A novel functional ultrasound image based on generalized Rayleigh scattering distribution for tissue characterization 以廣義雷利散射分佈為基礎之新世代功能性超音波影像 Po-Hsiang Tsui (崔博翔) and Chien-Cheng Chang (張建成) Division of Mechanics, Research Center for Applied Sciences, Academia Sinica 中央研究院應用科學研究中心 力學與工程科學專題中心

Ultrasonic imaging Noninvasive Soft tissues Real time Portable Non-ionizing Resolution: < 1 mm

Fundamental of imaging Scatterers Ultrasound transducer Reflection Scattering Backscattered echoes speckle B-mode image Reflected echoes

Ultrasonic imaging system

Shortcomings of ultrasound image TGC Image process Operator-dependent Qualitative information Morphology analysis Hard to characterize scatterers Gain Low gain High gain Imaging display settings

Shortcomings of ultrasound image B-scan (the same gain) B-scan (the same gain) Low scatterer concentration High scatterer concentration (but weak reflection coefficient) High scatterer concentration Low scatterer concentration (but the same reflection coefficient)

How to characterize scatterers by B-scan data?

Backscattering distribution If the resolution cell has a large number of scatterers (N scatterers), the complex ultrasonic echoes can be modeled as According to central limit theorem, Ar and Ai are Gaussian distributed random variables, the joint distribution of Ar and Ai is Change from rectilinear to polar coordinate, eq. (2) can be Rayleigh distribution A p(A) So the pdf of envelope A is the marginal density

Different backscattering conditions Ultrasound transducer Scatterers Pre-Rayleigh Rayleigh Post-Rayleigh

Generalized Rayleigh scattering model Nakagami distribution Γ(.): Gamma function U(.): Step function m < 1 m = 1 m > 1 R: Ultrasonic envelope m : Nakagami parameter Ω : Scaling parameter E : Mean

Ultrasonic Nakagami imaging - to visualize scatterer properties m mw Envelope signal Envelope image Nakagami image The appropriate size is determined when (Local mean = global mean) (sidelength = 3 times pulselength)

Simulation, animal model, and clinical experiment

Nakagami imaging Low scatterer concentration (4/mm2) High scatterer concentration (32/mm2)

Lens cataract PC Porcine lens Formalin solution to induce cataract In vitro scan by a 35 MHz probe saline lens capsule 40 mins 120 mins Pulser/ Receiver Diplexer Transducer AD converter Data storage Timer/ Counter Motor controller Motor driver Ultrasonic motor Encoder PC Sync. trigger Move transducer

Liver fibrosis Rat liver IMN injection to induce fibrosis In vitro scan by a 5 MHz probe Fibrosis scoring by doctors Normal case Fibrosis (score<1)

Tissue ablation Sample: pork tenderloin Microwave ablation (2.45GHz, 60 W) Imaging by portable system (7.5 MHz) (Terason 2000) B-scan Nakagami image Before before (antenna) heating heating heating and stop stop (antenna) stop t t= 0 40 sec 70 sec 100 sec 280 sec 300 sec

Breast tumors Patients come from Taiwan University Hospital In vivo scan by Terason 2000  Nakagami image Pathology   Total Malignant Benign 0.64 31 (TP) 9 (FP) 40 4 (FN) 26 (TN) 30 35 70 5 mm At threshold = 0.64, Sensitivity: 88.6% Specificity: 74.3% Accuracy: 81.4% Fibroadenomas Invasive ductal carcinoma

3-D Nakagami image of rat liver Potential: Resolution improvement Multi-directional information Pathological model (e.g., fibrosis growth model)

Comparison between B-scan and Nakagami images B-mode image Nakagami image Image pixel Grayscale Nakagami parameter Image physical meaning Echo intensity Envelope statistics Image type Qualitative Quantitative Resolution Relatively better Relatively poor Medical applications Morphology analysis Scatterer analysis

Summary and future works Nakagami imaging (2-D and 3-D modes) reflects scatterer properties, having ability to characterize tissues and discriminate benign and malignant tumors. Nakagami image can be complementary to the B-scan for morphology analysis and scatterers characterization Potential for monitoring tissue treatment process Developing very high frequency system for small scale analysis (e.g., cell)

Acknowledgements 中央大學數據分析方法研究中心: 黃鍔院士、張建中博士 台灣大學醫學院: 張金堅教授、 陳文翔醫師、郭文宏醫師、何明志醫師 南加州大學醫學工程系: 熊克平教授 台灣大學電機系: 李百祺教授 清華大學生醫工程與環境科學系: 葉秩光助理教授 輔仁大學電子工程系: 黃執中助理教授

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