Quantification of balanced SSFP myocardial perfusion imaging at 1.5 T: Impact of the reference image

Purpose: To investigate the use of a high flip-angle (HFA) balanced SSFP (bSSFP) reference image (in comparison to conventional proton density [PD]–weighted reference images) for conversion of bSSFP myocardial perfusion images into dynamic T₁ maps for improved myocardial blood flow (MBF) quantification at 1.5 T. Methods: The HFA-bSSFP (flip angle [FA] = 50°), PD gradient-echo (PD-GRE; FA = 5°), and PD-bSSFP (FA = 8°) reference images were acquired before a dual-sequence bSSFP perfusion acquisition. Simulations were used to study accuracy and precision of T₁ and MBF quantification using the three techniques. The accuracy and precision of T₁, and the precision and intersegment variability of MBF were compared among the three techniques in 8 patients under rest conditions. Results: In simulations, HFA-bSSFP demonstrated improved T₁/MBF precision (higher T₁/MBF SD of 30%-80%/50%-100% and 30%-90%/60%-115% for PD-GRE and PD-bSSFP, respectively). Proton density–GRE and PD-bSSFP were more sensitive to effective FA than HFA-bSSFP (maximum T₁/MBF errors of 13%/43%, 20%/43%, and 1%/3%, respectively). Sensitivity of all techniques (defined as T₁/MBF errors) to native T₁, native T₂, and effective saturation efficiency were negligible (<1%/<1%), moderate (<14%/<19%), and high (<63%/<94%), respectively. In vivo, no difference in T₁ accuracy was observed among HFA-bSSFP, PD-GRE, and PD-bSSFP (−9 ± 44 ms vs −28 ± 55 ms vs −22 ± 71 ms, respectively; p >.08). The HFA-bSSFP led to improved T₁/MBF precision (T₁/MBF SD: 41 ± 19 ms/0.24 ± 0.08 mL/g/min vs PD-GRE: 48 ± 20 ms/0.29 ± 0.09 mL/g/min and PD-bSSFP: 59 ± 23 ms/0.33 ± 0.11 mL/g/min; p ≤.02) and lower MBF intersegment variability (0.14 ± 0.09 mL/g/min vs PD-GRE: 0.21 ± 0.09 mL/g/min and PD-bSSFP: 0.20 ± 0.10 mL/g/min; p ≤.046). Conclusion: We have demonstrated the feasibility of using a HFA-bSSFP reference image for MBF quantification of bSSFP perfusion imaging at 1.5 T. Results from simulations demonstrate that the HFA-bSSFP reference image results in improved precision and reduced sensitivity to effective FA compared with conventional techniques using a PD reference image. Preliminary in vivo data acquired at rest also demonstrate improved precision and intersegment variability using the HFA-bSSFP technique compared with PD techniques; however, a clinical study in patients with coronary artery disease under stress conditions is required to determine the clinical significance of this finding.