Final answer:
For a suspected left lobar hemorrhage in an elderly patient, the best immediate diagnostic test is a Noncontrast head CT scan, as it provides rapid assessment crucial for stroke management.
Step-by-step explanation:
The best immediate diagnostic test of choice for a 72-year-old woman presenting with acute onset of obtundation, dense right hemiplegia, and mutism, suspecting a left lobar hemorrhage, is a Noncontrast head CT scan. This diagnostic tool is crucial in the acute setting for identifying hemorrhagic strokes, as it can quickly detect the presence of blood within the brain tissue and help distinguish between ischemic and hemorrhagic stroke. It is less time-consuming than an MRI and can be more readily available in most emergency rooms, allowing for rapid assessment and management, which is essential in acute stroke patients.