This article explores an innovative real-time microwave imaging technique appropriate to diagnose diseases such as sarcopenia where it is important to understand muscle loss, or potentially to detect breast cancer or measure bone density. The microwave sensor makes use of open-ended coaxial probes with the convenience of ultrasound and excellent differentiation between muscle and fat characteristic of an X-ray CT scan. A refinement of the open-ended coaxial probe design enlarges the aperture at the probe end to increase depth performance. Simulations were conducted from 100 MHz to 8GHz, and human trials indicated superior performance around 2GHz to accurately determine fat thickness, fat echo intensity and muscle echo intensity.