Eylem Seç
Mesh and Diffraction-based X-ray Phase Imaging
Başlık:
Mesh and Diffraction-based X-ray Phase Imaging
Yazar:
He, Congxiao, author.
ISBN:
9780438094277
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (106 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-11(E), Section: B.
Advisors: Carolyn MacDonald Committee members: Ariel Caticha; Alexander Khmaladze; Danhong Li; Carolyn MacDonald; Jonathan Petruccelli.
Özet:
More than a hundred years have passed since X-rays were detected by Wilhelm Rontgen. Due to their properties, they soon became widely applied in many areas, especially medical imaging. Recently, many new X-ray imaging techniques were designed, including phase imaging and diffraction enhanced imaging, DEI.
In conventional absorption X-ray images, the intensity contrast is proportional to differences in the imaginary parts of the refractive indices. In addition to these intensity differences, there is a phase shift. Contrast in phase images is proportional to the differences in the real part of the refractive indices. The real part of the refractive index decrements are usually three orders larger than the imaginary part, which means phase images could have much higher contrast than conventional attenuation images.
Phase cannot be imaged directly, and a number of techniques have been developed to detect the phase differences. In DEI, two crystals are used as monochromator and analyzer. If the analyzer crystal is aligned to the X-ray beam diffracted by the first crystal, and the deflection of the X-ray beam by the object is larger than Darwin width, the beam will not be diffracted by the second crystal, and a dark band would be created on the detector. The width of the dark band increases with the real index decrement of the object. This technique is not usually employed with lab sources because the diffracted intensity from the crystals is too low. To obtain sufficient intensity, a polycapillary collimating optic can be employed. A Monte Carlo simulation was performed to assess the potential for the use of DEI at low energies. It was demonstrated for the first time that the DEI method at low energy is promising if a polycapillary optic is employed.
Another technique to observe the phase is mesh based phase imaging. In this technique, the deflection of the X-rays due to phase of the object creates a displacement of the images of the mesh lines on a detector. That displacement is proportional to the phase gradient of the object and can be reconstructed by Fourier transform techniques. Because the phase changes rapidly at the edge of the objects, the differential phase contrast (DPC) image displays edge enhancement. This technique bad been developed for divergent broad band sources. A collimated monochromatic source was employed in mesh-based phase imaging for the first time. In addition, in the original technique, the window of harmonic in Fourier space is taken as limited by the harmonic separation. In that case, the resolution of the image is no better than the mesh period. Instead, a novel processing technique was demonstrated. Employing a wider window was shown to greatly improve the modulation transfer function of the absorption images, but creates artifacts in the phase image. The artifacts were successfully removed by combining images taken after shifting the mesh.
Notlar:
School code: 0668
Konu Başlığı:
Tüzel Kişi Ek Girişi:
Mevcut:*
Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(694703.1) | 694703-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
On Order
Liste seç
Bunu varsayılan liste yap.
Öğeler başarıyla eklendi
Öğeler eklenirken hata oldu. Lütfen tekrar deneyiniz.
:
Select An Item
Data usage warning: You will receive one text message for each title you selected.
Standard text messaging rates apply.