Innovations in Endoscopic Ear Surgery by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9789811379321
Publisher: Springer Singapore

6.2 Diffusion Weighted Imaging for Cholesteatomas

Middle ear CT imaging provides us with precise anatomical bony information. Not only cholesteatomas but also accumulation of fluid and granulation exhibit a soft tissue density in the CT. Thus, it is difficult to distinguish cholesteatomas from these other elements using only CT imaging. In contrast, middle ear cholesteatomas exhibit high intensity on diffusion weighted image (DWI) because they are histopathologically equivalent to epidermoid cysts. Therefore, DWI is useful for distinguishing cholesteatomas from granulation and fluid collection in the middle ear [2–7].

Conventional DWI has been used for diagnosing several conditions (e.g., acute cerebral infarction) and involves a very short scan duration sequence by using echo planar images (EPI). However, images of the middle ear are unclear on conventional DWI using EPI because conventional DWI is susceptible to artifacts due to the presence of air in the middle ear, especially in the mastoid air cells. In particular, it is difficult to detect small cholesteatomas, and the sensitivity is low [2–7]. Fortunately, clear middle ear images can be obtained by DWI without EPI although the scan duration is longer than that of DWI with EPI. DWI without EPI is also able to delineate the middle ear without distortion or artifacts. While conventional DWI usually involves 2- to 5-mm slice thicknesses [2–12], we have been performing non-EPI DWI with 1-mm slice thicknesses in order to detect smaller cholesteatomas. We use a 3-T MRI unit in our institute with the following parameters for thin-slice non-EPI DWI: repetition time (TR)/echo time (TE), 6248/84 ms; field of view (FOV), 240 mm; matrix, 128 × 128; slices, 32; slice thickness, 1 mm; flip angle, 90°; b-value, 800 s/mm2; coil, SENSE-Head-32ch; scan time, 8 min 7 s [13].

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