Research On Minimal Invasive Measurement Technology Of Bioimpedance And Its Application

At present,the most commonly used method for the detection of food freshness is physical and chemical testing.Although this method is accurate,it will destroy the food itself.And the method also have high requirements in detection equipment and time-consuming.Besides,hyperthermia technology has been commonly used in the treatment of cancer nowadays.But it's hard to determine the survival of the cancer cells during the treatment process,which may lead to relapse.In order to study the relationship between food freshness and electrical impedance and the electrical impedance of hyperthermia tissue,a microinvasive impedance probe and its measurement system have been designed and fabricated to solve these problems.A real-time,safe and quantitative detection method of food freshness based on electrical impedance characteristics has been proposed.A real-time monitoring method of thermotherapy quality based on biological tissue impedance has been proposed as well.The designed micro-invasive impedance probe consists of two pairs of electrodes and a temperature sensitive tip.The sensitive field of the probe is uniform and the range of which is small.The probe measuring system is composed of upper computer,electrical impedance measuring circuit and temperature measuring module.After performance test and calibration,it has been verified that performance of the probe is good.Relationship between freshness of tissues in vitro and electrical impedance characteristics and the changes of electrical impedance characteristics during the hyperthermia process were studied by using the designed impedance probe and measurement system.It has been found that the similar changes in electrical impedance characteristics are observed during the process of spoilage of the tissues in vitro,that is,the ratio of high/low frequency resistances of the tested tissues tends to 1 and a significant gradient appeares at the critical point,the phase difference between high and low frequencies tends to zero,and the ratio of longitudinal/transverse resistances in fibrous tissue also tends to 1 with the time.Experimental results show that food freshness can be quantitatively determined by measuring and calculating its high/low frequency resistance ratio,high/low frequency phase difference value,longitudinal/transverse resistance ratio and so on.The experimental results also provide general conclusions about the corrupt metamorphism time of tissues in vitro,fish and milk at typical temperature,which is of great significance for food storage.In this study,the changes in the electrical characteristics of tissues in vitro during the hyperthermia process have also been found to be similar to those in the food storage process.That is,the ratio of the high/low frequency resistances of the tested tissues tends to 1 with time.And there will be a significant gradient change in the critical point.Besides,with the hyperthermia temperature rises,the phenomenon occurs faster.Experimental study of the changes in impedance characteristics with the process of hyperthermia is of great significance,indicating that the survival of cells during hyperthermia can be determined by real-time monitoring of tissue resistance value.When the low-frequency resistance of tissue suddenly becomes smaller,high/low frequency resistance ratio tends to 1,the gradient mutation occues,the apoptosis occurred.If the tissue resistance tends to stabilize again,it indicates that the somatic cells in thermotherapy area have all been apoptosis and the desired therapeutic goals have been achieved.This study demonstrates that the apoptosis has obvious performance through temperature-resistance variation factor curve,and can be decided by the ratio of high/low frequency resistances during the hyperthermia process.Compared with the curve of temperature-resistance variation factor,this ratio has important clinical application value.It is expected to provide an effective basis for practical monitoring of hyperthermia process by electrical impedance tomography.In short,the real-time,economic and convenient minimally invasive probe and measurement system developed in this study can be applied to the quantitative detection of food freshness,and can be used in experimental study of tissue electrical impedance characteristics during thermotherapy.The change of the ratio of high/low frequency resistances in the process of hyperthermia is the direct basis for cell death.It can be used to judge the therapeutic effect of hyperthermia in real time and has important clinical significance.