Noninvasive Magnetic Sensing of Human Prostate Tumor
Despite the ability of noninvasive electromagnetic bioimpedance methods to measure low contrast changes in tissue, a perennial problem has been the precise localization of the change. Generally, the interrogation or sampling volume is gauged by the diameter of the coil used to impart the electrical signal to the tissue. Because of the intervening tissue between the coil and the region under study (e.g., skin, muscle, bone), it is difficult to precisely locate the depth of the physiological change since the conductance (or impedance) of the intervening tissue is also measured. Traditionally, the signal from a receiving coil is a broadly peaked function with poor spatial resolution and no definitive electrical conductivity (or impedance) data specific to the different kinds of tissue under illumination. Additionally, bioimpedance measurements have never been used to detect prostate tumors.
It is therefore an object of the invention to provide a bioimpedance measurement apparatus for detecting prostate tumors. It is another object of the invention to provide a bioimpedance measurement apparatus that is able to distinguish between tumors and non-tumors, cancerous tumors and benign tumors, edema and non-edema, and between fast-growing tumors and slow-growing tumors. It is a further object of the invention to provide a bioimpedance measurement apparatus that can determine the depth and size of a tumor. It is yet another object of the invention to provide a bioimpedance measurement apparatus that is able to provide a holographic image of a tumor. It is still another object of the invention to provide a bioimpedance measurement apparatus that is noninvasive.
In accordance with these and other objects of the invention, a bioimpedance measurement apparatus is provided having a portable processing device and a sensor probe. In an invasive embodiment of the invention, the sensor probe includes a pair of needle electrodes that are used to impart a constant magnitude current signal to the body segment under investigation. The portable processing device includes an oscillator circuit that generates the current that is then passed through the needle electrodes to the body segment under investigation and a sensor means.
In a noninvasive embodiment of the invention, the sensor probe includes a single coil or a pair of coils. The coil(s) apply a non-ionizing magnetic field to the body segment without contacting the body segment. The bioimpedance of the body segment invokes a change in the induced magnetic field, which is then sensed and used to determine the bioimpedance of the body segment. Under both the invasive and noninvasive embodiments, the bioimpedance measurement apparatus uses electromagnetic bioimpedance to measure very subtle conductivity changes between normal and cancerous prostate tissue. In the noninvasive embodiments, holographic signal processing can be used that provides a three-dimensional image of impedance contrast. The bioimpedance measurement apparatus is especially useful for health care applications, and in particular to detect prostate cancer.
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