Despite its recent discovery, fMRI is the most popular neuroimaging technique for mapping brain activation. The human brain is a heterogeneous and complex organ composed by functional components, at different spatial scales, finer than a millimeter, which works at different temporal scale. The goal of an imaging technique is to be able to fully resolve these complexities and this ability also depends on its spatial and temporal resolution. In order to improve efficiency, variations of the conventional fMRI techniques were developed.
Among advanced fMRI methods, Multi Band (MB) MRI and Multi Echo (ME) MRI, as well as their combination (MB-ME MRI), hold a paramount role, especially due to the advantage of being usable on the wide platform of installed clinical scanners.


Multi Band

fMRI experiments last several minutes in some cases, when several data have to be acquired. These acquisition sessions are uncomfortable for patients and are sensitive to several artifacts especially those due to motion.
In order to reduce examination time and to increase temporal and spatial resolution, an important goal in in vivo MRI is to optimize the speed of image acquisition. MB imaging provides an attractive and alternative solution to these challenges.
Differently from other approaches, such as the use of ultrahigh magnetic field, (above 7 T) MB sequences have the advantage of being usable on the wide platform of installed clinical scanners
The MB technique is based on the simultaneous excitation of multiple brain slices using a single NMR RF (Radio Frequency) pulse, tailored at multiple frequencies. Each receiving coil measures a signal that is a linear combination of signals from the excited slices modulated by the coil sensitivity. The real innovation of MB technique, compared with its ancestors, is that it allows to reduce the value of an important acquisition parameter, the TR (Repetition Time, the period between two consecutive RF pulses), with the resulting several improvement that this reduction involves. Today, MB approach has the potential to become an essential data acquisition strategy in the study of both functional and structural feature of human brain.


Multi Echo

Standard fMRI data are usually acquired in a single optimal TE (Echo Time, the time after the RF pulse at which the response signal is measured) in order to achieve a maximum functional contrast. This optimal value is set equal to the average T2* parameter (the transverse relaxation time, the time required for the response signal from a given tissue to decay) across brain tissue, at a certain field strength, in order to maximize the response of interest. Nevertheless, even if the optimal TE was chosen, thus a value which approximates the average T2*, this parameter varies considerably across brain so that the sensitivity of MRI technique with a fixed TE cannot be optimal across the whole brain, but could elicit great variability in the contrast of functional images. Moreover, functional MRI data are characterized by fluctuations of different origins. In addition to fluctuation of interest, which are the ones of neuronal origin and are TE-dependent, the MRI signal contains nuisance signal fluctuations. These latter are due to subject motion, respiration, cardiac function, hardware instabilities etc. and they are often TE-independent. Taking advantage of this, the combination of data from ME MRI sequence enable the separation of confounds from the signal of interest
Definitively, the combination of data from ME MRI sequences improves sensitivity of fMRI technique and it enables to achieve the maximum feasible functional contrast at a certain field strength in the whole brain.
Moreover, ME MRI acquisition is implemented by a small modification of single echo acquisition, and it could have a large everyday-life impact, since the improvement on repeatability and quality of data is especially true for clinical environment where patients exhibit high amount of movements or in clinical single subject studies.