How do I convert MTOM attachment to binary data

[prabhup1]

a. Create a SOAP based API Proxy that receives MTOM attachment b. Convert MTOM to binary data and store it in a variable. c. Create a new XML message (Assign Message) and insert the binary data into the new XML. d. Make a ServiceCallout to a virus scanning software using the new XML. e. If successful, pass the original message as-is to the backend service.

I need the binary data in step b. because the virus scanning software accepts inline binary data only not MTOM.