Modeling the respiratory motion of solitary pulmonary nodules for investigating SPECT tumor imaging

We have modeled the respiratory motion of solitary pulmonary nodules (SPN) based on the change of location of anatomic structures in the lungs determined from breath-held CT images of volunteers acquired at two different stages of respiration. The resulting 3D data was visualized in summed coronal, sagittal, and transaxial projections by drawing an arrow showing the direction and magnitude of motion during inspiration. The findings reveal that there is a three-dimensional component of the motion of structures within the lung and that the magnitude and direction vary based on the specific anatomic region of the lung. This information on respiratory motion within the lungs was combined with the NCAT phantom to allow the creation of source and attenuation maps for investigating the impact of respiratory motion in single photon emission computed tomographic (SPECT) imaging for SPN with Tc-99m labeled NeoTect. With the source and attenuation distribution thus defined, the SIMIND Monte Carlo program is used to produce SPECT projection images for the normal background Tc-99m NeoTect distribution and each of the tumors separately. These projections will be combined according to the desired tumor contrast and will be employed to investigate the impact of respiratory motion of SPN detection using human-observer localization receiver operating characteristics (LROC) studies.