A 58 year old female presented to the emergency room with sudden onset of dyspnoea and chest pain. Her past history included asthma as a child and idiopathic thrombocytopenia. She smoked 20 cigarettes a day and developed mild chronic airways limitation. Physical signs demonstrated decreased air entry in the right lung and tracheal deviation to the left. Vital signs were stable. CXR demonstrated 100% right sided pneumothorax. An intercostal drain was inserted which resulted in successful resolution of the pneumothorax. Physical examination then demonstrated crepitations in both lung bases and CXR showed ground glass opacities in the lower zones. A right pleurodesis and stapling of a bulla to the apex was performed. Lung biopsy at the time of surgery confirmed the presence of fibrosing alveolitis. Post-operative FEV1 was decreased at 1.8 litres (predicted 2.6) and DLCO decreased at 11 mls/min/mm Hg ( 40% predicted ). Pertechnegas lung clearance study demonstrated increased alveolar-capillary membrane permeability. The patient had not smoked during hospitalisation which otherwise given to a false positive study.The patient responded well to prednisone and cyclophosphamide and discharged.

IMAGE DESCRIPTION

Regions of interest are drawn around both lungs with background subtraction and time-activity curves obtained. Single exponential fit was applied and half-times calculated. Pertechnegas lung clearance was significantly increased in both lungs. The right lung half- time measured 5.45 mins and left 5.6 mins (normal >10.1mins). The increased clearances reflected damage to the alveolar-capillary membrane secondary to fibrosing alveolitis.

 

DISCUSSION

Alterations of alveolar-capillary membrane permeability is shown in a variety of pulmonary disorders such as fibrosing alveolitis, pneumocystis carinii pneumonia and sarcoidosis. Radiopharmaceuticals such as 99mTc-DTPA aerosol have been used to assess pulmonary clearance in patients with interstitial lung disease. Technegas is a relatively new ventilation agent used in the diagnosis of pulmonary embolism. It is an ultra-fine dispersion of 99mTc-labelled carbon particles prepared by the combustion of 99mTc-pertechnetate in a graphite crucible in 100% argon atmosphere. Superior ventilation images are obtained with minimal central deposition and improved peripheral penetration compared to other agents such as 99mTc-DTPA aerosol, 133 Xenon and 81m Kr. Only a few breaths are required to perform the study compared to other agents which is a distinct advantage in severely dyspnoeic patients.The particles of Technegas are trapped in the alveoli and clearance is secondary to radioactive decay. With the addition of 3% oxygen in the argon atmosphere the clearance from the lungs is cleared into the vascular compartment with the subsequent biodistribution resembling pertechnetate. Clearance of pertechnetate is more rapid compared to 99m Tc-DTPA by a factor of 3.3. Excellent count statistics are possibe with only a few breaths and allows easy quantitation by modern computers.

REFERENCES

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