Variability in the x-ray tube current used in computed tomography may affect quantitative features extracted from the images. To investigate these effects, we scanned the Credence Cartridge Radiomics phantom 12 times, varying the tube current from 25 to 300 mA∙s while keeping the other acquisition parameters constant. For each of the scans, we extracted 48 radiomic features from the categories of intensity histogram (n = 10), gray-level run length matrix (n = 11), gray-level co-occurrence matrix (n = 22), and neighborhood gray tone difference matrix (n = 5). To gauge the size of the tube current effects, we scaled the features by the coefficient of variation of the corresponding features extracted from images of non-small cell lung cancer tumors. Variations in the tube current had more effect on features extracted from homogeneous materials (acrylic, sycamore wood) than from materials with more tissue-like textures (cork, rubber particles). Thirty-eight of the 48 features extracted from acrylic were affected by current reductions compared with only 2 of the 48 features extracted from rubber particles. These results indicate that variable x-ray tube current is unlikely to have a large effect on radiomic features extracted from computed tomography images of textured objects such as tumors.

The National Aeronautics and Space Administration (NASA) performs organ dosimetry and risk assessment for astronauts using model-normalized measurements of the radiation fields encountered in space. To determine the radiation fields in an organ or tissue of interest, particle transport calculations are performed using self-shielding distributions generated with the computer program CAMERA to represent the human body. CAMERA mathematically traces linear rays (or path lengths) through the computerized anatomical man (CAM) phantom, a computational stylized model developed in the early 1970s with organ and body profiles modeled using solid shapes and scaled to represent the body morphometry of the 1950 50th percentile (PCTL) Air Force male. With the increasing use of voxel phantoms in medical and health physics, a conversion from a mathematical-based to a voxel-based ray-tracing algorithm is warranted. In this study, the voxel-based ray tracer (VoBRaT) is introduced to ray trace voxel phantoms using a modified version of the algorithm first proposed by Siddon (1985 Med. Phys. 12 252-5). After validation, VoBRAT is used to evaluate variations in body self-shielding distributions for NASA phantoms and six University of Florida (UF) hybrid phantoms, scaled to represent the 5th, 50th, and 95th PCTL male and female astronaut body morphometries, which have changed considerably since the inception of CAM. These body self-shielding distributions are used to generate organ dose equivalents and effective doses for five commonly evaluated space radiation environments. It is found that dosimetric differences among the phantoms are greatest for soft radiation spectra and light vehicular shielding.

Traditional film/screen mammograms are obtained using Molybdenum or Rhodium target x-ray tubes. The energy spectrum from these sources matches the limited latitude of film/screen systems. For digital imaging systems, the latitude is linear over a wide range of exposures and arbitrary H&D curves can be obtained with image processing. This allows the recorded contrast to noise ratio (CNR) to be optimized by considering a wide range of radiographic techniques. For this work, we modeled the radiographic process for a digital (amorphous selenium) mammography system. The optimal CNR relative to dose was determined for several target/filter combinations, for a wide range of kVp values, and for varying breast thickness. The target/filter combinations included: Mo/Mo, Mo/Rh, Rh/Rh, W/Al, W/Mo, W/Ag, and W/Sn. As breast thickness increased, the use of a tungsten target with a tin filter resulted in a 34% improvement in CNR for the same dose to the breast when compared to the use of a Molybdenum target with a Molybdenum filter. Notably, the W/Sn target/filter combination resulted in a significantly lower mA-s for the same breast dose (2/3 to 1/5 lower for a breast thickness from 4 to 8cm). In mammography applications, use of a Tungsten tube rather than the traditional Molybdenum tube should lead to significant reductions in exposure time and tube heat while maintaining similar image quality and dose.