Glossary Terms  Home

R

Raw Signal-to-Noise Ratio (raw SNR)

The ratio between the MR signal intensity associated with a sample (e.g. the brain) and the thermal noise that is measured outside the sample.

Radiofrequency Coils

Electromagnetic coils used to generate and receive energy at the sample's resonant frequency, which for field strengths typical to MRI is in the radiofrequency range.

Radiological Convention

The practice of displaying images of the brain so that the left side of the image is the right side of the brain and vice versa, as if one were facing the subject.

Random-effects analysis

Intersubject analysis that treats the effect of the experimental manipulation as variable across subjects, so that it could have a different effect upon different subjects.

Real-Time Analysis

A set of computational steps designed for rapid analysis of fMRI data, so that statistical tests are conducted immediately following acuisition of the images.

Reception

The process of receiving electromagnetic energy emitted by a sample at its resonant frequency (also called detection). As spins return to a low-energy state following the cessation of the excitation pulse, they emit energy that can be measured by a receiver coil.

Reference Volume

A target image volume to which other image volumes are to be aligned.

Relaxation

A change in net magnetization over time.

Region of Interest (ROI) analysis

Evaluating statistical tests on a predetermined collection of voxels, often chosen to reflect a priori anatomical distinctions within the brain.

Residual

The variability in the data that remains unexplained after accounting for the model factors.

Research Hypothesis

A proposition about the nature of the world that makes predictions about the results of an experiment.  For a hypothesis to be well formed, it must be falsifiable. 

Resolution Elements (or resels)

The independent statistical tests within an fMRI volume.

Resonant Frequency

The frequency of oscillation that provides maximum energy transfer to the system.

Retinotopic Mapping

A technique for dilineating functional regions within the visual cortex based upon their responses to stimuli presented at different retinal locations.

Right Hand Rule

A heuristic that can be used to determine the direction of a magnetic moment generated by a moving charge or electrical current. If the fingers of the right hand are curled around the direction of spin, then the magnetic moment will be in the direction indicated by the thumb.

Rigid Body Transformation

A spatial transformation that does not change the size or shape of an object; it has three translational parameters and three rotational parameters.

Rotating Frame

A reference frame that rotates at the Larmor frequency of the spin of interest. The rotating frame is adopted to simplify mathematical descriptions of the effects of excitation.

Rotation

The turning of an object around an axis in space (in the absence of translation).