Answer: Positron emission tomography (PET) scan
Step-by-step explanation:
Position emission tomography, also known as a PET scan, is a scan which purpose is to give the doctor a view of diseases in the individuals body. They reveal how the organs and tissue in the body work. This scan is done by using a radioactive drug known as tracer to carry out the scan. The PET scan is also known as an imaging test. From Tierney's description it is observed that a PET test was carried on him because radioactive chemicals were injected into his bloodstream to record the images of his brain cell.