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Magnetic induction tomography is used to image the electrical properties inside a region of interest. The systems differ in the construction of the receiver channels which can be composed of coils or gradiometers. We will compare and discuss the image quality subject to two different types of receivers, different arrangements for the exciters and receivers and different signal-to-noise ratios. In order to evaluate the image quality, the point-spread function (PSF) was determined which is used for the calculation of the resolution and the correctness of the location of a perturbation. The results show that the PSF depends on (a) the location inside the object, (b) the type of receivers and (c) the configuration used, especially the location of the receiving and excitation channels. According to this, the local resolution is changed and has the maximum near the border of the object and decreases towards the centre of the object. In addition, the evaluation of the PSF shows a dislocation with respect to the underlying point-source position. [ABSTRACT FROM AUTHOR]

Magnetic induction tomography (MIT) is a low-resolution imaging modality used for reconstructing the changes of the passive electrical properties in a target object. For an imaging system, it is very important to give forecasts about the image quality. Both the maximum resolution and the correctness of the location of the inhomogeneities are of major interest. Furthermore, the smallest object which can be detected for a certain noise level is a criterion for the diagnostic value of an image. The properties of an MIT image are dependent on the position inside the object, the conductivity distribution and of course on the location and the number of excitation coils and receiving coils. Quantitative statements cannot be made in general but it is feasible to predict the image quality for a selected problem. For electrical impedance tomography (EIT), the theoretical limits of image quality have been studied carefully and a comprehensive analysis for MIT is necessary. Thus, a simplified analysis on resolution, dimensions and location of an inhomogeneity was carried out by means of an evaluation of the point spread function (PSF). In analogy to EIT the PSF depends strongly on the location, showing the broadest distribution in the centre of the object. Increasing the amount of regularization according to increasing measurement noise, the PSF broadens and its centre is shifted towards the borders of the object. The resolution is indirectly proportional to the width of the PSF and increases when moving from the centre towards the border of the object and decreases with increasing noise. [ABSTRACT FROM AUTHOR]

Objective: Pharmacokinetic and pharmacodynamic studies of topically applied drugs are commonly performed by sampling of interstitial fluid with dermal open flow microperfusion and subsequent analysis of the samples. However, the reliability of results from the measured concentration-time profile of the penetrating drug suffers from highly variable skin permeability to topically applied drugs that is mainly caused by inter- and intra-subject variations of the stratum corneum. Thus, statistically significant results can only be achieved by performing high numbers of experiments. To reduce the expenditures needed for such high experiment numbers we aimed to assess the correlation between skin permeability and skin impedance/skin admittance. Approach: We performed an ex vivo drug penetration study with human skin, based on the hypothesis that inter-subject variations of the respective concentration-time profiles can be correlated with variations of the passive electrical properties of the skin. Therefore, skin impedance and skin admittance were related to the skin permeability to the model drug Clobetasol-17-proprionate. Main results: The measured low frequency skin impedance and the skin admittance correlated linearly with the drug concentration-time profiles from dermal sampling. Significance: Skin permeability can be assessed by measuring the passive electrical properties of the skin, which enables correction of skin permeability variations. This allows reduction of experiment numbers in future pharmacokinetic and pharmacodynamic studies with human skin ex vivo and in vivo and leads to diminished study costs. [ABSTRACT FROM AUTHOR]

Nuclear quadrupole resonance (NQR) spectroscopy is a method for the characterization of chemical compounds containing so-called quadrupolar nuclei. Similar to nuclear magnetic resonance (NMR), the sample under investigation is irradiated with strong radiofrequency (RF) pulses, which stimulate the emission of weak RF signals from the quadrupolar nuclei. The signals are then amplified and Fourier transformed so as to obtain a spectrum. In principle, narrowband NQR spectra can be measured with NMR spectrometers. However, pure NQR signals require the absence of a static magnetic field and several special applications require the characterization of a substance over a large bandwidth, e.g. 50–100% of the central frequency, which is hardly possible with standard NMR equipment. Dedicated zero-field NQR equipment is not widespread and current concepts employ resonating probes which are tuned and matched over a wide range by using mechanical capacitors driven by stepper motors. While providing the highest signal to noise ratio (SNR) such probes are slow in operation and can only be operated from dedicated NMR consoles. We developed a low-cost NQR wideband probe without tuning and matching for applications in the very high frequency (VHF) range below 300 MHz. The probe coil was realized as part of a reactive network which approximates an exponential transmission line. The input reflection coefficient of the two developed prototype probe coils is ≤ 20 dB between 90–145 MHz and 74.5–99.5 MHz, respectively. Two wideband NQR spectra of published test substances were acquired with an SNR of better than 20 dB after sufficient averaging. The measured signals and the SNR correspond very well to the theoretically expected values and demonstrate the feasibility of the method. Because there is no need for tuning and matching, our probes can be operated easily from any available NMR console. [ABSTRACT FROM AUTHOR]

This issue of Physiological Measurement follows the successful 13th ICEBI conference held at the Graz University of Technology, Austria, from 29 August to 2 September 2007. It was organized jointly with the 8th Conference on Electrical Impedance Tomography. The conference was co-organized by the Impedance Imaging Research Centre (IIRC) in Seoul and the Austrian Society for Biomedical Engineering (ÖGBMT), and it was kindly endorsed by the IFMBE. The combined conferences created a platform for investigators from both research communities of bio-impedance and EIT to engage in common areas of interest whilst also allowing an opportunity for the community to broaden its outlook in the areas of bio-sensors, clinical applications and new technologies. This upholds the tradition of successful conferences on biomedical applications of electrical impedance tomography and bio-impedance. It follows the 7th Conference on Biomedical Applications of Electrical Impedance Tomography combined with the World Congress 2006, which took place in Seoul from 27 August to 1 September 2006. The next EIT conference is scheduled to take place in Dartmouth College, USA, in June 2008. This issue contains papers produced from discussion and feedback during the conference in both bio-impedance and EIT research areas. It was also an opportunity for new researchers to join the community and propose recent innovations. Of the 259 papers presented at the conference, Springer Verlag published 207 in the IFMBE proceedings. All authors were invited to prepare new papers for inclusion in this issue of Physiological Measurement. The manuscripts were put through a process of careful review before selection. A total of 43 were accepted, covering an important range of topics from bio-impedance, hardware, algorithms, new technologies and clinical applications. From the scientific point of view, bio-impedance has a very long tradition that dates back to the days of Maxwell. Nevertheless, until the end of the 20th century, research was focused on the development of methods and basic experimental work while clinical or other practical applications remained limited. Consequently, there were not so many companies interested enough to produce professional equipment for easy and reliable data collection and interpretation. This may appear surprising as bio-impedance reflects so many (patho-) physiological processes, but on the other hand, a number of proposed applications, though sensitive, still exhibit low specificity, especially when aimed at processes far from the body surface. The 2007 conference may have shown a slight change of tendency. From 2000 to 2006, the number of papers cited in Medline and containing the keywords ''bio-impedance'' or ''impedance tomography'' increased by 56%. At the same time, we face an increasing number of applications related to micro- and nano-technologies that have emerged along with the tremendous growth of biochemical and cellular engineering. In recent years both the number of newly founded companies for bio-impedance devices and the involvement of established companies in bio-impedance research have increased. The papers included in this year''s issue clearly reflect this. New developments and trends are visible, such as non-contact methods using magnetic fields; MREIT, bringing together EIT and magnetic resonance imaging; and magnetic induction tomography (MIT), clinical applications, bio-impedance spectroscopy, new hardware and algorithms. The presentations of these new technologies continue to grow and it will be interesting to see how these contribute to future clinical applications. At this conference, clinical applications were strongly represented; they included brain function, breast imaging, and thorax and gastric applications. It is important that researchers do not neglect the challenges of clinical applications of bio-impedance and EIT as there are still many technical difficulties that the technology needs to overcome in order to provide valuable clinical tools; however, there are promising signs that these tools are close to realization. The future of both EIT and bio-impedance continues to provide researchers with new challenges. The high quality of research papers in this special issue shows clear evidence of significant advances in this research field. [ABSTRACT FROM AUTHOR]