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In seismic, radar, and sonar imaging the exact determination of the reflectivity distribution is usually intractable so that approximations have to be applied. A method called synthetic aperture focusing technique (SAFT) is typically used for such applications as it provides a fast and simple method to reconstruct (3D) images. Nevertheless, this approach has several drawbacks such as causing image artifacts as well as offering no possibility to model system-specific uncertainties. In this paper, a statistical approach is derived, which models the region of interest as a probability density function (PDF) representing spatial reflectivity occurrences. To process the nonlinear measurements, the exact PDF is approximated by well-placed Extended Kalman Filters allowing for efficient and robust data processing. The performance of the proposed method is demonstrated for a 3D ultrasound computer tomograph and comparisons are carried out with the SAFT image reconstruction.

Ultrasound Computer Tomography (USCT) records the interaction of ultrasonic waves with an imaged object from many different angles. The main advantage of such a system is simultaneous recording of reflection, absorption and speed of sound images, and higher image quality with fast data acquisition. Until now, it was not feasible to build a 3D USCT due to the high demands on the required number of transducers, high data rate, and time consuming post-processing. The aim of this first experimental setup for 3D USCT was to analyze the feasibility for breast cancer diagnosis of such a system built with today’s technology and draw conclusions for future setups. The results of this system are presented and discussed in regard of data acquisition, image quality, and duration of image reconstruction. The main conclusion is that 3D USCT is feasible with today’s technology, if a sparse aperture or long DAQ times can be accepted. A setup for a second-generation 3D USCT with the main aim to image volunteers and carry out a small preclinical study is proposed.

At Forschungszentrum Karlsruhe an Ultrasound Computer Tomography system USCT) is under development for early breast cancer detection. To detect morphological indicators in sub-millimeter resolution, the visualization is based on a SAFT algorithm (synthetic aperture focusing technique). The current 3D demonstrator system consists of approx. 2000 transducers, which are arranged in layers on a cylinder of 18 cm diameter and 15 cm height. With 3.5 millions of acquired raw data sets and up to one billion voxels for an image, a reconstruction may last up to months. In this work a performance optimized SAFT algorithm is developed. The used software environment is MathWorks' MATLAB. Several approaches were analyzed: a plain M-code (MATLAB's native language), an optimized M-code, a C-code implementation, and a low-level assembler implementation. The fastest found solution uses an SIMD enhanced assembler code wrapped in the C-interface of MATLAB. Additionally a 10% speed up is gained by reducing the function call overhead. The overall speed up is more than one order of magnitude. The resulting computational efficiency is near the theoretical optimum. The reconstruction time is significantly reduced without losing MATLAB's comfortable development environment.

The point spread function (PSF) of an imaging system may be used as measure for the imaging quality. The PSF usually depends on position and an several other system parameters. Our current 3D imaging system for ultrasound computer tomography consists of a rotatable cylinder with approx. 2000 ultrasound transducers. 3D images are reconstructed by means of synthetic aperture focusing technique (SAFT) using all available emitterreceiver-combinations. No analytical solution exists for determining the spatially varying PSF for arbitrary placement of the transducers. This work derives a new numerical approach for the approximation of the 3D PSF for arbitrary transducer geometries including the beam pattern of the ultrasound transducers, a directional point scatterer model, damping of the breast and arbitrary pulse shapes. As an exemplary application the spatially varying 3D PSF of the current cylindrical geometry is analyzed under idealized conditions (point sources, no damping, and isotropic scattering) and compared to non-idealized results of the PSF analysis. The results show the necessity to take the system specific parameters into account for a realistic prognosis of 3D imaging performance.

At Forschungszentrum Karlsruhe, a new imaging system for early diagnosis of breast cancer is currently developed. The 3D Ultrasound Computer Tomography (USCT) is based on approx. 2000 ultrasound transducers which produce 20 GB of raw data consisting of 3.5 mio. A-scans (amplitude scans) for one image. The large number of A-scans, the large amount of data and the complex relationship between raw data and reconstructed image makes analysis, understanding and further development difficult for the scientists and especially for new employees and students. For this reason, an interactive graphical user interface (GUI) was developed using MATLAB. It integrates existent analysis methods and is easily extendable with new functionality via a plugin concept. The software provides several visualization functions for the raw data, the reconstructed 3D images, the USCT aperture and the relationships between them. The software shows the capability of MATLAB as programming language for numerical solutions as well as GUIs and complex software systems. It has a large benefit to the working group by integrating analysis methods and sharing them. The GUI and the visualization of the complex relationships of the USCT reduces the training period for new employees and students.

At Forschungszentrum Karlsruhe a 3D ultrasound computer tomograph (USCT) for breast cancer diagnosis is currently under development. For many applications, i.e. reconstruction of speed of sound maps, signal denoising,signal compression and calibration, it is necessary to detect pulses and their parameters (center frequency, bandwidth factor, time of arrival, phase and amplitude) accurately and robustly. The pulse detection is demanding due to low signal-to-noise ratios (SNR) caused by unfocused pulses from single emitters. Besides that angle dependent pulse shapes result in ultrasonic echoes which are similar in their center frequency but vary strongly in their bandwidth factor. Additionally, in sum 3.5 million A-scans (20 GB) are acquired, so that the pulse detection has to be fast and efficient. This is achieved by using a fast pre-classifler in order to separate the ultrasonic echoes from the non-white system noise of our system. The detected echoes are then passed individually to a parameter estimation method to determine pulse parameters accurately. An analysis of several classifiers resulted in an alternating decision tree which is both fast and accurate. Classification performance of 95% could be achieved as well as robust parameter estimation with non-white system noise if the SNR is larger than 3 dB. A comparative image reconstruction resulted in significantly sharper images.

For our current 3D demonstrator system for ultrasound computer tomography (USCT) a synthetic aperture based image reconstruction is implemented whose calculation time is in the order of days. Faster approximations might lead to large errors for our USCT setup which uses many multistatic emitter-receiver combinations. The aim of this work is the analysis of non-linear signal to image mapping for a cylindrical aperture and quantify the errors of computational less complex approximations. Four approaches with increasing computational complexity were implemented, tested with the cylindrical setup and compared to a commonly used linear transducer setup. For the linear aperture the second approximation leads to satisfying results. For the more diverging USCT setup a more accurate approximation is needed: the third approximation, which is still less computational expensive as the ground-truth implementation, gives satisfying results.

At Forschungszentrum Karlsruhe an ultrasound computer tomograph is developed for breast imaging in 3D. The aim of this project is the support of early diagnosis of breast cancer. Our current setup consists of a cylindrical tank assembled with 384 emitter and 1536 receiver elements which are grouped to 48 rectangular transducer array systems (TAS). It has been shown in previous work that the cylindrical aperture has major drawbacks in the vertical resolution. Given a new square TAS pattern with 4 emitters and 9 receivers, a new aperture for 160 TAS is derived which optimizes the image quality regarding three criteria. The optimization criteria regard the resolution of this 3D imaging system, the image contrast and utilization of the available ultrasound energy. An optimization with equal weighting of these criteria resulted in an 40% improvement of the resolution regarding the size and isotropy compared to the current cylindrical aperture. The resolution could be improved by 40% regarding the size and isotropy. Yet the contrast is degraded by 13%. Further work will be to find a reasonable weighting of the the three criteria. It could be shown that the presented method for aperture optimization makes this high-dimensional optimization problem feasible. The most important physical parameters like tissue attenuation, beam profile and scatterer profile, could be included to increase the authenticity of the results.

Am Forschungszentrum Karlsruhe wird ein neuer Ultraschall-Computertomograph (USCT) entwickelt, welcher die Brustkrebsdiagnose entscheidend verbessern soll. Zielsetzung ist die Optimierung des Verfahrens und des Rekonstruktionsalgorithmus ohne Hardwareanderung und durch kontrollierbare Experimente ohne Phantomaufbau. Voraussetzung dafur ist die hinreichende ubereinstimmung der Simulation mit dem realen Experiment. Unter Verwendung von Wave3000, einer kommerziellen Software zur Ultraschallsimulation, wurde in Kombination mit einem Interface die Moglichkeit geschaffen die Schallausbreitung und die Interaktion mit Gewebe in der USCT-Geometrie nachzubilden. Vergleiche von Experiment und Simulation ergaben eine hohe Ubereinstimmung und auch Bildrekonstruktionen lieferten viel versprechende Ergebnisse.

Ultrasound computer tomography (USCT) is an imaging method capable of producing volume images with sub-millimeter resolution and high image quality. The long term goal of the system under construction is 3D imaging for early breast cancer diagnosis. In this paper the first images of a clinical breast phantom are presented and discussed in respect to further modifications of our system

At Forschungszentrum Karlsruhe a 3D ultrasound computer tomograph (USCT) is currently under construction aimed at early breast cancer diagnosis. Ellipsoidal backprojection is applied to reconstruct 3D images. As USCT is a system used for imaging, there is a profound interest in analyzing the image resolution and image quality of this system, especially with respect to its system parameters such as number of the sensors, the geometry of the aperture, applied signal processing, etc. In this paper the results of first assessments of the resolution are presented. The resolution is evaluated in terms of the 2D full width at half maximum (2D FWHM) of the system's 3D point spread function (PSF). Slice images of 3D PSFs have been calculated to assess the spatial variability of the PSF within the current setup of the system. However, calculating these results is very time-consuming, thus an approximative approach for the analysis of the 3D PSF in XY and Z has been developed. This approach allows the analysis of the PSF while changing a variety of system parameters in real time. The long term goal of this project is the optimization of the system parameters with respect to the image quality