New and rapid pulse sequences for two-dimensional D-T₁ correlation measurements

Area of Science:

• Physics
• Materials Science
• Biophysics

Background:

• Low-field Time Domain Nuclear Magnetic Resonance (TD-NMR) is crucial for material characterization.
• Key parameters like longitudinal relaxation time (T1), transverse relaxation time (T2), and diffusion coefficient (D) are vital.
• Multi-dimensional experiments (e.g., T1-T2, D-T2) reveal correlations between these parameters.

Purpose of the Study:

• To investigate novel D-T1 sequences for TD-NMR.
• To enhance the speed and efficiency of simultaneous D and T1 measurements.
• To evaluate the performance of new sequences compared to existing methods.

Main Methods:

• Developed four D-T1 sequences by combining Stejskal-Tanner Pulse Gradient Spin Echo (PGSE) for diffusion with Inversion-Recovery (IR), Saturation-Recovery (SR), CWFP-T1, and SAFF for T1.
• Compared the speed and signal-to-noise ratio of the new sequences.
• Assessed specific absorption rate (SAR) to evaluate sample heating.
• Validated sequences using phantom samples and plant tissues (asparagus).

Main Results:

• Single-shot CWFP-T1 and SAFF sequences significantly accelerate D-T1 measurements, being 2x and 8x faster than SR and IR-based sequences, respectively.
• Despite lower signal-to-noise ratio, these fast sequences match or exceed the speed of traditional D-T2 experiments by eliminating recycle delays.
• CWFP-T1 and SAFF exhibit lower SAR, reducing sample heating issues compared to SR or CPMG-based sequences.
• Anisotropic diffusion in asparagus tissues was successfully observed.

Conclusions:

• The developed CWFP-T1 and SAFF sequences offer rapid and efficient simultaneous D-T1 measurements in TD-NMR.
• These methods present practical advantages, including speed and reduced sample heating, making them suitable for diverse applications.
• The sequences are effective for studying complex biological systems, such as plant tissues, revealing anisotropic diffusion.