1. Presented by : Miss Kajal Jha
BSC MIT-2016
BPKIHS-Dharan
Presented to:
Dr Arun Gupta
Phd,Soeul University ,South Korea
BPKIHS Dharan
2. What is K in K Space?
Thousand????
Element Potassium???
3. It actually means “spatial frequency ”
Image resolution is often described in
terms of "line pairs per mm," the closest
spacing of black and white bars that can be
resolved. Since a pair of lines are like
crests and peaks of adjacent waves, line
pairs per mm is a measure of spatial
frequency.
4.
5. Image can be decomposed into planar
waves varying in amplitude, frequency,
phase and direction.
Spatial frequency is the number of wave
cycle (or line pairs) per unit distance.
6.
7. The concept is simple. A wave is characterized by
its wavelength (λ), the distance between two
corresponding points or successive peaks.
The wave number (k) is simply the reciprocal of
the wavelength, given by the expression
k = 1 / λ
The wave number (k) is therefore the number
of waves or cycles per unit distance.
Since the wavelength is measured in units
of distance, the units for wave number are
(1/distance), such as 1/m, 1/cm or 1/mm.
8.
9. The k-space representation of an MR
image is merely an organized collection of
these spatial frequencies reflecting that
image's spatial harmonic content.
10. So what exactly is K
SPACE??
K SPACE is the space in which MRI
imaging data is acquired .
Introduced in 1979.
11. In MRI physics K space is the 2D or 3D
transform of the mystery of the image.
Unit is rad/m
○ Its coz spatial frequency is represented as a
phase change over distance along a gradient.
○ Spatial frequency measures the change of
phase between the magnetic moments of a
row of spins along the gradient.
12. The frequency data of FID from our
body is stored in the K Space.
It is related to the Fourier
transformation technique which is
basicially just a method to store data, be
it 2D or 3D. It helps in the image
acquisitation as a image of human
body(part/organ).
13. What is there in K Space
Its imaginary
Still storage device
○ Stores digitized data produced from spatial
frequencies created from spatial encoding.
14. What does it look like?
Its rectangular
Has two axes perpendicular to each other.
1. Frequency axis
a. Horizontal
b. Centered in the middle of several horizontl
lines
c. Data from frequency encoding are positioned
in k space along this axis.
2. Phase axis
a. Vertical
b. Centered in the middle of K space
perpendicular to the frequency axis.
c. Data from phase encoding are placed in k
space along this axis.
15.
16. So how is K Space filled???
In simplest method of K space filling, data
are stored in horizontal lines that are
parallel to the frequency axis and
perpendicular to the phase axis of K
Space.
17. So does the single point of K space
determine single section of image??
18. Interstingly
Each k-space point contains spatial
frequency and phase information
about every pixel in the final image.
Conversely, each pixel in the image maps
to every point in k-space.
Its important to know that there is not a one
to one relationship between image and k
space.
Each individual point on image space
depends on all of the points contained in k
space.
19. K Space is NOT IMAGE.
Data stored in the top line do not end up
being the top of the image.
20.
21. Important facts about K Space
K space is not an image.
Data are symmetrical in the K Space
Data acquired in the central lines
contribute signal and contrast, while
data acquired in the outer lines
contribute reslution.
22.
23. S.N
O
FREQUENCY ENCODING
GRADIENT(FEG)
PHASE ENCODING
GRADIENT(PEG)
1 Determines how far to the left
and right K Space is travelled.
Determines how far up and
down a line of K space is filled.
2 Determines the size of FOV. Determines the phase matrix
of the image.
3 FEG positive: K space
transvered from left to right.
PEG positive: fills top hal;f of K
Space.
4 FEG negative: K space
transvered from right to left.
PEG negative : Fills bottom
half of K Space.
24.
25. Types of acquisition
There are three types of acquition of data
1) Sequential- it acquiries all the data from slice1 and
then go on to acquire all the data from slice 2(all
the lines in K Space are fille for slice 1 and then all
the lines of K Space are filled for slice 2,etc.).The
slice are so displayed as acquired(not likely as CT)
2) 2D Volumetric acquisition: fill one line of K Space
for slice 1 , and then go on to fill the same line of K
space for slice 2,etc. When this line has been
filled for all the slices, the next line of K Space is
filled for slice 1,2,3,etc. This is the most common
type of data acquisition.
3) 3D Volumetric
26. Fourier transform
The Fourier transform is a mathematical
technique that allows an MR signal to be
decomposed into a sum of sine waves
of different frequencies, phases, and
amplitudes.
27. Fourier transformation is the
mathematical
procedure connecting s(t) and S(ω).
If s(t) is specified, S(ω) may be
computed, and vice versa.
28.
29. Lets know that Fast Fourier
Transform(FFT) and Fourier
Transform(FT) is same.
GRADIENTS SPATIALLY LOCATE
SIGNAL ACCORDING TO THEIR
FREQUENCY,NOT THEIR DOMAIN
so FFT converts time domain to
frequency amplitudes in the frequency
domain.
30. To summarize
The central portion of K Space contains
data that have high signal amplitude and
low resolution.
The outer portion of K Space contains
data that have low signal amplitude and
high resolution.
