Fast spin echo 단국대학교 영상의학과 유 동 수

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

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

FSE Spin echo의 특성 Fast scan Long TR (Multiple RF pulse, Slice number) : 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

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

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

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

Fast Spin echo - 용어 Echo train length (ETL) Echo train spacing (ETS) : 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 180° 90° ETS + 128 전반적대조도 0 (Ky) 세부묘사 - 128 K-space 16

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

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

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

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

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

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

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

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

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

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

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

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

HASTE, SSFSE FSE (Single Shot) + Half fourier acq. Single shot Frequency encoding ( Kx) 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 Phase encoding ( Ky) K-space Partial fourier technique 64-128 90° 180° 3

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

Summary 감사합니다. 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