Michael Zapf

Realization of an optimized 3D USCT

A promising candidate for improved imaging of breast cancer is ultrasound computer tomography (USCT). Current experimental USCT systems are still focused in elevation dimension resulting in a large slice thickness, limited depth of field, loss of out-of-plane reflections, and a large number of movement steps to acquire a stack of images. 3DUSCT emitting and receiving spherical wave fronts overcomes these limitations. We built an optimized 3DUSCT with nearly isotropic 3D point spread function, realizing for the first time the full benefits of a 3D system. The 3DUSCT II is based on a semi-ellipsoidal transducer holder cut from polyoxymethylene. The aperture is implemented together with water supply, disinfection unit, temperature control, and movement mechanics in a patient bed. 2041 transducers are mounted in the aperture holder grouped into transducer array systems with embedded amplifiers and emitter electronics. The data acquisition is carried out with 480 parallel channels at 20MHz and with 12 bit resolution. 3.5 million A-Scans with 20 GByte of raw data are acquired for one breast volume. With data acquisition time of less than two minutes for one breast volume, the new system enables the next step of our research: a first clinical study.

P3D-5 Aperture Optimization for 3D Ultrasound Computer Tomography

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.

A comprehensive comparison of GPU- and FPGA-based acceleration of reflection image reconstruction for 3D ultrasound computer tomography

As today’s standard screening methods frequently fail to diagnose breast cancer before metastases have developed, earlier breast cancer diagnosis is still a major challenge. Three-dimensional ultrasound computer tomography promises high-quality images of the breast, but is currently limited by a time-consuming image reconstruction. In this work, we investigate the acceleration of the image reconstruction by GPUs and FPGAs. We compare the obtained performance results with a recent multi-core CPU. We show that both architectures are able to accelerate processing, whereas the GPU reaches the highest performance. Furthermore, we draw conclusions in terms of applicability of the accelerated reconstructions in future clinical application and highlight general principles for speed-up on GPUs and FPGAs.

3D ultrasound computer tomography of the breast: A new era?

A promising candidate for imaging of breast cancer is ultrasound computer tomography (USCT). The main advantages of a USCT system are simultaneous recording of reproducible reflection, attenuation and speed of sound volumes, high image quality, and fast data acquisition. The here presented 3D USCT prototype realizes for the first time the full potential of such a device. It is ready for a clinical study. Full volumes of a breast can be acquired in four minutes. In this paper images acquired with a clinical breast phantom are presented. The resolution and imaged details of the reflectivity reconstruction are comparable to a 3 tesla MRI volume of the phantom. Image quality and resolution is isotropic in all three dimensions, confirming the successful implementation experimentally.

Improvement of 3D ultrasound computer tomography images by signal pre-processing

Ultrasound computer tomography using synthetic aperture focusing technique is sensitive to phase aberration errors. We propose a signal preprocessing method for coherent imaging, which can take the system specific phase aberration into account. The method detects local maxima in the envelope of a matched filtered signal and convolutes the result with a truncated difference of sinc-functions, where the main lobe is scaled to represent the phase aberration. For our system we could show that reflectivity images reconstructed such pre-processed signals are approximately within a factor two of the ideal resolution, while increasing the contrast by a factor of 30.

2J-2 3D Ultrasound Computer Tomography: Results with a Clinical Breast Phantom

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

Hardware setup for the next generation of 3D Ultrasound Computer Tomography

We describe the second generation of a 3D-Ultrasound Computer Tomography (USCT) system. After we achieved in the first generation a device with sub-wavelength resolution and three imaging modalities (reflection, attenuation, speed of sound) and tested it with static phantoms, we developed a device for in-vivo imaging. In the new system the geometry of transducers and their spatial distribution is optimized in respect to uniformity and high value of: contrast, resolution, and illumination. Furthermore we developed new electronics which allows faster DAQ (≤ 2 min) and contains larger and faster FPGAs to use their processing power for data pre-processing.

Comparing different ultrasound imaging methods for breast cancer detection

Ultrasound is frequently used to evaluate suspicious masses in breasts. These evaluations could be improved by taking advantage of advanced imaging algorithms, which become feasible for low frequencies if accurate knowledge about the phase and amplitude of the wave field illuminating the volume of interest is available. In this study, we compare five imaging and inversion methods: time-of-flight tomography, synthetic aperture focusing technique, backpropagation, Born inversion, and contrast source inversion. All methods are tested on the same full-wave synthetic data representing a 2-D scan using a circular array enclosing a cancerous breast submerged in water. Of the tested methods, only contrast source inversion yielded an accurate reconstruction of the speed-ofsound profile of the tumor and its surroundings, because only this method takes effects such as multiple scattering, refraction, and diffraction into account.

Sound-speed image reconstruction in sparse-aperture 3-D ultrasound transmission tomography

The paper is focused on sound-speed image reconstruction in 3-D ultrasound transmission tomography. Along with ultrasound reflectivity and the attenuation coefficient, sound speed is an important parameter which is related to the type and pathological state of the imaged tissue. This is important in the intended application, breast cancer diagnosis. In contrast to 2-D ultrasound transmission tomography systems, a 3-D system can provide an isotropic spatial resolution in the x-, y-, and z-directions in reconstructed 3-D images of ultrasound parameters. Several challenges must, however, be addressed for 3-D systems-namely, a sparse transducer distribution, low signal-to-noise ratio, and higher computational complexity. These issues are addressed in terms of sound-speed image reconstruction, using edge-preserving regularized algebraic reconstruction in combination with synthetic aperture focusing. The critical points of the implementation are also discussed, because they are crucial to enable a complete 3-D image reconstruction. The methods were tested on a synthetic data set and on data sets measured with the Karlsruhe 3-D ultrasound computer tomography (USCT) I prototype using phantoms. The sound-speed estimates in the reconstructed volumes agreed with the reference values. The breast-phantom outlines and the lesion-mimicking objects were also detectable in the resulting sound-speed volumes.

First results of a clinical study with 3D ultrasound computer tomography

The KIT 3D USCT was tested in a pilot study on ten patients. The primary goals of the pilot study were to test the USCT device, the data acquisition protocols, the image reconstruction methods and the image fusion techniques in a clinical environment. The study was conducted successfully; the data acquisition could be carried out for all patients with an average imaging time of six minutes per breast. First reconstructions provide promising images. Overlaid volumes of the modalities show qualitative and quantitative information at a glance. The results led to further optimization of the system and the data acquisition protocol.