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Prospective Electrocardiogram-Gated Delayed Enhanced Multidetector Computed Tomography Accurately Quantifies Infarct Size and Reduces Radiation Exposure

Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland

^_* Reprint requests and correspondence: Dr. Albert C. Lardo, Johns Hopkins University School of Medicine/Division of Cardiology, 1042 Ross Building, 720 Rutland Avenue, Baltimore, Maryland 21205 (Email: al{at}jhmi.edu).

Objectives: This study sought to determine whether low-dose, prospective electrocardiogram (ECG)-gated delayed contrast-enhanced multidetector computed tomography (DCE-MDCT) can accurately delineate the extent of myocardial infarction (MI) compared with retrospective ECG-gated DCE-MDCT.

Background: For defining the location and extent of MI, DCE-MDCT compares well with delayed enhanced cardiac magnetic resonance. However, the addition of a delayed scan requires additional radiation exposure to patients. MDCT protocols using prospective ECG gating can substantially reduce effective radiation dose exposure, but these protocols have not yet been applied to infarct imaging.

Methods: Ten porcine models of acute MI were imaged 10 days after MI using prospective and retrospective ECG-gated DCE-MDCT (64-slice) 10 min after a 90-ml contrast bolus. The MDCT images were analyzed using a semiautomated computed tomography density (CTD) threshold technique. Infarct size, signal-to-noise (SNR) ratios, contrast-to-noise (CNR) ratios, and image quality metrics were compared between the 2 ECG-gating techniques.

Results: Infarct volume measurements obtained by both methods were strongly correlated (R = 0.93, p < 0.001) and in good agreement (mean difference: –0.46 ml ± 4.00%). Compared with retrospective ECG gating, estimated radiation dosages were markedly reduced with prospective ECG gating (930.1 ± 62.2 mGyxcm vs. 42.4 ± 2.3 mGyxcm, p < 0.001). The SNR and CNR of infarcted myocardium were somewhat lower for prospective gated images (22.0 ± 11.0 vs. 16.3 ± 7.8 and 8.8 ± 5.3 vs. 7.0 ± 3.9, respectively; p < 0.001). However, all examinations using prospective gating protocol achieved sufficient diagnostic image quality for the assessment of MI.

Conclusions: Prospective ECG-gated DCE-MDCT accurately assesses infarct size compared with retrospective ECG-gated DCE-MDCT imaging. Although infarct SNR and CNR were significantly higher for the retrospective gated protocol, prospective ECG-gated DCE-MDCT provides high-resolution imaging of MI, while substantially lowering the radiation dose.

Key Words: computed tomography • myocardial infarction • radiation • viability • perfusion

Abbreviations and Acronyms   CAD = coronary artery disease   CCTA = coronary computed tomographic angiography   CI = confidence interval   CNR = contrast-to-noise ratio   CMR = cardiac magnetic resonance   CT = computed tomography   CTD = computed tomography density   DCE = delayed contrast-enhancement   ECG = electrocardiogram   LAD = left anterior descending   LV = left ventricle/ventricular   MDCT = multidetector computed tomography   MI = myocardial infarction   MVO = microvascular obstruction   ROI = region of interest   SNR = signal-to-noise ratio

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