05 - Flow dependency of blood T1 measurements assessed in a perfusion phantom and in vivo

Friday, February 8

3:02 PM - 3:05 PM

Location: Grand C

Presenter(s)

Ingo Hermann, MSc

PhD Student
Heidelberg University

Author Only(s)

TU

Tanja Uhrig, MSc

PhD Student
Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University
JC

Jorge Chacon-Caldera, PhD

Postdoctoral Researcher
Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University
MA

Mehmet Akçakaya, PhD

Assistant Professor
Electrical and Computer Engineering, University of Minnesota; Center for Magnetic Resonance Research, University of Minnesota
LS

Lothar Schad, PhD

Professor
Computer Assisted Clinical Medicine, University Medical Center Mannheim, Heidelberg University
Sebastian Weingärtner, PhD

Post-Doctoral Associate
University of Minnesota

Background: Measurement of the blood T₁ time using conventional myocardial T₁ mapping methods has gained clinical significance in the context of ECV mapping [1] and synthetic Hct [2]. However, its accuracy is compromised by 1) inflow of non-inverted spins [3] and 2) inflow of spins which are not partially saturated by previous imaging pulses [4]. In this work we sought to study the effects of inflow on blood T₁ times in phantom and in-vivo measurements.

Methods: T₁ measurements of gadolinium doped water were performed using a perfusion phantom with adjustable flow velocities (Fig. 1) at 3T (Magnetom Skyra, Siemens). T₁ measurements were performed using 5(3s)3 MOLLI [5] with and without Look-Locker correction (MOLLI / MOLLI nLL) [6] for bSSFP and GRE readouts. Reference T₁ times were acquired using inversion-recovery turbo spin-echo measurements in the absence of flow. Additionally, in-vivo T₁ measurements were performed in two healthy subjects (28±0 years, 50% male). To study the T₁ time as a function of the current flow velocity, images were acquired in an axial slice and T₁ times were evaluated in the descending aorta. Velocity encoded CINE measurements were performed to quantify the flow velocity throughout the cardiac cycle.

Results: Phantom T₁ times are decreased by up to 200 ms in the dialysis compartment, for inflow of non-inverted spins (Fig. 1b). Fast flow velocities cause inflow of spins that lack partial saturation from the imaging pulses and lead to T₁ time deviation up to 100% in the pipe compartment (Fig. 1c). In-vivo measurements confirm substantial variation of the T₁ depending on the flow velocity (Fig. 2). The highest aortic T₁ times are observed at the time point of no flow and are comparable to left-ventricular T₁ times. However, increased flow velocity leads to reduction of the measured T₁ time by up to 400 ms at peak velocity (Table 1).

Conclusion: Blood T₁ measurements as assessed with commonly used cardiac T₁ mapping methods, are highly susceptible to inflow. Hence, alterations of the flow pattern, differences in the ejection fraction or increased amounts of non-inverted spins in larger patients might be confounding factors for blood T₁ based quantities in clinical studies.