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Expanding the Versatility of Cardiac PET/CT: Feasibility of Delayed Contrast Enhancement CT for Infarct Detection in a Porcine Model

¹ Division of Nuclear Medicine, Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland; ² Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland; and ³ Nuklearmedizinische Klinik der TU München, Munich, Germany

View larger version (18K): [in this window] [in a new window]   FIGURE 1.  Schematic of PET polar map analysis. (A) Long axis of left ventricle is defined in 2 different views. (B) A 3-dimensional brush of 460 search rays is placed along long axis and used for volumetric sampling. (C) Segmental myocardial activity is defined as maximum along each search ray. (D) Activity for all segments is displayed in polar map. Polar maps show apex in center, base in periphery, anterior wall on top, septum on left, inferior wall on bottom, and lateral wall on right.

View larger version (16K): [in this window] [in a new window]   FIGURE 2.  Schematic of CT polar map analysis. (A) Volumetric CT data are reoriented along cardiac long axis, and short-axis slices from apex to base are created. (B) Myocardial contours are semiautomatically defined in all short-axis slices. Mid-myocardial density is used for further analysis and defined as average of second and third quarter of distance between endo- and epicardium. (C) Circumferential density profiles are created for each slice. (D) All slices are combined and density is displayed in polar map. Apex is omitted to avoid partial-volume effects in short-axis slice analysis.

View larger version (21K): [in this window] [in a new window]   FIGURE 3.  Corresponding mid-ventricular short-axis slices for different CT acquisitions in representative animal. Shown are images at various times after contrast injection for higher-dose helical CT acquisition (top) and lower-dose CT acquisition using calcium score protocol (bottom). Note improved enhancement in anteroseptal infarct area vs. blood and remote myocardium over time. Also shown are fusion images of CT and rest perfusion PET (right). CTA = CT coronary angiography; Prosp. = prospective.

View larger version (10K): [in this window] [in a new window]   FIGURE 4.  Bar graphs for mean and SD of ratio of HUs in infarct area vs. blood (A) and infarct area vs. remote myocardium (B). Mean ± SD of 6 animals that underwent both CT acquisition protocols are shown.

View larger version (18K): [in this window] [in a new window]   FIGURE 5.  Linear regression plots (left) and Bland–Altman plots (right) for HUs in infarct area (A) and remote myocardium (B) using low-dose (calcium score) CT acquisition vs. higher dose (angiography) CT acquisition. Acquisitions at all times after contrast injection for available 6 animals were used.

View larger version (43K): [in this window] [in a new window]   FIGURE 6.  Representative rest perfusion PET (top) and low-dose delayed CT-enhancement images (bottom) in pig with chronic LAD infarction. Shown are mid-ventricular short-axis slices, polar maps of entire LV myocardium, polar maps showing global defect sizes in colored area after threshold analysis (60% of maximum for PET, 3.5 SDs above mean of remote myocardium for CT), and polar maps showing segmental model for regional analysis. Polar maps show apex in center, base in periphery, anterior wall on top, septum on left, inferior wall on bottom, and lateral wall on right.

View larger version (18K): [in this window] [in a new window]   FIGURE 7.  Agreement of CT and PET. (A) Regression plot and Bland–Altman plot for global infarct size measured by 10-min delayed enhancement using higher-dose angiographic acquisition and defect size from 13N-ammonia PET (thresholds used are 60% of maximum for PET, 3.5 SDs above mean of remote myocardium for CT; n = 10). (B) Regression plot for average retention of 13N-ammonia at rest in 16 myocardial segments vs. average HUs per segment at 10 min after contrast injection, imaged by high-dose and low-dose (C) CT. Data for B and C are derived from 6 animals imaged by both CT techniques.