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Biomedical subjects

D Firmin

Publications and source records attributed to D Firmin.

9 recordsLinked to original sources
PubMed2001

Dual contrast TrueFISP imaging for left ventricular segmentation.

Based on varying tissue contrasts at different RF flip angles, a new TrueFISP imaging strategy for cardiac function measurement is presented. A single breath-hold dual RF flip angle cine multi-slice TrueFISP imaging sequence was implemented which provides a significant increase in signal contrast between blood and myocardium. The increase in image contrast combined with different characteristics in RF response facilitates the delineation of cardiovascular borders. Based on this imaging strategy it is demonstrated how a simple 2D histogram clustering algorithm can be used for the fully automatic segmentation of the left ventricular (LV) blood pool. The method is validated with data acquired from 10 asymptomatic subjects, and the results are shown to be comparable to that of manual delineation by experienced observers.

Algorithms↗
PubMed2001

Navigator echoes in cardiac magnetic resonance.

Navigator echoes are frequently used in cardiac magnetic resonance to monitor respiratory motion and have proved particularly useful in coronary artery imaging techniques where they allow the acquisition of data over multiple reproducible breathholds and during free breathing. The large number of variables involved in their use, however, is such that an optimal method of application may yet have to be developed. In this review article, we examine the issues relating to their implementation and describe the ways in which the navigator information obtained may be used.

Coronary Vessels↗
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↗
PubMed1994

The application of breath hold phase velocity mapping techniques to the measurement of coronary artery blood flow velocity: phantom data and initial in vivo results.

A segmented kappa-space breath hold phase velocity mapping technique has been developed for the study of coronary artery blood flow velocity. In vitro validation has been performed using a number of pulsatile flow phantoms and the accuracy of the technique for determining the velocity increase at the site of a stenosis demonstrated in several phantom models. Examples of both in-plane and through-plane velocity maps of the left anterior descending and right coronary arteries of normal subjects in early diastole are presented. In one subject, through-plane velocity maps were obtained in the right and left anterior descending arteries throughout the cardiac cycle in order to generate flow velocity time curves. The problems associated with coronary artery velocity mapping are discussed.

Artifacts↗
PubMed1992

Inotropic polyazapentalene sulmazole analogues.

Aryl substituted 1H-imidazo[1,2-a]imidazole 8, imidazo[2,1-b]thiazole 9, 1,4-dihydroimidazo[4,5-d]imidazole 11, and 1(2),4-dihydroimidazo[4,5-c]pyrazoles 12-17 have been prepared. An X-ray crystallographic study confirmed the structure of 8 and showed this analogue to exist as the 1H-tautomer. These heterocycles were evaluated as inotropic agents and analogues 12, 15, and 17 found to display inotropic properties which were less potent in vitro, but more potent in vivo, than those of sulmazole. Structure-activity relationships are discussed.

Animals↗
PubMed1990

Inotropic "A" ring substituted sulmazole and isomazole analogues.

A series of "A" ring substituted sulmazole and isomazole analogues have been prepared and evaluated as inotropic agents. pKA's, protonation sites, and log P values were measured for selected compounds and their electronic properties were calculated. No simple correlation between inotropic activity and pKA, protonation site, or log P value was observed. However, in vitro inotropism did correlate with the calculated charge density of the "B" ring imidazo nitrogen atom. The 6-position of sulmazole appeared to be the most tolerant toward substituents, the 6-amino derivative 7 being a more potent inotrope than sulmazole itself. 4-Methoxyisomazole 13 had comparable in vivo inotropic properties to those of isomazole.

Animals↗
PubMed1988

Comparison of magnetic resonance imaging with echocardiography and radionuclide angiography in assessing cardiac function and anatomy following Mustard's operation for transposition of the great arteries.

The Mustard operation in infancy and childhood has successfully palliated many patients with transposition of the great arteries who have now survived to adulthood. Right ventricular dysfunction and tricuspid regurgitation are important determinants of late morbidity and mortality. The value of noninvasive magnetic resonance imaging (MRI) in the assessment of cardiac function and anatomy 9 to 20 years after this procedure has been investigated, and compared with findings on echocardiography, radionuclide ventriculography and angiography in 17 adult patients. Ejection fractions measured by MRI were higher compared with radionuclide ventriculography. The correlation for the left ventricle was closer (r = 0.75) than for the right ventricle (r = 0.49). Tricuspid regurgitation was assessed by Doppler echocardiography and by MRI using the right/left ventricular stroke volume ratio. The mean stroke volume ratio in those with Doppler evidence of tricuspid regurgitation was 1.6:1 compared to 1.1:1 in those without, and this difference reached significance (p less than 0.01). The anatomy of the great arteries was clearly visible in all patients. Five patients had a residual ventricular septal defect which, with the exception of 1 small defect, was easily visualized. The intraatrial baffle was best seen in transverse slices, and the systemic venous connection showed as a relatively narrow channel lying in the posterior part of the cavity. In general, baffle anatomy was easier to assess on 2-dimensional echocardiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

Nuclear magnetic resonance imaging of the heart. Current status and future prospects.

The basic principles and current status of proton nuclear magnetic resonance imaging are outlined. Nuclear magnetic resonance images of the heart have improved in quality with advances in technique and better gating but clinical experience remains very limited. Myocardial infarction has been shown in animals and man, and plaques of atheroma have been seen with nuclear magnetic resonance flow studies. Further improvements in image quality, faster examination times, 23Na imaging, and the use of paramagnetic contrast agents are advances that are anticipated in the near future.

Animals↗