Highly Accelerated SSFP Imaging with Controlled Aliasing in Parallel Imaging and integrated-SSFP (CAIPI-iSSFP).

Area of Science:

• Magnetic Resonance Imaging
• Medical Physics
• Biomedical Engineering

Background:

• Balanced steady-state free precession (bSSFP) sequences are susceptible to banding artifacts, limiting their acceleration potential.
• Controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) is a technique to accelerate MRI acquisition.
• Integrated SSFP (iSSFP) offers an alternative to bSSFP by modifying the pulse sequence to mitigate banding.

Purpose of the Study:

• To develop and evaluate a novel CAIPIRINHA technique combined with iSSFP (CAIPI-iSSFP) for accelerated 3T MRI.
• To assess the efficacy of CAIPI-iSSFP in eliminating banding artifacts.
• To quantify the impact of CAIPI-iSSFP on image quality, specifically contrast-to-noise ratio (CNR).

Main Methods:

• CAIPI-iSSFP was implemented by incorporating a dephasing gradient into the bSSFP sequence.
• Extended Phase Graph (EPG) simulations were used to model signal behavior.
• In vivo brain and abdominal imaging were performed at 3T using simultaneous multi-slice (SMS) acceleration factors of 2, 3, and 4, comparing CAIPI-iSSFP with CAIPI-bSSFP.

Main Results:

• CAIPI-iSSFP successfully removed banding artifacts in brain and liver imaging up to SMS factors of 4 and 3, respectively.
• CAIPI-bSSFP exhibited banding artifacts at higher acceleration factors.
• Relative CNR between gray and white matter was approximately 18% lower with CAIPI-iSSFP compared to CAIPI-bSSFP.

Conclusions:

• CAIPI-iSSFP enables significant acceleration (up to 4x) in SSFP imaging at 3T.
• The method effectively minimizes banding artifacts, a common limitation of bSSFP.
• A minor reduction in CNR (up to 20%) is observed, representing a trade-off for artifact reduction and acceleration.