Biomedical subjects

Yu Zou

Publications and source records attributed to Yu Zou.

24 records · Page 2Linked to original sources

PubMed2004

Impact of polychromatic x-ray sources on helical, cone-beam computed tomography and dual-energy methods.

Recently, there has been much work devoted to developing accurate and efficient algorithms for image reconstruction in helical, cone-beam computed tomography (CT). Little attention, however, has been directed to the effect of physical factors on helical, cone-beam CT image reconstruction. This work investigates the effect of polychromatic x-rays on image reconstruction in helical, cone-beam computed tomography. A pre-reconstruction dual-energy technique is developed to reduce beam-hardening artefacts and enhance contrast in soft tissue.

Algorithms↗

PubMed2004

Partial volume and aliasing artefacts in helical cone-beam CT.

A generalization of the quasi-exact algorithms of Kudo et al (2000 IEEE Trans. Med. Imaging 19 902-21) is developed that allows for data acquisition in a 'practical' frame for clinical diagnostic helical, cone-beam computed tomography (CT). The algorithm is investigated using data that model nonlinear partial volume averaging. This investigation leads to an understanding of aliasing artefacts in helical, cone-beam CT image reconstruction. An ad hoc scheme is proposed to mitigate artefacts due to the nonlinear partial volume and aliasing artefacts.

Algorithms↗

PubMed2004

Exact image reconstruction on PI-lines from minimum data in helical cone-beam CT.

The development of accurate and efficient algorithms for image reconstruction from helical cone-beam projections remains a subject of active research. In the last few years, a number of quasi-exact and exact algorithms have been developed. Among them, the Katsevich algorithms are of filtered backprojection type and thus possess computational advantages over other existing exact algorithms. In this work, we propose an alternative approach to reconstructing exactly an image from helical cone-beam projections. Based on this approach, we develop an algorithm that requires less data than do the existing quasi-exact and exact algorithms, including the Katsevich algorithms. Our proposed algorithm is also of filtered backprojection type with one-dimensional filtering performed along a PI-line in image space. Therefore, it is (at least) computationally as efficient as the Katsevich algorithms. We have performed a preliminary numerical study to demonstrate and validate the proposed algorithm using computer-simulation data. The implication of the proposed approach and algorithm appears to be significant in that they can naturally address the long object problem as well as the super-short scan problem and, most importantly, in that they provide the opportunity to reconstruct images within any selected region of interest from minimum data, allowing the use of detector with a reduced size, the selection of a minimum number of rotation angles and thus the reduction of radiation dose delivered to the imaged subject.

Algorithms↗

PubMed2003

The activator-binding site of Onchocerca volvulus S-adenosylmethionine decarboxylase, a potential drug target.

S-Adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in polyamine biosynthesis. In many eukaryotes its activity is stimulated specifically by putrescine. The AdoMetDC of the filarial parasite Onchocerca volvulus, however, is not only stimulated by putrescine but also by the naturally occuring polyamines spermidine and spermine. Several diamines, acetylated polyamines and polyamine analogues were used to analyse what molecular prerequisites are needed to stimulate nematode AdoMetDC activity. In the absence of an activator, the O. volvulus enzyme exhibits an extremely low specific activity. This fact, together with the unspecificity of activator binding, was thought to be useful for a new strategy to inhibit nematode AdoMetDC activity. Therefore, different polyamine analogues were tested as competitive inhibitors towards the stimulatory effect putrescine has on the O. volvulus and, in comparison, on the Caenorhabditis elegans and human AdoMetDC. Bis(aralkyl)- and bis(alkyl)-substituted polyamine analogues with a 3-7-3 backbone were found to inhibit AdoMetDC activities, however, probably without interfering with the putrescine stimulation. The best inhibitor, BW-1, was about 10-fold more effective against O. volvulus AdoMetDC than against the human enzyme. Unexpectedly, BW-1 was determined to be a competitive inhibitor with respect to AdoMet, having a Ki value of 310 microM for the putrescine-stimulated human AdoMetDC. Furthermore, we show for the O. volvulus and the human enzyme that the degree of inhibition by BW-1 depends on the actual putrescine concentration.

Adenosylmethionine Decarboxylase↗

PubMed2002

Short-scan SPECT imaging with non-uniform attenuation and 3D distance-dependent spatial resolution.

Image quality and quantitative accuracy in single-photon emission computed tomography (SPECT) can be degraded by, e.g., the effects of photon attenuation and finite spatial resolution. It is generally considered that adequate compensation for such effects on SPECT images requires data acquired over 2 pi. Recently, using the existing consistency condition on the data function, Noo and Wagner (2001 Inverse Problems 17 1357-72) have shown analytically that data acquired over only pi can be used to correct completely for the effect of uniform attenuation in SPECT. It remains unknown, however, whether data acquired only over pi in SPECT with non-uniform attenuation and/or 3D distance-dependent spatial resolution (DDSR) contain complete information for accurate image reconstruction. In this work, we develop a heuristic perspective, which is referred to as the potato peeler perspective to show conceptually that data in SPECT with non-uniform attenuation and/or 3D DDSR acquired over 2 pi contain redundant information and that such information can be used to reduce the scanning angle in SPECT. Specifically, we show heuristically that, in SPECT with only non-uniform attenuation, the scanning angle can be reduced from 2 pi to pi and that, in SPECT with both non-uniform attenuation and DDSR with a physically realistic form, the scanning angle can be reduced from 2 pi to pi in a practical sense. We conduct computer simulation studies, and the results from these studies corroborate the observations obtained based upon the heuristic potato peeler perspective.

Algorithms↗

PubMed2002

Resonance transition energies and oscillator strengths in lutetium and lawrencium.

The transition energies and oscillator strengths for nd (2)D(3/2)-(n+1)p (2)P(o)(1/2,3/2) transitions in Lu ( n = 5, Z = 71) and Lr ( n = 6, Z = 103) were calculated with the multiconfiguration Dirac-Hartree-Fock method. The present study confirmed that the ground state of atomic Lr is [Rn]5f(14)7s(2)7p (2)P(o)(1/2). The calculation for Lr required wave function expansions of more than 330 000 configuration states. In Lu, the transition energies, with Breit and QED corrections included, agree with experiment to within 126 cm(-1). In lighter elements, core correlation is usually neglected but was found to be of extreme importance for these heavy elements, affecting the oscillator strengths by a factor of 3 and 2 in Lu and Lr, respectively.

Journal Article↗