@ Agata: In addition to focussing on specific techniques, it is always worth remembering the fundamental question. @Agata, You may be interested in the following publications on examining connectivity in the resting state utilising a variety of techniques from the Max Planck by Daniel Margulies and Kristof Gorgolewski etc (see esp reference 2; reference 3 makes use of transcranial dcs to modulate resting state connectivity ) :

1. Kipping, J., Grodd, W., Kumar, V., Taubert, M., Villringer, A., & Margulies, D. S. (2013). Overlapping and parallel cerebello-cerebral networks contributing to sensorimotor control: An intrinsic functional connectivity study. NeuroImage, 83, 837-848

2. Rohr, C., Okon-Singer, H., Craddock, R. C., Villringer, A., & Margulies, D. S. (2013). Affect and the brain's functional organization: A resting-state connectivity approach. PLoS One, 8(7): e68015

3. Sehm, B., Schäfer, A., Kipping, J., Margulies, D. S., Conde, V., Taubert, M., Villringer, A., & Ragert, P. (2012). Dynamic modulation of intrinsic functional connectivity by transcranial direct current stimulation. Journal of Neurophysiology, 108(12), 3253-3263.

4. Taubert, M., Lohmann, G., Margulies, D. S., Villringer, A., & Ragert, P. (2011). Long-term effects of motor training on resting-state networks and underlying brain structure. NeuroImage, 57(4), 1492-1498

5. Böttger, J., Margulies, D. S., Horn, P., Thomale, U. W., Podlipsky, H., Shapira-Lichter, I., Chaudhry, S. J., Szkudlarek, C., Mueller, K., Lohmann, G., Hendler, T., Bohner, G., Fiebach, J. B., Villringer, A., Vajkoczy, P., & Abbushi, A. (2011). A software tool for interactive exploration of intrinsic functional connectivity opens new perspectives for brain surgery. ACTA NEUROCHIRURGICA, 153(8), 1561-1572

6. Gee, D. G., Biswal, B. B., Kelly, C., Stark, D. E., Margulies, D. S., Shehzad, Z. E., Uddin, L. Q., Klein, D., Banich, M. T., Castellanos, F. X., & Milham, M. P. (2011). Low frequency fluctuations reveal integrated and segregated processing among the cerebral hemispheres. NeuroImage, 45(1), 517-527.

7. Callard, F., & Margulies, D. S. (2011). The Subject at Rest: Novel conceptualizations of self and brain from cognitive neuroscience's study of the "resting state". Subjectivity, 4(3), 227-257

8. Lohmann, G., Margulies, D. S., Horstmann, A., Pleger, B., Lepsien, J., Goldhahn, D., Schlögl, H., Stumvoll, M., Villringer, A., & Turner, R. (2010). Eigenvector centrality mapping for analyzing connectivity patterns in fMRI data of the human brain. PLoS One, 5(4): e10232

9. Roy, A. K., Shehzad, Z. E., Margulies, D. S., Kelly, A. M. C., Uddin, L. Q., Gotimer, K., Biswal, B. B., Castellanos, F. X., & Milham, M. P. (2009). Functional connectivity of the human amygdala using resting state fMRI. NeuroImage, 45(2), 614-626.

10. Shehzad, Z. E., Kelly, A. M. C., Reiss, P. T., Gee, D. G., Gotimer, K., Uddin, L. Q., Lee, S. H., Margulies, D. S., Roy, A. K., Biswal, B. B., Petkova, E., Castellanos, F. X., & Milham, M. P. (2009). The resting brain: Unconstrained yet reliable. Cerebral Cortex, 19(10), 2209-2229

11. Di Martino, A., Scheres, A., Margulies, D. S., Kelly, A. M. C., Uddin, L. Q., Shehzad, Z. E., Biswal, B. B., Walters, J. R., Castellanos, F. X., & Milham, M. P. (2008). Functional connectivity of human striatum: A resting state fMRI study. Cerebral Cortex, 18(12), 2735-2747.

Hope this helps !

Multichannel receiver coils of greater density have the advantages listed above related to higher acceleration capabilities and greater surface SNR. Several complexities need to be considered when evaluating a coil for a given indication:

1. The old quadrature (single channel) head coils were far more uniform than phased array coils but have lower SNR, particularly at the cortical surface that PA coils. They also accentuated the central brain brightness commonly seen at 3T attributed to dielectric resonance effects (though this term may not be precise.)

2. The advent of phased array coil technology opened the door to parallel imaging and afforded greater SNR. This had the fortuitous virtue of greater signal at the superficial aspects of the brain, which balanced the 3T brightness of the central aspects of the brain.

3. Greater superficial signal with PA coils is due to the signal dropping by the square of the distance from a coil element. There is often a trade off of less "coil penetration" with greater coil density (higher number of coil elements) so that the fall off of signal at deep brain structures becomes more problematic.

4. Newer technology seems to be better at addressing #3 and I am looking forward to working with the Siemens 64 channel Head and Neck coil that recently received FDA approval.

5. Depending on your vendor and the sequences at your disposal, image intensity corrections may have an impact on the discussion. There are uniformity issues inherent in some of these algorithms. GE has SCIC and PURE and Siemens has "prescan normalize" and I would be grateful for insight from others as to the appropriateness of using these in fMRI data collection and analysis.

6. Dual transmit capabilities may also impact the discussion of uniformity. Looking forward to a Prisma installation this Spring, but again I would be interested in others experience.

Mark