Arterial Spin Labeling Read-Out Options

Transcription

1 Arterial Spin Labeling Read-Out Options Matthias Günther 1,2,3 1 Fraunhofer MEVIS, Institute for Medical Image Computing 2 Faculty 01 (Physics/Electrical Engineering), University Bremen 3 mediri GmbH, Heidelberg, Germany Learning objectives: to understand how ASL works on a sequence level to understand the pros and cons of various image acquisition approaches to understand the general difference of 2D and 3D approaches to be able to determine the appropriate sequence for certain applications ASL preparation and are independent (in most cases) ASL preparation Continuous (labeling over long period of time in a small region) Background suppression Image acquisition part () 1

2 Continuous ASL variants labeling-phase Inversion post-labeling delay control-phase ASL preparation and are independent (in most cases) ASL preparation Continuous Pulsed (labeling over long period of time in a small region) (labeling for short period of time in a large region) Background suppression Image acquisition part () Inversion ss/ns Pulsed ASL variants QUIPSSII Q2TIPS labeling-phase control-phase slice inversion slab saturation slab BS inversion 2

3 ASL preparation and are independent (in most cases) ASL preparation: Continuous Pulsed (labeling over long period of time in a small region) (labeling for short period of time in a large region) Background suppression: Additional preparation Not necessarily related to ASL Image acquisition part (): Background suppression (BS) ASL signal (blood signal) very small compared to tissue signal (e.g. about 2-3% in human brain) small fluctuations in tissue signal corrupt ASL signal Idea of BS: reduce tissue signal by (closely) nulling it at time of tissue signal and ASL signal of same order small fluctuations in tissue signal does not corrupt ASL signal blood signal tissue signal blood signal tissue signal Sanjay Mani, John Pauly, Steven Conolly, Craig Meyer, Dwight Nishimura, MRM 37: (1997) Background suppression (BS) DM Garcia et al., MRM 54: (2005) 3

4 Background suppression (BS) How can I null the signal at time of? Residual magnetization for different T1 One inversion pulse is needed for each T1-compartment to be nulled Sanjay Mani, John Pauly, Steven Conolly, Craig Meyer, Dwight Nishimura; MRM 37: (1997) Pulsed ASL variants Inversion ss/ns BS Inversion ns Q2TIPS labeling-phase control-phase slice inversion slab saturation slab BS inversion Continuous ASL variants BS Inversion ns Inversion post-labeling delay labeling-phase control-phase 4

5 EPI sequence scheme Inversion ss/ns BS Inversion ns multi-slice 2D-EPI slice 1 slice 2 slice 3 slice 4 DAQ Slice Phase Read perfusion measurement ASL in brain EPI-, 60 averages, measurement time 5 min, 3T MR-Scanner Wen-Ming Luh et al, MRM 41: (1999) Abdominal perfusion measurement ASL in heart EPI-, 108 averages, measurement time min, cardiac+breathing triggering anatomic Tissue perfusion B. Poncelet et al, MRM 41: (1999) 5

6 EPI sequence scheme Inversion ss/ns BS Inversion ns 3D-EPI (α) (α) (α) (α) DAQ Slice Phase Read 3D-EPI ASL perfusion weighted images at 7T 20 slices, 2x2x3mm3, SENSE P-2 and S 1.5, 634 ms shot length, 50 averages. E. L. Hall, P. A. Gowland, and S. T. Francis; Proc. Intl. Soc. Mag. Reson. Med. 18 (2010), p.517 bssfp sequence scheme Inversion ss/ns balanced SSFP (truefisp, FIESTA) DAQ Slice Phase Read 6

7 bssfp sequence scheme ASL in the brain, healthy male volunteer segmented true FISP ASL images acquired using eight averages, TI=1200ms, measurement time for single slice 2.5 min Grossman et al., JMRI June ; 29(6): Abdominal perfusion measurement ASL in kidneys, healthy male volunteer bssfp-, synchronized breathing, no cardiac triggering, hand-selected 26 (out of 36) datasets were averaged, measurement time 4 min 03 s sensitive to field inhomogeneities (banding artifacts) Renal cyst Martirosian P, MRM 51: (2004) HASTE sequence scheme Inversion ss/ns HASTE DAQ Slice Phase Read 7

8 STAR-HASTE: perfusion imaging without magnetic susceptibility artifact. Chen et al: MRM 38: (1997) Abdominal perfusion measurement Multi-Organ-Shot ASL-technique HASTE- 128x256-matrix TE = 56 ms TR = 4000 ms Meas. time: 2 min Günther M, PhD-Thesis, Heidelberg, Germany, 1999 Abdominal perfusion measurement ASL in lung, healthy male volunteer HASTE-, TI 1300ms, 4 averages, measurement time ~25 s, cardiac triggering V. Mai et al, JMRI 9: (1999) 8

9 Abdominal perfusion measurement ASL in kidneys, healthy 35y old volunteer HASTE-, TI 1000ms, 4 averages, measurement time 30 s S. Berr et al., JMRI 10: (1999) 3D-GRASE sequence scheme Inversion ss/ns BS Inversion ns single-shot 3D-GRASE (also called 3D-FSE on GE-scanners) DAQ Slice Phase Read segmented 3D GRASE pcasl Turbofactor12, 6, EPI-factor measurement time: 1:20 min, labeling time = 2000ms, PLD = 1200 ms 9

10 Imaging technique segmented 3D GRASE pcasl Turbofactor 6, EPI-factor 27 measurement time: 4 min, labeling time = 2000ms, PLD = 1200 ms, 3x3x2 mm3 Skyra 3T Sequence scheme Inversion ss/ns BS Inversion ns 3D-GRASE spiral (also called 3D-FSE on GE-scanners) DAQ Slice Phase Read 3D-FSE (3D-SPIRAL-GRASE) D.Alsop et al. 10

11 Readout technique Comparison 2D- and 3D- strategy 2D- 3D- Limited number of slices TI varies from slice to slice no background suppression low SNR whole brain coverage same TI for all slices background suppression rel. high SNR 3D Readout technique 300 After application No saturation of saturation pulses pulses Use of modulated saturation pulses eff. 3D-Slab eff. 3D-Slab 200 Overlap! Overlap! Overlap! Slice profile Water phantom Comparison EPI HASTE 3D-GRASE bssfp image quality poor blur along phase encode inplane: good, along z: blur excellent acquisition scheme multi-slice single-slice (inversions!) 3D single-slice whole brain limited limited yes limited SNR low middle high middle other remarks broad availability, quasi standard, sensitive to artifacts, less suited for abdominal imaging Suitable for abdominal imaging, often used for lung imaging excellent usability, background suppression, can also be used for abdominal imaging inflow-weighted (bright vessels!), suitable for abdominal imaging 11

12 Take home messages: Arterial Spin Labeling: Read-Out Options non-invasive, repeatable, flexible in general, ASL preparation and image acquisition are independent optimal combination depends on application, knowledge of available methods necessary for some applications (e.g. brain), 3D is preferred to 2D due to SNR, coverage and suitability for background suppression follow recommendation of next slide Vascular territory mapping Enjoy the flexibility of Arterial Spin Labeling! cor Times series at 3T, meas. time 3 min Bolus arrival time at 4T, meas. time 7 min cor sag left sag sag right left sag right single average ASL at 3T TI: 1500 ms, meas.time 5s! Dynamic angiography of AVM 12