Proton Diffusion in GM. Proton Diffusion in WM. Current Concepts. Proton Diffusion DWI. Department of Radiology Stanford University

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1 Perfusion MR () vs. (Perfusion PWI) Mike Moseley, Ph.D. Department of Radiology Stanford University Current Concepts Monterey October 2009 Start Proton displacement is the SLOW FAST End Perfusion Rate of contrast or proton delivery Proton measures proton motion: 5-20 µm/image. Samples µenvironment. Measured as. sensitive to: Water content- increases with water. Water compartments- Intracellular water slower. Map of Water hindrances- Ordered in WM. 5 µm Map of WM () in an isotropic medium (M) similar molecular displacements in all directions The Apparent is quantitated as average - Measure of translation (DTI) in an ordered environment (WM) greater molecular displacement along paths than across Deviation from random paths- Fractional Anisotropy -Measure of WM integrity Proton in M Proton in WM 10 um Olympus Medical Olympus Medical

2 Pulsed radient Sensitizes Proton RF 180 RF Pulsed radient Sensitizes Proton RF 180 RF Proton T2W T2W " weighted" Proton can be Measured as the RF 180 RF EPI is Ideal for 90 rf 180 rf δ=25 msec Δ= 40 msec δ=25 msec Δ= 40 msec EPI Readout SI=ke(-γ δ [Δ - δ/3] ) =ke(-b ) where b= sec/mm 2 Proton b0 b1000 map -Weighted images map T2-wt (b=0) e (-γδ [D-δ/3] ) b The Elements of : The Protocol 1. Acquire b0 image first, then add diffusion gradients. Calculate the! b0 acts as T2wt. b>800 sec/mm 2 ok. from b=0, 800 sec/mm Acquire gradient axes X, Y, Z avoid WM artifacts. Averaged as "trace" or average,. The Elements of : The Protocol Acquire gradient axes X, Y, Z also B0! Averaged as "trace" or average,. X Y Z b0 Average Average B0 (T2W) X Y Z Trace (averaged) reduced due to anisotropy Trace (averaged)

3 vs T2-wt Shine-Thru Exponential (e) 1. is easy to read/convenient but contains T2. 2. removes T2 shine-through, but CSF effects bright. 3, e offers both contrast with T2, CSF removed. S = S 0 e (-b ) Set S 0 to 100 e = 100 e (-b ) Mimics Beyond Clinical Stroke Reduced cytoxic vs. reduced mobility (bright on ). Screen for non-stroke events (TIA). Secondary ischemia (acute trauma, venous occlusion). reduced in cytotoxic edema: CJD, pediatric diseases. reduced in abscess ** vs. highly cellular tumor cores. Elevated vasogenic (usually seen also as elevated T2). MS plaques** (older), edema, inflammation, necrosis. ** ** x Tr Tr e Roberts, Rowley EJR, 2003 Evolving Roles for Beyond clinical stroke... Screening for CA? Very simple, fast Moving table OK. Low seen in CA. Replace PET/CT? The Elements of : The Protocol Acquire a b=0 image and make maps. Don t be fooled by T2 shine thru What is T2-shine thru? NOTE: DW images are also T2-wt. T2-wt hyperintensity adds to signal. ONLY the sorts this out. Courtesy Philips (128x128). B=1000s/mm 2. vs T2-wt Shine-Thru vs T2-wt Shine-Thru Don t be fooled 1. is also T2wt 2. Only can remove T2 shine thru T2wt (b=0)

4 vs T2-wt Shine-Thru T2 hyperacute (< 6hrs) iso high low acute (6hrs to 4 d) high high low subacute (4 to 10 d) high iso/h iso chronic (>10 d) high iso/l high Neuroimaging: Why Map Perfusion? T2 T Time After Onset of Stroke (h) Neumann-Haefelin et al., Neurology and Radiology, Dusseldorf () vs. (Perfusion PWI) Perfusion Imaging Strategies Start Proton displacement is the SLOW FAST End Perfusion Rate of contrast or proton delivery Diffusible Tracer Passes through BBB Xenon-gas O-15 PET H1 proton (ASL) Non-diffusible Tracer Contrast agent based d-dtpa (PWI or DSC) CTP Perfusion MRI: Destined for reatness! ASL? PWI? Perfusion PWI Imaging: How Does it Work? What is PWI? Collect serial EPI images Inject contrast agent: Perfused brain - dark Ischemic brain - bright Hemodynamics tracked rmtt Time-resolved transit Correlate with, T2 Perfusion deficit present: (low rcbf, long rmtt) rcbf rmtt

5 PWI: Non-Diffusible Dynamics with d d centers present big gradient = T2* loss d d d d At bolus peak area rcbv SI slice bolus Width rmtt capillary bed white matter flow rcbf The - Perfusion Mismatch PWI T2-wt Early stroke not seen -wt Clear depiction of lesion Blood Volume Lesion has reduced CBV Mean Transit large perfusion deficit gray matter (greater rcbv) seconds Apparent Acute stroke has low Blood Flow Reduced flow around lesion PWI: Is There a Need for CBF Quantitation? 73 yof Stenosis, MRI at 6hr. NIHSSS 13 PWI and Perfusion Challenges for Bolus-Tracking PWI CBF Vol (7 days)/ Vol (5 hrs) Signals from large arteries lost in noise. Degraded curves poor AIF. Underestimate true bolus max. 11 ml/100g/min MTT Mostly venous signal R. Bammer STANFORD S C H O O L OF M E D I C I N E Lucas MRS/I Center Parallel imaging and multi-coil OK. New sequences effective even at 1.5T. Pseudo-continuous labeling in arteries very efficient. Sp sat Sel Inv Labeling pulse train pulses Pulse Label time Why ASL? Non Sel Inv Pulses Inf Sat Pulses Post-label delay 3D FSE Stack of spiral readout 1.5T 48 slices 5 minutes Perfusion: Ready for ASL? ASL at Stanford: Standard on most research protocols. 600 pts scanned all at 1.5T. More convenient than PWI:: No d Rapid on-line recon (simple) Faster than PWI (including recon) Stroke protocols Neurosurgery- ASL for Moyamoya

6 vs. DTI: Which is which? vs. DTI: Which is which? in Stroke in Screening CNS in MSK Non- Neuro DTI FA Technique Development DTI FA Fiber tracking DTI in cognition FA in CNS disease Why DTI? A natural extension of plus measure of anisotropy Why map anisotropy and how? Present and future uses Clinical interest: is there a market? Where is the killer app for DTI? In DTI, We Simply Measure Along Many Axes vs. Direction = Tensor Magnet axis Y Fiber axis Z X xx xy xz = xy yy yz =Tensor xz yz zz b=0 In DTI, We Simply Measure Along Many Axes vs. Direction = Tensor 90 rf 180 rf z 1 δ=20 ms 2 -Weighted images = 40 ms b= Tensor calc EPI Readout SE-EPI TR6000, TE107, 128x128, b0-1000, 6 axes, 3.5min/NEX xy -xy yz -yz xz x-z Trace FA Math and DTI How Do We Show DTI: Tractography! DTI FA map Fiber Tractography Color FA map Pathway s z y x Model

7 DTI Tractography The New Artform? Fiber Tracking or Tractography Measure of Connectivity? STANFORD S C H O O L OF M E D I C I N E Lucas MRS/I Center T. Sherbondy, et al., Stanford FA Maps: Atlas of the Brain DTI and Personalized Neuro, 2010 Tumor Displacement, Infiltration, or Degradation of WM DTI in MS Sundgren, Neuroradiology, 46: 2004 WM Tumor deviation, Jellison, AJNR, 25: 2004 WM tumor degradation Jellison, AJNR, 25: 2004 The overwhelming surprise of the last decade is that DTI maps of white matter Integrity are related to many aspects of cognitive performance... DTI and Personalized Neuro, 2010 Parallel MR Imaging and Made for one another DTI maps relate to Personality

8 and PI: The Only Way Up is HD 64x64 128x x x 3.75 mm x 1.88 mm x 0.94 mm 2 Parallel Imaging for Perhaps the biggest immediate improvement affecting all of MR today is the development of parallel imaging High-Speed DTI at 3T rappa - SENSE Multiple coils acquire Partial k-space sampling Reduced d echo train length SNR or speed increases less susceptibility artifacts less image blurring less T2 decay (shorter TE) 128x128; R=1 4 directions3 repetitions (1 b0 + 4 directions)* 3 = 15 volumes in total 2:21 minutes scan time RAPPA with R=3 192x192, FOV 24 cm, slice = 5 / 1.5 mm. 256x256; R=2, 8-coil and PI: The Only Way Up is HD 256x seconds Skare, Holdsworth, Stanford 128x seconds