Ultrasound is one of the most important tools to differentiate between benign (non-cancerous) and malignant (cancerous) thyroid nodules. However, ultrasound cannot definitively diagnose malignancy; a biopsy is often required for that. Here's a comparison of some typical ultrasound characteristics that might suggest benign vs. malignant thyroid nodules: 

Benign Thyroid Nodules:

-Composition: Often cystic or mixed cystic and solid; more homogeneous.

-Margins: Generally smooth and well-defined.

-Shape: More likely to be round or oval.

-Echogenicity: Isoechoic or hyperechoic compared to the surrounding thyroid tissue.

-Halo Sign: Presence of a hypoechoic or anechoic halo around the nodule.

-Growth Pattern: Tends to grow slowly if at all.

-Calcifications: Rarely shows calcifications, and if present, they tend to be large and peripheral.

-Vascularity: May demonstrate peripheral vascularity if blood flow is present.

Malignant Thyroid Nodules:

-Composition: Predominantly solid; may be more heterogeneous.

-Margins: Irregular, lobulated, or poorly defined.

-Shape: Taller than wide on a transverse view, which is a suspicious finding.

-Echogenicity: Hypoechoic compared to the normal thyroid gland.

-Halo Sign: Typically absent.

-Growth Pattern: May grow more quickly, although this isn't always the case.

-Calcifications: Presence of microcalcifications (tiny, punctate echogenic foci) is highly suggestive of malignancy.

-Vascularity: May demonstrate increased intranodular vascularity.

It's important to note that these characteristics are not definitive, and there can be overlap between benign and malignant features. Clinical context, patient history, physical examination, and further diagnostic evaluation, such as a fine-needle aspiration biopsy, are often needed to make an accurate diagnosis.

The radiologist will often use these characteristics to categorize the nodule's risk of malignancy according to a standardized system such as the American College of Radiology (ACR) Thyroid Imaging Reporting and Data System (TI-RADS). This system helps guide further management and whether or not a biopsy is warranted.