Downloaded from www.ajronline.org by 182.59.58.20 on 10/22/15 from IP address 182.59.58.20. Copyright ARRS. For personal use only; all rights reserved
631
Technical
L: .
#{149}
.
.
..
.
Arterial
from Penetrating
Injury
Trauma: Evaluation Fat-Suppressed MR Imaging
Single-Acquisition James J. Yaquinto,1 Michael L. Foreman2
Steven
E. Harms,1
Paul I. Sierners,1
MR angiography is emerging as a clinical tool for the noninvasive diagnosis of intracranial, neck, and abdominal vascular abnormalities. The application of MR angiography for extremity vascular diagnosis, however, has been limited. Angiography
is often
required
to evaluate
arterial
integrity
after penetrating wounds to the extremities [1]. However, most studies performed because of the proximity of the trauma to major vessels in the absence of physical findings suggesting arterial injury have normal results [2]. The use of MR as a primary imaging method in cases of suspected injury close to major vessels in the extremities is explored with a new MR technique that allows noninvasive, high-resolution anatomic
as well as vascular
dimensional Subjects Patients
evaluation
from
a single
three-
(3-D) acquisition.
Duane
P. Flarnig,1
Richard
H. Gnffey,1
with and
We used a 3-D gradient-echo fast-scan sequence, fast adiabatic trajectory in the steady state (FATS), which produces fat-suppressed proton density-weighted images (Harms SE et al., presented at the Society
of Magnetic
Resonance
in Medicine
meeting,
August
1990).
FATS uses two sequentially applied (with opposing phase) adiabatic half-passage RF pulses placed on resonance for fat. The opposing positive and negative amplitudes of the adiabatic pulses produce no net magnetization from fat. Because the sequence is tuned for fat,
water signal is detected off-resonance.
A 20/2.8 (TRITE) sequence
is used with two excitations and an acquisition x 128 to produce a scan time of approximately
of 1024 x 128 1 0 mm. The displayed image matrix is I 28 x 256 x 256 for voxel dimensions of 1 .4 x 0.7 x 0.7 mm. A General Electric independent console was used for near real time multiplanar reconstruction of anatomic images. Also, a Sun Microsystems 3/260 workstation with a TAAC accelerator was used for tracing of vascular images.
matrix
maximum-intensity-projection
(MIP)
ray
and Methods were selected
the presence angiography.
prospectively
without
regard
to whether
or absence of injury had been identified by conventional Patients with possible arterial injury from residual ferro-
magnetic shotgun pellets were excluded. All patients were men and less than 41 years old. All patients had digital subtraction angiography (DSA) before MR imaging. The results of conventional angiography
were available when the MR angiogram was interpreted but were not available at the time of scanning. Images
Note
were obtained
on a Signa
1 .5-T magnet
(General
Electric,
Milwaukee, WI) 4.6-level software. A transmit-receive extremity coil (General Electric) was placed over the area of penetrating trauma. Received July 8, 1991 ; accepted after revision September I Department of Radiology, Magnetic Resonance Imaging
requests to S. E. Harms. 2 Department of Surgery, Baylor AJR 158:631-633,
March
1992
University
Medical
Center,
0361-803X/92/1583-0631
12, 1991. Section,
Baylor
Dallas,
TX 75246.
© American
Results
Twelve cases of penetrating trauma of the extremity in 11 patients were studied for suspected vascular injury. The injuries included 1 1 gunshot wounds and one knife wound. Eight
injuries
were
to lower
extremities
and four
to upper
extremities. All MR studies were technically satisfactory. FATS integrated anatomic and vascular images, and DSA was equally effective in depicting normal and abnormal vessels (Figs. 1
University
Medical
Roentgen Ray Society
Center, 3500 Gaston Ave., Dallas, TX 75246. Address
reprint
YAQUINTO
632
El
AL.
AJR:158,
Marth
1992
Fig. 1.-Occlusion of anterior tibial artery in a patient wIth gunshot wound
to the calf
A,
Coronal
In a steady image shows lal artery
fast adiabatic trajectory state (FATS) 20/2.8 MR truncation of anterior tib-
(arrow).
Downloaded from www.ajronline.org by 182.59.58.20 on 10/22/15 from IP address 182.59.58.20. Copyright ARRS. For personal use only; all rights reserved
B, MR anglogram
obtained
from
FATS 20/2.8 acquisItion confirms occluslon of anterIor tiblal artery (arrow). C, Dlgftal
subtraction
also shows tibial artery. leg
anglogram
occlusion
of
of anterior
of bra-
Fig. 2.-Pseudoaneurysm chial artery. A, Sagfttal fast adiabatic In a steady state (FATS)
trajectory 20/2.8 MR
image of arm shows abnormalIty of brachial artery (arrow). B, MR angiogram obtained from FATS 20/2.8 data shows brachial artery pseudoaneurysm (straight arrow). Superficlal venous flow (curved arrow) is also seen. C, Digital
subtraction
angiogram
of
arm confirms pseudoaneurysm.
A
B
C
and 2). Three vascular injuries were identified by both DSA and MR in one patient each. These included occlusion of the ulnar artery, occlusion, of the anterior tibial artery, and a
were identified in three patients. Workstation calculation of image reformations in near real time allowed the tomographic
nonoccluding
marks for accurate delineation of vascular ciated bone and soft-tissue injuries.
brachial
artery
pseudoaneurysm.
Soft-tissue anatomy was well depicted with good fat suppression by the FATS technique. Small focal areas of low signal were identified in soft tissues. These low-signal areas corresponded to small metallic fragments and/or small collections of air and were useful for indicating areas of possible trauma in the soft tissues. Osseous and soft-tissue injuries
depiction
of vessels
along
with
the display
of anatomic
injuries
land-
and asso-
Discussion MIP
ray tracing
angiographic
methods
images.
are often
Hyperintense
used to calculate signal
from
fat can
MR be
AJR:158,
confused produce
March
FAT-SUPPRESSION
1992
with hyperintense artifacts
with the MIP method.
Downloaded from www.ajronline.org by 182.59.58.20 on 10/22/15 from IP address 182.59.58.20. Copyright ARRS. For personal use only; all rights reserved
giography
signal from vessels,
in calculated
angiographic
Fat suppression
of the extremities
and thereby
images
is helpful
to reduce
signal
MR OF ARTERIAL
obtained
in MR an-
intensity
from
fat, which can obscure vascular detail on MIP ray tracings. Fat-suppression techniques such as chemical-shift presaturation or methods that use phase differences between fat and water require longer IR times or multiple excitations [3, 4]. FATS achieves fat suppression more efficiently by using a short IR with thin, high-resolution images. Vascular imaging in MR is generally achieved by enhancing signal from flowing tionary tissue [5].
blood while suppressing With the FATS technique,
signal from staflow-enhance-
ment data for MR angiography comes from time-of-flight (IOF) effects as well as the ability of adiabatic pulses to refocus off-resonance spins that are frequency shifted because of flow. A typical 3-D TOF method uses Ti -weighting to suppress background stationary tissue while potentiating flow-related enhancement effects, whereas FATS is a protondensity weighted method that has reduced flow-related enhancement. The adiabatic pulses used in the FATS sequence refocus the flowing spins that are frequency shifted to potentiate flow intensity. The flow-enhancement effects of the FATS technique are afforded without the need to suppress the signal from stationary tissue. Moreover, a larger region of interest can be surveyed by the FATS technique compared with the usual 3-D TOF method, which requires a thinner slab in order
to increase
The high-resolution in the current
study
flow-related
enhancement.
3-D anatomic allowed
accurate
data provided evaluation
by FATS
of soft-tissue
and bone injury for assessing the possibility of injury close to vascular structures before angiographic data were reviewed.
TRAUMA
633
Diagnostic information was not limited to distinguishing between occlusion and patency; for example, a small (6 mm) pseudoaneurysm was well depicted by this technique. The inability to visualize slow retrograde flow in a more proximally occluded artery and the loss of signal in the distal portion of arteries due to TOF effects might pose diagnostic problems with our method. However, if anatomic reformations indicate possible soft-tissue injury distal to the initial scanning region, the extremity coil can be repositioned for additional acquisitions.
Assessment
of upper
thigh
or shoulder
injuries
may be impossible if this part of the limb does not fit into the extremity coil. In the future, transmit-receive coils could be enlarged for this purpose. In summary, the combined soft-tissue and vascular display provided by FATS makes it a potentially effective technique for evaluating certain types of penetrating vascular proximity injuries. Further work needs to be done to determine the sensitivity and specificity of this method in the diagnosis of vascular injuries, including intimal flaps, arteriovenous fistulas, and nonoccluding arterial thrombi. REFERENCES 1 . Rose SC, Moore EE. Angiography in patients with arterial trauma: correlation between angiographic abnormalities, operative findings, and dinical outcome. 2. McCorkell
AJR 1987;149:613-619 SJ, Harley JD, Morishima MS, Cummings DK. Indications for angiography in extremity trauma. AiR 1985;145: 1245-1 247 3. Hasse A, Frahm J. Multiple chemical shift selective NMR imaging using stimulated echoes. J Magn Reson 1985;64:94-102 4. Dixon wT. Simple proton spectroscopic imaging. Radiology 1984; 153: 189-1 94 5. Dumoulin CL, Hart HR. Magnetic resonance angiography. Radiology 1986; 161:717-720
631
Technical
L: .
#{149}
.
.
..
.
Arterial
from Penetrating
Injury
Trauma: Evaluation Fat-Suppressed MR Imaging
Single-Acquisition James J. Yaquinto,1 Michael L. Foreman2
Steven
E. Harms,1
Paul I. Sierners,1
MR angiography is emerging as a clinical tool for the noninvasive diagnosis of intracranial, neck, and abdominal vascular abnormalities. The application of MR angiography for extremity vascular diagnosis, however, has been limited. Angiography
is often
required
to evaluate
arterial
integrity
after penetrating wounds to the extremities [1]. However, most studies performed because of the proximity of the trauma to major vessels in the absence of physical findings suggesting arterial injury have normal results [2]. The use of MR as a primary imaging method in cases of suspected injury close to major vessels in the extremities is explored with a new MR technique that allows noninvasive, high-resolution anatomic
as well as vascular
dimensional Subjects Patients
evaluation
from
a single
three-
(3-D) acquisition.
Duane
P. Flarnig,1
Richard
H. Gnffey,1
with and
We used a 3-D gradient-echo fast-scan sequence, fast adiabatic trajectory in the steady state (FATS), which produces fat-suppressed proton density-weighted images (Harms SE et al., presented at the Society
of Magnetic
Resonance
in Medicine
meeting,
August
1990).
FATS uses two sequentially applied (with opposing phase) adiabatic half-passage RF pulses placed on resonance for fat. The opposing positive and negative amplitudes of the adiabatic pulses produce no net magnetization from fat. Because the sequence is tuned for fat,
water signal is detected off-resonance.
A 20/2.8 (TRITE) sequence
is used with two excitations and an acquisition x 128 to produce a scan time of approximately
of 1024 x 128 1 0 mm. The displayed image matrix is I 28 x 256 x 256 for voxel dimensions of 1 .4 x 0.7 x 0.7 mm. A General Electric independent console was used for near real time multiplanar reconstruction of anatomic images. Also, a Sun Microsystems 3/260 workstation with a TAAC accelerator was used for tracing of vascular images.
matrix
maximum-intensity-projection
(MIP)
ray
and Methods were selected
the presence angiography.
prospectively
without
regard
to whether
or absence of injury had been identified by conventional Patients with possible arterial injury from residual ferro-
magnetic shotgun pellets were excluded. All patients were men and less than 41 years old. All patients had digital subtraction angiography (DSA) before MR imaging. The results of conventional angiography
were available when the MR angiogram was interpreted but were not available at the time of scanning. Images
Note
were obtained
on a Signa
1 .5-T magnet
(General
Electric,
Milwaukee, WI) 4.6-level software. A transmit-receive extremity coil (General Electric) was placed over the area of penetrating trauma. Received July 8, 1991 ; accepted after revision September I Department of Radiology, Magnetic Resonance Imaging
requests to S. E. Harms. 2 Department of Surgery, Baylor AJR 158:631-633,
March
1992
University
Medical
Center,
0361-803X/92/1583-0631
12, 1991. Section,
Baylor
Dallas,
TX 75246.
© American
Results
Twelve cases of penetrating trauma of the extremity in 11 patients were studied for suspected vascular injury. The injuries included 1 1 gunshot wounds and one knife wound. Eight
injuries
were
to lower
extremities
and four
to upper
extremities. All MR studies were technically satisfactory. FATS integrated anatomic and vascular images, and DSA was equally effective in depicting normal and abnormal vessels (Figs. 1
University
Medical
Roentgen Ray Society
Center, 3500 Gaston Ave., Dallas, TX 75246. Address
reprint
YAQUINTO
632
El
AL.
AJR:158,
Marth
1992
Fig. 1.-Occlusion of anterior tibial artery in a patient wIth gunshot wound
to the calf
A,
Coronal
In a steady image shows lal artery
fast adiabatic trajectory state (FATS) 20/2.8 MR truncation of anterior tib-
(arrow).
Downloaded from www.ajronline.org by 182.59.58.20 on 10/22/15 from IP address 182.59.58.20. Copyright ARRS. For personal use only; all rights reserved
B, MR anglogram
obtained
from
FATS 20/2.8 acquisItion confirms occluslon of anterIor tiblal artery (arrow). C, Dlgftal
subtraction
also shows tibial artery. leg
anglogram
occlusion
of
of anterior
of bra-
Fig. 2.-Pseudoaneurysm chial artery. A, Sagfttal fast adiabatic In a steady state (FATS)
trajectory 20/2.8 MR
image of arm shows abnormalIty of brachial artery (arrow). B, MR angiogram obtained from FATS 20/2.8 data shows brachial artery pseudoaneurysm (straight arrow). Superficlal venous flow (curved arrow) is also seen. C, Digital
subtraction
angiogram
of
arm confirms pseudoaneurysm.
A
B
C
and 2). Three vascular injuries were identified by both DSA and MR in one patient each. These included occlusion of the ulnar artery, occlusion, of the anterior tibial artery, and a
were identified in three patients. Workstation calculation of image reformations in near real time allowed the tomographic
nonoccluding
marks for accurate delineation of vascular ciated bone and soft-tissue injuries.
brachial
artery
pseudoaneurysm.
Soft-tissue anatomy was well depicted with good fat suppression by the FATS technique. Small focal areas of low signal were identified in soft tissues. These low-signal areas corresponded to small metallic fragments and/or small collections of air and were useful for indicating areas of possible trauma in the soft tissues. Osseous and soft-tissue injuries
depiction
of vessels
along
with
the display
of anatomic
injuries
land-
and asso-
Discussion MIP
ray tracing
angiographic
methods
images.
are often
Hyperintense
used to calculate signal
from
fat can
MR be
AJR:158,
confused produce
March
FAT-SUPPRESSION
1992
with hyperintense artifacts
with the MIP method.
Downloaded from www.ajronline.org by 182.59.58.20 on 10/22/15 from IP address 182.59.58.20. Copyright ARRS. For personal use only; all rights reserved
giography
signal from vessels,
in calculated
angiographic
Fat suppression
of the extremities
and thereby
images
is helpful
to reduce
signal
MR OF ARTERIAL
obtained
in MR an-
intensity
from
fat, which can obscure vascular detail on MIP ray tracings. Fat-suppression techniques such as chemical-shift presaturation or methods that use phase differences between fat and water require longer IR times or multiple excitations [3, 4]. FATS achieves fat suppression more efficiently by using a short IR with thin, high-resolution images. Vascular imaging in MR is generally achieved by enhancing signal from flowing tionary tissue [5].
blood while suppressing With the FATS technique,
signal from staflow-enhance-
ment data for MR angiography comes from time-of-flight (IOF) effects as well as the ability of adiabatic pulses to refocus off-resonance spins that are frequency shifted because of flow. A typical 3-D TOF method uses Ti -weighting to suppress background stationary tissue while potentiating flow-related enhancement effects, whereas FATS is a protondensity weighted method that has reduced flow-related enhancement. The adiabatic pulses used in the FATS sequence refocus the flowing spins that are frequency shifted to potentiate flow intensity. The flow-enhancement effects of the FATS technique are afforded without the need to suppress the signal from stationary tissue. Moreover, a larger region of interest can be surveyed by the FATS technique compared with the usual 3-D TOF method, which requires a thinner slab in order
to increase
The high-resolution in the current
study
flow-related
enhancement.
3-D anatomic allowed
accurate
data provided evaluation
by FATS
of soft-tissue
and bone injury for assessing the possibility of injury close to vascular structures before angiographic data were reviewed.
TRAUMA
633
Diagnostic information was not limited to distinguishing between occlusion and patency; for example, a small (6 mm) pseudoaneurysm was well depicted by this technique. The inability to visualize slow retrograde flow in a more proximally occluded artery and the loss of signal in the distal portion of arteries due to TOF effects might pose diagnostic problems with our method. However, if anatomic reformations indicate possible soft-tissue injury distal to the initial scanning region, the extremity coil can be repositioned for additional acquisitions.
Assessment
of upper
thigh
or shoulder
injuries
may be impossible if this part of the limb does not fit into the extremity coil. In the future, transmit-receive coils could be enlarged for this purpose. In summary, the combined soft-tissue and vascular display provided by FATS makes it a potentially effective technique for evaluating certain types of penetrating vascular proximity injuries. Further work needs to be done to determine the sensitivity and specificity of this method in the diagnosis of vascular injuries, including intimal flaps, arteriovenous fistulas, and nonoccluding arterial thrombi. REFERENCES 1 . Rose SC, Moore EE. Angiography in patients with arterial trauma: correlation between angiographic abnormalities, operative findings, and dinical outcome. 2. McCorkell
AJR 1987;149:613-619 SJ, Harley JD, Morishima MS, Cummings DK. Indications for angiography in extremity trauma. AiR 1985;145: 1245-1 247 3. Hasse A, Frahm J. Multiple chemical shift selective NMR imaging using stimulated echoes. J Magn Reson 1985;64:94-102 4. Dixon wT. Simple proton spectroscopic imaging. Radiology 1984; 153: 189-1 94 5. Dumoulin CL, Hart HR. Magnetic resonance angiography. Radiology 1986; 161:717-720
