Can Ultrasound detect cancer in lymph nodes?

It depends. Ultrasound is commonly used to check the condition of the lymph nodes. But the results are dependent on the experience of the sonographer(radiologist). A good sonographer can tell if a lymph node is benign or suspect for Cancer. The final answer(to be 100% certain) requires a biopsy of a suspicious lymph node(if it is enlarged to 1cm or more in size)