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.
| Identifer | oai:union.ndltd.org:uiowa.edu/oai:ir.uiowa.edu:etd-5704 |
| Date | 01 May 2015 |
| Creators | Judisch, Alexandra Lynae |
| Contributors | Sieren, Jessica C. |
| Publisher | University of Iowa |
| Source Sets | University of Iowa |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | Copyright 2015 Alexandra Lynae Judisch |
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