High spatial resolution is required in dental and oral health for fine-structure visualization of the periodontal region. To date, imaging performance evaluation criteria are established for computed tomography （CT） but not for dental-use cone-beam CT （CBCT）. In this study, the resolution characteristics of CBCT （FineCube） and Whole Body CT （Aquilion Lightning） were investigated using the Edge and Wire methods for modulation transfer function （MTF） analysis, along with clinical and physical evaluation performance. We arrived at the following conclusions.
1．FineCube obtained a better MTF than Aquilion in the high frequency MTF ranges, identified by the Edge and Wire methods.
2．CBCT has better spatial resolution than CT, thereby enabling microstructure imaging. However, CBCT is generally unable to visualize soft tissues, indicating that CT has an advantage in imaging soft tissue-containing subjects.

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Background and Purpose: After the accident at the Fukushima Daiichi Nuclear Power Station in 2011, detection of radioactive isotopes that were scattered in the atmosphere at that time has become necessary. Furthermore, the shortage of energy resources due to the current conflict between Ukraine and Russia has made it difficult for the EU and Japan to secure electricity. The use of nuclear power plants and detection of the levels of radioactivity are important issues. The aim of this research was to build a system that can easily detect low radioactivity associated with nuclear power.
Materials and Methods: To detect low radiation, a coin was placed on a dental imaging plate and a container containing radioactive cesium-contaminated soil was placed on top of it. After a period of exposure （1-30 days）, we detected radioactivity and assessed radiation protection. Using a standard sample （surface dose rate of 0.44μSv）, the detection period with and without post-irradiation X-ray were compared. The relationship between the detection period and the total dose was evaluated by varying the amount of radioactivity.
Result: The detection period for a standard sample without post-irradiation X-ray was about 25 to 30 days. Post-irradiation shortened the detection period to 40 hours （approximately 1/15 of the standard detection period）. As the amount of radioactivity increased, the detection period became shorter, but the total exposure dose remained unchanged at 14.4-18.7μSv; furthermore, detection of very low doses was possible.
Conclusion: Very low doses of radioactive cesium were detected by the method of post X-ray irradiation to dental imaging plate after exposure to radioactivity. Dental clinics may be useful in the implementation of a large-scale radioactivity detection system.

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Necrotizing sialometaplasia, first reported by Abrams et al., is a rare inflammatory disease that occurs mostly in the small salivary glands of the palatal region. It usually heals spontaneously in 6-12 weeks. It often forms necrotizing ulcers clinically and squamous epithelialization of salivary glands pathologically. It is classified as a tumor-like disease by the World Health Organization; however, it is difficult to distinguish it from malignant tumors. We report a case of necrotizing sialometaplasia of the hard palate. ［Case］ A 32-year-old woman. ［Main complaint］ Swelling and pain in the left palate and swelling of the parotid gland. ［Current medical history］ Five days before her first visit, her left hard palate suddenly swelled, and she felt pain. ［Intraoral findings］ An elastic 20-mm soft mass with redness was observed in the left hard palate with a clear boundary, and an ulcer of approximately 3mm was observed in the center. ［Image findings］ Contrast-enhanced computed tomography （CT） revealed a mass lesion on the left hard palate, with a clear boundary of approximately 24×20×10mm, and a slightly irregularly contrasted margin. No calcification was observed inside. ［Treatment / Prognosis］ Antibiotics and anti-inflammatory analgesics were administered. The lesion turned into a deep ulcer one week later, and biopsy was performed. A diagnosis of necrotizing sialometaplasia was made. One week after the biopsy, the ulcer tended to heal and was almost closed two weeks later. ［Discussion］ Necrotizing sialometaplasia has systemic causes, such as hypertension, diabetes, and immune disorders, and localized causes such as drinking and smoking. Although it may be clinically similar to a malignant tumor, it cures spontaneously; thus, it is important to avoid excessive treatment. The present patient had drinking habits. Blood tests showed high amylase levels, and serum amylase isoenzyme showed 81％ S-type and monocytosis. The C-reactive protein value was normal. CT showed swelling of the large salivary glands. These findings indicate an association with autoimmune disease in this patient. It was suggested that, although rare, this disease should also be considered as a differential diagnosis in mass lesions with necrotizing ulcers in the palatal region.

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The prevalence of oral cancer in Japan is higher in men aged 60 and over, and it is reported that the number is increasing. In recent years, it has been reported that its incidence in women and young people under the age of 40 is also increasing. Young patients generally have a good general condition and are often eligible for radical surgery, which has been reported to have a good prognosis. Early detection and therapeutic intervention are important because oral cancer progresses quickly.
The present case was a 17-year-old girl. In April 2018, she visited our hospital with a chief complaint of stomatitis at the base of her tongue. An induration mass with a diameter of 30mm was found on the left tongue edge. She was diagnosed with left tongue cancer （T3N0M0 Stage 3）. We performed tongue resection under general anesthesia and abdominal skin graft. Two months after the operation, we found metastatic findings （interval enlargement and internal echo of the left upper internal cervical lymph node） on US examination. On follow-up, there was no change in lymph node size and internal appearance for two months; however, after two months, the lymph nodes were large and swollen, and CT showed typical findings of metastases. We performed left neck dissection. The imaging findings of the present case may be useful for accurate imaging diagnosis in the future.

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