Development of an optimal X-ray beam for dual-mode emission and transmission mammotomography
✍ Scribed by Randolph L McKinley; Martin P Tornai; Ehsan Samei; Marques L Bradshaw
- Book ID
- 103853175
- Publisher
- Elsevier Science
- Year
- 2004
- Tongue
- English
- Weight
- 312 KB
- Volume
- 527
- Category
- Article
- ISSN
- 0168-9002
No coin nor oath required. For personal study only.
✦ Synopsis
Objectives: A dual-mode Single Photon Emission Computed Tomography (SPECT)/X-ray CT (XCT) system for fullfield mammotomography is proposed for evaluation of breast lesions, where dual-view X-ray mammography has proven to be ineffective or inconclusive, particularly in radiographically dense breasts. Investigated design parameters include combined SPECT/XCT system geometry, X-ray focal spot size, tube loading, kVp, filtration, and detector type to determine operating parameters for a novel quasi-monochromatic X-ray beam for use in X-ray computed mammotomography that would use a dose equal to that from dual view mammography and that could be combined in a dual-mode system with SPECT. Methods: The relatively compact design of the hybrid SPECT/XCT will allow both systems to rotate on the same gantry below a patient. The hybrid system will be composed of a versatile, goniometerbased SPECT gantry, and an XCT system with a fixed position tungsten target, cone-beam geometry and digital flat panel detector frame nearly orthogonal to the SPECT system. The X-ray beam was modeled by xSpect, a semiempirical simulation code for X-ray production, attenuation, and detection. The idealized operating parameters for the quasi-monochromatic beam were determined by evaluating a beam hardening (minimum) figure of merit (FOM) along with quantitative spectral characteristics, and an exposure efficiency (maximum) FOM. These FOMs were evaluated in 8-16 cm thick uncompressed breasts. Filters with atomic numbers (Z) from 51-65 with 10th to 1000th value attenuating layer thicknesses were modeled, while considering tube loading limitations. Results: Using a tungsten target, increased tube potential and filtration can yield minimal beam hardening with improved exposure efficiency and contrast for various thicknesses of uncompressed breasts. Optimal tube operating range between 50-70 kVp with filter thickness of between 100th and 500th value layer for Z filters 56-62 result in optimized FOMs while remaining at or below expected dose of two-view X-ray mammography for the entire breast. Mean quasi-monochromatic beam energies were near 40 keV, with beam widths of o15% FWHM. Diminishing improvements are seen for filters greater than Z=65 and for thicknesses greater than the 500th value layer. Heavy filtration also demonstrated near-independence of FOM outcomes based on breast size. Conclusion: Simulated data show that a quasi-monochromatic beam with minimal beam hardening can readily be generated. Given the small expected source-image distance, it is geometrically feasible for the XCT