Hi welcome to health care magic forum.
well, there is a difference but stomach x ray can reveal only few pathologies unlike ultrasoound which is more specific for abdomen. stomach xray can show signs of ilesu, ureetral or gallbladder
stones ,colon obstruction or larger tumors and hernias
but if there are some doubts about abdominal pathology then ct scan
should be performed. his weak legs should be checked by leg ultrasound
to verify blood flow .
Hope I have answered your query.