Satoshi Yoshioka

<p>Despite apparent ability of computed tomography (CT) in clinical practice, otology, which requires diagnosis and treatment of variaous diseases involve very small areas and sometimes entails a limitation on the performance of CT in depicting lesions located in such areas. Recently, ultra-high-resolution (UHR) CT, which can provide images at dramatically higher spatial resolution than ever before, has been developed and has become commercially available. UHRCT has a pixel size (0.25×0.25 mm) twice comparing dense in both vertical and horizontal directions as conventional high-resolution (CHR) CT and the maximum spatial resolution of 0.15mm or less in the axial direction. The maximum size image is 2048×2048 pixels. Here, we report our experience of the early stage development of UHRCT in the field of otology.</p><p>We performed UHRCT scan in otology patients and compared the images obtained from UHRCT with those obtained from CHRCT. Spatial resolution in UHRCT images was obviously improved. Tiny structures, such as the chorda tympani and ossicles, and small pathological changes caused by the progression of otitis media, etc. were clearly depicted. Due to an increase in the partial volume effect, improvements such as the performance of UHRCT in depicting soft-tissue lesions or lesions adjacent to the bone, were considered to be difficult to depict at CHRCT.</p><p>The tiny structures which had been indistinct before, became clearly visible due to UHRCT, indicating the possibility of providing important information for clinical practice. However, because the issues include the necessity of building infrastructure (including display) and a powerful computer system enough to save and handle huge volume of data, it is necessary to examine the further usage of UHRCT in the future.</p>

中耳から補聴器のイヤモールド印象材を手術的に除去した2症例を報告した。症例1は持続的な耳漏を主訴とする78歳男性。当初は慢性中耳炎と診断され保存的療法を受けていたが耳漏の改善は見られなかった。その後の検査で鼓室に異物を認め、その異物の素材分析により印象材であることが判明した。その後の問診で患者は約15年前に補聴器のイヤモールドを調製したことを思い出し、鼓室形成術を受けて異物除去に成功した。症例2はcanal wall down型鼓室形成術を受けた84歳女性で、左耳に印象材を注入されたが、その除去を受けていなかった。検査で乳突腔に埋入した印象材を認め、耳介後部の切開による異物を摘出した。いずれの症例でも、患者の病歴の問診、鼓膜の十分な検査、術後の補聴器フィッティング関連のリスクへの注意、ならびに不注意による補聴器フィッティング時の印象材押し込みの回避が重要になると考えられた。

Although modern multislice CT systems can quickly scan a wide range in fine detail, the high exposure dose and long examination time of CT studies are still important issues. CT is therefore generally considered to be unsuitable for screening. This is particularly true for pediatric patients, who are especially sensitive to radiation, and plain radiography is therefore frequently selected for examination of the temporal bone. We have developed an ultra-low-dose CT imaging method using a 320-row area detector CT (ADCT) scanner that may be suitable for screening for diseases of the ear even in pediatric patients.<BR>Temporal bone specimens were scanned with an ADCT scanner (Aquilion ONE^<TM>, Toshiba Medical Systems, Otawara, Japan) using various scan conditions. Image quality was evaluated, and the optimal scan conditions providing clinically acceptable images at the lowest possible exposure dose were identified. A human-body phantom was then scanned with ADCT using these scan conditions. Plain radiography using the Schu..ller method was also performed for the same phantom to acquire images of the temporal bones bilaterally. The CT and radiographic exposure doses were compared to assess the suitability of our ADCT method for screening.<BR>The gantry of the ADCT scanner includes an X-ray source unit and a detector (area detector) which is several times larger than that used in a conventional CT system. Three-dimensional data can be acquired over a wide range in a single high-speed rotation, making it possible to quickly obtain images in the same temporal phase.<BR>As the results, the optimal scan conditions were found to be tube voltage 100 kV, tube current 10 mA, and exposure time 1.5 s/rot. by 1 rotation. The CTDIVOL (standard dose) was 1.7 mGy, which is 0.7% of the usual value of 243.4 mGy. The maximum skin dose to the head in plain radiography of the temporal bones bilaterally was 2.12 mGy on average. The maximum skin dose to the external ear in CT scanning with the above conditions was 1.59 mGy on average, which was lower than that for the Sch&uuml;ller method. However, the dose in CT scanning was slightly higher at the front and rear.<BR>With our proposed CT imaging method, images are acquired in a very short time, three-dimensional image data is obtained, and the exposure dose is equal to or lower than that of plain radiography. This method is therefore expected to be a useful new tool for morphological screening examinations.

A 320-row area detector CT scanner was used to assess foreign bodies in the bronchi of pediatric patients. This system, which employs a detector of 0.5 mm &times; 320 rows, permits a range of up to 160 mm to be scanned in a single rotation at a maximum scan speed of 0.35 s/rot. This makes it possible to perform imaging with no temporal mismatch between any parts of the acquired images and to acquire consecutive three-dimensional dynamic image data over time by continuous rotation (4DCT).<br>The subjects were 4 pediatric patients in whom the presence of a foreign body in the bronchi was suspected. The system used was a 320-row CT scanner (Aquilion ONE, Toshiba). Multiplanar reconstruction (MPR) images and three-dimensional CT (3DCT) images were generated. In addition, consecutive four-dimensional dynamic CT (4DCT) images were obtained over time.<br>With this system, scanning can be completed instantly, permitting examinations to be performed without sedation. In stationary images, artifacts due to respiration and cardiac contraction (which are unavoidable with conventional scanning methods) can be completely eliminated, and the continuity of images as well as the visualization of peripheral bronchi are significantly improved.<br>This leads to greater diagnostic confidence when evaluating small or multiple foreign bodies. 4DCT permits dynamic observation to be performed easily, which is useful, for example, for detecting the presence of a foreign body in the peripheral bronchi or evaluating incomplete ventilation of a part of the lung. In other words, the CT system can also be used to assess lung function. In addition, the exposure dose can be reduced to within permissible limits. It is therefore concluded that 320-row area detector CT is very useful as a new imaging tool for the evaluation of the bronchi and lungs.

Morphological aberration of the Eustachian tube is a significant factor of various middle ear diseases.<BR>Traditionally, cadaveric specimens have been used for studies on the morphology of Eustachian tubes.However, this approach was not too efficient, as samples were limited in number as they were difficult to obtain, and biological conditions were not reflected due to rigor mortis and atrophy during specimen preparation.<BR>We thus decided to use Multi-Slice CT (MSCT) to perform 3-D anatomic measurements of the Eustachiantube. MSCT has benefits of isotropy and high resolution, and it is useful in preparing images of any plane.<BR>Forty-eight adults were studied. For the purpose of measurement, various anatomic indices were carefullyand precisely defined to identify each area on the image. Calculations based on each coordinate value enabledthe measurement of length, diameter and angle of the Eustachian tube of normal adults.<BR>Therefore, measurements of the Eustachian tube, which were traditionally difficult as it is located in the deeppart of the cranium, were simplified in many specimens.<BR>Mean value of total length was 39. 2&plusmn;3. 2 mm, cartilage part length of the tube 30.0&plusmn;2.7mm and bony part9.2&plusmn;1.6mm. Mean values of diameter of tympanic orifice were 5.2&times;3.2mm, and pharyngeal orifice 9.7&times;4.4mm. Mean value of angle between bony part and cartilage part was 160.9-13.6 degrees.<BR>This approach to anatomic measurement is expected to contribute greatly to investigation on various middleear diseases.

We demonstrated high-resolution multiplanner reformation (MPR) and 3-dimentional CT (3D-CT) imaging of Eustachian tube (ET) using a 1-mm, 8-row multislice CT scanner.<BR>CT scans were performed in 5 normal adult volunteers during quiet breathing and the Valsalva maneuver.<BR>Bony portion of ET was clearly detected on MPR, however cartilaginous portion of the ET was still elusive during quiet breathing scan.<BR>MPR and 3D-CT images during Valsalva maneuver improved visualization of cartilaginous portion of the ET and surrounding soft tissues including cartilage, muscle and fat.<BR>Imaging of the ET obtained by multislice CT during the Valsalva maneuver can propose further investigation for various middle ear disorders.