In-vitro evaluation of contrast media for assessment of regional perfusion distribution by Electrical Impedance Tomography (EIT)

Abstract

Electrical impedance tomography (EIT) has become an accepted tool for monitoring regional ventilation. Interest is growing to derive additional information on pulmonary perfusion and ventilation/perfusion distribution. Favoured approach is the impedance indicator dilution technique. Until now hyperosmolar sodium chloride solutions (5.8% and 20%NaCl) have been used as indicators in experiments which, however, may be problematic in view of side effects and are not approved for application in patients. Different radiographic contrast media (CM) approved for use in patients and five reference solutions were tested in vitro. Resistivities were measured in blood at 37°C by a conductivity meter (LF39, Meinsberg GmbH, Germany) in the indicator content range from 0 to 28 Vol%. Three non-ionic CM: Iodixanol, Iomeprol, Iobitridol and two ionic CM: Ioxaglate and Diatrizoate were examined. As references 0.9%, 5.8% and 20%NaCl as well as isotonic (4.5%) and hypertonic (18.2%) glucose solutions were included. Proportionality Proportionality between test solution concentration and determined resistivity changes was proven by regression/correlation analysis. Non-ionic CM induced linear increases of blood resistivity by 80% (Iodixanol), 75% (Iomeprol) and 66% (Iobitridol) at the highest test concentration of 28Vol%. Ionic CM changed resistivity by 13% (Ioxaglate) and 24% (Diatrizoate). The determined r 2 -values were > 0.988. Both hyperosmolar NaCl solutions caused marked but non-linear resistivity lowering by -82% resp. -95% with poor r 2 -values < 0.6. Glucose solutions increased resistivity by 17% resp. 29%, r 2 -value 0.98. Hyperosmolar NaCl-solutions effect impressive changes of resistivity but may imply errors in the evaluation of indicator dilution curves by non-linearity. The resistivity changes by the approved non-ionic radiographic CM are not complicated by linearity problems. A comparison with the simple blood dilution effect by isotonic non-ionic reference solutions indicates additional mechanisms of resistivity increment by CM. In conclusion CM should be evaluated further on in view of EIT-based perfusion assessment in patients.

Quantitative Analysis of Electrical Current Effect on Magnetic Resonance Image Tissue Intensity

“…This study shows each image group is entirely different; in T1-weighted images, the mean of tissue image intensity is significantly decreased in the electrical current group. This result is similar to the previous research that concludes although MREIT has poor SNR and low spatial resolution but has potential to be a non-chemical contrast agent [28,29,30]. Meanwhile, in T2-weighted images, the mean of tissue image intensity is significantly increased in the electrical current group.…”

Regional lung ventilation and perfusion by electrical impedance tomography compared to single-photon emission computed tomography

“…In contrast, bolus injection of an EIT contrast agent (Brown et al 1992) yields an indicator-based signal (IBS) that is clearly linked to perfusion (Borges et al 2012), but its invasiveness may prevent clinical application (Hellige et al 2012a). However, the use of the IBS to obtain Q is tempting and might become suitable for clinical application, if saline concentration can be lowered or alternatively, less-invasive contrast agents can be found (Hellige et al 2012b). Furthermore, a properly validated Q from the IBS can serve as a reference for studies investigating the CRS to obtain Q.…”

Evaluation of Different Contrast Agents for Regional Lung Perfusion Measurement Using Electrical Impedance Tomography: An Experimental Pilot Study

“…Depending on the electrochemical and physical properties of the employed indicator, different mechanisms can be responsible for this, which can amplify or counteract each other. [20].…”

“…Blood resistivity results predominantly from the electrical resistance of the erythrocytes and is therefore dependent on the hematocrit. Each bolus injection of an erythrocyte-free solution causes hematocrit dilution and consequently a reduced resistivity according to an increased conductivity (conductivity = 1/resistivity) [20]. This effect is enhanced by the use of a hyperosmolar fluid, as intravascular water shift increases hematocrit dilution [20].…”

“…These aspects warrant the investigation of clinically approved fluids to determine their suitability as contrast agents for EIT-based regional lung perfusion measurement. Such studies have so far only been carried out in-vitro by Hellige et al [20].…”