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Elastography based on MRI combined with ultrasound
Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Elastography based on MRI combined with ultrasound Lino Lemmer 2015-07-06 Lino Lemmer Elastography based on MRI combined with ultrasound 1/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary 1 Introduction 2 Physical principles 3 Elastography 4 Security 5 Advantages and disadvantages 6 Examples 7 Summary Lino Lemmer Elastography based on MRI combined with ultrasound 2/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Motivation É É cancer is a highly common, often deadly desease possible ways of diagnosis: É É É É É palpation x-rays MRI with contrast agent ultrasonography biopsy Lino Lemmer Elastography based on MRI combined with ultrasound 3/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Motivation É cancer changes elastic properties of human tissue É for breast and prostate cancer palpation is very common É É difficult if size of area with different elastic properties is small highly dependent on doctor’s experience ⇒ use same ansatz but other technique! Lino Lemmer Elastography based on MRI combined with ultrasound 4/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Elasticity of different kind of tissue Young‘s modulus [Pa] bone calcification cartilage palpable lump connective tissue carcinoma glandular breast tissue breast tissue fat Lino Lemmer Elastography based on MRI combined with ultrasound 5/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary MRI basics RF-pulse ~ B ~ M ~ M equilibrium É É ~ M ~ B ~ M ~ M ~ M excitation with RF-pulse ~ B ~ M ~ M ~ M measurable transversal magnetisation signal gives signal amplitude and phase from each voxel for motion sensitive MRI sequence one uses the phase Lino Lemmer Elastography based on MRI combined with ultrasound 6/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Ultrasound basics É É É É É Sound: periodic change in density ρ and pressure p in gas an liquids: longitudinal waves (in solids: also transversal waves possible) wave equation: 1 ∂ 2p 4p − 2 =0 c ∂ t2 velocity of sound: v tK c= (= 1485 m s−1 in Water) ρ0 K = compressability Lino Lemmer Elastography based on MRI combined with ultrasound 7/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Ultrasound basics É sound impedance: Z := É É Æ K ρ0 reflection of sound on surface between two media with different impedance perpendicular impact: Z2 − Z1 R= Z2 + Z1 2 É this is used in regular ultrasound diagnosis É sound with frequency of f > 20 kHz is called ultrasound Lino Lemmer Elastography based on MRI combined with ultrasound 8/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary ultrasound generation É piezo electric effect: É É pressure on piezo electric medium causes voltage reciprocal piezo electric effect: É É É applying voltage to a piezo electric medium causes deformation alternating voltage causes oscillating behaviour transfer of oscillation to surrounding medium Lino Lemmer Elastography based on MRI combined with ultrasound 9/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Acoustic radiation force É É absorption of ultrasound in human tissue ⇒ transfer of momentum more demonstrative description: É É É É different behaviour in expansion and contraction in high frequency region elongation greater than contraction inflow of particles from the sides stream in direction of US-propagation Lino Lemmer Elastography based on MRI combined with ultrasound 10/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Acoustic radiation force É radiation force in direction of propagation FUS = É É É É 2α −2αx I e c 0 I0 = initial intensity α = absorption coefficient x = depth in tissue in elastic medium resetting force: Ftissue ∝ E · ∆x Lino Lemmer Elastography based on MRI combined with ultrasound 11/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Motion sensitive MRI sequence 180° pulse 90° pulse echo t Gz TE TE É sliceselection t Gy É phasencoding t Gx frequencycoding TE, fill TE, fill TE, fill É t É IUS spin echo sequence with two additional gradients first gradient shifts phase depending on x-position second gradient shifts phase again depending on x-position ∆φ = −γ · G · TG · ∆x ultrasound t Δx elongation t Lino Lemmer Elastography based on MRI combined with ultrasound 12/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary MRI É É rapidly changing gradients can cause for example dizzyness contraindication É É É metal implants or pacemaker (also vessel clips) non removable body piercings claustrophobia Lino Lemmer Elastography based on MRI combined with ultrasound 13/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Ultrasound É É É heating of tissue due to energy absorption appearance of small gas bubbles in low pressure phase (cavitation) limit in intensity and time of ultrasound Lino Lemmer Elastography based on MRI combined with ultrasound 14/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Advantages and disadvantages É Advantages É É É É no harming radiation no contrast agent → absolutely non invasive propably distinction between benign and malign tumors Disadvantages É É contraindications cost Lino Lemmer Elastography based on MRI combined with ultrasound 15/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Example: Breast cancer diagnosis É without ultrasound amplitude picture É phase picture low resolution, aliasing, movement artefacts Lino Lemmer Elastography based on MRI combined with ultrasound 16/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Example: Breast cancer diagnosis phase amplitude Lino Lemmer Elastography based on MRI combined with ultrasound 17/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Example: Breast cancer diagnosis 100 -\ TQ 50 51 52 53 54 55 56 57 58 80 60 40 20 0 40 50 60 Lino Lemmer 70 80 90 100 TM\IPRYQFIV Elastography based on MRI combined with ultrasound 18/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Summary É elastography to diagnose (and differenciate) tumors É ultrasound causes elongation (acoustic radiation force) É readout of elongation with motion sensitive MRI sequence É advantages: non harming É still in research (among others in AG Maier, HISKP) Lino Lemmer Elastography based on MRI combined with ultrasound 19/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Thank you for your attention! Lino Lemmer Elastography based on MRI combined with ultrasound 20/21 Introduction Physical principles Elastography Security Advantages and disadvantages Examples Summary Sources É Literature É É É É DÖSSEL, O.: Bildgebende Verfahren in der Medizin. Von der Technik zur medizinischen Anwendung, Berlin, Heidelberg: Springer, 2000 MENDE, J.A.: Schallinduzierter Kontrast in MRT-Phasenbildern - Detektion von Kalkablagerungen und erste Brustuntersuchungen von Probanden Doktorarbeit. HISKP, Universität Bonn, 2010 SCHINDLER, J.: Schallstrahlungskontrast in der MRT Detektion von Mikrokalk Diplomarbeit. HISKP, Universität Bonn, 2010 Pictures É WILD, J HISKP, Universität Bonn Lino Lemmer Elastography based on MRI combined with ultrasound 21/21
