Table 1. Concurrent tES-fMRI (ContES 2021) Checklist: main items and recommendations of the TECHNOLOGICAL FACTORS category to report in concurrent tES-fMRI research.

Ratings for items (scores 1-5) are reported as mean (standard deviation) and ratings for recommendations (Yes/No) are reported as frequency of Yes (percent of Yes reports).

Categories/Sub-Categories	Main Items to Report	Item Importance (1 to 5)	Specific Recommendation	Recommendation Inclusion (Yes/No)
		Mean (SD)		Yes (%)
TECHNOLOGICAL FACTORS
1.1. Manufacturer of MR Conditional Stimulator	The brand and model (if a brand is providing different MR conditional models) for the MR conditional stimulator.	4.37 (0.96)
1.2. MR Conditional Electrode Details	The MR conditional electrode type (i.e., conductive polymer with or without a sponge or other conductive medium holders).	4.06 (1.01)	1.2.1. Report conductive properties of the MR conditional electrodes, cables, contact medium, and other conductive elements, including the position and materials used for the electrode-cable connections 69. This is especially important if they are not from an established manufacturer or not well described in the prior literature. However, even for wellestablished equipment, these details are critical to report to ensure replicability.	44 (85%)
1.3. Electrode Positioning	The method for electrode placement over the head inside the scanner (i.e., targeting software, 10-20 convention with or without EEG cap, functional targeting (fMRI), computational head models or others).	4.83 (0.60)	1.3.1. Report electrode positioning as precisely as possible to facilitate reproduction. It is usually inadequate to simply report an anatomical target, for example, “the anodal electrode was placed over M1”.	51 (100%)
			1.3.2. Report whether electrode positioning is based on the individual anatomy or a group template if imaging or head modeling is used for electrode positioning.	49 (98%)
			1.3.3. Report how electrode positioning is performed at the individual participant level. For example, was a neuronavigation system used or the EEG 10-20 system or something else.	49 (96%)
			1.3.4. Report the methods to ensure that the same electrode locations were used again if there are multiple sessions.	48 (94%)
			1.3.5. Report clearly how the electrodes are held in place inside the scanner including use of headgear or customized supports.	42 (86%)
			1.3.6. Report how electrodes and their connecting cables over the head are located in relationship to the MR head coil while the subject is laying down inside the scanner and how the head was held in place - e.g., pillows, foam, etc. to ensure that position of head/electrodes remain in the same place during the scans while the convenience of the participant is ensured.	37 (73%)
			1.3.7. Report a post-hoc validation of the electrode positioning based on anatomical images with the electrodes in place if practical. For optimal validation, current density models based on anatomical images may be used (e.g., ROAST, SIMNIBS, etc.). It would be even better to directly measure the electric fields using magnetic resonance current density imaging (MRCDI) and MR electrical impedance tomography (MREIT) 101, however, MREIT and MRCDI are still not available in most of the institutes.	27 (54%)
1.4. MR Conditional Skin-Electrode Interface	The MR conditional skin-electrode interface (saline solution, conductive paste, gel, etc.).	4.09 (0.90)	1.4.1. Report a photo or a schematic figure or technical details showing in a reproducible way how the electrode with the MR conditional skin-electrode interface is connected to the cranium (including a view from the underneath of the electrode if needed). If headgear or headstraps obscure the electrodes, you may provide an image without the headstraps.	32 (64%)
			1.4.2. Report any other MR-specific strategies to restrict the contact medium (such as within an electrode holder) to avoid short circuits.	36 (72%)
1.5. Amount of Contact Medium (Paste/Gel/Electrolyte	The amount or thickness of medium that is used for each electrode or a method to control this confounding variable	2.91 (1.13)	1.5.1. Report technical details/difficulties in measuring the thickness of the layer of conductive material underneath the electrodes and how cream/gel underneath the electrodes is evenly distributed. Although this can be important, mainly when having big electrodes, in practice, the amount of cream/gel underneath the electrodes may not be evenly distributed. Developing new methods to measure, control, and report this important variable are desired. Reporting the impedance (before, during, and after stimulation) provides insight on electrode contact quality, but is not in itself a substitute for controlling and reporting contact medium parameters.	21 (40%)
1.6. Electrode Placement Visualization	Any photo/diagram/figure to precisely visualize the electrode montage inside the scanner and make replication possible.	3.56 (1.17)
1.7. RF Filter	The RF filtering method (stimulator device connected to the subject via penetration panel (e.g., RF filters from different brands) or connected via waveguide with RF boxes on either end).	3.50 (1.07)	1.7.1. Report the attenuation characteristic of the RF filtering.	25 (50%)
			1.7.2. Report any potential regulatory consideration/limitation at the institute/university/country level.	13 (27%)
1.8. Wire Routing Pattern	Wire routing pattern (out back of bore and around the control room or straight down front of bore to control room).	3.43 (1.22)	1.8.1. Report whether/how the state of the cables is checked after the subject entering the scanner to avoid creating any loops.	29 (58%)
			1.8.2. Report the length of the cables required to connect inner with outer box using box cable, how the cables are connected to the electrodes, in which direction the cables are leaving the head, how multiple connecting cables are managed together, and depending on the geometry of the head coil, how the cables are entered into the coil. A sketch might be helpful to visualize these details.	31 (61%)
			1.8.3 Report how the cables and filter boxes are secured to prevent motion during the scan (i.e., sandbag, tape, etc.).	29 (59%)
			1.8.4. Report if there are any modifications from manufacturer recommendations.	39 (78%)
			1.8.5. Report any potential regulatory consideration/limitation at the institute/university/country level.	14 (29%)
1.9. tES-fMRI Machine Synchronization/Communication	The synchronization/communication method between the tES device, the stimulus delivery PC, and the scanner.	3.70 (1.09)	1.9.1. Report any synchronization between tES and MRI. Synchronization/communication can be TTL scanner sync pulse to trigger/sync (tES and/or non-tES) stimulus recorded via USB/parallel port/NI device; use of markers for tES, or manual triggering of the TES device.	49 (96%)