subject: Radioisotopic Investigation in Respiratory disorders [print this page] Isotopic techniques have made it possible to obtain visual images as well as precise quantitative information about the regional distribution of ventilation and perfusion. These methods are generally non-invasive. New machines incorporating computer facilities are available.
Perfusion imaging - This is employed to study the state of the pulmonary vasculature. The main clinical uses are in the investigation of pulmonary embolism, atresia or hypoplasia of pulmonary artery, presence of right-to-left intracardiac shunts and pulmonary venous hypertension.
Ventilation imaging - This can be made by using Xenon-133.
Aerosol inhalation studies - Aerosolized radioactive particles can be administered for inhalation. Commonly technetium-99m-labelled phytate, lactose, albumin or sulphur colloid are used. The radioactive particles are distributed in the lungs depending upon the patency of the air passages. The concentration of radioactivity is diminished in areas of poor ventilation. Another use of labeled aerosol particles is to study the efficiency of mucociliary function. When mucociliary function is impaired, the clearance of radioactivity from the lung delayed. Using perfusion and ventilation imaging studies, valuable information can be obtained. In pulmonary embolism ventilation is normal, but perfusion is diminished, whereas both ventilation and perfusion are diminished in parenchymal, pleural or obstructive airway disease.
Isotopic localization of pulmonary tumors Isotopes such as Gallium citrate-67 and Cobalt-57-labelled bleomycin which are concentrated by tumors are used to study neoplastic lesions.
Endoscopic studies several endoscopic procedures are available to study respiratory disorders. These include laryngoscopy. Bronchoscopy, mediastinoscopy, and thoracoscopy. Laryngoscopy visualizes the upper respiratory tract up to the larynx and the trachea. Availability of flexible fibreoptic bronchoscopes with facilities for aspiration and biopsy procedures has increased their importance in diagnosis and therapy in recent years. Flexible bronchoscopes can reach up to the second or third division of the bronchi whereas rigid bronchoscopes reach only up to the first division. Bronchoscopy is used to visualize the trachea, bronchi and their branches, aspirate secretions for investigations, obtain biopsy material, and remove obstructions. Clinical indications for bronchoscopy include bronchial obstruction, pulmonary neoplasms, unresolved pneumonia, lung abscess and recurrent hemoptysis. Broncho- alveolar lavage can be done during bronchoscopy and the specimen can be examined further. Mediastinoscopes are used to inspect the superior mediastinum and perform biopsy procedures under direct vision. Thoracoscopy is inspection of the thoracic contents with a thoracoscope after producing a partial pneumothorax.
Investigations using aspirated material
In the diagnosis of pleural diseases, the examination of pleural fluid is most important. So also examination of bronchial aspirates and material from other sites gives valuable diagnostic clues. Macroscopic appearance, microscopy, cytology, microbiological studies, and biochemical investigations are helpful in diagnosis.
Biopsy studies
Lymph node biopsy: Biopsy of the appropriate scalene lymph node or palpable axillary or cervical lymph nodes helps in establishing the diagnosis of granulomatous and neoplastic lesions.
Lung biopsy: Lung tissue can be obtained by percutanous biopsy or by open biopsy under vision. Percutaneous biopsy using a Vim-Silverman needle or a trephine is performed to disgnosie diffuse lesions and peripherally situated localized lesions. When the lesions are small and not accessible superficially, thoracotomy and open biopsy are preferable.
Pleural biopsy: This is resorted to when pleural lesions have to be diagnosed. Cope's needle or Abrams pleural biopsy punch is used for obtaining material from the parietal pleura. Vim-silverman needle can be used in the absence of the specialized needles.
Computerized tomography
Intrathoracic disease can be delineated by computerized tomography (CT). This can be distinguished between cysts, tumors and vascular abnormalities.
Broncho-alveolar lavage
This procedure is adopted to obtain material from the terminal protions of the respiratory tree and alveoli. The speciment is subjected to microscopy and cytological examination. The distribution of cells, especially the immunocytes gives valuable clue to diagnosis of diseases of the lower respiratory tract, such as firbosing alveolitis, sarcodosis etc.
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