Differential Diagnosis Of Pulmonary Embolism Research Articles

Radionuclide Imaging in Diseases of The Chest (Part 1)

Since the introduction of 13I-labeled macroaggregated human serum albumin in 1964, 1 Taplin GV Johnson DE Dore EK Kaplan HS Lung photoscans with macroaggregates of human serum radioalbumin: Experimental basis and initial clinical trials. Health Phys. 1964; 10: 1219 Crossref PubMed Scopus (31) Google Scholar radionuclide imaging studies of the chest have focused primarily on the noninvasive detection of pulmonary thromboembolism. 133Xe gas was introduced for the assessment of pulmonary ventilation in 1955 by Snipping et al. 2 Knipping HW Bolt W Ventrath H Valentin H Ludes H Endler P A new method for regional lung function with radioactive Xe-133 gas. Deutsch Med Wochenschr. 1955; 80: 1146 PubMed Google Scholar The use of combined ventilation and perfusion imaging to improve the specificity of radionuclide imaging for the detection of pulmonary emboli was introduced over a decade ago by Wagner et al 3 Wagner Jr, HN Lopez-Majano V Langan JK Joshi RC Radioactive xenon in the differential diagnosis of pulmonary embolism. Radiology. 1968; 91: 1168 Crossref PubMed Scopus (49) Google Scholar and DeNardo et al. 4 DeNardo GL Goodwin DA Ravasini R Dietrich PA The ventilatory lung scan in the diagnosis of pulmonary embolism. N Engl J Med. 1970; 282: 1334 Crossref PubMed Scopus (61) Google Scholar While the technique has undergone considerable refinement in terms of instrumentation, radiopharmaceuticals, and method of interpretation, ventilation/perfusion (V/Q) scintigraphy remains the most frequently performed radionuclide imaging procedure of the chest in most nuclear medicine laboratories.

The history of lung imaging with radionuclides

T WO TYPES of lung imaging test agents and procedures for their administration were developed at the UCLA Laboratory of Nuclear Medicine and Radiation Biology between 1963 and 1965./-4 The first of these was devised to image the blood flow pattern in the lungs by rectilinear scanning, after the i.v. injection of macroaggregates of human serum albumin (HSA) labeled with 131I, size range, 10-50pm? The macroaggregates were first produced in January 1963, but this agent stemmed from the development of a simplified method of preparing colloidal-size (10-20nm) 131l albumin suspensions by pH adjustment and heating in a water bath at 90-95~ for 8-10 min under gentle agitation? Albumin colloid labeled with 131I is useful in visualizing the liver, spleen, and bone marrow by scanning./In such studies, however, if the size of the particles exceeds 5-10#m, lung entrapment is easily demonstrable. Therefore, an extensive study was made to determine the optimal size for lung visualization by temporary capillary and arteriolar blockade. The size was adjusted so that pulmonary entrapment lasted no longer than a half-life of 4-8 hr. In the first animal trials, extremely low specific activity (approximately 50~tCi/mg of HSA) was used. Even so, the scan dose (300pCi in 6 mg HSA) was 50100 times below the minimum toxic dose level (20-30mg of HSA/kg). This work was first reported in a scientific exhibit at the Tenth Annual Meeting of the Society of Nuclear Medicine in Montreal, Canada, in June 1963. 6 Lung scanning in man was initiated in November 1963 at UCLA ~'2 after Wagner's Human Studies, using much higher specific activity HSA suspensions (1000pCi/mg of HSA). The second development was made in 1964 and first reported in 1965. 3 Radioaerosols were administered to anesthetized dogs via tracheal intubation. They were produced by a positive pressure nebulizer. Subsequently, similar procedures, radioaerosols, and nebulizer equipment were studied in man. 4 In 1966 colloidal radioactive gold, 198Au, was replaced by 99mTc-HSA and sulfur colloid 99mTC as test agents, to decrease radiation exposure to the lungs. 7 This communication describes in detail lung perfusion and airway patency inhalation procedures, along with an evaluation of their current value in the differential diagnosis of pulmonary embolism, and in the detection of obstructive airways disease. TM The relationship of both procedures to the findings from plain chest radiography and pulmonary angiography is compared in a variety of pulmonary and obstructive airways disorders.

67Ga lung scan. An aid in the differential diagnosis of pulmonary embolism and pneumonitis.

Twenty-three patients patients with clinical signs of pulmonary embolic disease and lung infiltrates were studied to determine the value of gallium citrate Ga 67 lung scan in differentiating embolic from inflammatory lung disease. In 11 patients without angiographically proved embolism, only seven had corresponding ventilation-perfusion defects compatible with inflammatory disease. In seven of these 11 patients, the gallium 67 concentration indicated inflammatory disease. In the 12 patients with angiographically proved embolic disease, six had corresponding ventilation-perfusion defects compatible with inflammatory disease. None had an accumulation of 67Ga in the area of pulmonary infiltrate. Thus, ventilation-perfusion lung scans are of limited value when lung infiltrates are present. In contrast, the accumulation of 67Ga in the lung indicates an inflammatory process. Gallium imaging can help select those patients with lung infiltrates who need angiography.

The use of radioisotope techniques for the evaluation of patients with pulmonary disease.

Although it is true that pulmonary perfusion scanning is generally accepted primarily in the differential diagnosis of pulmonary embolism, the introduction of regional ventilation studies with radioactive 133Xe, the use of the computer to provide quantitative data, and the advances being made in cardiovascular nuclear medicine indicate that nuclear medicine procedures will be used more and more in the evaluation of patients with a variety of lung and heart diseases. They have already proved of value in the following circumstances: (1) differential diagnosis of pulmonary embolism; (2) assessment of regional involvement in pulmonary parenchymal disease, including degenerative, neoplastic, and infectious diseases; (3) detection of bullous disease and the determination of the possible effectiveness of surgery; (4) assessment of the response to radiation therapy in patients with carcinoma of the lung; (5) detection of pulmonary venous hypertension in patients with mitral valve or left ventricular disease; (6) detection of cor pulmonale; (7) differential diagnosis of cyanosis in newborn infants.

Radioactive tracers in the differential diagnosis of pulmonary embolism

Radioactive tracers in the differential diagnosis of pulmonary embolism

Regional ventilation in the differential diagnosis of pulmonary embolism.

In the diagnosis of pulmonary embolism by lung scanning, clinical errors of interpretation may arise. Diseases that affect the distribution of pulmonary blood flow, such as pulmonary emphysema and bronchial asthma, may be confused with pulmonary embolism. With the addition of ventilation studies with 133 xenon to the perfusion scans, distinct differences appear between patients with emboli and those with obstructive lung disease. In patients with pulmonary emboli, ventilation is preserved in the areas of decreased perfusion, whereas patients with obstructive lung disease show both decreased ventilation and perfusion in the affected areas.

Current status of lung scanning.

Five years ago, in October 1963, the first lung scans carried out in man were presented at the Symposium on Dynamic Clinical Studies with Radioisotopes in Oak Ridge, Tenn. Since then, the procedure has become widely adopted as a diagnostic and research tool. While still short of being infallible, scanning of the lungs has been most helpful in the differential diagnosis of pulmonary embolism. At the same time, it has expanded our knowledge of the natural history of the disease and is aiding in the development of promising new therapies. One of the things that scanning has taught us about pulmonary embolism is that it is much more common and—on the average—rather less serious than was once thought. Some recent postmortem studies have shown evidence of emboli in as many as half the adult patients dying from all causes. It seems probable that many emboli are never detected because they are asymptomatic and, for the most part, resolve spontaneously with no known ill effects. As yet there is no single procedure that is sensitive, specific, safe, and inexpensive enough to serve as a screening test. The physician must therefore rely heavily upon the patient's history and the presenting symptoms. Pulmonary emboli usually originate as thrombi in the pelvic region or, less commonly, in the lower extremities. They occur most frequently postoperatively, postpartum, and, indeed, in any situation in which the patient has been more or less immobilized and has become predisposed to clot formation. With a suspicious history and symptomatology, the next step is generally a chest film. This can be useful, but most often not in the way one might suspect. In only about 20 per cent of even severe embolism cases are x-ray findings initially positive. Usually these are indicative of pulmonary infarction, which is most likely to occur in connection with congestive failure or systemic hypotension. In other patients negative roentgen findings together with a positive scan will actually strengthen the diagnosis of an embolism, since they can help to ride out alternatives such as early pneumonia. In discussing the interpretation of lung scans, it is important to define precisely the information they yield. They do not detect emboli as such; what they do show is the distribution of pulmonary arterial blood flow in the lungs. Whatever abnormalities exist in that distribution must be interpreted in the light of their specific form and location, the changes they may or may not undergo with time, and the patient's other signs and symptoms. It is also worth noting that scanning cannot pick up lesions less than 2 to 3 cm in diameter. A small lesion of this sort may produce a peripheral infarct, with pleural pain and perhaps hemoptysis. Here the scan may be normal, so that diagnosis must be made on other grounds.

Radioactive xenon in the differential diagnosis of pulmonary embolism.

LUNG SCANNING after the intravenous injection of radioactive particles is a useful procedure in the diagnosis of pulmonary embolism (1). At times the diagnosis cannot be made with certainty on the basis of the scan alone, since other diseases of the lung often result in pulmonary avascularity (2). The occurrence of the characteristic pattern of concave defects at the lateral borders of the lungs without evidence of a corresponding parenchymal lesion on the chest radiograph makes the diagnosis of pulmonary embolism more certain (3), but this is not a constant finding. The differential diagnosis between pulmonary embolism and chronic obstructive pulmonary disease is particularly difficult. For example, in a study of 62 patients with pulmonary emphysema, 95 per cent of the patients had regions of decreased pulmonary arterial blood flow as revealed by lung scanning (4). Such decreases in pulmonary arterial blood flow have been encountered in other pulmonary diseases, but the frequent finding of a normal chest...