Susceptibility weighted imaging (SWI) is an MRI technique that uses phase information to generate contrast based on magnetic susceptibility differences between tissues. It was introduced in 2002 and provides improved detection of hemorrhage, microbleeding, venous structures, iron deposits, and other pathologies compared to conventional MRI sequences. SWI acquisition involves collecting both magnitude and phase data using a 3D gradient echo sequence with thin slices, flow compensation, and parallel imaging to reduce scan time. Post-processing applies a high-pass filter to the phase image and uses the filtered phase to generate a mask that is multiplied with the magnitude image to create the final SWI.

4. Introduction

5. An 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
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6. SWI cont.
Introduced by E. Mark Haacke in 2002
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7. SWI by MR vendors
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SWI (Susceptibility-Weighted Imaging)
SWAN (Susceptibility Weighted ANgiography)
SWIp (SWI-phase, formerly called VenoBOLD)
BSI (Blood Sensitive Imaging)
FSBB (Flow Sensitive Black Blood)
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 Prismafit
• MAGNETOM Skyrafit
• MAGNETOM Avantofit
• Please Note: Additional technical pre-requisites may apply. Upon receiving your request, your local Siemens
representative will clarify whether your system meets the requirements.
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10. Basic Concept
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Data sampling & further dephasing
Applying a dephasing gradient
Data encoding
Creation of a component along y axis
Creation of transverse magnetization

12. Signal intensity & tissue susceptibility
• Gradient Recalled Echo:
S = k ρ (1-exp(-TR/T1)) Sinθ exp(-TE/T2*) / (1 -Cosθ exp(-TR/T1)
• ω = γB
All of ΔB, Δχ, ΔΦ and, therefore SI, are
dependent on the local tissue susceptibility.
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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
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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
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15. Acquiring Data
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16. Image obtaining
Running SWI sequence two image series are available:
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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
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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
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20. Phase mask
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21. minIP Reconstruction
minimum intensity projection
Recon thickness: 8-16 mm
To attenuate the background signal
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23. Imaging
Parameters
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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.
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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.
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26. Application &
Interpretation
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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
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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
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38. Pros & Cons
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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
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40. Pitfalls
Windowing and grey scale inversion
Contrast being affected by Oxygen level
Aliasing
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41. Development and
Prospective
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43. Must I buy expensive new SWI software? What's
wrong with using T2*-GRE sequences instead?
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