S Kanda

Volume Changes in Human Masticatory Muscles between Jaw Closing and Opening

Most jaw muscles are complex, multipennate with multiple components. The morphologic heterogeneity of masticatory muscles reflects their functions. We hypothesized that the volume of masticatory muscles changes between jaw closing and opening, and that there is a difference in the volume change among the muscles. Magnetic resonance images of the entire head were obtained in ten normal young adult subjects before and after maximum jaw opening. The volume changes of the masseter, medial, and lateral pterygoid muscles were measured. Only slight changes were seen in the masseter and medial pterygoid muscles. The lateral pterygoid muscle, however, significantly decreased its volume during jaw opening. The results provide normative values of muscle volume in living subjects, and suggest that the volume changes differ among jaw muscles.

THE COMBINED USE OF US AND MR IMAGING FOR THE DIAGNOSIS OF MASSES IN THE PAROTID REGION

Purpose: To evaluate the usefulness of the combination of the two non-invasive modalities US and MR imaging to diagnose masses in the parotid region. Material and Methods: The US and MR findings of 21 patients with parotid masses were analyzed retrospectively by two radiologists without any clinical or histopathological information. The specific points evaluated were location, shape, margin, internal architecture, and intensity level on both US and MR, posterior echo enhancement on US, and capsule-like lining of the tumor on MR. Results: The findings concerning the shape and margin on US and MR were in fairly good agreement. Concerning the findings of the internal architecture, US could reveal the minute structures of the tumor while MR demonstrated differences in the signal intensities of histological tissue types of the various tumors. The posterior echo enhancement on US and the capsule-like lining on MR of the tumors were also useful for the diagnosis. Conclusion: Our results suggest that the combination of US and MR is useful for examining soft tissue masses in the parotid region to make a more accurate diagnosis, and not just differentiate malignant lesions from those which are benign.

Florid cemento-osseous dysplasia : radiographic study with special emphasis on computed tomography

This article describes the computed tomographic and conventional radiographic findings for florid cemento-osseous dysplasia. A low-density thin layer or cystlike area was observed around the high-density masses in the tooth-bearing area in the seven cases studied. Expansion of the buccal and lingual cortical plates was observed in association with cystlike areas, but was infrequently observed in florid cemento-osseous dysplasia not having such areas. The computed tomographic number of the high-density masses ranged from 772 to 1587 Hounsfield Units and was equivalent to that of cementum or cortical bone.

Magnetic resonance imaging of oral and maxillofacial angiomas

Eleven patients with oral and maxillofacial angiomas (seven hemangiomas and four lymphangiomas) were evaluated with magnetic resonance imaging using a 0.2-T permanent system and spin-echo pulse sequences. These lesions typically had signal intensities that were iso T1-weighted, similar to muscle, and high T2-weighted, greater than subcutaneous fat. Nine tumors had well- or relatively well-defined margins, and seven cases had curvilinear structures of low signal intensities in the masses on T2-weighted images. It was impossible to distinguish hemangiomas from lymphangiomas on MR images. Our experience suggested that most angiomas of oral and maxillofacial regions present special characteristics on magnetic resonance images. It is thought that information obtained with magnetic resonance images can contribute significantly to the evaluation of the extent of these lesions.

Diagnostic value of magnetic resonance imaging for malignant tumors in the oral and maxillofacial region

The purpose of this study was to clarify the diagnostic value of magnetic resonance imaging for malignant tumors in the oral and maxillofacial region. Computed tomography and magnetic resonance images of 25 patients with malignant tumors of the oral and maxillofacial region were evaluated. Computed tomography scans were performed with intravenous contrast enhancement. A 0.2-Tesla (Hitachi Medical Corp., Tokyo, Japan) permanent magnetic resonance unit was used to obtain T1-, T2-, and proton-density-weighted images with spin-echo pulse sequences. Gadolinium-diethylene-triamine-pentaacetic acid was administered in 11 cases. Severe artifacts influencing image interpretation were observed in 10 (40%) cases on computed tomography but only in 5 (20%) cases on magnetic resonance imaging. There was no difference in the detectability of bone invasion between images from the two systems. Contrast enhancement with gadolinium-diethylene-triamine-pentaacetic acid provided additional useful information in only 3 of 11 cases compared with nonenhanced magnetic resonance images. Malignant tumors showed a higher signal intensity than that of muscle on T2-weighted images in all cases and on proton-density-weighted images in 23 (92%) cases. On T1-weighted images, an intermediate signal intensity similar to that of muscle was seen in 16 (64%) cases and a hyperintense signal in 9 (36%) cases. There was poor correlation between signal intensity and pathologic diagnosis of the tumors. These results suggest that in cases with severe artifacts that disturb the interpretation of the images on computed tomography, magnetic resonance examinations are preferable for defining the exact extent of the primary lesion.

Three-dimensional imaging of teeth and jaw bones using fluoroscopic computed tomography (FCT)

Introduction The appearance of CT has made it possible to get three-dimensional images of the human body, and recently it has come into use in dental medicine. Although CT will have an increasing role in dental diagnostic imaging, its use in this area is quite limited because of a large exposure dose, long examination time, and high cost. Owing to the developments in new technology, there is a possibility of realizing a very compact, low exposure CT system which can provide three-dimensional images in a single scan. This new type of CT, which utilizes an image intensifier and a TV camera as a two-dimensional detector system, is often called X-ray video CT or fluoroscopic CT (FCT) 1-3). We have developed a prototype of a microcomputer-based low dose fluoroscopic CT system for scanning the dento-maxi l lo fac ia l region. 4,~) Va r i ous images (such as transverse axial sections, longitudinal sections, and 3D display) were obtained, and the image quality as well as the exposure dose was compared between the present fluoroscopic CT and conventional CT. Method Conventional CT uses a one dimensional X-ray detector (NaI, BGO, Xe etc.) with a fan beam geometry, while fluoroscopic CT uses an image intensifier as a two-dimensional X-ray detector with a cone beam geometry. Therefore, it is nesessary to scan many times to get three-dimensional images in the case of conventional CT, but on the other hand, it is only needed a single scan for threedimensional imaging using FCT. Fig. 1 shows the difference between fluoroscopic and conventional CT schematically.