Neuroimaging

Introduction

Several techniques are currently available that provides images of the structure and the function of the human brain. Neuroimaging is the acronym for it. Imaging can be performed by the non-invasive method of Magnetic Resonance (MRI). The principles of MRI are fully described by interaction processes between matter (i.e. nuclei composed of protons and neutrons) and photons (the carrier of the electromagnetic forces) radiation. Due to the small dimensions of both interaction particles quantum physical description is needed. Moreover, a large number of interaction particles (i.e. mass phenomenon) are required in order that MR scanner may record the MR signal. Fortunately, the human brain contains large number of water molecules (i.e. protons) so that in most cases there is a genuine MR signal. Due to the non-invasive nature of the method, MRI can be repeatedly applied to a large cohort of subjects: from neuropediatric up to elderly patients. The technique has been successfully applied in medicine, neuroscience, psychology and psychiatry.

In structural MRI images of the gray matter (GM) and of the white matter (WM) are recorded. Dedicated MR sequences are sensitive to both tissue types are typically acquired at high resolution (i.e. 1 mm x 1 mm x 1mm iso-voxel). Both maps require rigorous pre-processing and artefacts removal, before quantitative and qualitative features are extracted.

Functional MRI are tipically acquired in 2D slices for a large number of volumes that eventually form a time series. A paradigm containing different stimuli (i.e. the task) is presented to the subjects and the human brain is then assumed to involve distinct brain regions for solving the task. The paradigm can be a repetition of the same stimulus for a certain interval (i.e. block-design) or can be a fast, balanced and randomly presented sequence of different stimuli (i.e. fast-event-related fMRI design [er-fMRI]). No matter which design type is applied, a rigorous pre-processing pipeline is needed before a 1-level analysis, and subsequently, a 2-level analysis can be computed. A majority of studies are performed on fMRI signal based on “blood oxygenation level-dependent” contrast [BOLD-fMRI].

However, fMRI can also be performed with non-BOLD techniques: such as Arterial Spin Labelling (ASL). This method allows the absolute quantification of cerebral blood flow (CBF) in units of [ml/100 g/min]. Moreover, by combining BOLD fMRI and CBF fMRI measurements under hypercapnia condition (i.e. administration of 5 % CO2), additional physiological features such as the cerebral metabolic rate of Oxygen (CMRO2).

can be estimated. Therefore, knowledge of the neurovascular-coupling can be assessed.

 

Find hereafter a few examples of maps as obtained by Neuroimaging methods.

sample mri pictures
cube brain images