<s>
Ghosting	B-Algorithm
is	O
a	O
visual	B-Algorithm
artifact	I-Algorithm
that	O
occurs	O
in	O
magnetic	O
resonance	O
imaging(MRI )	O
scans	O
.	O
</s>
<s>
These	O
artifact	B-Algorithm
are	O
a	O
consequence	O
of	O
environmental	O
factors	O
or	O
the	O
human	O
body	O
(	O
such	O
as	O
blood	O
flow	O
,	O
implants	O
etc	O
.	O
)	O
.	O
</s>
<s>
Ghosting	B-Algorithm
is	O
a	O
multidimensional	O
artifact	B-Algorithm
that	O
occurs	O
in	O
the	O
MRI	O
in	O
the	O
phase	O
encoded	O
direction	O
(	O
short	O
axis	O
of	O
the	O
image	O
)	O
after	O
applying	O
the	O
Fourier	B-Algorithm
transform	I-Algorithm
.	O
</s>
<s>
This	O
incompatibility	O
of	O
parameters	O
is	O
the	O
cause	O
of	O
ghosting	B-Algorithm
.	O
</s>
<s>
The	O
reasons	O
for	O
ghosting	B-Algorithm
could	O
be	O
physical	O
factors	O
such	O
as	O
temperature	O
or	O
humidity	O
of	O
the	O
environment	O
and	O
movement	O
caused	O
by	O
the	O
patient	O
or	O
in	O
the	O
patient	O
’s	O
body	O
.	O
</s>
<s>
There	O
are	O
two	O
types	O
of	O
movement	O
that	O
could	O
result	O
in	O
ghosting	B-Algorithm
:	O
</s>
<s>
k-space	B-Algorithm
is	O
a	O
graphic	O
matrix	O
of	O
an	O
MR	O
that	O
represents	O
the	O
Fourier	B-Algorithm
transform	I-Algorithm
domain	O
of	O
an	O
image	O
before	O
undergoing	O
the	O
Inverse	O
Fourier	O
transformation.The	O
phase	O
deviations	O
that	O
occur	O
in	O
the	O
k-space	B-Algorithm
of	O
an	O
MR	O
image	O
decide	O
the	O
characteristics	O
of	O
the	O
ghosts	O
that	O
appear	O
in	O
the	O
resulting	O
image	O
.	O
</s>
<s>
Even	O
though	O
most	O
of	O
the	O
ghosting	B-Algorithm
is	O
due	O
to	O
the	O
phase	O
deviation	O
in	O
the	O
phase	O
encoded	O
direction	O
,	O
they	O
also	O
appear	O
in	O
other	O
directions	O
of	O
the	O
k-space	B-Algorithm
.	O
</s>
<s>
The	O
basic	O
principle	O
of	O
ghosting	B-Algorithm
can	O
be	O
explained	O
with	O
the	O
help	O
of	O
Echo-Planar	O
Imaging	O
(	O
EPI	O
)	O
.	O
</s>
<s>
Several	O
algorithms	O
have	O
been	O
proposed	O
to	O
remove	O
ghosting	B-Algorithm
in	O
the	O
medical	O
images	O
.	O
</s>
<s>
This	O
is	O
followed	O
by	O
taking	O
the	O
Inverse	O
Fourier	B-Algorithm
transform	I-Algorithm
for	O
reconstruction	O
of	O
the	O
image	O
,	O
which	O
can	O
contain	O
ghosting	B-Algorithm
artifacts	B-Algorithm
.	O
</s>
<s>
The	O
iterative	O
method	O
is	O
then	O
applied	O
to	O
reduce	O
the	O
ghosting	B-Algorithm
artifacts	B-Algorithm
.	O
</s>
<s>
The	O
data	O
of	O
the	O
k-space	B-Algorithm
matrix	O
is	O
numbered	O
consecutively	O
and	O
is	O
split	O
into	O
odd	O
and	O
even	O
data	O
based	O
on	O
the	O
samples	O
of	O
the	O
index	O
.	O
</s>
<s>
This	O
method	O
was	O
developed	O
based	O
on	O
the	O
fact	O
that	O
the	O
difference	O
between	O
the	O
odd	O
and	O
even	O
virtual	O
k-space	B-Algorithm
data	O
is	O
the	O
Fourier	B-Algorithm
transform	I-Algorithm
of	O
the	O
underlying	O
sparse	O
image	O
.	O
</s>
<s>
The	O
occurrence	O
of	O
the	O
Ghosts	O
in	O
the	O
images	O
is	O
converted	O
into	O
missing	O
k-space	B-Algorithm
data	O
and	O
is	O
recovered	O
with	O
the	O
help	O
of	O
the	O
ALOHA	O
matrix	O
.	O
</s>
<s>
There	O
are	O
2	O
types	O
of	O
approaches	O
that	O
are	O
used	O
to	O
remove	O
the	O
Nyquist	O
Ghost	O
artifacts	B-Algorithm
:	O
</s>
<s>
The	O
odd	O
and	O
the	O
even	O
samples	O
of	O
data	O
are	O
taken	O
from	O
the	O
k-space	B-Algorithm
by	O
means	O
of	O
interpolation	B-Algorithm
.	O
</s>
<s>
A	O
high-performance	O
interpolation	B-Algorithm
method	O
would	O
be	O
able	O
to	O
find	O
the	O
missing	O
data	O
from	O
the	O
actual	O
even	O
and	O
odd	O
sequences	O
and	O
remove	O
the	O
ghosting	B-Algorithm
artifacts	B-Algorithm
from	O
the	O
images	O
.	O
</s>
<s>
ALOHA	O
converts	O
the	O
sparse	O
recovery	O
problem	O
into	O
a	O
k-space	B-Algorithm
interpolation	B-Algorithm
problem	O
using	O
a	O
low-rank	O
interpolator	O
.	O
</s>
<s>
Removes	O
the	O
ghost	O
artifact	B-Algorithm
without	O
pre-scan	O
data	O
or	O
the	O
modification	O
of	O
the	O
pulse	O
sequence	O
.	O
</s>
<s>
Other	O
artifacts	B-Algorithm
can	O
also	O
be	O
avoided	O
by	O
observing	O
the	O
existing	O
pre-scan	O
approach	O
.	O
</s>
<s>
The	O
method	O
of	O
generalized	O
projections	O
(	O
MGP	O
)	O
is	O
based	O
on	O
the	O
fact	O
the	O
discontinuities	O
in	O
the	O
phase	O
form	O
alternating	O
pattern	O
in	O
the	O
k-space	B-Algorithm
and	O
hence	O
leads	O
to	O
ghosting	B-Algorithm
.	O
</s>
<s>
This	O
EPI	O
ghosting	B-Algorithm
can	O
be	O
corrected	O
from	O
the	O
phase	O
using	O
2	O
or	O
more	O
reference	O
scans	O
.	O
</s>
<s>
The	O
Fourier	B-Algorithm
transform	I-Algorithm
of	O
the	O
masked	O
image	O
is	O
taken	O
.	O
</s>
<s>
The	O
phase	O
of	O
the	O
original	O
image	O
is	O
changed	O
to	O
the	O
model	O
image	O
(	O
the	O
image	O
that	O
is	O
modeled	O
as	O
ghosting	B-Algorithm
arising	O
from	O
the	O
phase	O
offsets	O
)	O
but	O
the	O
magnitude	O
is	O
kept	O
constant	O
.	O
</s>
<s>
The	O
assumption	O
in	O
the	O
MGP	O
method	O
is	O
that	O
the	O
model	O
k-space	B-Algorithm
phase	O
of	O
each	O
line	O
is	O
more	O
precise	O
than	O
that	O
of	O
the	O
original	O
k-space	B-Algorithm
image	O
.	O
</s>
