Development of Prospective Gating in Stationary Digital Chest Tomosynthesis Using a Carbon Nanotube X-ray Source Array

Purpose: To quantify the benefit of prospectively gated stationary digital chest tomosynthesis (Gs-DCT) using a carbon nanotube (CNT) x-ray source array in a free breathing porcine study. Methods: The Gs-DCT x-ray system consists of a linear x-ray array tube (80kVp, 0.125mAs per projection for 29 projections over a 12 angular span) and a flat panel detector (5 fps). Imaging was performed on an anesthetized, free-breathing 13.5kg pig. A respiratory trace was acquired through a transducer belt around the thorax. Each gated projection image was acquired at the temporal coincidence of the detector integration time and the peak inhalation of the pig. The projection images were reconstructed using iterative reconstruction with a 2mm slice thickness using iterative reconstruction. Image blur was assessed as the reproduction of the diaphragm in the reconstructed images. Respiratory phase timing quality was assessed through cross-correlation analysis. Results: Animal respiration rate was 24.3+/-3.5bpm. The scan time for the gated scan was 86.9 +/- 2.9s compared to the un-gated scanning time 6.3 .6s. An entrance dose of 0.4mSv was used. The blur in the reproduction of the diaphragm in the reconstructed images for gated study was 1.8 0.5mm where in the un-gated case the diaphragm was 2.60.6 mm. The average cross correlation coefficient between of the respiratory trace at the time of the x-ray pulse was .91.02 for the gated scan and .11+/- .01 for the un-gated scan. Conclusions: Prospective gated imaging significantly reduced the motion blur, substantially improving the image quality of the tomosynthesis images. The CNT based x-ray sources enable precise x-ray pulse generation on demand. If enabled clinically, the Gs-DCT system could potentially obtain 3D image stacks in patients that are unable to hold their breaths, such as the pediatric or intubated patient population. Prospectively gated human studies are planned.Doctor of Philosoph

Image reconstruction and processing for stationary digital tomosynthesis systems

Digital tomosynthesis (DTS) is an emerging x-ray imaging technique for disease and cancer screening. DTS takes a small number of x-ray projections to generate pseudo-3D images, it has a lower radiation and a lower cost compared to the Computed Tomography (CT) and an improved diagnostic accuracy compared to the 2D radiography. Our research group has developed a carbon nanotube (CNT) based x-ray source. This technology enables packing multiple x-ray sources into one single x-ray source array. Based on this technology, our group built several stationary digital tomosynthesis (s-DTS) systems, which have a faster scanning time and no source motion blur. One critical step in both tomosynthesis and CT is image reconstruction, which generates a 3D image from the 2D measurement. For tomosynthesis, the conventional reconstruction method runs fast but fails in image quality. A better iterative method exists, however, it is too time-consuming to be used in clinics. The goal of this work is to develop fast iterative image reconstruction algorithm and other image processing techniques for the stationary digital tomosynthesis system, improving the image quality affected by the hardware limitation. Fast iterative reconstruction algorithm, named adapted fan volume reconstruction (AFVR), was developed for the s-DTS. AFVR is shown to be an order of magnitude faster than the current iterative reconstruction algorithms and produces better images over the classical filtered back projection (FBP) method. AFVR was implemented for the stationary digital breast tomosynthesis system (s-DBT), the stationary digital chest tomosynthesis system (s-DCT) and the stationary intraoral dental tomosynthesis system (s-IOT). Next, scatter correction technique for stationary digital tomosynthesis was investigated. A new algorithm for estimating scatter profile was developed, which has been shown to improve the image quality substantially. Finally, the quantitative imaging was investigated, where the s-DCT system was used to assess the coronary artery calcium score.Doctor of Philosoph