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Biomedical subjects

T Parrish

Publications and source records attributed to T Parrish.

9 recordsLinked to original sources
PubMed1995

Bradykinin antagonism inhibits the antigrowth effect of converting enzyme inhibition in the dog myocardium after discrete transmural myocardial necrosis.

BACKGROUND: Converting enzyme inhibitor (CEI) therapy, but not angiotensin II subtype I receptor blockade, has been shown to attenuate left ventricular remodeling in the dog after transmyocardial direct current (DC) shock. The purpose of this study was to address the importance of preservation of bradykinin to the antiremodeling effect of CEI treatment in this model. METHODS AND RESULTS: Twenty-four hours after DC shock, adult mongrel dogs were assigned to one of three groups: a control group; a group treated with ramipril 10 mg BID; and a group treated with ramipril 10 mg BID along with a continuous subcutaneous infusion of HOE 140, a bradykinin antagonist. To assess change in left and right ventricular structure, a magnetic resonance imaging (MRI) study was performed 4 weeks after DC shock and compared with a baseline MRI study performed before DC shock. The increase in left ventricular mass (mean +/- SEM) in the control group was similar to that observed in the CEI-HOE 140 group (+0.73 +/- 0.19 versus +0.75 +/- 0.18 g/kg, P = NS), but both were greater than the change in mass in the ramipril group (-0.48 +/- 0.13 g/kg, P = .004 and P = .0005, respectively). No significant change occurred in left ventricular volume or right ventricular structure in any group. Mean arterial pressure was reduced by ramipril compared with the control group (-8 +/- 2 versus +7 +/- 2 mm Hg, P = .03), and this effect was not blunted by the addition of HOE 140 (-7 +/- 3 mm Hg). CONCLUSIONS: Prevention by ramipril of the early increase in left ventricular mass in the DC shock model appears to be related to the preservation of bradykinin.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

Continuous update with random encoding (CURE): a new strategy for dynamic imaging.

Although dynamic imaging is presently used for various applications, it is still limited by the temporal resolution. In this paper, we present a new technique that uses a random phase-encoding strategy to facilitate faster and smoother update of images and to improve the temporal resolution in dynamic studies. The technique was implemented on a conventional clinical scanner and demonstrated with various in vivo studies. Technical details, simulations, and experimental results are described. Images from experimental studies indicate that the new technique is robust in generating dynamic images and can be potentially utilized for clinical applications.

Abdomen↗
PubMed1995

Retrospective estimation and correction of physiological fluctuation in functional MRI.

Image-to-image fluctuation due to physiological motion is a major limitation to the accurate detection of neuronal activity with functional MRI. In this paper, a new and general technique for the estimation and compensation of the physiological effects is presented. By simultaneously monitoring the respiration and heart beat during the acquisition of imaging data, and retrospectively synchronizing the imaging data with physiological activity, physiological effects are estimated and removed. This technique does not rely on the periodicity of the respiration or the heart beat, does not affect the signal changes arising from neuronal activation, and is beneficial to images acquired with any speed. Experimental studies performed with FLASH and EPI sequences have demonstrated that the new technique is effective in reducing physiological fluctuation and improving the sensitivity of functional MRI and is generally applicable.

Algorithms↗
PubMed1994

Reduction of field of view for dynamic imaging.

This paper describes a simple technique that improves the temporal resolution for certain dynamic imaging applications. The technique is based on the assumption that the image to image intensity changes sought in dynamic imaging studies are sometimes localized, and a smaller field of view can be used to reduce imaging time. Technical details and experimental results are presented. Experimental results show that this technique works reasonably well for in vivo applications.

Algorithms↗
PubMed1994

A new T2 preparation technique for ultrafast gradient-echo sequence.

The T2 contrast in images obtained with driven equilibrium (90degreesx-180degreesx-90degreesx) prepared ultrafast gradient-echo sequence is compromised by the longitudinal magnetization build-up after the second 90degreesx pulse, which does not carry T2 information. This paper describes a new T2 contrast preparation technique for ultrafast gradient-echo sequence that suppresses the signal arising from the build-up. By dephasing in the preparation and rephasing in the acquisition of the gradient echoes, the new technique eliminates signals that are not dictated by the T2 contrast in a driven-equilibrium approach. Consequently, it generates an image that is essentially T2-weighted. Phantom and in vivo experiments were conducted to validate the technique and to demonstrate its clinical utility. These studies indicate that the technique works properly and can be used for in vivo studies.

Animals↗
PubMed1994

Concepts of myocardial perfusion imaging in magnetic resonance imaging.

Based on the major innovations in ultrafast magnetic resonance (MR) imaging in recent years, myocardial perfusion imaging with MR has become the focus of many investigators. Two major approaches to myocardial perfusion imaging involve either exogenous or endogenous contrast agents. For the first category of perfusion experiments, we review the characteristics of the common contrast agents and MR techniques for experimental and clinical first-pass studies and in particular address the question of extracting quantitative estimates for myocardial blood flow (milliliters per minute per gram) and volume (milliliters per gram). We demonstrated quantitative perfusion analysis using intravascular relaxation agents and heavily T1-weighted ultrafast gradient echo sequences. Signal time curves need to be transformed to content time curves and the resulting residue functions were analyzed with a multiple-pathway, axially distributed perfusion model. These preliminary results suggest that quantitative assessment of myocardial perfusion is feasible, but additional studies should provide further confidence for this novel MR approach. The exact sensitivity and specificity of MR first-pass imaging in conjunction with extracellular contrast agents in patient studies and its diagnostic accuracy as judged against coronary angiography and scintigraphic perfusion imaging remain yet undefined. The second category of perfusion experiments does not require exogenous contrast agents and has not yet been tested in patient studies. Progress is reported on several MR perfusion-sensitive methods that use the tissue water as an endogenous contrast agent in combination with magnetization transfer techniques as well as paramagnetic deoxyhemoglobin for measuring tissue oxygenation using heavily T2*-weighted sequences for blood oxygen-level-dependent contrast. Possible future directions and developments toward further improvements for MR myocardial perfusion measurements and contraction-perfusion matching are also addressed.

Blood Volume↗
PubMed1992

Rapid, accurate and simultaneous noninvasive assessment of right and left ventricular mass with nuclear magnetic resonance imaging using the snapshot gradient method.

Left ventricular, and possibly also right ventricular, mass is an important determinant of prognosis in cardiovascular disease. Consequently, noninvasive estimation of ventricular mass may be an important clinical investigation. The ideal technique for this purpose would be widely available and accurate, employ short study times and avoid exposure to contrast agents and radiation. Conventional nuclear magnetic resonance (NMR) imaging fulfills most of these criteria, but it is time-consuming and expensive. Moreover, its accuracy in estimating right ventricular mass has yet to be assessed. Accordingly, high speed NMR imaging using the snapshot gradient echo technique was used to assess right and left ventricular mass in 10 dogs and the results were compared with values obtained at autopsy, which ranged from 26.1 to 52.9 and 61 to 119.8 g, respectively. The mean absolute difference between the NMR imaging estimates and autopsy findings was 2 +/- 1.2 g (range 0.4 to 4.2) for right ventricular mass and 4.4 +/- 1.7 g (range 1.8 to 6.6) for left ventricular mass. Total NMR imaging time was less than or equal to 5 min. These data demonstrate that high speed NMR imaging can be used to accurately estimate right as well as left ventricular mass.

Animals↗
PubMed1990

3-D FLASH imaging using a single surface coil and a new adiabatic pulse, BIR-4.

A new adiabatic pulse, which can induce uniform and arbitrary flip angles despite the presence of transmitter coil magnetic field (B1) inhomogeneities, is employed for 3-D fast imaging using a single surface coil for pulse transmission and signal detection. Computer calculations and phantom, rat, and human surface coil imaging experiments demonstrate the utility of this adiabatic pulse for T1-weighted imaging with a transmitter coil which generates a highly inhomogeneous B1 field profile.

Animals↗