18Fluorodeoxyglucose uptake in relation to fat fraction and R2* in atherosclerotic plaques, using PET/MRI: a pilot study

Figure 1. Increased 18F-FDG uptake in a carotid plaque (shown by the red arrow) in fusion images consisting of T1W MRI and PET. The anatomy of the neck, including the carotid arteries is presented in the axial- (left), sagittal- (upper right) as well as the coronal (lower right) planes. The image was created using MIM, MIM Software version 6.9.3 (MIM Software Inc. Cleveland, OH, USA, www.mimsoftware.com.

Figure 2. The figure illustrates the principal behind the segmentation and fusion methodology applied in the current study. Segmented carotid plaque is shown in blue, and 18F-FDG uptake is shown in red in the corresponding fusion image. The segmented blue volume represents the part of the vessel wall that is thickened, therefore containing the plaque. The plaque visualized in this figure stretches along the lateral part of the carotid wall, explaining why not the circumferent vessel is segmented. Axial, coronal and sagittal planes are automatically aligned for PET, fat, R2* and T1W images. Fat, R2* and T1W images were obtained on a stand-alone scanner using a quantitative MRI protocol. The PET/MRI images were acquired at a national imaging facility. The image was created using MIM, MIM Software version 6.9.3 (MIM Software Inc. Cleveland, OH, USA, www.mimsoftware.com).

Figure 3. The figures show correlation plots, with plaque composition versus target-to-blood pool ratio. The plots illustrate plaque correlations for all 12 patients, based on the corresponding mean values in each segmented volume. (a) Correlations between mean FF and plaque TBR. (b) Correlations between R2* and plaque TBR. Simple linear regression was performed using GraphPad Prism version 9.0.0 for Windows, GraphPad Software, San Diego, California USA, www.graphpad.com. FF fat fraction, TBR target-to-blood pool ratio.

Figure 4. Slice by slice comparison throughout the plaques of target-to-blood pool ratio versus fat fraction and intraplaque hemorrhage. The left panels in the columns show FF and TBR per MRI slice, the right panels R2* and TBR per MRI slice. TBR values are shown on the right y-axis in the figures. The slice numbers are shown on the x- axis, slice numbers differ, as plaque length varies between the patients. The comparison of the 12 patients shows a large heterogeneity in both FF and R2* dispersion and no significant correlation between FF and TBR and respectively R2* and TBR. All graphs were created using GraphPad Prism version 9.0.0 for Windows, GraphPad Software, San Diego, California USA, www.graphpad.com. FF fat fraction, TBR target-to-blood pool ratio.