Biomedical subjects

G Z Yang

Publications and source records attributed to G Z Yang.

At least 37 records · Page 2Linked to original sources

PubMed2000

Interleaved spiral cine coronary artery velocity mapping.

Navigator-echo controlled interleaved spiral cine coronary-artery velocity maps were acquired in eight free-breathing volunteers. Good quality data were achieved in all subjects with phasic flow being clearly demonstrated. The improved efficiency of spiral k-space coverage compared to that of more conventional spin-warp techniques resulted in a mean scan time for 256 x 256 pixel-matrix studies of 94 sec (range 69 - 123 sec, SD = 20 sec), the navigator acceptance rate being typically 40-45%. Repeat scans in five subjects showed a high degree of reproducibility, with no significant differences occurring in the peak velocities (14.6+/-1.4 cm/sec vs. 14.5+/-1.5 cm/sec, P = ns) nor in the mean velocities measured over all cine phases (8.3+/-2.1 cm/sec vs. 8.7+/-1.6 cm/sec, P = ns). The potential benefits of using this sequence for assessing coronary blood flow and flow reserve are discussed. Magn Reson Med 43:787-792, 2000.

Blood Flow Velocity↗

PubMed2000

Transient streamlines: texture synthesis for in vivo flow visualisation.

Magnetic resonance (MR) imaging is a versatile technique for providing detailed information on blood vessel morphology and function. With its ability to acquire multi-dimensional cine flow data, MR is also an important tool for providing insight into blood flow patterns in vivo. The purpose of this paper is to describe the application of texture synthesis for flow visualisation. Two related issues are addressed, one is the removal of image noise from the acquired velocity data to ensure a correct representation of the underlying flow structure, and the other is the formation of transient streamlines through flow texture synthesis. The process of noise removal is achieved by using a convex projection algorithm based on the principle of mass conservation, whereas transient streamlines are formed via an iterative orientated pattern formation and enhancement procedure. The method described provides realistic visualisation of the flow patterns and avoids distortions caused by integration errors associated with conventional streamline tracking techniques. Effectiveness of the method applied to MR flow data acquired in healthy volunteers and patients is demonstrated.

Blood Flow Velocity↗

PubMed2000

[Fusion and expression of the gene encoding human Mn-SOD to anti-CEA single-chain antibody in Escherichia coli].

The gene encoding human manganese-superoxide dismutase (Mn-SOD) was fused to anti-carcinoembryonic antigen single-chain antibody gene to construct the fusion gene, then was ligated into prokaryotic expression vector pET-22b(+), The fusion gene was expressed in E. coli at high level, accounting for 24% of the total bacteria soluble protein; and was characterized by SDS-PAGE and Western-blot analysis; the expression product had the CEA-binding ability in RIA, and also had the SOD activity by pyrogallol autoxidation assay. So, the Mn-SOD moiety retains substantial enzymatic activity, where the ScFv moiety can deliver the fusion protein to tumor, Mn-SOD is a potential tumor-suppressor gene, maybe the fusion protein can provide a new pathway to tumor therapy.

Amino Acid Sequence↗

PubMed2000

[Cloning of the zot gene of Vibrio cholerae and its expression in Escherichia coli].

The zot gene encoding Zonula occludens toxin was amplified from classic Vibrio cholerae genomic DNA by PCR. The result of sequencing indicated that zot gene encodes 399 amino acid residues. The sequence of zot gene was a little bit different from that of reported including 14 nucleotides and four amino acid residues. The expression plasmid pET-ZOT was constructed by inserting zot gene into plasmid pET-28a(+) containing the T7 promoter. The expression plasmid was induced into E. coli BL21 (DE3) and expression strain BLZOT was selected. SDS-PAGE analysis revealed that the ZOT protein was expressed and accumulated up to above 15% of bacterial soluble protein after induced by IPTG. A protein of 47 kD was expressed as including body. Western blot analysis revealed that the expressed protein was ZOT.

Base Sequence↗

PubMed1999

Safety and preliminary findings with the intravascular contrast agent NC100150 injection for MR coronary angiography.

In this Phase I clinical study, a novel ultrasmall superparamagnetic iron oxide contrast agent, NC100150 Injection (Nycomed Imaging, Oslo, Norway, a part of Nycomed Amersham), was used in two-dimensional magnetic resonance coronary angiography (MRCA). Safety and imaging data were acquired from 18 healthy male volunteers at both 0.5 and 1.5 T, before and after the administration of NC100150 Injection. Through-plane and in-plane images of the right coronary artery were analyzed. The postcontrast imaging sequences used prepulses and a high flip angle, to introduce T1 weighting. At 1.5 T (TE 2.6 msec), the through-plane coronary artery signal-to-noise ratio (SNR) (P = 0.04), coronary artery-to-fat signal difference-to-noise ratio (SDNR) (P = 0.001), coronary artery-to-myocardium SDNR (P<0.001), and coronary artery delineation (P<0.001) were improved by the administration of NC100150 Injection. For in-plane imaging, coronary artery delineation improved, but there were no significant changes in the SNR and SDNR. At 0.5 T, with the longer TE (6.7 msec) imaging sequence used, there was a reduction in the SNR (P = 0.01), the fat SDNR (through-plane P = 0.02; in-plane P = 0.25), and the coronary artery diameter (P<0.01 in both imaging planes). There was a trend toward improvement in the myocardial SDNR and coronary artery delineation. In conclusion, NC 100150 Injection was given safely to 18 healthy subjects, with no major adverse reactions. Coronary artery delineation was improved in both imaging planes at 1.5 T, with a trend toward improvement at 0.5 T. At 1.5 T, with a short TE imaging sequence, the marked T1 shortening effects of NC100150 Injection were dominant, leading to an improvement in the quantitative parameters for the through-plane images. At 0.5 T, with a longer TE imaging sequence, the T2* effects of the contrast agent played a role in reducing the quantitative image parameters. With further optimization of imaging sequences, to take advantage of the long-lived intravascular T1 shortening effect of NC100150 Injection, further improvements in MRCA will be possible.

Adult↗

PubMed1999

First-pass myocardial perfusion imaging and equilibrium signal changes using the intravascular contrast agent NC100150 injection.

In this phase I clinical study, the new ultrasmall superparamagnetic iron oxide contrast agent, NC100150 Injection (Nycomed AS, Oslo, Norway, a part of Nycomed Amersham), was assessed for first-pass magnetic resonance myocardial perfusion studies and its ability to produce equilibrium signal changes, as a possible indicator of myocardial blood volume. Data were acquired in 18 healthy male volunteers at 0.5 T and 1.5 T. At both field strengths, first-pass studies using T1-weighted sequences were acquired. Long TE spin-echo echoplanar imaging (EPI) was used at 0.5 T and short TE fast low-angle shot (FLASH) imaging at 1.5 T. With both sequences, T1 effects dominated the images for low doses, and time intensity curves potentially suitable for perfusion analysis were generated. At higher doses, T2 and T2* effects were observed. At 1.5 T, these predominantly affected the blood pool signal; however, at 0.5 T the myocardial signal was also involved, reflecting the relative T2 and T2* sensitivity of the spin-echo EPI sequence as a result of the long TE and long readout window, respectively. Equilibrium changes were assessed at both field strengths using T1-weighted FLASH sequences and in addition at 1.5 T using T2*-weighted gradient-echo EPI. With the T1-weighted images at both field strengths, signal changes were observed in all subjects; however, no dose-response relationship could be shown. With the T2*-weighted EPI there was significantly lower signal (P < 0.05) with the 3 and 4 mg/kg doses than with the 2 mg/kg dose. In conclusion, NC100150 Injection is useful for first-pass myocardial perfusion using T1-weighted sequences; however, low doses in combination with short TE sequences are required to minimize sensitivity to T2* effects. Equilibrium signal changes can also be induced in the myocardium. More work is required to optimize the imaging sequences and dose of NC100150 Injection for first-pass studies and also to determine whether the equilibrium signal changes can be used to measure myocardial blood volume changes in ischemic heart disease.

Adult↗

PubMed1999

Locally focused 3D coronary imaging using volume-selective RF excitation.

This paper describes a locally focused magnetic resonance (MR) imaging method for three-dimensional (3D) zonal echoplanar coronary angiography using volume-selective radiofrequency (RF) excitation. Spatially variable resolution was used for delineating coronary arteries and reducing the effect of residual signals caused by the imperfect excitation profile of the RF pulse. The use of variable resolution enabled the derivation of basis functions having different spatial characteristics pertaining to regional object details, and a significantly smaller number of phase-encoded signal measurements was needed for image reconstruction. Based on the relative significance of each required phase-encoding step, real-time phase-encode reordering was used to minimize the effect of respiratory motion during coronary imaging. To eliminate Nyquist ghosting in oblique echoplanar imaging, the echoplanar data acquired during forward and reverse echoes were reconstructed separately and then averaged with spatial registration for improving the signal-to-noise ratio. The technique was evaluated with phantom experiments and right coronary artery images of 11 asymptomatic volunteers using a 0.5 T MR system. A marked improvement in image quality has been achieved despite a 30% reduction in imaging time.

Artifacts↗

PubMed1999

Coronary artery imaging in a 0.5-Tesla scanner: implementation of real-time, navigator echo-controlled segmented k-space FLASH and interleaved-spiral sequences.

Coronary angiography techniques have been implemented on a 0.5-Tesla scanner with a view to performing coronary artery imaging. Slice-followed, segmented k-space FLASH sequences and interleaved-spiral sequences have been employed with acquisitions under real-time navigator echo control with patient feed back, enabling poor signal-to-noise levels to be overcome by averaging data acquired over multiple, variable-length, reproducible breath holds. Good-quality, millimetre-resolution coronary images were obtained in ten normal subjects with both techniques. The mean percent of data segments or interleaves acquired with the navigator echo within the 5-mm diaphragm acceptance window was 57% [standard deviation (S.D.), 11%; range, 38-85%], and the average image-acquisition times were 123+/-22 sec and 71+/-14 sec for segmented FLASH and interleaved-spiral imaging, respectively. In addition to shorter acquisition times, the interleaved-spiral sequence has superior temporal resolution, allowing the acquisition of limited, multislice data sets. However, the sequence is particularly sensitive to the off-resonance effects of residual epicardial fat surrounding the artery and to field nonuniformities, both of which lead to image blurring and, unlike segmented FLASH acquisitions (which are very robust), the spiral data sets generally require postprocessing.

Adult↗

PubMed1999

Motion-selective encoding for fast cine imaging.

In magnetic resonance (MR) cine imaging applications, it is common that only a fraction of the field of view is used for delineating dynamic features whereas surrounding static structures are merely served as landmarks for three-dimensional orientation. This paper presents a method of using motion-selective encoding for fast cine imaging. By the use of a simple RF saturation pulse, the imaging field of view was divided into two areas, one with motion and the other without. This allowed the static material to be imaged by fast ungated acquisition and dynamic structures by reduced phase encoding. Issues related to phase error correction were addressed and the proposed algorithm was validated using images acquired from five normal subjects. The saving in imaging time was dependent on the size of the moving structures and a 35% reduction in imaging time did not cause visually noticeable changes in image quality. The application of the technique is limited to cine images with large surrounding static structures and a theoretical analysis of maximum savings in imaging time in relation to the size of the moving structures within the image field of view is provided. Magn Reson Med 42:430-435, 1999.

Adult↗

PubMed1999

Use of the intravascular contrast agent NC100150 injection in spin-echo and gradient-echo imaging of the heart.

This is the first study of the intravascular iron oxide particle contrast agent, NC100150 Injection (Nycomed Imaging AS, Oslo, Norway, a part of Nycomed Amersham) in magnetic resonance imaging of the human heart. Eighteen healthy male volunteers were studied at both 0.5 and 1.5 T before and after the administration of NC100150 Injection. Transaxial spin-echo images were acquired at both field strengths, conventional gradient-echo cine images at 0.5 T, and breathhold Turbo-FLASH cine images at 1.5 T. Optimized cine imaging sequences were used postcontrast, with a high flip angle of 60-70 degrees. In the spin-echo images there was a significant reduction in the blood pool flow artifact at the level of the right atrium (0.5 T, 57%, p < 0.01; 1.5 T, 41%, p = 0.01) and the left ventricle (LV) (0.5 T, 45%, p = 0.01; 1.5 T, 45%, p < 0.01). In the conventional gradient-echo cines at 0.5 T, there was a significant increase in the LV blood pool and myocardial signal difference-to-noise ratio (SDNR) in the diastolic (56%, p = 0.01) and systolic (141%, p < 0.001) frames. There was also a significant increase in the signal intensity (SI) gradient at the LV blood pool-myocardial border in the diastolic and systolic frames (both p < 0.001). At higher doses of NC100150 Injection (3 and 4 mg/kg), a rim of signal void around the LV blood pool was observed, perfectly defining the LV blood pool-myocardial border. In the Turbo-FLASH breathhold cines at 1.5 T, there was a significant increase in the LV blood pool-myocardial SDNR in the diastolic (221%, p < 0.001) and systolic (916%, p < 0.001) frames. Again, there was also a significant increase in the SI gradient at the LV blood pool-myocardial border in the diastolic and systolic frames (both p = 0.003). In conclusion, NC100150 Injection was given safely to 18 healthy subjects. Image quality and LV blood pool-myocardial definition were improved after the administration of NC100150 Injection. These improvements enable better spin-echo anatomical definition, better definition of myocardial wall motion, and should improve the capability of automated edge detection algorithms.

Adult↗

PubMed1999

[Expression of chimeric single-chain antibody with specificity for HBsAg in E. coli].

The Vk gene of MAb with specificity for HBsAg and human Ck gene have been combined to form chimeric light chain (Vk-Ck) by recombinant PCR, which has combined with VH to construct chimeric single-chain antibody(ScFv-Ck) by a linker encoding a flexible peptide[(Gly3 Ser)3]. The ScFv-Ck has been expressed in the heat-induced expression system and secreted expression system of E. coli respectively. Analysis by Western-blot and indirect ELISA shows that the ScFv-Ck product in two systems both have HBsAg-binding ability, and ScFv-Ck has been secreted from E. coli in the direction of secretion peptide.

Blotting, Western↗

PubMed1998

FID-based lung MRI at 0.5 T: theoretical considerations and practical implications.

Pulse sequences based on FID signals and projection reconstruction (PR) were investigated for lung MRI at 0.5 T and evaluated for artifacts caused by: (1) k-space mismapping due to either delay or distortion of the readout gradient waveform, (2) cardiac motion and pulsatile flow, and (3) respiratory motion. Nonstructured artifacts were described, simulated, and experimentally confirmed for the first time. Nonstructured artifacts did not impair the demonstration of structures of high signal-to-noise ratio (SNR) but generated quantitative errors in the image intensity analysis over the lung parenchyma. The use of FID-based PR techniques for lung MRI is not justified at 0.5 T.

Artifacts↗

PubMed1998

Three-dimensional coronary MR angiography using zonal echo planar imaging.

Using an adapted two-dimensional spatially selective RF excitation scheme, a novel yet practical three-dimensional (3D) zonal echo-planar imaging technique for MR coronary angiography has been developed. The robustness of the technique compared with the two-dimensional (2D) segmented fast low angle shot (FLASH) method was evaluated using the right coronary artery images of 16 asymptomatic volunteers with a 0.5-T mobile scanner. Each 3D acquisition required multiple breath-holds, and real-time navigator echoes were used to ensure consistent breath-holding. Advantages of the technique include an improved signal-to-noise ratio, clearer depiction of tortuous coronary vessels due to decreased partial volume effects, and reduced motion blurring by the use of a short echo-planar readout.

Adult↗

PubMed1998

Diversity of cDNAs encoding phospholipase A2 from Agkistrodon halys pallas venom, and its expression in E. coli.

As a step toward understanding the structure and function of phospholipase A2(PLA2), we isolated several novel cDNAs encoding Agkistrodon halys Pallas PLA2 isoenzymes including B-PLA2, Asn49-PLA2, A-PLA2, A'-PLA2 and BA1-PLA2 by polymerase chain reaction with oligonucleotide primers corresponding to the N- and C-terminus of these enzymes. The amino acid sequences of A-PLA2 deduced from cDNA are consistent with that isolated from venom except for four residues. Asn49-PLA2 and B-PLA2 are highly similar (> 95%), but the critical residue Asp49 in the active centre of B-PLA2 is replaced by Asn49 in Asn49-PLA2. The N-terminal residues (1-24) of BA1-PLA2 shows high similarity to that of B-PLA2 which has strong ability to hemolyze erythrocytes, while its C-terminal residues (72-125) are the same as that of A-PLA2 which can inhibit platelet aggregation. The successful cloning of these isoenzymes not only provide excellent native material to study the structure-function relationship of PLA2s, but also to disclose the genesis of structural diversity of PLA2s, namely DNA modification and gene rearrangement. The cloned cDNA for A-PLA2 has been expressed in E. coli. By Q-Sepharose column chromatography, denaturation-renaturation and FPLC, we obtained the active recombinant protein with the initiator Met. This is the first report of the production of an active recombinant PLA2 with the initiator Met.

Agkistrodon↗

PubMed1998

Motion and deformation tracking for short-axis echo-planar myocardial perfusion imaging.

The assessment of regional myocardial perfusion during the first-pass of a contrast agent bolus requires tracking of the signal time course for each myocardial segment so that a detailed perfusion map can be derived. To obtain such a map in practice, however, is not trivial because deformation of the shape of the myocardium and respiratory-induced motion render a major difficulty in this process. This study describes an automated approach for motion and deformation tracking of functional myocardial perfusion images. The effectiveness of the described method has been evaluated using a numerical phantom and results are compared with those from existing techniques which use deformable models. Preliminary results from applying our approach to 20 patients are discussed and compared with those from SPECT studies.

Aged↗

PubMed1998

Enhancement of subtle density differences of the lung parenchyma on CT.

Several pulmonary conditions are characterized by the finding of areas of decreased attenuation relative to adjacent normal lung parenchyma on computed tomography. In particular, the identification of areas of the lung affected by small airways disease is difficult as the reduction in lung density is subtle and the regions are poorly marginated. This paper presents a novel wavelet analysis technique which increases the conspicuity of differences between normal and abnormal lung parenchyma.

Humans↗

PubMed1997

Non-breath-hold lung magnetic resonance imaging with real-time navigation.

Magnetic resonance imaging (MRI) with navigating techniques based on consecutive breath-holds demand a level of respiratory control that is often beyond the capability of patients with lung disease. The objectives of this investigation were to develop and evaluate a navigating technique for lung MRI that does not rely on patient cooperation. Navigating techniques were implemented at 0.5 T using conventional imaging techniques of short echo-time and imaging during normal breathing in the diastolic phase of the cardiac cycle. A column of spins, orthogonal to the diaphragm, was excited both immediately before and after the imaging segment. These signals were processed in real time to provide the position of the lung-diaphragm interface. An imaging segment was considered correctly acquired only when the interface position was within the acceptance window both before and after the acquisition of the segment. A distribution of lung-diaphragm interface positions obtained during normal respiration was employed to define the acceptance window. In the case of multislice techniques, the position of the lung-diaphragm interface immediately before the imaging segment was also employed to decide which phase-encoding step to acquire next, therefore reducing the apparent frequency of the respiratory motion. A distribution of interface positions, updated in real time, served as a reference for the allocation of phase-encoding steps according to diaphragm position. The lung images obtained represent a significant advance in image quality, improving further the ability of MR to detect and monitor pulmonary disease. Motion artifacts were reduced, and images reliably demonstrated smaller vessels, which are not normally visible without navigation.

Computer Systems↗

PubMed1997

Three-dimensional computed tomography bronchoscopy using clinical datasets: a comparison with fibreoptic bronchoscopy.

OBJECTIVE: To assess three-dimensional computed tomography 'bronchoscopic' (3-DCTB) reconstruction of routine CT data as a non-invasive method of airway visualization, and compare it with fibreoptic bronchoscopy (FOB). METHODS: Fourteen datasets were acquired from 13 patients undergoing both FOB and CT examination of the chest. Standard continuous volume CT using 6 mm collimation and clinical FOB techniques were employed. Images were obtained from 3-DCTB reconstructions by segmentation and surface recognition algorithms generating surface rendered 'bronchoscopic views'. These were scored for technical quality and anatomical detail. The most distal bronchi seen in left upper and right lower lobes were recorded for FOB and 3-DCTB. RESULTS: On FOB, the subsegmental bronchi were seen in right lower and in left upper lobe in 10/14 cases and 4/14 cases, respectively. Visualization of the subsegmental airways was not achieved with 3-DCTB, as they could not be identified with confidence. 3-DCTB never achieved a more distal view than obtained by FOB. Using 3-DCT, the right, lower lobe segmental bronchi were seen in 10/14 cases, and lobar bronchus in 14/14 cases (two occluded). In the left upper lobe, 3-DCT showed segmental bronchi in 6/14 cases, lobar bronchus in 11/14 cases (one occluded) and the left main bronchus appeared occluded in 3/14 cases. Overall, technical quality and anatomical detail scores of the carina and proximal bronchi ranked significantly higher than views of segmental bronchi. CONCLUSIONS: 3-DCTB cannot routinely replace FOB for inspection of major and segmental bronchi. Subsegmental bronchi cannot be adequately demonstrated by 3-DCTB using 6 mm collimation datasets.

Adult↗