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DOI:10.2214/AJR.05.0622
AJR 2007; 188:228-232
© American Roentgen Ray Society

Clinical Observations

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
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
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
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
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
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
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.


Figure 1
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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.

 


Figure 2
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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.

 


Figure 3
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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.

 

Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
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.


Figure 4
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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.

 

Figure 5
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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).

 

Figure 6
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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).

 

Figure 7
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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).

 

Figure 8
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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).

 

Figure 9
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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).

 

Figure 10
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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.

 

Figure 11
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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).

 

Figure 12
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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.

 

Figure 13
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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).

 

Figure 14
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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.

 

Figure 15
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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.

 
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

 


Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
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.


References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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  9. Izumi M, Eguchi K, Nakamura H, Nagataki S, Nakamura T. Premature fat deposition in the salivary glands associated with Sjögren's syndrome: MR and CT evidence. AJNR1997; 18:951 -958[Abstract]
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  11. Szolar DH, Groell R, Braun H, et al. Ultrafast CT and three-dimensional image processing of CT sialography in patients with parotid masses poorly defined by MRI. Acta Otolaryngol1996; 116:112 -118[Medline]
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