Comparison of a 32‐channel with a 12‐channel head coil: Are there relevant improvements for functional imaging?

Abstract

Purpose: To evaluate the suitability of a 12-or 32-channel head coil and of a prescan normalization filter for functional magnetic resonance imaging (fMRI) studies at different brain regions.Materials and Methods: fMRI was obtained from 36 volunteers executing a visually instructed motor paradigm using a 12-channel head matrix coil and a 32-channel phased-array head coil with and without prescan normalization filtering at 3 T. The time-course signal-to-noise ratio (tSNR) and the magnitude of functional activation (betavalue, t-value, percent signal change) were statistically compared between experimental conditions for the contralateral primary motor and visual cortex, contralateral thalamus, and ipsilateral anterior cerebellar hemispheres.Results: tSNR was higher overall measuring with the 32-channel array and with prescan normalization. Without filtering, the 32-channel array delivered higher functional activation magnitudes for the visual cortex, whereas the 12-channel array seemed superior in this respect in thalamus and cerebellum. Filtering did not considerably affect the fMRI-activation magnitude detected from the 12-channel coil; its application favored the 32-channel coil at the subcortical and cerebellar locations but disfavored it at the cortical ones. Conclusion:The 32-channel coil detected more fMRI-activation cortically but less subcortically than the 12-channel coil; prescan normalization improved activation parameters only at central brain structures.

Contrast-Enhanced 3-Dimensional SPACE Versus MP-RAGE for the Detection of Brain Metastases

“…Nevertheless, choice of coil ultimately did not influence SNR in terms of statistical significance, most likely secondary to the marginal increases and, in some instances, decreases in SNR observed within the caudate and the pons with the 32-channel coil. This phenomenon of decreased central SNR has been observed previously 14,16 and was further confirmed in this study by comparison of peripheral to central SNR ratios (ie, Ratio p j c ) between the coils. This ratio was statistically significantly greater with the 32-channel relative to the 12-channel coil.…”

“…Seventeen consecutive patients at a Gamma Knife facility (mean [SD] patient age, 64 [14] years) with known brain parenchymal metastatic disease or metastatic disease seen on standard noncontrast MRI scans were recruited prospectively from December 2009 to May 2011. Informed consent was obtained in this institutional review boardYapproved study.…”

“…14,16 To examine this observation in the present study, a ratio of peripheral (p) to central (c) SNR was computed to assess for uniformity of SNR throughout the imaging volume. Because the image contrast between the 2 evaluated sequences differed considerably, the following calculation was obtained for each coil/sequence combination examined:…”

The human brain representation of odor identification

“…In the anatomic MTL ROI the statistical threshold for the OI event-related analysis was set to voxel level z ϭ 1.645 and P Ͻ 0.05, uncorrected for multiple comparisons, with a minimum of 9 continuous voxels. A more liberal statistical analysis was used in the OI analysis because of the lower number of observations in the event-related analysis, and due to the expected lower BOLD signal from the MTL due to susceptibility (Ojemann et al 1997(Ojemann et al , 2010) and coil effects (Kaza et al 2011). Moreover, entorhinal BOLD activity in response to odor stimulation has been shown to be substantially smaller than in piriform cortex and amygdala (Tabert et al 2007).…”

“…In the within-subject whole brain group level analysis of OI, entorhinal cortex activity was restricted to a small region and had a low z value, whereas many voxels were active with high max parameter estimate values in the anatomic entorhinal ROI. This discrepancy probably stems from a combination of MR technical (Kaza et al 2011;Ojemann 1997Ojemann , 2010 issues combined with local anatomic-physiologic characteristics of odor processing in the entorhinal cortex. In rats entorhinal neurons display odor selectivity (Young et al 1997), and thus both inter-and intraindividual activity to the identified odors may differ, thus contributing to a limited area of activation in the third level group analysis, although activity for each individual was high, as shown in the functional and anatomic entorhinal ROI analyses.…”