propeller mri n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Propeller MRI PowerPoint Presentation
Download Presentation
Propeller MRI

Loading in 2 Seconds...

play fullscreen
1 / 36

Propeller MRI - PowerPoint PPT Presentation


  • 191 Views
  • Uploaded on

Propeller MRI. In Chan Song, Ph.D. Seoul National University Hospital. Contents: Propeller sequence (Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction) Motion artifact Theoretical basis Applications. Motion

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Propeller MRI' - jerrod


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
propeller mri

Propeller MRI

In Chan Song, Ph.D.

Seoul National University Hospital

slide2

Contents: Propeller sequence

(Periodically Rotated Overlapping Parallel Lines with

Enhanced Reconstruction)

Motion artifact

Theoretical basis

Applications

slide3
Motion
      • Periodic: cardiac motion, respiration, blood flow
      • Sporadic: irritable patients’ motion
      • Translation, rotation, through-plane

      • Artifact in MRI
      • blurring and ghosting
  • Cause
      • Longer encoding step
slide4

Scan time=

TR x matrix x Average

 Long scan time

slide5

MR image reconstruction

under the assumption of object’s motion-free condition

during whole k space coverage

slide6

Motion artifacts

-Most ubiquitous and noticeable artifacts in MRI

due to voluntary and involuntary movement, and flow (blood, CSF)

-Mostly occur along the phase encode direction, since adjacent lines of phase-encoded protons are separated by a TR interval that can last 3,000 msec or longer

-Slight motion can cause a change in the recorded phase variation across the FOV throughout the MR acquisition sequence

slide8

Solution for motion compensation

    • -Navigator echo usage to estimate the motion or motion related
    • phase from extra collected data
    • -Cardiac and respiratory gating
    • -Respiratory ordering of the phase encoding projections based on
    • location in respiratory cycle
    • -Signal averaging to reduce artifacts of random motion
    • -Short TE spin echo sequences (limited to spin density,
    • T1-weighted scans). Long TE scans (T2 weighting) are
    • more susceptible to motion
slide10

Motion (abrupt)  phase error  position error

Solution

Phase information

Navigation

 Motion correction by phase information

slide11

Key ideas in propeller sequence

    • K space: partial covering for whole image
    • Motion detection: blade usage
    • Correction: FFT properties’ usage
slide13

Rectangular filling

Propeller filling

ky

kx

Data acquisition

slide14

Phase Correct

Redundant data must agree, remove phase from each blade image

Imperfect gradient balancing,

Eddy current effect:

 echo center shift

slide17

Windowing

Before

After

Phase correction

slide18

Bulk Transformation Correction

  • Fourier transform correspondence
  • Image space  k space
        • Translation  Phase roll
        • Rotation  Rotation
  • Separate estimation of rotation and translation
slide19

Fourier Transform Properties

rotate imagerotate data

slide20

Rotation correction (magnitude image)

Reference

(only inner circle)

Magnitude of the average of strips

Rotation

(only inner circle)

Correlation

slide21

Blade by blade operation

Rotation at maximum correlation

 Correction

slide22

Fourier Transform Properties

shift image  phase roll across data

b is blade image, r is reference image

slide24

Translation

Complex average k-space data

Reference

(only inner circle)

Complex of the average of strips

Multiplication

Inverse FT (maximum)

slide25

Blade by blade operation

Translation at maximum correlation

 Correction

slide26

Blade Correlation

throw out bad – or difficult to interpolate - data

slide27

Through-plane motion

:low weighting coeff.

slide28

Ky

Kx

Reconstruction (FFT)

non-Cartesian sampling

requires gridding  convolution

slide30

correlation correction only

motion correction only

full corrections

no correction

slide31

Artifact reduction due to head motion

T2-FSE

T2-Propeller

T2-Propeller(corrected)

slide32

DWI-EPI

B=1000s/mm2

DWI-Propeller

(FSE)

James G Pipe, 2002

slide33

DWI (b=700s/mm2)

a. EPI

(TR/TE/avg=2700/113/15)

b. Propeller EPI

(TR/TE/blade=1600/70/26)

Wang FN, 2005

slide34

Useful application in propeller sequence

  • Motion- or Bo-inhomogeneities – insensitive
      • Irritable patient
      • Diffusion weighted image
  • Limitations in propeller sequence
  • Redundant acquisition 
  • Long scan time:
  • High SAR: problem in higher field MR system
  • Solutions 
  • Undersampling (Konstantinos Arfanakis, 2005)
    • Parallel imaging
    • Turbopropeller (James G Pipe, 2006)
    • Propeller EPI
slide35

Propeller sequence

    • Low sensitivity to image artifacts,
    • Bo inhomogeneity and motion
    • T2-, Diffusion-weighted images
    • (High SNR, low geometric distortion, low SAR)
slide36

References

1. Pipe J, MRM 42(5): 963-62,1999.

2. Pipe J, et al., MRM 47(1): 42-53,2002

3. Wu Y, Field AS, Alexander AL. ISMRM, Toronto, Canada, 2003. 2125.

4. Roberts TP, Haider M. ISMRM, Kyoto, Japan, 2004. 946.

5. Sussman MS, White LM, Roberts TP. ISMRM, Kyoto, Japan, 2004. 211.

6. Pipe J and Zwart N. Magn Reson Med 55:380–385, 2006.

7. Cheryaukaa AB, et al. Magnetic Resonance Imaging 22:139-148, 2004