Neuroimaging – A Review

PM&R News   •   March 2021

Imaging Description Pros Cons Identifies/Utilized in the following:
CT  (computed tomography) head w/o contrast Analyzes residual radiation waves emitted from the body via a radiographic tube that is rotated axially. Utilizes mathematical algorithms of images to reconstruct a cross-sectional image.
  • Fast
  • Not sensitive to motion
  • Widely available
  • Primary choice: acute/emergent situations
  • Radiation exposure = increased lifelong risk of cancer (minimal)
    • “may impair long-term cognitive function”(UTD)
  • Identifies calcifications
  • Hemorrhagic CVA
  • Intracranial hematoma (<12 hrs)
  • Infraction
  • Bony/air space abnormalities
  • Edema, herniations, fx, hypoxic-ischemia injury, mass, hydrocephalus
  • ASPECTS score: assists to determine tx
  • Superior over MRI in the following: intracranial lesions, demyelinating diseases, acute trauma
CT head with contrast Analyzes residual radiation waves emitted from the body via a radiographic tube that is rotated axially. Utilizes mathematical algorithms of images to reconstruct a cross-sectional image.
  • Vascular enhancement compared to non-contrast
    • can see malformation or disruption of BBB
  • Distinguish acute vs chronic bleeding
  • Distinguish infarct from abscess/neoplasm
  • Used to guide tissue acquisition in open-bx
 Allergy to contrast
  • F/u for brain abscesses
  • Vascular malformation, infarction, neoplasm, abscess, empyema, head and neck masses.
MRI  (Magnetic resonance imaging) w/o contrast Analyzes/measures atomic nuclei via defined timing of magnetic movements; emission of radio signals when radio waves are administered. These changes reveal a MR image.

  • Images acquired: transverse, sagittal, oblique, & coronal views.
    • T1: magnetic changes in the Z-axis
    • T2: magnetic changes in x & y axes.
  • “Each tissue, normal or pathologic, has unique T1 and T2 for a given MRI field strength.”
  • W/ contrast: Gadolinium (gadopentetic dimeglumine) enhances vasculature
  • Diffusion-weighted*: Sn (88% – 100%) and Sp (95% – 100%) and accurate (95%)
  • higher ST contrast than CT
  • No ionizing radiation
  • Ability to have multiple viewpoints without moving pt.
  • Challenging to perform in morbidly obese pt.’s
  • Contraindicated with metal (unless MR compatible/conditional)
  • More difficult to utilize in those with claustrophobia
  • Inability to examine those w/ life-saving equipment on them
  • Visualizes linear structures (SC, vena cava)
  • Visualizes posterior fossa and other difficult CT areas
  • Unexplained hydrocephalus
  • Hypothalamic/pituitary disorders
  • New onset (esp. focal) seizures
  • Tx and follow-up for neoplastic diseases
  • Infectious encephalitides
  • Orbital pathology
  • Sensorineural hearing loss
  • CVA: ischemic/hemorrhagic
  • Spinal column evaluation
MRI with contrast See Above
  • Improved vascular visualization
  • Greater specificity with vascular/hemorrhagic etiologies, than CT
    • identifies staging better
  • Distinguishes infarction from hematoma in atypical presentation
  • Differentiates types of vascular malformation
  • Challenging to perform in morbidly obese pt.’s
  • Contraindicated with metal (unless MR compatible/conditional)
  • Difficulty utilizing: pt.’s allergic or renal issues
  •       GFR** > 30
  • Same as above but improved visualization in vasculature
CTA (computed tomography with angiography) Contrast: rapid bolus administration into antecubital fossa for visualization of a timed helical CT scan
  • Faster than MRA
  • Obtained concurrently with CT
  • Compared to CT for large vessel occlusion/stenosis:

Sn: 92-100%; Sp: 82-100%

  • Estimates perfusion
  • Assesses large vessel occlusion in candidates for mechanical thrombectomy
  • Difficulty utilizing: pt.’s allergic or renal issues
  • Radiation exposure
  • vessel thrombosis/occlusion
  • vascular malformations
  • dissection
  • vasculitis
  • aneurysm
  • stenosis/occlusion (large vessels)
  • pediatric CVA
MRA (magnetic resonance with angiography)
  • Utilizes “ultrafast acquisition of T1-weighted three-dimensional GE data sets, typically obtained during a breath hold.”
    • stationary tissue leads to decreased signal
    • Blood flow will have higher signal
  • Does not require contrast: Can be utilized in those with allergies to contrast
  • Doesn’t use ionizing radiation like in CTA
  • large vessel occlusion/stenosis compared to CT:

Sn: 86-97%; Sp: 62-91%

  • Assesses large vessel occlusion in candidates for mechanical thrombectomy

Differentiates arterial vs. venous occlusive disease
  • Challenging to perform in morbidly obese pt.’s
  • Contraindicated with metal (unless MR compatible/conditional)
  • Time consuming
  • Not available in all locations
  • large vessel occlusions
  • atherosclerotic lesions

*DWI: “The final result will be diffusion restriction of water molecules in the infarcted tissue, which can be detected by DW sequence”

**GFR = glomerular filtration rate

📸Photo by Milad B. Fakurian on Unsplash

References:

  1. https://www.ncbi.nlm.nih.gov/books/NBK546635/
  2. https://accessmedicine.mhmedical.com/content.aspx?sectionid=43074924&bookid=365#2695053
  3. https://www.uptodate.com/contents/approach-to-neuroimaging-in-children?search=CT%20with%20contrast&source=search_result&selectedTitle=4~150&usage_type=default&display_rank=4#H7
  4. https://www.uptodate.com/contents/neuroimaging-of-acute-ischemic-stroke?search=CT%20angiography&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2
  5. https://www.uptodate.com/contents/principles-of-magnetic-resonance-imaging?search=mri%20%20with%20contrast&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1

Review Question

What is the preferred imaging of choice in a patient suspected with a hemorrhagic stroke?

Answer

Non-Contrast CT (NCCT)