초음파 영상의 기초

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지혜 온
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1 초음파물성및 영상의해상도향상 대한초음파의학회 대진대학교 전자공학과 정목근

2 Contents Ultrasound physics 초음파영상의해상도 -focusing 초음파영상의 Penetration - coded imaging

3 Conventional B-scan sonogram B-scan instrument skin transducer organ organ Ultrasound beam scanline

4 초음파는파동이다 Ultrasound physics 진폭 파동의전달 시간축 동심원 : 물결의전달 주기 (period) 매질내에서의파동은압력의전달이다. 압력 : 밀소밀소밀소밀

5 Ultrasound physics - 파장 - 주기 - 주파수 - 진폭 정현파 : 위상 ( 신호의지연 ) 기준시간 360 도 7.0 MHz SIN wave 시간 시간 시간 3.5 MHz COS wave 시간 진폭정보 B-mode 영상 위상정보 도플러영상

6 Ultrasound physics Sound velocity (1400m/s~1600m/s) In air : 340m/s water : 1480m/s Soft tissue: 1540m/s Blood : 1566m/s Impedance tissue I 1 Z = ρ c Z Z2 tissue II Reflectivity R = Z Z Z Z 2 2 P i P t P r Z = ρ c

7 Ultrasound physics 감쇄 = 흡수 + 산란 A = A 0 exp( βfz) 증폭 TGC 신호의크기 = 영상의밝기 깊이방향 f = 3.5MHz, β = 0.5dB / MHz / cm, d = 20cm f = 0.5[ db / MHz / cm] 3.5[MHz] 20[cm] = 35dB 1/ 60 7MHz, A 1 / 3160 주파수가높을수록감쇄때문에깊이전달되지못한다

8 Ultrasound physics SNR: signal 과 noise 의비율 [db] SNR -> penetration -> coded imaging technique Signal Noise level High SNR 깊이방향 low SNR 20dB 40dB 60dB = 10배 = 100배 = 1000배

9 해상도향상 Axial resolution >> Lateral resolution Focusing

10 초음파영상의 Resolution 축방향 (Axial) 해상도 Transducer Targets Firing Pulse burst pulse Short pulse 시간 high frequency Short pulse

11 초음파영상의 Resolution 측방향 (lateral) 해상도 z w= 2 λ = 2 D v f z D λ : wave length z : propagation depth v : ultrasound velocity f :frequency D : transducer aperture length w 주사선 해상도향상 f, D 증가 attenuation 영상깊이감소

12 Harmonic Imaging 매질의비선형성 고압 : 고속도 c = c o + 1 2ρ c o o ( B / A) p( t) 비선형매질 저압 : 저속도 f0 -> harmonic frequency 발생 -> f0, 2f0, 3f0. 3.5MHz MHz, 7.0 MHz, 10.5 MHz,.. Harmonic imaging

13 Harmonic Imaging f o 2f o 2f0: high resolution f0: deep penetration Conventional Imaging: reverb noise at f o Harmonic Imaging: Receiver removes f o & reverb noise

Harmonic Imaging with Conventional US in Abdominal Disease --

14 Harmonic Imaging conventional image harmonic image Diffuse fatty infiltration in the liver 해상도증가 Comparison of Tissue Harmonic Imaging with Conventional US in Abdominal Disease -- Choudhry et al_ 20 (4) RadioGraphics.htm 깊이들어가지못한다

15 Ultrasonic Imaging System Focusing Transmitter Doppler Processor Pre -amp. Digital Receiver Scan Converter Probe TGC Digital Beam -former Display

16 Array Transducer Array Transducer 구조 Pre amp-tgc amp-beamformer 압전소자 : 전압 진동

17 Scanning Electric scanning and focusing with a linear array 64, 128, 192, 256 elements ~ 200us 20cm 영상깊이 200~300 Scanlines 20~30 frame/sec

18 Focusing Focusing : 빔의폭을좁게하자 -> 위상의일치 -> 송신시간제어 영상점 zero In-phase out of-phase

19 Tx Focusing Tx Focusing : 초점에서모든신호의위상이일치 Array Elements Delay Delay Focal Point 송신시간제어 Delay Delay Delay 늦음 빠름 한점에서만 focusing 가능 빔폭이가장좁다. 신호의크기가가장크다

20 Rx Focusing Dynamic Focusing : 모든소자에서각각의수신데이터를저장하고있다가 신호처리에의하여초점에서위상을일치시킨다. memory Focal point 변경이가능

21 TRx Focusing 송수신집속음장 = Tx focusing Rx focusing Tx Focal depth 송신시빔패턴 Tx focusing : one focal depth 수신시빔패턴 Rx focusing : dynamic focusing 송수신빔패턴

22 Tx Dynamic focusing 각각의송신소자에서자신이송신한신호를분리할수있다면 송신시빔패턴 Tx dynamic focusing? 수신시빔패턴 Rx dynamic focusing? 최상의해상도 송수신빔패턴

23 TRx focusing Synthetic Aperture Focusing Tx pulsar Target Rx Amp ADC Probe Memory 차례로한 element가송신 / 수신파형저장후집속 어레이를모두사용하여송수신한것과같은효과 2-way dynamic focusing 1 element Tx : SNR 문제

24 Synthetic Aperture Focusing bipbf TM 기존의 B-mode 영상에적용 송신음장이겹치는부분의영상점신호를합성하여송신집속효과를얻음 Tx focal depth #1 #2 sc1 sc

25 BiPBF bipbf TM 출처 : 메디슨 Conventional Tx Dynamic Rx. Focusing bipbf TM

26 BiPBF bipbf TM Conventional Dynamic Rx. Focusing bipbf TM LIVER SV PANCREAS AO SPINE 출처 : 메디슨

27 송수신집속을이용하여해상도를올린다

28 3-D 영상에적용 Volume image : 데이터를얻는시간이많이걸린다. Volume data 트랜듀서를이동시켜 volume 영상을얻는다

29 Rx Focusing : Multi-beam multi-beam 데이터를얻는속도를높인다 Tx beam pattern Parallel Receive Beams Array Probe 2~4 Rx scanlines per 1 Tx Increase frame-rate 복잡한 Rx Hardware

30 Multi-row array probes 2D Array Probe 1D array 1.25D array 1.5D array 1.75D array 2D array 2D array Electronic elevation focusing : Elevation resolution, SNR, contrast resolution 향상 Elevation beam steering : very fast 3D imaging without any mechanical movement Increased # of parallel receiving beam (beams in 3D volume) : Even faster 3D imaging

31 2D Array Probe Pre amp-tgc amp-beamformer A Two-Dimensional Array Probe that has a Huge Number of Active Channels, S. Tezuka, S. Hashimoto, T. Togasaki1, Y. Miyajima, and Y. Seo, 2003 IEEE Ultrasonic symposium

32 Interconnection Problem 2D Array Probe More then 2000 interconnections.. A Two-Dimensional Array Probe that has a Huge Number of Active Channels, S. Tezuka, S. Hashimoto, T. Togasaki1, Y. Miyajima, and Y. Seo, 2003 IEEE Ultrasonic symposium

위에수많이제작, 서로연결. 매우광대역, 2D Array 제작에유리 아직은감도문제 http://www.

33 CMUT Probe CMUT : Capacitive Micromachined Ultrasonic Transducer 일종의 MEMS 기술, 반도체공정기술등활용 매우작은 speaker 를 substrate 위에수많이제작, 서로연결. 매우광대역, 2D Array 제작에유리 아직은감도문제

34 3D image 출처 : 필립스 Dysplastic tricuspid valve (En face view tricuspid and mitral valves)

35 더깊은곳의영상 더희미한병변의발견 High SNR 초음파송신출력의증가 Coded Excitation

36 Coded Tx : 영상깊은곳에서 SNR 높이려면 면적 : 초음파출력 Tx 전압높이기 - 안전문제 -> HIFU 응용 Burst 개수늘리기 - 축방향해상도문제 Coded Pulse Train 대안 : Coded Tx Long code Tx : High Power : High SNR Axial resolution 은 compression filter 로복원

37 Coded Tx : Pulse Compression Display Transducer 신호처리부 Pulse compression R T p(t) pulser Code memory High amplitude Short pulse

38 Pulse compression Pulse Compression - matched filter ( 정합필터 ): 기준패턴과수신신호를비교하여유사성판별

39 Coded Tx High Frequency (7.5MHz) Coded Excitation 출처 : GE

40 Coded Tx : Clinical Application Conventional B-mode imaging vs. coded imaging 출처 : GE

41 Clinical Application B-flow Imaging : 혈류가보인다. 출처 : GE Dialysis Graft Pseudoaneurysm Common Carotid Ulceration Internal Carotid Artery Stenosis

42 Clinical Application: code+harmonic Coded Harmonics (left) vs. conventional harmonics(right) - harmonics resolution / codes penetration 출처 : GE a liver hemangioma (arrow)

43 Future Technology orthogonal coded tx - multi code를사용하여각각의송신신호를분리 - 기존의 B-mode image에서 Tx dynamic focusing code 1 code 2 code 3 code

44 Future Technology hardware complexity -ASIC 기술 복잡한장치의구현이가능해졌다. BF ASIC ADC Rx Amp Tx Pulsar Beamformer Board (32ch/BD)

45 감사합니다

THE JOURNAL OF KOREAN INSTITUTE OF ELECTROMAGNETIC ENGINEERING AND SCIENCE Jul.; 27(7),

THE JOURNAL OF KOREAN INSTITUTE OF ELECTROMAGNETIC ENGINEERING AND SCIENCE. 2016 Jul.; 27(7), 625634. http://dx.doi.org/10.5515/kjkiees.2016.27.7.625 ISSN 1226-3133 (Print)ISSN 2288-226X (Online) Near-Field