Acute pulmonary embolism: visualization of high attenuation clot in the pulmonary artery on noncontrast helical chest CT

Helical CT of the thorax is frequently utilized for the evaluation of chest pain or shortness of breath affecting the emergency patient. To improve diagnostic accuracy, thoracic CT examinations are frequently tailored to address specific conditions. Although tailored protocols may enhance diagnostic accuracy, implementing the wrong protocol could result in a misdiagnosis. The proper protocol choice may particularly difficult in the emergency patient due to the nonspecific nature of many chest pain syndromes. Recently, helical CT has been used for the evaluation of suspected pulmonary embolism (PE). Demonstration of an intravascular filling defect surrounded by contrast-enhanced blood is diagnostic of PE. However, because the clinical presentation of PE is frequently nonspecific, awareness of the many potential imaging manifestations of PE is important. Therefore, we present the rare circumstance of high-attenuation clot visible within the pulmonary arteries on noncontrast helical CT; PE was confirmed after the administration of iodinated contrast medium.     

The role of spiral CT using the pulmonary embolus protocol: a comparison of emergency department and hospitalized populations

Purpose: To compare the incidence of CT scan-detected pulmonary embolism, the CT scan-detected alternative findings (ancillary findings and alternative radiologic diagnoses), and the patient characteristics in emergency department and in hospitalized patients. Materials and methods: 81 spiral CT scans in 79 consecutive adult emergency department patients were retrospectively identified by computer search. During the same 9-month interval, 131 consecutive adult in-patients were similarly identified. The in-house and emergency department populations were compared in respect of incidence of pulmonary embolism and alternative findings using χ ² analysis. Results: 81 emergency department scans and 135 in-patient scans were evaluated. Of these, 22 emergency department scans (27.1 %) and 37 in-patient scans (27.4 %) were positive for pulmonary embolism. Of the scans that were negative for a pulmonary embolism, 45 emergency department scans (76.2 %) and 88 in-patient scans (89.8 %) were positive for alternative findings. These included atelectasis, adenopathy, metastatic disease, and pneumomediastinum. Alternative radiologic diagnoses on scans negative for pulmonary embolism occurred in 8/59 emergency department patients (13.5 %) and in 17/98 in-patients (17.3 %). These included pneumonia, tumor, mucus plugging, pericardial effusions, and thoracic aortic dissection. Conclusions: No significant difference exists between the emergency department and in-patient populations for the incidence of pulmonary embolism on spiral CT scans. Although a significant difference did exist between these populations in respect to alternative findings, the high percentage of alternative findings in both populations shows a possible advantage of CT over the traditional test, the ventilation-perfusion scan. Therefore, spiral CT should not be limited to the in-patient population as the first-line imaging modality for the diagnostic evaluation of pulmonary embolism.     

Change in regional pulmonary perfusion as a result of posture and lung volume assessed using technetium-99m macroaggregated albumin single-photon emission tomography

The purpose of this study was to evaluate the effects of gravity and lung volume on regional pulmonary perfusion using technetium-99m macroaggregated albumin (^99mTc MAA) single-photon emission tomography (SPET). Twenty-five subjects were classified into three groups according to their position during the injection of the tracer [11 subjects sitting, six supine and eight both supine and prone (S+P) positions]. All of these subjects were injected with the tracer during normal tidal breathing. In the S+P group, half of the tracer was injected while the subject was in each position. The remaining 11 subjects were classified into two groups according to their lung volume during the injection. Supine patients were instructed to hold their breath at residual volume (RV) (five subjects) or total lung capacity (TLC) (six subjects) while receiving the tracer injection. A region of interest with a ventrodorsal axis was defined in the centre of each lung. Profile curves were produced by plotting and normalizing the perfusion values as a percentage of the maximum value. The perfusion distributions for the sitting and S+P positions and at RV were relatively uniform. However, the distributions for the supine position and at TLC showed a gravitational influence [sitting vs TLC: 87.8%±10.4% vs 67.3%±8.7% for % maximum perfusion at +5 pixels from the midpoint of the upper lobe (P<0.00002)]. The gravity-related perfusion inhomogeneity was more prominent in the lower lobe than in the upper lobe. It is concluded that the physiological vertical gravitational gradient should be taken into consideration during the interpretation of lung SPET images. Preferably, patients should be injected with the tracer twice, once in the supine position and once in the prone position, while breathing normally. Alternatively, they may be injected with the tracer once while in the supine position and holding their breath at RV. Either of these protocols should ensure a uniform distribution of tracer. Received 4 November 1999 and in revised form 18 January 2000