Efficient standardization of clinical T₂-weighted images: Phase-conjugacy e-CAMP with projected gradient descent

To standardize T ${\hspace{0.17em}}_2$ -weighted images from clinical Turbo Spin Echo (TSE) scans by generating corresponding T ${\hspace{0.17em}}_2$ maps with the goal of removing scanner- and/or protocol-specific heterogeneity.

The T ${\hspace{0.17em}}_2$ map is estimated by minimizing an objective function containing a data fidelity term in a Virtual Conjugate Coils (VCC) framework, where the signal evolution model is expressed as a linear constraint. The objective function is minimized by Projected Gradient Descent (PGD).

The algorithm achieves accuracy comparable to methods with customized sampling schemes for accelerated T ${\hspace{0.17em}}_2$ mapping. The results are insensitive to the tunable parameters, and the relaxed background phase prior produces better T ${\hspace{0.17em}}_2$ maps compared to the strict real-value enforcement. It is worth noting that the algorithm works well with challenging T ${\hspace{0.17em}}_2$ w-TSE data using typical clinical parameters. The observed normalized root mean square error ranges from 6.8% to 12.3% over grey and white matter, a clinically common level of quantitative map error.

The novel methodological development creates an efficient algorithm that allows for T ${\hspace{0.17em}}_2$ map generated from TSE data with typical clinical parameters, such as high resolution, long echo train length, and low echo spacing. Reconstruction of T ${\hspace{0.17em}}_2$ maps from TSE data with typical clinical parameters has not been previously reported.