What is k-space in MRI?

What is k-space in MRI?

The k-space is an extension of the concept of Fourier space well known in MR imaging. The k-space represents the spatial frequency information in two or three dimensions of an object. The k-space is defined by the space covered by the phase and frequency encoding data.

How is k-space different from k-space normal image space?

k-space is an array of numbers representing spatial frequencies in the MR image. K-space is the Fourier transform of the MR image. Although the k-space “galaxy” and MR image appear quite different, they contain identical information about the scanned object.

What determines k-space coordinates?

The k-space location (kx and ky coordinates) of data is governed by the accumulated effect of gradient events and excitation pulses. As the duration of phase-encoding gradient is most often constant, the strength of the phase-encoding gradient governs the location on the vertical axis (ky-coordinate).

What is spatial frequency in radiography?

The number of line pairs per unit length is the spatial frequency, and for MRI systems it is expressed in line pair per centimeter (lp/cm). A low spatial frequency represents large objects, and a high spatial frequency represents small objects. A spatial frequency is a number of cycles in space or per unit distance.

Why is it called k-space?

In the 1950’s the American Society of Spectroscopy recommended that the wavenumber be given the units of the kayser (K), where 1 K = 1 cm-1. This was in honor of Heinrich Kayser, a German physicist of the early 20th Century known for his work measuring emission spectra of elementary substances.

What is k-space in EVE?

k-space is regular space, as opposed to w-space. K stands for “known.”

Why is the Centre of k-space usually the brightest?

There are two reasons the central area of k-space is the brightest. First, the central row (ky = 0) is acquired with no phase-encoding gradient (and hence no destructive wave interference caused by phase-encoding steps). Secondly, the central column of k-space (kx = 0) coincides with the peak of the MR echo.

What is high spatial frequency?

Spatial frequency describes the periodic distributions of light and dark in an image. High spatial frequencies correspond to features such as sharp edges and fine details, whereas low spatial frequencies correspond to features such as global shape.

What is the meaning of spatial frequency?

In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. The spatial frequency is a measure of how often sinusoidal components (as determined by the Fourier transform) of the structure repeat per unit of distance.

What is K in wavenumber?

The wavenumber (k) is simply the reciprocal of the wavelength, given by the expression. k = 1 / λ The wavenumber (k) is therefore the number of waves or cycles per unit distance. Since the wavelength is measured in units of distance, the units for wavenumber are (1/distance), such as 1/m, 1/cm or 1/mm.

How is k-space filled?

The easier way to fill the k-space is to use a line-by-line rectilinear trajectory. One line of k-space is fully acquired at each excitation, containing low and high-horizontal-spatial-frequency information (contrast and resolution in the horizontal direction).

How is Fourier transform used in MRI?

Fourier transform is integral to all modern imaging, and is particularly important in MRI. The signal received at the detector (receiver coils in MRI, piezoelectric disc in ultrasound and detector array in CT) is a complex periodic signal made of a large number of constituent frequencies (i.e., bandwidth).