Showing papers by "Johan M. Thijssen published in 1994"

Acoustic velocity and attenuation of eye tissues at 20 MHz.

Abstract: The ultrasound velocity and frequency-dependent attenuation of human and porcine eye tissues (cornea, lens, retina, choroid, sclera, vitreous body) were measured in the frequency range from 17 to 23 MHz. The results for the ultrasound velocity were compared to values taken from the literature and appeared to be in the same range. A comparison made between the acoustic parameters of human and porcine eyes showed that the porcine eye can serve as an animal model for the human eye. A mathematical operation is proposed to extrapolate the attenuation to the lower frequencies that are commonly used in clinical equipment. Finally, a first attempt was made to investigate the age dependence of the acoustic parameters of human tissues: some tissues showed a significant age effect.

Correlation of histology and acoustic parameters of liver tissue on a microscopic scale

Abstract: The correlation of several acoustic parameters with histological features was investigated in healthy White New Zealander rabbit liver (n = 10). Thin sections (10 μm) were studied by means of a light microscope in combination with a digital image processing system. Adjacent thick sections (250μm) were studied by means of a custom-designed acoustic microscope. Markers of black silk suture material, that could be identified both optically and acoustically, enabled the spatial correlation of both imaging modalities. Acoustic images were reconstructed from the velocity of ultrasound, the attenuation at the central frequency (30 MHz), the attenuation spectral slope, the backscatter spectral slope and the backscatter at the central frequency. The measurements comprised the frequency range from 10 to 50 MHz, yielding a resolution of approximately 50 μm. From the thin sections (10μm) the local histological composition was obtained by digital segmentation techniques. The features that were segmented are: the collagen rich fibrous tissue content, the area lumina, the area interstitial spaces, the number density of nuclei and the area parenchymal tissue. Correlation techniques revealed that the main feature responsible for attenuation is collagen. There was a fair correlation between area lumina and attenuation, but this was caused by a high correlation between the collagen that surrounds the lumina, and attenuation. No correlation was found between any histological feature and backscatter parameters or velocity.

Ultrasonic spectroscopy of the porcine eye lens

Abstract: The purpose of the work is to measure and study the acoustic characteristics of the porcine eye lens and find correlations with chemical and optical parameters, obtained from literature. Ultrasonic spectroscopy was performed by using a scanning acoustic macroscope (frequency 20 MHz, resolution 150 μm). The transducer performed a two-dimensional scan over a central slice (1 mm thickness) of porcine lens (number of lenses = 10). A double transmission pulse-echo method was used to acquire the ultrasonic data from the lens. Two-dimensional images were reconstructed of the local ultrasound velocity and the frequency-dependent ultrasound attenuation. Axial and equatorial profiles of these parameters were calculated from the images. The acoustic parameters are not constant, but show a systematic dependence on the location within the lens. The profiles of the acoustic parameters are similar in shape to profiles of the protein and water contents of eye lens and to the profiles of the optical refractive index. A thorough quantitative correlation study is indicated, which should be based on detailed protein content data in porcine lenses.

A new method to correlate acoustic spectroscopic microscopy (30 MHz) and light microscopy

Abstract: A powerful new method is used to investigate the correlation between light microscopic and acoustic properties of biological tissues. Specimens of liver were sectioned into successive slices, 250 micrometers and 10 micrometers thick. The thick sections were investigated acoustically, the thin sections by means of light microscopy. Markers that could be detected and located, both optically and acoustically, were used to find and reconstruct corresponding regions in the acoustic and optical sections (2.5 x 2.5 mm). Parameter images were reconstructed from the sections investigated acoustically. The acoustic parameters were attenuation at 30 MHz, the slope of the attenuation spectrum (between 10 and 50 MHz), backscattering at 30 MHz, the slope of the backscattering spectrum (between 10 and 50 MHz) and the local ultrasound velocity. Acoustic images were obtained in the frequency range from 10 to 50 MHz, yielding a lateral resolution of about 50 micrometers. The sections for light microscopy were stained according to the Goldner trichrome staining technique. The histological composition was determined quantitatively, using digital image segmentation techniques. The percentage of collagen-rich fibrous tissue, luminal structure and interstitial spaces, and the number of nuclei were calculated for regions of 250 x 250 micrometers. These histological features were correlated with the acoustic parameters obtained from the corresponding regions in adjacent sections. It was thus possible to find the histological components responsible for acoustic parameters.