MRI is a method which locates NMR（nuclear magnetic resonance）signal and creates an image. The method of the positioning is different from that of CT imaging.
Transmission and receive coils are used for handling electromagnetic wave in MRI. And 3-dimensionally independent three coils for application of gradient are equipped. One of the three coils is for slice selection of a patient, and the rest 2 coils are for locating signal on the 2-dimensional slice. This review explains the principle of image formation in MRI.

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In numerous tumor cells, heat shock protein 90 （Hsp90） is over-expressed and forms multi-chaperone complexes with client proteins that are involved in processes characteristic of malignant phenotypes, such as angiogenesis, invasion, and metastasis. Moreover, Hsp90 stabilizes several proteins such as Raf-1, Akt, ErbB2, and hypoxia-inducible factor 1α, which are known to be associated with protection against radiation-induced cell death. These findings suggest that Hsp90 inhibitors could be used in a multi-target-based approach to radio sensitize tumor cells. A number of studies have explored Hsp90 as a potential molecular target for sensitization of tumor cells after X-rays.
Some small studies have investigated the combined effects of Hsp90 inhibitors and high linear energy transfer carbon ion radiotherapy （C-ion RT）, a potential therapy against radio-resistant malignant tumors. In the case of aggressive malignant tumors, achieving a complete response to radiotherapy is difficult, which suggests that combination therapy might be necessary for such tumors. This review is to examine the effects of 17-llylamino-17-demethoxygeldanamycin （17-AAG, an Hsp90 inhibitor） based chemotherapy in combination with C-ion RT or X-rays on oral squamous cell carcinoma cells. 17-AAG and X-rays in combination showed enhanced antitumor effect compared to C-ion RT. The invasion cells significantly decreased after X-rays and C-ion RT, thus induced by irradiation showed dose-dependency for X-rays and C-ion RT. Moreover, when 17-AAG was added, X-rays and C-ion RT decreased invasion cells in an additive effect.
This review article describes the utility of combination therapy with an Hsp90 inhibitor and radiotherapy.

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Positron emission tomography （PET） is a functional imaging technique based on the detection of a short-lived radioactive tracer isotope. ［18F］ fluorodeoxyglucose （FDG）, which is the most commonly used radioactive tracer, is a glucose analog and so its concentration reflects the glucose metabolism rate within a tissue. As glucose metabolism is generally higher in malignant tumors than in normal tissue, FDG-PET is useful （and is widely used） for diagnosing malignant tumors. In this paper, we report the essentials of the FDG-PET-based diagnosis of primary tumors, nodal metastasis, tumor recurrence, and distant metastasis. Furthermore, we also discuss the pitfalls of this imaging technique.
FDG-PET can easily detect primary tumors because they usually exhibit marked FDG accumulation. However, it is not of great advantage for detecting oral cancers since most of them can be identified by clinical inspection. Although FDG-PET displays high diagnostic accuracy for nodal metastasis, inflammatory lymphadenopathy might sometimes produce false-positive results. Similarly, small metastatic lymph nodes and those containing necrosis can produce false-negative results. Concerning the evaluation of tumor recurrence, the diagnostic ability of FDG-PET might be superior to that of computed tomography （CT） and/or magnetic resonance imaging （MRI）. During the development of recurrent tumors, changes in glucose metabolism precede morphological changes, and thus, FDG-PET can detect recurrence earlier than CT or MRI. In addition, FDG-PET can provide whole-body images. Therefore, it can directly reveal distant metastasis and synchronous cancers.
In conclusion, it is essential to know the advantages and pitfalls of FDG-PET. Although it has some limitations, FDG-PET is a very useful imaging technique for managing patients with malignant tumors of the head and neck.

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We describe the purposes of the radiological imaging examinations performed at the Department of Oral and Maxillofacial Radiology at Kyushu Dental University Hospital over the last 10 years and related dynamic statistics. The aim of this study was to clarify the role of the Department of Oral and Maxillofacial Radiology. In the last 10 years, the X-ray computed tomography （CT） and magnetic resonance imaging （MRI） equipment in our hospital were renewed, and a cone-beam CT system was installed. In order to determine the changes in needs that occurred during this period and confirm the role of dental radiologists within the core hospital, we analyzed the numbers of patients and radiological examinations and the purposes of such examinations for each modality from 2007 to 2015. As a result, we found that the number of patients who visited our hospital and consulted our department did not change significantly during the study period. The numbers of CT, MRI, and ultrasonography examinations increased during the early part of the study period, but had plateaued in recent years. One of the major changes seen in this study was in the purposes of CT examinations. The number of examinations of impacted teeth increased during the study period, whereas the number of preoperative examinations performed prior to dental implant surgery decreased. Another change was the increase in the number of requests for MRI examinations for temporomandibular disorders from dental offices. The role of dental radiologists should reflect these changes and respond to medical needs.

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Objective: Dental materials can produce metal artifacts during magnetic resonance imaging（MRI）, which can be problematic in clinical practice. Recently, the use of MRI for disease diagnosis in patients with dental implants has increased. Concurrently, the range of sizes of dental implants has also expanded. However, there are few reports comparing the metal artifacts produced on MR images by dental implants of different sizes. The purpose of this study was to investigate the metal artifacts caused by pure titanium-based dental implants of various sizes（3.5mm×8.0mm, 3.5mm×9.5mm, 3.5mm×11.0mm, and 4.5mm×8.0mm）using a phantom.
Methods: The phantom used in our study was composed of a hollow cylinder with an outer diameter of 20cm, and a removable rod of 1.0cm in diameter was placed along the phantom’s central axis. MRI was performed with a 1.5 T MRI machine（Philips Co. Intera Achieva 1.5T）, using a SENSE head 8-channel coil. The imaging conditions included spin echo（SE） T1-weighted imaging, Turbo SE（TSE）T2-weighted imaging, short TI（inversion time）inversion recovery（STIR）, and diffusion-weighted imaging（DWI）. The TR/TE remained constant during the DWI and the b-value, field of view（FOV）, rectangular field of view（RFOV）, SENSE factor, frequency direction, and phase direction were changed. ImageJ was used to measure the changes in the gray values on coronal images. Gray value changes of up to 30% were evaluated depending on the imaging conditions.
Results: All of the pure titanium-based dental implants studied produced similar metal artifacts on SE T1, TSE T2, and STIR images. The largest（in dimension）metal artifacts were seen on the DW images. This study showed that the size of metal artifacts depends on changes in the FOV, RFOV, SENSE factor, frequency direction, and phase direction for DW images.
Conclusions: In the SE T1, TSE T2, and STIR imaging conditions, pure titanium-based dental implants produced small metal artifacts of similar size and intensity regardless of their size. On DWI, the implants produced larger metal artifacts than were seen on the SE T1, TSE T2, and STIR images.

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Background and purpose: Cone beam computed tomography （CBCT） is an imaging modality that is widely used in clinical practice. It allows physicians to obtain similar images to panoramic radiography. However, to the best of our knowledge, few studies have evaluated images, such as panoramic photographs, that have been reconstructed using CBCT （CBCT panoramic images）. The purpose of this study was to evaluate and compare CBCT panoramic images of the teeth and periodontal tissues with conventional panoramic radiographs and to clarify the usefulness of CBCT panoramic images.
Materials and methods: Panoramic images were reconstructed from CBCT images and compared with panoramic radiographs of 20 patients who underwent brain dock screening at our hospital. The images were evaluated by examining six teeth: the first molars and the right upper and lower middle incisors. The visibility of the crown, alveolar crest, root apex, pulp cavity, and periodontal ligament space were assessed, and appropriate scores were awarded. Three oral and maxillofacial radiologists independently reviewed the images, and any discrepancies were resolved by reaching a consensus. The Mann-Whitney U test was used to determine the significance of differences between the imaging modalities, with p-values of ＜0.05 were considered statistically significant.
Results and conclusion: The maxillary alveolar crest, root apex, pulp cavity, and periodontal ligament space of the middle incisor; the mandibular crown of the middle incisor; and the alveolar crest, root apex, and apical region of the right molar were significantly more visible on the CBCT panoramic images than on the panoramic radiographs （maxillary right molar pulp cavity, maxillary middle incisor pulp cavity, periodontal ligament space, and mandibular right molar apical region: P＜0.05, others: P＜0.01）. Conversely, the crown regions of all of the examined teeth except the lower middle incisor were significantly less visible on the CBCT panoramic images than on the panoramic radiographs （maxillary right molar and middle incisor: P＜0.05, others: P＜0.01）. The present study demonstrates the usefulness of reconstruction using CBCT compared with panoramic radiography.

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False-positive findings are sometimes observed on 2-deoxy-2-［¹⁸F］ fluoro-D-glucose （¹⁸F-FDG）-positron emission tomography （PET）/computed tomography （CT） images. They can be caused by skeletal muscles after exercise, tissues suffering from active inflammation, and tissue near to dental crowns. Herein, we report a rare case in which false-positive findings were seen on ¹⁸F-FDG PET/CT images, and none of the abovementioned causes applied. A 61-year-old male had undergone six ¹⁸F-FDG PET/CT examinations during the follow-up period after mandibular resection for gingival carcinoma, one of which produced negative results, and the rest produced positive results. Clinical examinations and CT and magnetic resonance imaging scans did not obtain any findings that were indicative of a tumor or inflammation. There were no differences in the ¹⁸F-FDG PET/CT imaging conditions between the scans that produced positive and negative results. We were not able to identify the cause of the false-positive findings. It is important to use multiple imaging modalities and physical examinations to diagnose recurrent malignant tumors.

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Objective: Myoepithelioma is a rare tumor, accounting for 1% of all salivary gland tumors. It clinically resembles pleomorphic adenoma in the palate, while on imaging modalities, such as computed tomography （CT） or magnetic resonance imaging （MRI）, its findings often correspond to those of a diverse range of diseases. Considerable attention is thus being given to the diagnosis of myoepithelioma based solely on its imaging findings.
Case: Here, we report a case of myoepithelioma of the left palate in a 13-year-old female. A 13×13-mm lump was palpable in the left hard palate. Axial CT showed an ovoid, expansile, hypodense lesion with well-circumscribed margins. The lesion exhibited signal hypointensity on T1-weighted imaging （repetition time ［TR］/echo time ［TE］: 500/7ms）, inhomogeneous signal hyperintensity on T2-weighted imaging （TR/TE: 5000/80ms）, and enhancement on contrast-enhanced T1-weighted imaging （TR/TE: 581/11ms）. The lesion was thus diagnosed as a benign salivary gland tumor, with a clinical diagnosis of pleomorphic adenoma. A histopathological examination performed after surgical resection resulted in a diagnosis of myoepithelioma.
Conclusion: Salivary gland tumors of the palate are often considered to show an increased frequency of malignancy, and their differential diagnoses must be carefully considered. However, myoepithelioma displays similar findings to a diverse range of diseases so its histopathological diagnosis might depend to a large degree on its imaging findings on MRI. It will be necessary to research the differential diagnoses of minor salivary gland tumors of the palate using various imaging modalities in the future.

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