Recommendations of Choice of Head Coil and Prescan Normalize Filter Depend on Region of Interest and Task

Abstract

The performance of MRI head coils together with the influence of the prescan normalize filter in different brain regions was evaluated. Functional and structural data were recorded from 26 participants performing motor, auditory, and visual tasks in different conditions: with the 20- and 64-channel Siemens head/neck coil and the prescan normalize filter turned ON or OFF. Data were analyzed with the MRIQC tool to evaluate data quality differences. The functional data were statistically evaluated by comparison of the β estimates and the time-course signal-to-noise ratio (tSNR) in four regions of interest, i.e., the auditory, visual, and motor cortices and the thalamus. The MRIQC tool indicated a better data quality for both functional and structural data with the prescan normalize filter, with an advantage for the 20-channel head coil in functional data and an advantage for the 64-channel head coil in structural measurements. Nevertheless, recommendations for the functional data regarding choice of head coils and prescan normalize filter depend on the brain regions of interest. Higher β estimates and tSNR values occurred in the auditory cortex and thalamus with the prescan normalize filter, whereas the contrary was true for the visual and motor cortices. Due to higher β estimates in the visual cortex in the 64-channel head coil, this head coil is recommended for studies investigating the visual cortex. For most of the research questions, the 20-channel head coil is better suited for functional experiments, with the prescan normalize filter, especially when investigating deep brain areas. For anatomical studies, the 64-channel head coil seemed to be the better choice.

Keywords: 20-channel head coil; 64-channel head coil; MRIQC; anatomical images; echo-planar imaging; prescan normalize.

FIGURE 1

(A) Raw data for functional (left column) and structural data (right column) with the prescan normalize filter OFF (first row) and ON (second row) from one participant. (B) Differences in brain masks for the different masking thresholds (0.8 = original in left column and 0.5 = adjusted in right column) between prescan normalize OFF (first row) and ON (second row). Brain masks are created during the whole-brain analyses with SPM. SPM, Statistical Parametric Mapping.

FIGURE 2

MRIQC results for the functional data: (A) results for the signal-to-noise ratio; higher values are better. (B) Results for global correlation; smaller values are better. (C) Results for the ghost-to-signal ratio; lower values are better. Each figure represents the different tasks (motor, auditory, and visual) separated for each head coil (blocks on the left side for the 20-channel head coil and on the right side for the 64-channel head coil) as well as the prescan normalize ON (black) and OFF (gray) condition.

FIGURE 3

Results of the interactions (A) ROI × task × prescan normalize and (B) ROI × head coil × prescan normalize, separated for each ROI. (A) Largest β estimates in each ROI correspond to the respective task. Note that participants saw numbers on the screen in the motor task, thus resulting in enhanced β estimates in the visual cortex also for the motor task. There were differences regarding the prescan normalize filter with larger β estimates for prescan normalize OFF (gray) in the visual and motor cortices, whereas there was no difference between prescan normalize ON (black) and OFF in the auditory cortex and even the contrary pattern with larger values for prescan normalize ON in the thalamus. (B) Regarding the differences in the head coils, there were larger β estimates for the prescan normalize OFF in the visual and motor cortices, whereas again, there was no difference in the auditory cortex, but larger values for prescan normalize ON in the thalamus. ROI, region of interest.

FIGURE 4

Whole-brain analyses with main effect of task separated for (A) motor, (B) auditory, and (C) visual tasks. Results are whole-brain FWE corrected (p < 0.05) with cluster level > 100. (D) Interaction between task and prescan normalize in whole-brain fMRI analysis. ROI analyses with activation in bilateral visual cortex and left auditory cortex, FWE corrected (p < 0.05). (E) Extraction of β estimates in peak maximum of the visual and auditory cortex. β estimates for prescan normalize OFF (gray) are larger in the visual cortex for both tasks involving visual cortex activity, i.e., the visual and the motor task. β estimates in the auditory cortex are larger for prescan normalize ON (black). FWE, family wise error; ROI, region of interest.

FIGURE 5

Visualization of the ROI × head coil × task × prescan normalize interaction of the tSNR ROI analyses. Individual subfigures show the results for the different ROIs separately for the different head coils (left 20-channel, right 64-channel), tasks (motor, auditory, and visual) and the prescan normalize filter ON (black) and OFF (gray). Results for the visual (A) and motor cortex (B) are comparable and in contrast to the auditory cortex (C) and thalamus (D), with a larger tSNR for prescan normalize OFF and with stronger differences between ON and OFF in the 20-channel head coil compared with the 64-channel head coil. In the (C) auditory cortex, there was a higher tSNR for the 64-channel head coil and the prescan normalize ON. In contrast, the (D) thalamus showed the similar pattern for the prescan normalize ON but higher tSNR in the 20-channel head coil. ROI, region of interest; tSNR, time-course signal-to-noise ratio.

FIGURE 6

tSNR maps for the 20-channel head coil (A,C left column) and the 64-channel head coil (B,D right column) with the prescan normalize filter OFF (A,B upper row) and ON (C,D lower row). tSNR, time-course signal-to-noise ratio.

FIGURE 7

MRIQC results for the structural data: (A) results for the analyses of the signal-to-noise ratio, larger values are better. (B) Results of analyses of the contrast-to-noise ratio; larger values are better. There is an advantage for the prescan normalize filter turned ON.