Advanced MR Imaging in Dementia Flashcards
What is Alzheimer’s pathology?
- Neuritic plaques - extracellular AB deposition + inflammatory cells
- Neurofibrillary tangles - insoluble tau protein inside neurons
What is multiple Micronleeds in AD relevance?
Defined as >8 MBs at 1.5T • Compared to AD w/o MBs – n=21 versus n=42 • Demographics similar – same age • MRI similar atrophy – more WMH • Worse cognition • Lower CSF Abeta
What is congophylic amyloid angiopathy?
Some of the amyloid are deposited on the vessel walls by refringent material around the vessels and leads to thickening of the vessels and narrowing of the vessels which become fragile and microhaemorrhage can occur in the vessel wall which leads to susceptibility weighted defect
What is cerebral amyloid angiopathy with inflammatory reaction?
Develop periods of inflammation spontaneously
Develop out blown of the venous and perivascular drainage and develop oedema and swelling
• Can become symptomatic – become drowsy and encephalitic
• May be responsive to steroid treatment
What is molecular imaging for Dementia?
11C-PIB – amyloid deposition (PET) – new 18F tracers licensed, not reimbursed • flutematemol, florbetaben, florbetapir – FDDNP less robust • 123I-FP-CIT – dopaminergic receptor (SPECT) – DAT-scan 123I-Ioflupane • 18F-AV1451 – tau deposition (PET) – others in development
What is Fluorinated tracers?
- Positive scan in AD
- Negative scan in HC and FTD
- See uptake in the white matter but not in the cortex
- There is similar behaviour for a negative and positive scanner
- Subtle differences between the tracers – some have stronger white matter binding in others
- In the negative scan you see no uptake in the white matter and see the white matter ramification – in the positive scan it gets all blurred
Amyloid PET in suspected AD:
- With amyloid you cannot look at the original pattern
- In positive scan amyloid is deposited all over the cortex while the atrophy/TAU uptake tends to be region specific either medial or parietal temporal
- TAU and atrophy in MRI have similar distribution in a typical Alzheimer’s patients
Combined amyloid and dopamine PET:
- Tease out various groups
- AD is amyloid positive with a normal dopamine scan
- DLB is amyloid negative scan with a positive dopamine scan
- FTD is both negative
PET tracers – TAU:
- There is uptake in the medial temporal lobe and also parietal areas
- In HC both tracers would be negative
What is functional imaging in Dementia?
18F-FDG – glucose metabolism (PET)
• Tc-HMPAO – cerebral blood flow (SPECT)
• ASL – cerebral blood-flow (MRI)
• Rs-FMRI – resting-state connectivity (MRI)
What is 18F-FDG PET ?
this is a fluorinated tracer
- It is a hot tracer, glucose-analogin
- The brain uses a lot of glucose
- You are looking at a hot background – making it slightly difficult to find the abnormality
- Amyloid and Tau are cold tracers – normally there is no uptake in the brain – it is much easier to look for an abnormality
- With FDG – you have to have a comparison to a normal data base or look for local differences
FDG-PET in AD – posterior cingulate:
- On the left, normal FDG – all of the cortex is red
- Looking for areas that have a reduced tracer uptake – occurs in the parietal, precuneus – it goes from parietal to temporal
- Look for hypo-metabolism
What is voxel-base mapping?
– have a series of normal PET scans and put subject in and produces a statistical map showing you were the subject deviates most from abnormality
• Red – the most abnormal
• Dark – the normal pattern – no difference compared to a reference of normal PET scans
FDG and Amyloid PET – AD vs FTD:
• Clinical AD
- Amyloid scans were positive
- FDG was abnormal with a posterior hypometabolism
- Both are consistent with AD and pathology was AD
• Clinical FTLD-ALS
- Various mutations such as C9ORF and also others produce both FDG and MND
- Amyloid scan was negative
- FDG was abnormal with hypometabolism in the frontal lobe consistent with FTLD
• Clinical AD
- Amyloid scan is positive
- FDG is much like the FTLD case
- Pathology was Alzheimer’s
RS – fMRI: a new window to the brain:
- Advantages – you do not need to inject anything contrary to PET
- Look at brain activity – do either task or show some specific areas to light up as a function of the task e.g. map language for epilepsy surgery or study brain function in general
- You study the brain at rest and look at various networks that are synchronised and drive the activity in the brain over time
- You can do this with a run of approximately 5 minutes
- Default-mode network (DMN) encompasses the precuneus – where atrophy occurs, where FDG shows hypometabolism
- Encompasses area more anteriorly in the anterior cingulate
