Real-time cardiovascular magnetic resonance at 1.5 T using balanced SSFP and 40 ms resolution

Abstract

BackgroundWhile cardiovascular magnetic resonance (CMR) commonly employs ECG-synchronized cine acquisitions with balanced steady-state free precession (SSFP) contrast at 1.5 T, recent developments at 3 T demonstrate significant potential for T1-weighted real-time imaging at high spatiotemporal resolution using undersampled radial FLASH. The purpose of this work was to combine both ideas and to evaluate a corresponding real-time CMR method at 1.5 T with SSFP contrast.MethodsRadial gradient-echo sequences with fully balanced gradients and at least 15-fold undersampling were implemented on two CMR systems with different gradient performance. Image reconstruction by regularized nonlinear inversion (NLINV) was performed offline and resulted in real-time SSFP CMR images at a nominal resolution of 1.8 mm and with acquisition times of 40 ms.ResultsStudies of healthy subjects demonstrated technical feasibility in terms of robustness and general image quality. Clinical applicability with access to quantitative evaluations (e.g., ejection fraction) was confirmed by preliminary applications to 27 patients with typical indications for CMR including arrhythmias and abnormal wall motion. Real-time image quality was slightly lower than for cine SSFP recordings, but considered diagnostic in all cases.ConclusionsExtending conventional cine approaches, real-time radial SSFP CMR with NLINV reconstruction provides access to individual cardiac cycles and allows for studies of patients with irregular heartbeat.

On the Temporal Fidelity of Nonlinear Inverse Reconstructions for Real- Time MRI – The Motion Challenge

“…With respect to previous NLINV applications to real-time cardiac MRI [13,14], a resolution of 33.3 ms (30 fps, 3.0 T, T1 contrast) turns out to adequately cover typical myocardial motions of up to 10 cm s -1 even when using a temporal median filter, while higher velocities of 15 to 20 cm s -1 are only accessible without temporal filtering. On the other hand, a resolution of 40 ms (25 fps, 1.5 T, SSFP contrast) appears to be the lower limit for cardiac MRI when using a temporal median filter as such conditions may already cause some geometric distortions for small structures moving at higher velocities.…”

“…Examples of human studies include examinations of cardiac function using T1 contrast at 3.0 T [8,13] as well as SSFP contrast at 1.5 T [14], cardiovascular blood flow [22,23], swallowing [24], and speaking [21]. Due to the absence of an in vivo gold standard, all present evaluations are based on a specialpurpose motion phantom built to rotate positive (or negative) objects at defined angular velocity.…”

“…Because in vivo applications of the real-time NLINV method may eventually lead to residual streaking artifacts, previous implementations forced these undersampling streakings to "flicker" in 5 sequential frames by using complementary sets of radial spokes [13,14]. The strategy allows for an efficient removal of such artifacts by a postprocessing temporal median filter that extends over the same range of 5 frames.…”

“…The chosen parameters resemble the conditions previously introduced for real-time cardiac MRI using T1 contrast (3.0 T) at 18 ms and 33 ms resolution [13] as well as SSFP contrast (1.5 T) at 40 ms resolution [14].…”

White Paper: Interventional MRI: Current Status and Potential for Development Considering Economic Perspectives, Part 1: General Application

“…Therefore, there is increased willingness to design the additional controls for interventions so that they can be easily removed from the MRI unit for diagnostic operation. New approaches in the sequencing technique allow high spatial and temporal resolutions [56] that can be combined with the total range of tissue contrasts in some cases [57]. This is the closest we've ever been to being able to use MRguided vascular intervention in the clinical routine.…”