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 Heartbeat Echo a a a a a a a a a a a aa ||||||||||||| N Heartbeat Echo • 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 aaaaaaaaaa aaaaa aaaaaaaaaa aaaaa 1234512345 12345 1234512345 12345 Heartbeat Echoes 1-5 N N Heartbeat 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 3 Cardiac Phases • • • • 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 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 slice sec breath-hold Higher resolution Realtime TrueFISP Cine • 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 Phase Phase 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