## 1 Introduction  
The simultaneous recording of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has enabled many researchers to investigate and study new possibilities in functional neuroimaging to understand the human brain and help in diagnosing and treating brain-related diseases and disabilities [1]. Because of the fusion of the excellent spatial resolution of fMRI [1,2] and the high temporal resolution of EEG in combined EEG-fMRI studies, this technique has enabled us to better understand the relationship between spontaneous or evoked electrical activity and hemodynamic response in the human brain [3, 4, 5]. In concurrent EEG-fMRI recordings, the magnetic fields of the MRI scanner generate artefacts in the EEG data [6,7]. These artefacts are larger than the neuronal activity of interest by an order of magnitude or more [8]. The major induced artefact voltage, known as gradient artefact (GA), in EEGdata is produced by magnetic field gradients [6; 7]. The GA ranges between 10 and 100 mv, which is far greater than the typical EEG signal (less than 200 \(\mu\)V). [PERSON] et al. [8] suggested that the position of the head and EEG cap with respect to the applied magnetic field gradients could affect the induced GA. The GA could be reproduced provided that the position of the head or the EEG cap remains steady during data recording [9]. This, in turn, helps to remove the GA using a post-processing method called Average Artefact Subtraction (AAS) [6]. There are two other kinds of artefact: pulse artefact (PA) and motion artefact (MA) [10; 11]. The magnitude of the PA is in the order of a few hundred microvolts in a 3T static magnetic field [12]. In contrast, head rotation is responsible for the MA, which could be in the order of 10 mV [13]. The induced MA due to head rotation could be temporally correlated with the task response in fMRI experiments, which could lead to cofounding effects in simultaneously acquired EEG-fMRI data [14]. Since the GA forms the largest artefact in EEG data recorded during simultaneous EEG-fMRI experiments, it is very essential to minimize this kind of artefact to avoid amplifier saturation [15]. Furthermore, GA amplitude reduction could also help in easing the constraints on the dynamic range and the bandwidth of the EEG amplifier and, thus, it could be beneficial in the future for many EEG-fMRI studies. In EEG-fMRI studies testing new configurations or settings with the aim to reduce or eliminate the GA from the EEG data, it is not always safe to use human subjects, because there is a risk of heating the subject's tissues following the emission of radiofrequency (RF) energy during the slice excitation procedure [16], which couples into the loops of the electrodes' cable and leads to dissipating energy in the human tissues or in the loop materials themselves in the form of heat [17; 18]. Thus, there is a common practice among EEG-fMRI researchers to use a phantom in the initial setup of any EEG artefact correction technique in simultaneous EEG-fMRI recording [8; 9; 15; 19; 20]. This is a primary step when testing and preparing any hardware-based methods and configurations or software-based EEG artefact reduction (more specifically, GA correction) techniques, before acquiring EEG data from a human subject. Furthermore, the use of a phantom helps the researchers to avoid PA and MA that are due to blood circulation and head movement, as it is not possible to prevent a human subject from moving their head. Thus, the use of a phantom could facilitate the study, allowing to focus only on the reduction of the GAs as they are the largest artefacts in EEG data. Moreover, it is not easy to conduct experimental tests on human subjects because ethical approval is required for EEG-fMRI analyses. Therefore, it could be more convenient and safe to conduct experiments on a phantom rather than on a human subject.