Hi,
Thanks for consulting HealthcareMagic!
Your excessive gas may be one of the reason for pain under
rib cage, radiating to back. If this is the case
ultrasound may look normal. However, Physical examination is mandatory to comment more.
Try eating fiber rich diet including good amount of fruits, cereals etc. Also, drink more water if it is not contraindicated due to coexisting conditions.
However, CT abdomen is sometimes more precise in finding abnormalities which are not found by ultrasound.
Hope I have answered your query. Let me know if you have have any clarifications.
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http://doctor.healthcaremagic.com/doctors/dr-vasanth/66057
Wish you good health!