Utility of 3D T2 Weighted sequences (Cube) in the evaluation of temporomandibular joint dysfunction

Introduction



 
 Internal
derangement
and
associated
complications
are
the
 most
common
pathologic
disorders
affecting
the
 temporomandibular
joint
(TMJ).

Less
frequently,
disorders
 include
trauma
and
inflammatory
arthritis
(1‐3).
The
term
 “internal
derangement”
refers
to
an
abnormal
positional
and
 functional
relationship
between
the
disk
and
the
articular
 surfaces.

These
entities
are
associated
with
clinical
findings
 including
pain,
joint
sounds
and
functional
disturbance.
 However
it
has
been
shown
that
up
to
35%
of
asymptomatic
 volunteers
have
temporomandibular
joint
disk
displacement

 even
if

it
was
less
prevalent
and
was
of
a
different
type
in
 asymptomatic
volunteers
compared
with
patients
with
pain
 and
dysfunction
(4).
MR
imaging
is
the
technique
of
choice
in
 evaluating

TMJ
anatomy
and
dysfunctions
given
its
inherent
 soft‐tissue
contrast,
high
spatial
resolution
and
multi
planar
 imaging
capabilities
(5‐7).
The
first
step
in
MR
imaging
of
the
 TMJ
is
to
evaluate
the
articular
disk
morphology
and
 localization
relative
to
the
condyle.
Concomitant
imaging
in


closed
and
open
mouth
position
allows
additional
functional
 and
morphologic
assessment
and
proper
grading
of
disease
 processes
of
the
articular
disk.
Other
findings
include
 thickening
of
an
attachment
of
the
lateral
pterygoid
muscle,
 rupture
of
retrodiskal
layers,
and
joint
effusion
and
can
serve
 as
indirect
early
signs
of
TMJ
dysfunction.
It
is
important
for
 the
radiologist
to
detect
early
MR
imaging
signs
of
 dysfunction,
thereby
avoiding
the
evolution
of
this
condition
 to
its
final
stage,
an
advanced
and
irreversible
phase
that
is
 characterized
by
osteoarthritic
changes
such
as
condylar
 flattening
or
osteophytes.
Traditional
MR
imaging
of
the
jaw
 utilizes
multiple
2D
multisection
acquisitions
to
evaluate
 internal
derangements.
The
limitations
of
these
sequences
 include
relatively
thick
sections
that
can
lead
to
partial
volume
 artifacts.
Moreover
the
anisotropic
voxels
produced
are
 inadequate
for
reformations
in
other
imaging
planes.
 Therefore
three‐dimensional
(3D)
sequences
capable
to
 reformat
images
in
different
planes

with
high
spatial
 resolution
would
be
a
useful
tool
for
evaluating
complex
 anatomical
structures
such
as
TMJ.

3D
Fast
Spin‐Echo
 sequences
have
been
used
to
image
intracranial
structures,
 female
pelvis,
spine
and
extremities
(8‐11).



The
aim
of
this
study
is
to
evaluate
the
utility
of
the
newly
 developed
3D
Fast
Spin
Echo
Cube
sequence
in
the
assessment
 of
TMJ
anatomy
and
disorders.
 





Materials
and
Methods


MRI
was
performed
in
the
TMJ
of
75
symptomatic
patients
 (mean
age,
36
years;
age
range,
11–75
years):
15
men
and
60
 women
for
a
total
of
150
joints
evaluated.

Images
were
 acquired
both
in
closed
and
in
open
mouth
position.






 MR
examinations
were
performed
between
November
2008
 and
February
2011
with
a
1,5‐T
MR
imaging
unit
(Signa
Twin;
 GE
Healthcare,
Milwaukee,
Wis)
equipped
with
high‐ performance
gradients
(amplitude,
40
mT/m;
slew
rate,
150
 mT/
m/msec)
using
a
3
INCH
dedicated
surface
coil;
in
the
 case
of
3D‐FSE‐Cube
scan
parameters
were
optimized
in
order
 to
maintain
acquisition
time
in
an
acceptable
range.

 Protol
examination
included:
 ‐3D‐FSE‐Cube
in
the
sagittal
plane
(repetition
time
msec/echo
 time
msec
1500/53;
matrix
224x224;
field
of

view
15cm;


section
thickness
1.4‐0.7mm
;
receiver
bandwidth
62,5
kHz;
 1NEX;
echo
train
length
69;
imaging
options
Zip
512/Zip
2
 with
an
acquisition
time
of
2:28
min:sec)






 ‐2D
FSE
images
in
the
sagittal
and
coronal
planes
(repetition
 time
msec/echo
time
msec
1800/63;
matrix
320x224;
field
of

 view
15cm;
section
thickness
2.8mm
with
a
spacing
of
0.3mm
;
 receiver
bandwidth
16,7
kHz
4NEX;
echo
train
lenght
11;
 imaging
options
TRF;
satutation
SI
RL;
acquisition
time
of

 2:42
min:sec)
When
needed,
fat
saturation
was
used.
 Signal
intensity
from
joint
disk,
muscle,
synovial
fluid
and
 background
noise
were
measured
in
all
patients
by
using
 regions
of
interest
(ROIs).
The
circular
ROI
for
cartilage
and
 fluid
measurements
was
3
mm2,
while
the
circular
ROI
for
 muscle
and
noise
measurements
was
50
mm2.

 The
standard
deviation
of
the
noise
was
measured
in
a
single
 ROI
placed
on
the
anterior
part
of
the
image
in
an
area
where
 there
was
no
phase
ghosting
(phase‐encoding
direction,
 anterior
to
posterior).

 Signal‐to‐noise
ratios
(SNRs)
for
disk,
muscle,
and
joint
fluid
 were
estimated
by
dividing
the
signal
intensity
value
by
the
 standard
deviation
of
the
noise.
The
fluid‐cartilage
contrast‐

to‐noise
ratio
was
calculated
by
subtracting
the
disk
SNR
from
 the
fluid
SNR.

Reformats
of
the
3DFSE‐Cube
images
were
 created
by
using
software
(GE,
Advantage
4.4)
and
were
 compared
with
2D
FSE
images
acquired
in
the
sagittal
and
 coronal
planes.
Two
readers
analyzed
and
scored
the
Cube
 and
FSE
images
concerning
the
overall
quality
(good
=2,
 discrete=1
and
poor
=0),
and
the
presence
of
artifacts.





Results


MRI
revealed
disk
dislocation
in
closed
mouth
position
in
59
 out
of

75
patients
evaluated:
18
patients
had
monolateral
 derangement

whether
41
patients
had
both
joints
affected.


 In
29
patients
the
dislocated
disk
regained
its
normal
position
 with
condylar
motion.





 MR
assessment
also
showed
articular
complications
in
25
 patients:
osteoarthritic
changes
of
the
condyle
(n=14),
 morphologic
changes
of
the
disk
(n=6
)
and
both
osseous
and
 disk

alterations
(n=5).





 Joint
fluid
SNR
was
significantly
higher
on
3D‐FSE‐Cube
 (mean=
137)
than
on
2D
FSE
(mean=81)
images.






 Muscle
SNR
was
also
higher
on
3D‐FSE‐Cube
(mean=21)
than


on
2D
FSE
(mean=17)
images.






 Finally,
disk
SNR
was
higher
on
3D‐FSE‐Cube
(mean=15)
than

 2D
FSE
(mean=
11)
acquisitions.






 Fluid‐cartilage
contrast‐to‐noise
ratio
was
higher
on
3D‐FSE‐ Cube
(mean=122)
than
2D
FSE
(mean=70).






 The
2D
FSE
and
3D‐FSE‐Cube
images
were
assessed
for
 overall
image
quality,
blurring,
and
artifacts.






 No
significant
difference
was
observed
comparing
the
overall
 image
quality
for
the
2D
FSE
and
3D‐FSE‐Cube
images
for
 either
coronal
or
sagittal
images.
Blurring
was
more
 pronounced
on
the
3D‐FSECube
images,
most
likely
because
of
 the
greater
T2
decay
during
the
long
echo
train.
Reformations
 of
the
3D‐FSE‐Cube
images
were
similar
to
the
directly
 acquired
2D
FSE
data,
except
that
the
3D‐FSE
Cube
sections
 were
much
thinner.
 
 Reader

 








Discussion


TMJ
dysfunction
is
a
common
condition
affecting
up
to
28%
of
 the
population,
most
often
affecting
females
(12‐13).
The
 principal
cause
of
TMJ
dysfunction
is
internal
derangement
 defined
as
an
abnormal
relationship
between
the
disk
and
the
 mandibular
condyle.






 MR
imaging
has
proved
to
be
the
standard
imaging
technique
 for
assessing
disk
abnormalities
such
as
displacement
and
 morphologic
changes.
Disk
displacements
may
be
uni
or
 multidirectional,
the
most
common
types
being
unidirectional
 anterior
and
multidirectional
anterolateral
or
anteromedial.
 Unidirectional
posterior
displacements
are
rare
(14‐15).

 Disk
position
is
first
assessed
in
closed
mouth
position.
 Unidirectional
disk
displacements
can
be
diagnosed
on
sagittal
 plane.

In
the
normal
TMJ
the
junction
of
the
posterior
band
of
 the
disk
and
the
posterior
attachment
of
the
disk
(the
so
called
 bilaminar
zone)
should
fall
between
10°
of
the
vertical
in
 closed
mouth
position.
A
pathologic
condition
is
considered
to
 be
present
if
the
angle
between
the
posterior
band
and
the
 vertical
orientation
of
the
mandibular
condyle
exceeds
10°
 (16‐18).
However,
some
studies
have
shown
that
this
grade
of


displacement
is
present
in
up
to
33%
of
asymptomatic
 volunteers
.





 Rammelsberg
et
al.

suggested
that
a
disk
displacement
of
30°
 could
be
considered
physiologic

and
that
this
displacement
 grading
could
better
correlate
with
clinical
symptoms
(19‐21).
 In
partial
displacements,
the
contact
between
the
disk
and
the
 articular
surface
of
the
disk
is
maintained;
this
relationship
is
 lost
in
case
of
complete
disk
displacements.





 The
assessment
of
multidirectional
disk
displacements
is
 based
on
the
combination
of
unidirectional
displacements
on
 both
sagittal
and
coronal
planes.
A
displaced
disk
can
regain
 its
normal
position
between
the
condyle
and
the
temporal
 bone
with
condylar
motion
in
open
jaw
position
and
that
 indicates
that
attachments
and
capsule
are
less
compromised
 than
in
joints
in
which
the
degree
of
subluxation
does
not
 change
with
jaw
opening.
Whether
a
disk
relocates
or
not
 during
mouth
opening
correlates
with
the
grading
of
the
 severity
of
internal
derangements
and
helps
identify
patients
 at
risk
for
developing
sequelae
such
as
inflammatory
arthritis.

 Another
pathologic
condition
is
the
stuck
disk;
in
this
 condition
the
disk
remains
in
a
fixed
position
between
the
 articular
surfaces
during
the
condylar
motion,
probably


secondary
to
the
formation
of
adhesions
(22‐23).
In
 subsequent
stages
of
internal
derangement
the
displaced
disk
 may
present
morphologic
changes
such
as
thickening
of
the
 posterior
band
and
reduction
of
the
anterior
and
central
 portions,
thus
leading
to
a
biconvex
or
rounded
or
irregular
 shape
(24‐27).




 Traditionally,
TMJ
MR
imaging
protocols
usually
include
 multiple
2D
FSE
sequences
acquired
in
orthogonal
planes,
 namely
sagittal
oblique
and
coronal
acquisitions
with
a
section
 thickness
of
3mm
or
less,
both
in
closed
and
open
mouth
 position.
It
must
be
kept
in
mind
that
decreasing
the
section
 thickness
inferior
to
2,5
mm
in
the
conventional
FSE
sequence
 can
lead
to
noisy
images.
However,
the
spatial
resolution
 provided
by
standard
two‐dimensional(2D)
fast
spin
echo
 (FSE)
sequences
is
still
a
significant
limitation
in
the
 evaluation
of
complex
structures.
 The
possibility
to
perform
3D
T2
weighted
imaging
has
always
 been
fascinating
although,
the
long
imaging
time
represented
 the
main
drawback.

 The
introduction
of
the
CUBE
sequence
has
considerably
 changed
the
technical
approach
of
MRI
exam
in
many
districts.


In
particular,
TMJ
can
take
advantage
from
the
3D
imaging
 because
of
its
small
size
and
complex
anatomy.
 Studying
the
TMJ,
the
main
advantage
of
the
3D‐Cube
 sequence
is
represented
by
the
possibility
to
perform
only
one
 acquisition
since
images
can
subsequently
be
reformatted
in
 multiple
orthogonal
planes.
This
makes
multiple
2D
 acquisitions
unnecessary
thus
saving
time.
This
make
the
MR
 exam
more
suited
in
case
of
patients
in
pain,
pediatric
patients
 who
are
unable
to
stay
still
for
long,
and
patients
with
 claustrophobia
who
are
able
to
tolerate
lying
in
the
magnet
 bore
only
for
short
periods
of
time.
 Moreover,
image
quality
for
the
3D‐Cube
resulted
to
be
 comparable
with
the
conventional
FSE.
Because
of
the
3D
 imaging,
the
section
thickness
of
the
cube
was
thinner
than
the
 standard
sequence.
The
section
thickness
in
3D‐FSE‐Cube
 imaging
was
approximately
three
times
less
than
that
in
2D
 FSE
imaging,
thereby
decreasing
partial‐volume
artifacts
and
 further
improving
depiction
of
anatomy.
This
can
be
especially
 useful
in
case
of
small,
degenerate
disk.


We
could
not
exploit
the
advantage
of
the
parallel
imaging
 strategy
because
it
was
not
compatible
with
the
3‐inch
 surfaced
dedicated
coil
that
we
use
in
our
department.
 The
possibility
of
apply
parallel
imaging
to
the
cube
sequence
 could
further
decrease
the
imaging
time
and
allow
to
get
 isotropic
imaging
(28‐29).

 Despite
a
minimal
blurring,
the
overall
image
quality
was
not
 significantly
different
between
the
two
sequences.

 
 In
conclusion
3D‐FSE‐Cube
is
a
promising
new
MR
imaging
 sequence
that
allows
the
rapid
acquisition
of
high
spatial‐ resolution
volumetric

data
that
can
be
reformatted
at
 arbitrary
section
thicknesses
and
in
oblique
and
curved
 planes,
making
it
ideal
for
evaluating
the
complex
anatomy
of
 the
TMJ
and
diagnosis
of
disease
with
improved
clinical
 efficiency
compared
with
protocols
that
use
multiple
planes
of
 2D
FSE
imaging
and
making
the
performance
of
numerous
 other
two‐dimensional
sequences
unnecessary.








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