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Ultrashort-T2* mapping at 7 tesla using an optimized pointwise encoding time reduction with radial acquisition
Carly A Lockard1,2, Bruce M Damon1,2,3,4,5,6,7, Hacene Serrai1,2,7
1Stephens Family Clinical Research Institute, Carle Health, Urbana, Illinois, United States of America.
Plos One
|April 17, 2025
Summary
Pointwise Encoding Time Reduction with Radial Acquisition (PETRA) is effective for ultrashort T2* mapping at 7 Tesla. This zero echo time sequence provides high signal-to-noise ratio and good repeatability for musculoskeletal imaging.
Area of Science:
- Medical Imaging
- Magnetic Resonance Imaging
- Biophysics
Background:
- Zero echo time (ZTE) sequences are crucial for imaging tissues with ultrashort T2* relaxation times.
- Pointwise Encoding Time Reduction with Radial Acquisition (PETRA) is a ZTE sequence with potential for musculoskeletal imaging.
- Limited evaluation of PETRA at 7 Tesla (T) exists.
Purpose of the Study:
- To evaluate the performance of the PETRA sequence at 7T for ultrashort T2* mapping.
- To assess image quality, signal-to-noise ratio (SNR), and repeatability of PETRA at 7T.
- To investigate sequence modifications for extended echo times to enable ultrashort T2* mapping.
Main Methods:
- PETRA imaging was performed on MnCl2 and collagen phantoms, and on human knees at 7T.
- Standard and modified PETRA sequences were used with a 1-transmit/28-receive-channel knee coil.
- Image artifacts, signal, SNR, ultrashort T2* values, curve fit quality, and repeatability were analyzed.
Main Results:
- PETRA at 7T demonstrated higher SNR in knee tissues compared to conventional-TE sequences (68-337 vs. 16-30).
- Ultrashort T2* mapping was feasible at 1.50 mm isotropic resolution with echo times ≤ 0.58 msec.
- Strong linear correlations were found between R2* and MnCl2 concentration, and signal and collagen concentration.
- High curve fit R2 and repeatability were observed for ultrashort T2* < 1 msec in phantoms and knees.
- PETRA achieved high resolution (0.34 mm isotropic) at TE = 0.07 msec and lower resolution (1.52 mm isotropic) at TE ≤ 0.58 msec with scan times < 11 minutes.
Conclusions:
- PETRA is a viable ZTE sequence for high-resolution, high-SNR musculoskeletal imaging at 7T.
- The sequence enables quantitative ultrashort T2* mapping with acceptable curve-fitting results for sub-millisecond T2* components.
- PETRA offers a promising tool for characterizing musculoskeletal tissues with ultrashort T2* properties at ultra-high field strengths.
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