CAD: New Methods

1354885 - Fast and efficient fat suppression in free-running whole-heart CMR using OptiPulse

Wednesday, January 25, 2023

Location: E-POSTER

Presenting Author(s)

XS

Xavier Sieber, MSc

PhD Student in MR sequence development
CHUV
Lausanne, Switzerland

Primary Author(s)

XS

Xavier Sieber, MSc

PhD Student in MR sequence development
CHUV
Lausanne, Switzerland

Co-Author(s)

LR

Ludovica Romanin, MSc

PhD doctorante
Siemens Healthineers and University Hospital of Lausanne (CHUV), Switzerland
CR

Christopher W. Roy, PhD

Post Doc
Lausanne University Hospital and University of Lausanne (UNIL)
Prilly, Vaud, Switzerland
Jerome Yerly, PhD

Postdoc
University Hospital (CHUV) and University of Lausanne (UNIL), Vaud, Switzerland
JR

Jonas Richiardi, PhD

Principal investigator
University Hospital (CHUV) and University of Lausanne (UNIL), Switzerland
Matthias Stuber, PhD

Professor
University Hospital (CHUV) and University of Lausanne (UNIL)
Lausanne, Switzerland
Ruud B. van Heeswijk, PhD

Principal investigator
University Hospital (CHUV) and University of Lausanne (UNIL)
Lausanne, Vaud, Switzerland

Background: Recently, short water-excitation (WE) radiofrequency (RF) pulses have been reported as an efficient solution for fat suppression in high-resolution imaging of the heart(1,2). Such WE RF pulses were designed using analytical methods and are constrained to low-dimensional (< 5) parameter optimization, which may limit the search to a small domain of solutions, while a more global optimum may be overlooked.
We therefore propose a flexible and efficient method of optimizing B-splines-interpolated [3] WE RF pulses, named OptiPulse. The goal of this study was thus to design an RF pulse with OptiPulse, to compare it to a 1-1 binomial WE RF pulse in phantoms, and to validate it in vivo in the heart.

Methods:

The optimization of B-splines interpolated (3) RF pulses was performed with 30 parameters (15 phase, 15 amplitude) by simulating the transverse magnetization using Bloch equations (Fig.1). Next, the performance of the pulse was evaluated with a loss function, which was minimized with the Covariance Matrix Adaptation Evolution Strategy CMA-ES (4).

A WE RF pulse with a duration 2.56 ms was optimized and implemented on a 1.5T clinical scanner (MAGNETOM Sola, Siemens Healthcare) as part of a prototype free-running 3D radial bSSFP sequence (α=70°, TR=5.4ms) (5). The fat suppression of the optimized RF pulse was compared to that of a non-fat-suppressing pulse and to that of a 1-1 WE pulse in an agar-oil phantom using the contrast-to-noise ratio (CNR). Finally, free-running 5D bSSFP (6) was performed in the heart of 5 healthy volunteers with the 1-1 WE pulse and the optimized RF pulse (voxel size 1.1mm3, duration 11:28min). The contrast ratios (CR=Sfat/Sblood) between both chest fat/epicardial fat and the blood pool were calculated, while the traceable length of the right coronary artery (RCA) was measured (7) for both acquisitions.

Results:

In the phantom, blood-fat CNRs were -369 (i.e., fat brighter than blood), 86, and 90 for the non-suppressing, the 1-1 WE and the optimized pulse, respectively (Fig.2).

In vivo, the blood-pool/chest-fat CR amounted to 1.99±0.57 for the 1-1 WE pulse and 3.42±1.24 for the optimized pulse (P=0.047; Fig.3). The blood-pool/epicardial-fat CR was also higher for the optimized pulse at CR=4.85±0.91 compared to the 1-1 WE pulse at CR=1.91±0.62 (p< 0.001). The RCA could be traced for 4.9±0.6 cm with the 1-1 WE pulse and for 5.3±1.0 (P=0.655) cm with the optimized pulse.

Conclusion: The RF pulse generated with OptiPulse demonstrated higher levels of fat suppression than the 1-1 WE pulse in both the phantom and in vivo studies. This was consistent with the measurement of the vessel length, which was hampered by residual strong fat signal in the 1-1 WE images, where they also prevented vessel sharpness analyses. While OptiPulse requires further validation in a large patient cohort, these preliminary results suggest fat suppression for 3D radial whole heart imaging can be improved with Optipulse, potentially leading to improved visualization of the coronary arteries.