SPEEDER™ is Toshiba's patented parallel imaging technology for high-speed imaging. This technique reduces examination time for MRI studies by a factor of up to three while enabling clinicians to capture high-quality images with detailed diagnostic information. With SPEEDER™, cardiac and MRA examinations are more patient-friendly and tolerable with shorter scan times and improved image quality.

See also Sensitivity Encoding.

The NMR, MRI relevant nuclear spin is the rotational movement of a subatomic particle (proton or neutron) around its axis. Whether a nucleus has an overall spin, depends on its amount of protons and neutrons. Nuclei with an identical number of protons and neutrons cancel out their overall spins. Nuclei with an odd number of protons or an odd number of neutrons or both have an overall spin. This spin is measured with a nuclear spin quantum number (I). The nuclear spin quantum number of a nuclei depends on the protons/neutrons which are not paired, and is a positive integer multiple of 0.5. 1H, 19F, 13C, 31P and 15N are examples of nuclei with an nuclear spin quantum number of 0.5, 2H and 14N have a nuclear spin quantum number of 1.

See also Spin Quantum Number.

(N) The SI units is moles/m³.
Definition: The concentration of nuclei in tissue processing at the Larmor frequency in a given region; one of the principal determinants of the strength of the NMR signal from the region.
For water, there are about 1.1 x 105 moles of hydrogen per m³, or 0.11 moles of hydrogen/cm³.
The signal intensity measured is related to the square of the xy-magnetization, which in a SE pulse sequence is given by
Mxy = Mxy0(1-exp(-TR/T1)) exp(-TE/T2)
where Mxy0 = Mz0 is proportional to the proton or spin density, and corresponds to the z-magnetization present at zero time of the experiment when it is tilted into the xy-plane.
True spin density is not imaged directly, but must be calculated from signals received with different interpulse times. The spin density contrast can be generated by using a long TR and sampling the data immediately after the RF pulse (with a TE as short as possible).

(SE) The Reappearance of the MR signal after the FID has apparently died away, as a result of the effective reversal (rephasing) of the dephasing spins by techniques such as specific RF pulse sequences or pairs of field gradient pulses, applied in time shorter than or on the order of T2. Proper selection of the TE time of the pulse sequence can help to control the amount of T1 or T2 contrast present in the image. Pulse sequences of the spin echo type, usually employs a 90° pulse, followed by one or more 180° pulses to eliminate field inhomogeneity and chemical shift effects at the echo. Caused by this 180° refocusing pulse, spin echo or fast spin echo (FSE, TSE) sequences are more robust against e.g. susceptibility artifacts than sequences of the gradient echo type.

MR imaging technique in which the spin echo is used rather than the FID. The proper selection of the echo and repetition time of the pulse sequence can help to control the amount of T1 or T2 contrast present in the image. Spin echo imaging can be used to create images that depend strongly on T2 if TE has a value on the order of or greater than T2 of the relevant image details. The spin echoes can be produced as a train of multiple echoes, e.g. using the CPMG pulse sequence.

See also Spin Echo Sequence.