Document Type

Thesis

Date of Degree

Spring 2015

Degree Name

MS (Master of Science)

Degree In

Biomedical Engineering

First Advisor

Jessica C. Sieren

Abstract

Lung disease affects tens of millions of Americans, making it one of the most common medical conditions in the United States. Many of these lung diseases are classified as chronic airway disease. Because of this, it is important to be able to catch the development early so as to begin treatment as soon as possible to delay the progression and subsequently monitor that progression. One method of doing so is the use of quantitative computed tomography (CT). Study of the airway anatomy can be quantified using such measures as minor inner diameter (MinD), major inner diameter (MajD), wall thickness (WT), inner area (IA), and outer area (OA). Changes in these measures can then be tracked over time to determine how the airways are being affected by disease. The challenge with the desired longitudinal imaging is that prolonged radiation exposure can be dangerous to the patient. In order to make longitudinal imaging more feasible, it is important to determine what quantitative measures can reliably be made at different radiations doses so as to optimize radiation dose and quantitative assessment.

Working to make this determination, three different radiation doses were tested to evaluate their quantitative outputs. A high dose (14.98 mGy), medium dose (6.00), and low dose (0.74 mGy) were used to image six different porcine subjects. Images were collected at these doses both while the lungs were in-vivo and once the lungs had been fixed and excised ex-vivo. All of the scans were then processed using APOLLO (VIDA Diagnostics). From the complete airway trees, quantitative measures were collected from thirty-five airways. For the whole lung analysis, the medium and low dose in-vivo scans and the high dose ex-vivo scans were compared to the high dose in-vivo scans to compare assess MinD, MajD, WT, IA, and OA. Then, in order to determine how well the CT measures represent the actual anatomy, a total of thirteen cube samples containing airways were segmented from one of the lungs (based on volume analysis of the lung pre- and post-fixation and visual inspection). The cubes were imaged in CT, for the purpose of aiding in the establishment of original location and studying the effect of a narrowed imaging window, and microscopic CT (μCT). Since μCT can have a resolution on the scale of microns, the values measured in these images were considered ground-truth. The CT and μCT cubes were then registered to the high dose ex-vivo scan so as to compare the cube values with the ex-vivo values from each of the three doses. The same five measures were collected and analyzed.

The MinD, MajD, WT, IA, OA were statistically analyzed between the three in-vivo radiation dose scan sets, the high dose in- and ex-vivo scans, and the µCT cube, CT cube, and the three ex-vivo radiation dose sets. Preliminary results for the in-vivo scans show that the low dose and medium dose scans can reliably (< 5% error) be used to evaluate airways with minor diameters between 3.42 mm and 10.34 mm and major diameters between 3.98 mm and 12.06 mm. Comparison of the high-dose in-vivo and ex-vivo scans showed that the fixation and excision of the lungs did not significantly affect the ex-vivo lungs' ability to be used as a model for the in-vivo lungs. Finally, analysis of the various forms of the ex-vivo airways showed that there were few statistically significant differences between the datasets.

These results support the use of using the low (0.74 mGy) radiation dose when studying airway disease affecting airways with minor diameters between 3.42 mm and 10.34 mm and major diameters between 3.98 mm and 12.06 mm. They also show that the quantitative measures from CT are representative of the true measures of the airways.

Public Abstract

Chronic lung airway disease affects millions of Americans. Because it is a permanent condition, it needs to be monitored over time. This can be done using computed tomography (CT) to track changes in lung airway measurements, such as minor inner diameter (MinD), major inner diameter (MajD), wall thickness (WT), inner area (IA), and outer area (OA). Since the radiation from doing repeated CT imaging over time could be dangerous to the patient, it important to determine the lowest CT radiation dose that yields accurate lung airway measurements.

Working to make this determination, three different CT radiation doses were tested on six pig lungs to compare the resulting CT derived airway measurements. This comparison was done between all of the scans of the entire airway tree in the lungs and individual airways that were removed from the lungs and re-imaged in CT and high resolution microscopic CT (μCT). The MinD, MajD, WT, IA, and OA were found for each of the airways and compared to the values found in the scans with the highest radiation doses.

Results show that for certain airways, the radiation dose used does not change accuracy of the measurements. The results also showed that while removing the lungs from the body did cause some changes in lung structure, these changes are proportional and can be used as a surrogate for the in-vivo situation. Finally, assuming the values from μCT are the true values, the measures from the identical samples imaged in CT accurately reflect the true values.

Keywords

publicabstract, CT, FWHM, lung disease, radiation dose, registration

Pages

xii, 112

Bibliography

111-112

Copyright

Copyright 2015 Alexandra Lynae Judisch

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