Neural networks with personalized training for improved MOLLI T₁ mapping

The aim of this study was to develop a method for personalized training of Deep Neural Networks by means of an MRI simulator to improve MOLLI native T₁ estimates relative to conventional fitting methods.

The proposed Personalized Training Neural Network (PTNN) for T₁ mapping was based on a neural network which was trained with simulated MOLLI signals generated for each individual scan, taking into account both the pulse sequence parameters and the heart rate triggers of the specific healthy volunteer. Experimental data from eleven phantoms and ten healthy volunteers were included in the study.

In phantom studies, agreement between T₁ reference values and those obtained with the PTNN yielded a statistically significant smaller bias than conventional fitting estimates (-26.69 ± 29.5ms vs. -65.0 ± 33.25ms, p < 0.001). For in vivo studies, T₁ estimates derived from the PTNN yielded higher T₁ values (1152.4 ± 25.8ms myocardium, 1640.7 ± 30.6ms blood) than conventional fitting (1050.8 ± 24.7ms myocardium, 1597.2 ± 39.9ms blood). For PTNN, shortening the acquisition time by eliminating the pause between inversion pulses yielded higher myocardial T₁ values (1162.2 ± 19.7ms with pause vs. 1127.1 ± 19.7ms, p = 0.01 myocardium), (1624.7 ± 33.9ms with pause vs. 1645.4 ± 18.7ms, p = 0.16 blood). For conventional fitting statistically significant differences were found.

Compared to T₁ maps derived by conventional fitting, PTNN is a post-processing method that yielded T₁ maps with higher values and better accuracy in phantoms for a physiological range of T₁ and T₂ values. In normal volunteers PTNN yielded higher T₁ values even with a shorter acquisition scheme of eight heartbeats scan time, without deploying new pulse sequences.