George P. Tatsis

Computational modeling of three-dimensional microwave tomography of breast cancer

The 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, the authors 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 the authors 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, the authors have developed a computer code to create images of the three-dimensional objects in dielectrical properties on microwave frequencies.

Three-dimensional microwave tomography: initial experimental imaging of animals

The purpose of this study was to construct a microwave tomographic system capable of conducting experiments with whole scale biological objects and to demonstrate the feasibility of microwave tomography for imaging such objects using a canine model. Experiments were conducted using a three-dimensional (3-D) microwave tomographic system with working chamber dimensions of 120 cm in diameter and 135 cm in height. The operating frequency was 0.9 GHz. The object under study was located in the central area of the tomographic chamber filled with a salt solution. Experimentally measured attenuation of the electromagnetic field through the thorax was about -120 dB. To obtain images, we used various two-dimensional and 3-D reconstruction schemes. Images of the canine were obtained. In spite of imperfections, the images represent a significant milestone in the development of microwave tomography for whole body imaging and demonstrate its feasibility.

Three-dimensional microwave tomography: experimental prototype of the system and vector Born reconstruction method

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.

Two-dimensional computer analysis of a microwave flat antenna array for breast cancer tomography

In this paper, we report a two-dimensional computer simulation of a microwave flat antenna array for breast cancer tomography. This new technology promises reduction of X-ray exposure and easier access to peripheral areas of the breast. Using our version of the Newton algorithm, we studied two simple mathematical objects and a more sophisticated two-dimensional model of the breast that takes into account dielectric properties of different human tissues and malignant tumors. Our calculations show that, operating at 2 GHz, this device may give very reasonable images of tissues located up to 3-4 cm beneath the surface.

Microwave tomography: a two-dimensional Newton iterative scheme

In this paper, a variant of the Newton method, which uses a fast solution of the direct problem and a dual mesh, is proposed. Computational and physical experiments with simple two-dimensional high-contrast phantoms are discussed, and a full-scaled image of a two-dimensional mathematical model of a human torso is obtained.

Three-dimensional microwave tomography. Theory and computer experiments in scalar approximation

The results of computer simulated experiments in three-dimensional microwave tomography in scalar approximation are presented. The gradient method is employed to solve three-dimensional high-contrast microwave tomographic problems. A computer model for full-scale three-dimensional imaging has been created. Three-dimensional tomographic images of mathematical models of the human torso were obtained. Significant differences between two-dimensional and three-dimensional cases are emphasized. Some illumination schemes which can be applied in the three-dimensional case are discussed. A dependence of image quality on the number of vertically placed transmitters has been demonstrated. The computer simulation showed that three-dimensional full-scale human torso dielectrical properties images can be produced with acceptable computational time.

Spatial resolution of microwave tomography for detection of myocardial ischemia and infarction-experimental study on two-dimensional models

An experimental study of spatial resolution of microwave tomography was performed. Our microwave tomographic system with operational frequencies of 0.9 and 2.36 GHz and with signal-to-noise ratio of 30 dB allowed us to achieve a spatial resolution between 7.3-9.5 mm and 6.3-7.8 mm at the former and latter frequencies, respectively. It was shown in experiments, with structurally complicated objects, that spatial resolutions of about the same distances can be expected in a practical application of microwave tomography to detect areas of myocardial ischemia and infarction.

Three-dimensional microwave tomography: experimental imaging of phantoms and biological objects

Microwave tomographic experiments have been performed on a three-dimensional (3-D) phantom and excised canine heart using a 3-D system operating at frequency of 2.4 GHz. A modified gradient reconstruction approach has been employed for the 3-D image reconstruction. To compare two-dimensional (2-D) and 3-D approaches, we also performed 2-D image reconstruction using an approach based on the Newton method. Experimental data acquired on experimental phantoms were analyzed using both 2-D and 3-D reconstruction approaches. High-quality images were reconstructed using the 3-D approach. The reconstruction procedure failed when the 2-D approach was applied to reconstruct images of the 3-D object. An image of the dielectric properties of the excised canine heart was obtained using a 3-D reconstruction approach. Images successfully revealed a complex internal structure of the heart, including both right-hand side and left-hand side ventricles.

Microwave tomography: theoretical and experimental investigation of the iteration reconstruction algorithm

Results of experiments on the two-dimensional (2-D) quasi real-time microwave tomographic system have been reported. Various reconstruction possibilities of this system have been demonstrated on phantoms and canine hearts. The early utilized Rytov approximation is appropriate for low-contrast inverse problems. A new iterative reconstruction algorithm is proposed in this paper. The iterations converge to an accurate solution of the scalar Helmholtz-equation inverse problem in the case of higher contrasts. The goal of the reported study is an experimental and theoretical investigation of the proposed iteration algorithm. The influence on the quality of the reconstructed images and on the spatial resolution of such factors as the number of receivers, the accuracy of the scattered field measurements, and the dielectric contrast have been investigated.

Microwave spectroscopy of myocardial ischemia and infarction. 1. Experimental study

AbstractThe 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 ∈′′ at frequencies of 0.2GHz(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 ∈′ between normal and central infarct zones were statistically significant (P < 0.05) for all frequencies. For ∈′′ 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.