Imaging sequence for joint myocardial T₁ mapping and fat/water separation

To develop and evaluate an imaging sequence to simultaneously quantify the epicardial fat volume and myocardial T₁ relaxation time.

We introduced a novel simultaneous myocardial T₁ mapping and fat/water separation sequence (joint T₁ -fat/water separation). Dixon reconstruction is performed on a dual-echo data set to generate water/fat images. T₁ maps are computed using the water images, whereas the epicardial fat volume is calculated from the fat images. A phantom experiment using vials with different T₁ /T₂ values and a bottle of oil was performed. Additional phantom experiment using vials of mixed fat/water was performed to show the potential of this sequence to mitigate the effect of intravoxel fat on estimated T₁ maps. In vivo evaluation was performed in 17 subjects. Epicardial fat volume, native myocardial T₁ measurements and precision were compared among slice-interleaved T₁ mapping, Dixon, and the proposed sequence.

In the first phantom, the proposed sequence separated oil from water vials and there were no differences in T₁ of the fat-free vials (P = .1). In the second phantom, the T₁ error decreased from 22%, 36%, 57%, and 73% to 8%, 9%, 16%, and 26%, respectively. In vivo there was no difference between myocardial T₁ values (1067 ± 17 ms versus 1077 ± 24 ms, P = .6). The epicardial fat volume was similar for both sequences (54.3 ± 33 cm³ versus 52.4 ± 32 cm³ , P = .8).

The proposed sequence provides simultaneous quantification of native myocardial T₁ and epicardial fat volume. This will eliminate the need for an additional sequence in the cardiac imaging protocol if both measurements are clinically indicated.