A. Pesavento

A time-efficient and accurate strain estimation concept for ultrasonic elastography using iterative phase zero estimation

In ultrasonic elastography, the exact estimation of temporal displacements between two signals is the key to estimating strain. An algorithm was previously proposed that estimates these displacements using phase differences of the corresponding base-band signals. A major advantage of these algorithms compared with correlation techniques is the computational efficiency. In this paper, an extension of the algorithm is presented that iteratively takes into account the time shifts of the signals to overcome the problems of aliasing and accuracy in the estimation of the phase shift. Thus, it can be proven that the algorithm is equivalent to the search of the maximum of the correlation function. Furthermore, a robust logarithmic compression is proposed that only compresses the envelope of the signal. This compression does not introduce systematic errors and significantly reduces decorrelation noise. The resulting algorithm is a computationally simple and very fast alternative to conventional correlation techniques, and the accuracy of strain images is improved.

Ultrasonic multifeature tissue characterization for the early detection of prostate cancer

The incidence of the prostate carcinoma is one of the highest cancer risks in men in the western world. Its position in cancer mortality statistics is also among the highest. The prostate carcinoma is only curable at an early stage. Therefore, early detection is extremely important. At an early stage the prostate carcinoma is limited to the prostate capsule and can hence be cured performing radical prostatectomy. The different types of diagnostics that are used today (digital rectal examination, transrectal ultrasound and PSA value analysis) lack reliability and are therefore not sufficient. Even a combination of these three methods is not sufficiently reliable. Diagnosis of the prostate carcinoma using multi-feature tissue characterization in combination with ultrasound allows the detection of tumors at an early stage. Also biopsy guidance and planning can be improved. This results in reduced costs for cancer treatment.

Prostatakarzinomdiagnostik durch Ultraschallelastographie

ZusammenfassungFrüherkennungsmaßnahmen haben im letzten Jahrzehnt zu einer verbesserten Prostatakarzinomdetektion geführt. Dies ist einerseits auf ein gestiegenes Krankheitsbewusstsein und andererseits auf eine verbesserte Diagnostik zurückzuführen. Das prostataspezifische Antigen (PSA) ist gegenwärtig der wichtigste diagnostische Parameter. Der transrektale Ultraschall konnte im Gegensatz dazu die in ihn gesetzten Erwartungen nicht erfüllen.Zielsetzung der vorliegenden Arbeit war es, ein System zu entwickeln und klinisch zu erproben, das es erlaubt, die Ultraschallelastographie hinsichtlich ihrer Einsatzmöglichkeiten in der Prostatakarzinomdiagnostik zu beurteilen.Eine rechnergestütze Aufarbeitung von hochfrequenten Ultraschallsignalen, die an einem handelsüblichen Ultraschallgerät mit technischen Modifikationen abgegriffen wurden, erlaubte uns eine erste klinische Evaluation. Die durchgeführten Untersuchungen an Patienten konnten zeigen, dass die Elastographie die Lokalisation und Ausdehnung eines Prostatakarzinoms genauer erfasst als es mit dem konventionellen Ultraschall möglich ist. Das gewählte Abbildungsverfahren nutzt eine unterschiedliche Gewebeelastizität zwischen Tumor und normalem Gewebe und erkennt auch Tumoren, die im B-Bild iso- oder hyperechoisch zur Darstellung kommen.AbstractDuring the last decade screening has improved prostate cancer detection. The main reason for this development is a better understanding of the margins of prostate-specific antigen (PSA) serum levels and the classification of PSA subtypes. In contrast, the introduction of transrectal ultrasound has not led to a measurable change in the prostate cancer detection rate. Our aim was to develop a novel ultrasound system for the acquisition of elastographic images of the prostate and evaluate the system regarding its clinical applicability. We used a technically modified conventional ultrasound system and analyzed the high-frequency ultrasonic data with a computer program. The first patient-based results suggest that elastography allows an accurate measurement of tumor size and localization in contrast to conventional transrectal ultrasound. Elastography visualizes different tissue elasticities to distinguish benign and cancerous tissue. Thus, we were able to even correctly classify prostate cancer lesions which are iso- or hyperechoic in B-mode sonography.

A new concept for a real-time ultrasound transmission camera

Ultrasound transmission imaging is an alternative promising modality because unlike x-ray transmission this concept is not ionizing and has a good contrast in tissue imaging. Our concept enables also real time imaging. Earlier designs of transmission cameras with a 2D-array and an acoustic lens suffered from high costs, large size and a limited imaging quality, which finally caused those cameras not to become a commercial product. We developed a novel compact low-cost ultrasound transmission camera. With a center frequency of 3 MHz a resolution of 1 mm in both lateral dimensions was achieved over a field of view of 80/spl times/80 mm/sup 2/. Real time images of moving joints and tendons are displayed with a frame-rate of 25 1/s. The major fields of application are orthopedics, pediatrics and diagnosis of rheumatic arthritis.

Compression of ultrasonic RF data

A compression algorithm is presented, which utilizes the special properties of ultrasonic radio frequency (RF) data. The compression is done in two steps: First, linear predictive coding (LPC) is applied, using an one-step-predictor. Further, the remaining error of the prediction is stored using only the necessary word length to store the signal. A lossy extension of the algorithm is presented, which stores only the upper bits of the error signal. The algorithm has been tested with both, data of a speckle phantom and in vivo data. The data could be compressed to approximately 30-55% of the original data size using the lossless algorithm. In comparison, a conventional compression tool achieves 65-75 % of the original data size.

Time-efficient and exact algorithms for adaptive temporal stretching and 2D-correlation for elastographic imaging using phase information

Recently, we developed an algorithm for fast and accurate time shift measurement using an iterative algorithm which calculates the time shift of two signals by iteratively seeking the zero of the phase of the complex correlation function. Typically only 2 or 3 iterations are needed. With this contribution we extended the algorithm to perform an estimation and correction of lateral displacements and adaptive temporal stretching. Both significantly reduce the noise of the strain estimation.

Three-dimensional strain imaging and related strain artifacts using an ultrasonic 3D abdominal probe

Presents a new system for fast and efficient acquisition of ultrasonic three-dimensional data sets for strain imaging. The authors apply their technique to a typical strain imaging phantom which consists of a soft sponge with a hard inclusion. With this set-up they demonstrate the applicability of the proposed system. Using this system they demonstrate the presence of a three-dimensional strain artifact.

Ultrasonic reflection tomography and tomographic parameter extraction for post-discotomic scarring diagnostics

An ultrasonic imaging system is presented for diagnostics of post discotomic scarring. The system consists of a conventional B-mode imaging system, using a 5 MHz sector scanner. The scanner is laterally moved over the patients back along a linear line. Thus several images of the same cross sectional plane are acquired by sampling the RF echo data. This data has been used for both, spatial compounding of the B-mode images and multidirectional extraction of the spectral parameters attenuation and backscattering.

Ultrasonic Reflection Tomography of Post-Discotomic Scarring

Up to 40% of all back surgery patients suffer from significant post-operative relapsing complaints frequently caused by scarring. Despite modern MR imaging systems there is still al lack of reliable screening diagnostics. Furthermore the image quality of conventional B- scans suffers from low contrast and shadows.

Neuro-fuzzy inference system for ultrasonic multifeature tissue characterization for prostate diagnostics

The incidence of the prostate carcinoma is one of the highest cancer risks in men in the western world. Its position in cancer mortality statistics is also among the highest. The different types of diagnostics that are used today lack reliability and are therefore not sufficient. Diagnosis of the prostate carcinoma using multifeature tissue characterization in combination with ultrasound allows the detection of tumors at an early stage and thus can aid the conducting physician in finding a diagnosis. Spatially resolved parameters and contextual information are used for the classification. Next to hypo- and hyperechoic tumors, also isoechoic tumors can be visualized.