Optimizing intra-arterial spin labeling for cardiac perfusion measurements (RF_TH_240)

Thursday, January 30, 2025

3:30 PM – 3:40 PM East Coast USA Time

Location: Blue Room PreFunction

Presenting Author(s)

FS

Felix Spreter, MSc

Student
University Medical Center Freiburg, University of Freiburg, Germany

Primary Author(s)

FS

Felix Spreter, MSc

Student
University Medical Center Freiburg, University of Freiburg, Germany

Co-Author(s)

Simon Reiss, PhD

Postdoctoral Researcher
University Medical Center Freiburg, University of Freiburg, Germany
AM

Alexander Maier, MD

MD
University Medical Center Freiburg, University of Freiburg, Germany
A�

Ali C. Özen, PhD

Head of RF & EMC Labs
University Medical Center Freiburg, Germany
Michael Bock, PhD

PhD
University Medical Center Freiburg, University of Freiburg, Germany

Background: Myocardial perfusion imaging is a crucial diagnostic tool for coronary artery disease, commonly performed using SPECT, PET, or cardiac MRI with gadolinium-based contrast agents (CA). An alternative MRI perfusion measurement technique is arterial spin labeling (ASL), which labels blood within an artery by saturating the longitudinal magnetization¹. Intra-arterial spin labeling (iASL) is a modified ASL technique in which the labeling RF-pulse is applied directly inside the artery using a small catheter-mounted RF-coil which enables perfusion measurements in a specific artery without exogenous CAs in the context of cardiac interventions^2–4. This study explores the feasibility of iASL, examining optimal parameters for the catheter coil and the transmitted labeling pulse through simulations, as well as in-vitro and in-vivo measurements.

Methods: The labeling efficiency of different catheter coil designs (single-loop, solenoid) was investigated through Matlab simulations and in-vitro measurements, focusing on labeling pulse amplitude, coil position within the artery, and orientation relative to B₀. An in-vivo experiment was conducted during a cardiac catheterization of a juvenile pig (German Landrace, 54 kg) at a clinical 3T system (Prisma, Siemens Healthineers). For this experiment, a catheter coil was constructed at the tip of a 6F catheter (Tiger II, Terumo), as shown in Fig. 1. This coil was used as a receive coil for active visualization during real-time guidance of the catheter. Once the catheter was positioned, the coil was connected to an external RF generator, and images were acquired both with and without labeling.

Results: The simulated mean magnetization shows a threshold behavior as function of the pulse amplitude with M_z close to 0 for amplitudes greater than 8 mA. The in-vitro measurements agree with the simulation results, showing a signal reduction followed by a constant plateau (Fig. 2). The in-vivo measurements revealed a signal reduction induced by the labeling of up to 45% in the aorta and up to 15% in the carotid artery, as shown in Fig. 3.

Conclusion: The simulation and in-vitro measurement demonstrate that saturation of the blood magnetization can be achieved using catheter-mounted coils with pulse amplitudes of more than 10 mA for a single-loop and 35 mA for a solenoid coil. The in-vivo experiment confirms that labeling can be measured using a commercial coronary catheter equipped with a single-loop coil; however, further improvements in catheter tip positioning and image acquisition are necessary for myocardial perfusion measurements.