Breath-held high-resolution cardiac T2 mapping with SKRATCH
Journal of Cardiovascular Magnetic Resonance volume 18, Article number: P27 (2016)
Several cardiac T2 mapping techniques with varying T2 preparation (T2Prep) times have been proposed for the quantification of cardiac edema [1–3]. Among these, radial T2 mapping, which is robust to motion artifacts, suffers from a low signal-to-noise ratio (SNR) caused by the undersampling of the k-space periphery and by its density compensation function (DCF) (Fig. 1a). However, since the contrast of an image is mainly determined by the center of its k-space, the T2-weighted images can share their k-space periphery using the KWIC (K-space Weighted Image Contrast) filter (Fig. 1b) to reduce undersampling artifacts . This allows for higher undersampling (Fig. 1c) and thus for a decrease in acquisition time .
We demonstrated that navigator-gated KWIC-filtered cardiac T2 mapping (Shared K-space RAdial T2 Characterization of the Heart, SKRATCH) enables a considerable decrease in acquisition time while maintaining the T2 precision . The goal of this study was to extend this approach to a short breath-held high-resolution T2 map acquisition and to compare its performance to navigator-gated T2 mapping.
The novel breath-held SKRATCH protocol consisted of a GRE sequence with a continuously increasing golden-angle radial acquisition. This ensured a unique k-space trajectory for all 64 lines of each of the 4 T2Prep durations (0/30/45/60 ms), pixel size of 1.2 × 1.2 × 8 mm3 and a total duration of 7 heartbeats. As reference, a navigator-gated radial cardiac T2 mapping GRE sequence was acquired with 3 T2Prep durations (0/30/60 ms), 308 lines/image and a pixel size of 1.25 × 1.25 × 5 mm3 . Images were acquired at 3T (Magnetom Prisma, Siemens Healthcare) in 17 healthy volunteers at the same midventricular short-axis orientation with both protocols. The T2 maps were segmented according to the AHA guidelines . The mean T2 value (μT2) and the relative standard deviation (σR = standard deviation/ μT2) of each segment as well as the myocardial area were calculated and tested for significant differences. The SKRATCH T2 map was acquired twice in 11 of the volunteers for Bland-Altman reproducibility analysis.
The SKRATCH T2 maps had average values of 39.9 ± 4.4 ms, while those of the reference T2 maps were 39.1 ± 3.1 ms (p = 0.04, Fig. 2a-c). σR increased from 8 ± 2% for the standard T2 maps to 11 ± 2% for the SKRATCH T2 maps (p < 0.001). The myocardial area decreased from 643 ± 155 to 585 ± 121 pixels for the SKRATCH T2 maps (a 10% decrease, p = 0.008). The repeatability analysis resulted in a confidence interval of ± 3.09 ms (Fig. 2d).
The SKRATCH T2 maps were highly similar to the reference high-resolution T2 maps, while the shortening to breath-hold duration came at the cost of an acceptably small increase in standard deviation and decrease in myocardial area. These encouraging results will need to be validated in future high-resolution studies in patients.
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Lugand, E., Yerly, J., Feliciano, H. et al. Breath-held high-resolution cardiac T2 mapping with SKRATCH. J Cardiovasc Magn Reson 18 (Suppl 1), P27 (2016). https://doi.org/10.1186/1532-429X-18-S1-P27