GUIDELINE ENDOMETRIAL THICKENING:
Premenopausal with or without bleeding:
Normal up to 18-20 mm or 16mm if morphologically abnormal or heterogeneous.
Post-menopausal with bleeding:
Normal up to 4 mm.
5 mm or greater needs further evaluation with histologic sampling or sonohysterography.
Post-menopausal without bleeding:
Normal up to 8 mm maximum thickness.
9 mm or greater needs further evaluation with histologic sampling or sonohysterography.

Ultrasound Guidelines for Pregnancy Loss

Radiopaedia

Gallbladder Polyps

Radiographics
Radiopaedia – Overview
Radiopaedia – Benign vs Malignant

Lung-RADS Criteria

ACR Guidelines
References:
Ultrasound Obstet Gynecol 2004; 24(5):558-65.
J Am Coll Radiol 2011;8:460-468.
J Ultrasound Med 2001 Oct; 20(10): 1025-36.