Advanced Imaging Techniques · 06.12.2018 1 Advanced Imaging Techniques Elastography Prof. Dr....
Transcript of Advanced Imaging Techniques · 06.12.2018 1 Advanced Imaging Techniques Elastography Prof. Dr....
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Advanced Imaging TechniquesElastography
Prof. Dr. Frank G. ZöllnerComputer Assisted Clinical MedicineMedical Faculty Mannheim Heidelberg University
Theodor-Kutzer-Ufer 1-3D-68167 Mannheim, Germany
[email protected]/inst/cbtm/ckm
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Learning Goals
� introduction to advanced imaging techniques in MR, CT and CBCT
� basic MRI principles -> Physics of Imaging Techniques
� Goals:
1. How does the technique work ?
2. What kind of images do we receive?
3. Where is this applied to ?
� Literature is given in the respective lectures
� Slides of the lectures at https://www.umm.uni-heidelberg.de/inst/cbtm/ckm/lehre/index.html
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Readings� Rosa M.S. Sigrist,1 Joy Liau,1 Ahmed El Kaffas,1 Maria Cristina Chammas,2 and
Juergen K. Willm. Ultrasound Elastography: Review of Techniques and Clinical Applications. Theranostics. 2017; 7(5): 1303–1329.
� Mariappan et al., Magnetic resonance elastography: A review. Clinical Anatomy, 2010.23(5)p.397-511
� Tse, H. Janssen, A. Hamed, M. Ristic, I. Young, and M. Lamperth, Magneticresonance elastography hardware design: a survey. Proc Inst Mech Eng H, vol. 223, pp. 497-514, May 2009.
� Lonbani, Zohreh & Wall, David & Paulsen, K & Weaver, J & Watts, R & Van Houten, Elijah. (2010). Magnetic resonance elastography artifacts due to actuationsystems. International Conference on Bioinformatics, Computational Biology, Genomics and Chemoinformatics 2010, BCBGC 2010. 61-69.
� Tomokazu Numano, Yoshihiko Kawabata Kazuyuki Mizuhara,Toshikatsu Washio, Naotaka Nitta, Kazuhiro Homm. Magnetic resonance elastography using an airball-actuator. Magnetic Resonance Imaging, 2013, 31(6):939-946
� Hwang SI, Lee HJ. The future perspectives in transrectal prostate ultrasound guided biopsy. Prostate Int. 2014 Dec;2(4):153-60
� Franiel, T., Asbach, P., Teichgräber, U., Hamm, B., & Foller, S. (2015). ProstateImaging--An Update. RoFo : Fortschritte auf dem Gebiete der Rontgenstrahlenund der Nuklearmedizin, 187 9, 751-9.
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Overview
� Basics of Elastography
� Ultrasound Elastography (USE)
� MR Elastography (MRE)
� Applications
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Introduction to stress, strain and elasticity
Elasticity : ability of a body to resist stress and to return to its original size and shape when the stress is removed
Strain : amount of deformation
Stress : ratio of the force to the cross-sectional area
Young’s modulus E : slope of stress-strain curve in the elastic deformation region. � A stiffer material has a higher elastic modulus
★ shear stress : component of stress coplanar to material cross section
� ��
2�1 � �
Background
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Introduction to stress, strain and elasticity
Sigrist et al. Theranostics 2017
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Elasticity, Young’s modulus E, shear modulus G
Viscosity : measure of its resistance to gradual deformation by stress
Viscoelasticity : elements with both properties will exhibit time-dependent strain
�∗ � �� � ���� � � ������ � ����
BackgroundIntroduction to stress, strain and elasticity
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Measurement techniques - Overview
Mariappan et al, Clin Anat 2010
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US Elastography
� three types of elastic moduli Γ defined by the method of deformation:
� Young's modulus (E),
� shear modulus (G)
� bulk modulus (K)
� elastic modulus Γ also characterizes the propagation speed of waves
� two types of wave propagation in ultrasound:
� longitudinal waves
� shear waves
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US Elastography
� Longitudinal waves
� particle motion parallel to the direction of wave propagation
� are defined using the bulk modulus K as
� Longitudinal waves used in B mode imaging -> not suitable for USE
� shear waves
� particle motion perpendicular to the direction of wave propagation
� are defined using the shear modulus G as
� shear wave speed (cS) is approximately 1-10 m/s in soft tissues
� allows for high differences in G
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US Elastography
Sigrist et al. Theranostics 2017
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US Elastography Techniques
Sigrist et al. Theranostics 2017
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US Elastography Techniques – Strain imaging
� Excitation methods:� the operator exerts manual compression on the tissue with the
ultrasound transducerworks fairly well for superficial organs (breast and thyroid) is challenging for assessing elasticity in deeper located organs
(liver) � the ultrasound transducer is held steady, and tissue displacement
is generated by internal physiologic motion (e.g. cardiovascular, respiratory)
not dependent on superficially applied compression, it may beused to assess deeper located organs
� induced tissue displacement measured in the same direction as theapplied stress� a number of different methods dependent on the manufacturer,
including radiofrequency (RF) echo correlation-based tracking, Doppler processing, or a combination of the two methods
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US Elastography Techniques – ARFI Strain imaging
� Acoustic radiation force impulse (ARFI) strain imaging
� a short-duration (0.1-0.5 ms) high-intensity acoustic “pushing pulse” (acoustic radiation force) is used to displace tissue
� spatial peak pulse average = 1400 W/cm2, spatial peak temporal average = 0.7 W/cm2
� displacement of ~ 10-20 µm in the normal direction, i.e. perpendicular to the surface
� displacement within a specified ROI is subsequently measured by thesame methods as in strain elastography
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US Elastography Techniques – Shear Wave Imaging
� Shear wave imaging (SWI) employs a dynamic stress to generateshear waves in the parallel or perpendicular dimensions
� shear wave speed results in qualitative and quantitative estimates oftissue elasticity
� three technical approaches for SWI:
� 1 dimensional transient elastography (1D-TE)
� point shear wave elastography (pSWE)
� 2 dimensional shear wave elastography (2D-SWE)
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US Elastography Techniques –Shear Wave Imaging
Sigrist et al. Theranostics 2017
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Technical Limitations
� general sonography limitations such as
� shadowing, reverberation, and clutter artifacts
� operator-dependent nature of free-hand ultrasound systems
� tissue attenuation decreases ultrasound signal as a function of depth, limiting accurate assessment of deeper tissue or organs
� Fluid or subcutaneous fat also attenuates propagation of the externalstimulus applied at the skin surface which can invalidatemeasurements in the setting of obesity or abdominal ascites
� system settings and parameters (i.e. ultrasound frequency, samplingrate, gains, etc.) can also produce biased results if not standardizedacross patient groups and time points in longitudinal applications
� lack of uniformity of commercial system design and settings makescomparing measurements from one manufacturer system to another a difficult task
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• Quantification of tissue stiffness during MR examinations
Magnetic Resonance ElastographyIntroduction
Generate of sinusoidal shear
waves by external source
Encode wave in MR Phase by
motion-encoding gradient
Reconstruct wave propagation into
viscoelastic maps
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E ∝ ��
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At present, solely one FDA-approved setup for liver fibrosis grading only
MRE – Impact on Diagnostic AreasIntroduction
0
1
2
3
4
5
Ord
ers
of M
agni
tude
Transducer-related issues:• Preserved transducer amplitude at
higher ������• No induction of image artefacts
• Accuracy of ������• Modularity of the setup
Goal: Establish MR elastography asnon-invasive diagnostic parameter
Atte
nuat
ion
coef
ficie
nt (c
m"�)
T1
Rel
axat
ion
(ms)
Bul
k m
odul
us (Pa)
She
ar m
odul
us (Pa)
Adapted from Mariappan et al., Magnetic resonance elastography: A review.Clinical Anatomy, 2010.23(5)p.397-511
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At present, solely one FDA-approved setup for liver fibrosis grading only
MRE – Impact on Diagnostic AreasIntroduction
Transducer-related issues:• Preserved transducer amplitude at
higher ������• No induction of image artefacts
• Accuracy of ������• Modularity of the setup
Goal: Establish MR elastography asnon-invasive diagnostic parameter
She
ar m
odul
us (Pa)
0
5000
10000
15000
20000
25000
30000
Liver Fat Muscle
She
ar m
odul
us (
Pa)
40 Hz 60 Hz 80 Hz 30 to 90 Hz average
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MR Elastography
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MR Elastography workflow
Phase encoding sequence
ImagingMechanical excitation
(Amp. & Freq.)
Signal Processing
Phase & Amplitude maps
Scanner
Construction of Elastogram
3D linear elastic tissue model
Shear modulus/ Elastogram
Inversion Technique
Mechanical Synchronization
DriverSynchronous
Trigger Pulses
Synchronous Motion Sensitizing
Gradient
Actuator
Z. T. Tse, H. Janssen, A. Hamed, M. Ristic, I. Young, and M. Lamperth, "Magnetic resonance elastography hardware design: a survey," Proc Inst Mech Eng H, vol. 223, pp. 497-514, May 2009.
Introduction
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Wave Induction in MRE� Acoustic driving systems
� most commonly used systems in earlier MRE studies are acousticdriving systems, also called remote pneumatic actuators
� Electromechanical driving systems
� actuator generally consists of a coil
� the actuator oscillates due to the magnetic induction (Lorentz force) in the coil about a fixed axis of rotation within the scanner
� Piezoelectric driving systems
� composed of a stack of piezoelectric crystals, placed between a spring and rigid housing wall
� expands when a voltage is applied, a precise longitudinal vibrationis generated
� Gravitational driving systems
� waves poduced a rotational eccentric mass
� driven by steper motor or pneumatic turbine
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Wave Induction in MRE
Mariappan et al, Clin Anat 2010
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MRE Actuator Examples
Lonbani et al. BCBGC 2010, Numano et al, MRI 2013, Neumann et al., Plos One 2018, http://mriquestions.com/mr-elastography.html
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MRE Actuator Examples
W. Neumann F. Zöllner . EP3384844A1, filed:5.Apr.2017, (2018).
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MRE Imaging – Encoding the induced vibration
Neumann, PhD Thesis 2018, Heidelberg University
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Motion Encoding Gradients
� in presence of a gradient field, a moving spin accumulates a phase
� assuming a sinusoidal motion in MRE, the displacement is given by
� sensitivity to small shear wave amplitudes can be achieved byaccumulating phase shifts over multiple cycle of mechanical excitation
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Motion Encoding Gradients
� accumulated phase shift is proportional to the dot product of
� the gradient vector and the displacement vector,
� number of gradient cycles
� periods of the gradient wave form
with ϕ the initial phase offset, N the number of gradient cycles, T the period of mechanical excitation, &0 the displacementamplitude, and k the wave vector
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Motion Encoding Gradients
Mariappan et al, Clin Anat 2010
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MRE - Sequence
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MRE Post-processing
� Shear modulus� Vs is the wave speed� ρ is the density of the material (typically assumed to be around 1000 kg/m3 for
tissue in MRE)� wave speed can be written as a product of the operating frequency and the spatial
wavelength� local frequency estimation (LFE)� phase gradient (PG)� direct inversion (DI)
µ = ρVs2
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ApplicationsTissue
Shear stiffness(kPa)
Frequency ofoperation
(Hz)References
Ocular Vitreous Humor 0.01 10 (Litwiller., 2010b)
Lung 0.95 40 (Goss et al., 2006)
Liver:HealthyCirrhotic 2.2
8.9
60 (Yin et al., 2007)
Prostate:CentralPeripheral 2.2
3.3
65 (Kemper et al., 2004)
Breast:Adipose tissueFibroglandular tissueTumor
3.37.525
100 (McKnight et al., 2002)
Brain:Gray matterWhite matter 5.2
13.6
100 (Kruse et al., 2008)
Muscle:HealthyNeuromuscular
disease 16.638.4
150 (Basford et al., 2002)
Cartilage 2000 5000 (Lopez et al., 2008)
Bone 0.8 × 106
1500 (Chen et al., 2009)Mariappan et al, Clin Anat 2010
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Applications - Liver
� Left: liver stiffness
� Right: top row: healthy volunteer, bottom row: patient with cirrhoticliver
Mariappan et al, Clin Anat 2010
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Applications - Breast
� (a) An axial MR magnitude image of the right breast of a patient volunteer is shown. A large adenocarcinoma is shown as the outlined, mildly hyperintense region on the lateral side of the breast.
� (b) A single wave image from MRE performed at 100 Hz is shown along with the corresponding elastogram (c).
� (d) An overlay image of the elastogram and the magnitude image shows good correlation between the tumor and the stiff region detected by MRE. Mariappan et al, Clin Anat 2010
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Applications - Muscleskeleton
� (a) A sagittal MR image of the calf soleus muscle with the location of the driver indicated by the arrow is shown.
� 100-Hz MRE wave images of the muscle are shown while exerting 0 (b), 5 (c) and 10 N/m (d) of force.
� The increase in the wavelength (and thus stiffness) with the increase in muscle force is easily visible and is indicated by the double sided arrows
Mariappan et al, Clin Anat 2010
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Applications - Prostate
� Contrast enhanced transrectalultrasound (TRUS) findings of prostate cancer in a 62-year-old man.
� Contrast enhanced TRUS image shows increase vascularity and contrast agent signals from left peripheral zone suggesting increased vascularity (arrows).
� Note that the focal lesion shows low echogenicity in gray-scale TRUS, which is one of common findings of prostate cancer.
� This lesion was confirmed as prostate cancer after TRUS guided targeted biopsy.
Hwang SI, Lee HJ. Prostate Int. 2014, Franiel et al. Rofo 2015
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Summary
� Elastography sensitive modality to detect tissuestiffness
� Allows for functionalcharacterisation of tissuestructure
� can be measured by US and MR
� needs actuator thatinduces wave
� several different USE imaging technqiues
� MRE uses motionencoding gradientssynchornised to the waveinduction