Fig. 1

Steady-state (SS) magnetization preparation methods for cardiac-gated balanced steady-state free precession (bSSFP) cine. CT: In simple cardiac-triggered (CT) acquisition with no SS preparation, all data acquired after the detection of a valid cardiac trigger are accepted for image formation (green boxes). BH: In conventional breath-hold (BH) SS preparation, data acquired during the first RR interval are discarded (black boxes). All subsequent data acquired with cardiac gating during suspended respiration are used for image formation. RG: In the respiratory-gated (RG) method, uninterrupted radiofrequency (RF) excitations applied throughout the acquisition act as the means for SS retention, and only those cardiac-gated data that are acquired when the respiratory bellows signal falls within the user-defined threshold (horizontal dotted lines) are accepted for image formation. RT: In the respiratory-triggered (RT) approach proposed in this paper, RF excitation commences after the detection of a respiratory trigger (e.g., inspiration or expiration), and only data acquired during an RR interval that lags the respiratory trigger point by at least a predefined duration of τ is used for image formation. Unlike RG, RF excitation ceases after the RR interval in which image data are acquired. Electrical signals from the cardiac leads and respiratory bellows are shown in blue. Note that this algorithm is fully compatible and is implemented with prospective rejection of cardiac arrhythmias and retrospective cardiac gating. Phase-encoding steps for the multi-phase segmented k-space acquisition are changed only after successful acceptance of the data. Red dot, expiration trigger; RF, radio frequency; black rectangle, data are discarded; green rectangle, data are accepted for further processing; t, time after respiratory trigger; τ, time to attain steady state; dotted line, respiratory acceptance window