Quick Fire Session
SCMR 22nd Annual Scientific Sessions
Background: Measurement of the blood T1 time using conventional myocardial T1 mapping methods has gained clinical significance in the context of ECV mapping  and synthetic Hct . However, its accuracy is compromised by 1) inflow of non-inverted spins  and 2) inflow of spins which are not partially saturated by previous imaging pulses . 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  with and without Look-Locker correction (MOLLI / MOLLI nLL)  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.