Qiu Huang

Tyrosine phosphorylation of paxillin/pp125FAK and microvascular endothelial barrier function

The transendothelial movement of solutes is a dynamic process controlled by a complex interaction between the cytoskeleton and adhesion proteins. The aim of this study was to examine whether protein tyrosine phosphorylation is involved in the regulation of endothelial barrier function. The apparent permeability coefficient of albumin ( P a) was measured in isolated and perfused coronary venules. Tyrosine phosphatase inhibitors, including phenylarsine oxide and sodium orthovanadate, dose and time dependently increased basal P a. Western blot analysis of cultured coronary venular endothelial cells revealed that inhibition of tyrosine phosphatase induced an increase in phosphotyrosine content in a number of proteins, including bands at 65-70 and 120-130 kDa, which were identified as paxillin and focal adhesion kinase (pp125FAK), respectively. The time course and dose responsiveness of protein tyrosine phosphorylation were tightly correlated with those of increases in P a. Furthermore, stimulation of endothelial cells with histamine or phorbol myristate acetate (PMA) enhanced tyrosine phosphorylation of paxillin and pp125FAK, which was blocked by the tyrosine kinase inhibitor damnacanthal. Correspondingly, the increases in venular permeability elicited by histamine and PMA were abolished in damnacanthal-treated venules. Taken together, the data suggest a possible involvement of protein tyrosine phosphorylation in the control of endothelial barrier function. Paxillin and its associated focal adhesion proteins may play a specific role in agonist-induced hyperpermeability responses in the endothelium of exchange vessels.

An FDK-like cone-beam SPECT reconstruction algorithm for non-uniform attenuated projections acquired using a circular trajectory

In this paper, Novikovs inversion formula of the attenuated two-dimensional (2D) Radon transform is applied to the reconstruction of attenuated fan-beam projections acquired with equal detector spacing and of attenuated cone-beam projections acquired with a flat planar detector and circular trajectory. The derivation of the fan-beam algorithm is obtained by transformation from parallel-beam coordinates to fan-beam coordinates. The cone-beam reconstruction algorithm is an extension of the fan-beam reconstruction algorithm using Feldkamp-Davis-Kresss (FDK) method. Computer simulations indicate that the algorithm is efficient and is accurate in reconstructing slices close to the central slice of the cone-beam orbit plane. When the attenuation map is set to zero the implementation is equivalent to the FDK method. Reconstructed images are also shown for noise corrupted projections.

Fast direct estimation of the blood input function and myocardial time activity curve from dynamic SPECT projections via reduction in spatial and temporal dimensions

PURPOSE Reconstruction of parametric images from dynamic single photon emission computed tomography (SPECT) data acquired with slow rotating cameras is a challenge because the estimation of the time-activity curves (TACs) may involve fitting data to an inconsistent underdetermined system of equations. This work presents a novel algorithm for the estimation of the blood input function and myocardial TAC with high accuracy and high efficiency directly from these projections. METHODS In the proposed dynamic reconstruction method, the information from the segmentation of functional regions from the static reconstructed image was used as a prior to construct a sparse matrix, through which the spatial distribution of the radioactive tracer was represented. Then the temporal distribution of the radioactive tracer was modeled by nonuniform B-spline basis functions which were determined according to a new selection rule. With reduction in both the spatial and temporal dimensions of the reconstructed image, the blood input function and myocardial TAC were estimated using the 4D maximum likelihood expectation maximization algorithm. The method was validated using data from both digital phantom simulations and an experimental rat study. RESULTS Compared with the conventional dynamic SPECT reconstruction method without the reduction in spatial dimensions, the proposed method provides more accurate TACs with less computation time in both phantom simulation studies and a rat experimental study. CONCLUSIONS The proposed method is promising in both providing more accurate time-activity curves and reducing the computation time, which makes it practical for small animal studies using clinical systems with slow rotating cameras.

An analytical algorithm for skew-slit imaging geometry with nonuniform attenuation correction

The pinhole collimator is currently the collimator of choice in small animal single photon emission computed tomography (SPECT) imaging because it can provide high spatial resolution and reasonable sensitivity when the animal is placed very close to the pinhole. It is well known that if the collimator rotates around the object (e.g., a small animal) in a circular orbit to form a cone-beam imaging geometry with a planar trajectory, the acquired data are not sufficient for an exact artifact-free image reconstruction. In this paper a novel skew-slit collimator is mounted instead of the pinhole collimator in order to significantly reduce the image artifacts caused by the geometry. The skew-slit imaging geometry is a more generalized version of the pinhole imaging geometry. The multiple pinhole geometry can also be extended to the multiple-skew-slit geometry. An analytical algorithm for image reconstruction based on the tilted fan-beam inversion is developed with nonuniform attenuation compensation. Numerical simulation shows that the axial artifacts are evidently suppressed in the skew-slit images compared to the pinhole images and the attenuation correction is effective.

Reconstruction From Uniformly Attenuated SPECT Projection Data Using the DBH Method

An algorithm was developed for the 2-D reconstruction of truncated and nontruncated uniformly attenuated data acquired from single photon emission computed tomography (SPECT). The algorithm is able to reconstruct data from half-scan (180deg) and short-scan (180deg+fan angle) acquisitions for parallel- and fan-beam geometries, respectively, as well as data from full-scan (360deg) acquisitions. The algorithm is a derivative, backprojection, and Hilbert transform (DBH) method, which involves the backprojection of differentiated projection data followed by an inversion of the finite weighted Hilbert transform. The kernel of the inverse weighted Hilbert transform is solved numerically using matrix inversion. Numerical simulations confirm that the DBH method provides accurate reconstructions from half-scan and short-scan data, even when there is truncation. However, as the attenuation increases, finer data sampling is required.

An analytical algorithm for skew-slit collimator SPECT with uniform attenuation correction

To replace the conventional pinhole (normal cone-beam) collimator, a novel skew-slit collimator was previously proposed and a Novikov-type algorithm developed to reconstruct images using the skew-slit geometry. The goal of this paper is to develop a reconstruction algorithm that has better noise control than the Novikov-type algorithm. The new algorithm is able to compensate for uniform attenuation, and computer simulation results show that reconstructed images are less noisy.

Two finite inverse Hubert transform formulae for region-of-interest tomography

Recently we published two explicit formulae for finite inverse Hilbert transforms [You, J and Zeng, GL, 2006]. This paper presents a straightforward proof of the formulae, the data requirements, and some computer simulations to verify the formulae. Examples of region-of-interest (ROI) tomography using truncated projections and the first formula of the finite inverse Hilbert transform are shown.

AN ANALYTICAL INVERSION OF THE 180° EXPONENTIAL RADON TRANSFORM WITH A NUMERICALLY GENERATED KERNEL

This work presents an inversion algorithm for the exponential Radon transform (ERT) over 180° range of view angles. The algorithm can be applied to two-dimensional parallel beam geometry in single photon emission computed tomography. First the differentiation of the ERT over π is backprojected. A convolutional relation between this backprojected differentiation and the original image is then established. In order to invert the convolution relation, the least-squares method is utilized to obtain a numerically generated filtering kernel, which readily restores the original image. The advantages of the proposed algorithm are, first, it only requires half the view angles of the conventional inversion algorithm, second, it deals with truncation in ERT data in certain situations, and third, the numerically generated filtering kernel can be pre-calculated and stored for later applications. The algorithm is an analytical approach except for the pre-calculated inverse kernel.

An alternative proof of Bukhgeim and Kazantsev's inversion formula for attenuated fan-beam projections

An inversion formula was developed by Bukhgeim and Kazantsev for attenuated fan-beam projections [Russian Academy of Science Siberian Branch: The Sobolev Institute of Mathematics (2002)]. The inversion formula was obtained by relating the attenuated fan-beam projections to unattenuated fan-beam projections and by trickily processing the unattenuated fan-beam projections. We show in this paper that the inversion formula can be readily obtained from Novikovs inversion formula for the two-dimensional (2D) attenuated radon transform. The derivation provides an alternative proof of Bukhgeim and Kazantsevs inversion formula by the use of transformation between parallel-beam coordinates and fan-beam coordinates and thus is quite elementary.

Longitudinal Evaluation of Sympathetic Nervous System and Perfusion in Normal and Spontaneously Hypertensive Rat Hearts with Dynamic Single-Photon Emission Computed Tomography.

The objective of this work was to evaluate the sympathetic nervous system and structure remodeling during the progression of heart failure in a rodent model using dynamic cardiac single-photon emission computed tomography (SPECT). The spontaneously hypertensive rat (SHR) model was used to study changes in the nervous system innervation and perfusion in the left ventricular (LV) myocardium with the progression of left ventricular hypertrophy (LVH) to heart failure. Longitudinal dynamic SPECT studies were performed with seven SHR and seven Wistar-Kyoto (WKY) rats over 1.5 years using a dual-head SPECT scanner with pinhole collimators. Time-activity curves (TACs) of the 123I-MIBG and 201Tl distribution in the LV blood pool and myocardium were extracted from dynamic SPECT data and fitted to compartment models to determine the influx rate, washout rate, and distribution volume (DV) of 123I-MIBG and 201Tl in the LV myocardium. The standardized uptake values (SUVs) of 123I-MIBG and 201Tl in the LV myocardium were also calculated from the static reconstructed images. The influx and washout rates of 123I-MIBG did not show a significant difference between SHRs and WKY rats. The DVs of 123I-MIBG were greater in the SHRs than in the WKY rats (p = .0028). Specifically, the DV of 123I-MIBG became greater in the SHRs by 6 months of age (p = .0017) and was still significant at the age of 22 months. The SUV of 123I-MIBG in SHRs exhibited abnormal values compared to WKY rats from the age of 18 months. There was no difference in the influx rate and the washout rate of 201Tl between the SHRs and WKY rats. The SHRs exhibited greater DV of 201Tl than WKY rats after the age of 18 months (p = .034). The SUV of 201Tl in SHRs did not show any significant difference from WKY at all ages. The higher DV of 123I-MIBG in the LV myocardium reveals abnormal nervous system activity of the SHRs at an age of 6 months, whereas a greater DV of 201Tl in the LV myocardium can only be detected at an age of 18 months. The results show that the abnormal nervous system activity appears earlier than perfusion. Furthermore, the comparison between the DV and the SUV indicates that dynamic SPECT with 123I-MIBG and 201Tl with the kinetic parameter DV is capable of detecting abnormalities of the LV at an early age.