Neuroimaging methods  

 Magnetic resonance imaging  (MRI) and  functional magnetic resonance imaging
 (fMRI) are the most common neuroimaging tools used in identifying
aphasia and studying the extent of damage in the loss of language abilities.
This is done by doing MRI scans and locating the extent of lesions or damage
within brain tissue, particularly within areas of the left frontal and
temporal regions- where a lot of language related areas lie. In fMRI studies a
language related task is often completed and then the BOLD image is analyzed.
If there are lower than normal BOLD responses that indicate a lessening of
blood flow to the affected area and can show quantitatively that the cognitive
task is not being completed.

There are limitations to the use of fMRI in aphasic patients particularly.
Because a high percentage of aphasic patients develop it because of stroke
there can be  infarct  present which is the
total loss of blood flow. This can be due to the thinning of blood vessels or
the complete blockage of it. This is important in fMRI as it relies on the
BOLD response (the oxygen levels of the blood vessels), and this can create a
false hyporesponse upon fMRI study.  [51]  Due to the limitations of fMRI such
as a lower spatial resolution, it can show that some areas of the brain are
not active during a task when they in reality are. Additionally, with  stroke
 being the cause of many cases of aphasia the extent
of damage to brain tissue can be difficult to quantify therefore the effects
of stroke brain damage on the functionality of the patient can vary.

**Neural substrates of aphasia subtypes**

MRI is often used to predict or confirm the subtype of aphasia present.
Researchers compared 3 subtypes of aphasia- nonfluent-variant primary
progressive aphasia (nfPPA), logopenic-variant primary progressive aphasia
(lvPPA), and semantic-variant primary progressive aphasia (svPPA), with 
primary progressive aphasia  (PPA) and Alzheimer's disease. This was done by
analyzing the MRIs of patients with each of the subsets of PPA.  [52]  Images
which compare subtypes of aphasia as well as for finding the extent of lesions
are generated by overlapping images of different participant's brains (if
applicable) and isolating areas of lesions or damage using third-party
software such as MRIcron. MRI has also been used to study the relationship
between the type of aphasia developed and the age of the person with aphasia.
It was found that patients with fluent aphasia are on average older than
people with non-fluent aphasia. It was also found that among patients with
lesions confined to the anterior portion of the brain an unexpected portion of
them presented with fluent aphasia and were remarkably older than those with
non-fluent aphasia. This effect was not found when the posterior portion of
the brain was studied.  [53]

**Associated conditions**

In a study on the features associated with different disease trajectories in 
Alzheimer's disease 
(AD)-related primary progressive aphasia (PPA), it was found that metabolic
patterns via PET SPM analysis can help predict progression of total loss of
speech and functional autonomy in AD and PPA patients. This was done by
comparing an MRI or CT image of the brain and presence of a radioactive
biomarker with normal levels in patients without Alzheimer's Disease.  [54]