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

NoninvasiveSoft tissuesReal timePortableNon-ionizingResolution: < 1 mm

Fundamental of imaging

Ultrasoundtransducer

Reflection

Scatterers

Scattering

Backscattered echoes

Reflected echoes

speckle

B-mode image

Ultrasonic imaging system

Shortcomings of ultrasound image

TGC

Gain

Imaging display settings

Image process

Operator-dependentQualitative informationMorphology analysisHard to characterize scatterers

Low gain High gain

Shortcomings of ultrasound image

Low scatterer concentration

High scatterer concentration

High scatterer concentration (but weak reflection coefficient)

Low scatterer concentration

B-scan (the same gain)B-scan (the same gain)

(but the same reflection coefficient)

How to characterize scatterers by B-scan data?

According to central limit theorem, Ar and Ai are Gaussian distributedrandom variables, the joint distribution of Ar and Ai is

)1(A1

irj

N

ni

j AAeaAe i

If the resolution cell has a large number of scatterers (N scatterers), the complex ultrasonic echoes can be modeled as

)2(2

1),(

)2

(

2

2

22

ir

ir

AA

irAA eAAp

)3(02

),()

2(

2

2

2

AeA

ApA

A

)4(),()()

2(

2

2

2

A

AA eA

dApAp

So the pdf of envelope A is the marginal density

Change from rectilinear to polar coordinate, eq. (2) can be

Backscattering distribution

Rayleigh distribution

A

p(A)

Different backscattering conditions

Ultrasoundtransducer

Scatterers

Pre-Rayleigh

Rayleigh

Post-Rayleigh

Γ(.): Gamma functionU(.): Step function

R: Ultrasonic envelope m : Nakagami parameterΩ : Scaling parameterE : Mean

)()exp()(

2)( 2

12

rUrm

m

rmrf

m

mm

222

22

)]([

)]([

RERE

REm

)( 2RE

m < 1 m = 1 m > 1

Generalized Rayleigh scattering model

Nakagami distribution

Ultrasonic Nakagami imaging- to visualize scatterer properties

Envelope image

mm w

m

m

mw

wm

Envelope signal

(Local mean = global mean)The appropriate size is determined when

Nakagami image

(sidelength = 3 times pulselength)

Simulation, animal model, and clinical experiment

Nakagami imaging

Low scatterer concentration (4/mm2)

High scatterer concentration (32/mm2)

Pulser/Receiver

Diplexer TransducerAD

converter

Data storage

Timer/Counter

Motor controller

Motor driverUltrasonic

motorEncoder

PC

Sync. trigger Move transducer

saline

lens

capsule

40 mins

120 mins

Porcine lensFormalin solution to induce cataractIn vitro scan by a 35 MHz probe

Lens cataract

Liver fibrosisRat liverIMN injection to induce fibrosisIn vitro scan by a 5 MHz probeFibrosis scoring by doctors

Normal case Fibrosis (score<1)

Tissue ablation

Before before (antenna) heating heating heating and stop stop (antenna) stop t t= 0 40 sec 70 sec 100 sec 280 sec 300 sec

B-scan

Nakagami image

Sample: pork tenderloinMicrowave ablation (2.45GHz, 60 W)Imaging by portable system (7.5 MHz)

(Terason 2000)

Breast tumors

Fibroadenomas Invasive ductal carcinoma

5 mm

Patients come from Taiwan University HospitalIn vivo scan by Terason 2000

1-Specificity

0.0 0.2 0.4 0.6 0.8 1.0

Sen

sitiv

ity

0.0

0.2

0.4

0.6

0.8

1.0

At threshold = 0.64,Sensitivity: 88.6%Specificity: 74.3%Accuracy: 81.4%

 Nakagami image

Pathology  Total

Malignant Benign

0.64 31 (TP) 9 (FP) 40

0.64 4 (FN) 26 (TN) 30

Total 35 35 70

3-D Nakagami image of rat liver

Resolution improvementMulti-directional informationPathological model (e.g., fibrosis growth model)

Potential:

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)

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

Thank you for your attention