In the last 30 days

• Open/close Infrared thermal imaging in medicine

  E F J Ring and K Ammer 2012 Physiol. Meas. 33 R33 Tag this article

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  This review describes the features of modern infrared imaging technology and the standardization protocols for thermal imaging in medicine. The technique essentially uses naturally emitted infrared radiation from the skin surface. Recent studies have investigated the influence of equipment and the methods of image recording. The credibility and acceptance of thermal imaging in medicine is subject to critical use of the technology and proper understanding of thermal physiology. Finally, we review established and evolving medical applications for thermal imaging, including inflammatory diseases, complex regional pain syndrome and Raynaud's phenomenon. Recent interest in the potential applications for fever screening is described, and some other areas of medicine where some research papers have included thermal imaging as an assessment modality. In certain applications thermal imaging is shown to provide objective measurement of temperature changes that are clinically significant.

• Open/close Breast EIT using a new projected image reconstruction method with multi-frequency measurements

  Eunjung Lee et al 2012 Physiol. Meas. 33 751 Tag this article

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  We propose a new method to produce admittivity images of the breast for the diagnosis of breast cancer using electrical impedance tomography (EIT). Considering the anatomical structure of the breast, we designed an electrode configuration where current-injection and voltage-sensing electrodes are separated in such a way that internal current pathways are approximately along the tangential direction of an array of voltage-sensing electrodes. Unlike conventional EIT imaging methods where the number of injected currents is maximized to increase the total amount of measured data, current is injected only twice between two pairs of current-injection electrodes attached along the circumferential side of the breast. For each current injection, the induced voltages are measured from the front surface of the breast using as many voltage-sensing electrodes as possible. Although this electrode configuration allows us to measure induced voltages only on the front surface of the breast, they are more sensitive to an anomaly inside the breast since such an injected current tends to produce a more uniform internal current density distribution. Furthermore, the sensitivity of a measured boundary voltage between two equipotential lines on the front surface of the breast is improved since those equipotential lines are perpendicular to the primary direction of internal current streamlines. One should note that this novel data collection method is different from those of other frontal plane techniques such as the x-ray projection and T-scan imaging methods because we do not get any data on the plane that is perpendicular to the current flow. To reconstruct admittivity images using two measured voltage data sets, a new projected image reconstruction algorithm is developed. Numerical simulations demonstrate the frequency-difference EIT imaging of the breast. The results show that the new method is promising to accurately detect and localize small anomalies inside the breast.

• Open/close A new algorithm for detecting central apnea in neonates

  Hoshik Lee et al 2012 Physiol. Meas. 33 1 Tag this article

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  Apnea of prematurity is an important and common clinical problem, and is often the rate-limiting process in NICU discharge. Accurate detection of episodes of clinically important neonatal apnea using existing chest impedance (CI) monitoring is a clinical imperative. The technique relies on changes in impedance as the lungs fill with air, a high impedance substance. A potential confounder, however, is blood coursing through the heart. Thus, the cardiac signal during apnea might be mistaken for breathing. We report here a new filter to remove the cardiac signal from the CI that employs a novel resampling technique optimally suited to remove the heart rate signal, allowing improved apnea detection. We also develop an apnea detection method that employs the CI after cardiac filtering. The method has been applied to a large database of physiological signals, and we prove that, compared to the presently used monitors, the new method gives substantial improvement in apnea detection.

• Open/close Chronic fatigue syndrome and impaired peripheral pulse characteristics on orthostasis–a new potential diagnostic biomarker

  John Allen et al 2012 Physiol. Meas. 33 231 Tag this article

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  Autonomic nervous system dysfunction is frequently reported in chronic fatigue syndrome (CFS) with orthostatic intolerance, a common symptom that can be objectively assessed. The frequent finding of autonomic dysfunction and symptoms on standing has the potential to provide a diagnostic biomarker in chronic fatigue. In this study we explored the clinical value of non-invasive optical multi-site photoplethysmography (PPG) technology to assess cardiovascular responses to standing. Multi-site PPG pulses were collected from tissue pads of the ears, fingers and toes of 14 patients with CFS and 14 age-matched sedentary subjects using a measurement protocol of a 10 min baseline (subject supine) followed by 3 min of tilting on a tilt table (head-up to 70°). Percentage change in pulse timing (pulse transit time, PTTf) and pulse amplitude (AMP) at each site were calculated using beat-to-beat pulse wave analysis. A significant reduction in the overall pulse timing response to controlled standing was found for the CFS group (using summed absolute percentage change in PTTf for ear, finger and toe sites, median change of 26% for CFS and 37% for control with p = 0.002). There were no significant differences between subject groups for the AMP measure at any site. Changes in AMP with tilt were, however, weakly significantly and negatively correlated with fatigue severity ( p < 0.05). Receiver operating characteristic (ROC) analysis of timing measures produced an area under the curve of 0.81. Experimental linear discriminant classification analysis comparing both timing and amplitude measures produced an overall diagnostic accuracy of 82%. Pulse wave abnormalities have been observed in CFS and represent a potential objective measure to help differentiate between CFS patients and healthy controls.

• Open/close Whither lung EIT: Where are we, where do we want to go and what do we need to get there?

  Andy Adler et al 2012 Physiol. Meas. 33 679 Tag this article

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  Breathing moves volumes of electrically insulating air into and out of the lungs, producing conductivity changes which can be seen by electrical impedance tomography (EIT). It has thus been apparent, since the early days of EIT research, that imaging of ventilation could become a key clinical application of EIT. In this paper, we review the current state and future prospects for lung EIT, by a synthesis of the presentations of the authors at the ‘special lung sessions’ of the annual biomedical EIT conferences in 2009–2011. We argue that lung EIT research has arrived at an important transition. It is now clear that valid and reproducible physiological information is available from EIT lung images. We must now ask the question: How can these data be used to help improve patient outcomes? To answer this question, we develop a classification of possible clinical scenarios in which EIT could play an important role, and we identify clinical and experimental research programmes and engineering developments required to turn EIT into a clinically useful tool for lung monitoring.

• Open/close Initiation of ventricular contraction as reflected in the aortic pressure waveform

  Marc J van Houwelingen et al 2012 Physiol. Meas. 33 557 Tag this article

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  Prior to aortic valve opening, aortic pressure is perturbed by ventricular contraction. The onset of this pressure perturbation coincides with the onset of the left ventricular (LV) isovolumic contraction, and hence will be referred to as the start of the arterially detected isovolumic contraction (AIC _start). In the present study we test the hypothesis that the pressure perturbation indeed has a cardiac origin. In ten Yorkshire–Landrace swine, waveform intensity analysis demonstrated that AIC _start was followed by a positive intensity wave (0.3 × 10 ⁵ ± 0.3 × 10 ⁵ W (m ² s ²) ^–1). Timing analysis of LV and aortic pressure waveform showed that AIC _start was preceded by a LV pressure perturbation (3.8 ± 1.8 ms, p < 0.001). These novel cardiac timing and aortic wave intensity findings reveal the cardiac origin of the pressure perturbation. In 15 Yorkshire–Landrace swine, myocardial motion analysis showed a significantly higher rate of segment shortening during the first part of the LV pressure perturbation. Therefore, both the LV and aortic pressure perturbation are most likely caused by the early phase of myocardial contraction, which also causes mitral valve closure. Consequently, AIC _start is useful in the determination of the isovolumic contraction period, a well-known marker to quantify cardiac dysfunction.

• Open/close A review on electrical impedance tomography for pulmonary perfusion imaging

  D T Nguyen et al 2012 Physiol. Meas. 33 695 Tag this article

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  Although electrical impedance tomography (EIT) for ventilation monitoring is on the verge of clinical trials, pulmonary perfusion imaging with EIT remains a challenge, especially in spontaneously breathing subjects. In anticipation of more research on this subject, we believe a thorough review is called for. In this paper, findings related to the physiological origins and electrical characteristics of this signal are summarized, highlighting properties that are particularly relevant to EIT. The perfusion impedance change signal is significantly smaller in amplitude compared with the changes due to ventilation. Therefore, the hardware used for this purpose must be more sensitive and more resilient to noise. In previous works, some signal- or image-processing methods have been required to separate these two signals. Three different techniques are reviewed in this paper, including the ECG-gating method, frequency-domain-filtering-based methods and a principal-component-analysis-based method. In addition, we review a number of experimental studies on both human and animal subjects that employed EIT for perfusion imaging, with promising results in the diagnosis of pulmonary embolism (PE) and pulmonary arterial hypertension as well as other potential applications. In our opinion, PE is most likely to become the main focus for perfusion EIT in the future, especially for heavily instrumented patients in the intensive care unit (ICU).

• Open/close Intraluminal ultrasonic probe for volumetric monitoring of liquid gastroesophageal reflux

  X Gao et al 2012 Physiol. Meas. 33 487 Tag this article

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  Methods for volumetric monitoring of liquid gastroesophageal reflux (GER) are still lacking. The aim of this study was to develop an automated intraluminal measurement technique which allows ambulatory volumetric quantification of liquid GER utilizing a minimum-cost intraluminal ultrasonic probe. This probe consists of two 2 MHz ultrasonic crystals longitudinally assembled along a multi-channel intraluminal impedance (MII) catheter. The proposed probe was initially tested with tubular phantoms of different diameters. Measurements of the cross-sectional areas of the phantoms showed high correlation with the actual areas ( R ² = 0.99). Subsequently, two in-vivo human tests were performed. For each human test the catheter assembly was inserted transnasally and the ultrasonic probe was placed in the area of the lower esophageal sphincter. Multiple liquid swallows of different volumes were invoked using electrolyte drinks. Sectional luminal volume (SLV) in the esophagus between the two ultrasonic crystals was obtained. Results of the swallows demonstrated that measured SLVs correlated with the actual swallowed liquid volume. The ultrasonic probe was combined with a MII catheter to discriminate between antegrade and retrograde bolus transit. Increases of SLVs during liquid GER episodes could be utilized to evaluate GER volume in the vicinity of the ultrasonic probe.

• Open/close Non-invasive continuous core temperature measurement by zero heat flux

  L P J Teunissen et al 2011 Physiol. Meas. 32 559 Tag this article

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  Reliable continuous core temperature measurement is of major importance for monitoring patients. The zero heat flux method (ZHF) can potentially fulfil the requirements of non-invasiveness, reliability and short delay time that current measurement methods lack. The purpose of this study was to determine the performance of a new ZHF device on the forehead regarding these issues. Seven healthy subjects performed a protocol of 10 min rest, 30 min submaximal exercise (average temperature increase about 1.5 °C) and 10 min passive recovery in ambient conditions of 35 °C and 50% relative humidity. ZHF temperature ( T _zhf) was compared to oesophageal ( T _es) and rectal ( T _re) temperature. Δ T _zhf– T _es had an average bias ± standard deviation of 0.17 ± 0.19 °C in rest, −0.05 ± 0.18 °C during exercise and −0.01 ± 0.20 °C during recovery, the latter two being not significant. The 95% limits of agreement ranged from −0.40 to 0.40 °C and T _zhf had hardly any delay compared to T _es. T _re showed a substantial delay and deviation from T _es when core temperature changed rapidly. Results indicate that the studied ZHF sensor tracks T _es very well in hot and stable ambient conditions and may be a promising alternative for reliable non-invasive continuous core temperature measurement in hospital.

• Open/close 12th International Conference on Biomedical Applications of Electrical Impedance Tomography (University of Bath, UK, 4–6 May 2011)

  Richard Bayford and Manuchehr Soleimani 2012 Physiol. Meas. 33 Tag this article

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  This focus issue of Physiological Measurement follows the successful 12th Conference on Biomedical Applications of Electrical Impedance Tomography (EIT). The conference was held in the UK and hosted at the University of Bath. It was co-organized by Dr Manuchehr Soleimani from the University of Bath and Professor Eung Je Woo of Kyung Hee University.

  The conference provided a platform for investigators in all aspects of biomedical applications of EIT to engage in common areas of interest, whilst also allowing an opportunity for the community to broaden its outlook in the clinical applications and new technologies associated with this area of research. It focused on the medical applications of electrical impedance tomography, magnetic induction tomography, and magnetic resonance electrical impedance tomography.

  This upholds the tradition of successful conferences on biomedical applications of EIT as was the case with the previous XIVth International Conference on Electrical Bio-Impedance (ICEBI) and the 11th Conference on Biomedical Applications of Electrical Impedance Tomography. The conference was held in the United States and hosted at the University of Florida, Gainesville. It was co-organized by Dr Rosalind Sadleir from the University of Florida and Professor Eung Je Woo of Kyung Hee University. The 13th Biomedical Applications of Electrical Impedance Tomography conference will be held in China in May 2012.

  This issue contains papers stemming from discussion and feedback during the conference in these research areas. It was also an opportunity for new researchers to join the community and propose recent innovations. There were over 80 oral papers presented at the conference, and all authors were invited to prepare new peer-reviewed papers for inclusion in this issue of Physiological Measurement. The manuscripts were put through a process of careful review before selection. A total of 13 were accepted covering an important range of topics. Of particular note is the paper by Adler et al (2012) that discusses both the current state of lung EIT and also its future direction. This issue also includes a review article by Nguyen et al (2012) that discusses the use of EIT for pulmonary perfusion imaging.

  The field of EIT imaging continues to provide researchers with new challenges and attract more researchers into this field, as evident by the number of attendees to this conference. A total of 120 delegates attended the conference. This wide participation shows a step change in interest in medical EIT imaging. In this conference we have seen a large number of clinical scientists attending, which further indicates the great excitement from the medical community for realization of EIT in a clinical setting. A range of important keynote speeches were presented in a 'Clinical Thoracic' session by Professor Brian Brown, Dr Stephan Böhm, and Dr Marc Bodenstein.

  The high quality of the research papers in this focus issue is clear evidence of the significant advances in the field.

  Richard Bayford and Manuchehr Soleimani
  Guest Editors

  References

  Adler A, Amato M, Arnold J H, Bayford R H, Bodenstein M, Böhm S, Brown B H, Frerichs I, Stenqvist O and Weiler N 2012 Whither lung EIT: where are we, where do we want to go, and what do we need to get there? Physiol. Meas. 33 679–94

  Nguyen D T, Jin C, Thiagalingam A and McEwanA L 2012 A review on electrical impedance tomography for pulmonary perfusion imaging Physiol. Meas. 33 695–706