Showing papers by "Johan M. Thijssen published in 1992"

Echographic Image Processing

Abstract: Publisher Summary The introduction of the concept of gray-scale echography and the development of scan converters for echographic imaging enabled the display of parenchymal tissues in addition to the outlining of the gross anatomy of organs. By using a simplified concept of the biological tissue, which is generally called an “acoustic tissue model,” the interaction mechanisms of ultrasound with tissue can be formulated analytically. The attenuating and backscattering characteristics may then be assessed quantitatively. Moreover, the involvement of the equipment performance and of the attenuation in the acquired echosignals can be compensated for. This chapter analyzes the echographic images resulting from these processing steps. The image analysis yields statistical texture descriptors that have been shown to be relevant for improving echographic diagnosis. The method of processing of B-mode (i.e., 2-dimensional) echograms is either to modify the original, preprocessed images for enhancing the visual diagnosis or else is used to generate parametric images.

Effects of tissue processing techniques in acoustical (1.2 GHz) and light microscopy.

Abstract: In this study the influence of various tissue processing and staining techniques on the acoustical properties of liver tissue was investigated. A qualitative study was performed using ultrasound attenuation as the imaged parameter of a combined optical/acoustical microscope with a 1.2 GHz transducer. Images were made of three sets of adjacent liver sections (6 μm in thickness) which were prepared in ten different ways: fixed by alcohol or formalin; stained by hematoxylineosin (HE), toluidine blue (TB) or non-stained; sectioned by a cryostat or by a paraffin microtome. It was concluded that the images obtained from cryostat sections were of much higher quality than those from paraffin sections. Images obtained from sections that were sectioned while embedded in paraffin displayed no detail at all. No consistent effect was noticed with respect to staining by HE or TB. Alcohol fixed sections gave more detailed images than formalin fixed sections. Formalin fixation in combination with cryostat sectioning yielded many cytoplasmic vacuoles.

In vitro classification of gallstones by quantitative echography.

Abstract: Gallstones (n = 20) were classified by dual energy Computer Tomography (CT) into three main classes: pure cholesterol stones (I), combination stones (II) and calcium stones (III). Further subclassification was possible by using morphological criteria. The acoustic measurements that were performed were measurements of the velocity of sound, the attenuation coefficient slope with frequency and intercept at 4.5 MHz, the attenuation coefficient slope per unit of time, the backscattering characteristics, and the appearance of B-mode echograms. The velocity of sound in calcium stones (c = 1695 ± 107 m/s) was distinctly lower than in those containing some cholesterol (c > 2000 m/s). The attenuation coefficient slope ranged from 4.3 to 16.2 dB/cm MHz, the 4.5 MHz intercept from 21 to 66.2 dB/cm. The lowest values were found for the pure cholesterol stones (class IA), the highest values for subclass IIB (combination stones with shell). The attenuation coefficient slope per unit of time was distinctly lower ( 0.64 dB/μs MHz). The backscattering spectrum was approximated by a straight line fit, and the slope for the cholesterol stones was lower than for the combination and calcium stones ( 1.0 dB/MHz, respectively). The latter two parameters were assessed by in vivo applicable methods. The front echo level was found to be more than 5 dB higher for class IIB as compared to the other classes, while the spectral backscatter level at 4.5 MHz was considerably higher for both classes IIB and III. The B-mode echograms showed that a strong front echo in combination with a strong attenuation of the remaining echo signals was mainly found for stones of classes IIB and III. A significant difference between the group of stones that are suitable for lithotripsy and dissolution treatment (classes IA, IB and IIA) and the nontreatable calcium-containing stones (classes IIB and III) was found for the velocity of sound (p < 0.01), the attenuation coefficient slope per time unit (p < 0.10), the slope of the backscattering spectrum (p < 0.05) and the 4.5 MHz intercept (p < 0.01). B-mode classification yielded no complete distinction of these two groups of stones. It can be concluded that in vivo assessment of quantitative characteristics (front reflection, backscattering characteristics, attenuation coefficient slope per unit of time) in combination with the B-mode characteristics might be useful for in vivo gallstone classification.

Preparation Techniques in Acoustical and Optical Microscopy of Biological Tissues, a Study at 5 MHz and 1.2 GHz

Abstract: A great number of studies has been performed on the estimation of acoustical properties of tissues in vitro. A problem which arises when tissues are investigated in vitro is autolysis which causes gaseous inclusions in the tissue and a degradation of the tissue (Bamber and Nassiri 1985). This can be solved by fixation of the tissue immediately after excision. Bamber et al. (1979) investigated the influence of various fixatives on the acoustic parameters of tissue. Presently there is a tendency to apply higher frequencies to enhance the resolution of the acoustical images. With acoustic microscopes it is possible to image sections at a cellular level. For this purpose the thickness of sections should be 2–10 μm. The standard cutting techniques which are used for optical microscopy should be employed then. In the studies presented here the influence of diverse fixatives and the preparation needed for various cutting techniques on the acoustic properties of liver tissue and on the quality of the images of an acoustic microscope are investigated. A quantitative study was performed at 5 MHz and a qualitative study at 1.2 GHz.