It is likely the size of the possible nodule or lump found in your thyroid area.
The CT scan or MRI are not very accurate to measure the size of lobes, but they may detect some tumor like abnormalities
Important Note: During your Carotid Artery screening, a suspected other abnormality has been identified. Please
take this report and the copy of your ultrasound images to your physician to determine the clinical significance of
this incidental finding. Please note that conditions may also exist that are not detected at the time of the screening.
Location: Thyroid Size: 1.7x1.0x1.3 cm
Is that all the information they gave you? Was that just one lobe or both lobes plus isthmus? What was the basis for their recommendation that you see your doctor?
If you have a printed report (which they should have given you), what exactly does it say?