Introduction. Parametric Imaging. The Ultrasound Research Interface: A New Tool for Biomedical Investigations

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1 The Ultrasound Research Interface: A New Tool for Biomedical Investigations Shelby Brunke, Laurent Pelissier, Kris Dickie, Jim Zagzebski, Tim Hall, Thaddeus Wilson Siemens Medical Systems, Issaquah WA Ultrasonix Medical Corporation, Vancouver, BC Department of Med. Physics, University of Wisconsin Department of Radiology, University of Tennessee Introduction Digitally controlled ultrasound scanners offer extensive levels of programmability, which enable manufacturers to explore and to readily incorporate alternative beam formation, signal and image processing, networking, and interfacing capabilities. Recent efforts have led manufacturers to share these tools for innovation with academic and clinical researchers. This discussion will present capabilities of two such machines and present examples of research uses. The Ultrasound Research Interface: A New Tool for Biomedical Investigations Examples of Use Jim Zagzebski, Tim Hall, Thaddeus Wilson * Department of Med. Physics, University of Wisconsin * Department of Radiology, University of Tennessee Parametric Imaging Except for Doppler, ultrasound imaging is based entirely on echo amplitudes Parametric images Acoustic attenuation Scatterer size Speed of sound Elasticity (many forms)

2 Ultrasound Attenuation Attenuation is used diagnostically in the liver, breast, etc. However, only qualitative estimates are made mass exhibits shadowing mass exhibits good through transmission Goals: incorporate methods for determining attenuation locally, and in the form of images. Measuring Attenuation Record RF echo data from ROI Filter, measure reduction of rf signal with depth In a clinical machine, signal amplitude changes with depth are also affected by: Beam focusing, beam shapes TGC settings set by operator Internal TGC set by the manufacturer Nonlinear processing in scanners Reference phantom techniques have been developed that effectively account for instrumentation effects. Ss ( ω) log S ( ω) r Depth Attenuation (db/cm).... Attenuation in liver vs. frequency Frequency (MHz) Human liver Tu et al Lu et al ROI outlined from B-mode image (blue line) Areas of inhomogeneity eliminated (red line) Algorithm retrieves RF echo data from ROI, computes attenuation Results in normal liver agree with many previous reports (. db/cm-mhz) Attenuation Imaging Siemens SONOLINE Antares. db/cm/mhz contrast, cm diameter Acquire RF data from multiple angles Compute α from ROI s at each angle Spatial and Frequency Compounding

3 Attenuation Imaging Siemens SONOLINE Antares. db/cm/mhz contrast, cm diameter Acquire RF data from multiple angles Compute α from ROI s at each angle Spatial and Frequency Compounding Scatterer Size Imaging RF data can be processed to yield the backscatter coefficient at frequencies throughout the signal bandwidth Values of backscatter vs. frequency reflect the size of scatterers contributing to the signal. By applying scatterer size dependent correlation models to the backscatter vs. data, possible to estimate size. Mouse tumor model (Oelze (Oelzeand O Brien, O IEEE IEEE UFFC, UFFC, ) ) Use single element transducer, MHz Carcinoma Fibroadenoma Overlaid B-mode B and Scatterer size Acquire RF echo data from normal human thyroid Siemens Antares, - MHz Histology book: - µm lobules Scatterer size image data appears to correlate with anatomy. Scatterer size Reflects histological structure

4 Patient with thyroid nodule (Wilson et et al) Near real-time scatterer size imaging mode on Ultrasonix RP Elasticity Imaging Improve on manual palpation Use a clinical ultrasound imaging system as a sensor of anatomic deformation Relative deformation quantifies the bulk mechanical properties of tissue Provides new diagnostic information Estimation of Strain (Uses RF data frames) Array Transducer Pre-compression RF line Implementation on Machine with URI τ T τ Post-compression RF line Strain τ τ = T (Gradient of the axial displacement)

5 Relative Size of Lesions 9 Breast Lesions; Observer Invasive Ductal Carcinoma Fibroadenoma Spatial Angular Compounded Elastograms (Ultrasonix RP) x - x - Spatial Angular Compounded Elastograms x - º x - º x - Elastogram Without Compounding x - º º (Ultrasonix, gel phantom, inclusion is x stiffer) SNRe (db) 9. o o o o Maximum Angle ( o ) - º ~ º Compounded Elastograms

6 Speed of sound Hayashi et al, A new method for measuring in vivo speed of sound speed in the reflection mode, J. Clin Ultrasound : -9, 9. Can you measure SOS in pulseecho mode? Speed of sound Beam former adds time delays to echo data picked up from elements in an array. Assumes SOS = m/s. Some URI s allow assumed speed of sound to be programmed. Proper focusing is obtained only when the assumed speed of sound matches the speed of sound in the subject. Affects image intensity, for example. Speed of sound Generate images of phantoms for different assumed SOS in the beamformer Measure image brightness vs assumed SOS Peak occurs near SOS of phantom RMI C= m/s ATS 9 C=m/s Conclusions Parametric imaging adds new information to improve diagnostic accuracy The research interface on high-end systems are somewhat limiting in what the user can control Extended control and system programming available through close working relationship with manufacturer The research interface on lower-end systems provide greater access to system resources and system parameters These research interfaces provide an opportunity to investigate imaging algorithms that were impractical with laboratory data acquisition systems