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Highly accelerated real-time T2-weighted imaging with through-time radial GRAPPA and low-latency GPU reconstruction


T2-weighted cardiac images are commonly used for edema detection [14]. However, neither black-blood TSE nor cine images can offer real-time edema monitoring, and are therefore not suitable for the guidance of cardiac ablation procedures. We proposed a radial T2-weighted interrupted balanced SSFP (rT2W-iSSFP), a real-time high temporal resolution sequence targeted at monitoring edema.



rT2W-iSSFP generates T2-weighting with a series of 180° RF pulses. TE-effective for the radial sequence is defined as the time from the beginning of the train to the median imaging echo. rT2W-iSSFP also incorporates through-time radial GRAPPA to achieve high temporal resolution with high degrees of acceleration (R = 8) [5], (Figure 1) which was implemented on a 48-core hybrid system with a GPU (Tesla C1060, NVIDIA), achieving 10-20 fps image acquisition with 20 ms latency reconstruction and image display [6].

Figure 1
figure 1

Illustration of the acquisition scheme, flip angles and k-space sampling pattern of rT 2 W-iSSFP. Four-fold acceleration is shown in this example. Images were reconstructed using through-time radial GRAPPA with a low-latency implementation. Typically a 192 × 192 matrix and an acceleration rate of R = 8 is used.


Bloch equation simulations were performed to evaluate the T2-weighting and the image quality of rT2W-iSSFP using a variant of the Shepp-Logan phantom containing 3 ellipsoids with different T1s and T2s to represent cerebrospinal fluid (CSF), liver, and myocardium (Figure 2a) [7, 8]. T2-weighted turbo spin echo (T2W-TSE) was also simulated [3, 9]. TE-effective was 60 ms for both T2W-TSE and rT2W-iSSFP.

Figure 2
figure 2

(a) Illustration of the Shepp-Logan phantom used for simulation. (b) T2W-TSE and (c) r T2W-iSSFP were simulated. Swine with acute injury was scanned by (d) breath-hold T2W-TSE and (e) free-breathing r T2W-iSSFP as well. The edema (the arrows in d) is depicted in both d and e. In both simulation and in-vivo imaging, T2W-TSE was used as the reference of T2-weighting. Tacq - acquisition time.

Animal Model

Swine with acute injury (N = 2) were imaged on a 1.5T scanner (Avanto, Siemens, Germany). Free-breathing ECG-triggered single-shot rT2W-iSSFP was acquired (TE-effective = 80 ms; TR = 3 ms; matrix = 192 × 192; 3 slices per heartbeats). ECG-triggered, breath-held T2W-TSE (TE = 80 ms, resolution = 1 × 1 mm2, matrix = 192 × 192) was used as a reference.


The results from simulation of T2W-TSE and rT2W-iSSFP are shown in Figures 2b and 2c. The intensity difference between CSF and liver is similar in T2W-TSE and rT2W-iSSFP. Streaking artifacts are seen in Figure 2c, but these are not pronounced in in vivo images. Four-chamber views of swine heart from T2W-TSE (breath-hold) and rT2W-iSSFP (free-breathing) are shown in Figures 2d and 2e. Edema at the anteroseptal region due to acute myocardial infarction is depicted (the arrows in d).


rT2W-iSSFP offers high temporal resolution T2-weighted imaging with image quality sufficient for visualization of edema from acute injury. rT2W-iSSFP can be applied to real-time monitoring of edema formation during cardiac interventions.


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Xu, D., Han, S., Saybasili, H. et al. Highly accelerated real-time T2-weighted imaging with through-time radial GRAPPA and low-latency GPU reconstruction. J Cardiovasc Magn Reson 16 (Suppl 1), W33 (2014).

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