Jiang Hsieh PhD, Presenter: Employee, General Electric Company

Robert Senzig, Abstract Co-Author: Employee, General Electric Company

Steven J. Woloschek, Abstract Co-Author: Employee, General Electric Company

Baojun Li PhD, Abstract Co-Author: Employee, General Electric Company

Darin R. Okerlund MS, Abstract Co-Author: Employee, General Electric Company

Naveen Chandra PhD, Abstract Co-Author: Employee, General Electric Company

Dual-energy (DE) CT has received much attention in recent years. Despite of its successes, radiation dose is significantly higher as compared to DE x-ray radiography. We investigate a low-dose spectral projection imaging (SPI) approach as a screening tool prior to the full CT examination.

In SPI, the x-ray tube remains stationary while the patient table travels along the patient long axis, similar to the scout acquisition. By switching the x-ray tube voltage rapidly (>2kHz) with synchronized sampling at a table speed of 100mm/s, projection samples are obtained for both 80kVp and 140kVp. Additional focal spot deflection in x provides overlapped sampling in both x and z to provide improved spatial resolution. The rapid sampling between kVps in SPI (0.5ms) is 0.4% of that of x-ray DE (125ms) and allows the elimination of potential mis-registration artifacts, especially in the chest. The projection samples undergo calibration steps to remove beam-hardening and other non-ideal conditions, and are processed by projection material decomposition procedures to create material-basis projection image pairs. Although the use of a scout as localizer is well recognized, SPI can be used not only to provide diagnostic information but also provide guidance to the DE CT acquisition and analysis.

Since the projection measurement in CT is accurately calibrated, the resulting projections at 80kVp and 140kVp representing more accurate line integrals than the conventional x-ray radiography. This results in improved removal of soft-tissue in “bone” images as compared to DE radiography. In addition, projection space material decomposition enables the production of other material-pairs. Phantom experiments have demonstrated the excellent capability of separating bone vs. soft-tissue or calcium vs. soft-tissue. Clinical experiments have shown its potential to identify calcified coronary artery and subtle lung diseases. The computation of a monochromatic projection is also possible to dynamically enhance the low-contrast structures.

We present a new SPI approach that may be used as a pre-screening tool for dual-energy CT. Phantom and clinical experiments show that SPI is capable of accurately separating different materials in the body to provide excellent information at very low dose.

SPI provides a low-dose diagnostic screening and material characterization tool for DE CT exams.

Hsieh, J, Senzig, R, Woloschek, S, Li, B, Okerlund, D, Chandra, N, Low Dose Spectral Projection Imaging.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8004823.html