1. Background and Principle of Elastography

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1 7/8/6 Disclosures Basics and Current Implementations of Ultrasound Imaging of Shear Wave Speed and Elasticity Some technologies described here have been licensed. Mayo and Dr. Chen have financial interests in the technologies. Shigao Chen, PhD Mayo Clinic College of Medicine August 6 MFMER slide- MFMER slide- Outline Significance and principle Generation of shear waves Detection of shear waves Shear wave speed calculation Sources of bias and variation. Background and Principle of Elastography MFMER slide- MFMER slide- Why Tissue Stiffness? Inherent Contrast THE BOOK OF PROGNOSTICS: Such swellings as are soft, free from pain, and yield to the finger, and are less dangerous than the others. then, as are painful, hard, and large, indicate danger of speedy death Limitations of palpation: subjective; small/deep lesions Hippocrates, B.C. Ultrasound in Medicine & Biology (9): 9-, MFMER slide- MFMER slide-6

2 7/8/6 Ultrasound Elastography US Elastography Strain elastography Shear wave elastography. Generation of Shear Waves Qualitative and Indirect Operator-dependent Insufficient for diffuse diseases c s kpa Quantitative and direct Shear wave speed Higher repeatability Shear modulus Density ( kg/m ) 7 MFMER slide-7 8 MFMER slide-8 A. External Vibration: Fibroscan B. Single Push Beam Shear Stiffness: μ = c ρ Image courtesy of Dr. Meng Yin. 9 MFMER slide-9 MFMER slide- Amplitude of Shear Waves by a Push Beam C. Supersonic Shear Imaging 8 6 D max (m) Increase push amplitude: Mechanical Index Increase push duration: heating MFMER slide- Bercoff et al., MFMER slide-

3 7/8/6 Directional Filter D. Comb-push Slow time (ms) Comb-push (cont d) t Wave Number (m - ) D FFT Comb-push - - Frequency (Hz) x Manduca et al., Deffieux et al., Slow time (ms) Slow time (ms) MFMER slide- d d cs c s t Song et al., IEEE TMI MFMER slide- Heterogeneous Medium. Detection of Shear Waves z (mm) z (mm) z (mm) Song et al., IEEE TMI, m/s m/s m/s MFMER slide- 6 MFMER slide-6 Plane wave imager vs. Line-by-line scanner Plane wave imager vs. Line-by-line scanner Plane wave imager Line-by-line scanner Plane wave imager Line-by-line scanner d d / d = cm -> Frame rate khz / d = cm, N = 8 -> Frame rate Hz 7 MFMER slide-7 / d = cm -> Frame rate khz / d = cm, N = 8, PB = -> Frame rate 6 Hz 8 MFMER slide-8

4 7/8/6 Challenge in Shear Wave Detection Plane wave imagers Line-by-line scanners Time Aligned Sequential Tracking (TAST) Transducer Research platform Less than % market Clinical scanner more than 9% of market 9 MFMER slide-9 Vectors MFMER slide- Vector Lateral dimension Vector Vector TAST GE LOGIQ E9 (LE9) with CUSE LE9 Vector Vector Time Data Alignment True data sample Interpolated data sample Data tracking trajectory Aligned data points Truncated data points SSI Diam. (mm) LE9 (kpa) MFMER slide- SSI (kpa) Song et al., IEEE UFFC MFMER slide- LE9 Invasive mammary carcinoma Nottingham grade III of III Breast cancer study SSI. Shear Wave Speed Calculation Normal Song et al., IEEE UFFC, MFMER slide- MFMER slide-

5 7/8/6 A. Time-to-Peak (TTP) B. Random Sample Consensus (RANSAC) soft stiff C=inverse slope =c C = inverse slope Image courtesy of Dr. Kathy Nightingale MFMER slide- Image courtesy of Dr. Kathy Nightingale Wang MH et al. Ultrasound Medicine and Biology, 6(): 8-8,. 6 MFMER slide-6 C. Cross Correlation t.sources of Bias d d cs t 7 MFMER slide-7 8 MFMER slide-8 A. Tissue Viscosity Shear wave speed (m/s) c s c s Voigt model =.8 kpa, =.8 Pa*s 6 B. Compression Probe compression, perfusion pressure Frequency of shear wave: push duration, f number 9 MFMER slide-9 Barr et. al. Journal of Ultrasound in Medicine :89, MFMER slide-

6 7/8/6 C. Shear Wave Reflections Summary Deffieus et. al. IEEE Trans. UFFC, 8:, MFMER slide- Significance and principle Generation of shear waves: mechanical, single beam, Supersonic, Comb Detection of shear waves: TAST Shear wave speed calculation: Time to peak, RANSAC, correlation Sources of bias and variation: viscosity, compression, boundary MFMER slide- MFMER slide- 6