A Tomographic Pregnant Woman Model (Segmented from CT Images)

Assessment of radiation dose and possible risk to a pregnant woman and her fetus is an important task in radiation protection. Although stylized models for male and female patients of different ages have been developed, to date no tomographic models for pregnant women have been developed.

This project represents an effort to construct a partial-body model of a pregnant woman from a set of CT images. The patient was 30-weeks pregnant, and the CT scan covered the portion of the body between the lower breast and the upper thigh in 70 slices, each 7 mm thick. The image resolution was 512 by 512 pixels in a 48 cm by 48 cm field. The images were carefully segmented to identify 34 organs and tissues.

It has been found that the organ masses are different from the Reference Woman. The characteristics of the resulting model are discussed and compared with one existing stylized mathematical model for pregnant women. Based on this tomographic model, a Monte Carlo code, EGS4-VLSI, was used to derive Specific Absorbed Fractions. Monoenergetic and isotropic photon and electron emitters distributed in different source organs were assumed and the energies ranged from 10 keV to 4 MeV for photons and from 100 keV to 4 MeV for electrons.

The results for high energy (> 50 keV) photons showed general agreement with previous studies, however, the results for lower energy (< 50 keV) photons showed differences of up to several hundred percent for some source and target organs. For electron results, several tens of percent differences were found. Those differences can be explained by mass differences and the relative geometry differences between source and target organs.

The stylized models for pregnant women are satisfactory for a very large size patient for most of the photon energies (between 50 keV and 4 MeV). However, a tomographic model has to be used to obtain acceptable dose assessments for electrons. The newly calculated SAF data set can provide the nuclear medicine dosimetry field a new perspective involving internal electrons. We have developed a tomographic model from CT images for a 30-week-pregnant woman. The developed model has been applied for internal dose calculations from photon and electron emitters.

Documents:

• "Development and Application of a Tomographic Model from CT Images for Calculating Internal Dose to a Pregnant Woman", Dissertation by Shi CY view
• "Development and Application of a Tomographic Model from
  CT Images for Calculating Internal Dose to a Pregnant Woman", PhD Defense by Shi CY view
• Shi CY and Xu XG. Development of a 30-Week-Pregnant Female Tomographic Model from CT-images for Monte Carlo Organ Dose Calculations. Med. Phys. 31(9):2491-2497, 2004. view
• Shi CY, Xu GX, Stabin MG. SAF values for internal photon emitters calculated for the RPI-P pregnant-female models using Monte Carlo methods. Med. Phys. 35(7): 3215-24,2008. view
• Shi CY, Xu GX. SAFs for Internal Electrons Using a Tomographic Pregnant Woman Model. ANS Conference Paper view
• Shi CY, Xu XG, Bai J. Development of a tomographic model for a pregnant woman and its application in nuclear medicine. Chinese Journal of Medical Imaging Technology. 20(8):1267-1272. 2004. view
• Calculated Results: Photon SAF's and Electron SAF's view
• 3D Visualizations view