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Motion correction for free breathing quantitative myocardial t2 mapping: impact on reproducibility and spatial variability

Background

Quantitative myocardial T2 mapping is a promising technique for in-vivo assessment of inflammation and edema [1]. Free breathing T2 mapping sequences increase the flexibility in the choice of the number of T2prep echoes times (TET2P), but should be combined with respiratory motion correction technique [2]. In this study, we sought to evaluate the performance of the Adaptive Registration of varying Contrast-weighted images for improved TIssue Characterization (ARCTIC) algorithm [3] for in-plane motion correction in T2 mapping data and its impact on in-vivo reproducibility and spatial variability of myocardial T2 estimates.

Methods

Seven healthy adult subjects (30±17y, 3male) were imaged using a 1.5 T Phillips scanner. T2 mapping was performed using either 1) a "T2P4TE" sequence (4 T2prep echo times=[0, 25, 50, ∞]), or 2) a "T2P20TE" sequence (20 T2prep echo times=[0, 25, 30, 35, …, 95, 100, ∞, ∞, ∞]) [4]. TET2P=∞ was simulated by acquiring an image immediately after a saturation pulse [4]. Each subject was imaged using eight T2 mapping scans in the following order: 1) breath-held T2P4TE (BH), 2) free breathing T2P4TE without respiratory navigator (FB), 3) free breathing T2P4TE with respiratory navigator (FB+NAV), and 4) free breathing T2P20TE with respiratory navigator (5 repetitions). The same 2D short axis slice was acquired with all scans using single-shot ECG-triggered acquisitions with balanced SSFP imaging readout (TR/TE/α=2.7ms/1.35ms/85°, FOV=240×240mm2, resolution=2.5×2.5×8mm3, 10 linear ramp-up pulses, SENSE rate=2, 51 phase encoding lines, linear ordering). Accuracy of in-plane motion correction was evaluated in the first three scans by measurements of the DICE similarity coefficients (DSC) (1: ideal registration, 0: none) and the myocardial boundary error (MBE) with and without using ARCTIC. T2 mapping reproducibility and spatial variability with and without using ARCTIC was evaluated over the entire myocardium using the 5 repetitions of the T2P20TE sequence and 1) a subset of 4 T2prep echo times=[0ms, 25ms, 50ms, ∞] (referred to as 4TE ) and 2) all 20 T2prep echo times (referred to as 20TE).

Results

ARCTIC increased DSC in BH data (0.90±0.02 vs. 0.87±0.05, p=0.09), FB data (0.91±0.02 vs. 0.79±0.15, p=0.009), and FB+NAV data (0.90±0.02 vs. 0.86±0.08, p=0.039), and reduced MBE in BH data (0.63±0.09 vs. 0.74±0.12, p=0.049), FB data (0.60±0.12 vs. 1.16±0.71, p=0.007), and FB+NAV data (0.61±0.13 vs. 0.83±0.28, p=0.025). ARCTIC improved the reproducibility (4TE: 5.0±2.3ms vs. 5.9±3.1ms, p=0.011; 20TE: 2.4±1.0ms vs. 4.3±3.9ms, p=0.002) and reduced spatial variability (4TE: 11.1±3.6ms vs. 13.7±4.3ms, p<0.001; 20TE: 7.9±1.8ms vs. 10.6±5.3ms, p=0.001) of in-vivo T2 mapping.

Conclusions

The ARCTIC technique substantially reduces spatial mis-alignment among T2-weighted images and improves both the reproducibility and the spatial variability of in-vivo T2 mapping.

Figure 1
figure1

T2 scans from one subject acquired using the T2P4TE sequence under breath-hold (BH), free breathing (FB), and free breathing with respiratory navigator gating (FB+NAV). Data are shown without (uncorrected) and with (motion corrected) in-plane motion correction. The endocardial contour of the left ventricular (LV) myocardium, drawn on the reference image (1st image) of each scan, is reported in all subsequent T2-weighted images to facilitate visual motion assessment. Misalignments observed among uncorrected images (white arrows) were substantially reduced after in-plane motion correction using ARCTIC. Furthermore, artifacts in uncorrected T2 maps (white arrows) were reduced in motion corrected T2 maps.

Figure 2
figure2

Example of multiple T2 maps acquired on the same subject using the five repetitions of the T2P20TE sequence acquired under free breathing conditions with respiratory navigator gating. T2 maps were reconstructed with all T2prep echo times (20 TEs) or only a subset of the T2prep echo times (0ms, 25ms, 50ms, ∞) (4 TEs). While the remaining in-plane motion generates artifacts on the directly reconstructed T2 maps (uncorrected), substantial improvement of T2 map quality was obtained using in-plane motion correction (motion corrected). As expected, the homogeneity of the T2 maps greatly improved when using all 20 T2prep echo times compared to only 4 T2prep echo times.

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Correspondence to Sébastien Roujol.

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Roujol, S., Basha, T.A., Weingartner, S. et al. Motion correction for free breathing quantitative myocardial t2 mapping: impact on reproducibility and spatial variability. J Cardiovasc Magn Reson 17, W5 (2015). https://doi.org/10.1186/1532-429X-17-S1-W5

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Keywords

  • Free Breathing
  • Dice Similarity Coefficient
  • Respiratory Navigator
  • Balance SSFP
  • Respiratory Motion Correction