Dipole Matched Filter with SWIFT
#5113
Curt Corum, Djaudat Idiyatullin,
Steen Moeller, Ryan Chamberlain,
and Mike Garwood
Center for Magnetic Resonance Research
University of Minnesota, Minneapolis, Minnesota,
USA
Declaration of Conflict of Interest or
Relationship
Speaker Name: Curt Corum
I have the following conflict(s) of interest to disclose with regard to the subject
matter of this presentation:
Dr. Corum is entitled to sales royalty from Steady State Imaging, which is
developing products related to the research described in this presentation.
5/4/2010
ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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Motivation
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MRI is sensitive to many physical parameters
So far much medical imaging depends on T1, T2, T2*,
proton density, and more recently diffusion
At higher fields intrinsic (tissue and pathology), and
extrinsic (contrast injection) suseptibility effects
become stronger
With T2* sensitive sequences these cause signal
dropout and phase effects due to the local field
changes
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ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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SWIFT Sequence
Idiyatullin, D.; Corum, C.; Park, J. Y. & Garwood, M., Fast and quiet MRI using a swept
radiofrequency., J Magn Reson, 2006, 181, 342-349
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ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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SWIFT Sequence
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SWeep Imaging with Fourier Transform
Acquisition occurs in the gaps of a frequency swept
(usually HSn) pulse
Excitation and Acquisition nearly simultaneous
“dead time” ~2 µs
No time for slice selection or phase encoding, is most
naturally a readout only, interleaved preparations are
possible
Aquired data are FIDs (after correlation with the RF
pulse shape)
Operates in 2d projection mode or 3d image mode
5/4/2010
ISMRM 2010 #5113 Dipole Matched Filter
with radial FID sampling
scheme and gridding
with SWIFT
reconstruction
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SWIFT Properties
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Very short excitation to aquisition interval (dead time)
often confusingly called ”TE”
Sensitivity to ultra short T2 spins. 100 µs or less...
Smooth gradient update (spiral ordered radial
aquisition scheme) leads to very low acuoustic noise
Low peak RF power compared to BLAST or RUFIS
(radial fid aquisition sequences)
Avoidance of gradient ramp sampling (and spatial
resolution loss) required for UTE sequences
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ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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Secular Dipole Field
B dip =
0
4
3
⋅ r r−
3
r
2
B secular =
0
4
1 3 cos
[
3
2
r
−1
] 3
z
z−
”Magic Angle”
54.7° from Bo
No component || to Bo
Angular dependence of secular dipole field
Cross section of total (vector) dipole field
Corum, C. A., Magnetic Resonance with the Distant Dipolar Field, pp. 8589, Ph.D. Thesis, University of Arizona, Optical Sciences Center, 2005
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ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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Secular Dipole Field, Intuitive
k
k
In real space a secular dipole has
the above shape, which is a
separable function of angle and
radius.
3cos 2 θ − 1
F=
2
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In k-space, due to the central slice
theorem, the angular component of the
dipole shape is the same as in real
space. Only the radial component is
transformed.
The radial component turns out to be
constant (scale invariant).
ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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Dipole Matched Filter
3cos 2 θ k − 1
F=
2
Bo
Unfiltered K-Space Data
(magnitude)
Shown as 2d,
but processing is 3d
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Dipole Matched Filter...
Multiply complex k-space
data by this function (in 3d)
ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
Filtered K-space
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Secular Dipole Field, Experiment
62kHz SWIFT at 4 T
Ti ball bearings (dipoles)
In Agar filled tubes
with saline surround
3cos 2 θ k − 1
F=
2
Bo
Unfiltered Magnitude Image
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Re Image
After dipole matched filter F
in k-space
ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
Mag Image
After dipole matched filter F
in k-space
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Secular Dipole Field, Experiment
62kHz SWIFT at 4 T
2 o'clock position has
MRI compatible catheter
tip
3cos 2 θ k − 1
F=
2
Bo
Unfiltered Magnitude Image
5/4/2010
Re Image
After dipole matched filter F
in k-space
ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
Mag Image
After dipole matched filter F
in k-space
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Discussion
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Very Simple, Computationally Efficient (just
multiplication in k-space)
•
Use to detect dipole field (from Fe particle
injection or interventional instrument) in a
cluttered background (as positive signal)
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Use to detect endogenous pathology such as
a calcification or abnormal iron concentration
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Use in conjunction with other quantification to
measure dipole strength, Fe concentration
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•
ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
Can be used with other MRI sequences, but
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Support
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NIH BTRR 5P41RR008079-17
CMRR Center Grant, Core 3 PI Mike Garwood
1R21CA139688-01, PI Curt Corum
IMPROVED BREAST DCE MRI WITH SWIFT
MN MED FDN/3932-9227-09, PI Curt Corum
MRI Utilizing SWIFT to Detect Breast Calcifications,
Minnesota Medical Foundation
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ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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Bonus: Detailed SWIFT Timing
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ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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Bonus: Mouse Lung Parenchyma
With Deepali Sachdev, Ph.D.
See talk #204 Tue 05/04, 12:06 PM, room A4
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ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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Bonus: Teeth
With Don Nixdorf, DDS, Hari Prasad, et al.
See talk #543 Thurs 05/06, 12:18 PM, room A5
5/4/2010
ISMRM 2010 #5113 Dipole Matched Filter
with SWIFT
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