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 2 Motivation 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 5/4/2010 ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 3 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 5/4/2010 ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 4 SWIFT Sequence 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 5 SWIFT Properties 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 5/4/2010 ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 6 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 5/4/2010 ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 7 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 5/4/2010 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 8 Dipole Matched Filter 3cos 2 θ k − 1 F= 2 Bo Unfiltered K-Space Data (magnitude) Shown as 2d, but processing is 3d 5/4/2010 Dipole Matched Filter... Multiply complex k-space data by this function (in 3d) ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Filtered K-space 9 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 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 10 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 11 Discussion • 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) • Use to detect endogenous pathology such as a calcification or abnormal iron concentration • Use in conjunction with other quantification to measure dipole strength, Fe concentration 5/4/2010 • ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Can be used with other MRI sequences, but 12 Support 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 5/4/2010 ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 13 Bonus: Detailed SWIFT Timing 5/4/2010 ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 14 Bonus: Mouse Lung Parenchyma With Deepali Sachdev, Ph.D. See talk #204 Tue 05/04, 12:06 PM, room A4 5/4/2010 ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 15 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 16