High-resolution magnetic resonance myocardial perfusion imaging at 3.0-Tesla to detect hemodynamically significant coronary stenoses as determined by fractional flow reserve.

OBJECTIVES: The objective of this study was to compare visual and quantitative analysis of high spatial resolution cardiac magnetic resonance (CMR) perfusion at 3.0-T against invasively determined fractional flow reserve (FFR).

BACKGROUND: High spatial resolution CMR myocardial perfusion imaging for the detection of coronary artery disease (CAD) has recently been proposed but requires further clinical validation.

METHODS: Forty-two patients (33 men, age 57.4 ± 9.6 years) with known or suspected CAD underwent rest and adenosine-stress k-space and time sensitivity encoding accelerated perfusion CMR at 3.0-T achieving in-plane spatial resolution of 1.2 × 1.2 mm(2). The FFR was measured in all vessels with >50% severity stenosis. Fractional flow reserve <0.75 was considered hemodynamically significant. Two blinded observers visually interpreted the CMR data. Separately, myocardial perfusion reserve (MPR) was estimated using Fermi-constrained deconvolution. RESULTS: Of 126 coronary vessels, 52 underwent pressure wire assessment. Of these, 27 lesions had an FFR <0.75. Sensitivity and specificity of visual CMR analysis to detect stenoses at a threshold of FFR <0.75 were 0.82 and 0.94 (p < 0.0001), respectively, with an area under the receiver-operator characteristic curve of 0.92 (p < 0.0001). From quantitative analysis, the optimum MPR to detect such lesions was 1.58, with a sensitivity of 0.80, specificity of 0.89 (p < 0.0001), and area under the curve of 0.89 (p < 0.0001). CONCLUSIONS: High-resolution CMR MPR at 3.0-T can be used to detect flow-limiting CAD as defined by FFR, using both visual and quantitative analyses. Tedric Thompson Authentic Jersey

PMID: 21185504

Posted in * Journal Club Selections, Invasive Imaging, Magnetic Resonance Imaging.

3 Comments

  1. Commentary by Michael Bolen, generated from Journal club discussion at Cleveland Clinic Imaging Institute, Cleveland OH Main Campus.

    What is the purpose of this study?
    Cardiac magnetic resonance (MR) myocardial perfusion imaging allows for non-invasive assessment of myocardial ischemia, without exposing patient to ionizing radiation, while concurrently providing information on function and viability. Newer acquisition strategies (namely, k-space and time sensitivity encoding, k-t SENSE) combined with high-field (3.0 Tesla) allow improved in-plane spatial resolution with diagnostic signal to noise ratio. While many studies have used coronary angiography as the gold standard of comparison for evaluation of flow limiting coronary stenosis, fractional flow reserve (FFR) is likely a more reliable measure of functionally significant stenosis. This study involved a comparison of the performance of high-resolution cardiac MR myocardial perfusion at 3.0 Tesla with invasively-measured FFR.

    What was the population evaluated? What were the exclusion criteria?
    42 patients with suspected or known coronary artery disease successfully underwent cardiac MR before invasive coronary studies. Exclusion criteria were contraindications to cardiac MR or gadolinium contrast, previous myocardial infarction, CABG, MI, impaired left ventricular function, and obstructive pulmonary disease. This may represent a limitation, as myocardium affected by ischemic damage (acute or chronic) can have unpredictable effect on the interpretation of perfusion. Excluding these patients may have lead to inflated performance results in this investigation.

    What were the acquisition parameters of interest?
    MR perfusion imaging was performed during adenosine-induced hyperemia (140 micrograms/kg/min) in 3 short axis images, with net acceleration (with use of k-t SENSE) of 3.8. Delayed post-contrast images were obtained after 15 minutes. FFR was performed with 0.014-inch pressure sensor-tipped wire in all vessels that showed >50% diameter stenosis in 2 orthogonal views.

    Were there any novel aspects to this study?
    MR perfusion data was analyzed both qualitatively and quantitatively, with myocardial perfusion reserve calculated (hyperemic flow/resting flow, 0.75 used as cut off).

    What was the prevalence of significant coronary artery disease in this population?
    Of the 126 vessels analyzed, 42% contained a >50% diameter stenosis on visual assessment, and subsequently received FFR evaluation. Of the 52 lesions assessed, 27 had FFR < 0.75.

    How did visual and quantitative cardiac MR perfusion fare in comparison to FFR?
    Visual assessment of cardiac MR perfusion imaging yielded a sensitivity of 0.82 to detect coronary ischemia as defined by FFR < 0.75, and specificity 0.94, with kappa value of 0.76; quantitative assessment resulted in a sensitivity of 0.80 and specificity of 0.89, kappa value of 0.70. Cardiac MR measurements of myocardial blood flow correlated better with FFR than with narrowing identified on coronary angiography.

    What is the take away message from this study? What are future steps?
    This study addressed the question of performance of high-resolution myocardial perfusion imaging in the detection of functionally significant coronary artery stenosis as defined by FFR. Previous work typically validated MR perfusion by comparison with narrowing as noted at angiography. Additionally, both visual and quantitative analysis of myocardial perfusion allowed detection of significant disease as defined by FFR, though possibly surprising is the slightly superior performance of visual assessment. The authors suggest that temporal filtering effects may account for this observation. The high prevalence of coronary artery disease in this group may limit how these results can be generalized (accuracy may be overestimated), and the results, as the authors acknowledge, could be considered preliminary, awaiting validation in a population with lower pre-test probability of significant coronary artery disease.

  2. As the Journal Club group in Cleveland, I found it interesting that the authors decided to evaluate both a visual and a quantitative assessment of the MR perfusion images.

    What I found surprising (and re-assuring for those of us who rather look at things rather than spend time doing tracings and measurements) is that the visual assessment fared BETTER than the quantitative one! (kappa=0.76 vs 0.70)

  3. What is the purpose of this study?
    To compare the performance of cardiac perfusion at 3T MR using FFR as the gold-standard.

    What was the population evaluated? What were the exclusion criteria?
    The population used was a pre-selected group of patients that met criteria for undergoing conventional catheter based angiography. This creates a selection bias, strictly speaking. However it is felt that the purpose of assessing perfusion during stress MR exams is the same as when ordering stress MPI or echo. Therefore no real clinical indication on healthy individuals.

    What were the acquisition parameters of interest?
    We found interesting the use of single Gad dosing on this patients. Double dosing is commonly used in cardiac studies. Was there a reason to not double dose? Especially if the late enhancement imaging was going to be performed over at least 30 minutes from the first injection of contrast (during stress).

    Were there any novel aspects to this study?
    We found very interesting that two separate analyses of the MR perfusion sequences were performed, a visual and a quantitative analysis. We also appreciated the double definition used to assign the defects when assessed visually. This may explain the slight greater correlation of visual assessment with FFR.
    We were a bit perplexed at the authors explanation on how they did their ICC analysis as it is not well explained on the paper.

    What was the prevalence of significant coronary artery disease in this population?
    42.1% of the vessels had a >50% stenosis identified on cath. Of these 1 was excluded from FFR assessment, while 27 of the remaining 52 had an FFR <0.75.

    How did visual and quantitative cardiac MR perfusion fare in comparison to FFR?
    It was interesting to see that the visual analysis correlated slightly better (see above comments).

    What is the take away message from this study? What are future steps?
    This seems to be a very expensive stress echo or MPI. However, it is another step closer to a one-stop shop where anatomy is well defined and scar imaging can be also added.

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