Fast and robust pulsed chemical exchange saturation transfer (CEST) MRI using a quasi-steady-state (QUASS) algorithm...

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Spectroscopy

Background:

• Chemical Exchange Saturation Transfer (CEST) is vital for imaging labile protons but is sensitive to saturation duration (Tsat) and relaxation delay (Trec).
• Existing quasi-steady-state (QUASS) solutions are unsuitable for pulsed-CEST MRI due to hardware and specific absorption rate constraints on clinical scanners.
• Accurate CEST measurements are crucial for diagnosing various medical conditions, particularly muscle diseases.

Purpose of the Study:

• To develop and validate a QUASS algorithm for pulsed-CEST MRI.
• To evaluate the algorithm's performance in muscle tissue.
• To assess the impact of Tsat/Trec on CEST measurements and compare with the new QUASS approach.

Main Methods:

• Developed a QUASS algorithm incorporating an approximated steady-state pulsed-CEST signal into an off-resonance spin-lock model.
• Conducted experiments using numerical simulations, a creatine phantom, and 3T MRI scans on healthy volunteers.
• Quantified CEST effects using asymmetry analysis and isolated specific CEST contributions (creatine, APT, PCr, MT/NOE) with a multi-pool Lorentzian model.

Main Results:

• Apparent CEST measurements were significantly affected by Tsat/Trec, showing smaller values compared to QUASS CEST, especially with short Tsat/Trec.
• The QUASS algorithm demonstrated robustness, mitigating the impact of Tsat/Trec and enabling accurate CEST measurements.
• The study confirmed the QUASS algorithm's ability to accelerate pulsed-CEST MRI and improve accuracy.

Conclusions:

• The proposed QUASS algorithm significantly improves the accuracy and efficiency of pulsed-CEST MRI.
• This advancement allows for robust CEST measurements even with short saturation and relaxation times.
• The QUASS algorithm holds promise for accelerated clinical evaluation of muscle diseases.