 The patient's spinal fluid is injected with a radiopharmaceutical tracer, such as DTPA tagged with indium 111, through a lumbar puncture (spinal tap).The tracer will diffuse up the spinal column and into the intracranial ventricles and the subarachnoid spaces around the brain.The progress of the tracer's diffusion through the CSF will be recorded by a nuclear medicine gamma camera.