Imaging the Nervous System Flashcards
What is the CNS imaging modality of choice in neonates and infants?
Cranial ultrasound
Why is cranial ultrasound the imaging modality of choice in neonates and infants?
Due to the ease of scanning via the open anterior fontanelle
What are the advantages of cranial ultrasound?
Quick and non-invasive
What are the disadvantages of cranial ultrasound?
Highly operator dependant
What do repeat cranial ultrasounds over time allow for?
Evolution and progression of lessons to be monitored
What is cranial ultrasound particularly used for?
- Intraventricular haemorrhage
- Ischaemic cysts of periventricular leukomalacia (PVL)
- Ventricular dilatation
- Range of cerebral malformations and other lesions, e.g. agenesis of the corpus callosum
What is MRI much better at than cranial ultrasound?
- Detecting ischaemic lesions, e.g. hypoxic-ischaemic encephalopathy or PVL
- Detailed anatomy of cerebral malformations
What are the advantages of cranial CT?
- Widely available
- Rapid
What is cranial CT used for?
- Head trauma
- If clinical condition unstable
- Intracranial calcification
- Haemorrhage
How can cranial CT images be enhanced?
With the use of contrast
Why has cranial CT been largely replaced by MRI?
- Does not require radiation
- Usually more informative
What is MRI imaging the technique of choice?
In most paediatric neurological disorders
What is the purpose of different sequences in MRI?
Can be used to interrogate the signal to answer particular clinical questions
What are the different sequences in MRI?
- T1
- T2
- FLAIR (fluid attenuated inversion recovery)
Describe the appearance of CSF, grey matter, and white matter on T1 MRI sequence?
- CSF appears black
- Grey matter is grey
- White matter is white or paler grey
What is T2 sequence used for?
Assessing tissue fluid contents, such as oedema
How does CSF appear on T2 MRI sequence?
White
What is FLAIR sequence used for?
Lesions close to the ventricles
What is the purpose of FLAIR sequence?
Signal from CSF is reduced to allow clearer tissue imaging
How does a solid mass appear on;
a. T1
b. T2
c. FLAIR?
a. T1 - dark
b. T2 - bright
c. FLAIR - bright
How does a fluid-filled cyst appear on;
a. T1
b. T2
c. FLAIR?
a. T1 - dark
b. T2 - bright
c. FLAIR - dark
How does subacute blood appear on;
a. T1
b. T2
c. FLAIR?
a. T1 - bright
b. T2 - bright
c. FLAIR - bright
How does a acute and chronic blood appear on;
a. T1
b. T2
c. FLAIR?
a. T1 - grey
b. T2 - dark
c. FLAIR - dark
How does fat appear on;
a. T1
b. T2
c. FLAIR?
a. T1 - bright
b. T2 - dark
c. FLAIR - bright
What has increased availability of MRI scanning in children allowed for in a wider sense?
Expand knowledge about pathological processes occurring in children with encephalopathy
What does functional MRI allow for?
Visualisation of regional oxygen consumption and blood flow
What is functional MRI used to examine?
Brain activity
What does functional MRI create?
A map showing which parts of the brain are involved in a particular task, such as movement or speech
Where is functional MRI being increasingly used?
In pre-surgical assessment of children being considered for epilepsy surgery
What does functional MRI allow in the pre-surgical assessment of children being considered for epilepsy surgery?
More accurate prediction of post-op functional outcome
Give an example of a disorder that functional MRI has enhanced understanding of?
Autism
What is MRA?
Magnetic resonance angiography
What does MRA permit?
Non-invasive assessment of the intracranial vascular system
Where is MRA of particular use?
Conditions such as intracranial arteriovenous malformations, e.g. Sturge-Weber syndrome, and blockages/stenosis
What is MRS?
Magnetic resonance spectroscopy
What does MRS rely on?
The individual resonance properties of certain molecules within brain tissue
Give three examples of molecules that have known resonance properties?
- Lactate
- Choline
- Creatinine
What can MRS detect?
High levels of metabolites or other target molecules in conditions
Give 5 examples of conditions that might have high levels of metabolites/other target molecules that might be picked up by MRS?
- HIE
- Brain injury
- Epilepsy
- Metabolic disorders
- MS
What does raised lactate on MRS signal?
A metabolic disorder
What is a promising area of research with MRS?
Into tumours, as choline signals are often elevated in tumour tissue
Is MRS widely available?
No, restricted to larger research centres
How does PET imaging work?
A labelled radioactive tracker is injected into the body, which gives off gamma rays that are detected by a scanner
What does the information gained from PET imaging depend on?
What molecule the tracker was attached to
Give an example of a molecule a tracker might be attached to on PET, and what these images would reflect?
Flurodeoxyglucose
Images will reflect regional glucose uptake, and therefore the metabolic activity of the tissue
What is the main indication of PET scanning in paediatric neurology?
To identify precise areas of seizure onset in focal epilepsy, therefore identifying possible targets for epilepsy surgery
