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Effective Methods to Correct Contrast Agent–Induced Errors in PET Quantification in Cardiac PET/CT

¹ Department of Nuclear Medicine, University of Münster, Münster, Germany; ² Department of Cardiology and Angiology, University of Münster, Münster, Germany; and ³ Department of Clinical Radiology, University of Münster, Münster, Germany

View larger version (18K): [in this window] [in a new window]   FIGURE 1.  From left to right, transversal, coronal, and sagittal views of NCAT software phantom. Specific PET activities and attenuation values can be assigned to every organ inside torso.

View larger version (78K): [in this window] [in a new window]   FIGURE 2.  CT images of heart: (A) Unenhanced CT scan, coronal view, soft-tissue window (center, 50 HU; width, 350 HU). (B) Contrast-enhanced CT scan, coronal view, soft-tissue window. Influence of contrast agent is clearly visible (attenuation value in left ventricle, 370 HU; reference value, 30–45 HU). (C) Cylinder-based CT segmentation of contrast agent in heart area, with transversal view on left and coronal view on right. Every CT pixel value above normal tissue value inside cylinder is considered to represent contrast agent and reduced to 35 HU (cylinder-threshold correction). (D) Size and location of ROI used to determine mean attenuation and uptake values in CT and PET images, respectively (Tables 1 and 2). Also shown is position of heart–lung borderline along craniocaudal axis. Difference in craniocaudal position in the 2 CT images (unenhanced and enhanced) serves as measure of respiratory motion shift of heart.

View larger version (50K): [in this window] [in a new window]   FIGURE 3.  PET attenuation maps and corresponding attenuation-corrected PET images of NCAT phantom (A–D) and typical patient scan (E–H), based on the following attenuation data: unenhanced data (reference data; mean CT attenuation in left ventricle in E, 40 HU) (A and E); nonprocessed contrast-enhanced data (mean CT attenuation in left ventricle in F, 370 HU) (B and F); contrast-enhanced data with cylinder-threshold contrast agent correction (C and G); and contrast-enhanced data with global-threshold contrast agent correction (D and H). Shown on right are differences between PET images based on CE attenuation data and PET images based on unenhanced CE data. PET images using nonprocessed enhanced CT scan information overestimate uptake in left ventricular wall. Arrow in E refers to line profile of Figure 4. CE = contrast-enhanced; CTC = cylinder-threshold correction; GTC = global threshold correction.

View larger version (13K): [in this window] [in a new window]   FIGURE 4.  Attenuation map (top) and PET (bottom) line profiles through heart (Fig. 3E), with attenuation data from unenhanced CT scan (A), nonprocessed contrast-enhanced CT scan (B), contrast-enhanced CT scan with cylinder-threshold contrast agent correction (C), and contrast-enhanced CT scan with global-threshold contrast agent correction (D).

View larger version (64K): [in this window] [in a new window]   FIGURE 5.  Polar maps of patient scans of Figure 3 using attenuation data from unenhanced CT scan (A), nonprocessed contrast-enhanced CT scan (B), contrast-enhanced CT scan with cylinder-threshold correction (C), and contrast-enhanced CT scan with global-threshold correction (D). Uptake in left ventricle is overestimated when using nonprocessed contrast-enhanced CT attenuation data. ant = anterior; lat = lateral; post = posterior; sep = septal.

View larger version (9K): [in this window] [in a new window]   FIGURE 6.  Correlation of polar map segments of left ventricle using original (A) and corrected (B and C) contrast-enhanced CT attenuation data. Corrected attenuation data provide more reliable quantification. CE = contrast-enhanced; CTC = cylinder-threshold correction; GTC = global threshold correction.

View larger version (7K): [in this window] [in a new window]   FIGURE 7.  Correlation of mean uptake in left ventricle relative to reference CT data corrected using global-threshold correction (Table 3) and respiratory motion shift of left ventricle. Determined correlation coefficient is 0.943; y-axis intercept is 0.995.