Journal of X-Ray Science and Technology - Volume 11, issue 4

Authors: Zhu, Fuping | Tian, Jie

Article Type: Research Article

Abstract: In this paper, an interactive segmentation method that combines fast marching and level set method is proposed. Level set segmentation involves solving the energy-based active contour minimization problems by the computation of geodesics or minimal distance curves. First, by selecting the seed point, the fast marching method is used to extract rough boundaries of the interested object. We modified the traditional fast marching method to capture the weak edges by introducing watershed transform. Then, the contour …obtained from the fast marching method mentioned above is regarded as an initialization and the level set method is used to finely tune the contour. The algorithm is demonstrated on some medical images: segmentation of knee tissues in CT image and segmentation of brain tissues in MR image. The results show that this method can remove the small regions obtained from fast marching method and converge the desired boundary. Show more

Citation: Journal of X-Ray Science and Technology, vol. 11, no. 4, pp. 193-204, 2003

Authors: Liu, Julian J. | Watt-Smith, Stephen R. | Smith, Stephen M.

Article Type: Research Article

Abstract: A new description for computed tomography, parallel and equal to Radon transformation but based on sinusoidal functions rather than line integrals, is introduced. This representation contributes an effective algorithm to reduce metal artefacts in reconstruction. Using this method, the information included in the scan data corresponding to the metal implants can be separated from the original projection, an amending method rather than interpolation is therefore provided to reach higher accuracy for reconstruction. …The method is with low complexity in computation, and can be combined online with filtered backprojection (FBP), which is the most widely used algorithm in practice, to improve the quality of the reconstructed image. Also, the method has the potential to deal with the artefacts caused by beam hardening and partial volume, and to be developed into a straight reconstruction algorithm based on the sinusoidal representation. Examples are presented for clearer description and demonstration. Show more

Citation: Journal of X-Ray Science and Technology, vol. 11, no. 4, pp. 205-218, 2003

Authors: Vedantham, Srinivasan | Karellas, Andrew | Suryanarayanan, Sankararaman

Article Type: Research Article

Abstract: Spatially coherent fiberoptic plates are important components of some charge-coupled device (CCD)-based x-ray imaging systems. These plates efficiently transmit scintillations from the phosphor, and also filter out x-rays not absorbed by the phosphor, thus protecting the CCD from direct x-ray interaction. The thickness of the fiberoptic plate and the CCD package present a significant challenge in the design of a digital x-ray cassette capable of insertion into the existing film-screen cassette holders of digital mammography …systems. This study was performed with an aim to optimize fiberoptic plate thickness. Attenuation measurements were performed on nine fiberoptic plates varying in material composition that exhibit desirable optical characteristics such as good coupling efficiency. Mammographic spectra from a clinical mammographic system and an Americium-241 (Am-241) source (59.54 KeV) were used. The spectra were recorded with a high-resolution cadmium zinc telluride (CZT)-based spectrometer and corrected for dead time and pile-up. The linear attenuation coefficients varied by a factor of 3 in the set of tested fiberoptic plates at both mammographic energies and 59.54 keV. Our results suggest that a 3-mm thick high-absorption plate might provide adequate for shielding at mammographic energies. A thickness of 2-mm is feasible for mammographic applications with further optimization of the fiberoptic plate composition by incorporating non-scintillating, high-atomic number material. This would allow more space for cooling components of the cassette and for a more compact device, which is critical for clinical implementation of the technology. Show more

Keywords: X-ray imaging, charge coupled devices (CCDs), fiberoptic plates, attenuation coefficient, digital cassette

Citation: Journal of X-Ray Science and Technology, vol. 11, no. 4, pp. 219-230, 2003

Authors: Prince, Martin R. | Zhang, Hong Lei | Chabra, Shalini G. | Jacobs, Paula | Wang, Yi

Article Type: Research Article

Abstract: Purpose: To evaluate the imaging potential of ferumoxytol, a new superparamagnetic iron oxide colloidal blood pool contrast agent. Materials and Methods: Magnetic resonance (MR) imaging at 1.5 Tesla was performed before and after intravenous injection of ferumoxytol using escalating doses of 0.4, 0.8, 1.2 and 1.6 mg Fe/kg for a total of 4 mg Fe/kg in five subjects imaged with 3D MR Angiography (MRA) of the trifurcation after each dose. In five subjects cardiac cine MRI was performed pre …and post 4.0 mg Fe/kg. Image quality was assessed by measuring signal to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in the vascular structures. Pre- and post-dose urine and blood tests as well as EKG/vital sign monitoring were performed to evaluate safety and blood samples were collected for T1 relaxivity measurements. Results: Cumulative doses of 0, 0.4, 1.2, 2.4 and 4 mg Fe/kg yielded mean SNR in the arteries of 10, 16, 39, 57 and 69 respectively indicating that the higher doses produced higher SNR on 3D vascular images. Similarly aorta SNR on 2D time-of-flight increased from 11.8 without Fe to 15.4 post Fe (p = 0.004) indicating improved image quality on MRA sequences optimized for use without contrast. At 4 mg Fe/kg there was a substantial T1 shortening measured in the blood from 1990 ± 573 ms to 80 ± 42 ms (p < 0.0001), corresponding to the increased SNR. Images of large vascular structures including cardiac chambers, aorta, and pulmonary arteries were excellent post ferumoxytol but images of smaller arteries of the trifurcation were difficult to evaluate due to enhancement of the overlapping veins. No serious adverse events occurred. Conclusion: The new superparamagnetic iron oxide colloid ferumoxytol is a promising blood pool agent especially for cardiac, aorta and pulmonary imaging. Show more

Keywords: magnetic resonance angiography, contrast media, iron oxide, cardiac imaging, aorta

Citation: Journal of X-Ray Science and Technology, vol. 11, no. 4, pp. 231-240, 2003

Authors: Kim, Junhwan | Zabih, Ramin

Article Type: Research Article

Abstract: Medical imaging often involves the injection of contrast agents and the subsequent analysis of tissue enhancement patterns. Many important types of tissue have characteristic enhancement patterns; for example, in MR mammography, malignancies exhibit a characteristic "wash out" temporal pattern, while in MR angiography, arteries, veins and parenchyma each have their own distinctive temporal signature. In such time resolved image series, there are substantial changes in intensities; however, this change is due primarily to …the contrast agent, rather than to motion. As a result, the task of automatically segmenting contrast-enhanced images poses interesting new challenges. In this paper, we propose a new image segmentation algorithm for time resolved image series with contrast enhancement, using a model-based time series analysis of individual pixels. We take an energy minimization approach to ensure spatial coherence. The energy is minimized in an expectation-maximization fashion that alternates between segmenting the image into a number of non-overlapping regions and finding the temporal profile parameters which describe the behavior of each region. Preliminary experiments on MR angiography and MR mammography studies show the algorithm's ability to find an accurate segmentation. Show more

Citation: Journal of X-Ray Science and Technology, vol. 11, no. 4, pp. 241-251, 2003