Pressure gradient measurement in the coronary artery using phase contrast (PC)-MRI: initial patient results towards noninvasive quantification of fractional flow reserve
Journal of Cardiovascular Magnetic Resonance volume 18, Article number: P218 (2016)
Fractional flow reserve (FFR) is an invasive procedure evaluating the functional significance of an intermediate coronary stenosis in patients with coronary artery disease (CAD) . Quantification of pressure gradient (ΔP) across a particular stenosis is the key to the determination of FFR. Noninvasive ΔP measurement (ΔPMR) using phase-contrast (PC)-MRI in conjunction with Navier-Stokes (NS) equations has been attempted in various vessels [2-4]. Our previous work has shown the feasibility of deriving ΔPMR at various vessel diameters in a phantom (fig.1a) and excellent correlation between ΔPMR and ΔP measured via a pressure-transducer (fig.1b). This study aimed to investigate the feasibility of deriving ΔPMR in healthy and diseased coronary arteries.
Coronary PC-MRI acquisitions were ECG triggered (mid-diastole) and navigator gated (end-expiration) . Fat-suppression pre-pulses were applied prior to the acquisitions to avoid chemical shift effects and increase vessel contrast . Contiguous slices (4-9) were consecutively collected across the proximal coronary segment (healthy controls) or stenotic lesion (patients). Imaging parameters were: VENC=35-65 cm/s in all 3 directions, FA=15o, cardiac phase=2(~70 ms/phase), in-plane resolution = 0.5-0.6 × 0.5-0.6 mm2, slice thickness=3.2 mm and TA=2-4 min/slice at 3T. Eddy-current correction was done offline followed by NS calculations . Protocol was performed on 11 healthy controls and 6 patients (one with known invasive FFR). Patient inclusion criteria: known/suspected CAD, ≥1 coronary lesion (proximal stenosis ≥30%) detected by CTA and/or invasive coronary angiography (ICA).
A significant (p<0.001) increase in ΔPMR was seen in the patient group (6.40 ± 4.43 mmHg) vs. healthy controls (0.62 ± 0.49 mmHg) (figre 2a). CTA/ICA reports in 5/6 patients showed a range of stenoses of 30-50% (proximal left anterior descending coronary artery (pLAD)), but not significant enough to perform invasive FFR. ICA/FFR was performed in 1/6 patients (diffused, 50% lumen narrowing at pLAD, fig 2b-c) with FFR=0.56, suggesting a functionally significant lesion. The same patient showed a ΔPMR of ~14 mmHg, likewise suggesting a functionally significant lesion (relatively high pressure drop).
Preliminary results suggest that noninvasive quantification of ΔPMR in both healthy and diseased coronary arteries is feasible. The patient with low FFR (high pressure drop), corroborating the ΔPMR results, showed the feasibility of ΔPMR in differentiating between a functionally significant and a non-significant lesion within the patient group. More patient studies with invasive FFR comparison are underway to further validate the approach. In addition, technical improvements in terms of spatial, temporal resolutions and reduction of noise are also being developed to further improve accuracy.
Pijls , et al: NEJM. 1996
Bock , et al: MRM. 2011
Lum , et al: RY. 2007
Bley , et al: RY. 2011
Deng , et al: ISMRM. 2014
Middione , et al: MRM. 2013
Yang , et al: MRM. 1996
About this article
Cite this article
Deng, Z., Lee, S.E., Fan, Z. et al. Pressure gradient measurement in the coronary artery using phase contrast (PC)-MRI: initial patient results towards noninvasive quantification of fractional flow reserve. J Cardiovasc Magn Reson 18 (Suppl 1), P218 (2016). https://doi.org/10.1186/1532-429X-18-S1-P218