Potential impact of a 32-channel receiving head coil technology on the results of a functional MRI paradigm

The feasibility of half-dose contrast-enhanced scanning of brain tumours at 5.0 T: a preliminary study

PURPOSE

This study investigated and compared the effects of Gd enhancement on brain tumours with a half-dose of contrast medium at 5.0 T and with a full dose at 3.0 T.

METHODS

Twelve subjects diagnosed with brain tumours were included in this study and underwent MRI after contrast agent injection at 3.0 T (full dose) or 5.0 T (half dose) with a 3D T1-weighted gradient echo sequence. The postcontrast images were compared by two independent neuroradiologists in terms of the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and subjective image quality score on a ten-point Likert scale. Quantitative indices and subjective quality ratings were compared with paired Student's t tests, and interreader agreement was assessed with the intraclass correlation coefficient (ICC).

RESULTS

A total of 16 enhanced tumour lesions were detected. The SNR was significantly greater at 5.0 T than at 3.0 T in grey matter, white matter and enhanced lesions (p < 0.001). The CNR was also significantly greater at 5.0 T than at 3.0 T for grey matter/tumour lesions, white matter/tumour lesions, and grey matter/white matter (p < 0.001). Subjective evaluation revealed that the internal structure and outline of the tumour lesions were more clearly displayed with a half-dose at 5.0 T (Likert scale 8.1 ± 0.3 at 3.0 T, 8.9 ± 0.3 at 5.0 T, p < 0.001), and the effects of enhancement in the lesions were comparable to those with a full dose at 3.0 T (7.8 ± 0.3 at 3.0 T, 8.7 ± 0.4 at 5.0 T, p < 0.001). All subjective scores were good to excellent at both 5.0 T and 3.0 T.

CONCLUSION

Both quantitative and subjective evaluation parameters suggested that half-dose enhanced scanning via 5.0 T MRI might be feasible for meeting clinical diagnostic requirements, as the image quality remains optimal. Enhanced scanning at 5.0 T with a half-dose of contrast agents might benefit patients with conditions that require less intravenous contrast agent, such as renal dysfunction.

Reproducibility of functional connectivity metrics estimated from resting-state functional MRI with differences in days, coils, and global signal regression

In multisite studies, differences in imaging acquisition systems could affect the reproducibility of the results when examining changes in brain function using resting-state functional magnetic resonance imaging (rs-fMRI). This is also important for longitudinal studies, in which changes in equipment settings can occur. This study examined the reproducibility of functional connectivity (FC) metrics estimated from rs-fMRI data acquired using scanner receiver coils with different numbers of channels. This study involved 80 rs-fMRI datasets from 20 healthy volunteers scanned in two independent imaging sessions using both 12- and 32-channel coils for each session. We used independent component analysis (ICA) to evaluate the FC of canonical resting-state networks (RSNs) and graph theory to calculate several whole-brain network metrics. The effect of global signal regression (GSR) as a preprocessing step was also considered. Comparisons within and between receiver coils were performed. Irrespective of the GSR, RSNs derived from rs-fMRI data acquired using the same receiver coil were reproducible, but not from different receiver coils. However, both the GSR and the channel count of the receiver coil have discernible effects on the reproducibility of network metrics estimated using whole-brain network analysis. The data acquired using the 32-channel coil tended to have better reproducibility than those acquired using the 12-channel coil. Our findings suggest that the reproducibility of FC metrics estimated from rs-fMRI data acquired using different receiver coils showed some level of dependence on the preprocessing method and the type of analysis performed.

A methodological checklist for fMRI drug cue reactivity studies: development and expert consensus

Cue reactivity is one of the most frequently used paradigms in functional magnetic resonance imaging (fMRI) studies of substance use disorders (SUDs). Although there have been promising results elucidating the neurocognitive mechanisms of SUDs and SUD treatments, the interpretability and reproducibility of these studies is limited by incomplete reporting of participants' characteristics, task design, craving assessment, scanning preparation and analysis decisions in fMRI drug cue reactivity (FDCR) experiments. This hampers clinical translation, not least because systematic review and meta-analysis of published work are difficult. This consensus paper and Delphi study aims to outline the important methodological aspects of FDCR research, present structured recommendations for more comprehensive methods reporting and review the FDCR literature to assess the reporting of items that are deemed important. Forty-five FDCR scientists from around the world participated in this study. First, an initial checklist of items deemed important in FDCR studies was developed by several members of the Enhanced NeuroImaging Genetics through Meta-Analyses (ENIGMA) Addiction working group on the basis of a systematic review. Using a modified Delphi consensus method, all experts were asked to comment on, revise or add items to the initial checklist, and then to rate the importance of each item in subsequent rounds. The reporting status of the items in the final checklist was investigated in 108 recently published FDCR studies identified through a systematic review. By the final round, 38 items reached the consensus threshold and were classified under seven major categories: 'Participants' Characteristics', 'General fMRI Information', 'General Task Information', 'Cue Information', 'Craving Assessment Inside Scanner', 'Craving Assessment Outside Scanner' and 'Pre- and Post-Scanning Considerations'. The review of the 108 FDCR papers revealed significant gaps in the reporting of the items considered important by the experts. For instance, whereas items in the 'General fMRI Information' category were reported in 90.5% of the reviewed papers, items in the 'Pre- and Post-Scanning Considerations' category were reported by only 44.7% of reviewed FDCR studies. Considering the notable and sometimes unexpected gaps in the reporting of items deemed to be important by experts in any FDCR study, the protocols could benefit from the adoption of reporting standards. This checklist, a living document to be updated as the field and its methods advance, can help improve experimental design, reporting and the widespread understanding of the FDCR protocols. This checklist can also provide a sample for developing consensus statements for protocols in other areas of task-based fMRI.

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

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.

Brain γ-aminobutyric acid (GABA) detection in vivo with the J-editing (1) H MRS technique: a comprehensive methodological evaluation of sensitivity enhancement, macromolecule contamination and test-retest reliability

Abnormalities in brain γ-aminobutyric acid (GABA) have been implicated in various neuropsychiatric and neurological disorders. However, in vivo GABA detection by (1) H MRS presents significant challenges arising from the low brain concentration, overlap by much stronger resonances and contamination by mobile macromolecule (MM) signals. This study addresses these impediments to reliable brain GABA detection with the J-editing difference technique on a 3-T MR system in healthy human subjects by: (i) assessing the sensitivity gains attainable with an eight-channel phased-array head coil; (ii) determining the magnitude and anatomic variation of the contamination of GABA by MM; and (iii) estimating the test-retest reliability of the measurement of GABA with this method. Sensitivity gains and test-retest reliability were examined in the dorsolateral prefrontal cortex (DLPFC), whereas MM levels were compared across three cortical regions: DLPFC, the medial prefrontal cortex (MPFC) and the occipital cortex (OCC). A three-fold higher GABA detection sensitivity was attained with the eight-channel head coil compared with the standard single-channel head coil in DLPFC. Despite significant anatomical variation in GABA + MM and MM across the three brain regions (p < 0.05), the contribution of MM to GABA + MM was relatively stable across the three voxels, ranging from 41% to 49%, a non-significant regional variation (p = 0.58). The test-retest reliability of GABA measurement, expressed as either the ratio to voxel tissue water (W) or to total creatine, was found to be very high for both the single-channel coil and the eight-channel phased-array coil. For the eight-channel coil, for example, Pearson's correlation coefficient of test vs. retest for GABA/W was 0.98 (R(2)  = 0.96, p = 0.0007), the percentage coefficient of variation (CV) was 1.25% and the intraclass correlation coefficient (ICC) was 0.98. Similar reliability was also found for the co-edited resonance of combined glutamate and glutamine (Glx) for both coils. Copyright © 2016 John Wiley & Sons, Ltd.

Resting-state networks in healthy adult subjects: a comparison between a 32-element and an 8-element phased array head coil at 3.0 Tesla

BACKGROUND

Little research exists on the influence of a magnetic resonance imaging (MRI) head coil's channel count on measured resting-state functional connectivity.

PURPOSE

To compare a 32-element (32ch) and an 8-element (8ch) phased array head coil with respect to their potential to detect functional connectivity within resting-state networks.

MATERIAL AND METHODS

Twenty-six healthy adults (mean age, 21.7 years; SD, 2.1 years) underwent resting-state functional MRI at 3.0 Tesla with both coils using equal standard imaging parameters and a counterbalanced design. Independent component analysis (ICA) at different model orders and a dual regression approach were performed. Voxel-wise non-parametric statistical between-group contrasts were determined using permutation-based non-parametric inference.

RESULTS

Phantom measurements demonstrated a generally higher image signal-to-noise ratio using the 32ch head coil. However, the results showed no significant differences between corresponding resting-state networks derived from both coils (p < 0.05, FWE-corrected).

CONCLUSION

Using the identical standard acquisition parameters, the 32ch head coil does not offer any significant advantages in detecting ICA-based functional connectivity within RSNs.

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

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 (beta-value, 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.