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ObjectivesThis study sought to establish an accurate and reproducible T2-mapping cardiac magnetic resonance (CMR) methodology at 3 T and to evaluate it in healthy volunteers and patients with myocardial infarct.BackgroundMyocardial edema affects the T2 relaxation time on CMR. Therefore, T2-mapping has been established to characterize edema at 1.5 T. A 3 T implementation designed for longitudinal studies and aimed at guiding and monitoring therapy remains to be implemented, thoroughly characterized, and evaluated in vivo.MethodsA free-breathing navigator-gated radial CMR pulse sequence with an adiabatic T2 preparation module and an empirical fitting equation for T2 quantification was optimized using numerical simulations and was validated at 3 T in a phantom study. Its reproducibility for myocardial T2 quantification was then ascertained in healthy volunteers and improved using an external reference phantom with known T2. In a small cohort of patients with established myocardial infarction, the local T2 value and extent of the edematous region were determined and compared with conventional T2-weighted CMR and x-ray coronary angiography, where available.ResultsThe numerical simulations and phantom study demonstrated that the empirical fitting equation is significantly more accurate for T2 quantification than that for the more conventional exponential decay. The volunteer study consistently demonstrated a reproducibility error as low as 2 ± 1% using the external reference phantom and an average myocardial T2 of 38.5 ± 4.5 ms. Intraobserver and interobserver variability in the volunteers were –0.04 ± 0.89 ms (p = 0.86) and –0.23 ± 0.91 ms (p = 0.87), respectively. In the infarction patients, the T2 in edema was 62.4 ± 9.2 ms and was consistent with the x-ray angiographic findings. Simultaneously, the extent of the edematous region by T2-mapping correlated well with that from the T2-weighted images (r = 0.91).ConclusionsThe new, well-characterized 3 T methodology enables robust and accurate cardiac T2-mapping at 3 T with high spatial resolution, while the addition of a reference phantom improves reproducibility. This technique may be well suited for longitudinal studies in patients with suspected or established heart disease.

Background In recent years, several successful variations of T2-prepared cardiac T2 mapping techniques have been described for the quantification of cardiac edema [1,2,3]. Radial imaging for high-resolution T2 mapping [3] has the advantage of reduced motion sensitivity, but suffers from a lower signal-to-noise ratio (SNR) due to the undersampling of the periphery of k-space and the density compensation function (DCF) that increases the weight of the relatively noisy and less densely sampled k-space periphery (Fig.1a). Since the contrast of an image is defined by the center of k-space, a KWIC (kspace weighted image contrast [4]) filter can be used to share only the periphery among radial images that have the same geometry and different contrast, such as those used to generate a T2 map (Fig.1b). Furthermore, when undersampling is used to acquire more images per T2 map (resulting in more k-space peripheries that can be shared), KWIC filtering further reduces the noise-like undersampling artifacts (Fig.1c). The goal of this study was therefore to test whether the use of the KWIC filter leads to a higher precision in radial T2 maps for a given acquisition time.

Background Recently, T2-weighted MRI for the characterization of edema after myocardial infarction has attracted considerable attention (Friedrich, NatRevCardiol2010). Furthermore, the recently proposed combination of bSSFP imaging and T2Prep for T2-mapping at 1.5T has enabled a rapid quantitative cardiac T2 estimation (Huang et al., MRM2007). However, the accuracy of this method may still be limited due to the complex T2/T1 signal weighting. Especially for longitudinal studies designed for monitoring and/or guiding therapy, accurate and reproducible T2 measurements will be critical. A novel quantitative 3T T2-mapping protocol was therefore developed and tested in both healthy volunteers and patients.

Background Cardiac T2 mapping using a variable T2 preparation module (T2Prep) has recently gained attention for its ability to quantify the extent of edema (Giri, JCMR 2009). Due to time constraints, the T2 maps are commonly acquired as one or several two-dimensional slices, while the underlying pathology has a three-dimensional (3D) structure. The next logical step would therefore be to exploit recent hardware and software advances to directly acquire 3D T2 maps. To this end, we tested the feasibility of using a self-navigated 3D radial acquisition with a variable T2Prep for 3D T2 mapping at 3T.

Background T2 mapping through variation of the T2 preparation (T2Prep) duration has been increasingly used to robustly detect and quantify cardiac edema (Giri et al., JCardiovMagnReson2009). However, if images with incremental T2Prep duration are acquired in a sequential fashion, irregular breathing patterns and heart rates may adversely affect the quality of the T2 maps due to misalignment of the source images. A logical alternative is then to acquire all images in an alternating manner (Figure 1ab), where the T2Prep duration changes cyclically from one heartbeat to the next. Combined with a radial signal readout, this may minimize the vulnerability to respiratory or RR variability. We therefore simulated, implemented and tested the utility of an alternating magnetization preparation approach to T2 mapping.