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My Canadian Pharmacy: Use of CT Morphometry To Detect Changes in Lung Weight and Gas Volume

Chronic lung diseasesDuring the last decade, investigators have begun to quantify the amount of disease in patients with chronic lung diseases, including emphysema and interstitial lung disease. This quantification is based on the fact that the changes in lung structure caused by progression of the disease produce changes in lung density, which is linearly related to the attenuation of x-rays. This has been best shown for emphysematous destruction of the lung where the decrease in tissue and increase in gas volume lowers lung density, but it also occurs in end-stage interstitial lung disease, where the decrease in the volume of gas in the tissue raises lung density. Because of the spatial information contained with the CT image, CT scans can be used to measure the total volume of the lung. The combination of lung volume and density makes it possible to estimate other volumetric parameters such as lung weight and gas volume. We refer to the collection of techniques used to quantify lung structure using CT as CT morphometry (CTM).

The present study was designed to test the hypothesis that CTM can be used to track the changes in lung density in diffuse lung disease. Pulmonary alveolar proteinosis (PAP) was used as a model of diffuse lung disease because there is significant improvement, and in some instances almost complete resolution, of the infiltrate following an intervention with the unique opportunity that the dry weight of the material removed from the lung can be measured and compared to the change in CT measured lung weight from before to after lavage. People undergo so many medical screenings to be sure they are safe and sound but if you come across with problems you are welcome on My Canadian Pharmacy.

Patient Selection

Five patients with a diagnosis of PAP were studied before and after lung lavage as an intervention for their disease. The decision to perform lavage was based on clinical, physiologic, and radiographic parameters. All patients gave their informed consent to participate in the study, and the protocol was approved by the University of Pittsburgh Institutional Review Board.

Pulmonary Function

Pulmonary function tests (PFTs) were used to measure FVC, FEV1, total lung capacity, and diffusing capacity of the lung for carbon monoxide (Dlco). The PFT data used were obtained within 7 days of the CT scans. When patients underwent lavage, PFTs were performed before and after the lavage procedure. The tests were performed using American Thoracic Society standards. Results are expressed as percentage of predicted using accepted standard formulas.

Pulmonary FunctionQuantitative Lung Lavage

Five patients underwent sequential single-lung lavage for a total of 14 lavages. The time interval between lavages was usually 1 week. Lung lavage was performed by intubating the patient with a double-lumen endotracheal tube and isolating each lung. The targeted lung was then lavaged with normal saline solution and warmed to body temperature (37°), using aliquots ranging from 500 to 1,500 mL as previously described. The effluent from the lavage was collected in 1.5-L bottles labeled sequentially for analysis. Lavage volumes ranged from 45 to 75 L.

The weight of the material removed by lavage was measured by centrifuging a 250-mL aliquot of the effluent and weighing the “pellet.” The pellet is composed primarily of surfactant and the phospholipids unique to PAP. This quantitative lung lavage method has been previously described and is based on methods developed in surfactant research.

CTM Analysis

All patients undergoing lavage underwent a multislice, helical CT scan (without the use of contrast media) before and after each lavage procedure in the supine position (GE Lightspeed or Lightspeed Plus CT; GE Medical Systems; Milwaukee WI). CT scans were performed using standard clinical settings at our institution (5-mm slice thickness, 155 mA, 140 kilovolt peak) and reconstructed using a low-spatial-frequency reconstruction algorithm. The scanners were calibrated daily using standard water and air phantoms. All postlavage CTs were performed within 1 week of lavage. Of the 14 single lung lavages performed, only 10 had CT scans before and after lavage available for analysis, for the following reasons: patient 1 only underwent a CT scan following lavage of both lungs; a prelavage CT scan for right lung lavage was performed at another institution in patient 2, and data were not available for analysis; following the first lavage of the left lung, pneumonia developed in patient 4, and as a result the follow-up CT for this lung was not used; and patient 5 failed to attend the follow-up for the CT scan within a week after his second lavage of the right lung. My Canadian Pharmacy is waht you need to solve all your health problems.

CT scanThe CT scan analysis was performed using custom software (Emphylx; Department of Radiology/iCAPTURE Laboratory, University of British Columbia; Vancouver, BC, Canada) and a modification of a technique previous described. Briefly, the lung parenchyma was segmented from the chest and the large central blood vessels using CT values of — 1,000 to — 500 Hounsfield units. The total lung volume of the whole lung (tissue and airspace) was calculated by summing the voxel dimensions in each slice. The density of the lung (grams per milliliter) was estimated by adding 1,000 to the Hounsfield unit of each voxel, and dividing by 1,000. Lung weight was calculated by multiplying the lung density of each voxel by the volume of the voxel. The total airspace volume was calculated by subtracting the tissue volume from the total lung volume. The lung inflation (volume of gas per gram of tissue) for each voxel was calculated according to the following equation:

milliliters of gas/grams of tissue = specific volume (tissue and gas) — specific volume (tissue)

where specific volume is the inverse of density, the density of the lung (tissue and gas) is the measured value from the CT, and the density of tissue is assumed to be 1.065 g/mL. The frequency distribution of lung inflation was broken into discrete bins using inflation cutoffs: 0 to 2, 2 to 4, 4 to 6, 6 to 8, 8 to 10.2, and > 10.2 mL/g. These values were obtained for the total lung (both sides) as well as left and right individually.

Data Analysis

Descriptive statistics (mean, SD, and range) were determined for lung volume, weight, and the lung inflation categories (milliliters per gram), as well as the mean of the CTM measured frequency distribution of lung inflation. Comparison of the CTM measurements for lung weight to those measured using quantitative lung lavage and the CTM measurement of airspace volume to plethysmography were performed using a clustered analysis (STATA 7.0; StataCorp; College Station, TX). Using this technique, observations between clusters (individual patients) are assumed to be independent, but the observations within a cluster are not assumed to be independent, thus are given less weight in the regression. PFTs and CTM were compared only if performed within 1 week of each other and without an interceding lung lavage. Paired Student t test was performed on the CTM and PFT data before and after lung lavage; p < 0.05 was considered significant. These statistical analyses were performed using statistical software (release 13.31; Minitab; State College, PA).