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Fast spin echo

Fast spin echo

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Fast spin echo

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  1. Fast spin echo 단국대학교 영상의학과 유 동 수

  2. Contents • FSE의 원리와 특성 : (C)SE와 비교 • FSE의 장점,단점 • FSE의 변형 22

  3. FSE • RARE (1986) (Rapid Acquisition with Relaxation Enhancement) • FSE (Fast spin echo) TSE (Turbo spin echo) 21

  4. FSE • Spin echo의 특성 : Image quality ↑, Artifact ↓ • Fast scan • Long TR (Multiple RF pulse, Slice number) - T2강조 Conventional SE Fast SE 1 NEX 4 NEX 9 min 28 sec 2 min 25 sec 20

  5. 90° 180° 90° RF Pulse + 128 위상 (Phase) 부호화 경사 ( Gy ) 위상(Phase)부호축 ( Ky) 0 주파수 (Frequency) 부호화 경사( Gx ) - 128 RF signal (Echo) Spin Echo, k-space k-space Fourier Transform 주파수(Frequency) 부호 축 ( Kx) 256개의 phase encoding을 채울 경우 TR 256번을 반복 19

  6. TE30 TE80 TE100 TE60 90° 180° 180° 180° 180° 90° K-space TEeff 80 FSE vs CSE Multiple 180° pulse FSE CSE TR 90° 180° 90° RF Pulse 위상 (Phase) 부호경사 TE80 TE 80 Time saving No time saving 18

  7. 90° 180° 180° 180° 180° 90° TE30 TE60 TE80 TE100 TE30 TE80 TE100 TE60 90° 180° 180° 180° 180° 90° K-space TEeff 80 TE30 (PD) TE60 TE80 (T2WI) FSE vs CSE (CPMG) FSE Multiple 180° pulse CSE (CPMG) TR RF Pulse 위상 (Phase) 부호경사 Single image Time saving Multiple image No time saving 17

  8. 180° 180° 180° 180° 180° 180° 180° 180° 90° Fast Spin echo - 용어 ETL • Echo train length (ETL) : Number of 180° RF pulse : Scan time ∝ (1/ETL) • Echo train spacing (ETS) : Space between 180° RF pulse • Effective echo time (TE eff) : SE의 TE와 유사하게 사용되나 다른 개념 : TE of k-space mid-line (위상(Phase) 부호화경사 = 0) : Echo ↑↑ : Contrast, SNR에 주로 기여 ETS + 128 전반적대조도 0 (Ky) 세부묘사 - 128 K-space 16

  9. TE eff ETL (8) TE1 TE2 TE3 TE4 TE6 TE7 TE8 Ky=0 SNR, Contrast에 기여 Fast Spin Echo ETS 90° 180° 180° 180° 180° 180° 180° RF Pulse Phase-encoding gradient Echo TE5 + 128 0 (Ky) - 128 15

  10. Effective TE TEeff 40.36 msec 80.72 msec 96.86 msec 137.22 msec Blurring ↑ T2 effect ↑, SNR ↓ TEeff 100 TEeff 40 TE 40 TE 100 14

  11. Echo Train Length TR 5000msec, NEX = 2 ETL 4 ETL 8 ETL 16 ETL 32 1 min 25 sec 10 min 45 sec 5 min 25 sec 2 min 45 sec ETL ↑ : Time ↓ 문제점: Slice number ↓ 보정 : TR ↑, Slice thickness ↑ 13

  12. Ny NEX ETL : : : Phase-encoding steps Number of excitation Echo Train Length CSE 5000(TR) * 512(Ny) * 1(NEX) = 2560초 (42.7분) FSE 5000(TR) * 512(Ny) * 1(NEX) / 16 = 160초 (2.7분) Scan Time • Scan Time(SE) = (TR)(Ny)(NEX) • Scan Time(FSE) = (TR)(Ny)(NEX) /ETL 예제 : TR이 5000 msec, 1NEX, 512 X 512의 해상도로 CSE와 ETL을 16으로 했을 때 FSE에서 영상을 얻는 시간은 ? 12

  13. Advantage • Scan time↓: ∝ETL • Image quality ↑ : Scan time saving 단계를 trade off – NEX ↑, resolution ↑ • Spin echo와 유사한 contrast, imaging parameter • Artifact (motion, susceptibility) ↓ : by 180° refocusing pulse • Shimming magnet ↓ 11

  14. Disadvantage • Bright fat signal : J-coupling↓, diffusion mediated susceptibility ↓, MTC effect : Fat suppression image Conventional SE Fast SE Fast SE Fat suppression 10

  15. Disadvantage • Magnetic transfer contrast effect ↑ • Magnetic susceptibility ( Hmr, Ca+ ) ↓ Conventional SE Fast SE 9

  16. ETL ↑ ↑ : Reduced coverage (slice number ↓) Dual TE image :Time consuming Incorrect TEeff : Use multiple TE Disadvantage 8

  17. FSE의 변형 • 3D FSE (+ 3D) • GRASE (+ GRE) • Fast IR (+ IR) • HASTE, SSFSE (+ Single shot) (+ Half fourier acquisition) 7

  18. 3D FSE • Phase encoding : z 방향(Nz)을 추가 • Multiple slices → Slap • Scan time = (TR*NEX*Ny*Nz)/ETL • More scan time • Thinner image 2D Image 3D Image 6

  19. FSE GRASE 180° 180° 180° 90° Gradient echo Spin echo GRASE (Gradient and Spin Echo) • FSE + GRE • Spin echo를 일부가 GE로 대치 • FSE와 유사한 대조도 • GRE - Susceptibility ↑ (hemorrhage) Faster 5

  20. Fast IR (Inversion Recovery) • 180° inversion pulse + FSE • Fast STIR, Fast FLAIR Fast STIR Fast FLAIR 180° 90° 180° 180° 180° 180° 90° TI FSE IR 4

  21. 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° 180° HASTE, SSFSE • FSE (Single Shot) + Half fourier acq. • Single shot : 매우 긴 하나의 echo train(64-128개)를 이용 • Partial fourier technique : K-space의 일부에 date를 채움 Frequency encoding ( Kx) Phase encoding ( Ky) K-space Partial fourier technique 64-128 90° 3

  22. HASTE, SSFSE • Ultra-fast : 1-2초 (single breath hold) • Abdomen, chest imaging MRCP Liver MR 2

  23. Summary • Spin echo의 특성 • Fast scan ∝ETL • Advantage : Image quality ↑, Artifact↓ • Disadvantage : Fat signal ↑, Slice number↓ • ETL, ETS, TE eff • Advance of HW, pulse sequence – better image quality 감사합니다. 1