Diagnostics

I don’t understand this Health & Medical question and need help to study.

Recommend a type of diagnostic image, with or without contrast for the following patients:

• A patient with persistent lower back pain resistant to conservative interventions
• A 74-year-old male with dyspnea, productive green phlegm, fever and chills, and malaise
• A 48-year-old female who is 48-hours postoperative complaining of right-calf pain

Part-2

• When are computed tomography (CT) scans indicated?
• When are magnetic resonance imaging (MRIs) indicated?
• What helps the FNP decided whether to use contrast or not when ordering a CT scan or MRI?

at least 200 words