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Glossary • D

D: diffusion coefficient.

DAC → Digital to analog converter.

Data system → Computer.

DB/Dt (ΔB/Δt): the rate of change of the magnetic field (induction) with time. Because changing magnetic fields can induce electrical fields, this is one area of potential concern for safety limits.

Decoupling: when acquiring spectra of nuclei other than protons the effects of proton coupling can be removed (to improve the S/N ratio and simplify the spectra) by applying a train of 180° pulses at the proton frequency while acquiring at the frequency of the other nucleus.

Demodulator: another term for detector, by analog to broadcast radio receivers.

Detector: portion of the receiver that demodulates the RF NMR signal and converts it to a lower frequency signal. Most detectors now used are phase sensitive (e.g. quadrature demodulator/detector), and will also give phase information about the RF signal.

Dewar: thermos container to retain liquid gases, such as helium, at low temperatures (after Sir Janner Dewar).

Diamagnetic: a substance that will slightly decrease a magnetic field when placed within it (its magnetization is oppositely directed to the magnetic field, i.e., with a small negative magnetic susceptibility).

Diffusion: the process by which molecules or other particles intermingle and migrate due to their random thermal motion. NMR provides a sensitive technique for measuring diffusion of some substances.

Digital to analog converter (DAC): part of the interface that converts digital numbers from the computer into analog (ordinary) voltages or currents; used to generate gradient and RF wave forms.

Display window → Window.

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