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A 60-year-old woman was referred for 64-slice multidetector computed tomography because of the incidental findings of abnormality on a chest radiograph. Her computed tomography showed an absent right lung and a rudimentary main bronchus ending in a blind pouch; this established the diagnosis of pulmonary aplasia. We report here on a rare case of incidentally found right pulmonary aplasia, and we include a brief review of the relevant literature.

Digital radiography is often performed at a higher dose rate than analogue radiography for image acquisition. The authors measured the Entrance Surface Dose (ESD) of analogue and digital radiography techniques for 14 radiographic examinations from randomly selected medical centres in the central district of Korea. It was that the mean ESD of the digital examinations was 2.84 mGy (range, 0.37-6.38 mGy) and that of the analogue examinations was 1.83 mGy (range, 0.38-4.74 mGy), resulting in a 55.25 % higher ESD for digital technique. Although this survey is not completely representative of Korea, findings of this study indicate a need for closer exposure management in digital radiography to minimise patient dose.

Within the past 20 years, the radiographic examination in the medical field has increased by a factor of about 3 to 5 times, while the total radiation dose has increased by a factor of about 200-400. This has ascribed to the rapid increase in CT usage (1). The increased demand for CT scans has drawn the public's attention about radiological hazards and paved the way for the effort to reduce radiation exposure in every medical imaging field. There are some evidences why the radiation exposure management has become the most important issue nowadays. One study by Berrington et al. (2) estimated 29,000 cancer patients due to 70 million scans in the USA. The other study by Brenner and Hall (3) reported that 600,000 CTs performed on children under age 15 could lead to 500 deaths. CT scans for the pediatric imaging played a significant role in the raised incident rate of leukemia or brain tumors (4). Two things should be considered to reduce radiation exposure dose (5-7). The first one is justification. The justification is based by the fact that radiographic examinations are essential for the diagnosis, which needs to be recognized first and then the examination is carried out subsequently. Justification includes a legitimate explanation to patients, and this ought to be always considered with the ethical issues. The medical ethics and the healthcare environment ethics have to hold a dominant position. Physician autonomy over the prescription along with obligation has to be ensured for this process. If the qualification for justification is sufficed, the second conception, optimization, should be reckoned to reduce radiation exposure dose. In other words, provided the radiographic examination has been prescribed for the diagnosis, now think of how to minimize the detrimental effect from radiation. In spite of the minimum amount of radiation, it may produce delayed radiation damage such as cancer statistically 10-20 years later (8). That's why the dose of radiation has to be reduced to prevent radiation hazard. It is recommended to comply with a standard guide for radiographic examination to have the optimal imaging condition for a variety of situations and to wear proper radiation protection devices. If feasible, radiographic examinations have to be taken based on the principle of As Low As Reasonably Achievable (ALARA), which means that making every reasonable effort to maintain exposures to ionizing radiation as far below the dose limits as practical. In addition to justification and optimization, another one which should be kept in mind is that the amount of radiation is not everything to be concerned in the medical radiological examination. The inappropriate treatment by neglected or omitted procedures owing to the expected radiation exposure damage may give rise to disastrous consequences. Nowadays, CT screening is new topic issue in the point of radiation safety. CT is a very useful examination in the early detection of cancer because of its diagnostic accuracy. However, in the periodic CT screening, radiation hazards may be greater than the diagnostic benefit. So, if necessary, screening CT may be carried out with strict indications. It is crucial for the medical institutions to monitor the amount of radiation exposure dose from CT scans or radiological procedures in optimization. Currently, the international organizations and each country are running or preparing various programs for the reduction of radiation exposure dose such as Smart card project in IAEA, My Child's Medical Imaging Record in American College of Radiology, Wallet card in Beaumount Hospital in Pennsylvania, California Senate Bill 1237 (Regulating CT Radiation Dose Practices in California into Law), Radiation Passport Project in Canada, Patient Exposure Registry (PER) in European Union (Dose DataMed (DDM) ProjectPACS), and Radiation Exposure Monitoring (REM) Integration Profile in Japan. Rehani et al. (9) has investigated with the help of the IAEA about the implementation of radiation exposure monitoring program. In a total survey of 76 countries, 11% are running a research on this program and 4% are drawing a blueprint only for the medical tests performed. Of them, 89% responded that these kinds of programs were assumed effective on reduction of radiation exposure dose, and 99% of the participating countries in this survey displayed an interest in such programs. By 2015, patient dose management systems which are developed in each country will be embodied. The government of Korea recognized the importance of the management of the radiation dose tracking in patients. Since 2012, they have been developing a method for measuring the radiation dose. In 2012, that system for CT scan had built up frames already, and the thing for the plain radiography will be created in 2013. It is very important to acknowledge the correct information about the radiology in the reduction of radiation exposure dose. In other countries, websites such as Image Gently (the society for pediatric radiology) and Image Wisely (radiation safety in adult medical imaging) provide the radiology-related information, education, and campaign. Also radiology-related organizations work together through these websites where tasks are publicized to accomplish justification and optimization for patients, physicians, radiological technologists, medical physicists and radiologists. In recent years, Choosing Wisely contributes to decrease unnecessary examinations in each medical field. In Korea, the Korean Alliance for Radiation Safety and Culture in Medicine (KARSM) was founded by the medical radiation related society, which aims promotion, education, and campaign of radiology-related affairs. Endeavor to reduce radiation exposure dose can be done by national systematization. The government recommends Diagnostic Reference Level (DRL), which suggests medical institutions to limit the radiation exposure levels in each examination. DRL in CT scans and the plain radiograph has been established and recommended in Korea. When taking a closer look at the recommendation, CT scans set the bounds CTDIvol for skull 60 mGy, and for abdomen 20 mGy, and dose length product (DLP) for skull 1,000 mGy*cm, and for abdomen 700 mGy*cm. The radiation exposure dose for plain radiograph is delimitated skull AP 2.23 mGy, skull lateral 1.87 mGy, Chest PA 0.34 mGy, Chest lateral 2.80 mGy, Abdomen AP 2.77 mGy, Pelvis AP 3.42 mGy, C-spine AP 1.86 mGy, C-spine lateral 1.03 mGy, T-spine AP 3.79 mGy, T-spine lateral 8.15 mGy, L-spine AP 4.08 mGy, L-spine lateral 10.53 mGy, and L-spine oblique 6.35 mGy (10, 11). Nevertheless, the research and the recommendation of the safe radiation exposure levels in radionuclide imaging, cardiac CT, or cardiac catheterization and other imaging procedures have not done yet. Therefore, it is absolutely imperative that a strenuous study for the safety level should be completed for each medical radiation field and needs to be presented soon. In conclusion, those who concern about reduced radiation exposure dose insist a greater effort to achieve their goal. Doctors are demanded to prescribe a radiographic imaging under the medically justified ethics in the optimal condition so that the maximal benefit from the examinations and the minimal unforeseen injuries are guaranteed. Not only radiologists or related specialists but also patients and the government should cooperate fully to resolve this issue, thereby excluding pruning away gratuitous examinations and fostering better environment for radiographic examinations. Fear of the unknown accidents with a probability of 1 of 100,000 can be vanquished by collaboration firmly by justification and optimization with a wide variety of means. This collaboration connects every single nation into one to attain the true healthy medical environment.

Medical imaging is an indispensible diagnostic tool in modern medicine enabling fast and accurate diagnosis. Recent technological advances in medical equipment and increased utilization of the imaging modality have resulted in a significant increase in the exposure to ionizing radiation. After the rapid adoption of multi-detector computed tomography, computed tomography (CT) is now the single largest source of diagnostic radiation exposure to patients. The risks and benefits from radiation must be carefully considered in all examinations using ionizing radiation, and the principles of justification and optimization should be considered in the proper use of CT examination. Justification means that the examination must be medically indicated and useful. Optimization means that the imaging should be performed using doses that are ALARA (as low as reasonably achievable), consistent with the diagnostic task. This includes understanding and changing CT protocols to perform the same diagnostic task with the minimal amount of radiation exposure while maintaining diagnostic accuracy. Protocols and guidelines are important tools for radiation dose reduction. Understanding the parameters and dose information for CT examination is essential for optimization. If the exam is justified, then the parameters must be optimized to the imaging indication, scan area, body size, age, and weight of the patients. The physician should always assess the radiation risk-benefit ratio for each patient before ordering an examination that uses radiation. Continuing education is essential for the implementation of the principles of patient radiation dose reduction. Physicians and radiologists must be aware of the radiation risks associated with CT exams.

Malignant melanoma accounts for 1.5% of all reported cancers with prevalence increasing in the past decade. Skin is the most common site for primary malignant melanoma, but it can involve virtually every organ system where melanin cells exist. They can frequently metastasize to the liver, lung, brain and bone before the primary lesion in the skin is clinically evident (1). Here, we report a case of malignant melanoma representing superior mediastinal mass without extrathoracic primary lesion.

An acute aortic thrombosis in the absence of atherosclerosis, aortic dissection, or aneurysm is an infrequent clinical entity and has been rarely reported in the literature. However, because of serious complications such as an embolism that can be fatal, one should always pay attention to the possibility of its occurrence. We report two cases of an acute aortic thrombosis of lung cancer patients treated with chemotherapy and a review of the literature.

We report a very rare case of mediastinal tuberculosis in a 57-year old woman who presented with a large mediastinal cyst on chest radiography. She had a 10-year history of exertional dyspnea, but felt comfortable at a rest. A subsequent chest CT suggested a mediastinal cyst with mediastinal lymphadenopathy and communicating pericardial sac. She underwent a thoracotomy and excision of the mass, which was histologically revealed to be of tuberculous origin. Although rare, the apparent increase in the incidence of tuberculosis may result mediastinal cysts being diagnosed mediastinal tuberculosis. We also briefly review mediastinal lymphadenopathy due to tuberculosis.

Many disorders and abnormalities are accompanied by cavitary lesoin of the lung and one of the most common causes of cavitary lung disease are primary and metastatic lung neoplasms. but cavitary formation of primary lung cancer is not frequent and cavitary or cystic pulmonary metastases of this is also rare. We report a case of cavitary pulmonry metastases of primary lung cancer proven by bronchoscopic biopsy and chest CT. The patients was 60 year-old heavy smoker who had no known underlying lung diseases 7 years ago and complained chronic cough. The chest CT showed primary lung cancer in right low lobe with multiple cavitary or cystic metastases in both lungs and multiple lymphatic metastases.

Leiomyomas are the most common benign tumors found in the esophagus. They are mostly solitary and multiple diffuse lesions are rare, occurring in only 2.4% of cases (1). We describe the case of a 13-year-old boy with a history of Alport syndrome who complained of progressive dysphagia and postprandial vomiting, and in whom diffuse leiomyomatosis of the esophagus was diagnosed. Chest PA showed mediastinal widening, and a barium study revealed diffuse esophageal wall thickening with dilatation, and obstruction at the level of the distal esophagus. Manometry showed increased pressure in the lower esophagus, and CT demonstrated diffuse thickening of the entire esophageal wall and an intraluminal mass in the distal esophagus. Follow-up CT three years later showed further esophageal wall thickening, as well as luminal narrowing. By means of distal esophagectomy, diffuse leiomyomatosis involving the entire esophageal wall and intraluminal mass was diag-nosed.

Purpose : To evaluate the incidence and type of low attenuation seen on high resolution computed tomogra-phy (HRCT) performed after artificially induced pulmonary embolism. Materials and Methods : Using permanent embolic materials, pulmonary embolism was induced in ten Yorkshire pigs. Pre- and postembolic pulmonary angiography was performed, and HRCT was performed im-mediately and 1, 3, and 6 weeks after embolization. The incidence and type of low attenuation of all segments, as seen on HRCT, was evaluated. Low attenuation was classified as mottled, lobular, segmental, or peripheral. The pigs were sacrified after 6 weeks and contact radiographs were obtained. Results : Low attenuation developed in eight of ten pigs. Pulmonary angiography revealed arterial occlusion in 15 large and 19 small segmental arteries (34 of 45 segments). In the remaining 11 segments, follow-up HRCT demonstrated areas of low attenuation. This was present in 25 of 35 segments (71%) as seen on HRCT images obtained immediately; in 16 of 41 segments (39 %) on images obtained 1 week after embolization; in 17 of 41 segments (41 %) on those acquired at 3 weeks; and in 25 of 45 segments (56 %) on those acquired at 6 weeks. The overall incidence of low attenuation was 83/166 (50 %). The types of low attenuation were mottled in 32/83 cases, lobular in 13/83, segmental in 13/83, and peripheral in 25/83. In large segmental arterial occlusion, the incidence of low attenuation on HRCT was 100% immediately, 57% at 1 week, 60% at 3 weeks, and 80 % at 6 weeks. In small segmental arterial occlusion, the incidence was 47%, 25 %, 11 %, and 21 % respectively. The overall incidence of low attenuation was 40/55 (73 %) in large segmental arterial occlusion and 18/71 ( 25%) in small segmental arterial occlusion. Conclusion : Low attenuation on HRCT is a finding of pulmonary embolism and is more common on HRCT performed immediately after embolization (71%) and in large segmental arterial occlusion (73%). Low attenu-ation on HRCT is an ancillary finding and may be useful in the diagnosis of pulmonary embolism.

Superior mediastinal widening on chest radiograph in patients with trauma has been considered the hallmark of mediastinal hemorrhage. The usual causes of superior mediastinal widening are hematoma, aortic rupture, and rupture of the esophagus or tracheobronchial tree. Very rarely, a cause of superior mediastinal widening is leakage of the cerebrospinal fluid. This report descrbes a case of superior mediastinal widening from traumatic cerebrospinal fluid leakage with spinal fracture.