Measurement of left ventricular (LV) chamber volume and shape from three-dimensional (3-D) CT images, generated by the fast X-ray CT scanner known as the dynamic spatial reconstructor, has previously been done using manual slice-image editing. To reduce the exorbitant operator analysis time and operator-dependent measurement variations of manual slice-image editing, we have devised a semiautomatic method for LV-chamber extraction. The method draws upon a minimum requirement for selective manual slice-image editing and mostly makes use of automatic image-analysis operations. Detailed validation results over a wide range of hemodynamic and image-analysis conditions show that the measurements of the semiautomatic method strongly correlate with those made via manual slice-image editing and exhibit a lower intertrial variability. Further, the method reduces operator interaction time by nearly an order of magnitude over that of manual slice-image editing, but provides more detailed 3-D structural definition.

Animals↗

PubMedDate not supplied

Parametric display of myocardial function.

Quantitative assessment of regional heart motion has significant potential to provide more specific diagnosis of cardiac disease and cardiac malfunction than currently possible. Local heart motion may be captured from various medical imaging scanners. In this study, 3-D reconstructions of pre-infarct and post-infarct hearts were obtained from the Dynamic Spatial Reconstructor (DSR)[Ritman EL, Robb RA, Harris LD. Imaging physiological functions: experience with DSR. Philadelphia: Praeger, 1985; Robb RA, Lent AH, Gilbert BK, Chu A. The dynamic spatial reconstructor: a computed tomography system for high-speed simultaneous scanning of multiple cross sections of the heart. J Med Syst 1980;4(2):253-88; Jorgensen SM, Whitlock SV, Thomas PJ, Roessler RW, Ritman EL. The dynamic spatial reconstructor: a high speed, stop action, 3-D, digital radiographic imager of moving internal organs and blood. Proceedings of SPIE, Ultrahigh- and High-speed Photography, Videography, Photonics, and Velocimetry 1990;1346:180-91.] (DSR). Using functional parametric mapping of disturbances in regional contractility and relaxation, regional myocardial motion during a cardiac cycle is color mapped onto a deformable heart model to facilitate appreciation of the structure-to-function relationships in the myocardium, such as occurs in regional patterns of akinesis or dyskinesis associated with myocardial ischemia or infarction resulting from coronary artery occlusion.

Animals↗

PubMedDate not supplied

An electron-beam CT approach for transvenous coronary arteriography.

OBJECTIVE: The goal is to image the 3D anatomy of the major coronary arteries within a single breath-hold and using a single intravenous injection of contrast agent. MATERIALS AND METHODS: With use of an electron-beam CT (EBCT) scanner, operated in its multislice scan mode (using all four target rings, each scanning two nominal 8 mm thick slices in a total time interval of 224 ms), a radiologically realistic thorax phantom containing a heart with coronary arteries (opacified with 40 mg iodine/ml) was scanned six times with the patient table advanced by a 2 mm step into the scanner between each scan. The normalized and scaled sinogram data were transferred to an off-line computer and reconstructed using our own implementation of a 3D algebraic reconstruction technique that takes into account the exact 3D relationship of the X-ray source and detector elements of the EBCT. RESULTS: A single volume image consisting of 40 slices, at 2 mm intervals and each uniformly 3.7 mm thick, depicted the lumina of the coronary arteries with greater anatomic detail than the "original" images at 8 mm, primarily because of the reduced partial volume effect. CONCLUSION: Our preliminary results suggest that EBCT, operated in multislice scan mode, may be useful for transvenous coronary angiography performed within a single breath-hold.

Coronary Angiography↗

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Measurement of in vivo myocardial microcirculatory function with electron beam CT.

PURPOSE: The purpose of this work was to examine the capability of electron beam CT (EBCT) to characterize responses of recruitable (capillaries and small arterioles) compared with nonrecruitable (small to large arterioles) myocardial microvessels to vasoactive substances. METHOD: Myocardial perfusion (F) and total intramyocardial blood volume (BV) of the anterior cardiac wall were quantitated in 36 pigs, using EBCT and intravenous contrast agent injections, before and after intracoronary administration of either NG-monomethyl-L-arginine (L-NMMA), nitroglycerin, adenosine, or saline. Plotting the relationship of BV and F provided values for the recruitable and nonrecruitable microvascular transit times and BV allotment. RESULTS: Nitroglycerin increased nonrecruitable BV by 84.5+/-7.4%, whereas adenosine increased both recruitable and nonrecruitable microvascular BV (47.1+/-18.9 and 66.0+/-10.9%, respectively). L-NMMA led to a 25.1% decrease only in the recruitable BV. In the control group, no changes were observed. CONCLUSION: Characteristic responses of different-size myocardial microvessels may be inferred with EBCT, which provides a unique opportunity to portray intramyocardial microcirculatory function noninvasively.

Animals↗

PubMedDate not supplied

Temporospatial heterogeneity of myocardial perfusion and blood volume in the porcine heart wall.

Spatial heterogeneity of myocardial perfusion has been recognized for many years. Whether this is primarily the result of heterogeneity of parameters such as myocardial metabolism, of intramyocardial mechanical forces, or of vasomotor function within the myocardial microcirculation, is not clear. A practical problem is that it has been almost impossible to measure any two of these parameters simultaneously in the same piece of myocardium so that an unambiguous correlation, much less a cause-and-effect relationship, has been difficult to establish. In this study of six anesthetized pigs, we propose that whole-body computed tomography is a method for providing the simultaneous measurement of heterogeneity of myocardial perfusion (F) and myocardial blood volume (rho). The first finding was that the empirical relationship rho=AF+BF(0.5) between myocardial blood flow (F) and intramyocardial blood volume (rho) is maintained over a range of sizes of regions of interest (approximately 1 to 0.125 cm3) within the myocardium of each individual animal despite the spatial heterogeneity of the F and the rho values. The value of A ranges from 0.014 to 0.021 min and of B ranges from 0.061 to 0.076 ml(0.5) g(-0.5) min(0.5). A second finding was that the pattern of spatial heterogeneity of F and of rho remained reasonably stable over at least a 1 h period.

Animals↗

PubMedDate not supplied

Mayo Clinic and Medical School Biodynamics Research Unit.

The facilities that make up the Mayo Biodynamics Research Unit include the dynamic spatial reconstructor (DSR), which when fully operational will generate raw data at 200 million samples per second. Processing of these data will require a computer capable of several billion arithmetic operations per second.

Biomechanical Phenomena↗

PubMedDate not supplied

Dynamic image-adaptive x-ray beam limiters.

The imaging capability of the dynamic spatial reconstructor (DSR), a fast (60/second), synchronous, multislice (up to 240) computed x-ray tomography scanner, has been limited by the suboptimal match of the dynamic range of the x-ray projection images with that of the image-intensified charge-coupled device (CCD) video sensors. Effective blockage of the "raw" beam component of the projection images by fixed shutters is generally impossible because of the rapid change in the multiple angles of view that result from the 15 RPM rotation of the scanner assembly about the object of study. For this reason a programmable, dynamic, image-adaptive x-ray beam shutter system has been developed to reduce the "raw" beam component of the x-ray image without degrading the image in the region of interest. This system is designed to dynamically position 28 shutters (two for each of 14 x-ray sources) continuously and independently, as a function of the angle of view, so as to selectively obscure any unattenuated "raw" x-ray beam passing alongside the object of study at all angles of view for each x-ray source.

Equipment Design↗

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Effect of heparin-binding growth factor-1 on bronchial healing in canine lung allograft transplantation.

Failure of airway healing complicates lung transplantation. Local application of heparin-binding growth factor-1 induces neovascularization in vivo. To determine the effect of direct application of heparin-binding growth factor-1 on bronchial healing, we performed single left lung allotransplantations in 12 dogs, and wrapped the bronchial anastomosis with Gelfoam impregnated with either recombinant heparin-binding growth factor-1 (100 micrograms, n = 6) or saline solution (n = 6) in a blinded fashion. After 21 days, the bronchial anastomosis was studied by gross examination, light and electron microscopy, bromodeoxyuridine uptake, measurement of bronchial breaking strength, and high-speed computerized tomography to assess bronchial cross-sectional area and distensibility. The transplanted lung was examined histologically for concomitant lung rejection. No significant difference was found between the two groups in histologic bronchial healing scores, proliferation index, bronchial breaking strength, cross-sectional area, anastomotic distensibility, or local blood flow as estimated by high-speed computerized tomography scan. In the growth factor group, both increased neovascularization and lung rejection were found at histologic evaluation. We conclude that, although the use of heparin-binding growth factor-1 increased perianastomotic neovascularization, it did not contribute to improved bronchial healing, possibly because of increased lung rejection.

Anastomosis, Surgical↗

PubMedDate not supplied

Effects of acute changes in canine LV-chamber volume and shape on accuracy of impedance catheter estimates of LV-chamber volume.

The accuracy with which a multiple-electrode impedance catheter (IC) tracks instantaneous global, in-situ left ventricular (LV) volumes was tested in 13 anesthetized dogs scanned in the Dynamic Spatial Reconstructor (DSR), a fast volumetric computed tomographic (CT) scanner. All dogs were scanned during control conditions and during an acute hemodynamic intervention. Hypertonic saline calibrations were performed for the IC prior to each DSR scan. In six of the dogs the IC-derived LV end-diastolic volume (Y) correlated with the DSR-derived global LV end-diastolic volume (X) as follows: end-diastolic volume, Y = 1.01X - 9.9, r = 0.812. The IC-derived LV end-diastolic volume, under control conditions, correlated with the DSR-derived truncated (i.e., that region of the LV chamber between the proximal and distal electrodes of the IC catheter) LV end-diastolic volume, Y = 1.00X + 17.4, r = 0.803. Under reduced preload the relation was Y = 1.3X - 15.26, r = 0.911. The segmental volume (between adjacent sensing electrodes on the IC) at the basal portion of the LV correlated poorly (Y = 1.88X + 3.3, r = 0.459 etc.), but correlated better at mid- and more apical LV levels (Y = 0.97X + 2.7, r = 0.762). Correlations between segmental stroke volumes were similar at basal (Y = 1.31X + 1.60, r = 0.815) and mid- and more apical levels (Y = 1.42X + 0.11, r = 0.763). Stroke volume during acute ischemia (two dogs) was Y = 1.33X - 1.41, r = 0.717; during acutely decreased preload (four dogs) it was Y = 1.24X - 2.88, r = 0.572). Thus, the IC tracks the changes in LV-chamber volume throughout a cardiac cycle quite well under a variety of conditions, but accuracy deteriorates as the shape of the LV chamber changes in response to changes in hemodynamic loading or local myocardial ischemia.

Animals↗

PubMedDate not supplied

Noninvasive numerical vivisection of anatomic structure and function of the intact circulatory system using high temporal resolution cylindrical scanning computerized tomography.

A high temporal resolution cylindrical scanning computerized tomographic system (DSR) is being built for study of anatomic structural/functional relationships of heart, lungs, vascular anatomy, and circulatory dynamics in any region of the body. Unlike current commercial CT scanners which scan only one or, at most, a few cross sections at a time, cylindrical scanners such as the current Mayo SSDSR and upcoming DSR scan nearly 250 cross sections simultaneously. Twenty-eight or more multiplanar images over a range of 160 or more degrees of an entire rapidly moving structure such as the heart or a segment of the circulation will be recorded in periods as short as 10 msec by the DSR at 60/sec rates and stored in computer memory. The scanned volumes can then be sectioned mathematically in any direction at will, including zooming in on regions of interest to problems at hand (e.g., clinical diagnoses). Progression from biomedical investigation to practical clinical and health care uses requires development of special-purpose, readily replicable, economical (but very high speed and volume) data handling and computational devices. The ultimates overall objective is to quantitatively characterize the performance of the human cardiopulmonary and circulatory systems utilizing pertubations associated with various types of physiologic stress and congenital or acquired disease processes including neoplasia.

Animals↗