A 70 year old man with prostatic cancer has had severe acute back pain waking him up at night for 6 weeks. What is the most appropriate investigation?

The key is B. Radionuclide bone scan. [MRI is good for soft tissue but not for bone. If it was radiculopathy, spinal cord compression or prolapsed disc creating pressure on nerve MRI would be fine but not for bony metastasis. Here investigation of choice is radionuclide bone scan].