SWI for radiation technologists

Introduction
Basic Concept
Acquiring Data
Imaging Parameters
Application & Interpretation
Pros & Cons
Development and Prospective

1. In the name of God

2. SWI (Susceptibility-Weighted Imaging) Seyede Shokoofe Mousavi Seyede Shabnam Mousavi

3. Table of content Introduction Basic Concept Acquiring Data Imaging Parameters Application & Interpretation Pros & Cons Development and Prospective

4. Introduction

5. A n Introduction to SWI A 3D high-spatial resolution fully velocity corrected gradient echo MRI sequence Uses tissue magnetic susceptibility differences to generate a unique contrast Numerous neurologic disorders can benefit dramatically from this very sensitive method Phase is used for large-vessel flow quantification 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 5

6. SWI cont. Introduced by E. Mark Haacke in 2002 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 6

7. SWI by MR vendors 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 7 Siemens GE Philips Hitachi Toshiba

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9. General Requirements System Biograph mMR MAGNETOM Aera MAGNETOM Amira MAGNETOM Avanto MAGNETOM ESSENZA MAGNETOM Espree MAGNETOM Prisma MAGNETOM Skyra MAGNETOM Spectra MAGNETOM Symphony MAGNETOM Trio, A Tim System MAGNETOM Vida Minimum Software Version syngo MR A30 syngo MR B13 syngo MR C11 syngo MR D11 Other Also available for: MAGNETOM Prisma fit MAGNETOM Skyra fit MAGNETOM Avanto fit Please Note: Additional technical pre-requisites may apply. Upon receiving your request, your local Siemens representative will clarify whether your system meets the requirements. 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 9

10. Basic Concept 12/17/2017

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12. Signal intensity & tissue susceptibility Gradient Recalled Echo: S = k ρ (1- exp (-TR/T 1 )) Sin θ exp (-TE/T 2 *) / (1 -Cos θ exp (-TR/T 1 ) ω = γ B All of Δ B, Δχ , ΔΦ and , therefore SI, are dependent on the local tissue susceptibility . 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 12

13. Magnetic Susceptibility Magnetic response of a substance when it is placed in an external magnetic field Each tissue or substance behaves somewhat differently in a magnetic field 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 13

14. Geometry Effects The induced magnetization in an object within a uniform external magnetic field distorts the uniform field outside the object The spatial distribution of this deviation in the external applied field is a function of the geometry of the object The local field deviation inside and around an object is of interest because it gives rise to local phase differences in MR imaging 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 14

15. Acquiring Data 12/17/2017

16. Image obtaining Running SWI sequence two image series are available: 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 16 Unfiltered phase image Unprocessed original SWI image

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18. Applying an HP filter To remove the low-spatial frequency components Done by using a 64x64 low-pass filter divided into the original phase image 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 18

19. Designing “phase mask” To enhance the contrast in the original magnitude image by suppressing pixels having certain phase values . Magnitude and phase data are brought together as a final magnitude SWI dataset by multiplying a phase mask image into the original magnitude image The phase mask is designed to be a number between zero 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 19

20. Phase mask 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 20

21. minIP Reconstruction minimum intensity projection Recon thickness: 8-16 mm To attenuate the background signal 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 21

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23. Imaging Parameters 12/17/2017

24. Protocol's details Both magnitude and phase data are separately acquired and reconstructed. Are typically acquired in 3D mode thinner slices and smaller voxel sizes Flow compensation in all three directions: to reduce artifacts parallel imaging: to reduce imaging time. Typical imaging parameters TR = 25-50 ms , TE = 20-40 ms , and flip angles = 15-20º. 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 24

25. Protocol cont. Shorter times and smaller flip angles are used as field strength increases. SWI on 3T will be faster and will have higher SNR. 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 25

26. Application & Interpretation 12/17/2017

27. Applications SWI detects substances with different susceptibilities than their neighboring tissues better than conventional MR techniques. deoxygenated blood, products of blood decomposition, microscopic iron deposits ,cerebral hemorrhage and high resolution display of venous cerebral vessels 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 27

28. Clinical Applications Improved detection of hemorrhage, microbleeding (diffuse axonal injury), hemorrhagic transformation (stroke) Detection of occult vascular disease ( cavernomas , angiomas , telangiectasias ) Diagnosis of cerebral venous thrombosis, intra-arterial clot detection Identification of iron and other mineral deposition Helpful in MR diagnosis of neurodegenerative diseases (Alzheimer’s, multiple sclerosis, etc.) Tumor characterization 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 28

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38. Pros & Cons 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc

39. Plus points Small Vessel Imaging Better diagnosis of disease Better follow up for longitudinal studies SWI is compatible with iPAT Lower power deposition An opportunity to open new doors in clinical MRI   12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 39

40. Pitfalls Windowing and grey scale inversion Contrast being affected by Oxygen level Aliasing 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 40

41. Development and Prospective 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc

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43. Must I buy expensive new SWI software? What's wrong with using T2*-GRE sequences instead? 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 43

44. Thanks for your attention 12/17/2017 S.Sh.Mousavi, Med.Phys. M.Sc 44