Optimal flip angle for high contrast balanced SSFP cardiac cine imaging.

PURPOSE

To determine the optimal flip angle (FA) for cardiac cine imaging that maximizes myocardial signal and blood-myocardium contrast.

METHODS

Bloch equation simulations of stationary myocardium and flowing blood with an imperfect slice profile were compared to in vivo measurements of blood and myocardium signal-to-noise ratio (SNR) and blood-myocardium contrast-to-noise ratio (CNR) in healthy subjects (N = 10) in the short-axis and four-chamber views and in patients (N = 7) in the three-chamber imaging plane.

RESULTS

Left ventricular (LV) and right ventricular (RV) blood SNR and blood-myocardium CNR increases with increasing FA up to ≈105° in the short-axis view. A similar trend is seen in the RV four-chamber view, but a marked SNR difference between the LV and RV blood appears for FA>75°, especially during systole. Notable RV and LV SNR and CNR differences are also evident in the three-chamber view due to the predominant LV in-plane flow versus RV through-plane flow.

CONCLUSION

Very high blood-myocardium CNR can be obtained with a FA of ≈105° in the short-axis plane and ≈75° in the three-chamber and four-chamber imaging planes. However, if through-plane flow is limited, as may occur for patients with low ejection fraction or low heart rates, then the FA may be limited to ≈ 75°.