18F-FDG-PET/CT

Arterial inflammation: Aortic inflammation will be assessed as previous [15, 22]. In brief CT and PET scan images will be co-registered automatically. The aorta will be divided into axial slices, and the tracer standardised uptake value (SUV) measured from a point distal to the origin of coronary vessels to avoid myocardial spill-over. Regions of interest will be drawn around the aorta in the axial position, repeated along the length of the aorta. A mean arterial SUV will be derived from the average of the maximum SUV values in serial axial measurements. Similarly the average of SUV measurements from the  venous pool will derive the mean venous background SUV. The target-to-background (TBR) ratio will then be calculated by dividing the mean arterial SUV by the mean venous SUV.

Myocardial inflammation: Myocardial uptake will be assessed as previous [23–27]. In brief CT and PET scan images will be co-registered. Analysis will be performed on short-axis cardiac slices for later comparison with CMR using 17 segment model [28]. Liver SUV uptake will be measured by drawing a hepatic region of interest. Uptake in the heart as a whole will be scored according to a visual scale to assess cardiac suppression of FGD uptake (ie adequate fasting/dietary preparation).

Visual assessment of myocarditis:

A visual assessment of FDG uptake (on diagnostic scans) that signifies myocarditis will be categorised: None—1, focal on diffuse—2, Focal—3, Diffuse—4.

Objective assessment of myocarditis:

Each segment of the 17 segment model, will be assessed for myocardial uptake visually. In addition, regions of interest within each myocardial segment of the 17-segment model will be drawn avoiding the blood pool and liver.

A mean cardiac SUV will be derived from the average of the maximum SUV values in serial short axis measurements (Sum of each segment /17).

Assessment of each segment of the 17 segment model will be performed in 3 different ways as follows.

Raw SUV uptake compared to blood pool uptake will be calculated for each segment, and categorised.

TBR (target-to-background-ratio) will be calculated by dividing each cardiac segment SUV by the mean blood pool SUV

Each segment indexed to the mean blood pool will also be categorised (0—uptake < mean blood pool uptake),1—uptake = mean blood pool uptake,2—uptake > mean blood pool uptake but < liver uptake, 3—(uptake > liver uptake)