The emphysemas: radiologic-pathologic correlations.

There are several forms of emphysema that should be considered as distinct disease entities. No university accepted classification system of these forms exists, but correlations of autopsy findings in 1,823 cases over a 12-year period confirm that the radiographic and pathologic features of the emphysemas are readily understood when centrilobular, panlobular, paracicatricial, and localized types of the disease are recognized. Centrilobular emphysema associated with cigarette smoking is the most common form. Panlobular emphysema is associated with alpha 1-protease inhibitor deficiency and pathologically produces uniform enlargement of all air spaces, with a mild basilar predominance. Paracicatricial emphysema is seen adjacent to areas of parenchymal scarring. Localized emphysema represents focal enlargement or destruction of air spaces with otherwise normal lung. A clear understanding of the computed tomographic appearance of all forms of emphysema is essential for the correct diagnosis of parenchymal lung abnormalities.

Magnetic resonance imaging of the brachial plexus.

Magnetic resonance (MR) imaging has become the method of choice for evaluating patients with brachial plexopathy. The multiplanar capability of MR imaging and its superior ability to differentiate nerves from vessels and surrounding soft tissues contribute to its success. The article describes the MR anatomy of the brachial plexus in the axial, coronal, and sagittal planes and reviews the MR characteristics of traumatic and nontraumatic etiologies of brachial plexopathy.

Analysis of the solitary pulmonary nodule by means of digital techniques.

Currently the radiographic determination of the benign or malignant nature of solitary pulmonary nodules relies on growth characteristics determined by comparison radiographs or the detection of calcification in the nodule with either low-peak kilovoltage fluoroscopy or CT of the chest. An alternative approach is analysis of the optical densities within the nodules by means of digital radiography. Two techniques have been described: histogram analysis of chest radiographs digitized with a laser scanner and dual-energy digital radiography. Although both techniques remain experimental, they offer a potential advantage over CT in that a single radiographic exposure is sufficient, thus decreasing the radiation dose to the patient and providing the patient with a less complex work-up.

Image optimization in a computed-radiography/photostimulable-phosphor system.

Photostimulable phosphor imaging is an exciting new technology that has several advantages over film/screen radiography, the most important of which is the linearity of the photostimulable phosphor system over a wide exposure latitude. The photostimulable phosphor image is digital, and as such, provides options of how the image is viewed by radiologists. This report discusses the various image-processing parameters available for a photostimulable phosphor system and describes a rational approach for selecting these parameters in portable chest radiography. As photostimulable phosphor imaging becomes more widely implemented, an understanding of the processing parameters will facilitate the production of images that take full advantage of the benefits of these systems.

Pulmonary lymphangioleiomyomatosis: CT findings.

Lymphangioleiomyomatosis, a rare disease occurring in women of childbearing age, is characterized by proliferation of smooth muscle in pulmonary lymphatic channels and mediastinal and abdominal lymph nodes. Chest radiographs typically reveal interstitial disease with normal lung volume. Pneumothorax and pleural effusions may be present. CT scans in eight patients with biopsy-proved pulmonary lymphangioleiomyomatosis were reviewed. The prominent feature of the disease was multiple thin-walled cysts throughout the lungs, best visualized on scans made with 1.5-mm collimation. Mediastinal and/or retrocrural lymphadenopathy, often not appreciated on the chest radiograph, was present in four of eight patients. CT can suggest a diagnosis of lymphangioleiomyomatosis when diagnosis by clinical presentation and chest radiographs is uncertain.

Chronic multiple pulmonary emboli. Regional response of the bronchial circulation.

In pulmonary embolism, the bronchial circulation can dramatically increase perfusion to the lung and prevent infarction. The physiology of this response is incompletely understood. The authors studied the regional changes in the bronchial circulation in an animal model after multiple chronic pulmonary emboli to the periphery of one lung. The gross anatomy of the bronchial circulation was studied using Batson's solution to produce vascular casts of the pulmonary and bronchial circulations. These casts were prepared in a normal sheep and in a sheep with multiple chronic microemboli in the periphery of one lung. The normal bronchial arteries are visible as threadlike structures covering the surface of the tracheobronchial tree with ramifications extending to the lung periphery. In a sheep with multiple chronic microemboli, the bronchial arteries supply the pulmonary parenchyma deprived of pulmonary arterial flow. The bronchial arteries following pulmonary arterial embolization markedly dilate and are serpentine.

Effects of image processing on nodule detection rates in digitized chest radiographs: ROC study of observer performance.

To evaluate the effects of image processing in digitized chest radiographs when high-resolution images are used, an examination was done in which the detection of pulmonary nodules in unprocessed digitized chest radiographs was compared with that in images that had undergone processing with two methods, adaptive filtration and histogram equalization. The processing techniques have been optimized in previous work to selectively enhance the retrocardiac and subdiaphragmatic areas without significant alteration of detail in the lung. Eight observers were shown 150 test radiographs (50 unprocessed, 50 processed with adaptive filtration, 50 processed with histogram equalization) containing 150 nodules. The results indicate a statistically significant (P less than .03) difference, with highest observer performance in the chest radiographs processed with adaptive filtration (median area under ROC curve = 0.78), compared with unprocessed images (median = 0.68) and chest radiographs processed with histogram equalization (median = 0.62). Performance in the lung was not significantly different. Adaptive filtration applied to selectively enhance underexposed areas of film images may improve nodule detection. Histogram equalization provided no improvement in performance.

Differentiation of benign from malignant pulmonary nodules with digitized chest radiographs.

To assess whether it is possible to distinguish benign from malignant solitary pulmonary nodules with digital techniques, a retrospective study of 68 patients with proved solitary nodules was performed. The conventional chest radiograph for each patient was digitized to 2,048 X 2,048 X 12 bits, and changes in the optical density within the nodule were analyzed. A number (the corrected gradient number) was then generated that reflected this variation. Striking differences were noted between 26 malignant nodules and 21 calcified granulomas. The technique was then applied to 21 benign nodules that had initially required thoracotomy or further study for diagnosis. In nine of these 21 patients (43%), the corrected gradient number allowed correct classification as a benign lesion.

Performance of high-resolution monitors for digital chest imaging.

High-resolution cathode-ray tubes (CRT's) are currently the most viable soft-copy display for digital radiography. We present here methods for measuring large-area contrast ratio and detail contrast ratio. A two-dimensional charge coupled device (ccd) array signal-averaged with a video frame buffer permits linear microradiometric measure of individual beam lines. Results from three different 1000-line monitors demonstrate the shift variance of resolution. The detail contrast ratio (or modulation depth) was found to vary from 100% to less than 10% across the face of one CRT. Dynamic focus in both the horizontal and vertical deflection circuitry proved effective in reducing this shift variance. Comparisons of three phosphors demonstrate the utility of long persistence phosphors (P164) for static display in producing brighter images with less flicker. Recommendations for CRT design and selection for high-resolution digital radiography are included.

Regionally adaptive histogram equalization of the chest.

Advances in the area of digital chest radiography have resulted in the acquisition of high-quality images of the human chest. With these advances, there arises a genuine need for image processing algorithms specific to the chest, in order to fully exploit this digital technology. We have implemented the well-known technique of histogram equalization, noting the problems encountered when it is adapted to chest images. These problems have been successfully solved with our regionally adaptive histogram equalization method. With this technique histograms are calculated locally and then modified according to both the mean pixel value of that region as well as certain characteristics of the cumulative distribution function. This process, which has allowed certain regions of the chest radiograph to be enhanced differentially, may also have broader implications for other image processing tasks.

Digital synthesis of lung nodules.

Studies evaluating observer accuracy and visual perception of pulmonary nodules usually are based upon test films obtained from clinical practice in patients with proven pulmonary nodules. Unfortunately, such nodules do not always occur in the optimal size and location to facilitate testing. Such studies would be enhanced by the ability to place nodules of desired size and location on chest radiographs. This report describes a method of placing a computer-generated (synthesized) nodule on a digitized chest radiograph. To demonstrate the similarity of these synthesized nodules to real nodules, each digitized radiograph with a computer-generated nodule was paired with a digitized chest radiograph of a patient with a clinically proven pulmonary nodule. A total of 22 pairs of chest radiographs were then shown to 13 radiologists, who were asked to distinguish the synthesized nodule from the real nodule. With this two alternative forced-choice test, the radiologists were only able to distinguish the synthesized nodule in 51% of the cases, strongly suggesting that computer generated nodules may be used to simulate real pulmonary nodules in future tests of nodule detection.