Steffen Kaufmann

A FPGA-Based Broadband EIT System for Complex Bioimpedance Measurements—Design and Performance Estimation

Electrical impedance tomography (EIT) is an imaging method that is able to estimate the electrical conductivity distribution of living tissue. This work presents a field programmable gate array (FPGA)-based multi-frequency EIT system for complex, time-resolved bioimpedance measurements. The system has the capability to work with measurement setups with up to 16 current electrodes and 16 voltage electrodes. The excitation current has a range of about 10 µA to 5 mA, whereas the sinusoidal signal used for excitation can have a frequency of up to 500 kHz. Additionally, the usage of a chirp or rectangular signal excitation is possible. Furthermore, the described system has a sample rate of up to 3480 impedance spectra per second (ISPS). The performance of the EIT system is demonstrated with a resistor-based phantom and tank phantoms. Additionally, first measurements taken from the human thorax during a breathing cycle are presented.

A high accuracy broadband measurement system for time resolved complex bioimpedance measurements.

Bioimpedance measurements are useful tools in biomedical engineering and life science. Bioimpedance is the electrical impedance of living tissue and can be used in the analysis of various physiological parameters. Bioimpedance is commonly measured by injecting a small well known alternating current via surface electrodes into an object under test and measuring the resultant surface voltages. It is non-invasive, painless and has no known hazards. This work presents a field programmable gate array based high accuracy broadband bioimpedance measurement system for time resolved bioimpedance measurements. The system is able to measure magnitude and phase of complex impedances under test in a frequency range of about 10-500 kHz with excitation currents from 10 µA to 5 mA. The overall measurement uncertainties stay below 1% for the impedance magnitude and below 0.5° for the phase in most measurement ranges. Furthermore, the described system has a sample rate of up to 3840 impedance spectra per second. The performance of the bioimpedance measurement system is demonstrated with a resistor based system calibration and with measurements on biological samples.

An in-ear pulse wave velocity measurement system using heart sounds as time reference

Abstract Pulse wave measurements provide vital information in medical diagnosis. For this reason, a measurement system is developed for determining the transient time of the pulse wave between the heart and the ear. To detect pressure variations in the sealed ear canal, caused by the arriving pulse wave, an in-ear sensor is developed which uses heart sounds as time reference. Furthermore, for extracting the heart sounds from the pressure measurements and calculating the pulse wave transient time, a MATLAB-based algorithm is described. An embedded microcontroller based measurement board is presented, which realizes an interface between the sensor and the computer for signal processing.

Concept of a rabbit-sized FFL-scanner

In the past years, different Magnetic Particle Imaging (MPI) scanners for small animals using a field free line (FFL) have been presented. In this work, a novel concept of a pre-clinical FFL MPI scanner which can accommodate rabbits is presented.

Multi-frequency Electrical Impedance Tomography for Intracranial Applications

Electrical impedance tomography (EIT) is a functional real-time imaging technique based on measurement and reconstruction of electrical impedance distributions.

In-Ear Pulse Wave Measurements: A Pilot Study

The measurement of the Pulse wave Arrival Time (PAT) has proven to be a vital tool in medical diagnosis. Whereby most PAT measurements are carried out at ex- tremities, this work proposes the interior of the ear as a new site. Due to pressure variations inside the auditory canal a pulse wave can be measured by using a pressure sensor or by simple in-ear headphones. To verify the signal origin, a reflectance photoplethysmograph (PPG) measurement inside the ear is carried out. All sensors are integrated for accurate and comfortable fit, in a custom made mould.

A device for measuring the trajectory dependent magnetic particle performance for MPI

In ferrofluids, the magnetization undergoes magnetic relaxation processes, which are affected by the concentration of the fluid, the viscosity of the medium, the strength and frequencies of an external magnetic field and the structure of the magnetic core [1,2]. In many models the particles are assumed to have an uniaxial anisotropy that results in one preferred magnetization direction called the easy axis. If the particles are exposed to a magnetic field that is aligned with this easy axis, the corresponding signal response is higher compared to other excitation directions [3]. For a one dimensional excitation this alignment will be reached shortly if the particle is able to mechanically rotate and the hydrodynamic friction is low. In more dimensional excitations, such as in dynamic field free line (FFL) scanners, or in field free point (FFP) scanners, the excitation direction changes constantly [4]. If this change in direction exceeds the maximum mechanical rotation speed of the particles, they are not able to align. As a result, the particle signal will drop. In this work, we present a new device that is able to generate FFP and FFL field sequences while applying different possible offset fields.

Analyzing superparamagnetic iron oxide nanoparticles (spions) using electrical impedance spectroscopy

Conventional methods to evaluate the size of superparamagnetic iron oxide nanoparticles (SPIONs) and their coatings used in magnetic particle imaging (MPI) include photon cross-correlation spectroscopy (PCCS) [1], atomic force microscopy (AFM) [1] and transmission electron microscopy (TEM) [2]. There is however still a potential for improvement as they are expensive and only able to analyze small sample quantities. In this work, a new method using electrical impedance spectroscopy is evaluated. With this method, it is possible to analyze macroscopic samples at low costs.

A micro Electrical Impedance Tomography System for Vessel Studies

Electrical Impedance Tomography (EIT) is a real-time imaging modality that measures and reconstructs the spatial impedance distributions inside an object under test. Based on the injection of small well know alternating currents (AC) and the measurement of resulting voltages, EIT has no known hazards and is even painless for human beings. Advantages of EIT over other classical imaging modalities are functional real-time imaging and portability, without utilizing ionic radiation. Until now EIT is mainly used as medical imaging technique, as well as for industrial and geophysical applications.

A Multi-frequency EIT System for irreversible Electroporation Feedback

Electrical Impedance Tomography (EIT) is a functional real-time imaging technique, used mainly in medical applications. EIT is based on impedance measurements and its spatial reconstruction within an object under test. For the measurements small well known alternating currents (AC) are injected via electrodes into the object under test. The resulting voltages at the boundary are measured and used in combination with the known current values for the subsequent reconstruction of the spatial impedance distribution. EIT is a low-cost technique, which works without ionic radiation, is painless and has no known hazards.