In the routine management of patients in the ICU, imaging studies may be frequent and many times urgent. Metal cup electrodes cause a streak artifact on CT that may obscure vital findings (Fig. 2). Additionally, most are not MRI compatible because the metal can produce heating and displacement as well as artifacts. As a result, traditional metal cup electrodes require removal and reapplication for imaging studies, which can result in scalp abrasions and discomfort. This also places an additional workload on the EEG technologist. Fortunately, there are other electrode options that are safe for use with MRI and/or CT imaging (Table 1). These include plastic electrodes with a conductive coating. They have been proven safe for use in MRI and do not produce the streak artifact on CT scans (Figs. 3 and 4) [3, 4]. Like metal cup electrodes, they require the use of a conductive gel and for long-term monitoring are typically applied with collodion. Benefits to their use include continuous recording during imaging procedures, minimizing downtime, and decreased need for repeated removal and reapplication. While allowing for minimal interruption in recording, conductive plastic electrodes still require routine maintenance to maintain high-quality signal. This includes reapplication after accidental removal and refreshing with conductive gel that may dry over the course of a 24-h recording. Subdermal needle and subdermal wire electrodes are another option to consider for imaging compatibility. Subdermal needles are thin enough to not cause artifact on most CTs; compatibility with MRI depends on needle length, with longer needles having greater concern for injury. Subdermal wires cause minimal to no artifact on CT and are compatible with MRI as well. For all types of electrodes, the length of the leads connecting the electrodes must be kept in mind; longer leads or lead that are coiled to make loops are a potential source of induced currents that could place the patient at risk while in the MRI scanner.

As previously stated, good-quality EEG recording requires low impedance at the electrode junction. When using cup electrodes, regardless of material, technicians rub an abrasive paste to remove dirt, oils, and the outer layer of the skin, all of which contribute to skin impedance. Cup-style electrodes also typically require that a conductive paste or gel be used to facilitate transduction of ionic currents. Skin preparation and electrode application should lead to electrode impedances that meet the same standards as for routine EEG, impedances below 5–10 kΩ. Although modern EEG amplifiers can record from higher impedance electrodes, there will be some degradation in quality. Beyond the absolute value, the impedances of all the electrodes used should be similar to each other – mismatched impedances will also compromise signal quality. Impedances should be rechecked periodically as drying out of the conductive paste or loss of electrode contact with the skin can occur.