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Non-Contrast Enhanced MR Angiography for Selective Pulmonary Artery and Aorta imaging at 1.5T
Yajing Zhang1, Qian Jiang1, and Jiazheng Wang2

1Philips Healthcare, Suzhou, China, 2Philips Healthcare Greater China, Beijing, China

Synopsis

Non-contrast enhanced pulmonary MRA has been increasingly used for the diagnosis of abnormality of vessels such as pulmonary arteriovenous malformation (PAVM). This study aims to validate the vessel-selective MRA using time-spatial labeling inversion pulse. The pulmonary vessel or aorta could be intendedly selected with a high intensity against the surrounding anatomies. The contrast between vessels were evaluated using an ROI approach.

Introduction

The imaging of pulmonary vessels are important for diagnosis of vessel abnormalities such as the pulmonary arteriovenous malformation (PAVM) or pulmonary embolism. Although CE-MRA or (CT Angiography) CTA have been considered the gold standard in clinical pulmonary angioraphy [1], its use is limited on patients with allergies to the contrast agent and radiation damage. Non-CE MRA has been increasingly developed by employing a time-spatial labeling inversion pulse (T-SLIP) [2] to obtain a bright blood contrast in vessels and a selective suppressed pulse for labeling the blood of the selected vessels. This study validated the vessel-selective MRA on pulmonary vessel imaging.

Method

The Thoracic-MRA was performed on an Ingenia Prodiva 1.5 Tesla MRI system (Philips Healthcare, the Netherlands). A cohort of eight volunteers with informed consent were included in this study. The MRA coronal image was acquired by a 3D TSE sequence with refocusing controlled TSE factor of 66, TE/TR=139/808ms; 1.65×1.65 mm2 in-plane resolution, FOV = 320x380x120mm3, slice thickness=3mm. The fat suppression was achieved through inversion relaxation with TI=160ms. Trigger delay was set to 1400ms and combined respiratory- and electrocardiography (ECG)-trigger were used during the scan.

For a pulmonary artery selected (PA-selected) scan, a non-selective inversion pulse was applied to invert the tissue signal of whole chest, then a narrow free labeling slab was set to cover the precava, postcava, right ventricle (RV) of the heart and the partial pulmonary artery (PA), which could recover the signal of corresponding region, TE/TR = 139/2500ms. Other imaging parameters were the same as abovementioned. Similarly, the aorta selected (AO-selected) image was acquired using the same imaging protocol, but with labelling slab set to cover the left ventricle (LV) and aorta (AO) instead.

To quantitatively evaluate the performance of the selected vessel imaging, two regions of interest (ROIs) were delineated on the region of Pulmonary Artery (PA) and Aorta (AO) respectively for the images of thoracic MRA, PA-selected and Aorta-selected images for each volunteer data. The images were histogram-matched and the mean and standard deviation of the ROI intensities were measured. MIP reconstruction was performed to visualize the three images as shown in Figure 1.

Results

The MIP reconstruction of thoracic MRA, the PA-selected MRA and the AO-selected MRA were shown in Figure 1. In Fig.1B, the pulmonary vessels and its branches were imaged with obviously high intensity difference from other vessels such as aorta. In Fig.1C, the aorta was shown as high contrast against the rest of the vessels. In Figure 2, noticeable vessel contrast difference was shown for the two vessels and the ROIs for statistic was delineated as shown in Figure 2. Figure 3 showed that there was no significant difference of the relative intensities between PA and AO in the thoracic (non-selective) MRA image. For PA-selected image, the ROI intensity of PA was much higher than that of AO; and vice versa for the AO-selected image.

Discussion and Conclusion

While there was study to compare the T-SLIP technique with FSE acquisition versus true SSFP for vessel-selective MRA [3], quantitative evaluation of 3D TSE sequence with T-SLIP at 1.5 T has been understudied. In this work, we demonstrated the reproducibly distinct intensity level for a selected vessel versus the background vessels using 3D T-SLIP TSE, which could therefore be considered a potential tool for the clinical diagnosis and evaluation of pulmonary diseases. Further studies will held be conducted on the feasibility of this technique in the imaging of other vessels such as those in the liver and kidney.

Acknowledgements

No acknowledgement found.

References

[1] D. Benson, et al. Contrast-enhanced pulmonary MRA for the primary diagnosis of pulmonary embolism: current state of the art and future directions. BJR 2016.

[2] Kanazawa H. et al., Time-spatial labeling inversion tag (t-SLIT) using a selective IR-tag on/off pulse in 2D and 3D half-Fourier FSE as arterial spin labeling. ISMRM 2002

[3] Shimada K. et al., Non-contrast-enhanced MR Portography with Time-Spatial Labelling Inversion Pulses: Comparison of Imaging with Three-Dimensional Half-Fourier Fast Spin-Echo and True Steady-State Free-Precession Sequences. JMRI 2009. 29: 1140-1146

Figures

Figure 1 The MIP reconstruction images of thoracic MRA (Fig.1A), MRA with Pulmonary Artery (PA) selected (Fig.1B) and MRA with Aorta (AO) selected (Fig.1C).

Figure 2. Demonstration of the ROI delineation on the region of pulmonary artery (in cyan) and Aorta (in yellow) for the thoracic MRA (Fig2A), the PA-selected MRA (Fig2B) and the AO-selected MRA (Fig2C). The Mean and standard deviation of the ROI intensities were calculated. Image intensity from different volunteer scans was normalized for cross-subject comparison.

Figure 3. The mean and standard deviation of the signal intensity for both the pulmonary vessels (in blue) and Aorta (in orange) on the three MRA scan schemes as shown in the axis.

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