Changes in body temperature have clinically significant effects on nerve excitation. However, the mechanisms of these effects still further explored. In this paper, we studied the effects of temperature on the propagation properties of action potential on unmyelinated afferents by action-potential-sensitive second harmonic generation (SHG). A mathematical model was presented which combining with SHG imaging to study the action potential properties in an unmylinated fiber affected by temperature. The results showed that the action potential propagation along an unmyelinated fiber was sensitively probed by optical SHG imaging in real time. Meanwhile, the action potential properties on an unmyelinated fiber is obviously changed at innocuous temperatures through analyzing the changes of action-potential-sensitive SHG signals, including the increase of conduction velocity and the decrease of duration at higher temperatures. Our study indicates that optical second harmonic generation imaging may be a potential tool to investigate the underlying mechanisms of complex physiological phenomena such as nerve excitation.
Demyelination of a nerve fiber was simulated by action potential encoded second harmonic generation (SHG). The
dynamics of action potential propagation along a nerve fiber with a multi-internode demyelination happening to
successive internodes or intermittent internodes was studied. The results showed the attenuation and delay of action
potential could obviously occur, and the refractory period increased when a nerve was demyelinated. In addition, under
the same thickness and number of the demyelination, the peak of SHG signals attenuated much more along successive
injured internodes than along intermittent injured internodes. It indicated that action potential encoded SHG could be a
useful tool for detecting nerve demyelination.
Axonal demyelination is a common phenomenon in the nervous system in human. Conventional measured approaches
such as surface recording electrode and diffusion tensor imaging, are hard to fast and accurately determine the
demyelinated status of a fiber. In this study, we first presented a mathematical model of nerve fiber demyelination, and it
was combined with second harmonic generation(SHG) technique to study the characteristics of action-potential-encoded
SHG and analyze the sensitivity of SHG signals responded to membrane potential. And then, we used this approach to
fast examine the injured myelin sheaths resulted from demyelination. Each myelin sheath of a fiber was examined
simultaneously by this approach. The results showed that fiber demyelination led to observable attenuation of action
potential amplitude. The delay of action potential conduction would be markedly observed when the fiber demyelination
was more than 80%. Furthermore, the normal and injured myelin sheaths of a myelinated fiber could be distinguished via
the changes of SHG signals, which revealed the possibility of SHG technique in the examination of a demyelinated fiber.
Our study shows that this approach may have potential application values in clinic.
Thermal imaging is an emerging method for early detection of female breast tumor. The main challenge for thermal
imaging used in breast clinics lies in how to detect or locate the tumor and obtain its related parameters. The purpose of
this study is to apply an improved method which combined a genetic algorithm with finite element thermal analysis to determine the breast tumor and its parameters, such as the size, location, metabolic heat generation and blood perfusion rate. A finite element model for breast embedded a tumor was used to investigate the temperature distribution, and then the influences of tumor metabolic heat generation, tumor location and tumor size on the temperature were studied by use of an improved genetic algorithm. The results show that thermal imaging is a potential and effective detection tool for early breast tumor, and thermal simulation may be helpful for the explanation of breast thermograms.