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Design of an adiabatic T2-preparation method optimized for cardiac motion and flow insensitivity at 3T
Journal of Cardiovascular Magnetic Resonance volume 13, Article number: P2 (2011)
To develop a T2-prep method for cardiac imaging at 3T which is less sensitive toward B1 inhomogeneity, flow and motion than previously described techniques.
T2 contrast is important for the assessment of acute myocardial edema and coronary morphology. At 1.5T, the standard T2-prep method uses 4 composite 180° pulses (MLEV4) providing robust and uniform T2-preparation, but at 3T, increased B1 inhomogeneity causes artifacts. Decreasing inter-pulse spacing improves refocusing in the presence of motion and flow. We developed a configurable T2-preparation allowing up to 4 adiabatic refocusing pulses (B1-insensitive) to study the effect of inter-pulse spacing on motion-robustness. We compared image homogeneity using MLEV4 as reference.
The modules employed 800 µs rectangular tip-down /flip-back pulses and a series of adiabatic refocusing pulses (BIREF-1). With these modules, we acquired mid-ventricular short axis cardiac images in healthy volunteers at 3T (MAGNETOM Verio, Siemens) using an ECG-gated, TurboFLASH sequence and different T2-prep times ranging from ≤35 ms to 120 ms, in systole and diastole. Four modules were used: A1 (1xBIREF-1), A2 (2xBIREF-1), A4 (4xBIREF-1), and MLEV 4. Separate contours were drawn for myocardium and cavity using ImageJ (NIH). The coefficient of variation was used as a measure of inhomogeneity. Readers (n=3) blinded to the T2-preparation scored images on a four-point scale for myocardial/cavity inhomogeneity and endocardial border definition. Statistical comparisons were made by ANOVA with Bonferroni correction.
The effect of the number of pulses and inter-pulse delay is demonstrated in figure 1a and 1b. Signal and homogeneity of myocardium and cavity increased with the number of pulses. The inhomogeneity of the cavity in diastole as measure of flow sensitivity (T2-prep time 40 ms) decreased with increasing pulse number (A1 = 0.3, A2 = 0.12, A4 = 0.11 and MLEV4 = 0.13). A comparison of A4 with MLEV4 (figure 1c) highlights the improvement due to adiabatic pulses. MLEV4 and A4 have similar inter-pulse spacing, yet across all T2-prep times, A4 performed better. From the visual scores, A4 scored higher and was ranked first among all sequences.
We developed a B1, motion and flow insensitive T2-prep method using adiabatic pulses. Using BIREF-1 refocusing pulses allows shorter inter-pulse spacing without exceeding SAR limitations, and improves homogeneity over the MLEV4 composite pulses.
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Jenista, E., Rehwald, W., Klem, I. et al. Design of an adiabatic T2-preparation method optimized for cardiac motion and flow insensitivity at 3T. J Cardiovasc Magn Reson 13, P2 (2011). https://doi.org/10.1186/1532-429X-13-S1-P2
- Myocardial Edema
- Flow Sensitivity
- Composite Pulse
- Adiabatic Pulse
- Border Definition