Brain imagingEdexcel A-Level Biology A: Subtopic test

1. 1
   A 68-year-old woman arrives at an accident and emergency department after a sudden, severe headache and weakness down one side of her body. Doctors need to find out quickly whether she has bleeding inside her skull.

   (a)

   Which scan is most suitable as the first investigation for this patient?

   [1 mark]

   • AAn fMRI scan, because it shows which areas are active, even though it takes a long time
   • BA PET scan, because it gives detailed structural images of blood vessels
   • CAn MRI scan, because it is quicker than CT and needs no preparation
   • DA CT scan, because it is quick and shows structural damage such as bleeding

   (b)

   Which is a disadvantage of a CT scan?

   [1 mark]

   • AIt cannot distinguish bone from soft tissue
   • BThe patient is exposed to ionising radiation
   • CIt uses a strong magnetic field that can move metal implants
   • DIt needs a radioactive glucose analogue to be injected

   (c)

   Explain how a CT scan can show the difference between brain tissue, skull bone and a collection of blood.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A research team wants to find out which areas of a volunteer's brain are most active while she solves arithmetic problems. The team compares two functional imaging techniques, fMRI and PET.

   (a)

   What does an fMRI scan detect?

   [1 mark]

   • AGamma rays produced when positrons meet electrons
   • BX-rays that have been absorbed differently by tissues
   • CChanges in the oxygen content of the blood supplying active brain areas
   • DElectrical impulses produced directly by neurones

   (b)

   Which is an advantage of fMRI over PET for this volunteer?

   [1 mark]

   • AThe volunteer is not injected with a radioactive tracer or exposed to ionising radiation
   • BfMRI measures glucose uptake directly, whereas PET does not
   • CfMRI can be used safely on people with pacemakers or metal implants
   • DfMRI uses X-rays to show bone more clearly than PET

   (c)

   Explain why an active area of the brain shows up on an fMRI scan.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A patient with suspected Alzheimer's disease is injected with a glucose analogue labelled with a radioactive isotope that emits positrons. A PET scan shows much less uptake of the tracer in some regions of the cerebral cortex than in a healthy brain.

   (a)

   Explain how a PET scan produces an image of activity in the brain.

   [3 marks]

   (b)

   The patient is also given an MRI scan. Explain what the two scans together can show and state one limitation of the PET scan.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A regional hospital can afford only some of the brain scanning equipment available: CT, MRI, fMRI and PET. A neurologist is asked to advise on how each technique would be used in diagnosis and in research.

   (a)

   Compare CT and MRI scans for investigating the structure of the brain.

   [6 marks]

   (b)

   Evaluate the use of fMRI and PET scans to investigate brain function.

   [6 marks]

   Total for question 4: 12 marks

End of questions