Gradient-Echo. Spin-Echo. Echo planar. Assessment of Regional Function Assessment of Global. Parallel Imaging. Function. Steady State Imaging

Transcription

1 Gradient-Echo Spin-Echo James W. Goldfarb Ph.D. Department of Research and Education St. Francis Hospital Program in Biomedical Engineering SUNY Stony Brook Echo planar Assessment of Regional Function Assessment of Global Function Detection of Infarction Perfusion Valvular Assessment Tissue Characterization Parallel Imaging Steady State Imaging Tagging Black-blood Imaging Navigator gating Intro: Pulse Sequence, ECG gating, k-space segmentation Part 1: Static Imaging Part 2: CINE Imaging Part 3: Single Shot Imaging Along the way: Preparation Pulses Definition: The pulse sequence is the computer program that controls the MR imagers hardware. Pulse sequences create the images. Pulse sequences have inherent contrast dependent on imaging parameters Gradient Echo Spin-Echo

2 Slice Selection (z) (y) Frequency (x) Slice Selection (z) (y) Frequency (x) TR: Repetition Time Collect one line of k-space TR: Repetition Time RF and Gradient Pulses Slice Selection (z) (y) Frequency (x) S lice Selection (z) (y) Frequency (x) S lice S election (z) (y) Frequency (x) S lice S election (z) (y) Frequency (x) TR: Repetition Time TR: Repetition Time TR: Repetition Time TR: Repetition Time RF and Gradient Pulses Spin-echo: 180 O refocusing Pulse SSFP: Balanced Gradient Waveforms Repeat (Ny) times to create an image TR = 2ms Ny = 128 Acquisition time of 1 image = 256ms

3 Imaging Time = R-R Interval x Ny =1 s* 128 = 2 min TOO LONG FOR A BREATH-HOLD!!!! Imaging Time = R-R Interval x Ny / (Number of k-space lines per heartbeat) =1 s* 128 /10 = 13 seconds JUST RIGHT FOR A BREATH-HOLD!!!!

4 ECG Purpose: To Remove or Reduce the Blood Signal Pair of inversion 180 O RF pulses (selective and non-selective) Pulse Sequence Black Blood Preparation Black Blood Preparation Delay Time=700 ms Imaging Acquisition Imaging Parameters: Delay time, slice thickness

5 Non- selective Non-selective 180 o 180 o 180 o = 360 =0 180 o Non 180 o Inversion

6 ECG Black Blood Preparation Imaging Acquisition Pulse Sequence Black Blood Preparation Delay Time=700 ms Mz time (ms) t () (1 2 1) Mz t Mo e T TI NULL 0.693* T1 Purpose: To Remove or Reduce Fat Signal Frequency RF pulse Imaging Parameter: Frequency Adjustment (Hz)

7 ECG Purpose: To add T1 weighting (Sensitivity to contrast agent) 180 preparatory degree rf pulse Imaging Parameter: Inversion Time (ms) Pulse Sequence Inversion Recovery Preparation Delay Time Inversion Time (TI) ms Imaging Acquisition TI =132ms TI = 170ms TI =208ms TI =132ms TI = 170ms TI =208ms TI =246ms TI =360ms TI =284ms TI =398ms TI =322ms TI =436ms 30 Minutes After contrast administration TI =246ms TI =360ms TI =284ms TI =398ms TI =322ms TI =436ms 10 Minutes After contrast administration TI too short - Infarct hypoenhancement TI too long - reduced contrast TI too short - Infarct hypoenhancement TI too long - reduced contrast TI = 150ms (Optimal TI = 250ms) Short TI Long TI M z Infarct M z Viable TI = 150ms (Optimal TI = 250ms) Short TI Long TI M z Infarct M z Viable Optimal TI Optimal TI

8 Magnitude Magnitude Sensitive Sensitive DHE DHE w/ Fat Saturation Sven Zühlsdorff, Siemens Medical Systems Precontrast Muscle Nulled TI=225ms 8 y.o. MI AO LM LAD Intermediate AO LAD Precontrast Fat Nulled TI=525ms LCx Postcontrast DHE Muscle Nulled TI=280ms

9 Purpose: To Remove or Reduce Fat Signal Frequency RF pulse Imaging Parameter: Frequency Adjustment (Hz)

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11 Pulmonary Systemic Flow Ratio Qp / Qs = Aortic Forward Flow / Pulmonic Forward Flow = 125 / 65 = : 1

12 Imaging Time = TR x Ny =3 ms* 128 = 384 ms N ky =60 Rest TR=2ms Time=120 ms Adenosine Stress

13 N ky =60 TR=2ms Time=120 ms Purpose: To add T1 weighting (Sensitivity to contrast agent) 90 degree preparatory RF pulse Imaging Parameter: Delay Time (ms)

14 N ky =30 Parallel Imaging TR=2ms Time=45ms N ky =30 Parallel Imaging TR=2ms Time=45ms N ky =30 Parallel Imaging TR=2ms Time=45ms Assessment of Regional Function Assessment of Global Function Detection of Infarction Perfusion Valvular Assessment Tissue Characterization 1: Static Imaging 2: CINE Imaging 3: Single Shot Imaging Preparation pulses to enhance contrast for specific applications

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