Neuroimaging Flashcards
CT/ CAT Scanning
narrow beam x rays passing through tissue at different angles
used to detect brain disease
small structures cannot be distinguished
What color does bone, gasses/ liquids, and tissues in a CT/CAT scanning?
Bone= white (hyper-intensity)
gases and liquids= black (hypo- intensity)
Tissues= grey
CT/ CAT Scan Methodology: How many dimensions?
2-D measurement taken in a helical manner
How is x-ray intensity reduced?
Attenuation coefficient of the materials it passes through
What can you add to make internal organs more visible in a CT scan?
contrast dye
What is a tomographic image?
picture of a slab of the patient’s anatomy
2D CT image corresponds to to a 3D section of the patient
Each pixel on the CT image displays the average x-ray attenuation properties of the tissue in the corresponding voxel (volumetric pixel)
What is an MRI?
Magnetic Resonance Imaging
contains a magnetic field up to 60,000 times as strong as the Earth’s magnetic field
MRI equipment is VERY expensive
How does an MRI work?
Patient is bathed in a magnetic field
- causes nuclei in the body to line up, spinning on it’s axis
- atom= HYDROGREN ATOM
- Protons are strongly affected by the magnetic field
The nuclei are hit by pulsing radio waves -> Resonance bit
- Nuclei go back to their state induced by the magnet once RF pulses stop
- Energy now released by the nuclei acts as a mini radio stations
- The coil now picks up the excess energy and sends the signal to the computer, where the imaging is scanned
Can you inject contrast dye in patients during an MRI scan?
Yes. The dye will reach different tissues at different rates.
What can an MRI diagnose?
- MS
- strokes
- infections of the brain/ spine/ tendonitis
MRI’s can visualize what?
Injuries:
- torn ligaments (wrist, ankle, knee)
What can MRI’s evaluate?
Masses in soft tissue
Cysts
Bone tumors
Disc problems
Advantages of an MRI
- does not use ionizing radiation
- contrast dye has low chance of side effects
- non- invasive view before surgery
- provides comparable resolution with far better CONTRAST RESOLUTION (distinguishing two different structures)
- variable thickness, any plane
- many details without IV contrast
What is spatial resolution? What type of imaging is good at this?
The ability to distinguish two separate structures an arbitrarily small distance from each other
CT
Disadvantages of MRI
- Claustrophobia
- Weight and size – pt limitations
- Noise
- Keeping still
- Cost
- Medical contraindications
- Time consuming
- not easily available
- limitations
MRI contraindications
- pace makers
- metal objects in the body
MRI limitations
- bone
- air pain abdomen?
- time consuming
- expertise
MRI Safety Concerns
- Internal cardiac pacemakers
- steel cerebral aneurysm clips (ferromagnetic)
- small steel silvers embedded in eye
- cochlear implants
- stents anywhere in the body
No phones or credit cards!!
T1 Weighted MRI
Water and fluid containing tissues are dark
Fat containing tissues are bright
T2 Weighted MRI
Water and fluid containing tissues are bright
Fat containing tissues are dark
- Damaged tissue tends to develop edema, making T2 weighted sequence sensitive for pathology, and generally able to distinguish pathologic tissue from normal tissue
FLAIR (MRI)
Fluid Attenuated Inversion Recovery
- achieved by additional manipulations of the magnetic field on a T2 weighted image
free water= dark
edematous tissue= bright
** MOST SENSISTIVE WAY to evaluate the brain for demyelinating diseases (ex: MS)
What type of MRI provides good gray matter/ white matter contrast?
T1 Weighted Images highlight fat deposition
What type of MRI is well suited to edema?
T2 Weighted Images light up liquid on the images being visualized— high water content
What type of MRI targets blood vessels?
Magnetic Resonance Angiography (MRA)
- evaluates arteries for stenosis or aneurysms
