The Lung Aerosol Study, using DTPA, demonstrates the distribution of ventilation within the lungs in multiple projections. Tc-99-DTPA is effective, easy to use and gives a lower radiation dose to the mucosa of the lungs than other ventilation agents (Xenon).
The aerosol is breathed for a period of approximately 5 minutes to insure sufficient lung deposition is acquired. The length of the time the aerosol stays in the airspace depends on the permeability of the pulmonary epithelium. It then enters the vascular space where it is filtered by the renal system. The aerosol does not stay in the lungs as long in smokers because of the increased epithelium permeability seen in these patients. Oxygen should not be used during imaging unless it is necessary because of the patient’s condition.
The quality of the study can be degraded if some of the aerosol deposits on the bronchi and does not reach the alveoli.
- Diagnosis of pulmonary embolism.
- Evaluation of ventilation.
Prior to the acquisition of a Lung Perfusion Scan, the patient will be instructed on the breathing protocol necessary for the ventilation. The patient will have a mouthpiece placed in their mouth making sure to keep a tight seal and a clip placed on their nose in order to prevent leakage of the radiopharmaceutical. The patient will be allowed to “practice breathing” to become accustomed to the mouthpiece and closed breathing system prior to the start of the radiotracer ventilation.
There is a constant supply of oxygen and the patient should not have difficulty breathing, however some patients become apprehensive and feel "trapped" by the system. If this should happen and the patient feels they cannot tolerate the study, the procedure can be interrupted at any point by hand signaling the technologist. It is very important that the patient does NOT try to remove the mask.
When adequate lung filling has occurred, approximately 4-5 minutes, the technologist will remove the mask and breathing system and a series of images will be acquired.
- 30-45 Minutes
- 1 ½ hours if in conjunction with “Lung Perfusion” (normal protocol majority of the time)
- A chest x-ray must be taken within 24 hours of the lung scan for comparison.
- Rehearse the breathing procedure to assure optimal patient cooperation; instruct the patient to breathe normal through their mouth.
- Contraindication: Patient with severe pulmonary hypertension, right to left shunt, pneumonectomy, and poor respiratory function.