Glossary Terms  Home

D

dB/dt

The change in magnetic field strength (dB) over time (dt).

Degrees of Freedom (df)

The number of independent observations within a data set.  For many statistical tests, there are n-1 degrees of freedom associated with n data points.

Deoxygenated Hemoglobin (Hb)

Hemoglobin with attached oxygen; it is diamagnetic

Descriptive Statistics

Statistics that summarize the sample data but do not allow inferences about the larger population

Design Matrix

In fMRI implementations of the general linear model, the specification of how the model factors change over time.

Detector Coil

An electromagnetic coil that measures energy emitted back to the environment after its initial absorption by the sample.

Diamagnetic

Having the property of a weak repulsion from a magnetic field.

Diffusion Tensor Imaging (DTI)

The collection of images that provide information about magnitude and direction of molecular diffusion.  It is often used to create maps of fractional anisotropy.  DTI is frequently used to test the integrity of white matter tracts. 

Distribution

The pattern of variation of a variable under some conditions.  For example, the normal distribution has a characteristic bell shape.

Dot Product

The scalar product of two vectors, it is created by summing the products along each dimension.