(PRESS) Point resolved spectroscopy is a multi echo single shot technique to obtain spectral data. PRESS is a 90°-180°-180° (slice selective pulses) sequence. The 90° radio frequency pulse rotates the spins in the yx-plane, followed by the first 180° pulse (spin rotation in the xz-plane) and the second 180° pulse (spin rotation in the xy-plane), which gives the signal.
With the long echo times used in PRESS, there is a better visualization of metabolites with longer relaxation times. Many of the metabolites depicted by stimulated echo technique are not seen on point resolved spectroscopy, but PRESS is less susceptible to motion, diffusion, and quantum effects and has a better SNR than stimulated echo acquisition mode (STEAM).

Quadrature detection is used in magnetic resonance imaging as well as in Doppler ultrasound and is also called quadrature demodulation or phase quadrature technique.
With this phase sensitive demodulation technique the complex demodulated signal is separated into two components. One is called the real channel; the second part is called the imaginary channel and is located 90° away from the real channel. The signals from both channels are combined to produce a single set of quadrature detected real and imaginary spectra. In MRI, the parts of the demodulated MR signal are further processed by Fourier transformation analysis. All information on the MR signal components e.g. amplitude, phase, and frequency is given by this quadrature detection combined with Fourier analysis.

Quick Overview

Fat suppression (SPIR or FatSat) is very critical to the magnetic field homogeneity. Eddy currents in the patient results in B1 disturbance from left to right and from anterior to posterior. The artifact is seen as signal intensity variations with SPIR, like a signal intensity loss diagonal in the image. The short T1 inversion recovery (STIR) sequence is due to another type of fat suppression insensitive to this artifact.

Take short T1 inversion recovery (STIR) instead spectral presaturation inversion recovery (SPIR) for fat suppression.

A measure of the non-spherical distribution of electrical charge possessed by nuclei with a nuclear spin number greater than 1/2. The resulting interaction with electric field gradients in the molecule can lead to a shortening of relaxation times and a broadening of spectral lines.

Standard compound used as a standard reference spectral line for defining chemical shifts for a given nucleus. As recommended by the ASTM, for 1H it is tetramethylsilane (TMS) and for 31P it is phosphoric acid, although for practical biological applications water and PCr have been used as secondary references for hydrogen and phosphorus spectroscopy, respectively. The reference compound can be in a capsule outside of the subject (external) or can be in the subject (internal); internal references are generally preferable where possible, as external references may be subject to different conditions.