Neuroradiology Flashcards
What are the different imaging modalities?
CT MRI Plain film radiography vascular doppler ultrasounds transcranial ultrasound radioisotope studies minimally invasive diagnostic procedures
What is a CT scanner?
uses XR to obtain detailed images of the body
widely available technique
fast technique making it very useful in acute care
more efficient but radiation dose remains a concern which is governed by a comprehensive set of regulations
What is meant by the terms CT attenuation or density?
density can be quantified using hounsfield units: -1000 to 1000 (-1000= air and 1000= cortical bone)
hyperattenuating (hyperdense) e.g. bone, bleed, mineralisation
hypoattenuating (hypodense) = air, fat, fluid containing spaces and oedema
isoattenuating (isodense)
What are CT artefacts?
due to patient, physics or hardware related factors
- have a variety of densities depending on the type
What occurs in ischemia of the brain?
cell damage => retention of salt and water in the cells
What happens in vasogenic oedema?
abnormal vessels => fluid leak into extracellular space
- seen in tumour, infection and inflammation
How does MRI work?
image acquisition technique based on the behaviour of proteins in the body while subjected to a magnetic field and radiowaves
modality of choice due to high tissue contrast and wide variety of acquisition technique
widely available but access remains limited due to the length of scanning which is considerably longer than CT
What are the contraindications for MRI?
Non MR conditioned pacemakers
What other factors limit the use of MRI?
length of image acquisition makes it a less likely choice for a confused patient, certain headand whole spine protocol can take up to 90mins
bore is narrower than CT so less likely tolerated by claustrophobic patients = there are wide bore and open scanners available now
occassionally pts are sedated or scanned under GA
What is meant by MRI sequences?
variety of acquisition techniques available depending on radiofrequency pulse and gradient used
most widely used are T1 and T2 sequences - fluid and fat suppressed techniques e.g. STIR and FLAIR
occasionally MR spectroscopy, MR perfusion and function MRI can be performed
What does hyperintense and hypointense mean in terms of MRI?
Hyperintense = high signal Hypointense = low signal
What are some different IV contrasts in neuroimaging?
CT- iodine based = iodine is highly attenuating of XR beam
MRI - gadolinium-based
- paramagnetic metal that hastens T1 relaxation
- tissues become brighter after admin of IV contrast =”enhancing” - however its important to compare to non-contrast images as not all bright tissues are enhancing
e. g. BBB keeps IV away from the brain tissue - enhancement therefore indicates the BBB is dysfunctional (anterior pituitary is outside the BBB)
What are the risks of iodinated contrast?
contrast reaction
- 1 in 10,000 true anaphylactic reaction
- 1 in 100,000 to 1 in 1,000,000 die
medical issues
- acute renal failure
- lactic acidosis in diabetics (if on Glucophage pts must stop it for 48 hours after to prevent serious lactic acidosis)
- cardiac
extravasation
What are the RF for contrast induced acute renal failure?
pre-existing renal insufficiency contrast volume dehydration advanced age drugs multiple myeloma cardiac failure
What are the advantages of CT?
Quick, cheap + accessible
tolerated by claustrophobics
no absolute contraindications
What are the disadvantages of CT?
Risk associated with ionising radiation
limited range of tissue contrasts
What are the advantages of MRI?
high quality tissue contrast
significantly better anatomic detail
multiple sequences allow more comprehensive analysis of pathology
no ionizing radiation
What are the disadvantages of MRI?
Higher cost, limited access
difficult for unstable pts
several contraindications = cardiac pacemaker (exp MR conditional), some aneurysm clips
claustrophobics may need sedation
What diagnostic interventional neuroradiology techniques are there?
cerebral angiography
spinal angiography
vertebral lesion biopsy
image guided LP
What therapeutic interventional neuroradiology techniques are there?
embolisations e.g. AVM, aneurysm and tumours
thrombectomy for stroke
vertebroplasty
nerve root block
What is digital subtraction angiography used for?
assessment of vascular abnormalities
What are the advantages and disadvantages of digital subtraction angiography?
Adv
- time resolved blood flow dynamics
- high spatial and temporal resolution
Disadv
- invasive, risk of vascular injury and stroke
- iodinated contrast and ionising radiation related risks
What are the indications for US in neuroradiology?
carotid assessment
assess post subarachnoid haemorrhage
infant brain imaging
What are the advantages of US?
Non-invasive, well tolerated, readily available, low cost
quantitative assessment of blood velocity
morphological assessment of atheromatous plaques
What are the disadvantages of US?
Difficult to assess severe stenosis
limited coverage
operator dependent
