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MaaritPalomäki

Clinical Use of Neuroradiological Imaging

Essentials

  • Always consider, whether the possible benefit from the investigation is greater than the harm to the patient due to radiation exposure.
  • Computed tomography (CT) is the easiest and most rapid method for identifying intracranial haemorrhages and for acute differential diagnosis between cerebral haemorrhage and infarction.
  • Magnetic resonance imaging (MRI) is the best method for the examination of the brain and the back. It is, however, slower than CT and not so easily available.
  • Carotid ultrasonography is a non-invasive and easily available first-line procedure for detecting carotid artery stenoses and changes in the arterial walls. It is often used when investigating the aetiology of disturbances of the cerebral circulation.

Computed tomography (CT) Magnetic Resonance Imaging Versus Computed Tomography for Detection of Acute Vascular Lesions in Patients Presenting with Stroke Symptoms

  • Usually the first examination especially in the investigation of cerebral events due to its rapidity and easy availability. If needed, it may be combined with angiography and perfusion study.
  • CT scan is often normal at the initial phase (< 3 hours) of acute cerebral infarction. It can be used to exclude cerebral haemorrhage before initiation of thrombolytic therapy.
  • Contrast medium enhancement adds accuracy to the diagnosis, if the disease process involves blood-brain barrier damage or abnormal neovascularisation, but MRI is often needed for further evaluation of the findings.
  • CT scan is not suitable for studying spinal canal processes unless information on bony structures is sought for.

CT angiography

  • High radiation exposure must be kept in mind.
  • Can be used for imaging of the carotid arteries e.g. when ultrasonography has aroused suspicion of stenosis and endarterectomy is planned.
  • Indications for emergency CT angiography
    • Fresh subarachnoid haemorrhage (CT angiography of the cerebral arteries)
    • Suspected sinus thrombosis (CT angiography of the venous sinuses)
    • Suspected carotid artery dissection
    • Critical/significant stenosis of the carotid artery detected by ultrasonography, if emergency endarterectomy is planned.

Magnetic resonance imaging (MRI) Imaging of Vertebral Artery Stenosis, Magnetic Resonance Imaging Versus Computed Tomography for Detection of Acute Vascular Lesions in Patients Presenting with Stroke Symptoms

  • See also Incidental Findings on Brain Magnetic Resonance Imaging (Mri)
  • Does not use ionizing radiation.
  • Produces image planes of different orientations and several different image types that help in the assessment of the changes.
  • The examination is targeted according to the problem. A well-formulated referral form is essential for a successful examination.
  • Well suited for longitudinal examination of the vertebral canal, and often yields more information on the brain than CT. Processes in the posterior cranial fossa and in the brainstem can only be excluded by MRI.
  • Contraindications
    • Pacemaker (nowadays not always an absolute contraindication) and other implanted electronic devices
    • Intracorporeal magnetizing metal objects (older aneurysm clips), metallic inner ear prostheses
    • Claustrophobia (sedation may be used if necessary)

Magnetic resonance angiography (MRA)

  • MRA can be used to visualize blood vessels. It is suited e.g. for screening for aneurysms in SAH families.
  • MRA of the carotid arteries is used in planning of endarterectomy if CT angiography is not feasible (e.g. in renal failure).
  • MRA of the cerebral arteries is used e.g. in suspected cerebral vasculitis or aneurysm.

Ultrasonography of carotid arteries

  • When the examination is performed by an experienced practitioner, the results correlate well with angiographic findings.
  • The procedure is used
    • as a screening method when looking for carotid artery stenoses in patients with disorders of the cerebral circulation
    • before coronary surgery when looking for possible symptomless carotid stenoses that may affect anaesthesia.

Digital subtraction angiography (DSA)

  • Sometimes neuroradiological angiographies require admitting the patient to the hospital.
  • Indications for carotid artery angiography
    • The planning of endarterectomy due to the stenosis of carotid artery is nowadays carried out by CTA or MRA. DSA is used in exceptional cases only (planning and execution of an endovascular procedure).
    • SAH, suspected aneurysm in exceptional cases (CTA is the primary method); treatment of the aneurysm by endovascular coiling
    • Investigation of the vascularisation of a known brain tumour or arterio-venous (AV) malformation before surgery. Endovascular treatment is usually performed in association with the investigation.
  • Indications for vertebral angiography
    • In principle these are the same as those for carotid angiography, when the lesion is located in the region of vertebrobasilar circulation.
    • The risk of complications is clearly greater than with carotid angiography, and the examination can only be performed on young patients (ca 50 years or less).
  • Indications for aortic arch angiography
    • Subclavian steal syndrome, if endovascular treatment is considered (CTA or MRA are sufficient for diagnostics)
  • All the mentioned angiography examinations carry a risk of stroke of approximately 1%.

Echoencephalography

  • Primary investigation in infants with open fontanels
  • Detection of peri- and intraventricular haemorrhages in neonates and evaluation of the amount of CSF in cerebral ventricles in case of hydrocephalus suspicion
  • Assessment of the structures in the central parts of the brain

Radioisotope investigations

  • Radioisotope techniques (PET, SPET) have clinical significance as additional investigations supplementing structural imaging modalities in certain cases where differential diagnosis is problematic.

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