Biomedical subjects

J Ylitalo

Publications and source records attributed to J Ylitalo.

4 recordsLinked to original sources

PubMed1995

Comparison of linear array B-mode scanning and computed synthetic aperture ultrasonographic imaging.

The current trend in ultrasonography is toward digital systems that allow more freedom in beam formation and produce improved images. In this paper, conventional linear array B-mode sonograms of a tissue-mimicking phantom are compared to sonograms obtained with a synthetic aperture technique employing numerical image focusing. Sonograms in both cases were obtained using the same equipment to ensure identical imaging conditions. The computed synthetic aperture approach produced uniform spatial resolution of about 1 mm, which could not be achieved with the B-scan technique. In addition, the contrast resolution of the computed synthetic aperture method was found to be superior. We conclude that the computed synthetic aperture method is feasible for real-time clinical applications.

Algorithms↗

PubMed1990

Ultrasonic reflection mode computed tomography through a skull bone.

An ultrasonic reflection-mode CT method was applied to transskull imaging of brain. The method involves only a single transducer and a single scan to acquire data from the object. In reconstruction an ordinary Fourier slice theorem is applied. The average velocity changes of ultrasound due to the skullbone can be compensated. In experiments the object immersed in water was scanned by a wide-angle transducer through the viewing angle of 360 degrees. When imaging through bone a simplified approach was employed in which a piece of skullbone (thickness 3-4 mm) was attached firmly to the transducer. For comparison, the same object was then imaged without the skullbone. A two-point resolution better than 3 mm was achieved for transskull imaging using 1 MHz ultrasound. The experiments with brain specimens show that transskull images compare well with the images of the same specimens obtained without the bone interference. The findings are clinically significant in terms of pediatric brain diagnosis and postoperative follow up. Based on the method, a clinical prototype imager is currently being developed especially for diagnosis of children's brain diseases.

Adult↗

PubMed1989

Completely computer-focused ultrasound imaging. First clinical imaging results.

Completely computer-focused ultrasound imaging has been achieved using the UHB (ultrasound holographic B) method. This is a synthetic aperture method that combines ultrasonic holography and the conventional B-scan method. A wide-angle ultrasound burst (4 MHz) is transmitted into the object and the reflected echoes are measured as a function of the propagation time, but both the amplitude and phase angle are recorded, giving multiple one-dimensional holograms in a cross-sectional plane. This UHB data is rearranged to obtain one-dimensional wave fields, which represent the wave fronts reflected from each depth. The image is then reconstructed by propagating these wave fields backward to their original positions on the image using Fourier transform, a spectrum shift theorem, and inverse Fourier transform. The whole UHB image is obtained by calculating the intensity lines from these wave fields and by scanning these lines one by on the cathode ray tube (CRT) monitor. Following extensive laboratory testing with single and multielement transducers, special 32- and 64-element linear array transducers were fabricated, as was computer software capable of producing a UHB image in 40 seconds. Tissue imaging tests followed by clinical imaging of 30 patients showed that images obtained with this prototype compared favorably with those obtained by state-of-the-art conventional ultrasound scanners. The potential advantages of the new method are enhanced lateral resolution and the incorporation of phase information in tissue characterization. This would be important in diagnostic and intraoperative, especially neurosurgical, imaging.

Brain↗

PubMed1986

Three-dimensional ultrasound imaging of brain for neurosurgery.

The ultrasound study group at the Departments of Neurosurgery and Electrical Engineering, University of Oulu, has worked since 1980 on the development of ultrasound holographic B (UHB) imaging for clinical use. It has produced images of human brain based on synthetic focusing of data obtained by wide-angle nonfocused transducers. At the same time, clinical ultrasound B-imaging has been applied to brain and spinal cord surgery. On the basis of laboratory and clinical investigations, some of the possibilities of three dimensional ultrasound imaging in neurosurgery are presented. Particularly the role of supplementary three-dimensional ultrasound imaging data in computer-controlled brain surgery is stressed.

Animals↗