Purpose This study aimed to develop a new 3D dual‐echo rosette k‐space trajectory, specifically designed for UTE MRI applications. The imaging of the ultra‐short transverse relaxation time (uT2) of brain was acquired to test the performance of the proposed UTE sequence. Theory and Methods The rosette trajectory was developed based on rotations of a “petal‐like” pattern in the kx–ky plane, with oscillated extensions in the kz‐direction for 3D coverage. Five healthy volunteers underwent 10 dual‐echo 3D rosette UTE scans with various TEs. Dual‐exponential complex model fitting was performed on the magnitude data to separate uT2 signals, with the output of uT2 fraction, uT2 value, and long‐T2 value. Results The 3D rosette dual‐echo UTE sequence showed better performance than a 3D radial UTE acquisition. More significant signal intensity decay in white matter than gray matter was observed along with the TEs. The white matter regions had higher uT2 fraction values than gray matter (10.9% ± 1.9% vs. 5.7% ± 2.4%). The uT2 value was approximately 0.10 ms in white matter . Conclusion The higher uT2 fraction value in white matter compared to gray matter demonstrated the ability of the proposed sequence to capture rapidly decaying signals.

Background: The iron concentration increases during normal brain development and is identified as a risk factor for many neurodegenerative diseases, it is vital to monitor iron content in the brain non-invasively. Purpose: This study aimed to quantify in vivo brain iron concentration with a 3D rosette-based ultra-short echo time (UTE) magnetic resonance imaging (MRI) sequence. Methods: A cylindrical phantom containing nine vials of different iron concentrations (iron (II) chloride) from 0.5 millimoles to 50 millimoles and six healthy subjects were scanned using 3D high-resolution (0.94x0.94x0.94 mm3) rosette UTE sequence at an echo time (TE) of 20 us. Results: Iron-related hyperintense signals (i.e., positive contrast) were detected based on the phantom scan, and were used to establish an association between iron concentration and signal intensity. The signal intensities from in vivo scans were then converted to iron concentrations based on the association. The deep brain structures, such as the substantia nigra, putamen, and globus pallidus, were highlighted after the conversion, which indicated potential iron accumulations. Conclusion: This study suggested that T1-weighted signal intensity could be used for brain iron mapping.

Purpose: This study aimed to develop a new 3D dual-echo rosette k-space trajectory, specifically for applications of ultra-short echo time (UTE) magnetic resonance imaging (MRI). The direct imaging of the myelin bilayer, which has ultra-short transverse relaxation time (uT2), was acquired to test the performance of the proposed UTE sequence. Theory and Methods: The rosette trajectory was developed based on rotations of a "petal-like" pattern in the kx-ky plane, with oscillated extensions in kz-direction for 3D coverage. Five healthy volunteers were recruited and underwent ten dual-echo rosette UTE scans with varied echo times (TEs). Dual-exponential model fitting was performed to separate uT2 signals, with the output of uT2 fraction, uT2 value and long T2 value. Results: The reconstructed images' signal contrast between white matter (WM) and grey matter (GM) increased with longer TEs. The WM regions had higher uT2 fraction values than GM (10.9% ± 1.9% vs. 5.7% ± 2.4%). The uT2 value was about 0.12 milliseconds in WM. Conclusion: The higher uT2 fraction value in WM compared to GM demonstrated the ability of the proposed sequence to capture rapidly decaying signals.

This study aimed to develop a new 3D dual-echo rosette k-space trajectory, specifically for applications of ultra-short echo time (UTE) magnetic resonance imaging (MRI). The direct imaging of the myelin bilayer, which has ultra-short transverse relaxation time (uT2), was acquired to test the performance of the proposed UTE sequence. The rosette trajectory was developed based on rotations of a ‘petal-like’ pattern in the kx-ky plane, with oscillated extensions in kz-direction for 3D coverage. The higher uT2 fraction value in white matter (WM) compared to grey matter (GM) demonstrated the ability of the proposed sequence to capture rapidly decaying signals.

We developed a method of acquiring high-resolution MRI for the generation of Quantitative Susceptibility Mapping (QSM) using Ultra-short echo time (UTE) MRI with a novel 3D rosette k-space trajectory. This method was used to generate high-resolution (0.94 mm3 isotropic) magnetic susceptibility maps in an Iron-Chloride phantom and the human brain. Generated maps were then compared with the susceptibility maps reconstructed from low-resolution data acquired using multi-echo UTE acquisition. Susceptibility values were comparable with current literature demonstrating the promise of this novel method in the generation of QSM.