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.

In order to decrease artifacts from tissue, contrast enhanced perfusion imaging is usually conducted using low transmit power (low MI). However, with low MI echo signals from deeper structures are weak and often miss higher harmonics due to attenuation. Furthermore, shadowing artifacts may occur as a result of high concentration of contrast agent. Imaging an object (e.g. female breast) from multiple angles of view (spatial compounding) may overcome this issue. In addition, spatial compounding achieves an isotropic resolution and reduces speckle and further common artifacts. Here, first in-vitro results of contrast enhanced spatial compounding are presented

2E-6 Contrast Enhanced Perfusion Imaging by means of Spatial Compounding

For semiquantitative analyses of tissue perfusion using contrast-enhanced ultrasound the acquisition and processing of time intensity curves (TIC) is required. These TICs can be computed for each pixel of an image plane, yielding parametric images of classification numbers like "blood volume" and "flow rate." The expenditure of time for data acquisition and analysis typically limits semiquantitative perfusion imaging to a single image plane in 2-D. 3-D techniques, however, provide a higher diagnostic value since more information (e.g., of an entire lesion) is obtained. Moreover, spatial compounding, being a 2-D-technique where an object is imaged from different viewing angles, is known to improve image quality by reducing artifacts and speckle noise. Both techniques, 3-D and compounding, call for optimized acquisition and processing of TICs in several image planes (3-D) or in several (overlapping) sections of the same image plane (compounding) to decrease the time needed for data acquisition. Here, an approach of interleaved imaging is presented which is applicable, among others, to contrast perfusion imaging using the replenishment method. The total acquisition time is decreased by sequentially scanning image planes twice for short time spans-first, immediately after microbubble destruction to record the initial rise of the TICs, and second, a sufficient time thereafter to assess final values of the TIC. Data from both periods are combined to fit a model function from which parameters are extracted such as perfusion rate and blood volume. This approach was evaluated by in vitro measurements on a perfusion-mimicking phantom for both, individual images such as would be used for volume reconstruction in 3-D and compound images obtained from full angle spatial compounding (FASC, 360deg). An error analysis is conducted to derive the deviation of the extracted parameters of the proposed method compared with the conventional one. These deviations are entailed by a reduction in acquisition time of the proposed method, which can be adjusted by several parameters, depending on the prevailing flow. Optimization strategies are proposed to find optimal values for those settings.

A method to expedite data acquisition for multiple spatial-temporal analyses of tissue perfusion by contrast-enhanced ultrasound

Previous research showed that 2D refraction and time of flight (TOF) corrections in full angle spatial compounding (FASC) can improve image quality significantly. In this paper we focus on three dimensional beamline corrections (i.e. TOF and refraction) in 3D FASC. A tissue mimicking phantom was imaged using a conventional ultrasound scanner and a custom made mechanical applicator. The phantom contains a reservoir, filled with an NaCl solution to realize an inhomogeneous distribution of speed of sound (SOS). Two wires are placed inside the reservoir to verify the system's ability to image 3D structures with sub-wavelength dimensions. Pulse-echo-data was recorded fully around the object and in multiple cross-sectional planes. Via a reflector the SOS distribution in the imaged volume was reconstructed with the algebraic reconstruction technique (ART). In a second compounding process ultrasound beamlines were corrected in 3D for refraction at the surface and TOF inside the phantom using the reconstructed SOS distribution. Finally, corrected volume data sets from all viewing angles were superimposed to form a new FASC volume data set, corrected for refraction and TOF. With this method, spatial courses of thin structures can be imaged in 3D, with suppression of double line artifacts and correction of geometrical distortions.

Refraction and time of flight corrections in 3D ultrasound computed tomography

For sequential perfusion measurements in several image planes with replenishment method, we propose a fast technique by consecutively scanning respective image planes twice: Firstly using only a short period of imaging pulses after micro- bubble destruction to assess slope and secondly using few imaging pulses to assess final value. Both scans are combined to extract perfusion rate and blood volume.

P5B-1 A Fast Method for Data Acquisition in Contrast Replenishment Analyses

In a project of the Ruhr Center of Excellence for Medical Engineering at the Ruhr University Bochum, a system was developed for ultrasound computed tomography of the female breast. A high precision mechanical system was realized to implement a tomography system around a commercial ultrasound scanner [1]. With this setup ultrasound data was acquired in reflection mode to generate a 360° compound scan of a flow mimicking phantom fed with contrast agent. In clinical diagnostics contrast agent imaging gives access to parameters like perfusion and vascularization. Native spatial compounding achieves an isotropic resolution and reduces speckle and artefacts. Combining both techniques limitations of common contrast enhanced imaging (depth dependency, shadowing etc.) can be overcome efficiently. In this paper, first in-vitro results of contrast enhanced ultrasonographic spatial compounding are presented.

N. Huttebrauker

Papers

2E-6 Contrast Enhanced Perfusion Imaging by means of Spatial Compounding

A method to expedite data acquisition for multiple spatial-temporal analyses of tissue perfusion by contrast-enhanced ultrasound

Refraction and time of flight corrections in 3D ultrasound computed tomography

P5B-1 A Fast Method for Data Acquisition in Contrast Replenishment Analyses

Ultrasonographic Spatial Compounding for Contrast Agent Imaging