Preliminary Study to Detect Pulmonary Nodules by Tomosynthesis Using a Small Number of Projections

Abstract

Lung cancer is one of the most important diseases to overcome, and chest radiography and low-dose computed tomography (CT) have been used for lung cancer screening. In chest radiographs, nodules overlying the ribs and mediastinum are occasionally difficult to detect. Therefore, CT is used as the gold standard modality to diagnose lung cancer, despite the high radiation exposure it entails. Recently, tomosynthesis has been used to detect pulmonary nodules, but mechanical scanning and a long data acquisition time (approximately 10 seconds) are required to obtain the image. Under this circumstance, tomosynthesis using a small number of projections has been anticipated to allow omission of the mechanical system and shortening of the exposure time. A chest phantom with artificial pulmonary nodules of various sizes was imaged in rotating 360-degree projections. Tomosynthesis images were reconstructed using back projection (BP) from ±32-degrees projection data, and the projection numbers were set at 4, 6, 8, 16, 32 and 64. The images were evaluated visually and quantitatively by measuring the contrast noise ratio (CNR) and artifact spread function (ASF). Tomosynthesis images reconstructed from 4 projection images allowed visualization of an artificial nodule 10mm in diameter without overlapping the ribs or the mediastinum. The CNR of a 4-projection image normalized to that of a 64-projection image was approximately 0.34, and the ASF obtained indicated that fewer number of projections was associated with greater z-axis resolution. Thus, 4-projection tomosynthesis allows visualization of pulmonary nodules 10mm or larger in diameter, and image quality appears to be useful.