PURPOSE

To quantify the reduction in RF energy deposition of a real-time adaptive cardiorespiratory synchronized (CS) balanced Steady State Free Precession (bSSFP) sequence compared to conventional respiratory gating (RG).

BACKGROUND

Despite the advantages of breath-hold cine bSSFP imaging, respiratory suspension—an essential mechanism for acquiring bSSFP cine images in the steady state —is not suitable for all patients, such as sedated patients and patients with impaired breath-holding capacity and/or cardiac arrhythmias. Therefore, it would be of clinical interest to obtain cine bSSFP images in individuals without the constraint of breath holding. Traditional approach to obviate the need for breathholding via respiratory gating (RG) imposes a significant RF energy deposition for bSSFP cine imaging, due to the uninterrupted application of high-flip angle RF pulses throughout the respiratory cycle. A respiratory triggered (RT) approach could mitigate these challenges1. In this prospective study on 14 consecutive clinical patients, we compared the specific energy deposition (SED) of a real-time adaptive, cardiorespiratory synchronized (CS) bSSFP sequence with RG sequence with identical acquisition parameters.

METHODS

Fourteen consecutive patients (54(32-80)yrs, 70(58-104)hbm, 19(18-22)rpm) undergoing clinically indicated cardiac MR, provided written informed consent to participate in this IRB approved, prospective study. All imaging was performed on 1.5T(9)/3T(5) commercial MR scanners (Achieva/Ingenia, Philips Healthcare). CS sequence that performs a) respiratory synchronized drive to steady state, b) prospective cardiorespiratory synchronized cine data acquisition with arrhythmia rejection, and c) retrospective cardiac gating was implemented (Fig 1). Cine bSSFP data was acquired with CS and conventional breath-hold (BH) sequence with identical acquisition parameters (TR/TE/flip angle = 2.5-3.2ms/1.25-1.6ms/ 65°(40°,3T); acqd voxel size = 1.7-2.0×1.6-2.0×8mm3; SENSE factor = 1.3-1.9; temp resolution 40-50ms; imaging time : 6-8 RR intervals/slice) for LV function evaluation. The data acquisition and physiology log was analyzed to compute RF duty cycle, and specific energy deposition for both the sequences.

RESULTS

The CS sequence ran successfully in all 14 patients. Total image acquisition time for CS (7.4±1.8 min) was significantly longer than conventional BH-SSFP (5.6±1.7 min). Reduction in SED for the CS sequence (0.68 ± 0.24 kJ/kg) compared to RG sequence (1.2 ± 0.36 kJ/kg) was statistically significant (Fig 2). The mean rate of energy deposition (kJ/kg/min) for the CS sequence was 40% lower than that of RG sequence (Fig 3). Clinical scores indicate diagnostically equivalent image quality with CS sequence as that of conventional BH techniques­.

CONCLUSION

The CS sequence provides the ability to prescribe multi-slice, multi-phase bSSFP sequences with significantly lower SED burden than that of RG sequence. This extends the utility of bSSFP sequences to acquire high spatial or temporal resolution images during free breathing with greater latitude in terms of RF energy deposition in sedated subjects.

Acknowledgements

No acknowledgement found.

References

[1] Krishnamurthy et al., JCMR, 17:1, 2015.