Brain Imaging

Question 1

What is radiation dose measured in? What is 1yr background radiation? What is the dose of CT head?

Answer 1

Milliseverts (mSv)

2.7

2

Question 2

How does a CT scan work?

Answer 2

Uses XRs (pass through tissues dif depending on their density)

Scanner has an XR tube and multiple detectors that rotate around the patient

XRs taken from many angles –> 1 rotation has 1000 profiles taken and is the equivelent to 1 slice

The profiles data are reconstructed into 1 slice (5-10mm CTH) which is a 2D image

Question 3

What is the measurement for tissue density in CT?

Answer 3

Hounsefield unit

Question 4

What is the appearance of subdural haemorrhage on CT? Why does this occur?

Answer 4

Crescent shaped due to blood collecting between dura and arachnoid mater, so haematoma conforms to the Brain surface and can cross suture lines)

Question 5

Typical presentation of subdural haemorrhage?

Answer 5

Progressive headache, drowsy, confusion, N/V, confusion, personality changes

Question 6

What is the appearance of extradural haemorrhage on CT?

Answer 6

Convex shaped due to blood collecting between skull and dura mater –> doesn’t cross sutures

May see skull fracture on CT

Question 7

What is the appearance of SAH on CT?

Answer 7

Bright blood in fissures and in ventricles

Question 8

What are the NICE criteria for for CTH after head injury?

Answer 8

1. GCS <13 at initial ED assessment
2. GCS <15 2 hrs after injury
3. Focal neurological deficit
4. > 1 episode vomiting
5. Post traumatic seizure
6. Suspected skull fracture (depressed or open)
7. Signs of base of skull fracture (battles sign, panda eyes, haemotympanum, CSF leakage ear/nose)

Question 9

Why would you use MRI over CT for imaging the brain?

Answer 9

MRI gives better anatomical detail, better at visualising vasculatuee and intracranial pathology

Also better for posterior cranial fossa

Can be used in suspected stroke if CT unremarkable

Modality of choice in MS (shows lesions)

Question 10

what are the indications of acute CTH?

Answer 10

1. Exclude life-threatening intracranial pathology
2. Confirm Dx intracranial pathology
3. Head injury pts (esp. dementia + intoxicated)

Question 11

What contrast mediums can be used for brain imaging?

Answer 11

1. Iodine contrast w/ CT
2. Gadolinium w/ MRI

For tumours!!!!!! (BBB disrupted therefore uptake of contrast)

Question 12

How can SPECT be used to image the brain?

Answer 12

Look at blood flow –> T99 labelled w/ exametazine