8/11/2009. Common Areas of Motion Problem. Motion Compensation Techniques and Applications. Type of Motion. What s your problem

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1 Common Areas of Motion Problem Motion Compensation Techniques and Applications Abdominal and cardiac imaging. Uncooperative patient, such as pediatric. Dynamic imaging and time series. Chen Lin, PhD Indiana University School of Medicine & Clarian Health Partners Type of Motion What s your problem In-coherent: Diffusion and Perfusion Coherent: Bulk Motion Flow MR Angiography Flow Quantification Flow Artifact Reduction Characteristics of Bulk Motion Degree of freedom: Rigid Body Motion (translation and rotation) Non-rigid Body Motion ( + deformation) Temporal Property: Cyclic: Cardiac (~1 Hz) Respiratory (~1/6 Hz) Sporadic: Random Spatial Property: In-plane / Through-plane Time Scale Relative to Acquisition 1. Intra-view Motion: Motion between preparation and excitation: incomplete suppression / reduced contrast Reduce preparation time increase preparation region Motion between excitation and data acquisition: phase shift and/or dispersion lost of signal Use short TE gradient moment nulling 1

2 Time Scale Relative to Acquisition 2. Inter-view Motion: Motion between multiple views/segments of k-space -> inconsistent phase encoding ghosting/blurring. 3. Inter-frame Motion: Motion between time points (longitudinal, dynamic or multi contrast study) Miss-registration. Displacement -> Error in Phase Encoding G y y Can we get around with some easy tricks How to deal with motion? 1. Minimize the degree of motion: Patient Training Better positioning. Use stabilization device ( e.g. form wedges,, bit bar) Patient cooperation (e.g. Breath hold). Pharmacological intervention ( e.g. Sedation, GA, O2, ) 2. Suppress the signal from moving tissue: Spatial and/or chemical shift selective saturation Use/select appropriate coils Reduced FOV imaging 3. Change the appearance of motion artifact Swap phase and frequency directions Use multiple averages But, none of my tricks works Okay, let s try scan faster than it moves How to deal with motion? 3. Use motion insensitive techniques: Faster imaging: Use short essential protocols and scan critical series first SS-EPI, SS-FSE (HASTE), SSFP (TrueFISP), etc Partial k-space acquisition (e.g. parallel imaging) Radial sampling (PR), Spiral SSFP + Parallel Imaging 2

3 Segmented versus Single Shot TSE with MBH versus HASTE Segmented DB TSE 8 heartbeats High spatial resolution High temporal resolution Sensitive to arrhythmia and breathing Single Shot DB HASTE 1 heartbeat Low spatial resolution Low temporal resolution Less sensitive to motion Breath Hold TSE Free Breathing HASTE Radial k-space Sampling Higher Resolution with Radial Cartesian k-space Radial k-space No phase encoding and less sensitive to motion Higher spatial and/or temporal resolution Isotropic in-plane resolution No phase wrap at smaller FOV Radial streaks artifact, more pronounced near edge FOV Cartesian Real-Time Cine Echo-sharing 50 lines 55 ms frame rate 300mm x 300mm FOV 2.3mm x 6.0mm res Radial Real-Time Cine Interleaved Echo-sharing 50 lines 55 ms frame rate 300mm x 300mm FOV 2.3mm x 2.3mm res How to deal with motion? 4. Apply motion compensation techniques 5. Take advantage or visualize/quantify motion Motion Detection Techniques 1. Physiological signal: ECG, Pulse, Respiratory Bellow 2. Direct measurement: optical 3. Navigator: 1D, 2D, 3D, Spherical, 4. Motion info from extracted acquired data. 5. Comparison of overlapping k-space segments 6. Image registration 7. Combination of the above Now, we are getting serious 3

4 Motion Correction Schemes 1. Prospective triggering. 2. Retrospective gating. 3. Sorting data according to the phase of periodical motion (CINE). 4. Reordering of phase encoding steps. 5. Update spatial encoding gradients. 6. Correct phase error due to motion. Tell me how it moves, and we can deal with it Obtaining a Reliable ECG signal 1. Place ECG leads in correct locations. 2. Prepare surface and use gel to ensure good contact. 3. Check ECG signal after body coil placement. 4. Wait until ECG is stable before advancing patient to iso-center. 5. Switch between different ECG vectors for optimal detection. Prospective and Retrospective CINE ECG Trigger Pulses Data Lines a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a Prospective Retrospective Sorted based on the location in Cardiac cycle Under-sampled cardiac cycle Prospective Triggered CINE Setup Retrospective Gated CINE Setup Trigger Delay + Acquisition Window = ~ 90% Average Cycle TR (Temporal Resolution) X (Phases+1) = Acquisition Window User defined Calculated phases ( typically ) 4

5 Retro Gating with Arrhythmia Rejection Arrhythmia Rejection Min. RR Max. RR Target RR Prospectively triggered blurred by arrhythmias Retrospectively gated with arrhythmias rejection Prospective versus Retrospective Prospective Triggering Data acquisition take place after predetermined delay from trigger signal. Measures less than entire cardiac cycle Acquisition Window manually adjusted CINE frame-rate determined by data segments Sensitive to arrhythmias Retrospective Gating Continuously acquired data is sorted according to measured delay from trigger signal. Measures through entire cardiac cycle Acquisition Window automatically adjusted Variable user-defined CINE frame-rate Arrhythmia rejection is available Navigators (PACE) PACE: Prospective Acquisition CorrEection 1D PACE Acquired data from a narrow column Measure diaphragm position for cardiac applications 2D PACE Acquired data from a slice Measure diaphragm position for abdominal applications 3D PACE Acquire data from a volume Measure head position and orientation for functional imaging 2D PACE Coronary MRA with ECG Trigger and PACE 2D low resolution gradient echo image Low flip angle to prevent saturation The center of the acceptance window is determined during the training phase. The width of the acceptance window is defined by user. Finn, JP. et al. Radiology 2006;241:

6 Displacement Displacement 8/11/2009 Coronary Artery with 3D TrueFISP 2D PACE Artifact LAD Finn, J. P. et al. Radiology 2006;241: MRCP with 3D SPACE & PACE Reordering of Phase Encoding t K y Motion Artifact Reduction with Phase Reordering 3D PACE Acquire 3D data Partial volume Fast acquisition technique e.g. EPI Detect rigid body motion Register to a reference data set Adjust the spatial encoding gradients for the next acquisition 6

7 Head Motion Correction with 3D PACE Real Time Motion Correction for Functional Imaging Ensures accurate slice location. Provides real-time monitoring of patient motion. Reduce false activations. Uncorrected Corrected Other Navigators Cloverleaf Navigator 2D Orbital Navigator (ONAV) 3D Spherical Navigator (SNAV) van der Kouwe AJ et al MRM 2006 Nov;56(5):1019 Auto Align and super navigators Acquire Auto Align Scout Automatically aligns to atlas Automatically prescribes slices Reproducible slice prescription 7

8 Matching Slice Position with Auto Align Don t worry. Go ahead and get the data. We will figure out later May 7 June 3 Self Navigation Acquire central k-space data: From interleave FID Or Radial views Motion Correction with Overlapping k- space Segments BLADE/Propeller SNAILS 1 TRELLIS 2 Ringlet/Shell trajectory 3 1. Liu C et al MRM 2004 Dec;52(6): Maclaren JR et al MRI 2008 May;26(4): Shu Y et al MRI 2006 Jul;24(6):739 Buehrer M et al MRM 2008 Sep;60(3):683 Larson AC et al MRM Jan;51(1): Assumption: The discrepancy between the redundant k-space data is due to motion. BLADE/Propeller Motion Correction Procedure Phase Correction of BLADEs 1. Apply motion correction of each BLADE Remove phase shift due to spatial translation. Remove phase rotation due to spatial rotation. Iteratively search for maximum correlation. Weight the data from each BLADE based on the correlation. 2. Combine the BLADEs to construct final image Pipe JG MRM 2006, 55(2) 380 8

9 BLADE for Pediatric Imaging Head with BLADE Without BLADE With BLADE T2 TSE coronal, PAT 2 with GRAPPA, TR 5500 ms, TE 113 ms, TA 3:07 min, SL 4 mm, 25 slices, 448 matrix, 200 mm FoV T2 TSE coronal,pat 2 with GRAPPA, TR 7340 ms, TE 113 ms, TA 5:09 min, SL 4 mm, 12 slices, 384 matrix, 200 mm FoV Children s Hospital, Philadephia, USA Alibek S et al. Acad Radiol Aug;15(8):986 Motion Artifact Reduction with BLADE BLADE for 3T T2 TSE without BLADE SL 3 mm, FoV 110 mm TA 6:00 min T2 TSE with BLADE SL 3 mm, FoV 230 mm TA 1:44 min T2 TSE T2 TSE with BLADE Mayo Clinic Jacksonville BLADE and 2D PACE Conventional BLADE With 2D PACE and ipat x 2 BLADE Considerations Over sampling of central k-space (longer scan time than Cartesian) Wider BLADE More reliable motion correction Higher SNR Longer scan time May produce streak artifact. Non-rigid body motion not corrected, but artifacts are dispersed. 9

10 Motion Correction in Time Series Retrospective Image Registration Rigid body registration: Head Non-rigid body registration: Liver, Breast Prospective Acquisition Correction Adjust spatial encoding gradients prior to data acquisition Oh well, I am really busy. Let s get computer science people to help you Auto Align Motion Correction by Co-registration Define a cost function such as Sum of the square residuals Mutual information Select reference image Apply transformations to other images. Spatial translations and rotations Non-rigid body transformations Spatial interpolations Calculate the cost function Iterative search the transformations until the cost function is minimized. Improve Subtraction with Registration without regisrtation with registration Real Time Prospective Correction Auto Correction t-test: t=+10 t=+5 Motion Correction None ART 3D PACE Assume motion history, e.g. SI motion for shoulder Define image quality metric, e.g. the entropy of the gradient of the image. Both are application dependent. t=-5 t=-10 3D spatial filter & t-test: Finger tapping fmri: trained stimulus-correlated 1.5 rotation head motion Manduca A, et al Radiology. 2000;215:904 10

11 Secondary Effects due to Physiology & Motion It s not really motion. Since I am so nice, I will fix it for you Magnetic field (B 0 ) and shim fluctuation For spectroscopy in body region. Align the frequency of each FID before average. Correcting physiological fluctuation in BOLD and ASL Record physiological data along with time series. Eliminate frames associate with abnormal physiological conditions. Apply retrospective correction (RETROPCOR) Pulse Triggered Spectroscopy Sometimes, I become nosy and want to know more about the motion No trigger Pulse triggered DirectVisualization of Valve Movement and Flow Jet Motion Visualization with Tagging Distortion of grid pattern shows myocardial strain -> DENSE 11

12 Gradient-Echo MRE 8/11/ Amplitude (mm) 0 Amplitude (mm) Velocity ECG Triggered NCE MRA Or, even play with it Time after R-Wave (Trigger Time) Diastolic - = Systolic MRA Dynamic NATIVE MRA Dynamic NATIVE MRA Systolic Phase Early systolic phase Diastolic phase Dynamic MIP images with trigger delay times (TD) from 150 to 260 ms after R wave for depiction of delayed or differential flow. Probing with Motion - MR Elastography 1. Driver ( Hz) 2. MRE Sequence 3. Inversion Phase Difference MR Elastography of the Liver +70 θ -70 Gel phantom with stiff inclusions Plastic Tube cm Active Driver Passive Driver Conventional MR Image Displacement (mm) Wave Chen Images Lin PhD 8/ Shear Stiffness (kpa) Elastogram

13 Summary There are a variety of motion compensation strategies, from simple modification of protocol to sophisticated motion quantification and correction. Different motion correction techniques maybe combined to achieve optimal results. Ability to visualize and quantify motion may aid the diagnosis in some situations. Thank you 13