To begin, perform MicroPET and CT imaging on female apolipoprotein E-deficient mice. After importing DICOM files in DICOM viewer software, turn off all PET images and turn on the base CT image. Click on one of the 2D views.
Under the window leveling box, locate the opacity mapping dropdown and slide the opacity scale to the center. Then turn on the overlay CT image and repeat the opacity adjustment. To change the filter of the overlay CT image to distinguish it from the base CT image, go to the window leveling dropdown in the main tab and find the lookup table or LUT.
Scroll through the LUT dropdown and select the red filter. In the data properties and settings dropdown, select the overlay image and click once to select one of the 2D views. Then locate the translate or rotate dropdown under the main tab and click the displace icon.
Now click and drag the translate box in the lower left corner and rotate the pivot point in the center of the 2D view to move the overlay image roughly into alignment with the base image. Fine-tune the alignment by further translating and rotating the overlay CT image using the chest structures such as the thoracic cage, upper spine, and sternum as reference. Next, turn on the overlay CT image and its corresponding PET image by clicking the eye icon to the left of each image name.
Change the opacity of both the PET and CT images to 50%Then use translate or rotate tools in the 2D views to align the PET image with its corresponding CT image based on the bone structure in the CT image and fluoride-18 labeled sodium fluoride bone surface in the PET image. To identify cardiovascular calcification, select the time point with the largest predicted calcified regions in the longitudinal study. Choose the image corresponding to this time point as the reference image.
Then turn on the reference CT image by clicking the eye icon to the left of the image. Select the track tool under the manipulate dropdown and move the axis center around the cardiac region. Now zoom in to locate calcified regions superimposed over the cardiac silhouette between the thoracic cage, sternum, and spine.
Then move the track axis to hover over the calcified region, ensuring visibility in all 2D views. Turn on the corresponding PET image to validate the presence of calcification. Turn off the PET reference image.
Then make sure the CT reference image is turned on and selected. Find the shapes dropdown and choose the sphere shape. After that, navigate through the 2D views to carefully position the sphere.
In the data properties and settings dropdown, right-click on the sphere name and choose add to region of interest. Then select new region of interest. Now assign an appropriate name to the newly created region of interest.
Under geometry, select the CT image for which the region of interest is to be generated. To turn on the region of interest, click the eye icon to the left of the region of interest name and observe the colored region of interest corresponding to the size of the previously drawn sphere. Then find the segment tab to the left of the display screen next to the main tab.
Select the reference region of interest in the data properties and settings dropdown. Locate the range dropdown under the segment tab and check the defined range option. Use the selected range box to change the defined range.
Ensure the defined range encapsulates all noncalcified pixels with Hounsfield unit values below the calcium threshold. Once the selected range is configured, click remove to eliminate all pixels beneath the specified threshold from the sphere region of interest. Select the region of interest to be quantified from the data properties and settings dropdown.
Find the statistical properties dropdown on the right side located below the basic properties dropdown. Then locate the dataset table under statistical properties. Using the dropdown menu on the right, choose the appropriate imaging dataset corresponding to the region of interest being quantified.
Click refresh to acquire the quantified values of the selected calcified region. Use the mean values displayed for quantification. Locate the volume calculation at the top of the statistical properties box and use this volume for quantification.
Calculate the volumetric calcium content by multiplying the mean region of interest value by the volume of the region of interest. To quantify the PET image, select the PET dataset corresponding to the region of interest. Convert the result to Becquerel's per cubic millimeter by dividing the mean region of interest value by the volume of the region of interest.
The volumetric calcium content in the mouse increased from 15 months to 18 months. The fluoride-18 labeled sodium fluoride PET activity, which measures the surface area of the calcified region, decreased from 15 months to 18 months.
