High-resolution free-breathing automated quantitative myocardial perfusion by cardiovascular magnetic resonance for the detection of functionally significant coronary artery disease

Abstract

Aims: Current assessment of myocardial ischaemia from stress perfusion cardiovascular magnetic resonance (SP-CMR) largely relies on visual interpretation. This study investigated the use of high-resolution free-breathing SP-CMR with automated quantitative mapping in the diagnosis of coronary artery disease (CAD). Diagnostic performance was evaluated against invasive coronary angiography (ICA) with fractional flow reserve (FFR) measurement.

Methods and results: Seven hundred and three patients were recruited for SP-CMR using the research sequence at 3 Tesla. Of those receiving ICA within 6 months, 80 patients had either FFR measurement or identification of a chronic total occlusion (CTO) with inducible perfusion defects seen on SP-CMR. Myocardial blood flow (MBF) maps were automatically generated in-line on the scanner following image acquisition at hyperaemic stress and rest, allowing myocardial perfusion reserve (MPR) calculation. Seventy-five coronary vessels assessed by FFR and 28 vessels with CTO were evaluated at both segmental and coronary territory level. Coronary territory stress MBF and MPR were reduced in FFR-positive (≤0.80) regions [median stress MBF: 1.74 (0.90-2.17) mL/min/g; MPR: 1.67 (1.10-1.89)] compared with FFR-negative regions [stress MBF: 2.50 (2.15-2.95) mL/min/g; MPR 2.35 (2.06-2.54) P < 0.001 for both]. Stress MBF ≤ 1.94 mL/min/g and MPR ≤ 1.97 accurately detected FFR-positive CAD on a per-vessel basis (area under the curve: 0.85 and 0.96, respectively; P < 0.001 for both).

Conclusion: A novel scanner-integrated high-resolution free-breathing SP-CMR sequence with automated in-line perfusion mapping is presented which accurately detects functionally significant CAD.

Keywords: CMR; cardiovascular magnetic resonance; coronary artery disease; myocardial blood flow; myocardial perfusion; quantitative perfusion.

Graphical Abstract

High-resolution free-breathing stress perfusion cardiovascular magnetic resonance (SP-CMR) with in-line automated quantitative mapping is accurate in the diagnosis of functionally significant coronary artery disease. Diagnostic performance was compared with invasive fractional flow reserve (FFR) with myocardial blood flow (MBF) at hyperaemic stress and myocardial perfusion reserve (MPR) reduced in patients with inducible ischaemia. CTO, chronic total occlusion; AUC, area under the curve.

Figure 1

Contrast transit over time during sequence acquisition in a patient with normal MBF. Row (A) represents AIF slice acquisition over time and row (B) demonstrates the basal myocardial slice at the same time points. (C) Automated segmentation of the AIF longitudinal relaxation rate (R1) map series used as a region of interest (ROI) for assessment of the AIF. (D) Basal myocardial R1 series with an ROI placed in the interventricular septum. (E) Time–R1 curves of both the automated AIF ROI and manual ROI seen in the R1 series.

Figure 2

Example of perfusion maps in a patient with no evidence of CAD [FFR in the left anterior descending (LAD) artery 0.90, other vessels not assessed]. Global stress MBF 2.97 mL/min/g, global rest MBF 1.03 mL/min/g. The corresponding AHA segmentations for both stress and rest MBF maps are demonstrated.

Figure 3

Automated quantitative perfusion maps from two different patients at hyperaemic stress with inducible perfusion defects identified. (A) Defect within the inferior/inferoseptal segments, highlighted by white arrows. LGE imaging was normal. FFR in the right coronary artery (RCA) = 0.69. RCA territory stress MBF = 1.50 mL/min/g; MPR = 1.58. (B) Near-circumferential epicardial-to-endocardial gradient in the basal and mid-slices, suggestive of microvascular dysfunction. Corresponding FFR in the LAD artery = 0.87; circumflex artery (LCx) = 0.96. LAD territory stress MBF = 2.29 mL/min/g; MPR = 2.73. LCx territory stress MBF = 2.06 mL/min/g; MPR = 2.53.

Figure 4

Comparison of perfusion values from whole territory and lowest two AHA segments analysis methods: (A) stress MBF and (B) MPR. Both stress MBF and MPR were lower in FFR-positive territories, regardless of the method used for assessment.

Figure 5

The relationship between FFR and territorial stress MBF (A) and MPR (B) in all vessels. A positive correlation is seen for both (Rho and R² values as shown, P < 0.001 for both stress MBF and MPR). The dashed lines (at FFR = 0.80) represent the boundary between functionally normal and abnormal FFR values.

Figure 6

ROC curves assessing the effectiveness of quantitative perfusion map analysis in identification of functionally significant CAD (as defined by FFR ≤ 0.80) on a per-vessel level. Each curve represents a different analysis approach with both stress MBF and MPR shown. (A) Whole territory perfusion values. (B) Mean of lowest two AHA segment perfusion values.

Figure 7

A patient with CTO and inducible perfusion defect included in analysis. (A) Stress MBF maps with a defect seen in the LAD artery territory (mean MBF 1.70 mL/min/g vs. 2.35 mL/min/g in the other territories). (B) Dark-blood LGE imaging demonstrating sub-endocardial infarction in the LAD territory, smaller in distribution than the perfusion defect seen in (A). ICA demonstrated a CTO in the LAD with collaterals from the circumflex artery.

Figure 8

Perfusion values across ischaemic categories (defined by invasive coronary assessment). Both stress MBF (A) and MPR (B) values were significantly lower in FFR-positive and CTO categories compared with FFR-negative categories. Whole group analysis showed increased perfusion values across ischaemic categories (P < 0.001). No significant difference was seen between both FFR-negative categories (both stress MBF and MPR).