Variability in the cardiac EIT image as a function of electrode position, lung volume and body position

Abstract

A study was conducted using the Sheffield electrical impedance tomography (EIT) portable system DAS-01 P to determine the change in the cardiac image with electrode position, lung volume and body position. Sixteen electrodes were positioned in three transverse planes around the thorax at the level of the second intercostal space, at the level of the xiphisternal joint, and midway between upper and lower locations. Data were collected at each electrode level with the breath held at end expiration and after inspiring 0.5, 1 and 1.5 l of air with the subject in both the supine and sitting position. These data were analysed using a Matlab developed program that calculates the average resistivity change in the cardiac region from automatically determined borders. Results show significant individual variability with electrode position and air volume. The middle electrode most consistently shows an increase in impedance in the region of the heart during systole. In some subjects the change in the ventricular-volume-like curve showed a greater than 50% change as a function of lung volume. The pattern of variability with electrode position was not consistent among subjects. In one subject MRI images were obtained to compare actual structures with those seen in the EIT image. The results suggest that using these electrode locations reliable and consistent data, which could be used in clinical applications, cannot be obtained.

Measurement of ventilation and cardiac related impedance changes with electrical impedance tomography

“…Several methods have been suggested to separate these signals, the simplest being breath holding to remove respiratory changes [3], which also removes the ability to assess cardio-pulmonary interaction. Alternatively ECG gating and frequency filtering has been suggested, which would allow acquisition of the perfusion components of the EIT signal without respiratory interference [4-6]. …”

Assessment of Changes in Distribution of Lung Perfusion by Electrical Impedance Tomography

“…Regarding the cardiac- and perfusion-related changes in electrical impedance, further improvement still would be desirable although the device used in our study already exhibited improved characteristics [36] compared with the DAS 01P device (IBEES, Sheffield, UK) [37] used in most of the earlier perfusion-oriented studies [20,21,22,23,24, 30, 31]. …”

“…An assignment of local changes in electrical impedance to known anatomical structures has been attempted for the first time shortly after the invention of EIT [16]. Frequency filtering [17,18,19] and ECG-triggered data acquisition [11,20,21,22,23,24] have been used to access the cardiac- and perfusion-related components of the EIT signal without interference from ventilation and noise. Recently, a novel approach using dynamic frequency filtering has been proposed which may improve the separation of different frequency components of the EIT signal [25].…”

Conductivity Imaging and Generalized Radon Transform

“…In addition to the preceding medical uses, EIT may benefit monitoring of the cardiovascular system. Related applications involve measurement of cardiac output (Eyuboglu et al, 1987(Eyuboglu et al, , 1989Hoetink et al, 2002;McArdle et al, 1993;Patterson et al, 2001), detection of deep venous thrombosis (Kim et al, 1989), blood flow imaging (Brown et al, 1991), and diagnosis of pelvic congestion (Thomas et al, 1991).…”