Calf pain is a very common clinical condition that can be caused by a variety of causes, including deep vein thrombosis (DVT). Ultrasound is one of the most commonly used imaging modalities to detect the cause of calf pain because it clearly shows the anatomy of the calf. Lee et al. from South Korea reviewed various causes of calf pain other than DVT and their ultrasound presentation and clinical features, and the article was published in the 9th issue of Clinical Imaging in 2015. This is a well-developed article for diagnosing calf pain, and I have learned a lot to share with the channel. Technique and equipment: 1, Before each ultrasound examination, the patient should be asked for a medical history and asked to indicate the most uncomfortable areas. 2, Try to use a high-frequency probe (≥ 7MHz), supplemented with a low-frequency convex array probe if necessary. 3.In addition to two-dimensional ultrasound, color and spectral Doppler are added to assess the blood flow in and around the lesion. 4. The patient is usually placed in a supine position with a small soft pad placed proximal to his ankle. Cystic lesions: 1. N fossa cyst (Baker Cyst) N fossa cyst is an enlarged semimembranose-gastrocnemius bursa between the medial head of the gastrocnemius muscle and the semimembranosus tendon. It is the most common cystic lesion near the knee joint and is usually asymptomatic. Pain and progressive swelling of the lower leg can result from enlargement of the cyst, rupture, or leakage of bursa fluid between the gastrocnemius muscles. traffic between the bursa and the knee joint can occur in more than half of patients over 50 years of age. Ultrasonographically, N-fossa cysts appear as a tubular fluid-free or hypoechoic area between the semimembranous tendon and the medial head of the gastrocnemius muscle with postero-lateral extension to the medial gastrocnemius muscle. This tubular echo is key to differentiating N-fossa cysts from cysts or cystic tumors of other causes in the N-fossa. Some N fossa cysts can be clearly visualized only in the standing position because gravity and postural factors increase the intra-articular pressure during standing, thereby enlarging the semimembranosus-gastrocnemius bursa. rupture of the N fossa cyst may present as a small anechoic area caudal to the cyst or as a large dark area of fluid extending to the lateral aspect of the medial head of the gastrocnemius muscle.