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31.
GZ Yang PD Gatehouse J Keegan RH Mohiaddin DN Firmin 《Canadian Metallurgical Quarterly》1998,39(5):833-842
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. 相似文献
32.
SM Forbat RH Mohiaddin GZ Yang DN Firmin SR Underwood 《Canadian Metallurgical Quarterly》1995,5(6):635-639
The reproducibility of MR imaging for the measurement of aortic compliance was studied in 47 healthy volunteers. Long and short term reproducibility and intraobserver variability were tested. The method was modified to improve image quality and short term reproducibility and intraobserver variability retested. For comparison, spin echo imaging was compared with cine gradient echo imaging. Initial long term reproducibility showed a mean difference (+/-SE) of 3% (+/- 7%) with 95% confidence interval (CI) for limits of agreement of +/- 69%. Short term reproducibility (7% +/- 6%, 95% CI +/- 46%) and intraobserver variability (1% +/- 2%, 95% CI +/- 31%) were better. After modification of the technique and optimization of image quality, both short term reproducibility and intraobserver variability improved (0% +/- 3%, 95% CI +/- 17% and 5% +/- 2%, 95% CI +/- 16% respectively). Aortic compliance can be measured using spin echo MR imaging with good reproducibility provided care is taken to obtain good quality images with high spatial resolution. 相似文献
33.
RH Mohiaddin HG Bogren F Lazim J Keegan PD Gatehouse M Barbir DN Firmin MH Yacoub 《Canadian Metallurgical Quarterly》1996,7(8):591-597
BACKGROUND: Magnetic resonance angiography (MRA) using segmented k-space fast low-angle shot imaging has recently been used to demonstrate the proximal coronary arteries in healthy subjects and in patients with coronary artery disease. We assessed the sensitivity and specificity of coronary MRA in heart transplant recipients and investigated the feasibility of coronary MRA in patients with metallic sutures and clips in the chest. MATERIALS AND METHODS: Sixteen cardiac transplant patients aged 57.2 +/- 7.9 years (mean +/- SD) were recruited. Forty-eight arterial segments were evaluated, including the left main artery (LMA), left anterior descending artery (LADA) and right coronary artery (RCA). We excluded the left circumflex artery which could not be imaged accurately. The average time between heart transplant operation and MRA was 6 years, whereas that between MRA and X-ray angiography was 4 months. The coronary MRA was interpreted by two experienced investigators who were blinded to the coronary X-ray angiography results. Similarly, the coronary X-ray angiography results were interpreted by two experienced investigators blinded to the MRA results. The coronary arterial segments were classified by MRA as being normal or as having an amount of disease that was significant (> 50% lesion) or insignificant (< 50% lesion). RESULTS: There were 28 true-negative, five true-positive, four false-negative and six false-positive results. Of the 28 true-negative cases, 13 were in the LMA, six in the LADA and nine in the RCA. There was one false-positive LMA, two false-positive LADA and three false-positive RCA stenoses. There were four false-negative results in the LADA and one in the RCA. Clips precluded evaluation in one LMA, one LADA and one RCA. One LMA and one LADA were not evaluated as a result of poor images. One false-positive RCA stenosis was caused by a metallic clip. Three of the false-negative LADA stenoses had lesions in the distal third of the artery. The sensitivity, specificity, negative and positive predictive values were generally poor for the left coronary artery. The best results were for the RCA (sensitivity 100%, specificity 75%, positive predictive value 50% and negative predictive value 100%). The specificity in the left coronary arteries (LMA and LADA) was 86%, but the other indicators were all poorer. For the RCA, LMA and LADA combined, the overall sensitivity was 56%, specificity 82%, predictive accuracy 45% and negative predictive value 88%. In three patients, < 50% RCA lesions were seen in the MRA data, which were all confirmed by angiography. No < 50% lesions were seen in the LMA or in the LADA by MRA or by X-ray angiography. CONCLUSION: Coronary MRA using the segmented fast low-angle shot technique is feasible in heart transplant recipients but the sensitivity and specificity of this method are limited. Further developments in coil design, rapid imaging techniques and respiratory monitoring methods are necessary to improve the accuracy of coronary MRA. 相似文献
34.
Philip J. Kilner David N. Firmin Raad H. Mohiaddin Cynthia Sampson S. Richard Underwood 《Magma (New York, N.Y.)》1994,2(3):339-342
Shortening the echo times of magnetic resonance (MR) sequences used for phase-shift velocity mapping to 3.6 ms has extended use of the technique to measurement of velocities in turbulent, poststenotic jet flows. We used a 0.5-T MR machine and field even-echo rephasing (FEER) sequences with 3.6 ms echo times for jet velocity mapping.In vitro trials used continuous flow through a phantom with a 6-mm stenosis. Fifteen patients with mitral and/or aortic valve stenosis and 20 patients with repaired aortic coarctation were studied prospectively, with Doppler ultrasonic measurement of peak jet velocity performed independently on the same day. The clinical contribution of MR jet velocity mapping, used during a 3-year period in 306 patients with congenital and acquired disease of heart valves, great vessels, and conduits, was assessed retrospectively. The 3.6-ms sequence allowed accurate measurement of jet velocities up to 6 m s–1
in vitro (r=0.996). Prospective studies in patients showed good agreement between MR and Doppler measurements of peak velocity:n=38; range, 1.2–6.1 m s–1; mean, 2.7 m s–1; mean of differences (Doppler-MR), 0.22 ms–1; standard deviation of differences, ±0.38 m s–1 (±14%). MR jet velocity mapping proved particularly valuable for assessment and localization of stenoses at sites where ultrasonic access was limited. The technique represents a diagnostic advance which can obviate the need for catheterization in selected cases. 相似文献
35.
Developing motions for simulated humanoids remains a challenging problem. While there exists a multitude of approaches, few of these are reimplemented or reused by others. The predominant focus of papers in the area remains on algorithmic novelty, due to the difficulty and lack of incentive to more fully explore what can be accomplished within the scope of existing methodologies. We develop a language, based on common features found across physics‐based character animation research, that facilitates the controller authoring process. By specifying motion primitives over a number of phases, our language has been used to design over 25 controllers for motions ranging from simple static balanced poses, to highly dynamic stunts. Controller sequencing is supported in two ways. Naive integration of controllers is achieved by using highly stable pose controllers (such as a standing or squatting) as intermediate transitions. More complex controller connections are automatically learned through an optimization process. The robustness of our system is demonstrated via random walkthroughs of our integrated set of controllers. 相似文献
36.
M. A. Schmidt G. Z. Yang J. Keegan P. Jhooti P D. Gatehouse D. H. Carr D. M. Hansell D. N. Firmin 《Magma (New York, N.Y.)》1997,5(2):123-128
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 reducting
the apparent frequency of the respiratory motion. A distribution of interface position, 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. 相似文献
37.
GH Draffan PJ Lewis JL Firmin TW Jordan CT Dollery 《Canadian Metallurgical Quarterly》1976,3(3):489-495
Bacterial luciferase from Photobacterium phosohoreum was found to produce bioluminescence on reaction with FMN and H2O2 in the presence of aldehyde. This luminescence is presumably produced by the same X1 intermediate as that found in FMNH2-O2 initiated luminescence. From the ratio of the light intensities of the FMN-H2O2 initiated reactions, we calculated the association constant of the reaction, luciferase+FMN+H2O2in equilibriumX1, and estimated its temperature dependence. From these results we calculated the thermodynamic parameters of the reaction, luciferase+FMNH2+O2in equilibriumX1. We found that the free energy level of X1 is only 3.2 kcal below that of fr-e FMN and H2O2. We also estimated the thermodynamic parameters of other steps of the luminescent reaction. The values obtained showed that the formation of X1 from luciferase, FMNH2 and O2 involves a positive entropy change, but the intermediate is in a state stabilized against decomposition. Results also suggest a considerable degree of electronic rearrangement on formation of the excited-state molecule from the X1-aldehyde complex. 相似文献
38.
Vassilios S. Vassiliou Katharina Wassilew Donnie Cameron Ee Ling Heng Evangelia Nyktari George Asimakopoulos Anthony de Souza Shivraman Giri Iain Pierce Andrew Jabbour David Firmin Michael Frenneaux Peter Gatehouse Dudley J. Pennell Sanjay K. Prasad 《Magma (New York, N.Y.)》2018,31(1):101-113