Cardiac gating calibration by the Septal Scout for magnetic resonance coronary angiography

BACKGROUND: Electrocardiogram (ECG) gating is commonly used to synchronize imaging windows to diastasis periods over multiple heartbeats in magnetic resonance (MR) coronary angiography. Calibration of the ECG gating parameters is typically based on a cine cardiovascular MR (CMR) video of the beating heart. Insufficient temporal resolution in the cine-CMR method, however, may produce gating errors and motion artifacts. It was previously shown that tissue Doppler echocardiography (TDE) can identify accurate diastasis window timings by observing the movement of the interventricular septum (IVS). We present a new CMR technique, the Septal Scout, for measuring IVS motion. We demonstrate that cardiac gating windows determined by the Septal Scout produce sharper coronary MR angiography images than windows determined by cine-CMR. METHODS: 9 healthy volunteers were scanned on a GE Optima 450w 1.5T MR system. Cine-CMR was acquired and used to identify the start and end times of the diastasis window (W(cine)). The Septal Scout employs a one-dimensional steady-state free precession (SSFP) readout along the ventricular septum prescribed from the 4-chamber view. The Septal Scout data is processed to produce a septal velocity function, from which the diastasis window was determined (W(sep)). Non-contrast-enhanced MR angiography was performed twice for each volunteer: once gated to W(cine), once to W(sep). Vessel sharpness was assessed subjectively by two experienced observers, and quantitatively by full width half maximum (FWHM) measurements of cross-sectional vessel profiles. In addition, TDE was performed on a subcohort of 6 volunteers where diastasis windows (W(TDE)) were determined from the IVS velocity measured in the 4-chamber view. W( sep ) and W( TDE ) were compared using Pearson’s correlation. RESULTS: MRA acquisitions were successful in all volunteers. Vessel segments produced smaller FWHM measurements and were deemed sharper when imaged during the Septal Scout gating windows (p < 0.05). Subjective assessment of sharpness also improved for the Septal Scout-gated scans (p < 0.01 for both observers). Lastly, W( sep ) and W( TDE ) were highly correlated (R > 0.98, p < 0.001). CONCLUSIONS: The MR Septal Scout technique was introduced and demonstrated to be more accurate at determining cardiac gating windows than cine-CMR, yielding sharper coronary MR angiography images.