Could an ultrasound detect what an mri doesn't?

US vs MRI: Generally MR is more robust than ultrasound (US). It has better spatial resolution and is also not limited by bone or air which causes artifact and shadowing on ultrasound. It also has much better tissue contrast. Ultrasound can resolve smaller tissue abnormalities than MR, but not by much. US is often first but then MR unless there is a contraindication to MR (retained metal, pacemaker, etc)