Aerosol Ventilation Research Articles

Tracheobronchial Aspiration Observed During Ventilation Perfusion Lung Scanning

A 49-year-old man with a history of athetoid cerebral palsy, cervical spondylosis, and swallowing dysfunction underwent an anterior decompressive cordectomy and spinal fusion of C4 through C6. Approximately 1 month following surgery, the patient experienced acute shortness of breath and ventilation-perfusion lung imaging was performed to rule out pulmonary embolus. The Tc-99m DTPA aerosol ventilation scan demonstrated tracheobronchial aspiration and correlated well with the patient's subsequent development of aspiration pneumonia and the adult respiratory distress syndrome

Obliterative Bronchiolitis Following Lung Transplantation Diagnostic Utility of Aerosol Ventilation Lung Scanning and High Resolution CT

A serious and often fatal complication of heart-lung transplantation is the development of obliterative bronchiolitis (OB). Currently the screening for OB is based on symptoms, pulmonary function tests, and transbronchial biopsies. The chest radiographs are often normal with OB. Obliterative bronchiolitis produces luminal narrowing of both bronchioles and bronchi resulting in areas of peripheral consolidation and occasional bronchiectasis. We report a patient in whom a chest film was normal, an aerosol ventilation lung scan was abnormal while a perfusion study was mildly abnormal. Simultaneously, routine CT was essentially normal while high resolution CT with 1 mm thick sections was clearly abnormal and demonstrated areas of consolidation. These imaging modalities detected clear-cut abnormalities at a time when the patient was symptomatic but prior to the development of demonstrable abnormality on chest radiograph.

The effect of forced expiration on the uniformity of 99 Tcm-DTPA aerosol ventilation images in patients with excess sputum production

This study examines the use of the forced expiratory technique (FET) as a means of improving the uniformity of radionuclide aerosol ventilation images in patients with excess sputum production. Ventilation images are objectively classified by two computer derived indices to characterize the degree of radioaerosol clumping and overall uniformity. In a series of twenty five patients with a long-standing history of daily sputum production, images acquired before and after forced expiration and again after a second ventilation immediately following FET showed no significant change in either index. The results obtained do not provide evidence to support the routine use of FET in conjunction with radioaerosol scintigraphy. The method of image classification correlates well with a visual assessment of image uniformity and has general application.

Comparison of Biello, McNeil, and PIOPED criteria for the diagnosis of pulmonary emboli on lung scans.

The McNeil, Biello, and newly proposed PIOPED (from the National Institutes of Health-sponsored study, Prospective Investigation of Pulmonary Embolism Detection) interpretive methods for detection of pulmonary embolism on lung scans were compared in 96 patients who also underwent pulmonary angiography. Segmental findings on 99mTc perfusion and aerosol ventilation scans, chest radiographs, and pulmonary angiograms obtained within 48 hr of each other were encoded along with other information into a data base to facilitate analysis. The McNeil, Biello, and PIOPED criteria were applied to the encoded data. Although the PIOPED set of criteria yielded the most favorable likelihood ratio for predicting an angiogram showing pulmonary emboli and a favorable likelihood ratio for predicting an angiogram not showing pulmonary emboli, it had the highest number of indeterminate studies. The McNeil criteria demonstrated the least favorable likelihood for predicting pulmonary emboli on an angiogram. The Biello and McNeil criteria showed the most favorable likelihood ratio for predicting an angiogram not showing pulmonary emboli. Analysis of receiver-operating-characteristic (ROC) curves yielded the greatest area under the ROC curve for the Biello criteria, but there were no statistically significant differences among the three sets of criteria. This study suggests that the Biello scheme represents the best compromise of the sets of criteria studied.

Aerosol-perfusion lung scintigraphy: value of ventilation subtraction.

99Tcm-labelled aerosol ventilation and 99Tcm-macroaggregate albumin (99Tcm-MAA) perfusion can be performed in the diagnosis of pulmonary embolism (PE). If both examinations are performed on the same day, the superposition of activity from the first scintigraphic examination might mask defects in the second. In this study, 106 examinations were carried out for suspected PE. Aerosol ventilation was performed first with 20 to 30 mCi 99Tcm-labelled rhenium sulphur (four views, 200,000 counts). Immediately afterwards, with the patient remaining in the same position, 5 to 7 mCi of 99Tcm-MAA were injected (four views, 400,000 counts). After normalization, aerosol activity was subtracted from perfusion images and unprocessed perfusion (UP) and ventilation subtraction perfusion (SP) images were compared. Interobserver diagnostic reproducibility between three readers was calculated both for UP and SP images. Intraobserver reproducibility between UP and SP images was calculated for each reader. Interobserver reproducibility was comparable for SP and UP images. Intraobserver reproducibility was good. Thus, whether ventilation was subtracted or not from perfusion images, there was no appreciable effect on perfusion defect detection. However, some perfusion abnormalities showed up more clearly on SP images. Perfusion can be performed immediately after aerosol ventilation; the images thus obtained are reliable for interpretation, and subtraction of ventilation is not necessary.

Aerosol lung scintigraphy in the detection of bronchiectasis

Twenty patients were studied to assess the value of aerosol ventilation scintigraphy, using 99Tc m diethylene triamine penta-acetic acid (DTPA) as a screening test for bronchiectasis. All patients had previously undergone bronchography for suspected bronchiectasis. Nine had cylindrical bronchiectasis and 11 had no demonstrable abnormality. Only two of the 20 patients had features suggestive of bronchiectasis on their chest radiographs. Segmental defects in ventilation were demonstrated by scintigraphy in five of the nine patients with bronchiectasis (56%). Regional ventilation appeared normal in 26 of the 27 lungs which were bronchographically normal (96%). Whilst the sensitivity of aerosol ventilation scintigraphy in detecting bronchiectasis is low (56%), it compares favourably with that of the chest radiograph (22%) in this group of patients with mild disease and non-specific symptoms. Thus, in some, it may obviate the need for bronchography.

Tracers for aerosol ventilation scintigraphy: Tc-99m versus In-113m.

113mIn has been proposed as a suitable tracer for aerosol ventilation scintigraphy in combination with 99mTc pulmonary perfusion scintigraphy. The high energy (393 keV) of 113mIn allows it to be detected in the presence of 99mTc, but degrades the spatial resolution which can be achieved. We have compared the resolution obtained with 99mTc and 113mIn in phantom experiments and in aerosol ventilation scans in 14 patients with airways disease. The resolution at the distances from the collimator encountered in lung scintigraphy was 10-20 mm for 99mTc and 15-40 mm for 113mIn. Aerosol ventilation images were abnormal in all patients. The 99mTc images showed peripheral defects and frequently central hot spots reflecting increased local aerosol deposition. In the 113mIn images, the lower resolution had a smoothing effect, the central hot spots were less striking, and the distribution of activity appeared more uniform, some detail was lost in the periphery. It is suggested that 113mIn is useful for ventilation scintigraphy in the diagnosis of pulmonary embolism, but that 99mTc is the tracer of choice if aerosol ventilation scintigraphy is used to study airways disease.

Pulmonary ventilation and perfusion studies in infants and children.

Ventilation and perfusion imaging techniques may be applied successfully to the diagnosis of many pulmonary disorders in children. These studies may be performed with relative ease and safety in all patients, even if they are unable to cooperate. The choice of radiopharmaceuticals applicable to children includes inert gases such as xenon 133 and krypton 81m as well as technetium 99m particles for perfusion and aerosol ventilation imaging. Quantitation of regional lung function is readily performed with available techniques. The indications for ventilation and perfusion lung imaging in children differ significantly from those in the adult.

Radioaerosol ventilation imaging in ventilator-dependent patients. Technical considerations.

The differentiation of pulmonary embolism (PE) from regional ventilatory abnormalities accompanied by reduced perfusion requires contemporary perfusion and ventilation studies. Distinguishing these conditions in ventilator-dependent patients is aided by administering a Tc-99m aerosol to characterize regional ventilation, and by performing a conventional Tc-99m MAA perfusion study. The technique uses a simple "in-house" constructed apparatus. Simple photographic techniques suffice, but computer subtraction of perfusion from the combined perfusion-ventilation image renders interpretation easier if aerosol administration follows perfusion imaging. Multiple defects can be examined in a single study. Excluding normal or near-normal perfusion studies, PE was thought to be present in eight of 16 patients after perfusion imaging alone, but in only one of eight after added aerosol imaging. Angiography confirmed the diagnosis in that patient. Of the eight patients who had abnormal perfusion but were thought unlikely to have PE from the perfusion study alone, two had normal ventilation, and subsequently were shown to have PE by angiography. Because angiography was only performed on patients who were thought to have a high probability of PE on sequential perfusion-ventilation imaging, the true incidence of PE may have been higher. Aerosol ventilation imaging is a useful adjunct to perfusion imaging in patients on ventilators. It requires an efficient delivery system, particularly if aerosol administration follows perfusion imaging, as it does in this study. The major disadvantage of aerosol imaging compared to a gas in intubated patients is the significant bronchial deposition due to retained mucus secretions.(ABSTRACT TRUNCATED AT 250 WORDS)

A combined procedure for 99mTc aerosol ventilation and perfusion imaging.

For several years, radioaerosols have been successfully used to provide detailed images of regional ventilation to aid in the differential diagnosis of pulmonary embolism. It has been widely advocated that the ventilation images should follow the perfusion scan and that the amount of aerosol deposited in the patient's lungs should be three times greater than the perfusion dose. We employed an alternative approach which avoided the deposition of an unpredictable amount of aerosol in individual patients. The aerosol study was performed first, and the activity of the microspheres used for the perfusion images was then tailored to the actual amount of aerosol which the patient had retained. This allowed a microsphere/aerosol activity ratio of 10:1 to be readily achieved, thus successfully masking the ventilation pattern by the perfusion activity. The faster biological clearance of 99mTc-DTPA aerosol from the lung fields, as compared to 99mTc-sulphur-colloid aerosol, allowed higher initial activities to be deposited in the lungs, thus enabling a high-resolution collimator to be used. When the perfusion study was delayed by 1 h (one effective half-life for the 99mTc-DTPA aerosol), it was not necessary to increase the perfusion activity required to mask the ventilation image.

The use of single photon emission computed tomography in lung imaging with aerosols

The use of technetium-99m labelled diethylenetriaminopentaacetic acid (99Tcm-DTPA) aerosol and single photon emission computed tomography (SPECT) to obtain sectional ventilation images of the lung is demonstrated in a limited series of patients. SPECT perfusion and planar ventilation and perfusion are also obtained and the SPECT studies compared with the planar views to assess the efficacy of SPECT aerosol ventilation images when used in conjunction with SPECT perfusion studies. The problems encountered in SPECT aerosol lung imaging, particularly the image noise associated with the limited number of detected counts, are described. On the basis of the results it is concluded that the technique is worth further assessment.

99mTc particle perfusion/99mTc aerosol ventilation imaging using a subtraction technique in suspected pulmonary embolism

It is generally acknowledged that ventilation-perfusion mismatch is diagnostic of pulmonary embolism. Lung ventilation imaging with radioactive gases is a good method for the detection of pulmonary embolism, but it is not in widespread use because of the limited availability of 81mKr gas and the poor physical properties of 133Xe. Aerosols have been proposed, instead of gases for use in lung ventilation imaging. As perfusion and ventilation distributions may change very rapidly, the two imaging procedures should be done in rapid succession. The cheapest way to perform the combined perfusion-ventilation (Q/V) imaging is to use 99mTc-labelled macroaggregates and aerosols. In our method the perfusion imaging was done first, immediately followed by the ventilation imaging with 99mTc-labelled aerosols. A computer program was used to subtract the contribution of the perfusion from the combined Q/V image so that the pure ventilation image alone was obtained. The method was tested in 41 patients with suspected pulmonary embolism.

Enzyme studies of the testis in myotonic dystrophy.

Aerosol ventilation studies are assumed to have negligible room contamination when used correctly. This study was undertaken to determine whether a measurable amount of surface contamination is associated with routine technetium-99m DTPA aerosol ventilation studies. Three potential sources of contamination were evaluated: aerosol leakage related to the patients, aerosol leakage at the exhaust of the delivery system, and aerosol leakage related to operator error. A predefined protocol was used for setting up the apparatus and performing wipe tests. A GM survey was performed, and in all cases, no levels above background were detected. The results of the wipe tests, however, showed that 57% of patient studies had contamination underneath the exhaust of the device; 35% of the studies had floor contamination; and 39% of the studies contaminated the area adjacent to the patient.