Computer simulation of MRS localization techniques: an analysis of ISIS

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering

Background:

• The ISIS (Image Selected In Vivo Spectroscopy) technique is crucial for spatial localization in Magnetic Resonance Spectroscopy (MRS).
• Accurate signal localization is essential for reliable in vivo metabolite quantification.

Purpose of the Study:

• To evaluate the performance of the ISIS localization technique using computer simulations.
• To investigate the impact of various experimental parameters on signal loss and contamination in ISIS experiments with head and surface coils.

Main Methods:

• Utilized computer simulations to model ISIS experiments with head and surface coils.
• Examined the effects of chemical shift, B1 inhomogeneity, repetition time, T2 relaxation, saturation pulse, and observation pulse.
• Analyzed signal integrals over the volume of interest (VOI) and surrounding regions.

Main Results:

• Significant signal loss from the VOI and contamination from outside the VOI were observed in both head and surface coil ISIS.
• The saturation pulse, acquisition order, and repetition time influenced contamination but not signal loss.
• Short T2 relaxation and high radiofrequency (RF) power synergistically degraded selective inversion pulses, increasing contamination and signal loss.

Conclusions:

• The ISIS technique is susceptible to signal loss and contamination, impacting quantitative accuracy in MRS.
• Careful selection of acquisition parameters, including saturation pulse application and repetition time, can mitigate contamination.
• Short T2 tissues and high RF power present significant challenges, necessitating further optimization strategies for robust ISIS performance.