behavior, in day to day function at home, or at work, and in
taking care of oneself. Some symptoms are reversible,
whereas others are irreversible, depending upon the etiol-
ogy of the disease. If the dementia can be diagnosed at its
early stage, it is still possible to repair some reversible
damages and thus slow down the process of irreversible
damages, since evidences showed that the currently avail-
able medications for dementia, which can help people to
maintain daily function and quality of life as well as sta-
bilize cognitive decline , may be more beneficial if given
early in the disease process. For instance, about 10–30 %
of people with the mild cognitive impairment (MCI), which
is usually thought to be the incubation of AD in clinical
practice, develop to AD every year, whereas the conversion
rate of normal aging group is just 1–3 % [16]. According to
recent research, diagnosing MCI at its early stage and
taking corresponding measures to protect certain neuro-
logical functions of patients will help to slow down the
conversion from MCI to AD.
There exist some brief (5–15 min) tests that have rea-
sonable reliability and can be used in the office or other
settings to screen cognitive status for deficits which are
considered pathological. Examples of such tests include the
abbreviated mental test score (AMTS), mini-mental state
examination (MMSE), modified mini-mental state exami-
nation (3MS) [17], cogniti ve abilities screening instrument
(CASI) [18], and clock drawing test [19]. Although these
tests can help diagnosing different types of dementia, they
are generally recognized to be inadequate to classify the
types of dementia at an early stage. Some people perform
well on brief screening tests, but their memory and think-
ing impairments may be found with more comprehensive
testing. Moreover, some tests have been shown to have
educational, social, and cultural biases.
Medical imaging offers the ability to visualize degener-
ative histological changes, includin g the amyloid plaques,
hypo-metabolism, and atrophy introdu ced by neurological
disorders, which occur long before the neurodegenerative
disorder is clinically detectable [20]. Hence, the widespread
applications of medical imaging have led to a revolution in
the early diagnosis of dementia [21–24]. The commonly used
imaging modalities in dementia diag nosis include the mag-
netic resonance imaging (MRI), positron emission tomog-
raphy (PET), and single-photon emission computed
tomography (SPECT). Structural MRI uses a magnetic field
and radio waves to create detailed images of the organs and
tissues within human body and has been shown to be a sur-
rogate for early diagnosis of AD, particularly in subjects
clinically classified as amnestic MCI (aM CI) [25]. This
technique offers several advantages, including greater
availability, better soft tissue contrast, faster data acquisi-
tion, lower cost, and the possibility of automatically deriving
quantitative indices of regional atrophy [26]. Accordingly,
the validation of structure MRI as a marker of AD progres-
sion is the core project of the Alzheimer’s Disease Neu-
roimaging Initiative (ADNI). Functional PET with various
radioactive tracers, e.g., 2-[
18
F]fluoro-2-deoxy-D-glucose
(FDG) and
18
C-Pittsburgh Compound (
11
C-PiB), can detect
subtle changes in cerebral metabolism or amyloid deposition
prior to anatomical changes are evident or a symptomato-
logical diagnosis of probable dementia can be made with
structure imaging [27– 30 ]. Functional SPECT is similar to
PET in its use of radioactive tracer material and detection of
gamma rays. SPECT scans have low spatial resolution than
PET scans, but are significantly less expensive. However, the
interpretation of PET and SPECT images remains a chal-
lenge because the changes can be subtle in the early course of
the disease and there can be some overlap with normal aging
and other dementia types [31].
In medical imaging based dementia diagnosis, the acquired
3D images are still analyzed almost entirely through visual
inspection on a slice-by-slice basis in search of familiar dis-
ease patterns. This requires a high degree of skill and con-
centration, and is time-consuming, expensive, and prone to
operator bias. Thus, there is a strong demand for computer-
aided automated dementia classification, which is expected to
provide a useful ‘‘second opinion’’ and enable doctors to
bypass the aforementioned issues. As a result, a great number
of computer-aided automated dementia identification
approaches have been proposed. The targets of those
approaches are in threefold: (1) differentiating dementia cases
from normal controls (NCs); (2) identifying different stages of
dementia, such as separating MCI from AD cases; and (3)
identifying different types of dementia, such as separating AD
from FTD. There exist several publically available databases,
including the Early Lung Cancer Action Program (ELCAP)
[32], Open Access Series of Imaging Studies (OASIS) [33,
34], and Alzheimer’s disease Neuroimaging Initiative (ADNI)
[35]. These databases have been broadly used as the test bed in
many studies, and thus tremendously promoted the research
on automated dementia identification.
In this paper, we provide a surve y of automated
dementia identification approaches in the literature from a
pattern classification perspective. Similar to other pattern
classification solutions, various dementia identification
approaches consist of two major steps: feature extraction
and classification. Hence, we review the feature extraction
methods and classifiers used in those approaches, respec-
tively. We also provide a comparison of the reported per-
formance of many available approaches.
2 Methods
Automated identification of dementia using medical
imaging with the aid of computers is essentially an image-
C. Zheng et al.
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