Dipole Matched Filter with SWIFT

1. Dipole Matched Filter with SWIFT • Curt Corum, Djaudat Idiyatullin,Steen Moeller, Ryan Chamberlain,and Mike GarwoodCenter for Magnetic Resonance ResearchUniversity of Minnesota, Minneapolis, Minnesota, USA #5113

2. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 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.

3. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 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

4. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 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. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 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 with radial FID sampling scheme and gridding reconstruction • Most similar to BLAST/RUFIS in concept

6. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 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

7. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Secular Dipole Field ”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. 85-89, Ph.D. Thesis, University of Arizona, Optical Sciences Center, 2005

8. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Secular Dipole Field, Intuitive k k 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). In real space a secular dipole has the above shape, which is a separable function of angle and radius.

9. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Dipole Matched Filter Bo Unfiltered K-Space Data (magnitude)Shown as 2d, but processing is 3d Dipole Matched Filter... Multiply complex k-space data by this function (in 3d) Filtered K-space

10. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Secular Dipole Field, Experiment 62kHz SWIFT at 4 T Ti ball bearings (dipoles) In Agar filled tubes with saline surround Bo Unfiltered Magnitude Image Re Image After dipole matched filter F in k-space Mag Image After dipole matched filter F in k-space

11. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Secular Dipole Field, Experiment 62kHz SWIFT at 4 T 2 o'clock position has MRI compatible catheter tip Bo Unfiltered Magnitude Image Re Image After dipole matched filter F in k-space Mag Image After dipole matched filter F in k-space

12. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT 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 • Can be used with other MRI sequences, but SWIFT preserves off resonance signal best due to short dead time

13. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Support • NIH BTRR 5P41RR008079-17CMRR Center Grant, Core 3 PI Mike Garwood • 1R21CA139688-01, PI Curt CorumIMPROVED BREAST DCE MRI WITH SWIFT • MN MED FDN/3932-9227-09, PI Curt CorumMRI Utilizing SWIFT to Detect Breast Calcifications,Minnesota Medical Foundation

14. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Bonus: Detailed SWIFT Timing

15. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Bonus: Mouse Lung Parenchyma With Deepali Sachdev, Ph.D.See talk #204 Tue 05/04, 12:06 PM, room A4

16. ISMRM 2010 #5113 Dipole Matched Filter with SWIFT Bonus: Teeth With Don Nixdorf, DDS, Hari Prasad, et al.See talk #543 Thurs 05/06, 12:18 PM, room A5