TwinTree Insert


Glossary • I

I → Nuclear spin quantum number.

Image acquisition matrix: maximum image matrix, e.g., 256×256 pixels.

Image acquisition time: time required to carry out a magnetic resonance imaging pro­ce­dure. The additional image reconstruction time will also be important to determine how quickly the image can be viewed. In comparing multiple slice and volume imaging techniques, the equivalent image acquisition time per slice must be considered, as well as the actual image acquisition time.

Image guided spectroscopy → Localized spectroscopy.

Image matrix: grid of columns and rows, for instance 256×256, in this case with a total number of 64,536 pixels.

Image orientation: a recommended standard orientation for the presentation of MR images is: (1) transverse: patient's right on the left side of the image, anterior or ventral on top; (2) coronal: patient's right to left side of image, superior or head to the top; (3) sagittal: patient's head to the top, anterior to the left side of image. R (right), L (left), P (posterior), A (anterior), and if necessary S (superior) should be shown on the screen and the hardcopies, as appropriate. In displaying sagittal images, it is helpful to indicate whe­ther a slice is to the left or right of the midline.

Inductance: measure of the magnetic coupling between two current carrying loops (mu­tu­al inductance) (reflecting their spatial relationship) or of a loop (such as a coil) with itself (self inductance). One of the principal determinants of the resonance fre­que­ncy of an RF circuit.

Inhomogeneity: degree of lack of homogeneity, for example the fractional deviation of the local magnetic field from the average value of the field.

Interface: set of devices that enables the interaction of the computer and the spec­tro­me­ter. Particularly, this includes an analog to digital converter (ADC), which turns the ana­log voltages, such as the output of the RF receiver, into numbers that can be read by the computer. It also includes a digital to analog converter (DAC), which does the reverse, en­ab­ling the computer to produce control voltages.

Integer: a whole number (e.g. 1, 2, 3); 1.23 is a real number.

Intermediately weighted images: preferred term for proton-density weighted ima­ges.

Interpulse time: times between successive RF pulses used in pulse sequences. Par­ti­cu­lar­ly important are the inversion time (TI) in inversion recovery, and the time τ between a 90° pulse and the subsequent 180° pulse to produce a spin echo, which will be ap­pro­xi­ma­te­ly one-half the spin echo time (TE). The time between repetitions of pulse se­quen­ces is the repetition time (TR).

Intra-voxel incoherent motion: perfusion both act to reduce the signal observed in- vivo; the two effects are difficult to separate and the term intra voxel incoherent motion is used to describe their combined effect.

Inversion: a nonequilibrium state in which the macroscopic magnetization vector is re­ver­sed so that its orientation is opposite to the magnetic field; usually produced by adia­ba­tic fast passage or 180° RF pulses.

Inversion recovery (IR): pulse MR technique, wherein the nuclear magnetization is inverted at a time on the order of T1 before the regular imaging pulse-gradient se­quen­ces. The resulting partial relaxation of the spins in the different structures being imaged can be used to produce an image that depends strongly on T1.

Inversion time (TI): time between inversion (180° pulse) and the subsequent 90° pul­se which elicits an NMR signal in inversion recovery sequences.

Inversion transfer → Saturation transfer.

IR → Inversion recovery.

ISIS (Image Selective In Vivo Spectroscopy): a localization scheme consisting of eight scans with different combinations of three inversion pulses and receiver phase for each scan. Summation in the correct manner causes all the signals outside of the desired volume to cancel. Widely used for phosphorus spectroscopy.

IVIM → Intra Voxel Incoherent Motion.

Glossary • J

Joule, symbol J. 1 J is equal to the energy expended (or work done) in applying a force of one Newton through a distance of one meter (1 newton meter or N × m), or in passing an electric current of one ampere through a resistance of one ohm for one second.

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