Kspace strategies

Cardiac
Function
K-space
Techniques


Non-segmented K-space
ECG

Trigger

Acquisition Window

Acquisition Window

TR
Echoes
Cardiac Phases

a a a a a a a a a a a aa
|||||||||||||
N

1 2 3
Heartbeat 1
Echo 1

a a a a a a a a a a a aa
|||||||||||||
N

1 2 3
Heartbeat 2
Echo 2

• Single echo measured for each phase
• Temporal resolution very good
• Scan duration very long


Segmented K-space
ECG

Trigger

Acquisition Window

Acquisition Window

TR

Echoes
Cardiac Phases

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...

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...

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1234512345

. . .

12345

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. . .

12345

1

2
Heartbeat 1
Echoes 1-5

N

1

2

N

Heartbeat 2
Echoes 6-10

• Multiple echoes measured for each phase
• Short scan duration but poor temporal resolution


Echo-shared, Segmented K-space
ECG

Trigger

Acquisition Window

Acquisition

TR

Echoes

a a a a a a a a a a a a a . . .

a a a

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

3 4 5

Cardiac Phases

•
•
•
•

1

3
2

4

N

Multiple echoes measured for odd phases
Central echo measured for even phases
Even phases interpolated between odd phases
Short scan duration and good temporal resolution

1

3
2

4


Real-time Single-Shot K-space
(multiple slices, multiple phases, free-breathing)

R

ECG
Trigger
Acquired temp res about 150ms

slice #1

Effective temp res about 75ms

slice #2

With iPAT temp res about 50ms

slice #3
slice # m
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
phase #1

#2

#3

#n


Real-time Single-shot K-space
•

Benefit:

Can be used non-triggered and free-breathing with multiple slices.

•

However: Less temporal and spatial resolution than Segmented Echo-shared.

Real-time
Multiple slices
Free breathing
Lower resolution

Segmented Echo-Shared
Only 1 slice
8 sec breath-hold
Higher resolution


Realtime TrueFISP Cine
•

7 short-axis cine slices covering from base to apex of heart, with matrix
70*128.

•

Acquired in 14 heartbeats with triggering and breath-hold, but it could
have been untriggered and free-breathing for very sick patients.

•

Each slice was triggered on an R-wave and cine images were acquired in
rapid succession during the Acquisition Window.

•

In non-triggered mode, Number of Phases is used to define how long the
scan will run.


Radial K-space Sampling
•

Radial K-space trajectory

•

Higher spatial and temporal resolution

•

No phase wrap at smaller FOV

•

Isotropic in-plane resolution

•

Less sensitive to motion

•

Radial streaks more pronounced near edge FOV

Cartesian
K-space

Radial
K-space


Shared-Echo Radial K-space Sampling

Phase 1

Phase 2

Phase 3

etc

= Measured

= Shared


Radial Real-Time TrueFISP Cine
Improved resolution in real-time

• Cartesian Real-Time Cine
• Echo-sharing
• 50 lines
• 55 msec frame rate
• 300mm x 300mm FOV
• 2.3mm x 6.0mm res

• Radial Real-Time Cine
• Interleaved Echo-sharing
• 50 lines
• 55 msec frame rate
• 300mm x 300mm FOV
• 2.3mm x 2.3mm res


Radial Real-Time TrueFISP Cine
No phase wrap at smaller FOV

Cartesian Real-time Cine

Radial Real-time Cine

50x64, Shared temporal res 65 ms, Small 140mm FOV


Radial Real-Time vs. Radial Segmented

Radial Real-time
Free Breathing

Radial Segmented
Breath-hold