Hidenori Otake

Radiation Exposure from CT Examinations in Japan

BackgroundComputed tomography (CT) is the largest source of medical radiation exposure to the general population, and is considered a potential source of increased cancer risk. The aim of this study was to assess the current situation of CT use in Japan, and to investigate variations in radiation exposure in CT studies among institutions and scanners.MethodsData-sheets were sent to all 126 hospitals and randomly selected 14 (15%) of 94 clinics in Gunma prefecture which had CT scanner(s). Data for patients undergoing CT during a single month (June 2008) were obtained, along with CT scan protocols for each institution surveyed. Age and sex specific patterns of CT examination, the variation in radiation exposure from CT examinations, and factors which were responsible for the variation in radiation exposure were determined.ResultsAn estimated 235.4 patients per 1,000 population undergo CT examinations each year, and 50% of the patients were scanned in two or more anatomical locations in one CT session. There was a large variation in effective dose among hospitals surveyed, particularly in lower abdominal CT (range, 2.6-19.0 mSv). CT examinations of the chest and upper abdomen contributed to approximately 73.2% of the collective dose from all CT examinations. It was estimated that in Japan, approximately 29.9 million patients undergo CT annually, and the estimated annual collective effective dose in Japan was 277.4 *103 Sv person. The annual effective dose per capita for Japan was estimated to be 2.20 mSv.ConclusionsThere was a very large variation in radiation exposure from CT among institutions surveyed. CT examinations of the chest and upper abdomen were the predominant contributors to the collective dose.

Diagnostic reference level of computed tomography (CT) in japan

Optimisation of computed tomography (CT) parameters is important in avoiding excess radiation exposure. The aim of this study is to establish the diagnostic reference levels (DRL) of CT in Japan by using dose-length product (DLP). Datasheets were sent to all hospitals/clinics which had CT scanner(s) in Gunma prefecture. Data were obtained for all patients who underwent CT during a single month (June 2010), and the distributions of DLP were evaluated for eight anatomical regions and five patient age groups. The DRL was defined as the 25th and 75th percentiles of DLP. Datasheets were collected from 80 of 192 hospitals/clinics (26 090 patients). DLP for head CT of paediatric patients tended to be higher in Japan compared with DRLs of paediatric head CTs reported from the EU or Syria. Although this study was performed with limited samples, DLP for adult patients were at comparable levels for all anatomical regions.

Variability of lesion detectability and standardized uptake value according to the acquisition procedure and reconstruction among five PET scanners

ObjectiveThe objective of this study was to assess differences in the semiquantitative values of 18F-fluorodeoxyglucose (18F-FDG) uptake among different positron emission tomographic (PET) systems.MethodsA phantom study was performed to compare standardized uptake value (SUV) in five PET scanners including a dedicated PET scanner and four PET/computed tomography (CT) scanners. Radioactivity simulating the SUV of 2.5 was filled in the hot spheres (8 mm, 11 mm, 14 mm, 18 mm, 22 mm, and 27 mm) that were set in the cylindrical phantom with the background SUV of 1.0. Data acquisition and reconstruction were performed according to routine and standardized conditions. The standardized condition was as follows: CT acquisition (120 kVp, 50 mA) and PET acquisition (2-min acquisition with a slice thickness of 2 mm); reconstruction was performed by ordered subsets expectation maximization + Fourier rebinning. Detectability of hot spheres and SUV was compared between routine condition and standardized condition with five PET scanners.ResultsOn routine condition, two cameras could detect a 14-mm sphere clearly. On the other hand, the visualization of hot spheres by the standardized condition was remarkably variable. Semiquantitative evaluation revealed that a maximum of 45.7% error was recognized with the 27-mm sphere by the routine condition, although the standardized condition could reduce the error to 22.6%.ConclusionsDetectability depends not only on the PET machine but also on the imaging protocol. The results indicate that SUV is variable with PET machines under routine conditions of data acquisition and reconstruction. Standardization of the reconditions can reduce variability and maximum difference in the SUV by half.

Use of postmortem computed tomography to reveal an intraoral gunshot injuries in a charred body

A 53-year-old man was found dead after a fire at his residence had been extinguished. Although a pistol was recovered beside the body, external examination was unable to indicate any gunshot wound because of severe charring of the body. Postmortem computed tomography (CT) scan performed prior to autopsy suggested an entrance gunshot wound in the posterior pharynx with loss of soft tissue and an internal bullet path through the right anterior and posterior parts of the occipital bone. Autopsy revealed an entrance gunshot wound with hemorrhage in the soft tissue of the posterior pharynx, massive contusion of the right occipital lobe, and subarachnoid hemorrhage in the right temporal lobe, both occipital lobes and the superior surface of the left cerebellar hemisphere, thus being consistent with the findings of postmortem CT. A carboxyhemoglobin concentration of 5% in blood from the cadaver was consistent with the lack of soot deposition from the larynx to the bronchus. These observations confirmed that death had been caused by an intraoral gunshot resulting in severe brain damage, before the body had been burned.

Scintigraphic "doughnut sign" on bone scintigraphy secondary to metastatic hepatocellular carcinoma.

A 57-year-old man noticed two bumps on the right fronto-parietal region of his head. Head CT showed an osteolytic lesion with soft tissue density in the right parietal bone. Tc-99m HMDP bone scintigraphy demonstrated a ring-like accumulation in the right parietal bone, and an area of Increased uptake in the right temporal bone and at the left pedicle of the twelfth thoracic vertebral body. Abdominal CT scan was performed to look for a primary focus, and revealed numerous small round tumor lesions in the enlarged liver. Ga-67 citrate scintigraphy was performed for further confirmation and to look for metastatic foci, and showed an area of increased uptake in the calvarium, the twelfth thoracic spine, and the enlarged liver. Metastatic hepatocellular

Metastatic calcification. Difference of uptake between Tc-99m HMDP and Ga-67 citrate.

Tc-99m HMDP bone scintigraphy clearly demonstrated metastatic calcification in a lung and stomach in a patient with renal failure and hypercalcemia. Ga-67 citrate scintigraphy showed increased lung activity, but failed to demonstrate the stomach. The difference in uptake between Ga-67 citrate and Tc-99m HMDP in the regions of metastatic calcification could suggest there is a different uptake mechanism at various sites of metastatic calcification.

A case of fatal drug intoxication showing a high-density duodenal content by postmortem computed tomography

A 22-year-old woman was found dead in her bed, and subsequent postmortem examination was performed using ordinary methods such as external examination, Triage®, and computed tomography (CT) scan which demonstrated a high-density content of the duodenum. Autopsy and quantitative analysis of drugs present in the GI tract showed that high amounts of radiopaque psychotic agents such as fluvoxamine maleate, carbamazepine, and zolpidem tartrate had been responsible for the high-density profile of the duodenum. Postmortem quantitative analysis of drugs in the blood suggested that death had been caused by fatal intoxication with fluvoxamine maleate. Thus, postmortem CT could offer an opportunity to suspect drug intoxication due to radiopaque psychotic agents such as chloral hydrate, phenothiazine, bromovaleryl urea, fluvoxamine maleate, and probably zolpidem tartrate, although it is neither a specific nor a quantitative test for drugs. Therefore, postmortem CT happened to provide clues to investigation of drug intoxication in the present case.

Radiation safety management of residual long-lived radioactivity distributed in an inner concrete wall of a medical cyclotron room

The depth distribution of residual long-lived radioactivity in the inner concrete wall of a medical cyclotron room was measured by assaying concrete cores. Seven long-lived radioactive nuclides ((46)Sc, (60)Co, (65)Zn, (134)Cs, (152)Eu, (22)Na and (54)Mn) were identified by gamma-ray spectrometry of the concrete samples. It was confirmed that the gamma-ray-emitting radionuclides induced by thermal neutrons through the (n, γ) reaction are dominant, and that the activity induced by thermal neutrons is greater at a depth of 10-30 cm, rather than at the surface of the concrete, and decreased exponentially beyond a depth of ~40 cm. Although the specific activity at the surface was greater than the clearance level for radioactive waste indicated in IAEA RS-G-1.7, the mean specific activities in the walls and floor were less than the clearance level.

Chronic mastoid sinusitis mimicking metastatic disease demonstrated by Tc-99m HMDP bone scintigraphy.

A 46-year-old woman who had a middle ear infection 15 years earlier underwent Tc-99m HMDP bone scintigraphy as a follow-up for breast carcinoma. Intense uptake was seen in the right temporal calvarium on planar and SPECT images. Cranial CT showed diffuse sclerotic change in the hypoplastic right mastoid air cells, probably related to the prior inflammatory change.

Incidental finding of Herpes zoster infection by Tc-99m HMPAO

Tc-99m HMPAO brain SPECT study incidentally demonstrated a large area of increased accumulation in the soft tissue of the face and fronto-parietal region of the head, corresponding to the distribution of the ophthalmic and maxillary branches of the trigeminal nerve, which had been infected by herpes zoster.