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Non-triggered, Non-Contrast-Enhanced Lower Extremity MR Angiography using Artery-Weighted REACT
Hiroshi Hamano1, Masami Yoneyama1, Yasutomo Katsumata2, Ryuji Baba3, and Kenji Iinuma1

1Philips Japan, Tokyo, Japan, 2Philips Healthcare, Tokyo, Japan, 3Sasebo Chuo Hospital, Nagasaki, Japan

Synopsis

Non-contrast enhanced lower extremity MR angiography, such as TOF, PC and TRANCE, is commonly used to diagnose peripheral arterial disease, but these techniques are occasionally unstable due to presence of arrhythmia, atrial fibrillation or tachycardia. Relaxation-Enhanced MR Angiography without Contrast and Triggering (REACT) derives high intravascular signal from T2prep pulse followed by STIR pulse and dual-echo gradient echo DIXON readout. However conventional REACT cannot distinguish arterial and venous signals clearly. We validate optimum T2prep time and TFE factor to improve the contrast between artery and vein. We demonstrate that REACT-Art provided more artery-dominant contrast compared to conventional REACT.

Introduction

Non-contrast-enhanced lower extremity MR angiography techniques, such as gated-TOF, PC and TRANCE, are commonly used to diagnose peripheral arterial disease. (PAD) These techniques certainly require ECG-triggering or gating, they are occasionally unstable and challenging due to presence of arrhythmia, atrial fibrillation or tachycardia. Alternatively, Relaxation-Enhanced MR Angiography without Contrast and Triggering (REACT) derives high intravascular signal from T2 preparation pulse (T2prep) followed by STIR pulse and dual-echo gradient echo DIXON readout. A combination of T2prep, STIR pulses and DIXON emphasizes arterial and venous signal while effectively suppressing signal from surrounding tissues including muscle and fat1-3. One of the challenge of conventional REACT is to distinguish arterial and venous signals clearly. Contamination of venous signals might interfere accurate diagnosis of PAD. The aim of this study is to improve the contrast between artery and vein in REACT technique for enabling robust and easy lower extremity MRA without ECG triggering/gating.

Methods

REACT sequence (Fig.1); REACT utilizes two pre-pulses and mDIXON, to exploit the long T1 and T2 times of unenhanced blood and suppress background signals. A longer T2prep-time basically suppresses venous signal because venous blood has shorter T2 value than arterial blood4-5. Additionally, reducing turbo factor (increase of the actual number of T2prep-times during total acquisition time) can increase the effect of T2prep pulse. Hence, we focused on the T2prep-time and TFE factor and mainly optimized these two parameters to improve the contrast between arteries and veins.

Subjects: Conventional REACT and REACT-Art, 2D gated TOF in five healthy volunteers were examined on 3.0T MR scanner (Ingenia, Philips Healthcare) after obtained informed consent and approved by institutional review board.

Evaluation: To compare the image quality of conventional REACT, REACT-Art and 2D gated TOF, coronal maximum intensity projection (MIP) images were evaluated. Circular region-of interests (ROIs) were placed on popliteal artery (PopA), popliteal vein (PopV) and background muscle. We evaluated contrast noise ratio (CNR) between signal intensity of PopA (SI PopA) and signal intensity of PopV (SI PopV) comparison of conventional REACT and REACT-Art. CNR was calculated as CNR = (SI PopA – SI PopV) / SD muscle. Here SI PopA and SI PopV is the respective mean signal intensity in the ROIs, and SD muscle is the standard deviation in the muscle ROI. Sequence parameters we used in this study are summarized in Table 1.

Results

Fig. 2 shows the comparison of calculated CNRs among conventional REACT and REACT-Art with different T2prep-times. The CNR of REACT-Art with using lower TFE factor was higher than that of conventional REACT, and the CNR of REACT-Art with T2prep-time 90ms was the highest in all sequences. Therefore, T2prep-time 90ms is the optimal value for emphasizing artery-dominant contrast. Representative lower extremity MRA images using three sequences are shown in Fig. 3. REACT-Art images with T2prep-time 90ms showed similar contrast to 2D gated TOF.

Conclusion

We have demonstrated that REACT-Art provided more artery-dominant contrast similar to ECG-based MRA, compared to conventional REACT in the lower extremity without use of contrast-enhancement and ECG-triggering.

Acknowledgements

No acknowledgement found.

References

1 Bardo DME. et al. Magnetic resonance imaging of the pediatric mediastinum. Pediatric Radiology. 2018; 48: 1209-1222.

2 Yoneyama M et al. In:Proc 24th Annual Meeting of ISMRM, Singapore 2016;2252.

3 Toyonari N et al. In:Proc 24th Annual Meeting of ISMRM, Singapore 2016;2684.

4 Brittain JH et al. Coronary Angiography with Magnetization-Prepared T2 Contrast. MRM. 1995; 33: 689-696.

5 Shea SM et al. Three-Dimensional True-FISP Imaging of the Coronary Arteries: Improved Contrast with T2-Preparation. JMRI. 2002; 15: 597–602.

Figures

Fig.1. REACT sequence. REACT utilizes two pre-pulses and mDIXON, to exploit the long T1 and T2 times of unenhanced blood and suppress background signals.

Table.1. Sequence parameters of Conventional REACT and REACT-Art.

Fig.2. Comparison of calculated CNRs among conventional REACT and REACT-Art with different T2prep-times. The CNR of REACT-Art with T2prep-time 90ms was the highest in all sequences.

Fig.3. Representative lower-leg MRA images using conventional REACT, REACT-Art and 2D gated TOF. REACT-Art provided more artery-dominant contrast similar to 2D gated TOF compared to conventional REACT.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)
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