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  • Open Access

Reproducibility of phase-contrast MRI in the coronary artery: towards noninvasive pressure gradient measurement and quantification of fractional flow reserve

  • 1, 2,
  • 1,
  • 3,
  • 1 and
  • 1, 2
Journal of Cardiovascular Magnetic Resonance201517 (Suppl 1) :Q11

https://doi.org/10.1186/1532-429X-17-S1-Q11

  • Published:

Keywords

  • Fractional Flow Reserve
  • Coronary Stenosis
  • Quiescent Period
  • Acquisition Window
  • Adjacent Slice

Background

Fractional Flow Reserve (FFR) is an invasively determined index of the functional severity of an intermediate coronary stenosis by measuring the pressure drop across the lesion [1]. Noninvasive pressure gradient (ΔP) measurements using phase-contrast (PC)-MRI have been attempted in the aorta, carotid, and renal arteries [24]. The purpose of this study is to assess the reproducibility of PC-MRI and noninvasive ΔP calculations in the coronary artery, which is relevant for establishing the robustness of the noninvasive FFR technique.

Methods

2D PC-MRI was used to acquire two-cardiac-phase data at mid-diastole and end-expiration via ECG-triggering and navigator-gating on 3T MAGNETOM Verio (Siemens). K-space phase-encoding ordering is designed to allow offline view sharing [5], which is applied in cases where the acquisition window exceeds the quiescent period (~100ms). The sequence measures the velocity field (vx, vy, vz) of a single cross-section per acquisition and 4-5 consecutive slices were obtained in the proximal LAD. Reproducibility was assessed with two repeat scans on 4 healthy subjects. VENC ranged 30-45 cm/s for each flow encoding direction was determined from a VENC scout scan. The Navier-Stokes equations were used to derive ΔP [6]. In addition, a flow phantom (gadolinium-doped water flow at 300 mL/min in a silicone tubing of 4.8mm ID) with 40% stenosis (VENC=130z30xy cm/s) was likewise tested for reproducibility. Imaging parameters were: in-plane resolution = 0.58-0.67mm, slice thickness = 3.2 mm, flip angle = 15°, 65-71 ms/phase with the first phase strictly coinciding with the quiescent period, scan time = 1-3 min per slice. Absolute maximum and averaged velocities at each slice in all three directions and the ΔP between adjacent slices obtained from both scans were statistically compared via intra-class correlation (ICC).

Results

Volunteer studies: averaged maximum through-plane velocity over all healthy volunteers was 16.5±4.0 cm/s. A total of 19 slices were acquired from all subjects. For velocity measurements, excellent correlations were seen in the through-plane velocities (vz), with ICCs of 0.93/0.96 and slightly lower in vx and vy with ICCs of 0.83/0.86 and 0.80/0.78 for cardiac phases 1 and 2, respectively. For ΔPs, ICC was 0.51 with an average of 0.1039±0.28 mmHg among all subjects. Phantom studies: stenosis with 40% narrowing showed excellent correlations in all velocity directions and ΔPs (table 1).
Table 1

Intra-Class Correlation (ICC) between two scans.

 

Velocity Encoding Direction

Averaged Velocity

Absolute Maximum Velocity

Pressure Gradient (ΔP)

  

Phase 1

Phase 2

Phase 1

Phase 2

r = 0.508 p<0.05

Volunteers

Z

0.932

0.968

0.935

0.959

 
 

X

0.578

0.447

0.828

0.861

 
 

Y

0.931

0.918

0.804

0.779

 

Phantom

Z

0.992

0.988

r = 0.768 p<0.05

 

X

0.918

0.934

 
 

Y

0.979

0.969

 

Conclusions

Our preliminary results suggest that the noninvasive quantification of flow velocities and ΔPs are reproducible in the coronary arteries, demonstrating the robustness and feasibility of 2D PC-MRI. Patient studies are underway to determine ΔP and FFR thresholds between healthy and patient populations. Further technical improvements are warranted to reduce noise and improve reproducibility.

Funding

N/A.

Authors’ Affiliations

(1)
Cedars Sinai Medical Center, Los Angeles, CA, USA
(2)
Bioengineering, University of California, Los Angeles, Los Angeles, CA, USA
(3)
R&D, Siemens Healthcare, Los Angeles, CA, USA

References

  1. Pijls et al: NEJM. 1996Google Scholar
  2. Bock et al: MRM. 2011Google Scholar
  3. Lum et al: RY. 2007Google Scholar
  4. Bley et al: RY. 2011Google Scholar
  5. Deng et al: ISMRM. 2014Google Scholar
  6. Yang et al: MRM. 1996Google Scholar

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