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Transcript of Past Developing 4D-MRI For 4D Radiation Therapy · PDF fileDeveloping 4D-MRI For 4D Radiation...

  • 8/12/2011

    1

    Developing 4D-MRI For 4D Radiation Therapy

    Jing Cai, PhD

    Department of Radiation Oncology

    Duke University Medical Center, Durham NC

    Disclosure: No conflict of interest

    OutlinePast

    - MRI for motion imaging

    - 4D-MRI strategies

    Current

    - Sequences

    - Surrogates

    Future

    - Clinical implementation

    - Future directions

    Pros and cons of MRI

    Pros

    - Superior soft-tissue contrast to CT

    - No risk of radiation exposure (long time imaging)

    - Flexible in image plane selection

    - Functional/molecular imaging

    - Variety of image contrasts

    Cons

    - Poor spatial accuracy (image distortion)

    - Various image artifacts (ghost, susceptibility)

    - Signal not correlated to electron density

    MRI for Motion Imaging

    Sites: lung, esophagus, liver, spinal cord, H&N,

    pancreas, etc.

    Tumor motion ~ location/size/type of cancer, etc.

    Correlation: external motion ~ tumor motion

    Statistical tumor motion (PDF)

    4D-CT pitfalls

    Lung deformation

    4D tumor motion in patients (hemi-diaphragmatic

    paralysis)

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    2

    Tumor Motion Probability2 2 2

    , , , , , , , , , ,

    , , , ,

    1( ) ( ( ) ) (1 sgn( ))

    2m

    tumor

    i j k m i j k i j k m i j k i j k

    i j k lung i j k CTVlung

    Vobj w d p d P d P

    V

    Tumor Motion PDF Evolution

    Large variation during the scan

    Tends to stabilize after certain time

    Simulate 4D-CT using MRI

    Respiratory signals from internal surrogate

    1st couch 2nd couch 3rd couch

    Image Acquisition

    Couch Movement

    MRI 4DCT

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    3

    4DCT MIP under-

    estimates tumor ITV

    MRI 4DCT

    y = 91.703x

    R2 = 0.7747

    y = 55.104x

    R2 = 0.8469

    y = 36.334x

    R2 = 0.8523

    0

    10

    20

    30

    40

    50

    60

    70

    80

    0.00 0.20 0.40 0.60 0.80

    Breathing Varibility

    ITV

    Err

    or

    (%)

    1cm

    3cm

    5cm

    Linear (1cm)

    Linear (3cm)

    Linear (5cm)

    y = 45.917x - 0.4786

    R2 = 0.7558

    0

    10

    20

    30

    40

    50

    60

    70

    80

    0.00 0.50 1.00 1.50 2.00

    vR/S

    ITV

    Err

    or

    (%)

    4D-CT AIP: inaccurate probability?

    4DCT MRI 4DCT MRI 4DCT MRI

    4D-CT AIP: Patients Spinal Cord Motion

    4 frames/sec, 20 sec continuous

    Cord motion generally < 0.5 mm

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    4

    Brain Pulsatile Motion

    CC AP

    DENSE sequence

    Pulsatile motion originated from brain stem and radiates toward peripheral brain regions.

    CSF can be easily identified due to its opposite movement

    Lung Deformation using HP Gas MRI

    2D Dynamic Tagged Lung: Sagittal

    0.0s 0.7s 1.4s 2.1s 2.8s

    Strategies of 4D-MRI

    Real time 3D

    - ultra-fast 3D MR sequence

    - fast gradient, multi-channel coils

    - parallel processing

    - current: voxel 3-4mm, 1.5 sec/frame

    Retrospective-sorted 2D

    - fast 2D MR sequence

    - respiratory signals (external, internal, etc.)

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    5

    Retrospective 4D-MRI

    Fast 2D cine MR

    Multiple slices

    Cine duration > 1 cycle

    Frame rate: ~3 frames/sec

    Slice thickness: 3-5 mm

    In-plane pixel size: 1-2 mm

    Image Acquisition

    Surrogates

    - External

    - Internal

    - Image-based

    Signal processing

    Phase determination

    Respiratory Signal

    Aim: simple, robust, quickly implementable

    Potential MR Sequences

    TrueFISP/FIESTA (balanced steady state gradient echo)

    - T2*/T1, sensitive to fluid, band artifacts from long TR

    HASTE/SSFSE (single shot fast spin echo)

    - T2, good CNR, signal decay from lung echo train, blurring

    FLASH/Fast SPGR (fast spoiled gradient echo)

    - T1 (poor), tumor hypo-intensity

    EPI (echo-planner imaging)

    - GE-EPI (T2*), SE-EPI (T2), IR-EPI (T1)

    - susceptibility, ghosting, chemical shift, fat suppression

    Examples: 2D cine-MRI

    HASTE: visualize parenchyma better, tumor blurred

    TrueFISP: visualize vascular better, motion artifact

    HASTE v.s. TrueFISP

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    Dependence on Cancer Type

    Heterogeneous structure of squamous cell carcinoma may

    reduce its conspicuity in TrueFISP images.

    0

    20

    40

    60

    80

    100

    Perc

    en

    tag

    e (

    %)

    .

    Adenocarcinoma Squamous Cell

    CNR reduction in TrueFISP relative to HASTE

    SummaryHASTE and TrueFISP both can monitor lung

    tumor motion during free breathing.

    Tumor conspicuity and image artifacts depend upon tumor characterizations.

    HASTE images show better tumor conspicuity than TrueFISP images.

    HASTE has local blurring artifact; TrueFISP has motion artifacts in the phase encoding direction.

    Surrogates: external

    RPMBelt

    SpirometerSurface Imaging

    Surrogates: internal/image-based

    Implanted markers

    Diaphragm

    Air content

    Lung density

    Lung area

    Body area (axial, sagittal)

    Normalized cross correlation

    Deformable image registration

    Fourier transform (magnitude, phase)

    Implanted Makers

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    Erik Tryggestad, et al. 2011 Joint AAPM/COMP Meeting

    Time (seconds)

    Am

    pli

    tud

    e (

    A.U

    .)

    Acquire external respiratory signal(Physiological Monitoring Unit --

    PMU)

    PMU logging:

    synchronized with the image acquisition computer, auto started/stopped within sequence run sampled at 50 Hz

    External surrogate: PMU

    TrueFISP in lung volunteer

    (dark blood pulse on)

    Average

    frames/bin/slice = 17

    HASTE in abdo volunteer

    Average

    frames/bin/slice = 26

    4D-MRI with PMU

    Erik Tryggestad, et al. 2011 Joint AAPM/COMP Meeting

    Slice 3/10 Slice 5/10 Slice 7/10

    Slice 2/9 Slice 4/9 Slice 6/9

    Internal surrogate: diaphragm

    von Siebenthal, et al., "4D MR imaging of respiratory organ motion and its variability," Phys Med Biol 52, 1547-1564 (2007).

    Image-based surrogate: Body Area

  • 8/12/2011

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    AxialBA

    Sagittal BA

    Pre-sorted 4DCT Images (n=31)

    Breathing signal

    from RPM

    Breathing signal

    from BA

    Phase Comparison

    ( R, D, DA )

    4DCTBA 4DCTRPM

    Image Quality Comparison

    ( SBA, SRPM )

    Marker position (P)

    Breathing period (T)

    Breathing amplitude (A)

    Period variability (VT)

    Amplitude variability (VA)

    Space-dependent phase shift (F)

    Correlations

    Validation of BA as Surrogate

    Signal and phase: BA v.s. RPM4DCTBA

    4DCTRPM

    4DCT: BA v.s. RPM

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    Patient P T (s) VT A (mm) VA R D DA F (s) SBA SRPM

    Lung Cancer Patients

    Mean L2 3.4 0.18 6.5 0.20 0.90 -5.1 13.8 0.47 3.1 2.6

    Abdominal Cancer Patients

    Mean L2 3.7 0.19 6.8 0.21 0.94 -1.3 8.5 0.32 2.8 2.6

    All Patients

    Mean L2 3.6 0.19 6.6 0.20 0.92 -3.3 11.4 0.40 2.9 2.6

    p * 0.61 0.34 0.50 0.78 0.52 0.04 0.28 0.001 0.03 0.23 0.92

    Significant differences in R, DA, and F between the two

    groups of patients.

    Summary of measurements Image quality evaluation

    Image-based surrogate: FFT

    FFT

    FFT surrogate: patient example

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    Validation of FFT surrogate

    10 Subjects, 2 min MRI scan, sagittal / coronal

    Respiratory signal: ROI tracking v.s. FFT phase angle

    Small phase difference (-3.134.85%), high correlation (r2=0.970.02 )

    Phantom Study

    Fixed

    MotorSpring

    Bolus

    Gel

    MRI-compatible phantom driven by a sinusoidal pattern

    Mimics tumor and body motion

    1.5T GE clinical scanner

    FIESTA: ~ 3 frames/sec, 6 sec/slice

    BA is the area under bolus

    Phantom: axial BA

    Axial Coronal Sagittal Sagittal

    4D-MRI Single slice cine-MRI

    Axial Coronal Saggittal

    Phantom: sagittal FFT

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    11

    XCAT: axial BA

    XCAT: sagittal BA

    4DCT

    4DMRI

    Single slice cine MRI

    Clinical Implementation

    End points:

    Tumor-to-tissue CNR (4DMRI v.s. 4DCT)

    Tumor ITV accuracy (4DMRI v.s. cine MRI)

    Dosimetric impact (4DMRI v.s. 4DCT)

  • 8/12/2011

    12

    Future Directions Study tumor CNR v.s. cancer characteristics (sequences)

    Optimize imaging parameters (CNR, irregularity)

    Improve respiratory surrogate accuracy and robustness

    Use contrast: SPIO (super-paramagnetic iron oxide, CNR)

    Real 4D (sequence programming, hardware)

    Functional 4DMRI (ventilation, perfusion)

    Clinical implementations

    - Immediate needs

    S. A. Schmitz, et al. Iron-Oxide-Enhanced MRI of the Liver, ACTA RADIOLOGICA, 2006; 634-642

    MIP imaging without sorting

    Goal: to develop a simple MRI technique to generate MIP for treatment planning in radiation therapy

    Why: many cases only need MIP, no need of individual phases (respiratory-gated RT)

    2D MIP

    2D MIP

    2D MIP

    2D MIP

    2D MIP

    2D MIP

    2D MIP

    2D MIP

    2D MIP

    2D MIP

    2D MIP

    3D MIP

    Phanto