Table 1.
Comparison of water T1, water T2, and FF values for different scans in a phantom
| Water T1 (ms) | ||||
|---|---|---|---|---|
| Interleaved fully sampled MRF | Interleaved undersampled MRF | Noninterleaved undersampled MRF | Fat‐suppressed IR | |
| Vial 1 | 278 ± 15 | 289 ± 20 | 287 ± 21 | 292 ± 5.4 |
| Vial 2 | 288 ± 11 | 288 ± 16 | 291 ± 22 | 305 ± 8.3 |
| Vial 3 | 318 ± 17 | 325 ± 30 | 333 ± 28 | 309 ± 11 |
| Vial 4 | 315 ± 22 | 319 ± 30 | 321 ± 31 | 316 ± 16 |
| Vial 5 | – | – | – | – |
| Water T2 (ms) | ||||
|---|---|---|---|---|
| Interleaved fully sampled MRF | Interleaved undersampled MRF | Noninterleaved undersampled MRF | MSE with tri‐exponential fit | |
| Vial 1 | 83 ± 6.9 | 86 ± 8.3 | 80 ± 6.0 | 66 ± 4.1 |
| Vial 2 | 77 ± 11 | 75 ± 11 | 79 ± 13 | 62 ± 6.9 |
| Vial 3 | 86 ± 10 | 86 ± 14 | 91 ± 15 | 67 ± 6.2 |
| Vial 4 | 79 ± 10 | 78 ± 12 | 77 ± 12 | 68 ± 7.7 |
| Vial 5 | – | – | – | – |
| FF (%) | ||||
|---|---|---|---|---|
| Interleaved fully sampled MRF | Interleaved undersampled MRF | Noninterleaved undersampled MRF | DIXON | |
| Vial 1 | 3.3 ± 1.4 | 3.5 ± 1.3 | 2.9 ± 1.4 | 5.7 ± 1.1 |
| Vial 2 | 22 ± 2.2 | 22 ± 2.4 | 20 ± 1.6 | 24 ± 1.1 |
| Vial 3 | 27 ± 2.8 | 27 ± 2.9 | 28.0 ± 2.0 | 32 ± 3.9 |
| Vial 4 | 38 ± 2.0 | 38 ± 1.8 | 39 ± 1.7 | 46 ± 1.3 |
| Vial 5 | 96 ± 1.8 | 95 ± 2.0 | 95 ± 2.1 | 98 ± 0.5 |
The phantom consists of 5 vials, each containing a different FF: 0%, 20%, 30%, 40%, and 100%. The MRF scans include an interleaved fully sampled, an interleaved undersampled (R = 20), and a noninterleaved undersampled (R = 20) experiment. Parameter values are reported as mean over an ROI in each tube ± SDs. The water T1, water T2, and FF values for an interleaved fully sampled experiment are close to that of the interleaeved undersampled experiment: 2‐sided paired t‐tests show no significant difference for the T1 (P = .1), T2 (P = 1), and FF (P = .5) values. This shows the robustness of the water–fat‐resolved MRF approach to undersampling. Comparison with the noninterleaved undersampled experiment shows that interleaving 2 flip angle trains introduces only minor differences: 2‐sided paired t‐tests show no significant difference for the T1 (P = .3), T2 (P = .9), and FF (P = .8) values. The T1 values obtained with standard measurements (fat‐suppressed IR for T1) show no significant difference compared with those obtained with MRF (P = 1.0), but T2 (P = 7.5·10−3) and FF (2.2·10−2) values are significantly different between MRF and standard measurements (MSE with a tri‐exponential fit for T2, DIXON for FF). There is a statistically significant increase in T1 value with increasing FF (P < 1−2), which is observed both with MRF and inversion recovery. The dependence of T1 on FF was previously reported in Hu and Nayak,58 and was attributed to a changing molecular lattice with changing FF, which leads to variations in the lattice tumbling rate and hence in T1 . Standard deviations for the fat T1 and T2 values (not reported) are slightly larger, but overall the performance is similar to that of the water component. Water T1 and water T2 values are not reported for vial 5, because this vial contained only fat. The measured FFs correspond well with the expected fat content in the different vials (0%, 20%, 30%, 40%, and 100%).
Abbrevation: IR, inversion recovery.