Effects of organ dose modulation applied to a part of the scan range on radiation dose in computed tomography of the body.

In computed tomography (CT), organ dose modulation (ODM) reduces radiation exposure from the anterior side to reduce radiation dose received by the radiosensitive organs located anteriorly. We investigated the effects of ODM applied to a part of the scan range on radiation dose in body CT. The thorax and thoraco-abdominopelvic region of an anthropomorphic whole-body phantom were imaged with and without ODM. ODM was applied to various regions, and the tube current modulation curves were compared. Additionally, the dose indices were compared with and without ODM in thoracic and thoraco-abdominopelvic CTs in 800 patients. ODM was applied to the thyroid in male patients and to the thyroid and breast in female patients. In phantom imaging of the thorax, the application of ODM below the scan range decreased the tube current, and that to the breast showed a further decrease. Decreased tube current was also observed in phantom imaging of the thoraco-abdominopelvic regions with ODM below the scan range, and the application of ODM to the whole scan range, thyroid, breast, and both thyroid and breast further reduced the tube current in the region to which ODM was applied. In patient imaging, the dose indices were significantly lower with ODM than without ODM, regardless of the scan range or sex. The absolute reduction in dose-length product was larger for thoraco-abdominopelvic CT (male, 43.2 mGy cm; female, 59.7 mGy cm) than for thoracic CT (male, 30.8 mGy cm; female, 37.6 mGy cm) in both sexes, indicating dose reduction in the abdominopelvic region to which ODM was not applied. In conclusion, The application of ODM in body CT reduces radiation dose not only in the region to which ODM is applied but also outside the region. In radiation dose management, it should be considered that even ODM applied to a limited region affects the dose indices.

99mTc-Sn-colloid SPECT/CT in thoracic splenosis after esophageal cancer surgery.

Splenosis occurs as a result of autotransplantation of splenic tissue following splenic injury or splenectomy. A 56-year-old man with esophageal cancer underwent thoracoscopic-assisted subtotal esophagectomy accompanied by three-field lymph node dissection, and retrosternal gastric tube reconstruction. The spleen was injured during the surgery and was removed. A retrosternal nodule of 12 mm in diameter was detected near the reconstructed gastric tube on computed tomography (CT) performed 3 years and 6 months postoperatively. Retrospectively, the nodule was observed in the same area on early postoperative CT and gradually increased in size. No accessory spleen was identified on the preoperative CT. Splenosis was suspected, and 99mTc-Sn-colloid single photon emission computed tomography (SPECT)/CT was performed. It revealed intense uptake in the retrosternal nodule, consistent with the diagnosis of thoracic splenosis. Subsequently, the patient has been under observation without treatment. 99mTc-labeled colloid SPECT/CT allowed confident diagnosis of thoracic splenosis following esophageal cancer surgery. This examination is considered valuable for the evaluation of ectopic splenic tissue.