슬라이드 제목 없음

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은혜 누
8 years ago
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1 MR Angiography 김재형 서울의대방사선과학교실 ( 분당서울대병원 )

2 Contents Time-of-flight (TOF) MRA Phase contrast (PC) MRA Contrast-enhanced (CE) MRA Basic principles Clinical application

3 I. Time-of-flight (TOF) MRA Principles: flow phenomenon Various TOF sequences - 2D vs 3D technique - venography Through-plane saturation of 3D TOF MRA

4 1. Flow Phenomenon Time-of-flight effect Inflow effect SE T2-weighted image SE T1-weighted image

5 Time-of-flight effect (wash-out effect) 90 o 180 o signal long TE 영상단면 SE T2-weighted image 혈류

6 Inflow effect (entry slice phenomenon) 90 o 180 o signal short TE 영상단면 SE T1-weighted image 혈류

7 Inflow effect vs repetition time (TR) stationary tissue 에서 Mz 고주파 (RF pulse)

8 고주파 (RF pulse) Mxy

9 Mxy signal

10 T1 relaxation

11 Long TR next RF pulse Mz T1 relaxation

12 Short TR 일때는 next RF pulse incomplete T1 relaxation Mz

13 Short TR Mxy weak signal

14 Short TR next RF pulse 계속 weak signal saturation of tissue

15 그러면 short TR 에서 flowing blood RF pulse 혈관

16 Flowing blood signal

17 Flowing blood next RF pulse fresh blood signal (not weak)

18 정리하면 TOF (inflow) MR angiography short TR 의 RF pulses 영상 slab fresh blood (unsaturated proton) Saturation of tissue proton weak signal Inflow effect of flowing proton strong signal

19 TOF MRA sequence - short TR/ TE gradient-echo MRA source image

20 Source image processing MIP or volume rendering MIP source images (0.5 ~ 1mm 두께 )

21 Short T1 of subacute hematoma not saturated by short TR pulse TOF MRA T1 강조영상

22 2. Various TOF sequences 2D vs 3D TOF technique Venous saturation for arteriography Venography

23 2D TOF MRA Sequential multi-slice imaging Every slice is entry slice 장점 : sensitive to slow flow (vein) 단점 : slice thickness, larger than 3D RF pulses

24 3D TOF MRA Large slab excitation with phase-gradient at z-axis 장점 : effective slice (< 1mm) high resolution 단점 : saturation of the distal slab slab RF pulses 3D-FT

25 TOF arteriography: venous saturation venous flow 포화펄스 90 o α o signal 영상 slab arterial flow

26 venous flow Venous saturation 영상 slab arterial flow

27 TOF venography venous flow 영상 slab 포화펄스 90 o α o signal arterial flow

28 3. Through-Plane Saturation of 3D TOF MRA 3D 영상 slab repetitive RF pulse To overcome -TONE -MOSTA arterial flow

29 TONE 기법 (tilted optimized non-saturation excitation) 30 영상 slab ramped RF pulse flip angle arterial flow z-axis

30 TONE (-) TONE (+)

31 TONE (-) TONE (+)

32 MOTSA 기법 (multiple overlapping thin-slab acquisition) one-slab 3D multi-slab 3D 3D 3D 3D 3D 3D

33 MOSTA 기법 (5-slab) Venetian blind Venetian blind artifact

34 MOSTA with TONE 대나무 artifact

35 One slab 에만국한된 motion artifact

36 II. Phase contrast (PC) MRA Principles: flowing proton vs phase difference VENC (velocity encoding) Comparison with TOF MRA

37 1. Principle: flowing protons vs phase Flow-sensitizing gradient (bi-polar) - stationary protons bipolar gradient 후에 complete refocusing - flowing protons bipolar gradient 후에 phase difference 존재

38 Stationary protons flow-sensitizing 경사자장

39 flow-sensitizing 경사자장

40 일정시간후에 phase difference ( 위상차 ) 발생 flow-sensitizing 경사자장

41 flow-sensitizing 경사자장

42 일정시간후에위상차는없어짐 flow-sensitizing 경사자장

43 Flowing protons flow-sensitizing 경사자장

44 혈류에의해 proton 이인접자기장속으로이동 추가적인위상차발생 flow-sensitizing 경사자장

45 Bipolar gradient 를반대로걸어주어도 혈류에의해발생한위상차는회복안됨 신호감소 flow-sensitizing 경사자장

46 Acquisition of 4 images 3 flow-sensitizing images control image: No gradient subtract x-axis gradient y-axis gradient z-axis gradient 위상차가발생한즉 moving proton 만영상으로남는다

47 2. VENC (velocity encoding) Adjusting the velocity sensitivity Bipolar gradient의세기를조절 원하는flow velocity를최대위상차 (180 ) 로 신호가최대로감소하도록 VENC ( 단위, cm/sec) - fast flow (artery): 50cm/sec, weak gradient - slow flow (vein): 15cm/sec, strong gradient

48 Different VENC 15 cm/sec 45 cm/sec 75 cm/sec slow flow fast flow

49 Phase contrast venography 포화펄스 VENC=15cm/sec

50 TOF veno PC veno (VENC=15cm/sec)

51 3. Comparison with TOF MRA Advantages Subtraction-based image - no flow no signal - fat, subacute hematoma no signal Flow quantification: 혈류속도측정 Disadvantages Long scan time: parallel imaging으로극복 Optimal VENC

52 III. Contrast-enhanced (CE) MRA Principles: role of contrast media Comparison with TOF MRA

53 1. Principles of CE MRA Very short T1 relaxation of blood by contrast Very short TR/ TE sequence short scan time Narrow time window for imaging Synchronization between contrast bolus and imaging sequence k-space: central encoding at contrast peak

54 Shortening of blood T1 relaxation by contrast TOF MRA Gd-injected TOF MRA 포화펄스 arterial flow vein visualization

55 Very short TR/ TE Short scan time (10s - 1min) Narrow time window for imaging 농도 artery vein k-space central narrow time window 시간

56 Synchronization between contrast bolus and imaging sequence k-space encoding methods: - linear - central-to-periphery - elliptical centric or CENTRA

57 bolus arrival time 농도 artery vein scanning scanning 시간

58 How to estimate the bolus arrival time test bolus automatic triggering: signal > 20% MR fluoroscopy MR fluoroscopy (0.5 ~ 1 sec interval)

59 early scan start optimal timing ringing artifact late scan start vein contamination

60 2. Comparison with TOF MRA Advantage - 짧은시간에 head & neck vessel을영상화 - slow flow, turbulent flow를 imaging: contrast media - susceptibility artifact ( 예, 보철 ): short TE - subacute hematoma의 high signal : too short TR Disadvantage - poor spatial resolution

61 Traumatic pseudo-aneurysm TFCA TOF MRA CE MRA slow flow

62 Susceptibility artifact due to dental prosthesis TOF MRA shorter TE cemra

63 Subacute hematoma CE MRA TOF MRA too short TR short T1

64 Time-resolved MR angiography - ultra-short scan time 의 CE MRA (1-2 sec) - catheter angiography와같은역동적정보 - 단점 : 낮은공간, 시간해상도

65 Summary TOF MRA - inflow effect - 2D vs 3D, venography, through-plane saturation PC MRA - flowing proton vs bipolar gradient - VENC (cm/sec) CE MRA - synchronization between contrast bolus and scan - k-space: central encoding at contrast peak

66 Intracranial 3D-TOF Neck vessel 3D-TOF + Venography 3D-PC or CE MRA

슬라이드 제목 없음

슬라이드 제목 없음 뇌신경계 MRI: 어떻게시행하고무엇을알아야하는가? 최승홍 서울대학교병원 영상의학과 Contents CT, MRI의유용성비교 MRI 기법의종류, 특성 - T1강조영상, T2강조영상, FLAIR, --- 각종 MRI protocol - routine, stroke, dementia, --- CT, MRI 유용성비교 MRI > CT (almost all disease)