Water–fat Dixon cardiac magnetic resonance fingerprinting

Figure 1. Proposed Dixon‐cMRF framework. (A) A 3‐echo gradient echo golden radial acquisition is ECG‐triggered to acquire k‐space data at the mid‐diastolic cardiac phase for 15 heartbeats (i.e., ~15 s). Magnetization preparation includes inversion pulses every 5 heartbeats (with inversion delays of 10, 300, and 10 ms, respectively) and variable T2 preparation modules (no T2 preparation, no T2 preparation, 40, 80, and 160 ms repeated over 15 heartbeats). (B) The 3 echoes are reconstructed as separate time series from which a B0 map estimate and water–fat separated time series are obtained. (C) After a matching step, water‐ and fat‐specific T1, T2, and M0 maps and fat fraction can be extracted

Figure 2. Dixon‐cMRF T1/T2 phantom experiment. (A) Single echo cMRF (echo 1) and Dixon‐cMRF water‐specific T1 and T2 maps. (B) T1 and T2 values for all vials measured with water Dixon‐cMRF and single echo cMRF (echo 1) in comparison to reference spin echo values. For both single echo cMRF and water Dixon‐cMRF high determination coefficient (R2 ≥ 0.99) and low NRMSE (~5%) were obtained when compared with reference values

Figure 3. (A) Reference in‐house phantom values and map measured with proton density fat fraction (PDFF). (B) Dixon‐cMRF fat fraction (FF) measurement compared to the reference PDFF for all phantom vials. (C) T1 estimation using single echo cMRF (echo 1) and Dixon‐cMRF (water‐ and fat‐specific) in comparison to the reference water selective IRSE acquisition. (D) T2 estimation using single echo cMRF (echo 1) and Dixon‐cMRF (water‐ and fat‐specific) in comparison to the reference water‐selective T2 MESE measurement

Figure 4. Water–fat separated Dixon‐cMRF singular images for a representative healthy subject

Figure 5. Dixon‐cMRF in a representative healthy subject. (A) Good image quality and water–fat separation is seen on the whole FOV of the 1st singular images leading to good quality water and fat T1 and T2 maps. (B) Comparison of Dixon‐cMRF and single echo cMRF (echo 1) in a zoomed region around the heart. Myocardium wall recovery with Dixon‐cMRF in both T1 and T2 maps in regions with water–fat partial volume is indicated by the white arrows. Additional water‐ and fat‐specific M0 can be estimated with Dixon‐cMRF to obtain a fat fraction map

Figure 6. Comparison of water Dixon‐cMRF, single echo cMRF (echo 1), and conventional MOLLI, SASHA, and T2‐GRASE maps for a representative healthy subject

Figure 7. (A) Water and fat magnitude images and reference proton density fat fraction (PDFF) map obtained from a 6 echo Dixon GRE Cartesian scan. (B) Dixon‐cMRF water and fat M0 images as well as the resulting fat fraction (FF) estimate. The ROIs used for the analysis in Supporting Information Table S1 and Figure S9 are shown for this particular volunteer superimposed on the water M0 and fat M0 images. (C) Absolute difference image between the reference PDFF and Dixon‐cMRF FF maps

Figure 8. Top: T1, T2, and FF septum measurements in 10 healthy subjects for the different mapping techniques. Average across subjects ± SD (ms) are reported for each technique on the top of each plot. Bottom: spatial variability on the T1, T2, and FF septum measurements for the different mapping techniques. Average spatial variability (ms) of the measurements are reported for each technique on the top of each plot. Differences with statistical significance are identified by * (P < 0.025 for T1 and P < 0.05 for T2)

Figure 9. Regional T1 and T2 assessment of the different mapping techniques. T1 (top) and T2 (bottom) mean values and spatial variability reported for each segment as average measurements over 10 subjects. The value in the central segment represents the average over all segments. Average measurements/spatial variability for Dixon‐cMRF water T1 and T2 were 1032/55 ms and 42.1/5.5 ms, respectively. Overall Dixon‐cMRF presented lower spatial variability than MOLLI and SASHA measurements but higher than T2‐GRASE measurements

Figure 10. (A) Single echo (echo 1) cMRF T1, Dixon‐cMRF water T1 and water–fat partial volume mask (with FF ϵ [0.3; 0.7]). The mask was used to obtain the T1 and T2 values of single echo cMRF for echoes 1, 2, 3, and Dixon‐cMRF water and fat maps that are shown in (B) as point clouds (top) and ellipses (bottom). The ellipse is centered on the mean and the horizontal and vertical radius represent the SD over T1 and T2 measurements, respectively. (C) Same plots in (B) using the values obtained from all the subjects included in the study. The 2 compartments of water and fat are clearly separated in (B) and (C). Mean T1 and T2 measurements in the masked pixels for water are 1174 ms and 60.9 ms, respectively, whereas mean values for single echo cMRF for each of the 3 echoes are: echo 1 T1/T2 = 537/80.1 ms, echo 2 T1/T2 = 549/89.3 ms, and echo 3 T1/T2 = 541/90.6 ms