flow data acquisition

Flow ImagingData Acquisition... Prospective Triggering• Measures less than entire cardiac cycle • Very sensitive to arrhythmias and variable heartrates • Acquisition Window manually adju

Flow Imaging

Data Acquisition

Prospective Triggering

• Measures less than entire cardiac cycle

• Very sensitive to arrhythmias and variable heartrates

• Acquisition Window manually adjusted

• Cine frame-rate determined by # of measured segments

Ecg-Triggering Strategies

Retrospective Triggering

• Measures through entire cardiac cycle

• Arrhythmia rejection is available

• Acquisition Window automatically adjusted

• Interpolates to any desired cine frame-rate Most Common

Trigger Pulses

a a a a a a a a a a a a a

| | | | | | | | | | | | |

Retrospective

(most common)

a a a a a a a a a a a a a

| | | | | | | | | | | | |

1 2 3 4 5 6 N

a a a a a a a a a a

| | | | | | | | | |

1 2 3 4 5 6 N

1 2 3 4 5 6 N Prospective 1 2 3 4 5 6 N

Measured

Echoes

Undersampled cardiac cycle = 10-20%

Ecg-Triggering Strategies

Copyright ©Radiological Society of North America, 2002

Lotz, J et al Radiographics 2002;22:651-671

Temporal Resolution

Echoes 6-10 Echoes 1-5

Acquisition Window Acquisition Window

a a a a a a a a aa a a a a a

6 7 8 9 10 6 7 8 9 10 6 7 8 9 10

1

a a a a a a a a a a a a a a a

1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

1

TR

K-space Segmentation

ECG

Trigger

Echoes

Cardiac Phases

• Multiple k-space lines measured per cardiac phase (segment)

• More lines/segment = faster scan, but larger TR (worse temporal resolution)

repeat to fill K-space

• Multiple velocity-encodings measured per cardiac phase (segment)

• More encodings/segment = more velocity info, but larger TR (worse temporal resolution)

ECG

Cardiac Phases

r = reference (zero) velocity encoding y= velocity encoding in y direction x= velocity encoding in x direction z= velocity encoding in z direction

r x

r x r x r x r x r x r x r x r x

1 2 3 4 5 6 7 8 9 10

r x y z

r x y z r x y z r x y z r x y z r x y z r x y z r x y z r x y z

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

r x r x r x r x r x r x r x

r x y z

r x

Multiple VENC’s

3 VENC’s

1 Venc

TR

Single VENC

1 velocity in 1 direction

Phase Images Rephased Images

VENC Scout

3 velocities in 1 direction

aliasing

VENC 90 VENC 200 Rephased VENC 150

3-D VENC

1 velocity in 3 directions

Rephased Ant-Post

Right-Left Through-Plane

H >> F

3-D VENC

1 velocity in 3 directions

Rephased Head>Foot

Through-Plane Ant-Post

Typical Retrospective Triggering

1 VENC

Calc Phases 25

TR 39 ms

Segments 3

Time 20 sec

3 VENC‘s Calc Phases 20

TR 59 ms Segments 2 Time 30 sec

3x more velocity info but

less temporal resolution and

longer scan time or