Neuroradiology and Neuroplasticity Flashcards
1
Q
Focus on Common Images Modalities
A
Computerized Tomography- CT
Magnetic Resonance Imaging- MRI (T1 and T2, functional MRI)
2
Q
Computerized Tomography (CT)
A
- Developed from a conventional x-ray
- Xray has a flat plate detector and radiation source
- One single projection
- CT uses the same mechanism but with 2 difference
- CT slices are obtained simultaneously
- Multiple x-ray beams are passing through the patient so the same structure image is captured from a variety of angles
- The x-ray source moves really fast
- Projections are mathematically combined to create a 2D or 3D image
- Measures the density of tissues
- Bone or calcification/dense structure appears white/lighter = hyperdense
- Air/water/less dense structure appears darker = hypodense
- Brain/intermediate structure appears gray = isodense
3
Q
Hyperdense
A
Bone or calcification/dense structure appears white/lighter
4
Q
Hypodense
A
Air/water/less dense structure appears darker
5
Q
Isodense
A
Brain/intermediate structure appears gray
6
Q
Abnormal Findings in CT
A
- Hemorrhage
- Acute Cerebral Infarction
- Neoplasms
- Mass Effect
- Calcifications
7
Q
Hemorrhage (abnormal findings in CT)
A
The appearance depends on the chronicity
- Acute hemorrhage = Isodense
- Two-three weeks post hemorrhage = Hypodense
8
Q
Acute Cerebral Infarction (abnormal findings in CT)
A
Cannot be seen within first 6-12 hours
- Cell death and edema occurs = hypodensity
- After weeks/months = hypodensity (areas surrounding may shrink, enlarged ventricles)
9
Q
Neoplasms (abnormal findings in CT)
A
Appear as hypodense, hyperdense, or isodense - Intravenous contrast dye is helpful in imaging these disorders
10
Q
Mass Effect (abnormal findings in CT)
A
Anything that distorts the brain’s usual anatomy by displacement
11
Q
Calcification (abnormal findings in CT)
A
Appears hyperdense
12
Q
Intravenous contrast (CT)
A
- Used to facilitate visualization of suspected neoplasm or brain abscess
- The contrast contains iodine - which is denser than brain and appears as hyperdense (white)
13
Q
Magnetic Resonance Imaging - MRI
A
- Radio frequency magnetic waves are generated from an electrical coil that excites protons, causing some to flip their spins anti-parallel
- Signal detected by reception coil
- Multiple pulse frequency sequence will direct the protons to the patient and originates better images
14
Q
Super Conducting Magnet (MRI)
A
Where pt needs to be positioned
15
Q
Gradient Coils (MRI)
A
Perturbs the magnetic field to allow spatial localization
16
Q
Different coil
A
17
Q
Repetition Time (TR) (MRI Image: described in terms of intensity)
A
The amount of time between successive pulse sequences applied to the same slice.
18
Q
Time to Echo (TE)(MRI Image: described in terms of intensity)
A
The time between the delivery of the RF pulse and the receipt of the echo signal.
19
Q
T1 weighted MRI
A
-Looks like an anatomical brain section
Gray matter appears gray, white matter appears white
- H20, CSF appears dark
- Fatty tissue appears white
- Air and bone appears black
- “Spin-lattice” relaxation
- White matter brighter than gray
- Most lesions dark
20
Q
T2 Weighted MRI
A
-Looks like a negative film
Opposite to T1
- Gray matter appears light gray, white matter appears dark gray
- Bone and air are black
- CSF appears white
- Myelinated areas appear dark
- “Spin-spin” relaxation
- Most lesions bright
21
Q
MRI relates to brightness of the signal as compared to density in CT
A
Hyperintense = brighter areas
Hypointense = darker areas
Related to: Water content (dark in T1 and white T2), Fat content (white T1, dark T2)
22
Q
MRA and MRV
A
contrast to blood vessels
23
Q
CT Advantages
A
- Low cost
- It takes 5 – 10 min
- Head trauma
- Accessible in any ER
- More bone detail
- Screening test
24
Q
CT Disadvantages
A
- Doesn’t detect brainstem and cerebellar stroke
- Images not so clear
- Radiation
25
MRI Advantages
- Clear images
- More structures and tissue details
- Detect brainstem and cerebellar stroke
- No radiation
26
MRI Disadvantages
- High cost
- It takes 20-45 min
- Less accessible
27
CT Indications
- Acute neurological deficit/trauma
- Subarachnoid hemorrhage
- Acutely ill or unstable patient
- Contradiction to MRI scan (ex. pacemaker)
28
CT Contradiction
- Pregnancy (we ask- you should)
- Allergic reactions (contrast media)
- Pediatric patient (radiation concerns)
29
MRI Indications
- Brainstem and cerebellar strokes
- Normal CT and persistent clinical suspicion
- Contraindications to CT (pediatric)
30
MRI Contraindications
- Certain implanted ferromagnetic devices
- Claustrophobia (can be done with sedation)
- Renal failure (when gadolinium necessary)
- Early pregnancy (?)
31
Structures
32
Neuroplasticity
Definition: It is the adaptative capacity of the brain (CNS). The brain's ability to reorganize itself by forming new neural connections throughout life. Mechanisms involve neurochemical, receptor, or neuronal structural changes.
Types:Structural and Functional
33
Structural/Neural Plasticity
Changes in the organization and numbers of connections among neurons.
- Unmasking of “silent” synapses
- Synaptogenesis: development of new synapses
- Collateral sprouting
34
Functional Plasticity
- Changes in the efficiency or strength of synaptic connections.
- It can happen during therapeutic intervention
35
Neuronal Function (effect of injury)
- Interrupting axonal projections from areas injured
- Denervation of the population of neurons innervated by the injured neurons
- Removing some neurons entirely
36
Cellular Level (effect of injury)
- Neuronal Shock: Diaschisis
- Loss of synaptic effectiveness
- Alternative mechanisms are substituted
37
Factors That Affect Recovery
- Genes
- Age
- Size, type and location of lesion
- Onset time
- Experience/your environment
- Pharmacology
- Use/training
38
Principles of Neuroplasticity
- Use it or lose it: Failure to drive specific brain functions can lead to loss of abilities
- Use it and improve it
- Specificity: Plasticity specific to the training
- Repetition matters
- Intensity matters
- Time matters
- Salience matters: The training experience must be meaningful
- Age matters
- Transference: Training experience can even lead to learning other similar skills
- Interference: Brain changes that result in bad habits can interfere with learning good habits
39
Neuromodulation
Used to promoting neuroplasticity.
- Medications
- Rehabilitation
- Neuromodulation tools: TMS, tDCS, DBS
40
Techniques that may prime motor learning
- TMS (increase or decrease corticomotor excitability) used to drive motor learning. Pulsating magnetic fields on the scalp to induce an electrical current within the brain
- tDCS
- Deep Brain Stimulation
- Aerobic exercise
- Neuropharmacology
41
tDCS (Neuromodulation tools)
- Transcranial direct current stimulation
- Delivers low-intensity direct electrical current to the brain
- Delivers low-intensity direct electical current to the brain
- Enhance neuronal excitability or inhibit overexcitability of neural networks
- Cathodal inhibits, anodal excites
- tDCS is a safer, more comfortable, easier to do, more affordable and produces a more robust response
42
Deep Brain Stimulation/DBS (Neuromodulation tools)
- Helps with tremor, rigidity, slowness of movement, balance
| - Surgically implanted electrodes to provide electrical impulses
43
Aerobic Exercise
- Indirect Effects: Improves general health and fitness
| - Direct effects: Increase in neurotrophic factors (such as BDNF) and neurotransmitters (dopamine, serotonin)
44
Brain Derived Neurotrophic Factor (BDNF)
- Protein encoded by BDNF gene.
- Member of neurotrophin family
- Involved in neuroprotection, neurogenesis, neuroplasticity
- A key mediator of motor learning and getting the brain ready for neuroplasticity
- Secreted by 2 mechanisms: constitutive and activity-dependent pathways (aerobic exercises)
- Enhances BDNF levels and leads to increased BDNF gene expression in hippocampus, cerebral cortex and cerebellum.
45
BDNF role in facilitating neuroplasticity
- BDNF facilitates long term potentiation through an activity-dependent secretion: vital to neuroplasticity
- Evidence supports in increase in BDNF benefits cognitive functions
- Systemic levels of BDNF are increased for 10-60 minutes following a bout of aerobic exercise
46
“Priming the system” with aerobic exercise
- Timing: engage patient in aerobic exercise close in time to your therapy (training pair exercise)
- Evidence: High intensity exercise before motor task enhanced performance in young adults
47
Recommendation for practice FITT principle
Frequency: 4x/wk
Intensity: 70% max HR
Time: Aerobic session more 30 min
Type: combination aerobic exercise and resistance training
Evidence that 30 min at 60% max HR is effective for increasing BDNF in patients with chronic disorders
48
Genetic Considerations
- Genetic variations may influence the efficacy of rehab
- Common single nucleotide polymorphism (SNP) on the BDNF gene (Valine replaced by Methionine) - VAL66MET Polymorphism
- Patient with VAL66MET Polymorphism present 25% reduction in activity-dependent secretion of BDNF in the CNS
49
Neural Plasticity
- Can be “good” or “bad”
- Occurs throughout the CNS
- Occurs with motor learning
- Occurs with recovery of function
50
How is neuroplasticity detected?
Non Invasive Brain Stimulation
| TMS: Measures excitability of motor cortex maps
51
Aerobic Exercise Effects on Brain Function
Enhances BDNF levels and leads to increased BDNF gene expression in:
- Hippocampus
- Cerebellum
- Cerebral cortex
- Spinal cord-
52
BDNF Gene VAL66MET Polymorphism
-30-50% of population have this SNP
-The presence of the MET allele results in a 25% reduction in activity dependent secretion of BDNF in the CNS
Associated with (abnormalities in brain structure and physiology):
-Decreased hippocampal activation
-Decreased motor system activation
-Increased gray matter atrophy
-Poorer memory function
-Pooreroutcomeafterstroke
-Poorer learning and memory
