Time series analysis and its applications

Ultrasound image enhancement: A review

Under a contract with the National Cancer Institute, we have developed a research interface to an ultrasound system. This ultrasound research interface (URI) is an optional feature providing several basic capabilities not normally available on a clinical scanner. The URI can store high-quality beamformed radio-frequency data to file for off-line processing. Also, through an integrated user interface, the user is provided additional control over the B-mode receive aperture and color flow ensemble size. A third major capability is the ability to record and playback macro files. In this paper, we describe the URI and illustrate its use on three research examples: elastography, computed tomography, and spatial compounding

An ultrasound research interface for a clinical system

Errata - An ultrasound research interface for a clinical system

Breast ultrasound tomography has the potential to improve the cost, safety, and reliability of breast cancer screening and diagnosis over the gold-standard of mammography. Vital to achieving this potential is the development of imaging algorithms to unravel the complex anatomy of the breast and its mechanical properties. The solution most commonly relied upon is time-of-flight tomography, but this exhibits low resolution due to the presence of diffraction effects. Iterative full-wave inversion methods present one solution to achieve higher resolution, but these are slow and are not guaranteed to converge to the correct solution. Presented here is HARBUT, the hybrid algorithm for robust breast ultrasound tomography, which utilizes the complementary strengths of time-of-flight and diffraction tomography resulting in a direct, fast, robust and accurate high resolution method of reconstructing the sound speed through the breast. The algorithm is shown to produce accurate reconstructions with realistic data from a complex three-dimensional simulation, with masses as small as 4 mm being clearly visible.

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High-resolution imaging without iteration: a fast and robust method for breast ultrasound tomography.

A high precision mechanical add-on module was realized to implement a transmission tomography system around a commercial analog ultrasound system. The modular nature of the add-on lets it be used, however, more universally. Without enormous effort the module could be programmed to be coupled to a fully digital high end commercial ultrasound system. A Siemens Antares was used for this work, which allows the acquisition of RF data of high quality B-scans and tissue harmonic imaging (THI) over the Axius Direct Ultrasound Research Interface (URI). This possibility was exploited to explore some more intricate processing options for image compounding in addition to the conventional spatial compounding approach. Several compounding schemes were implemented. One of the two new strategies for compounding consists of calculation of a compound image from the THI data, as the latter is known to possess a better contrast and lateral resolution. While the RF data acquired from various transducer positions provides all the essential input for monostatic synthetic aperture focusing (SAFT), the other strategy was to implement SAFT imaging. The effect of inhomogeneous speed of sound was studies carefully and two different schemes were implemented to overcome the problems of image registration arising from it. The algorithms were tested on polypropylene fiber phantoms in water and ethylene glycol. While the monostatic synthetic aperture reconstruction technique was found to be best in enhancing signal to noise ratio, the speckle reduction was notably better for the THI compounding scheme than that of the conventional compounding strategy. The resulting spatial resolution of the compound images was comparable for the latter two cases and the former technique outperformed the other ones in this respect.

Spatial compounding with tissue harmonic images and monostatic synthetic aperture reconstruction

For the detection of breast cancer, ultrasound is conventionally used in addition to mammography However, ultrasound is highly operator-dependent since speckle, depth dependency and other artifacts (eg shadowing) affect image quality Full Angle Spatial Compounding (FASC) may overcome those limitations by superimposing ultrasound data acquired in one cross-sectional plane from aspect angles all around an object Furthermore, we showed in vitro that FASC also improves contrast perfusion imaging To apply FASC to breast imaging, we developed an add-on system to a conventional ultrasound scanner, integrated in a custom-made examination couch Here, we present first in-vivo results from test persons and patients with breast lesions

Ultrasound breast imaging using Full Angle Spatial Compounding: In-vivo results

For full angle spatial compounding, an object is imaged in one plane from multiple aspect angles and the obtained images are superimposed in correct geometric orientation. Thus, information about the distribution of speed of sound inside the object is required for a correction of individual images with respect to transit time and refraction of the ultrasonic waves. In this paper, we present a method to reconstruct such a distribution by a filtered backprojection of echo data from a reflector positioned behind the object. Using the reconstructed distribution, individual ultrasound images were corrected by a ray tracing algorithm before spatial compounding. Here, refraction was only accounted for at the outer boundary of the object, while inside only transit time was corrected. In vitro analyses are presented that prove the applicability of this approach.

9C-2 Reconstruction of Speed of Sound for a Correction of Transit Time in Full Angle Spatial Compounding

For contrast enhanced perfusion imaging semi-quantitative methods (such as the bolus-, replenishment- or depletion-method) are commonly used to analyze the dynamic changes in concentration of contrast agent induced by insonification. In order to apply these methods and to decrease artifacts from tissue nonlinearity, perfusion imaging is conducted using decreased transmit power. However, echo signals from deeper structures are often too weak to be successfully analyzed. Furthermore, shadowing artifacts may occur as a result of high concentration of contrast agent in the beam path. Thus, those semi-quantitative methods often fail or yield ambiguous diagnoses. Imaging an object (e.g., the female breast) from multiple viewing angles (spatial compounding) may overcome these issues. In addition, spatial compounding achieves an isotropic resolution and reduces speckle and further common artifacts. In this paper we present results obtained from a combination of spatial compounding with contrast-enhanced perfusion imaging. Applying the replenishment method, we extracted perfusion-related parameters and compared the conventional parametric images with the compound parametric images. We found that the compounded parametric images outperform the conventional images due to reduced noise and suppression of artifacts.

Full angle spatial compounding for improved replenishment analyses in contrast perfusion imaging: In vitro studies

PURPOSE: To test a system using ultrasound computed tomography (USCT) that superimposes ultrasound data acquired in one cross-sectional plane from multiple angles around the breast (Full Angle Spatial Compounding, FASC) and to reconstruct the distribution of the speed of sound in the breast (SoS reconstruction). MATERIALS AND METHODS: We developed a system combining a conventional ultrasound scanner with a PC-controlled mechanical setup integrated in a custom-made examination couch. In a feasibility study, 3 volunteers (age 26 – 74 years) and one patient with breast cancer were studied. Subjects were placed in the prone position on this couch, with the breast hanging in a water tank. The ultrasound probe was moved in several planes around the breast. A curved reflector that followed the movement of the probe behind the breast was used to calculate the SoS within the breast tissue. Echo-data was processed offline by custom-made software to calculate both FASC and SoS images. RESULTS: In FASC images a reduction of artifacts (i. e. shadowing of Cooper’s ligaments and irregular edges of inhomogeneous lesions) and speckles as well as clear visualization of the inner architecture of the breast was achieved. SoS images delivered further diagnostic information and helped to compensate for geometric distortions in the computed images. Difficulties in the visualization of lesions near the thoracic wall and/or the axillary are limitations of this technique. CONCLUSION: The first clinical results of USCT imaging have proven its feasibility as an automated and standardized technique for breast imaging.

N. Huttebrauker

Papers

Spatial compounding with tissue harmonic images and monostatic synthetic aperture reconstruction

Ultrasound breast imaging using Full Angle Spatial Compounding: In-vivo results

9C-2 Reconstruction of Speed of Sound for a Correction of Transit Time in Full Angle Spatial Compounding

Full angle spatial compounding for improved replenishment analyses in contrast perfusion imaging: In vitro studies

Ultrasound computed tomography in breast imaging: first clinical results of a custom-made scanner.