3D-FIESTA序列在内耳及内听道MRI中的应用探讨

目的:探讨3D-FIESTA序列内耳及内听道成像技术及其临床应用价值.方法:用GE signa 3.0T超导型磁共振对25例共50耳应用3D-FIESTA序列做颞骨三维容积扫描,采用多平面重组(MPR)、最大强度投影(MIP)及仿真内窥镜(VE)行后处理,观察3D-FIESTA序列对内耳及内听道内各解剖结构的显示.结果:3D-FIESTA序列扫描结合MPR、MIP和VE重组对内耳迷路及内听道内神经及血管显示清晰,能够清晰显示两者之间的关系,MPR和VE重组对神经的显示优于MIP重组,MIP对半规管显示与双斜面MPR并无明显差别,VE和斜矢状面对于内听道内各神经孔的位置关系具有重要意义.结论:3D-FIESTA序列对内耳及内听道的结构显示清晰,具有较高的临床应用价值.     

MR imaging of the internal auditory canal and inner ear at 3T: comparison between 3D driven equilibrium and 3D balanced fast field echo sequences

OBJECTIVE: To compare the use of 3D driven equilibrium (DRIVE) imaging with 3D balanced fast field echo (bFFE) imaging in the assessment of the anatomic structures of the internal auditory canal (IAC) and inner ear at 3 Tesla (T). MATERIALS AND METHODS: Thirty ears of 15 subjects (7 men and 8 women; age range, 22-71 years; average age, 50 years) without evidence of ear problems were examined on a whole-body 3T MR scanner with both 3D DRIVE and 3D bFFE sequences by using an 8-channel sensitivity encoding (SENSE) head coil. Two neuroradiologists reviewed both MR images with particular attention to the visibility of the anatomic structures, including four branches of the cranial nerves within the IAC, anatomic structures of the cochlea, vestibule, and three semicircular canals. RESULTS: Although both techniques provided images of relatively good quality, the 3D DRIVE sequence was somewhat superior to the 3D bFFE sequence. The discrepancies were more prominent for the basal turn of the cochlea, vestibule, and all semicircular canals, and were thought to be attributed to the presence of greater magnetic susceptibility artifacts inherent to gradient-echo techniques such as bFFE. CONCLUSION: Because of higher image quality and less susceptibility artifacts, we highly recommend the employment of 3D DRIVE imaging as the MR imaging choice for the IAC and inner ear.     

Screening protocol for MR imaging of the internal auditory canal

We have previously shown that 5 mm axial T1-weighted images following Gd-diethylenetriamine pentaacetic acid (DTPA) administration were sufficient as a screening examination of the internal auditory canal (IAC) and cerebellopontine angle cistern in 80% of cases with sensorineural hearing loss. In the remaining 20% of cases 3 mm slices were necessary for confirmation of the diagnosis. To reduce the number of cases requiring the additional examination, we have modified our protocol to include a coronal "scout" T1-weighted sequence followed by 5 mm axial sections angled through the IACs. Routine axial T2-weighted images of the posterior fossa were also obtained. One hundred eleven patients were studied with this protocol. In all but two of these the 5 mm sections unequivocally provided the diagnosis and in those two cases the coronal images confirmed the diagnosis suspected on the axial study. Three millimeter slices were not necessary in any patient. This three sequence, post-Gd-DTPA protocol, which requires only 12 min of scan time, is recommended as a screening protocol for IAC and cerebellopontine angle disease.     

Intracranial aspergillosis involving the internal auditory canal and inner ear in an immunocompetent patient

We report the MR imaging findings in a case of intracranial aspergillosis involving the internal auditory canal (IAC) and inner ear in an immunocompetent patient. The presence of rim enhancement of the vestibulocochlear nerve, abnormal signal intensity involving the labyrinth, and adjacent meningeal enhancement might help clinicians to make a correct diagnosis in patients with a mass in the IAC and previous history of ear surgery.     

Role of slice thickness in MR imaging of the internal auditory canal

The relative efficacy of post-Gd-DTPA 5 and 3 mm axial T1-weighted images was compared in the detection of lesions in the internal auditory canal and cerebellopontine angle. One hundred twenty consecutive patients were prospectively evaluated with 5 mm axial T1-weighted slices. If these were negative or questionable. 3 mm axial slices were immediately obtained as the next sequence. Eighteen percent of cases were positive and in none of these was the 5 mm study normal. However, in 22 negative cases and two positive cases, a 3 mm study was necessary for confirmation. Five millimeter axial scanning post Gd-DTPA is recommended as the initial study for detection of masses in the internal auditory canal and cerebellopontine angle. Because this study requires fewer acquisitions than 3 mm sections and can be done satisfactorily on low and midfield systems, there are potential time- and cost-saving benefits to this approach.     

Virtual endoscopy of the inner ear and the auditory canal

To assess the role of virtual endoscopy (VE) in the examination of intracisternal structures and of the inner ear, we studied the anatomy of the labyrinth and internal auditory canal using the original CT slices and VE on the unaffected side in three female and three male patients, age range 3–46 years, with contralateral retrocochlear hearing loss. We also examined seven patients with different pathological findings. VE was performed using an advanced postprocessing program with high- resolution 3D data sets of CT (1–1.5 mm thickness, pitch 1.25) and MRI-CISS-3D (constructive interference in steady state) images of the basal cisterns (1.5 T, slice thickness 0.7–1 mm). VE provides an endoscopic-like view from a given point within the basal cisterns of vessels and nerves (on MRI) or of the structures of the inner ear (on CT). The complex anatomy and pathological changes in the inner ear can be faithfully shown. The main advantage is not basic diagnostic information but demonstration of topographically complex situations, such as the canalicular system of the inner ear, for discussion, preoperative planning and teaching. Received: 12 July 1999 Accepted: 3 September 1999     

The effect of patient positioning on MR imaging of the internal auditory canal

Summary Identification of individual cranial nerves and complete exclusion of tumor in the internal auditory canal may be difficult with MR, especially in imperfectly positioned patients. MR studies of the temporal bones in patients and in normal volunteers positioned non-rotated or canted were correlated with corresponding cryomicrotomic sections. Especially in axial images, oblique sectioning of cranial nerves VII and VIII may cause difficulty in identifying individual nerves. A combination of axial and coronal short TR and TE images can be used to confidently exclude intracanalicular tumor in most cases.     

MR detection of tumor in the internal auditory canal

The MR appearance of 15 tumors within or near the internal auditory canal was analyzed in detail and compared with the subsequent surgical observations. In most cases, nonenhanced MR showed the precise extent of the intracanalicular and extracanalicular tumor despite minor variations in appearance. In a case of facial nerve neurinoma, the extent to which the tumor invaded the canal was underestimated by MR. Gadolinium-DTPA enhancement is expected to eliminate uncertainties in MR imaging of the internal auditory canal.     

MR of the normal and abnormal internal auditory canal

MR performed with thin, contiguous sections has replaced CT for the study of the cerebellopontine angle and for diagnosis of acoustic neuromas. In our experience large acoustic neuromas are well seen in all pulse sequences. Tumors with small extracanalicular components are seen in the T1- and spin-density-weighted sequences whereas purely intracanalicular lesions are often visualized only in the T1-weighted images. Small acoustic neuromas producing thickening of the nerve are easily recognizable in narrow internal auditory canals but may be missed in large canals because of partial volume averaging. Since further enhancement of the signal intensity of tumors can be obtained by IV injection of paramagnetic agents, we foresee the use of such agents in the near future in the diagnosis of acoustic neuromas.