Final answer:
A physician may use ultrasound, MRI, or CT scans to determine the depth of an infection and might also perform a tissue biopsy for laboratory analysis to identify specific pathogens.
Step-by-step explanation:
To determine the depth of an infection, particularly if a deeper structure like muscle or fascia is involved, a physician may perform various diagnostics. Imaging studies such as an ultrasound, MRI (Magnetic Resonance Imaging), or a CT scan (Computed Tomography) can be employed to visualize the extent of the infection beneath the skin's surface. In some cases, a tissue sample or biopsy might be taken for laboratory analysis to identify any specific bacteria or pathogens, and this can help tailor antibiotic treatment effectively.