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Biomedical subjects

L E Fencil

Publications and source records attributed to L E Fencil.

8 recordsLinked to original sources
PubMed1992

Metabolic effects of adenosine on regional myocardial ischemia by phosphorus 31 nuclear magnetic resonance spectroscopy.

The metabolic effects of adenosine on regionally ischemic myocardium were investigated in an open-chest rabbit model by means of phosphorus 31 nuclear magnetic resonance (NMR) spectroscopy. Sixteen anesthetized New Zealand white rabbits were subjected to thoracotomy; a reversible snare occluder was placed around a large branch of the left circumflex coronary artery, and an NMR surface coil was positioned adjacent to the myocardium perfused by this vessel. The animals were placed in a 2.0 T CSI spectrometer (GE Medical Systems, Fremont, Calif.), and baseline spectra were acquired. Eight animals were treated with intravenous adenosine (25 mg/kg), and eight rabbits served as control subjects. All animals were subjected to a 10-minute period of ischemia followed by a period of reperfusion. NMR spectra were acquired during both intervals. During the occlusion period, expected increases in inorganic phosphate levels and decreases in phosphocreatine levels were observed in both groups; however, inorganic phosphate increased less in adenosine-treated animals (adenosine: 33 +/- 2.8% total spectral area during occlusion vs control: 41 +/- 3.1%) and phosphocreatine diminished less with adenosine (adenosine: 26 +/- 3% vs control: 13 +/- 1.2%; p < 0.002). No significant differences were seen in beta-adenosine triphosphate levels. In both groups the metabolite levels during reperfusion recovered to near baseline values, although phosphocreatine remained slightly higher in the treated group during early reperfusion. An apparent cardioprotective effect of adenosine on relative phosphocreatine and inorganic phosphate levels can be observed in intact rabbits by means of phosphorus 31 NMR spectroscopy.

Adenosine↗
PubMed1991

Determination of instantaneous and average blood flow rates from digital angiograms of vessel phantoms using distance-density curves.

We have developed a new method for quantitation of blood flow rates based on determination of the spatial shift of the distribution of contrast material in opacified vessels in digital angiograms that are acquired while the contrast material proceeds through the vessel. The distance that the contrast material travels during the time between image acquisitions is determined by comparison of density-vs.-distance curves, which represent the distribution of contrast material along the length of the vessel in the respective images. The flow rate between image acquisitions is calculated by multiplication of the distance traveled by the frame rate and the vessel cross-sectional area. Therefore, for high-frame-rate acquisitions, "instantaneous" flow rates can be determined. In these vessel-phantom studies, the root-mean-square (RMS) difference between instantaneous flow rates measured with our technique and those measured with an electromagnetic method was 2.9 ml/sec; the RMS difference for average flow rates was 0.8 ml/sec.

Absorptiometry, Photon↗
PubMed1989

Measurement of absolute flow rate in vessels using a stereoscopic DSA system.

We used a stereoscopic digital subtraction angiography (DSA) system to measure absolute blood flow rates in vessels. The magnification factor and the three-dimensional orientation of a selected vessel are obtained from automated analysis of stereoscopic DSA images. The cross-sectional area of the vessel is determined from the vessel diameter, which is measured with an iterative deconvolution technique. The time required for fluid to flow through a selected segment of a vessel is determined from the automated analysis of contrast medium 'time-density' curves. The effectiveness of these combined techniques was demonstrated in measurement of rates of both continuous and pulsatile flow in a vessel phantom, with the actual flow rate calibrated volumetrically or by an electromagnetic flowmeter. We have obtained accuracies in measured flow rates of approximately 5% and 18% for continuous and pulsatile flow respectively.

Angiography↗
PubMed1988

Accurate analysis of blood vessel sizes and stenotic lesions using stereoscopic DSA system.

We have developed a technique to determine accurately the magnification factor and three-dimensional orientation of a vessel segment from a stereoscopic pair of digital subtraction angiograms (DSA). Our DSA system includes a stereoscopic x-ray tube with a 25-mm focal spot shift. The magnification and orientation of a selected vessel segment are determined from the distance and direction of the focal spot shift and the stereoscopic discrepancy in image positions for that segment. Our results indicate that the accuracies of determining the magnification and orientation are less than 1% and approximately 5 degrees, respectively. After the magnification and orientation are determined accurately, an iterative deconvolution technique for the measurement of vessel image size is applied to the selected vessel segment. This iterative deconvolution technique provides the best estimate of vessel image size by taking into account the unsharpness of the digital system. With this technique, the vessel image size can be determined to an accuracy of approximately 1.0 mm, which corresponds to one third the pixel size of our DSA system. Information derived from stereoscopic analysis and iterative deconvolution thus allows accurate calculation of actual vascular dimensions from DSA images.

Angiography↗
PubMedDate not supplied

Image feature analysis and computer-aided diagnosis in digital radiography. 2. Computerized determination of vessel sizes in digital subtraction angiography.

We developed an iterative deconvolution technique to determine the size of a "blurred" vessel in a digital subtraction angiographic (DSA) image by taking into account the unsharpness of the DSA system. Initially, a region of interest over a small segment of the contrast-filled vessel was selected in a DSA image, and the center line of the opacified vessel was determined by polynomial curve fitting of the locations of the peak pixel values along the vessel image. The blurred image profile was then obtained from pixel values across the vessel in a direction perpendicular to the center line. This measured profile was compared iteratively with a calculated profile for various size vessels, which was obtained from a cylindrical vessel model and from the line spread function, until the root-mean-square difference between the two profiles was minimized. The size of a cylindrical vessel yielding the matched profile was considered the best estimate of the unknown vessel size. Studies with a blood vessel phantom indicated that vessels larger than 0.5 mm could be measured with an accuracy and precision of approximately 0.1 mm, which is about 1/3 of the pixel size used in our DSA system. Details of our approach and some clinical vessel images with and without simulated stenotic lesions are presented.

Angiography↗
PubMedDate not supplied

Determination of three-dimensional structure in biplane radiography without prior knowledge of the relationship between the two views: theory.

A novel method allows the determination of three-dimensional object structure from two projection images that are obtained at arbitrary, unknown orientations. Only minimal prior information concerning the imaging system is required. First, the image coordinates of eight or more object points that can be identified unambiguously in both views are used to determine the relative geometry of the two projections. Subsequently, the three-dimensional coordinates of the identified object points are determined, to within a scale factor, from the image coordinates of the points and the calculated imaging system geometry. A theoretical description of the overall method is provided, along with techniques for the reduction of effects of experimental errors and numerical errors that may arise in the course of the calculations. Methods to retrieve the absolute scale of the object are discussed also.

Mathematics↗
PubMedDate not supplied

Propagation and reduction of error in three-dimensional structure determined from biplane views of unknown orientation.

We are developing a technique for determination of the three-dimensional (3-D) structure of vascular objects from two radiographic projection images acquired at arbitrary and unknown relative orientations. No separate calibration steps are required with this method, which exploits an inherent redundancy of biplane imaging to extract the imaging geometry as well as the 3-D locations of eight or more object points. The theoretical basis of this technique has been described previously. In this paper, we review the method from the perspective of linear algebra and describe an improvement, not heretofore reported, that reduces the method's sensitivity to experimental error. We then examine the feasibility and inherent accuracy of this approach by computer simulation of biplane imaging experiments. The precision with which 3-D object structure may be retrieved, together with the dependence of precision on the actual imaging geometry and errors in various measured quantities, is studied in detail. Our simulation studies show that the method is not only feasible but potentially accurate, typically determining object-point configurations with root-mean-square (RMS) error on the order of 1 to 2 mm. The method is also quite fast, requiring approximately one second of CPU time on a VAX 11/750 computer (0.6 MIPS).

Angiography↗