The transition from technegas to pertechnegas.

UNLABELLED: We set out to determine the oxygen concentration of the argon-oxygen mixture in the technegas generator where technegas-like behavior changes to pertechnegas-like behavior which allows [99mTc]pertechnetate to enter the solution. METHODS: We prepared radioaerosols analogous to technegas and pertechnegas, with oxygen concentrations between 0% and 5%. They then were examined by thin-layer chromatography using saline as a solvent to measure the amount of [99mTc]pertechnetate moving with the solvent front as a function of oxygen concentration. RESULTS: The amount of mobile pertechnetate markedly increased when the radioaerosols were created in an atmosphere containing between 0.1% and 0.2% oxygen. The transition from technegas-like to pertechnegas-like behavior occurs when the oxygen-argon gas mixture contains lower concentrations of oxygen than those used in the preparation of pertechnegas. CONCLUSION: Argon intended for the preparation of technegas should contain no more than 0.1% oxygen.

Bone mineral measurement in the human spine using computed tomography.

A new method to measure bone mineral mass and density in human vertebrae was developed and clinically implemented. Using single-energy CT in the lumbar spine, it is possible to measure trabecular and cortical bone mineral mass regardless of the amount of soft tissue "background" present. Although the method is sensitive to the fat that resides in the marrow space of the vertebral body, an estimate of fat content can be incorporated into the calculations. We present and demonstrate the conceptual model upon which the method rests, and show that the results derived from its clinical use are highly correlated with those obtained from the conventional method of determining bone mineral concentration.

Effective doses to patients undergoing thoracic computed tomography examinations.

The purpose of this study was to investigate how x-ray technique factors and effective doses vary with patient size in chest CT examinations. Technique factors (kVp, mAs, section thickness, and number of sections) were recorded for 44 patients who underwent a routine chest CT examination. Patient weights were recorded together with dimensions and mean Hounsfield unit values obtained from representative axial CT images. The total mass of directly irradiated patient was modeled as a cylinder of water to permit the computation of the mean patient dose and total energy imparted for each chest CT examination. Computed values of energy imparted during the chest CT examination were converted into effective doses taking into account the patient weight. Patient weights ranged from 4.5 to 127 kg, and half the patients in this study were children under 18 years of age. All scans were performed at 120 kVp with a 1 s scan time. The selected tube current showed no correlation with patient weight (r2=0.06), indicating that chest CT examination protocols do not take into account for the size of the patient. Energy imparted increased with increasing patient weight, with values of energy imparted for 10 and 70 kg patients being 85 and 310 mJ, respectively. The effective dose showed an inverse correlation with increasing patient weight, however, with values of effective dose for 10 and 70 kg patients being 9.6 and 5.4 mSv, respectively. Current CT technique factors (kVp/mAs) used to perform chest CT examinations result in relatively high patient doses, which could be reduced by adjusting technique factors based on patient size.

Unilateral pulmonary edema after talc pleurodesis.

Talc is commonly given after drainage of the pleural space to create pleural symphysis. Recognized complications of pleural drainage followed by talc pleurodesis include reexpansion pulmonary edema, pneumonia, and adult respiratory distress syndrome. This report describes a complication of talc pleurodesis that appears not to have been appreciated previously. Chest radiographs obtained before and after talc pleurodesis were evaluated in a total of 108 patients in three groups; 89 of these patients were receiving palliative therapy for malignant pleural effusion. Approximately 16% of the 108 patients developed a transient interstitial process in the lung ipsilateral to the treated pleural space. The recognized complications are inadequate to account for these radiographic findings. Other interstitial diseases such as hydrostatic pulmonary edema and lymphangitic carcinomatosis also are not adequate explanations. The observed complication is most likely the result of endothelial damage leading to a capillary leak type of pulmonary edema.

Chest radiographic features of engraftment syndrome.

About the time of hematopoietic engraftment, patients undergoing autologous hematopoietic stem cell transplantation in the form of peripheral blood stem cell transplantation (PSCT) may develop an "engraftment syndrome" that includes fever, skin rash, and capillary leak. This condition is usually self-limited, as opposed to other early complications of bone marrow transplantation such as infection and drug reactions. This article describes the chest radiographic manifestations of engraftment syndrome. The medical records and chest radiographs of 50 consecutive breast cancer patients who underwent PSCT were retrospectively reviewed. Engraftment syndrome was diagnosed if the expected clinical findings occurred at the time of engraftment of neutrophils and no other cause was identified. The chest radiographs were correlated with the clinical course. Sixteen patients were found to have engraftment syndrome (32%). Of these, eight had abnormal radiographs. Radiographic findings consisted of pleural effusions and interstitial pulmonary edema. No patient progressed to adult respiratory distress syndrome. Interstitial pulmonary edema and pleural effusions were observed in association with engraftment syndrome from PSCT. Correlation of these findings with clinical history and neutrophil count is important so that engraftment syndrome can be distinguished from other causes of fever.

Pleuropulmonary blastoma simulating an empyema in a young child.

Pleuropulmonary blastoma is a rare childhood malignancy that may simulate an empyema both clinically and radiographically. A 3-year-old boy with fever, cough, and abdominal pain developed complete opacification of the left hemithorax with contralateral mediastinal shift over the course of several weeks. At thoracotomy, a pleuropulmonary blastoma was discovered. The radiology, pathology, and clinical course of this rare neoplasm are discussed.

Radiology teaching file cases on the World Wide Web.

The presentation of a radiographic teaching file on the World Wide Web can be enhanced by attending to principles of web design. Chief among these are appropriate control of page layout, minimization of the time required to download a page from the remote server, and provision for navigation within and among the web pages that constitute the site. Page layout is easily accomplished by the use of tables; column widths can be fixed to maintain an acceptable line length for text. Downloading time is minimized by rigorous editing and by optimal compression of image files; beyond this, techniques like preloading of images and specification of image width and height are also helpful. Navigation controls should be clear, consistent, and readily available.

Experimentally produced pulmonary arterial occlusion in the dog: identification with pertechnegas inhalation.

Pertechnegas, a variant of technegas, is a fine, dry aerosol formed when technetium-99m pertechnetate is vaporized in a technegas generator under appropriate conditions. After inhalation, the aerosol is deposited almost entirely on the surfaces of terminal respiratory structures. Unlike technegas, however, pertechnegas crosses the alveolar-capillary membrane and leaves the lung through the pulmonary circulation. To demonstrate prolonged retention of pertechnegas in regions of lung supplied by an occluded pulmonary artery, 12 pulmonary arterial occlusions were experimentally produced in two dogs. After inhalation of pertechnegas, a transient focus of increased pulmonary radioactivity was seen in 11 occlusions; 10 of these 11 foci were easily confirmed by means of subsequent perfusion scintigraphy. All 11 foci of retained pertechnegas corresponded to the location of the non-perfused lung. Thus, it is possible to identify ischemic lung with focal retention of pertechnegas (a finding that indicates preserved ventilation but diminished perfusion) by use of a single examination.

Technique factors and image quality as functions of patient weight at abdominal CT.

PURPOSE: To investigate how changes in kilovolt peak and milliampere second settings, and patient weight affect transmitted x-ray energy fluence and the image contrast-to-noise ratio (CNR) at abdominal computed tomography (CT). MATERIALS AND METHODS: Cylinders of water were used as patient models, and x-ray spectra, including x-ray tube potentials of 80-140 kVp, were investigated. The mean photon energy and energy fluence transmitted through water cylinders with varying diameters and the image contrast for fat, muscle, bone, and iodine relative to water were determined. The effect of changing the x-ray tube potential on CNR also was investigated. RESULTS: At a constant kVp, increasing patient weight from 10 kg to 120 kg reduced the transmitted energy fluence by two orders of magnitude. Changing the x-ray tube potential from 80 kVp to 140 kVp increased the mean photon energy from approximately 52 keV to approximately 72 keV and thus reduced the image contrast relative to water by 12% for muscle, 21% for fat, 39% for bone, and 50% for iodine (approximate reduction values). Increasing the x-ray tube potential from 80 kVp to 140 kVp increased the CNR by a factor of 2.6 for muscle and by a factor of 1. 4 for iodine. CONCLUSION: With changes in patient weight at abdominal CT, x-ray tube potentials must be varied to maintain a constant detector energy fluence. Increasing the x-ray tube potential generally improves CNR.

Pulmonary veno-occlusive disease presenting with thrombosis of pulmonary arteries.

Pulmonary veno-occlusive disease is a rare cause of pulmonary hypertension. An unusual case presenting with thrombosis of the right pulmonary artery and serological evidence of autoimmunity is reported.

Radiation exposure and image quality in chest CT examinations.

OBJECTIVE: The purpose of this study was to determine how changes in radiographic tube current affect patient dose and image quality in unenhanced chest CT examinations. SUBJECTS AND METHODS: Ten sets of CT images were obtained from patients undergoing CT-guided chest biopsies. For each patient, six images of the same region were obtained at settings between 40 and 280 mAs. CT data were used to reconstruct tomographic sections with a field of view limited to the normal contralateral lung. Images were printed using lung and mediastinal image display settings. Image quality was determined by asking radiologists to assess the perceived level of mottle in CT images. Five chest radiologists ranked the relative image quality of six images. Patient effective doses were computed for chest CT examinations performed at each milliampere-second setting. Radiologists indicated whether any perceived improvement of image quality at the higher radiation exposures was worth the additional radiation dose. RESULTS: The differences in quality of chest CT images generated at greater than or equal to 160 mAs were negligible. Reducing the radiographic technique factor below 160 mAs resulted in a perceptible reduction in image quality. Differences in CT image quality for radiographic techniques between 120 and 280 mAs were deemed to be insufficient to justify any additional patient exposure. However, the use of 40 mAs results in an inferior image quality that would justify increased patient exposure. CONCLUSION: Radiographic techniques for unenhanced chest CT examinations can be reduced from 280 to 120 mAs without compromising image quality.

Vertebral mineralization after parathyroidectomy: measurement by quantitative CT.

Quantitative CT has been used to document abnormally low levels of vertebral bone mineral in hyperparathyroid states. No one has yet reported an improvement in vertebral bone mineral concentration after parathyroidectomy. Quantitative CT was used to measure mineralization of lumbar vertebral bodies in five women with primary hyperparathyroidism, at the time of surgical resection of a parathyroid adenoma and again 4 months after surgery. Four of the patients had increased vertebral mineralization after 4 months; the increase for the entire group (13%) was statistically significant. In one patient, examined for a third time 8 months after surgery, a continuing increase in vertebral bone mineral concentration was seen. A final examination, obtained 20-33 months after surgery, revealed that in every patient the bone mineral concentration was lower than on the first postoperative study and in some cases was less than the original preoperative measurement. We conclude that a temporary increase in vertebral trabecular mineralization occurs after parathyroidectomy for primary hyperparathyroidism. During the following 3 years, however, this increase is not sustained.

Developmental lymphatic disorders of the thorax.

Developmental disorders that involve the lymphatic channels of the thorax, although rare, are important and must be distinguished from the more common causes of chest masses or diffuse lung disease. There are four major types of developmental lymphatic disorders that affect the thorax: lymphangiectasis, characterized by congenital anomalous dilatation of pulmonary lymph vessels; localized lymphangioma, a rare and benign, usually cystic, lesion characterized by masslike proliferation of lymph vessels; diffuse lymphangioma, a proliferation of vascular, mainly lymphatic, spaces in which visceral and skeletal involvement are common; and lymphangioleiomyoma, which involves a haphazard proliferation of smooth muscle in the lungs and dilatation of lymphatic spaces. These characteristic findings can be seen with radiographic studies as well as with histologic evaluation. The discovery of one of these lymphatic disorders may prompt an investigation for associated congenital anomalies, including Noonan syndrome, asplenia, Gorham syndrome, and tuberous sclerosis.

MR imaging in the evaluation of the chest after uncomplicated median sternotomy.

Although complications of median sternotomy are infrequent, they are associated with high morbidity and mortality. Current imaging modalities have proved to be of limited value in the evaluation of these abnormalities. The search for more efficacious means of assessment is continual. The appearance of the thorax was evaluated in 10 patients who were undergoing median sternotomy for coronary artery bypass graft surgery. Three serial magnetic resonance (MR) imaging examinations were performed on each patient. These examinations included a baseline preoperative study and two postoperative studies. Each patient included in the study had an uncomplicated postoperative clinical course. Usual postoperative findings included pleural effusions, pulmonary parenchymal abnormalities, mediastinal edema, and pericardial effusions. On the basis of this limited study, the authors believe that MR imaging is a feasible means of evaluating the chest after surgery. An appreciation of the normal postoperative appearance is essential before complications can be reliably identified and characterized.

Pulmonary arterial hypertension: a contemporary review.

Pulmonary arterial hypertension has many causes, only some of which are well understood. The radiographic findings in pulmonary arterial hypertension are very similar regardless of the cause. Some radiographic features such as cardiac chamber enlargement, occur secondary to elevation of pulmonary pressures. In addition, sequential radiographs may demonstrate dramatic changes as the hypertension develops. This article presents examples of the various forms of pulmonary arterial hypertension, with pathologic correlation. Included are chronic pulmonary thromboembolism, plexogenic pulmonary arteriopathy, pulmonary venooclusive disease and persistent fetal circulation. Examples of lesions causing secondary pulmonary arterial hypertension: parenchymal lung disease, pulmonary venous hypertension, and congenital heart disease, are also illustrated.