X-ray vs airport x-rays

Recently we went on vacation and at the airport scanner TSA pulled my husband aside and asked him if he knew he had a mass on his back. Then leaving our vacation site, thousands of miles away, the airport scanner personnel again pulled my husband aside and asked the same question. After we were home he said something to me. You can't see or feel anything. He went to his doctor, got a x-ray and it was negative. My question is can the 3 D airport scanner see something reg x-ray can't? Should he insist on MRI? Any thoughts or input would be appreciated.
I can see where that would cause concern. We cannot offer medical advice other than to encourage you to seek further advice from your physician or obtain a second opinion.We wish you luck in obtaining further information.