppler-shifted frequency spectra which correspond to cross-range projections of the scattering and reflecting structures within the object. The relative motion can be circular or linear. These data are then backprojected to reconstruct the two-dimensional image of the object cross section. By using coherent processing, the spatial resolution of ultrasonic DT is close to an order of magnitude better than that of traditional pulse-echo imaging at the same ultrasound frequency.

Microrobots for minimally invasive medicine

Microrobots have the potential to revolutionize many aspects of medicine. These untethered, wirelessly controlled and powered devices will make existing therapeutic and diagnostic procedures less invasive and will enable new procedures never before possible. The aim of this review is threefold: first, to provide a comprehensive survey of the technological state of the art in medical microrobots; second, to explore the potential impact of medical microrobots and inspire future research in this field; and third, to provide a collection of valuable information and engineering tools for the design of medical microrobots.

Real-Time Three-Dimensional Ultrasound for Guiding Surgical Tasks

OBJECTIVE

As a stand-alone imaging modality, two-dimensional (2D) ultrasound (US) can only guide basic interventional tasks due to the limited spatial orientation information contained in these images. High-resolution real-time three-dimensional (3D) US can potentially overcome this limitation, thereby expanding the applications for US-guided procedures to include intracardiac surgery and fetal surgery, while potentially improving results of solid organ interventions such as image-guided breast, liver or prostate procedures. The following study examines the benefits of real-time 3D US for performing both basic and complex image-guided surgical tasks.

MATERIALS AND METHODS

Seven surgical trainees performed three tasks in an acoustic testing tank simulating an image-guided surgical environment using 2D US, biplanar 2D US, and 3D US for guidance. Surgeon-controlled US imaging was also tested. The evaluation tasks were (1) bead-in-hole navigation; (2) bead-to-bead navigation; and (3) clip fixation. Performance measures included completion time, tool tip trajectory, and error rates, with endoscope-guided performance serving as a gold-standard reference measure for each subject.

RESULTS

Compared to 2D US guidance, completion times decreased significantly with 3D US for both bead-in-hole navigation (50%, p = 0.046) and bead-to-bead navigation (77%, p = 0.009). Furthermore, tool-tip tracking for bead-to-bead navigation demonstrated improved navigational accuracy using 3D US versus 2D US (46%, p = 0.040). Biplanar 2D imaging and surgeon-controlled 2D US did not significantly improve performance as compared to conventional 2D US. In real-time 3D mode, surgeon-controlled imaging and changes in 3D image presentation made by adjusting the perspective of the 3D image did not diminish performance. For clip fixation, completion times proved excessive with 2D US guidance (> 240 s). However, with real-time 3D US imaging, completion times and error rates were comparable to endoscope-guided performance.

CONCLUSIONS

Real-time 3D US can guide basic surgical tasks more efficiently and accurately than 2D US imaging. Real-time 3D US can also guide more complex surgical tasks which may prove useful for procedures where optical imaging is suboptimal, as in fetal surgery or intracardiac interventions.

A new ultrasound imaging concept for laparoscopy in urology

Intraoperative imaging performed by a video laparoscope is the gold standard during laparoscopic resections of tumors in urology. In contrast to ultrasound, laparoscopes cannot provide the surgeon with crucial information that could improve surgical outcome. Therefore, we developed a new concept for ultrasound imaging through the back of a supine patient during laparoscopic interventions. In this article we present a mock-up system to answer initial questions that were raised by the concept. The results of the performed experiments show that the concept is feasible.

Ultrasound emitter localization in heterogeneous media

A novel algorithm to accurately determine the location of an ultrasound source within heterogeneous media is presented. The method obtains a small spacial error of 748 microm+/-310 microm for 100 different measurements inside a circular area with 140 mm diameter. The new algorithm can be used in targeted drug delivery for cancer therapies as well as to accurately locate any kind of ultrasound sources in heterogeneous media, such as ultrasonically marked medical devices or tumors.

Characterization of in vitro healthy and pathological human liver tissue periodicity using backscattered ultrasound signals

This work studied the periodicity of in vitro healthy and pathologic liver tissue, using backscattered ultrasound (US) signals. It utilized the mean scatterer spacing (MSS) as a parameter of tissue characterization, estimated by three methods: the spectral autocorrelation (SAC), the singular spectrum analysis (SSA) and the quadratic transformation method (SIMON). The liver samples were classified in terms of tissue status using the METAVIR scoring system. Twenty tissue samples were classified in four groups: F0, F1, F3 and F4 (five samples for each). The Kolmogorov-Smirnov test (applied on group pairs) resulted as nonsignificant (p > 0.05) for two pairs only: F1/F3 (for SSA) and F3/F4 (for SAC). A discriminant analysis was applied using as parameters the MSS mean (MSS) and standard deviation (sigmaMSS), the estimates histogram mode (mMSS), and the speed of US (mc(foie)) in the medium, to evaluate the degree of discrimination among healthy and pathologic tissues. The better accuracy (Ac) with SAC (80%) was with parameter group (MSS, sigmaMSS, mc(foie)), achieving a sensitivity (Ss) of 92.3% and a specificity (Sp) of 57.1%. For SSA, the group with all four parameters showed an Ac of 75%, an Ss of 78.6% and an Sp of 66.70%. SIMON obtained the best Ac of all (85%) with group (MSS, mMSS, mc(foie)), an Ss of 100%, but with an Sp of 50%.

Estimation of surface pose with a physically-based ultrasonic image model

State-of-the-art approaches to shape analysis in medical images use a variety of sophisticated models for object shape. We have developed an image model that permits the application of these approaches to ultrasonic images, with detailed methods for representing rough surfaces. Our physically-based, probabilistic image model incorporates the combined effects of the system point-spread function (PSF), the tissue microstructure, and the gross tissue shape. At each image pixel, the amplitude mean and variance are computed directly from the model, characterizing the combined influence of shape, microstructure, and system PSF. Calculation of the SNR0 is used to further classify each pixel as Rayleigh- or non-Rayleigh-distributed. This characterization was used here to generate a data likelihood representing any set of images of a given surface by a probability density conditioned on the surface pose, or rotation and translation. The utility of this likelihood was demonstrated by applying maximum likelihood estimation to infer the pose of a cadaveric vertebra from simulated images of its surface. Successful results were achieved using derivative-based optimization algorithms for a data set of only three images. With a quasi-Newton BFGS algorithm, error in 15 of 20 trials was less than 0.4 degrees in rotation and 0.2 mm in translation. Estimation was inaccurate in only 1 of 20 trials. These results illustrate the potential of a physically-based image model in a rigorous approach to image analysis and also serve as an example of quantitative assessment of the model via performance in a specific application.

Visualisation of 4-D colour and power Doppler data

Mechanically scanned, cardiac-gated, 4-D colour Doppler and power Doppler data were acquired and rendered using multiplanar slice display, surface-fitting (S-F) and direct volume rendering (DVR), with interactive viewpoint control or tool command language (Tcl)-scripted generation of animation sequences across the cardiac cycle. S-F applied the marching cubes algorithm within a YCbCr colour space to extract time-varying Doppler regions; supplementally generated surfaces enclosed all regions across the full cardiac cycle, partially to alleviate the problem of incomplete vessel filling. DVR used integrated intensity, maximum intensity and front-to-back projection; the latter applied an opacity function to the Cb, Cr and Y colour channels to control the appearance of the blood flow signal relative to the background B-mode image. Our most detailed display was a hybrid approach that combined multiplanar slicing and DVR.

Ultrasound tomography imaging of radiation dose distributions in polymer gel dosimeters: preliminary study

A novel imaging system for investigation of absorbed dose distributions in radiotherapy polymer gel dosimeters using ultrasound is introduced. A prototype transmission ultrasound computed tomography (UCT) imaging system is developed and evaluated. The imaging capabilities of the system are assessed through investigation of an irradiated polyacrylamide gel test phantom. Images based on transmitted signal amplitude and time of flight (TOF) of the ultrasonic signal through the phantom are reconstructed using a filtered backprojection technique. In general, the reconstruction of the square field in the TOF image was superior to the transmission image, however, transmission images displayed superior contrast to TOF images. The image quality achieved with this prototype system is promising and could be significantly enhanced through improvements, in particular through the development of more sophisticated experimental equipment. It is concluded that UCT is a viable technique for imaging absorbed dose distributions in polymer gel dosimeters and investigations are continuing to further improve the system.

Improvement in breast tumor discrimination by support vector machines and speckle-emphasis texture analysis

Recent statistics show that breast cancer is a major cause of death among women in developed countries. Hence, finding an accurate and effective diagnostic method is very important. In this paper, we propose a high precision computer-aided diagnosis (CAD) system for sonography. We utilize a support vector machine (SVM) to classify breast tumors according to their texture information surrounding speckle pixels. We test our system with 250 pathologically-proven breast tumors including 140 benign and 110 malignant ones. Also we compare the diagnostic performances of three texture features, i.e., speckle-emphasis texture feature, nonspeckle-emphasis texture feature and conventional all pixels texture feature, applied to breast sonography using SVM. In our experiment, the accuracy of SVM with speckle information for classifying malignancies is 93.2% (233/250), the sensitivity is 95.45% (105/110), the specificity is 91.43% (128/140), the positive predictive value is 89.74% (105/117) and the negative predictive value is 96.24% (128/133). Based on the experimental results, speckle phenomenon is a useful tool to be used in computer-aided diagnosis; its performance is better than those of the other two features. Speckle phenomenon, which is considered as noise in sonography, can intrude into judgments of a physician using naked eyes but it is another story for application in a computer-aided diagnosis algorithm.

Ultrasound evaluation of polymer gel dosimeters

A new method for the evaluation of radiotherapy 3D polymer gel dosimeters has been developed using ultrasound to assess the significant structural changes that occur following irradiation of the dosimeters. The ultrasonic parameters of acoustic speed of propagation, attenuation and transmitted signal intensity were measured as a function of absorbed radiation dose. The dose sensitivities for each parameter were determined as 1.8 x 10(-4) s m(-1) Gy(-1), 3.9 dB m(-1) Gy(-1) and 3.2 V(-1) Gy(-1) respectively. All parameters displayed a strong variation with absorbed dose that continued beyond absorbed doses of 15 Gy. The ultrasonic measurements demonstrated a significantly larger dynamic range in dose response curves than that achieved with previously published magnetic resonance imaging (MRI) dose response data. It is concluded that ultrasound shows great potential as a technique for the evaluation of polymer gel dosimeters.