Compressed-Sensing MP2RAGE sequence: Application to the detection of brain metastases in mice at 7T

Abstract

Purpose: To develop a Compressed Sensing (CS)-MP2RAGE sequence to drastically shorten acquisition duration and then detect and measure the T₁ of brain metastases in mice at 7 T.

Methods: The encoding trajectory of the standard Cartesian MP2RAGE sequence has been modified (1) to obtain a variable density Poisson disk under-sampling distribution along the k_y -k_z plane, and (2) to sample the central part of the k-space exactly at TI₁ and TI₂ inversion times. In a prospective study, the accuracy of the T₁ measurements was evaluated on phantoms containing increasing concentrations of gadolinium. The CS acceleration factors were increased to evaluate their influence on the contrast and T₁ measurements of brain metastases in vivo. Finally, the 3D T₁ maps were acquired with at 4-fold increased spatial resolution. The volumes and T₁ values of the metastases were measured while using CS to reduce scan time.

Results: The implementation of the CS-encoding trajectory did not affect the T₁ measurements in vitro. Accelerating the acquisition by a factor of 2 did not alter the contrast or the T₁ values of the brain metastases. 3D T₁ maps could be obtained in < 1 min using a CS factor of 6. Increasing the spatial resolution enabled more accurately measurement of the metastasis volumes while maintaining an acquisition duration below 5 min.

Conclusion: The CS-MP2RAGE sequence could be of great interest in oncology to either rapidly obtain mouse brain 3D T₁ maps or to increase the spatial resolution with no penalty on the scan duration.

Keywords: 7T; MP2RAGE; compressed sensing; metastases; mouse brain.