Record P M
University of Keele, School of Post Graduate Medicine, Department of Biomedical Engineering and Medical Physics, Hospital Centre, Hartshill, Stoke, UK.
Physiol Meas. 1994 May;15 Suppl 2a:A29-35. doi: 10.1088/0967-3334/15/2a/004.
When tissue interacts with electromagnetic radiation it exhibits resistivity and permittivity changes, which decrease with frequency. Above 100 kHz it is expected that dielectric changes in tissue (permittivity) will allow one to distinguish damaged and necrotic tissue. Furthermore, tissue impedance at medium frequencies (100 kHz-1 MHz) have not been well characterized. The aim of this work was to design instrumentation for an impedance tomographic spectrometer to cover the minimum band 10 kHz-1 MHz. In order to produce images sensitive to small changes in resistivity, voltage measurement must be accurate to at least 0.1%. Using commercially available operational amplifiers, PSPICE simulations demonstrated 0.1% accuracy up to 800 kHz, falling off to 0.5% at 1 MHz. Implementation achieved a reasonably flat amplitude (+/- 0.5 dB) and a phase shift of 50 degrees from 10 kHz to 3 MHz and a receive response of 0.13 dB to 5 MHz and phase shift of -40 degrees at 3 MHz. With channel correction this design will provide useful readings up to 3 MHz.
当组织与电磁辐射相互作用时，它会表现出电阻率和介电常数的变化，这些变化会随频率降低。预计在100 kHz以上，组织中的介电变化（介电常数）将使人们能够区分受损和坏死组织。此外，中频（100 kHz - 1 MHz）下的组织阻抗尚未得到很好的表征。这项工作的目的是设计一种用于阻抗断层扫描光谱仪的仪器，以覆盖10 kHz - 1 MHz的最小频段。为了生成对电阻率微小变化敏感的图像，电压测量必须精确到至少0.1%。使用市售运算放大器，PSPICE模拟表明，在高达800 kHz时精度为0.1%，在1 MHz时降至0.5%。实际实现达到了相当平坦的幅度（±0.5 dB），从10 kHz到3 MHz的相位偏移为50度，在5 MHz时接收响应为0.13 dB，在3 MHz时相位偏移为 - 40度。通过通道校正，该设计将在高达3 MHz时提供有用的读数。
