High spatial resolution quantitative MR images: an experimental study of dedicated surface coils

Area of Science:

• Medical Imaging
• Biophysics
• Biomedical Engineering

Background:

• Quantitative MR imaging of spin-spin relaxation times (T2) offers insights into physicochemical properties.
• Image noise in T2 mapping introduces uncertainties, limiting parametric tissue analysis accuracy.
• Adequate signal-to-noise ratio (SNR) is crucial, with higher requirements for biexponential T2 relaxation.

Purpose of the Study:

• To establish maximum spatial resolution and depth limits for reliable in vivo T2 quantitative MR imaging.
• To evaluate the performance of dedicated surface coils for high-resolution T2 mapping of superficial tissues.
• To provide practical guidance for achieving precise T2 measurements in microimaging.

Main Methods:

• Investigated T2 relaxation behaviors and required SNR levels for mono- and biexponential relaxation.
• Assessed the impact of voxel size and dedicated surface coils on SNR and spatial resolution.
• Employed a non-linear selective blurring filter to enhance spatial resolution while preserving T2 precision.

Main Results:

• Reliable biexponential T2 analysis requires a minimum voxel size of 13 mm³ (birdcage coil) vs. 1.7 mm³ (smallest surface coil).
• Surface coils, despite sensitivity fall-off with depth, enable higher spatial resolution for superficial structures.
• Image filtering reduced effective voxel size to 0.8 mm³, allowing microstructure visualization (e.g., fibrous septae) without compromising T2 accuracy.

Conclusions:

• Dedicated surface coils significantly improve spatial resolution for quantitative T2 MR imaging of near-surface tissues.
• Image filtering is a valuable technique for enhancing detail in T2 parametric maps.
• This work provides essential parameters for performing reliable in vivo T2 quantitative MR microimaging, particularly for conditions like HIV-associated lipodystrophy affecting the hypodermis.