PROPELLER Acquisition on the PROPELLER Acquisition on the Philips AchievaPhilips Achieva

Philips Medical Systems, E. Brian Welch 2

What is PROPELLER?What is PROPELLER?

• Periodically Rotated Overlapping ParallEL Periodically Rotated Overlapping ParallEL Lines with Enhanced ReconstructionLines with Enhanced Reconstruction – JG – JG PIPE MRM 1999PIPE MRM 1999

• k-space is sampled by multiple cartesian k-space is sampled by multiple cartesian “blades”“blades”

• Blades overlap in circular region at center of Blades overlap in circular region at center of k-spacek-space

• Overlap allows for Overlap allows for – in-plane motion correction in-plane motion correction

(rigid rotation/translation)(rigid rotation/translation)– reject/underweight of inconsistent blades reject/underweight of inconsistent blades

(through-plane or non-rigid motion)(through-plane or non-rigid motion)

circular region of overlap at center

of k-space

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PROPELLER does address other motionsPROPELLER does address other motions

From Pipe MRM 1999

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What’s the big deal about PROPELLER?What’s the big deal about PROPELLER?

• Allows dramatic motion correction of axial T2W brain images – Allows dramatic motion correction of axial T2W brain images – heavily marketed by GEheavily marketed by GE

• Promising results as a multi-shot high resolution DWI/DTI technique Promising results as a multi-shot high resolution DWI/DTI technique (fewer B0-related artifacts than single-shot techniques)(fewer B0-related artifacts than single-shot techniques)

• Many recent papers and abstracts extending it usesMany recent papers and abstracts extending it uses

– Term “PROPELLER” occurs 33 times in ISMRM 2005 programTerm “PROPELLER” occurs 33 times in ISMRM 2005 program

• Improved GraSE and EPI versions with parallel imagingImproved GraSE and EPI versions with parallel imaging

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GE Healthcare web page on PROPELLERGE Healthcare web page on PROPELLER

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PROPELLER at ISMRM 2005PROPELLER at ISMRM 2005

• T1W PROPELLER - #2236T1W PROPELLER - #2236

• Variable pitch PROPELLER for MRA - #2239Variable pitch PROPELLER for MRA - #2239

• Mapping the anterior commissure - #12Mapping the anterior commissure - #12

• High resolution DTI at 3T – #9High resolution DTI at 3T – #9

• T2* mapping – #291T2* mapping – #291

• SPIO-enhanced DWI of Liver - #1881SPIO-enhanced DWI of Liver - #1881

• Imaging of the female pelvis - #2698Imaging of the female pelvis - #2698

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Is PROPELLER more RADIAL or or Is PROPELLER more RADIAL or or more CARTESIAN?more CARTESIAN?

RADIAL CARTESIAN

PROPELLER

? ?

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Ans: RADIAL and CARTESIAN are special Ans: RADIAL and CARTESIAN are special cases of PROPELLER!cases of PROPELLER!

RADIAL CARTESIAN

PROPELLER

L=1N= Mπ/2

LN=Mπ/2L = # lines/blade

N = # bladesM = Readout matrix size

N=1L= M

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PROPELLER implementation on the PROPELLER implementation on the Philips AchievaPhilips Achieva

• Treat PROPELLER as a Treat PROPELLER as a “cartesian-like” scan“cartesian-like” scan

• Allow prescription of very low Allow prescription of very low resolution cartesian scanresolution cartesian scan

• Repeat the cartesian scan and Repeat the cartesian scan and rotate about the slice-select axisrotate about the slice-select axis

• Add new “propeller” option for Add new “propeller” option for ““Acquisition ModeAcquisition Mode” that is ” that is treated internally as “cartesian”treated internally as “cartesian”

• New lower bound for “New lower bound for “Scan Scan PercentagePercentage””

• Take advantage of the Take advantage of the O_MATRIXO_MATRIX object available in object available in Philips pulse programmingPhilips pulse programming

Strategy Implementation

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PROPELLER patch interfacePROPELLER patch interface

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PROPELLER patch interfacePROPELLER patch interface

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PROPELLER : patch acquisition resultsPROPELLER : patch acquisition results

Matrix size = 256Matrix size = 256Scan % = 9.38%Scan % = 9.38%17 blades17 blades

TSE Factor = 24TSE Factor = 2418 slices18 slicesScan time = 102 secsScan time = 102 secs

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PROPELLER: Image ReconstructionPROPELLER: Image Reconstruction

• Regridded using Kaiser-Bessel convolutionRegridded using Kaiser-Bessel convolution• Iterative sampling density compensationIterative sampling density compensation

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Motion Correction ValidationMotion Correction Validation

1.1. Acquire multiple phantom PROPELLER datasetsAcquire multiple phantom PROPELLER datasets

2.2. Each has different known Offsets and AngulationsEach has different known Offsets and Angulations

3.3. 11stst scan undergoes FULL preparation phases scan undergoes FULL preparation phases subsequent scans skip prep. phases (SAMEPREP)subsequent scans skip prep. phases (SAMEPREP)

4.4. A set of blades randomly selected from datasets to A set of blades randomly selected from datasets to create composite set containing “motion corruption”create composite set containing “motion corruption”

5.5. PROPELLER algorithm reconstructs (and motion PROPELLER algorithm reconstructs (and motion corrects) composite data setcorrects) composite data set

6.6. Detected motions compared to known differencesDetected motions compared to known differences

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Motion Correction Validation:Motion Correction Validation:in-plane rotation + in-plane translationin-plane rotation + in-plane translation

UNCORRECTED CORRECTED

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Motion Correction Validation:Motion Correction Validation:in-plane rotation + in-plane translationin-plane rotation + in-plane translation

UNCORRECTED CORRECTED

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PROPELLER Motion Correction: PROPELLER Motion Correction: Low-Resolution “Disk Images” Low-Resolution “Disk Images”

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PROPELLER PLUS – for lack of a better namePROPELLER PLUS – for lack of a better name

1.1. DC value based blade rejectionDC value based blade rejection• May allow recollection of problems bladesMay allow recollection of problems blades• Should improve motion correction results by removing severely Should improve motion correction results by removing severely

inconsistent blades from motion correction stepsinconsistent blades from motion correction steps

2.2. Center of Mass translation correction (before rotation)Center of Mass translation correction (before rotation)• Allows use of complex k-space values for rotation correction stepAllows use of complex k-space values for rotation correction step• Uses full resolution of long axis of each bladeUses full resolution of long axis of each blade

3.3. Iterative rotational alignmentIterative rotational alignment• Each blade is rotationally aligned to the “average” blade which iterative Each blade is rotationally aligned to the “average” blade which iterative

updated until the rotational alignment convergesupdated until the rotational alignment converges• Should improve results in date with larger rotationsShould improve results in date with larger rotations

4.4. Combination with original published stepsCombination with original published steps• Image based rotation and translation correction can still be performed – Image based rotation and translation correction can still be performed –

may refine/improve resultsmay refine/improve results

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PROPELLER PLUS on the Philips AchievaPROPELLER PLUS on the Philips Achieva

• Translation correction before rotation correction

• k-space magnitude and phase used for rotational alignment

• Iterative rotational alignment

Phantom-based Motion Detection Validation ResultsMean Absolute Error0.14 mm and 0.11°

Correction results of subject executing in-plane motion

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PROPELLER: ISMRM 2006 submissionPROPELLER: ISMRM 2006 submission

** Accepted for presentation as electronic poster **

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PROPELLER: ISMRM 2006 submissionPROPELLER: ISMRM 2006 submission

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PROPELLER: completed stepsPROPELLER: completed steps

• Patch for acquisition of PROPELLER data Patch for acquisition of PROPELLER data • Kaiser-Bessel convolution kernel regridding Kaiser-Bessel convolution kernel regridding • Implement motion correction steps: Implement motion correction steps:

– in-plane rotation in-plane rotation – in-plane translation in-plane translation – inconsistent blade rejection inconsistent blade rejection --

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PROPELLER: next stepsPROPELLER: next steps

• GraSE and EPI reconstructionGraSE and EPI reconstruction

• Modifications for add’l prep. phase correctionsModifications for add’l prep. phase corrections

• Modifications for T1W PROPELLERModifications for T1W PROPELLER

• Modifications for improved TSE PROPELLER DWIModifications for improved TSE PROPELLER DWI

• On-host reconstruction using Gyrotools (Zurich) On-host reconstruction using Gyrotools (Zurich) reconstruction paradigmreconstruction paradigm

• SENSE reconstructions SENSE reconstructions

• Real-time feedback to recollect inconsistent bladesReal-time feedback to recollect inconsistent blades

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What to call PROPELLER on the What to call PROPELLER on the Philips system?Philips system?

• GE already uses PROPELLERGE already uses PROPELLER

• Rumors are that Siemens Rumors are that Siemens will call it BLADE will call it BLADE

• Why not WINDMILL? Why not WINDMILL? Philips is Dutch afterall! Philips is Dutch afterall!