Reproducibility of slice-interleaved myocardial T₂ mapping sequences

Background

Myocardial T₂ mapping sequence allows quantitative assessment of myocardial edema and inflammation. Commonly, a series of T₂ weighted images with steady-state free-precession (SSFP) are acquired after T₂ magnetization preparation (T₂Prep) with different echo times. Conventionally, a single slice per breath-hold is acquired to image one single slice. Because inflammation/edema is often regional, multiple breath-holds are needed to cover the entire ventricle. The slice-interleaved T₂ mapping sequence was recently proposed to image multiple slices in a single scan by using a slice-selective T₂Prep. While accuracy of this sequence to quantify T₂ was previously studied, the measurement reproducibility is not known. Therefore, we sought to investigate the reproducibility of myocardial T₂ mapping using the slice-interleaved T₂ mapping sequence.

Methods

Eleven healthy subjects (age: 33 ± 16 years, 6 males) were imaged on 2 different days with the same scan protocol using a 1.5T MRI scanner (Philips Achieva). On each day, slice-interleaved T₂ sequence was repeated twice. Subsequently, subjects were removed from the scanner and repositioned, followed by another 2 repetitions of the same scan. The following imaging parameters were used: In-plane resolution = 2.1 × 2.1 mm², slice thickness = 8 mm, slice gap = 4 mm, Field of View = 320 × 320 mm², TR/TE/α = 2.8 msec. / 1.38 msec. /55°, SENSE-rate = 2.3, and acquisition window = 191 ms, bandwidth = 1879.7 Hz/pixel. Motion correction was performed between different images. T₂ maps were calculated using a 3-parameter fit model. The epicardial and endocardial contours in the left ventricle were manually drawn in 5 short axis-slices to calculate global and slice-based myocardial T₂ values. Coefficient of variation (CV) analysis for each slice was generated to assess the variability. Bland-Altman plots were used to test for significant differences between repetitions, sessions and days.

Results

Figure 1 shows mean T₂ values for different imaging sessions, averaged over all subjects and low CVs between subjects (7.2 ± 4.3%). There were low CVs between days (6.3 ± 4.0%) and between sessions (5.0 ± 4.3%). Fig. 2 shows Bland-Altman plots for T₂ values between first scan of day 1 and day 2 (A), between first scan of session 1 and session 2 (B), and between scan 1 and 2 within each first session (C).

Figure 1

Mean T2 estimates per repetition, session and day (A) and coefficients of variation for different slices and subjects for slice-interleaved T2 sequence (B).

Figure 2

Bland-Altman plots for comparison of global T2 for first scans per day (A), session (B) and repetition (C).

Conclusions

Slice-Interleaved T₂ mapping sequence yields reproducible T₂ measurements with highest CV of 7.2 ± 4.3% for between day scans.