ABSTRACT
Microwave tomographic approach is proposed to detect and image breast cancers. Taking into account the big difference in dielectrical properties between normal and malignant tissues, we have proposed using the microwave tomographic method to image a human breast. Because of the anatomical features of the objects, this case has to be referred to the tomography with a limited angle of observation. As a result of computer experiments we have established that multiview cylindrical configurations are able to provide microwave tomograms of the breast with a small size tumor inside. Using the gradient method, we have developed a computer code to create images of the three-dimensional objects in dielectrical properties on microwave frequencies.
Subject(s)
Breast Neoplasms/diagnosis , Image Processing, Computer-Assisted , Microwaves , Algorithms , Female , Humans , Mathematical Computing , Models, AnatomicABSTRACT
A model of dielectrical properties of cellular structures of a tissue has been proposed. Cellular structures were presented as a composition of membrane covered spheres and cylinders that do not interact with each other. No restrictions were applied to the thickness of cellular membranes. The model was further generalized into a case of electrically interacting cells. The difference in dielectrical properties calculated with the model of electrically noninteracting versus interacting cells is inversely dependent on frequency. At biological values of cellular volume fraction near 0.7 (packed configuration) the difference is about 10%-15% in resistance and in epsilon' for frequencies near 0.1 MHz. Experimental data for myocardial tissue and theoretical data, for both interacting and noninteracting models, reasonably agree at frequencies of 1-100 MHz.
Subject(s)
Heart/physiology , Microwaves , Models, Cardiovascular , Radio Waves , Animals , Biomedical Engineering , Cell Membrane/physiology , Dogs , Electric Conductivity , Electrophysiology , Female , MaleABSTRACT
The purpose of this study was to assess whether physiologic changes in canine myocardium due to coronary blood flow reduction, ischemia, and infarction could be detected by changes in dielectrical properties. Measurements were made in the frequency range of 0.2-6.0 GHz. Percent coronary blood flow reduction was linearly related to the decrease in epsilon" at frequencies of 0.2 GHz(R =-0.997) and 1.1 GHz (R =- 0.9987). In 2 h occlusions, increased conduction time in the infarct area mirrored the temporal changes in dielectrical properties. In 2-week-old infarctions differences, in epsilon' between normal and central infarct zones were statistically significant (P<0.05) for all frequencies. For epsilon" the differences between normal and central infarct zones were also significant for all frequencies (P<0.01). In conclusion, coronary blood flow reduction, ischemia, and infarction can be detected by microwave spectroscopy and potentially can form the basis for a physiologic microwave tomographic imaging system.
Subject(s)
Microwaves , Myocardial Infarction/pathology , Myocardial Infarction/physiopathology , Myocardial Ischemia/pathology , Myocardial Ischemia/physiopathology , Tomography/methods , Animals , Biomedical Engineering , Blood Flow Velocity , Disease Models, Animal , Dogs , Electrophysiology , Female , Male , Temperature , Time FactorsABSTRACT
The proposed dielectrical relaxation model of the myocardium in the microwave spectrum has been verified both on test solutions and on normal canine myocardium. Furthermore, the model was utilized to reconstruct the changes in tissue properties (including myocardial bulk resistance and water content) following myocardial acute ischemia and chronic infarction. It was shown that the reconstructed myocardial resistance and water content correlate dynamically with the process of the development of acute myocardial ischemic injury. In chronic cases the reconstructed resistance and water content of infarcted myocardium are significantly different from that of normal myocardium: the resistance is lower and water content is higher than in normal myocardium.
Subject(s)
Microwaves , Myocardial Infarction/pathology , Myocardial Infarction/physiopathology , Myocardial Ischemia/pathology , Myocardial Ischemia/physiopathology , Tomography/methods , Acute Disease , Animals , Biomedical Engineering , Biophysical Phenomena , Biophysics , Body Water/metabolism , Chronic Disease , Dogs , Electrophysiology , Female , Male , Models, CardiovascularABSTRACT
A method of image reconstruction in three-dimensional (3-D) microwave tomography in a weak dielectric contrast case has been developed. By utilizing only one component of the vector electromagnetic field this method allows successful reconstruction of images of 3-D mathematical phantoms. A prototype of the 3-D microwave tomographic system capable of imaging 3-D objects has been constructed. The system operates at a frequency of 2.36 GHz and utilizes a code-division technique. With dimensions of the cylindrical working chamber z = 40 cm and d = 60 cm, the system allows measurement of an attenuation up to 120 dB having signal-to-noise ratio about 30 dB. The direct problem solutions for different mathematical approaches were compared with an experimentally measured field distribution inside the working chamber. The tomographic system and the reconstruction method were tested in simple experimental imaging.
Subject(s)
Image Processing, Computer-Assisted/methods , Microwaves , Models, Cardiovascular , Tomography/methods , Electromagnetic Fields , Equipment Design , Humans , Nonlinear Dynamics , Phantoms, Imaging , Tomography/instrumentation , Vectorcardiography/methodsABSTRACT
Microwave tomographic imaging is one of the new technologies which has the potential for important applications in medicine. Microwave tomographically reconstructed images may potentially provide information about the physiological state of tissue as well as the anatomical structure of an organ. A two-dimensional (2-D) prototype of a quasi real-time microwave tomographic system was constructed. It was utilized to reconstruct images of physiologically active biological tissues such as an explanted canine perfused heart. The tomographic system consisted of 64 special antennae, divided into 32 emitters and 32 receivers which were electronically scanned. The cylindrical microwave chamber had an internal diameter of 360 mm and was filled with various solutions, including deionized water. The system operated on a frequency of 2.45 GHz. The polarization of the incident electromagnetic field was linear in the vertical direction. Total acquisition time was less than 500 ms. Both accurate and approximation methods of image reconstruction were used. Images of 2-D phantoms, canine hearts, and beating canine hearts have been achieved. In the worst-case situation when the 2-D diffraction model was used for an attempt to "slice" three-dimensional (3-D) object reconstruction, we still achieved spatial resolution of 1 to 2 cm and contrast resolution of 5%.
Subject(s)
Microwaves , Tomography/methods , Animals , Dogs , Heart/anatomy & histology , Image Processing, Computer-Assisted/methods , Models, Cardiovascular , Phantoms, Imaging , Sensitivity and SpecificityABSTRACT
Tissue samples ranging from 2 to 16 mm in thickness were irradiated at 1064 nm with energies ranging from 40 to 2400 J. Coagulation lesions of in vitro and in vivo experiments were subjected to temperature profiling and submitted for histology. Irreversible damage was calculated with the damage integral formalism, following the bioheat equation solved with Monte Carlo computer light-distribution simulations. Numerical temperature rise and coagulation depth compared well with the in vitro results. The in vivo data required a change in the optical properties based on integrating sphere measurements for high irradiance to make the experimental and numerical data converge. The computer model has successfully solved several light-tissue interaction situations in which scattering dominates over absorption.
ABSTRACT
Biosynthetic preparation of(2)H- and(13)C- labeled amino acids was studied using a leucine-producing mutant of the obligate methylotroph,Methylobacillus flagellatum. The strain was cultivated in various media containing(13)C- or(2)H-analogs of methanol. The total protein from each experiment was subjected to acid hydrolysis and converted into a mixture of dansyl amino acid methyl esters. The samples of excreted leucine were converted into methyl esters of dansyl and benzyloxycarbonyl derivatives. Electron impact mass spectrometry was performed to detect stable isotope enrichment of the amino acids. According to the mass spectrometric analysis it is feasible to use methylotrophic microorganisms for the preparation of(2)H- and(13)C- analogs of amino acids by labeled methanol bioconversion; the excreted amino acids can be convenient for express analysis as an indicator of isotopic enrichment of the total protein. The data obtained testified to a high efficiency of dansyl derivatization for mass spectrometric analysis of complex amino acid mixtures.
