Essay revision Flashcards
Describe the mechanism of CT scans
- A motorized table moves the patient through a circular opening in the CT imaging system.
- As the patient passes through the CT imaging system, a source of x rays rotates around the inside of the circular opening. A single rotation takes about 1 second.
- The x-ray source produces a narrow, fan-shaped beam of x rays used to irradiate a section of the patient’s body. The thickness of the fan beam is between 1mm to 10mm.
- In typical examinations there are several phases; of about 10 to 50 rotations of the x-ray tube around the patient in coordination with the table moving through the circular opening.
- The patient may receive an injection of a “contrast material” to facilitate visualization of vascular structure.
- Detectors on the exit side of the patient record the x rays exiting the section of the patient’s body being irradiated as an x-ray “snapshot” at one position (angle) of the source of x rays. Many different “snapshots” (angles) are collected during one complete rotation.
- The data are sent to a computer to reconstruct all of the individual “snapshots” into a cross-sectional image (slice) of the internal organs and tissues for each complete rotation of the source of x rays.
Describe the mechanism of MRI scans
- The human body is largely composed of water molecules, each containing two hydrogen nuclei, or protons.
- When inside the magnetic field of the scanner, the magnetic moments of these protons align with the direction of the field either parallel in direction of magnetic field or anti-parallel. In the resting state it aligns parallel (as it is low energy state)
- A radio frequency pulse is then applied, which can excite protons from parallel to anti-parallel alignment
- In response to the force bringing them back to their equilibrium orientation, the protons undergo a rotating motion (precession) returning to low energy state. They do so by emitting photons corresponding to the energy difference between the two possible alignments.
- This appears as a magnetic flux, which yields a changing voltage in receiver coils to give the signal.
- The frequency at which a proton in a voxel resonates depends on the strength of the local magnetic field around the proton, a stronger field corresponds to a larger energy difference and higher frequency photons.
- Contrast agents may be injected intravenously to enhance the appearance of blood vessels, tumours or inflammation. Patients with some metal implants, cochlear implants, and cardiac pacemakers are prevented from having an MRI scan due to effects of the strong magnetic field and powerful radio frequency pulses
T1 vs T2 Description Fluid (e.g. urine, CSF) Muscle Fat Grey matter White matter
T1 weighted sequences obtains signal from time for protos to realign with magnet
Low - Black
Intermediate – Grey
High – White
Intermediate – Grey
Hyperintense compared to grey matter – White-ish
T2 weighted sequences obtains signal from time for measured signal to decay
High - White
Intermediate – Grey
High – White
Intermediate – Grey
Hypointense compared to grey matter – Dark-ish
What is the first sign you see on CT from thrombolytic stroke?
o Pressman et al: For a thrombotic stroke - The earliest CT sign is a hyper-dense segment of vessel which is the direct visualisation of the intravascular thrombus/ emboli. Most commonly seen in the MCA.
Describe POCS
1 of 5 of the following:
- Cranial nerve palsy + contralateral motor/sensory deficit
- Bilateral motor/sensory deficit
- Conjugate eye movement disorder (dues to palsy and therefore eye muscles don’t work)
- Cerebellar dysfunction
- Isolate homonymous hemianopia or cortical blindness
Describe global ischaemia and silent infarcts
Global ischaemia: Caused by cardiac arrest and lead to laminar necrosis, white matter infarcts, watershed infarcts and hippocampal necrosis
Silent infarcts: Assymptomatic and can possibly cause behavioural changes.
89% is subcortical and lacuna region affecting basal ganglia giving you a 2x risk of demential and steeper cognitive decline
How do we investigate PD?
DAT scan is the only approved scan in the market to detect the substantia nigra.
INDICATIONS FOR DATSCAN – I-IOFLUPANE IMAGING:
• Detection of loss of functional dopaminergic neuron terminals in the striatum of patients with clinically uncertain parkinsonian syndromes
• Differentiation of essential tremor, psychogenic parkinsonism, or neuroleptic induced parkinsonism from presynaptic parkinsonian syndromes (Parkinson’s disease, multiple‐system atrophy, cortico-basal degeneration, progressive supranuclear palsy)
• Early detection of Parkinson’s disease
• Assessment of disease severity and progression
• Differentiation of dementia with Lewy bodies from other dementias
What are the pathological hallmarks of PD?
- Formation of proteinaceous and intraneuronal inclusions (Lewy bodies, and Lewy neurites - made by alpha synuclein)
- Progressive neuronal loss particularly targeting the substantia nigra pars compacta (dopaminergic systems)
- There is neuro-melanin that form the dark parts in the substantia nigra. In PD, neuro-melanin is lost as there is loss of dopaminergic cells in the substantia nigra. Lost neurons is replaced by gliosis
What sporadic genes are affected in parkinsons?
Done in GWAS study: MAPT, GBA, APOE, HLA-DRA, LRRK2
What are the symptoms of MS?
- Optic neuritis
- Transverse myelitis
- Brainstem syndromes:
- Pure cranial nerve lesions
- Double vision and Nystagmus
- Facial palsy/ numbness
- Ataxia
- Dysarthria
• Paroxysmal syndromes:
- Lhermitte’s phenomenon (bending of neck send a shock down arms and legs. This is causes by the haptic rubbing of exposed nerves)
- Trigeminal neuralgia
- Uhthoff’s phenomenon (Raise in body temperature leads to features of MS)
What are the elctrophysiology tests for MND?
Electromyograph
Nerve conduction studies
Describe the electromyograph test
EMG:
o Needle electromyography is the most important component of the electro diagnostic evaluation in MND. It allows identification of LMN involvement often before it becomes clinically evident, extending the physical examination and enabling earlier diagnosis.
o However, two EMG features are required for confirmation of neurogenic change consistent with a diagnosis of ALS:
Evidence of chronic neurogenic change.
Evidence of acute denervation.
Describe the nerve conduction studies
Nerve conduction studies:
Motor conduction studies are an essential part of the electro diagnostic evaluation of a patient suspected of having a MND.
These studies allow the exclusion of treatable neuropathies, such as multifocal motor neuropathy with conduction block, from the differential diagnosis.
Common findings observed from motor NCS in patients with MND include
1. asymmetric side-to-side Compound Muscle Action Potential (CMAP) differences
2. CMAPs with decreased amplitude
3. prolonged distal motor latency
4. slowed conduction velocity consistent with axon loss.
Sensory conduction studies – it is generally accepted that sensory nerves are normal in ALS – although this may not always be the case.
Describe the EAR mouse model hypothesis
EAE MOUSE MODEL:
• Experimental autoimmune encephalitis, this is a model inflammatory demyelinating system in rodents. Rodents are sensitised by proteins from the myelin sheath by injection of myelin proteins into circulatory system. This activates T-cells and leads to the MS phenotype.
• The microbiota and EAE: Berer at al 2011
o Models of microbiome free mice were made, these were then exposed to myelin proteins in attempt to sensitise T-cells to the CNS. This process did not result in an EAE model, when the microbiome was introduced in these mice, the EAE model developed.
o Recruitment and activation of autoantibody B-cells is dependent on the availability of MOG antigen
o Anti-MOG B lymphocytes and TH17 numbers profoundly decreased in intestine of Germ Free RR mice
Describe the eptiope spreading hypothesis
RELAPSING REMITTING IS CAUSED BY EPITOPE SPREADING:
• Immune activation of a specific epitope can cause inflammation and immune responses to different epitopes in the inflamed area. This can be intramolecular (to subdominant or cryptic epitopes) or intermolecular (to whole new antigens).
• In MS this means that an immune response to one antigen (e.g. MBP) can subsequently cause an immune response to another (e.g. Myelin Oligodendrocyte Glycoprotein - MOG)
• Various myelin proteins are autogenic, MBP, MOG, PLP, S100beta. Theories suggest this could be the reason behind the heterogeneity of the disease.
