Quantitative cardiac 31P spectroscopy at 3 Tesla using adiabatic pulses

Area of Science:

• Medical Imaging
• Biophysics
• Magnetic Resonance Spectroscopy

Background:

• Cardiac phosphorus magnetic resonance spectroscopy (MRS) at 3 Tesla (T) offers improved signal-to-noise and spectral resolution compared to 1.5 T.
• Efficient quantitative MRS protocols at 3 T are limited by radiofrequency (RF) power and power deposition, especially with adiabatic pulses (BIR4/BIRP).
• Longer adiabatic pulse durations to reduce power can cause T2-decay errors in metabolite quantification and T1 measurements.

Purpose of the Study:

• To introduce a novel dual-repetition-time (2TR) T1 method for cardiac phosphorus MRS at 3 T.
• To alleviate RF power requirements and mitigate T2 relaxation errors during RF pulses.
• To validate the 2TR method against conventional techniques for accurate metabolite T1 quantification.

Main Methods:

• Developed a 2TR T1 method using frequency-sign-cycled adiabatic-half-passage pulses.
• Validated the 2TR method against inversion-recovery in phantoms using a specialized cardiac phosphorus MRS coil.
• Measured T1 values of phosphocreatine (PCr) and adenosine triphosphate (gamma-ATP) in calf and heart muscles at 3 T.

Main Results:

• The 2TR method effectively reduced RF power requirements and avoided T2 relaxation issues.
• T1 values for PCr and gamma-ATP were determined in calf muscle (6.8±0.3 s and 5.4±0.6 s) and heart muscle (5.8±0.5 s and 3.1±0.6 s).
• Measurements using the 2TR protocol showed agreement within 10% of conventional methods.

Conclusions:

• The new 2TR T1 method is a viable and accurate approach for cardiac phosphorus MRS at 3 T.
• This method overcomes limitations of RF power and T2 relaxation, enabling more reliable metabolite quantification.
• The 2TR technique provides precise T1 measurements essential for assessing cardiac energy metabolism.