Adaptive Method for Black Blood Cardiac Imaging in End-Systolic Rest Improves Visualization of the Right Ventricular Wall

INTRODUCTION: The Double Inversion Recovery Fast spin echo (DIR-FSE) sequence [1] is a key component of cardiac MR examination. It allows to homogenously suppress blood signal for a better depiction of the myocardium. Black blood imaging of the heart is usually performed during the mid-diastolic rest. This is a consequence of the long inversion time (TI) required to suppress the blood signal which is constrained by the T1 of the blood as well as the heart rate (HR) [2]. Moreover, the optimum TI does not necessarily match a cardiac rest period (i.e. the mid-diastolic or the end-systolic rest period). In case of high HR or significant RR interval changes, DIR-FSE are almost impossible to acquire [3]. To overcome these constraints, black blood images can be acquired during the endsystolic rest since it is less sensitive to RR interval variations [4]. Furthermore, images acquired during the end-systolic rest may provide a better determination of the right ventricle (RV) due to its thickening. Two methods have been suggested to perform DIR-FSE during the end-systolic rest, independently of HR and RR interval variations [5]. Briefly, they both rely on delaying the beginning of the DIR-FSE sequence so that the acquisition occurs during the end-systolic rest of the next cardiac cycle. Both methods used a cardiac cycle model to compute the delay. The first one relies on the assumption that the RR intervals are constant (Fixed Delay Method, FDM) whereas the second method is based on an adaptive RR interval prediction algorithm (Adaptive Method, AM). After a quick review of the two methods, robustness and RV visualization enhancement is investigated on 14 healthy volunteers. METHODS: Both AM and FDM methods used a cardiac cycle model that provided the systolic duration (T) as a linear function of the RR interval Δ with parameters A and B [4] (fig.1). The common framework for both methods in the delay computation before starting the DIR-FSE sequence was based on the following formula TD TI D + − Δ = , with TD the trigger delay defined as the time between the R-wave and the FSE (fig.2). By tuning TD, this formula allows to position the FSE in any cardiac phase. The main problem and difference between the two methods were then howΔ and TD were computed to acquired images in end-systolic rest. Fixed Delay Method (FDM): For the FDM (fig.2-a), the DIR-FSE sequence was simply started after a fixed delay D defined as: FSE T A B TI D − Δ − + − Δ = −1 , with Δ the average RR interval (over 9 RR intervals before