Purpose

Cardiac catheterisation is a common diagnostic and interventional procedure in patients with congenital heart disease (CHD). This procedure is commonly performed under X-ray guidance, associated with ionizing radiation and increased risks for cancer[1]. MRI-guided cardiac catheterization has been proposed to provide better soft tissue contrast, avoid ionizing radiation. Current passive catheter tracking approaches employ positive and negative contrast using gadolinium or CO2 filled balloon wedge catheters[2-4], respectively. Visualization of the Gadolinium filled balloon appears to be easier compared to the CO2-filled balloon[5]. However, gadolinium-filled balloon methods rely on real-time bSSFP images acquired without saturation (non-SAT) prepulse, which leads to poor catheter balloon/blood contrast or with saturation (SAT) prepulse which suppresses soft tissue/blood signal[5]. In this study, we developed and optimized a novel gadolinium-filled balloon positive contrast sequence to provide simultaneous high contrast visualization of soft tissue, blood and catheter balloon using a partial saturation (pSAT) pre-pulse.

Methods:

The proposed sequence uses a real-time single shot acquisition with bSSFP readout (TR/TE=2.6ms/1.3ms, flip angle=60°, FOV=370×370mm2, voxel size=2.2×2.5mm2, bandwidth=1190Hz, SENSE factor=2.5, partial Fourier=0.65, acquisition time=145ms, linear ordering). Each image was acquired immediately after a saturation pre-pulse with a reduced saturation angle to only achieve partial saturation. Optimization of the pSAT angle was first performed using Bloch equation simulations. Different levels of intra-voxel partial voluming of the balloon wedge catheter (Arrow®) where analyzed with the balloon at the tip filled in with 1% gadolinium (DotaremÒ). The entire setup was initially tested using a 3D printed heart phantom and optimized in volunteers. Two patients aged 12 and 39 years in whom an XMR was clinically indicated for pulmonary vascular resistance assessment were recruited. Underlying diagnosis were severe right pulmonary stenosis and atrioventricular septal defect (child and adult, respectively). In the adult patient, the pSAT sequence was initially run several times to study the influence of the pSAT angle. Catheter balloon/blood CNR, catheter balloon SNR, blood SNR, and overall subjective assessment (by a cardiologist blinded from the simulation findings) of contrast quality were measured in the last image of each acquisition. MR-guided catheterization was performed in both patients using the pSAT sequence with a 30° SAT angle. The sequence was run in interactive mode and the imaging plane location was modified in real time by the interventional cardiologist using a set of pre-programmed pedals inside the scanner room. 1% gadolinium (Dotarem®) was used to fill the balloon of the wedge catheter for positive contrast visualization.

Results:

Numerical simulations showed a 20-40° pSAT angle provides a good compromise between high catheter balloon/blood contrast, high SNR and reduced sensitivity to intra-voxel partial voluming of the catheter balloon (Figure 2). The proposed pSAT approach also provides better contrast than conventional non-SAT sequences (pSAT angle=0°) and better SNR than SAT sequences (pSAT angle=90°). The proposed sequence with a 20-40° pSAT angle provided a good in-vivo compromise between catheter balloon/blood CNR and blood SNR (Figure 1). The balloon of the wedge catheter was clearly depicted during navigation in the phantom with the pSAT sequence (Figure 2). Quantitative and qualitative assessment of the pSAT acquisitions with different pSAT angles confirmed the optimality of a 30° pSAT angle (Figure 3). In both patients the catheter was inserted via the femoral vein and directed through the inferior vena cava to the right atrium, right ventricle, pulmonary artery and its branches (Figure 4). The pSAT sequence was found successful to passively track the catheter and simultaneously visualize soft tissue and blood. However, in the first patient, the catheter lacked the stiffness required to cross the pulmonary valve. In this patient, the procedure was completed with X-ray support using a braided non-MRI compatible catheter over a wire with higher stiffness. The procedure was completed solely under MRI guidance in the second patient. Total procedure time was 172 and 170 minutes, cardiac catheterisation time was 55 and 25 min in child and adult, respectively

Discussion:

The proposed pSAT sequence provides real-time simultaneous high contrast visualization of the balloon wedge catheter, soft tissues and blood. This technique provides superior contrast than conventional non-SAT sequences and simultaneous visualization of soft tissues with excellent passive tracking capabilities during MR-guided catheterization in patients with congenital heart disease. This method uses modified commercially available sequences and could provide an alternative to catheterization in centers in which cardiac MRI is established as an imaging diagnostic tool.

Conclusions:

In this preliminary experience, the described pSAT sequence offered real-time MR-guided passive tracking of catheters, with simultaneous high contrast visualization of human blood, soft tissue and the balloon of the wedge catheter.

Acknowledgements

No acknowledgement found.

References

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