ABSTRACT
We have demonstrated previously that the dielectric properties of myocardium at microwave spectrum are a sensitive indicator of its blood content, ischemia, and infarction. The purpose of this study is to validate the feasibility of microwave tomography for detection of myocardial infarction based on the differences in dielectric properties between normal and infarcted tissues. Excised canine heats with two weeks myocardial infarction were imaged. Tomographic imaging experiments were conducted using a three-dimensional (3D) microwave tomographic system operating at a frequency of 1.0 GHz. To obtain the images, we used 3D reconstruction algorithms. Images of excised canine hearts with myocardial infarction were obtained at a frequency of 1 GHz, applicable for whole body imaging. Microwave tomographic images were compared with anatomical slices. The comparison confirms that microwave tomography is capable of detection of myocardial infarction.
Subject(s)
Image Interpretation, Computer-Assisted/methods , Imaging, Three-Dimensional/methods , Microwaves , Myocardial Infarction/diagnosis , Myocardial Infarction/pathology , Tomography/methods , Animals , Dogs , Electric Impedance , Feasibility Studies , Heart/physiopathology , Myocardial Infarction/physiopathology , Myocardium/pathology , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
We studied dielectrical properties of canine myocardium during acute ischemia and hypoxia using dielectrical spectroscopy method at frequency spectrum from 100 kHz to 6 GHz. This study was conducted on a group of six canines with acute ischemia and seven canines with hypoxia. Hypoxia (10% for 30 min) decreases myocardial resistance (rho), while the dielectrical permittivity (epsilon') of the myocardial tissue remains statistically unchanged. Acute ischemia for 2 hr causes significant frequency-dependent changes in both epsilon' and rho of myocardial tissue. Myocardial resistance increases, while the sign and amplitude of changes in the myocardial epsilon' are frequency and time dependent. These observations open up an opportunity for assessing the properties of myocardial tissue using dielectrical spectroscopy as well as noninvasively with the help of imaging methods based on electrical impedance and microwave tomography.
Subject(s)
Electric Impedance , Heart/physiopathology , Hypoxia/physiopathology , Myocardial Ischemia/physiopathology , Spectrum Analysis/methods , Acute Disease , Animals , Dogs , Electromagnetic Fields , Hypoxia/complications , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
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.
