Patient Evaluation of Modified Golden Angle Spiral Real-time Phase Contrast MRI on a 0.55 T System (RF_TH_233)

Low field cardiovascular magnetic resonance (CMR) has gained renewed interest due to its inherent cost-effectiveness and recent advances in pulse sequences and image reconstruction methods [1]. Flow assessment by free breathing real-time phase contrast MR (RT-PCMR) eliminates the need for respiratory control and electrocardiogram (ECG) gating required by conventional breath-held (BH) PCMR. This is particularly advantageous for patients with underlying respiratory conditions and cardiac rhythm abnormalities. We previously demonstrated the feasibility of a spiral 2D RT-PCMR research prototype sequence on a wide-bore 0.55 T clinical MR system in normal volunteers [2]. This abstract evaluates the technique’s use in patients with cardiovascular disease indications, to facilitate RT-PCMR access for obese and claustrophobic patients who may struggle with breath holding and be better accommodated by an 80 cm bore.

Methods: 16 patients (mean age= 44.8±17.1 years, 10 females, BMI = 33.5±13.1 kg/m²) were imaged on a commercial 80 cm bore 0.55T system with 26 mT/m gradient amplitude and 45 T/m/s slew rate (MAGNETOM Free.Max, Siemens Healthineers). Seven of the patients were recruited as research subjects while the other nine were referred for clinical CMR on the wide-bore low field scanner because of body habitus and/or claustrophobia (Obesity Class I, n=3; Class II, n=1; and Class III, n=4). The indications for CMR varied and included evaluations for arrhythmias, valvular disorders, intracardiac shunting, and routine surveillance. PCMR images were acquired perpendicular to the ascending aorta and main pulmonary artery (MPA). Peak velocity, peak flow, and net flow were averaged for all complete heart beats available from a four second free-breathing RT-PCMR acquisition, implemented with a modified golden-angle spiral trajectory [2] and employing inline SENSE based compressed sensing image reconstruction, using the prototype Siemens framework for image reconstruction environments (FIRE) [3].  These flow parameters were compared to the reference results from a corresponding BH segmented GRAPPA accelerated (r=2) PCMR acquisition. The spatio-temporal resolution of the two sequences were 2.3.x.2.3x8 mm/44 ms and 1.7x2x8 mm/53 ms respectively.

Results:

Figure 1 shows PCMR images and flow profile from a Class III obese patient. Overall, there was good agreement between RT and BH-PCMR for net flow (p >0.05), but RT-PCMR slightly underestimated peak velocity and peak flow (p< 0.05) (Figure 2). Figure 3 shows beat-to-beat flow variability characterized by RT-PCMR in a patient with atrial fibrillation and hence excluded from quantitative comparison.

Conclusion: Our proposed RT-PCMR technique is feasible on a 0.55 T MR system. Its successful application in obese and claustrophobic individuals, as well as its ability to characterize beat-to-beat variability in arrhythmia, is particularly promising and underscores the potential of this approach across various clinical settings.