Diagnosis of pulmonary embolism.

An accurate diagnosis of pulmonary embolism is essential to prevent excessive morbidity and mortality from lack of therapy or inappropriate anticoagulation. Clinical signs and symptoms are reported to be nonspecific, although published studies do not allow calculation of true specificity. Since certain clinical characteristics or groups of findings may be sensitive enough for pulmonary embolism, the diagnosis is unlikely in their absence. Ventilation-perfusion lung scanning has high sensitivity but variable specificity for pulmonary embolism. Patients with scans showing multiple segmental or lobar perfusion defects with normal ventilation have a high probability of pulmonary embolism. Scans with less extensive perfusion abnormalities or matching ventilation defects do not reliably exclude pulmonary embolism. Pulmonary angiography is the most definitive procedure for diagnosing pulmonary embolism. Digital subtraction pulmonary angiography and radiolabeled platelet scanning are promising but require more extensive validation before routine use.

Utilization of lung scans by clinicians.

To determine the effect of clinical assessments and lung scan results on the management of patients, we studied 566 consecutive patients referred for lung scans because of suspected pulmonary embolism. Prior to the lung scan, the clinician was asked to estimate the probability of pulmonary embolus. Two or three days later the physician was contacted to determine how the patient was managed. The results of the lung scan strongly influenced patient management. Patients with high probability lung scans were treated for pulmonary embolism regardless of the clinical pretest estimate. Low and intermediate probability lung scans resulted in most patients not being treated for pulmonary embolism and not referred for pulmonary angiography. Only 55 of the 566 patients were referred for pulmonary angiography, and approximately one-half of these patients had lung scans with an intermediate probability for pulmonary embolism.

Thoracocentesis of loculated pleural effusions using grey scale ultrasonic guidance.

Six patients with either malignant pleural effusion or empyema, in whom multiple conventional attempts at thoracocentesis were unsuccessful, were evaluated by ultrasound. In each case, a subsequent thoracocentesis guided by ultrasound produced sufficient fluid to enable a diagnosis to be established. In no case was pneumothorax produced.

Intercostal artery laceration during thoracocentesis: increased risk in elderly patients.

Two cases of intercostal artery laceration following thoracocentesis are reported. Subsequent analysis of 29 thoracic aortograms demonstrated a definite trend toward increasing tortuosity of intercostal arteries with advancing age. Consequently, the amount of space available for safe insertion of the thoracocentesis needle tends to decrease with advancing age. As a result, elderly patients are more prone to intercostal artery laceration during thoracocentesis, and careful attention must be paid to the proper technique for performing this examination in such patients.

Occult spontaneous esophageal perforation. Unusual clinical and radiographic presentation.

We report a unique presentation of spontaneous esophageal perforation or Boerhaave's syndrome. Our patient had no risk factors predisposing her to barogenic rupture of the esophagus, and she had none of the "classic" presenting signs. She was asymptomatic, and her clinical course appeared to be chronic. Her chest roentgenogram demonstrated bilateral thick-walled cavities with air-fluid levels. Computerized axial tomography of the chest and swallow of meglumine diatrizoate (Gastrografin) showed the cavities and esophagus to communicate. This patient's presentation and radiographic studies extend the reported description of Boerhaave's syndrome.

Mediastinal masses of vascular origin. A review.

Vascular lesions must be considered in the differential diagnosis of mediastinal masses. Knowledge of the vascular anatomy of the mediastinum and the clinical setting, as well as an awareness of key radiographic features, should suggest the vascular origin and guide appropriate diagnostic imaging. Although angiography is used most often, radionuclide flow studies and computed tomographic scanning may also be useful.

Imaging of the axillary subsegment of the right upper lobe.

The bronchial supply of the lateral or axillary area of the right upper lobe is variable. In 16 percent of normal subjects, an independent ramus of the posterior right upper lobe bronchus supplies an axillary subsegment. Airspace disease in the axillary subsegment has a characteristic appearance on radiographs. The CT appearance of disease in the axillary subsegment correlates closely with classic anatomic studies. Recognizing that disease is located in the axillary subsegment can help in directing bronchoscopy or biopsy.

In vitro effects of lidocaine on anaerobic respiratory pathogens and strains of Hemophilus influenzae.

Lidocaine is commonly employed as a topical anesthetic agent during fiberoptic bronchoscopic procedures or transbronchial brushing. Previous studies have demonstrated an inhibitory effect of lidocaine on the growth in culture media of gram-positive and gram-negative organisms, as well as several species of Mycobacterium and various fungi. The current in vitro investigation demonstrates an inhibitory, as well as a bactericidal, effect of lidocaine hydrochloride (in concentrations identical to those encountered during fiberoptic bronchoscopic procedures) on the common anaerobic respiratory pathogens and on multiple strains of Hemophilus influenzae. The finding helps to explaint the difficulty in producing proof via culture of the specific etiologic agent in inflammatory lesions from specimens obtained by fiberoptic bronchoscopic procedures or transbronchial brushing.

Cytomegaloviral infection presenting as a solitary pulmonary nodule.

Cytomegaloviral infection presenting in an immunologically compromised host as a solitary pulmonary nodule has not previously been reported. A patient with a renal transplant and with no pulmonary symptoms was noted to have a single nodule on a chest roentgenogram. At autopsy, this proved to be secondary to cytomegaloviral infection. Differential diagnostic considerations in the immunosuppressed patient are discussed.

Physical principles governing the interrelationships of pressure, flow and volume in collapsible tubes.

Basic principles of fluid mechanics may be used to analyze the relationships of flow, pressure and cross-sectional area of any collapsible tube, including pulmonary blood vessels. The cross-sectional area of a collapsible tube is a direct function of transmural pressure. Alterations in pressure inside the tube may result from changes in fluid velocity, downstream constriction in the tube, or direct increase in internal pressure, as with a manometer. This paper reviews the basic equations applicable to flow in collapsible tubes and illustrates the principles of such flow with a physical model. Depending upon the circumstances, changes in size of the tube may or may not reflect changes in flow or changes in fluid velocity.

Digital radiography with photostimulable storage phosphors. Control of detector latitude in chest imaging.

RATIONALE AND OBJECTIVES: A widely used digital radiography system based on a photostimulable storage phosphor (PSP) detector was analyzed with regard to radiographic contrast changes that result from the adjustment of detector latitude (x-ray sensitivity range) in the normal processing of chest images. METHODS: Images of an acrylic step wedge were acquired using the digital system in a mode that permitted direct control of effective detector latitude. The images were post-processed in conditions duplicating those used for portable chest examinations, and contrast was measured. RESULTS: Increases in effective detector latitude provided only marginal radiographic contrast gains in the subdiaphragm-equivalent areas of the laser-printed digital film image, while causing large reductions in radiographic contrast in the lung-equivalent region. CONCLUSION: Detector latitude is an important variable that should be monitored or controlled in investigations that compare reader performance using conventional and digital systems.

Medical student perceptions of diagnostic radiology. Influence of a senior radiology elective.

To assess the impact of a four-week elective on medical student perceptions of diagnostic radiology, we gave questionnaires to 96 senior students on the first and last days of the rotation. Eighty-five anonymous entrance responses and 73 exit responses were obtained during a 13-month interval. Compared with other clinical specialties, the students viewed radiology as third, behind surgery and medicine, in terms of required breadth of knowledge, skill, training, and "glamour." Radiology was also perceived to have the lightest workload with the exception of psychiatry. Responses did not significantly change after completion of the elective. Perceived advantages and disadvantages of radiology were studied in detail in a subset of students. Exit responses indicated that the elective promoted favorable perceptions of radiology but did not change the relative rankings of the various specialties. It appears that at our institution basic attitudes concerning radiology are formed prior to the senior radiology elective and are affected only moderately during the elective.

Scatter-reduction characteristics of an infinity-focused gridded radiographic cassette.

RATIONALE AND OBJECTIVES: The scatter-reduction properties of a new infinity-focused grid incorporated into a radiographic imaging cassette were analyzed. METHODS: A polystyrene chest phantom was imaged using the cassette and bedside radiographic procedure. Scatter fractions were measured using a beam-stop technique at several anatomically equivalent locations. The performance of this cassette also was evaluated as a function of the orientation angle. RESULTS: The gridded cassette provided a decrease in scatter fraction from 61% to 49% in the lung and from 87% to 76% in the mediastinum. To obtain equivalent film density when the grid was used, the exposure was increased by a factor of 3.0. While there was a decrease in scatter clean-up as the film cassette was tilted from the perpendicular, the grid performed well out to an angle of 10 degrees. CONCLUSION: The gridded cassette for portable radiography provides scatter reduction with little sensitivity to alignment. The availability of this device could improve scatter rejection, and therefore, contrast in portable radiographic imaging.

Scatter compensation in digital chest radiography using Fourier deconvolution.

The authors present a numerical deconvolution technique to compensate for image degrading effects caused by scattered photons in radiographic chest images. Fourier transform techniques are used to deconvolve a shift invariant model of the two dimensional point spread response functions of the scattered radiation. This approach uses a digitized radiograph acquired with a standard chest imaging protocol, so no specialized imaging equipment is required. While the shift variant shape of the scatter model is optimized for the lung field, effective compensation is provided when this model shape is applied to other chest regions. Preliminary evaluation suggests that this technique can provide improved image contrast over the entire chest region.

Three-dimensional imaging of the thoracic cavity.

Three-dimensional (3D) surface reconstruction techniques were applied to sets of computed tomographic (CT) images of the thoracic cavity. Emphasis was placed on extracting lung images. High quality, detailed 3D images of the lung surface and internal bronchial and vascular structures were produced.

Posterior beam-stop method for scatter fraction measurement in digital radiography.

The authors presented a new posterior beam-stop (PBS) technique for measuring the ratio of scattered to total-detected photon flux (scatter fraction) in a radiographic examination while preserving the diagnostic quality of the image. The scatter measurement was made using a standard imaging geometry with both beam stops and an additional x-ray detector placed behind the standard imaging detector. This PBS geometry differs from the standard beam-stop (SBS) technique for scatter measurement. With SBS, a beam-stop shadow appears on the image. To evaluate the PBS technique, scatter fraction measurements were performed on an anatomic phantom using both the PBS and SBS techniques. When compared with the standard technique, PBS provided accurate estimation of scatter fractions. Since the measurement can be performed without degrading a standard clinical radiographic examination, the PBS technique allows simultaneous acquisition of scatter measurements from human patients in combination with a standard radiographic examination.

Experimental pulmonary infarction in dogs: a comparison of chest radiography and computed tomography.

Transcatheter electrocoagulation of the pulmonary artery was used to successfully create experimental pulmonary infarcts in 15 to 16 dogs. The animals were evaluated from one to 13 weeks by chest radiography, computed tomography (CT), angiography, and pathologic examination. The abnormal densities in the dogs' lungs cleared in two to three weeks. The majority of the chest radiographs were normal in two weeks, and all were normal after three weeks. Prior to sacrifice, CT showed abnormal densities in the lungs in only two of eight animals. CT proved to be more sensitive than chest radiography for showing the densities in the lungs due to pulmonary infarction.

Accuracy of the chest radiograph in diagnosis of pulmonary embolism.

In an effort to determine the sensitivity and specificity of the chest roentgenogram for the diagnosis of pulmonary embolism, roentgenograms of 152 patients who were all suspected of having pulmonary embolism were randomized and presented to nine interpreters. One hundred eight patients in the series were proven to have pulmonary embolism on the basis of a positive pulmonary angiogram. Forty-four patients were assumed not to have embolism on the basis of either a normal perfusion isotope scan or a pulmonary angiogram which did not show embolism. The interpreters were requested to indicate whether pulmonary embolism was present or absent, or whether they could not tell from the roentgenogram. Readers had no prior knowledge of the actual disease state. The average true-positive ratio (sensitivity) was 0.33, with a range of 0.52 to 0.88. The average true-negative ratio (specificity) was 0.59, with a range of 0.31 to 0.80. The false-positive and false-negative ratios were respectively, 0.21 (range 0.05 to 0.39) and 0.41 (range 0.15 to 0.70). A predictive index, reflecting the overall accuracy of diagnosis, was calculated for the entire group and was 0.40, with a range of 0.17 to 0.57. There appeared to be no correlation between training or experience and accuracy of performance in this study.

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.

Single-exposure conventional and computed radiography image acquisition.

A technique for simultaneously acquiring a conventional film-screen radiographic image and a digital computed radiography (CR) image with a single x-ray exposure is described. Measurements of image contrast, spatial resolution, and signal-to-noise ratios demonstrate that a modified film cassette in which the first intensifier screen has been replaced with a CR imaging plate permits dual-image, single-exposure imaging with only nominal degradation in film and CR image quality relative to the two standard image counterparts. This technique may be used to acquire matched image pairs for research or as a way to provide full-size conventional film images in the clinical environment, while retaining the advantages offered by computed radiography systems.