DOI:10.2214/AJR.05.0622
AJR 2007; 188:228-232
© American Roentgen Ray Society
Balanced Turbo Field-Echo Sequence for MRI of Parotid Gland Diseases
Misa Sumi1,
Marc Van Cauteren2,
Yukinori Takagi1 and
Takashi Nakamura1
1 Department of Radiology and Cancer Biology, Nagasaki University School of
Dentistry, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan.
2 Philips Medical Systems, 2-13-37, Kohnan Minato-ku, Tokyo 108-8507,
Japan.
Received April 11, 2005;
accepted after revision July 13, 2005.
Address correspondence to T. Nakamura
(taku{at}net.nagasaki-u.ac.jp).
Abstract
OBJECTIVE. A balanced turbo field-echo (FE) sequence is a balanced
steady-state free precession sequence used for achieving rapid and high
imaging. We tested whether this imaging technique is applicable to the
diagnosis of parotid gland diseases.
CONCLUSION. The balanced turbo FE sequence is a novel alternative
MRI technique for the diagnosis of various parotid gland diseases.
Keywords: head and neck imaging • MRI • MR technique • parotid gland
Introduction
Balanced turbo field-echo (FE) and balanced fast-field echo sequences are
steady-state free precession MR techniques for achieving rapid and high
signal-to-noise ratio (SNR) imaging
[1,
2]. These sequences have been
successfully applied, for example, to cardiac MRI
[3,
4] and angiography of the
abdominal arteries [5]. These
imaging techniques recently became achievable on clinical systems thanks to
improved high-magnetic-field homogeneity through improved magnet design and
active magnetic field shimming and to radiofrequency pulses with shorter TRs
and TEs and with large flip angles through high-performance radiofrequency
coils.
The balanced turbo FE sequence yields high signal of blood vessels and body
fluids and can reliably differentiate fat tissues from water by combining with
a fat-suppression prepulse, such as spectral presaturation with inversion
recovery [6]. These properties
of the balanced turbo FE sequence appear suitable for imaging the parotid
gland because it is composed of varying amounts of water and fat. Moreover,
the balanced turbo FE sequence allows high-resolution imaging using a
microscopy coil to be performed with ultrashort image acquisition times.
Therefore, the purpose of this study was to test whether a balanced turbo FE
sequence is applicable to diagnostic imaging of the parotid glands. We expect
that the sequence combined with a spectral presaturation with inversion
recovery technique and a microscopy coil may provide a novel alternative
high-resolution MRI sequence for diagnosis of parotid gland diseases.
Materials and Methods
Six healthy volunteers (four women and two men; mean age, 27 years; age
range, 24-38 years) and 20 patients (13 women and seven men; mean age, 52
years; age range, 29-73 years) with parotid gland diseases were studied using
a superconductive 1.5-T MR unit (Gyroscan Intera 1.5-T Master, Philips Medical
Systems) with a 47-mm microscopy coil. The patient cohort included those with
Warthin's tumor (n = 5), pleomorphic adenoma (n = 4),
Sjögren's syndrome (n = 4), lymphadenitis (n = 2),
lymphoma (n = 1), cyst (n = 1), sialoadenitis (n =
1), sialodochitis (n = 1), and branchial cleft cyst (n = 1).
Diagnoses of salivary gland tumors, lymphoma, and cyst were made by histologic
examinations of the excised tumors. The diagnosis of Sjögren's syndrome
was made on the basis of classification criteria proposed by the
American-European Consensus Group
[7]. We diagnosed inflammatory
lesions on the basis of MRI findings and the presence of clinical symptoms,
such as pain and swelling, and remission after treatment with antiinflammatory
drugs.
After a conventional spin-echo T1-weighted sequence (TR/TE, 550/10; number
of signal acquisitions, 3) and a fat-suppression spectral presaturation with
inversion recovery turbo spin-echo T2-weighted sequence (3,000/90; number of
signal acquisitions, 6; turbo factor, 11) were performed, the parotid glands
were imaged with a balanced turbo FE sequence that was combined with a
spectral presaturation with inversion recovery prepulse sequence (6.2/3.1;
number of signal acquisitions, 2). A 3D image acquisition technique was used
with a field of view of 80 mm, a flip angle of 90°, matrix dimensions of
140 x 160, a slice thickness of 1.2 mm, and a slice gap of -0.6 mm. Full
maximum-intensity-projection (MIP) axial images were then obtained from
contiguous axial balanced turbo FE images. The time required for balanced
turbo FE imaging of the whole parotid gland was less than 3 minutes. When
selected sialography was required, a targeted MIP technique was used on the
original set of axial balanced turbo FE images of the parotid glands.
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Fig. 1A —Healthy 24-year-old woman. eca = external carotid artery, ica
= internal carotid artery, ijv = internal jugular vein, mm = masseter muscle,
mpm = medial pterygoid muscle, mr = mandibular ramus, pd = intraglandular main
duct, rmv = retromandibular vein, st = Stensen duct. Representative axial
balanced turbo field-echo (FE) MR image (TR/TE, 6.2/3.1; number of signal
acquisitions, 2) shows parotid gland (arrowheads) and surrounding
structures.
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Fig. 1B —Healthy 24-year-old woman. eca = external carotid artery, ica
= internal carotid artery, ijv = internal jugular vein, mm = masseter muscle,
mpm = medial pterygoid muscle, mr = mandibular ramus, pd = intraglandular main
duct, rmv = retromandibular vein, st = Stensen duct.
Maximum-intensity-projection (MIP) image obtained from sequential axial
balanced turbo FE MR images shows sialographic image of parotid duct and
special relationship between gland and surrounding structures such as blood
vessels.
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Fig. 1C —Healthy 24-year-old woman. eca = external carotid artery, ica
= internal carotid artery, ijv = internal jugular vein, mm = masseter muscle,
mpm = medial pterygoid muscle, mr = mandibular ramus, pd = intraglandular main
duct, rmv = retromandibular vein, st = Stensen duct. Targeted MIP image shows
parotid duct.
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Results
The balanced turbo FE sequence steadily depicted the parotid ducts and the
branches of the external carotid artery and of the jugular vein (Figs.
1A,
1B, and
1C). The sequence delineated
the locations of parotid tumors relative to the gland and the internal
structures of the tumors (Figs.
2A,
2B,
2C,
3A,
3B, and
3C). Displaced ducts and blood
vessels were also observed around tumors. However, a clear separation of the
intraglandular duct ramifications and the blood vessels may be difficult. On
the other hand, the sequence steadily showed dilatations of the ducts in
patients with parotitis (Figs.
4A,
4B, and
4C). The balanced turbo FE
sequence also depicted changes in the gland parenchyma where varying
sialectatic changes of punctate, globular, and cystic (Figs.
5A,
5B, and
5C) patterns were
characteristically seen in patients with Sjögren's syndrome; these
findings are representative of the severity of the disease.
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Fig. 2A —55-year-old man with Warthin's tumor of parotid gland.
Representative axial balanced turbo field-echo (FE) MR image (TR/TE, 6.2/3.1;
number of signal acquisitions, 2) shows multiple tumor masses (t) with
homogeneous signals occupying deep part of parotid gland
(arrowheads). eca = external carotid artery, n = lymph node, pd =
intraglandular main duct, rmv = retromandibular vein.
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Fig. 2B —55-year-old man with Warthin's tumor of parotid gland.
Maximum-intensity-projection (MIP) image obtained from sequential axial
balanced turbo FE MR images shows course of displaced intraglandular main duct
(pd) and branches from external carotid artery (arrowheads) around
and through tumor (t).
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Fig. 2C —55-year-old man with Warthin's tumor of parotid gland.
Volume-rendering image shows spatial relationship between tumor masses (t) and
surrounding blood vessels (arrowheads, branches of external carotid
artery) or intraglandular main duct (pd).
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Fig. 3A —59-year-old woman with pleomorphic adenoma. eca = external
carotid artery, ica = internal carotid artery, ijv = internal jugular vein,
pav = posterior auricular vein, pd = intraglandular main duct, rmv =
retromandibular vein. Representative axial balanced turbo field-echo (FE) MR
image (TR/TE, 6.2/3.1; number of signal acquisitions, 2) shows lobulated tumor
(t) in superficial portion of parotid gland (arrowheads). Tumor is
heterogeneous in signal intensity and is distant from intraglandular main duct
(pd).
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Fig. 3B —59-year-old woman with pleomorphic adenoma. eca = external
carotid artery, ica = internal carotid artery, ijv = internal jugular vein,
pav = posterior auricular vein, pd = intraglandular main duct, rmv =
retromandibular vein. Maximum-intensity-projection image obtained from
sequential axial balanced turbo FE MR images shows tumor (t) is close to
posterior auricular vein (pav).
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Fig. 3C —59-year-old woman with pleomorphic adenoma. eca = external
carotid artery, ica = internal carotid artery, ijv = internal jugular vein,
pav = posterior auricular vein, pd = intraglandular main duct, rmv =
retromandibular vein. Volume-rendering image shows spatial relationship
between tumor masses (t) and surrounding blood vessels and intraglandular main
duct (pd).
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Fig. 4A —41-year-old woman with parotitis (sialodochitis). eca =
external carotid artery, ejv = external jugular vein, ica = internal carotid
artery, ijv = internal jugular vein, rmv = retromandibular vein.
Representative axial balanced turbo field-echo (FE) MR image (TR/TE, 6.2/3.1;
number of signal acquisitions, 2) shows dilated intraglandular main duct (pd).
Parenchymal signals of parotid gland (arrowheads) are normal.
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Fig. 4B —41-year-old woman with parotitis (sialodochitis). eca =
external carotid artery, ejv = external jugular vein, ica = internal carotid
artery, ijv = internal jugular vein, rmv = retromandibular vein.
Maximum-intensity-projection (MIP) image obtained from sequential axial
balanced turbo FE MR images shows sausagelike dilatation of intraglandular
main duct (pd).
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Fig. 4C —41-year-old woman with parotitis (sialodochitis). eca =
external carotid artery, ejv = external jugular vein, ica = internal carotid
artery, ijv = internal jugular vein, rmv = retromandibular vein. Target MIP
for MR sialography shows dilated intraglandular main duct (pd) and
ductules.
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Fig. 5A —60-year-old woman with Sjögren's syndrome (severely
affected). eca = external carotid artery, ica = internal carotid artery, ijv =
internal jugular vein, pd = intraglandular main duct, rmv = retromandibular
vein. Representative axial balanced turbo field-echo (FE) MR image (TR/TE,
6.2/3.1; number of signal acquisitions, 2) shows high-intensity spots in
parotid gland (arrowheads).
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Fig. 5B —60-year-old woman with Sjögren's syndrome (severely
affected). eca = external carotid artery, ica = internal carotid artery, ijv =
internal jugular vein, pd = intraglandular main duct, rmv = retromandibular
vein. Maximum-intensity-projection (MIP) image obtained from sequential axial
balanced turbo FE images shows globular pattern of sialectasia involving
superficial and deep portions of gland. Note cyst (lymphoepithelial cyst,
arrowheads) formation in gland.
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Fig. 5C —60-year-old woman with Sjögren's syndrome (severely
affected). eca = external carotid artery, ica = internal carotid artery, ijv =
internal jugular vein, pd = intraglandular main duct, rmv = retromandibular
vein. Targeted MIP image from MR sialography shows "fruit-laden
tree" pattern that is characteristic of Sjögren's syndrome. Note
cyst (arrowheads) formation in gland.
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In Table 1, we summarize
signal intensity levels of the normal anatomic structures and pathologic
findings in the parotid region that were detectable on fat-suppressed spectral
presaturation with inversion recovery balanced turbo FE images.
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TABLE 1: Signal Intensity Levels of Normal Anatomic Structures and Abnormal
Findings of Parotid Gland Region on Fat-Suppressed Balanced Turbo Field-Echo
Images
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Discussion
In this report, we have presented our findings that the balanced turbo FE
technique is applicable to diagnostic imaging of parotid gland diseases. The
proposed rapid high-resolution MRI technique reveals changes in the gland
parenchyma, gland ducts, blood vessels that supply the gland, and tumors
arising in and around the gland. In addition, we can combine the balanced
turbo FE sequence with a fat-suppression prepulse, such as a spectral
presaturation with inversion recovery technique, for imaging the parotid
gland; the combined technique efficiently differentiates water components from
fat components in the gland [8,
9].
A clinical advantage of the balanced turbo FE sequence is that it can
provide MR images with high SNR within short image acquisition times. This
property is advantageous for visualizing the detailed architecture of the
parotid gland using a microscopy coil. This advantage holds for balanced turbo
FE sequence-based 3D MR sialography using a microscopy coil: We found that the
image acquisition time was less than 3 minutes. A recent report showed that
the optimal 2D MR sialography sequence using a microscopy coil requires an
acquisition time of approximately 1 minute
[10]. Three-dimensional MR
sialography using a microscopy coil significantly improved the duct smoothness
of the intraglandular branches, albeit at the expense of longer imaging times
(
5 minutes). Therefore, the balanced turbo FE technique may be suitable
for 3D MRI of the parotid glands.
Furthermore, the balanced turbo FE technique for 3D MR sialography is
superior to the previous technique in that it shows neighboring intra- or
extraglandular lesions (Figs.
2A,
2B,
2C,
3A,
3B,
3C,
4A,
4B,
4C,
5A,
5B, and
5C). A unique aspect of this
balanced turbo FE technique is that it is able to reveal the relationship
between the ducts and the intraglandular tumor; previous MR sialographic
techniques did not consistently show those findings
[11]. To compensate for the
image intensity inhomogeneity that is inherent to the use of small microscopy
coils, we used the constant level appearance (referred to as
"CLEAR") postprocessing technique, which enables improved
visualization of deep parotid tumors.
The balanced turbo FE technique is a powerful tool for visualization of the
blood vessels without using contrast medium. This is mainly due to the fact
that blood produces high signals that can be depicted by the balanced turbo FE
sequence. However, in some patients, definite separation of the blood vessels
and parotid ducts was difficult. Notwithstanding that shortcoming, the
application of the balanced turbo FE technique to visualization of blood
vessels, such as the external carotid artery and its branches and the
retromandibular vein, may be beneficial for evaluating tumor extent and
predicting the location of the facial nerve
[12].
We expect that the balanced turbo FE technique using a microscopy coil is
applicable to diagnostic MRI for a wide range of diseases of the head and
neck, where high-resolution imaging with high SNRs is required to image the
superficial organs. Rapid real-time imaging is also beneficial for functional
diagnosis in the head and neck regions. Thus, the balanced turbo FE sequence
may be useful for diagnosis of diseases in the salivary glands and tongue and
for functional imaging of temporomandibular disorders.
In conclusion, the balanced turbo FE technique using a microscopy coil is a
novel, alternative rapid high-resolution MRI technique associated with high
SNRs for the diagnosis of parotid gland diseases.
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Abstract
Introduction
