Initial results from a prototype whole-body photon-counting computed tomography system

X-ray computed tomography (CT) with energy-discriminating capabilities presents exciting opportunities for increased dose efficiency and improved material decomposition analyses. However, due to constraints imposed by the inability of photon-counting detectors (PCD) to respond accurately at high photon flux, to date there has been no clinical application of PCD-CT. Recently, our lab installed a research prototype system consisting of two x-ray sources and two corresponding detectors, one using an energy-integrating detector (EID) and the other using a PCD. In this work, we report the first third-party evaluation of this prototype CT system using both phantoms and a cadaver head. The phantom studies demonstrated several promising characteristics of the PCD sub-system, including improved longitudinal spatial resolution and reduced beam hardening artifacts, relative to the EID sub-system. More importantly, we found that the PCD sub-system offers excellent pulse pileup control in cases of x-ray flux up to 550 mA at 140 kV, which corresponds to approximately 2.5×10¹¹ photons per cm² per second. In an anthropomorphic phantom and a cadaver head, the PCD sub-system provided image quality comparable to the EID sub-system for the same dose level. Our results demonstrate the potential of the prototype system to produce clinically-acceptable images in vivo.

Derivation of myocardial fiber stiffness equation based on theory of laminated composite

The constitutive equation with stress-dependent coefficients for laminated composite is derived and employed for iterative determination of myocardial fiber's stiffness equation E(f) = Ksigma(f) + C from myocardial strip's stiffness equation E(s) = K(s)sigma(s) + C(s). The strip's stiffness constants K(s) and C(s) are estimated by the least-square curve fitting of the stress-strain data experimentally obtained from uniaxially stretching of strips of left ventricular heart wall excised from seven canine hearts. The values of K and C computed at selected fiber orientations across the thickness of the strip and using three, five, and ten-layer approximations are reported.

Low vasa vasorum densities correlate with inflammation and subintimal thickening: potential role in location--determination of atherogenesis

OBJECTIVES

To assess the role of coronary vasa vasorum (VV) spatial distribution in determining the location of early atherosclerotic lesion development.

METHODS AND RESULTS

Six, 3-month-old, female, crossbred swine were fed 2% high-cholesterol (HC) diet for 3 months prior to euthanasia. Six other pigs were fed normal diet (N) for the entire 6 months. Right coronary arteries were harvested and scanned intact with micro-CT (20mum cubic-voxel-size). After scanning, randomly selected cross-sectional histological sections were stained for nuclear-factor kappaB (NF-kappaB), hypoxia-inducible factor-1alpha (HIF-1alpha), macrophages, von-Willebrand-factor, dihydroethidium (DHE), tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). The number of positive stained cells, as well as intima-to-media ratio, were compared with VV density (#/mm(2)) obtained from micro-CT images (which closely matched the location of the histological sections) in each of four equal quadrants of the coronary vessel wall. In normal, as well as HC pigs, the number of NF-kappaB (r=0.73 and 0.70), HIF-1alpha (r=0.74 and 0.77), TNF-alpha (r=0.58 and 0.72) and IL-6 (r=0.70 and 0.72) positive cells as well as the expression of DHE (Kendall tau coefficient -0.64 and -0.63) inversely correlated with VV density. In HC the VV density also inversely correlated with intima/media ratios (r=0.65).

CONCLUSIONS

Our data suggest that low VV density territories within the coronary vessel wall are susceptible to hypoxia, oxidative stress and microinflammation and may therefore be starting points of early atherogenesis.

A technical solution to avoid partial scan artifacts in cardiac MDCT

Quantitative evaluation of cardiac image data obtained using multidetector row computed tomography (CT) is compromised by partial scan reconstructions, which improve the temporal resolution but significantly increase image-to-image CT number variations for a fixed region of interest compared to full reconstruction images. The feasibility of a new approach to solve this problem is assessed. An anthropomorphic cardiac phantom and an anesthetized pig were scanned on a dual-source CT scanner using both full and partial scan acquisition modes under different conditions. Additional scans were conducted with the electrocardiogram (ECG) signal being in synchrony with the gantry rotation. In the animal study, a simple x-ray detector was used to generate a signal once per gantry rotation. This signal was then used to pace the pig's heart. Phantom studies demonstrated that partial scan artifacts are strongly dependent on the rotational symmetry of angular projections, which is determined by the object shape and composition and its position with respect to the isocenter. The degree of partial scan artifacts also depends on the location of the region of interest with respect to highly attenuating materials (bones, iodine, etc.) within the object. Single-source partial scan images (165 ms temporal resolution) were significantly less affected by partial scan artifacts compared to dual-source partial scan images (82 ms temporal resolution). When the ECG signal was in synchrony with the gantry rotation, the same cardiac phase always corresponded to the same positions of the x-ray tube(s) and, hence, the same scattering and beam hardening geometry. As a result, the range of image-to-image CT number variations for partial scan reconstruction images acquired in synchronized mode was decreased to that achieved using full reconstruction image data. The success of the new approach, which synchronizes the ECG signal with the position of the x-ray tube(s), was demonstrated both in the phantom and animal experiments.

Reproducibility of global and local reconstruction of three-dimensional micro-computed tomography of iliac crest biopsies

Variation in computed tomography (CT) image gray-scale and spatial geometry due to specimen orientation, magnification, voxel size, differences in X-ray photon energy and limited field-of-view during the scan, were evaluated in repeated micro-CT scans of iliac crest biopsies and test phantoms. Using the micro-CT scanner on beamline X2B at the Brookhaven National Laboratory's National Synchrotron Light Source, 3-D micro-CT images were generated. They consisted of up to 1024 x 2400(2), 4-microm cubic voxels, each with 16-bit gray-scale. We also reconstructed the images at 16-, 32-, and 48-microm voxel resolution. Scan data were reconstructed from the complete profiles using filtered back-projection and from truncated profiles using profile-extension and with a Local reconstruction algorithm. Three biopsies and one bone-like test phantom were each rescanned at three different times at annual intervals. For the full-data-set reconstructions, the reproducibility of the estimates of mineral content of bone at mean bone opacity value, was +/-28.8, i.e., 2.56%, in a 4-microm cubic voxel at the 95% confidence level. The reproducibility decreased with increased voxel size. The interscan difference in imaged bone volume ranged from 0.86 4-microm 0.64% at 4-microm voxel resolution, and 2.64 4-microm 2.48% at 48 microm.

Long-term risedronate treatment normalizes mineralization and continues to preserve trabecular architecture: sequential triple biopsy studies with micro-computed tomography

The objective of the study was to assess the time course of changes in bone mineralization and architecture using sequential triple biopsies from women with postmenopausal osteoporosis (PMO) who received long-term treatment with risedronate. Transiliac biopsies were obtained from the same subjects (n = 7) at baseline and after 3 and 5 years of treatment with 5 mg daily risedronate. Mineralization was measured using 3-dimensional (3D) micro-computed tomography (CT) with synchrotron radiation and was compared to levels in healthy premenopausal women (n = 12). Compared to the untreated PMO women at baseline, the premenopausal women had higher average mineralization (Avg-MIN) and peak mineralization (Peak-MIN) by 5.8% (P = 0.003) and 8.0% (P = 0.003), respectively, and lower ratio of low to high-mineralized bone volume (BMR-V) and surface area (BMR-S) by 73.3% (P = 0.005) and 61.7% (P = 0.003), respectively. Relative to baseline, 3 years of risedronate treatment significantly increased Avg-MIN (4.9 +/- 1.1%, P = 0.016) and Peak-MIN (6.2 +/- 1.5%, P = 0.016), and significantly decreased BMR-V (-68.4 +/- 7.3%, P = 0.016) and BMR-S (-50.2 +/- 5.7%, P = 0.016) in the PMO women. The changes were maintained at the same level when treatment was continued up to 5 years. These results are consistent with the significant reduction of turnover observed after 3 years of treatment and which was similarly maintained through 5 years of treatment. Risedronate restored the degree of mineralization and the ratios of low- to high-mineralized bone to premenopausal levels after 3 years of treatment, suggesting that treatment reduced bone turnover in PMO women to healthy premenopausal levels. Conventional micro-CT analysis further demonstrated that bone volume (BV/TV) and trabecular architecture did not change from baseline up to 5 years of treatment, suggesting that risedronate provided long-term preservation of trabecular architecture in the PMO women. Overall, risedronate provided sustained benefits on mineralization and architecture, two key determinants of bone strength, over 5 years lending support for its long-term efficacy in fracture risk reduction.

[Minimally invasive quantitation of myocardial microvascular function using computed tomography: the blood volume-to-flow relationship]

The intramyocardial coronary microvasculature has an important role in regulating regional myocardial perfusion. Pathologic alterations of microvascular function may be present in early stages of coronary artery disease, myocardial hypertrophy, cardiomyopathy or systemic diseases such as arterial hypertension and diabetes mellitus. Fast computed tomography permits noninvasive simultaneous quantitation of regional intramyocardial blood volume and myocardial perfusion using indicator dilution principles. Our data indicate that especially the blood volume-to-flow relationship is sensitive enough to characterize and quantitate the functional impact of different pathologies along the coronary tree on microvascular function. This could be demonstrated for 1) acute impairment of microvascular function following coronary microembolization, 2) endothelial dysfunction induced by chronic hypercholesterolemia, 3) chronic epicardial non-significant stenoses, 4) physiologic maturation of the normal microvasculature and 5) quantification of heterogeneity of microvascular function. These findings, the methodological background and the concept itself are presented in this article. Application of the blood volume-to-flow relationship is not limited to fast-CT but may be used in any cross sectional imaging technique, such as MRI or echocardiography, as long as intramyocardial blood volume and perfusion can be quantitated simultaneously. This new noninvasive approach to the quantification of intramyocardial microvascular function may prove a useful adjunct to those imaging techniques that are used to noninvasively quantitate epicardial stenoses or regional wall motion abnormalities.

Impact of coronary vasa vasorum functional structure on coronary vessel wall perfusion distribution

Noncoronary vasa vasorum have been described as networks of microvessels in the wall of arteries and veins. However, we have shown, using microcomputerized tomography (micro-CT) imaging methods, that porcine coronary vasa vasorum have a tree-like branching structure similar to the vasculature in general. In this study, we elucidate functional aspects of coronary vasa vasorum perfusion territories. Three pig hearts were injected with radiopaque Microfil via the coronary sinus to fill the left anterior descending coronary arteries (LADs) retrogradely at atmospheric pressure. In three other hearts, LADs were injected antegradely at 100-mmHg pressure via the left main carotid artery. Additionally, six LADs were injected in vivo with a suspension of 100- or 300-microm-diameter microspheres before harvesting of the hearts and injection of the LADs with Microfil. All harvested LADs were scanned intact with micro-CT (20 microm cubic voxels). The spatial density of vasa vasorum (no. of vasa/mm2) was measured in 20-microm-thick cross sections (at 0.4-mm intervals). Retrogradely injected LADs showed high and uniformly distributed vasa vasorum densities in the adventitia (means +/- SE; 5.38 +/- 0.09 vs. 3.58 +/- 0.1 vasa/mm2 in antegradely prepared LADs; P < 0.001). Antegradely prepared LADs showed patchy distributed, low-vasa-vasorum-density territories especially on the myocardial side of the coronary artery wall (epicardial density: 4.29 +/- 0.13 vasa/mm2 vs. myocardial density: 2.80 +/- 0.1 vasa/mm2, P < 0.001). Microembolization reduced vasa vasorum densities significantly (100-mum-diameter microspheres: 3.26 +/- 0.07 vasa/mm2, P < 0.05; 300-microm-diameter microspheres: 2.66 +/- 0.07 vasa/mm2, P < 0.001 vs. antegrade controls) and increased the size of low-vasa-vasorum-density territories. We conclude that coronary vasa vasorum are functional endarteries not connected via a plexus. This characteristic may have a significant impact on the spatial distribution of perfusion and drainage of the coronary vessel wall.

Effects of implant healing time on crestal bone loss of a controlled-load dental implant

The universally accepted concept of delay-loaded dental implants has recently been challenged. This study hypothesizes that early loading (decreased implant healing time) leads to increased bone formation and decreased crestal bone loss. We used 17 minipigs to study implants under a controlled load, with non-loaded implants for comparison. Radiographic and histological assessments were made of the osseointegrated bone changes for 3 healing times (between implant insertion and loading), following 5 months of loading. The effect of loading on crestal bone loss depended on the healing time. Early loading preserved the most crestal bone. Delayed loading had significantly more crestal bone loss compared with the non-loaded controls (2.4 mm vs. 0.64 mm; P < 0.05). The histological assessment and biomechanical analyses of the healing bone suggested that loading and bioactivities of osteoblasts exert a synergistic effect on osseointegration that is likely to support the hypothesis that early loading produces more favorable osseointegration.

Measurement of gene expression following cryogenic mu-CT scanning of human iliac crest biopsies

An important consideration in interpreting indices of gene expression in human bone is relating mRNA levels to functional endpoints such as bone architecture. In the present study, a method was developed for quantitative measurement of gene expression and bone morphology in the same specimen. Three-dimensional images of iliac crest bone biopsies from healthy premenopausal women were obtained using a novel high resolution cryogenic mu-CT scanner. RNA was isolated from the biopsies and mRNA levels were measured for genes related to bone metabolism. The gene expression profile and variability of expression within iliac crest biopsies of women was similar to human osteoblastic cell lines and rat long bones. mRNA for alkaline phosphatase, bone matrix proteins, and selected cytokines and cytokine receptors were consistently detected in biopsies. As previously shown in rat bone, there was a tight correlation between mRNA levels for type 1 collagen and osteonectin, a weaker correlation between type 1 collagen and osteocalcin and no correlation between bone matrix proteins and alkaline phosphatase. The relative abundance of the mRNA for the three most prevalent transforming growth factor-beta (TGF-beta) isoforms in bone (TGF-beta(1)>> TGF-beta(3)> TGF-beta(2)) was the same as the known abundance of the corresponding TGF-beta peptides in bone matrix. The results demonstrate the feasibility of analyzing the three-dimensional architecture of a bone biopsy using cryogenic mu-CT imaging and then measuring expression of genes related to bone cell function within the same specimen following RNA extraction and analysis.

Time course of epiphyseal growth plate fusion in rat tibiae

Although the rat is the most common animal model used in studying osteoporosis, it is often used inappropriately. Osteoporosis is a disease that most commonly occurs in humans long after growth plate fusion with the associated cessation of longitudinal bone growth, but there has been a question as to when or to what extent the rat growth plate fuses. To investigate this question, we used microcomputed X-ray tomography, at voxel resolutions ranging from (5.7 micro m)(3) to (11 micro m)(3), to image the proximal epiphyseal growth plates of both male (n = 19) and female (n = 15) rat tibiae, ranging in age from 2 to 25 months. The three-dimensional images were used to evaluate fusion of the epiphyseal growth plate by quantitating the amount of cancellous bone that has bridged across the growth plate. The results suggest that the time course of fusion of the epiphyseal growth plate follows a sigmoidal pattern, with 10% of the maximum number of bridges having formed by 3.9 months in the male tibiae and 5.8 months in the female tibiae, 50% of the maximum number of bridges having formed by 5.6 months in the male tibiae and 5.9 months in the female tibiae, and 90% of the total maximum of bridges have formed by 7.4 months for the males and 6.5 months for the females. The total volume of bridges per tibia at the age at which the maximum number of bridges per tibia has first formed is 0.99 mm(3)/tibia for the males and 0.40 mm(3)/tibia for the females. After the maximum number of bridges (-290 for females, -360 for males) have formed the total volume of bridges per tibia continues to increase for an additional 7.0 months in the males and 17.0 months for the females until they reach maximum values (-1.5 mm(3)/tibia for the males and -2.2 mm(3)/tibia for the females).

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.

Noninvasive measurement of concurrent single-kidney perfusion, glomerular filtration, and tubular function

To assess the reliability of electron beam computed tomography (EBCT), measurements of single-kidney renal blood flow (RBF), glomerular filtration rate (GFR), and intratubular contrast medium concentration (ITC) of radiographic contrast media were quantified in anesthetized pigs before and after acetylcholine-induced vasodilation and diuresis. EBCT measurements were compared with those obtained with intravascular Doppler and inulin clearance. The capability of EBCT to detect chronic changes in single-kidney function was evaluated in pigs with unilateral renal artery stenosis, and their long-term reproducibility in normal pigs was studied repeatedly at 1-mo intervals. EBCT-RBF (ml/min) correlated with Doppler-RBF as RBF(EBCT) = 45 + 1.07 * RBF(Doppler), r = 0.81. EBCT-GFR (ml/min) correlated with inulin clearance as GFR(EBCT) = 11.7 + 1.02 * GFR(inulin), r = 0.80. During vasodilation, RBF and GFR increased, whereas ITC decreased along the nephron. In renal artery stenosis, single-kidney GFR decreased linearly with the degree of stenosis, and ITC increased along the nephron, indicating increased fluid reabsorption. EBCT-RBF, GFR, and ITC were similar among repeated measurements. This approach might be invaluable for simultaneous quantification of regional hemodynamics and function in the intact kidneys, in a manner potentially applicable to humans.

Coronary microvascular functional reserve: quantification of long-term changes with electron-beam CT preliminary results in a porcine model

PURPOSE

To evaluate the ability of electron-beam computed tomography (CT) to help quantify long-term changes in coronary microvascular functional reserve in a porcine model.

MATERIALS AND METHODS

Electron-beam CT-based intramyocardial blood volume and perfusion and Doppler ultrasonography (US)-based intracoronary blood flow were obtained in 13 pigs at baseline and again 3 months later. Measurements were obtained at rest and after the administration of adenosine. The short-term variation during 30 minutes of electron-beam CT measurements was assessed in nine additional pigs.

RESULTS

Short-term variation of blood volume and perfusion averaged 8% and 9%, respectively, and was similar for both weight groups at rest and after adenosine administration. At rest, intracoronary blood flow, blood volume, and perfusion remained unchanged from baseline to follow-up. Long-term increases (percentage change with adenosine relative to that at rest) in blood volume and perfusion reserves were consistent with increasing intracoronary blood flow reserves. Despite these long-term changes in intracoronary blood flow, blood volume, and perfusion, the blood volume-to-perfusion relationship suggests a similar blood volume distribution among different microvascular functional components in normal porcine myocardium at both weight groups.

CONCLUSION

Electron-beam CT may be of value for quantifying long-term changes in intramyocardial microvascular function.

Coronary vasa vasorum neovascularization precedes epicardial endothelial dysfunction in experimental hypercholesterolemia

OBJECTIVE

Experimental hypercholesterolemia is associated with vasa vasorum neovascularization, unknown to occur before or after initial lesion formation. Thus, this study was performed to determine the temporal course of neovascularization of coronary vasa vasorum in relation to endothelial dysfunction, a hallmark of early atherosclerosis.

METHODS

Female domestic pigs were fed a normal diet (Group 1), a hypercholesterolemic diet for 2 and 4 weeks (Group 2), or a hypercholesterolemic diet for 6 and 12 weeks (Group 3). In vitro analysis of relaxation response to bradykinin served as an index for epicardial endothelial function. Spatial pattern and density of coronary vasa vasorum were assessed by three-dimensional microscopic computed tomography.

RESULTS

Relaxation response of coronary arteries to bradykinin was normal in both Group 1 (93+/-6%) and Group 2 (89+/-7%) but impaired in Group 3 (71+/-11%; P<0.05 vs. Group 1 and 2). In contrast, density of coronary vasa vasorum was significantly higher in both Group 2 (4.88+/-2.45 per-mm(2)) and Group 3 (4.50+/-1.37 per-mm(2)) compared to Group 1 (2.97+/-1.37 per-mm(2); P<0.05 vs. Group 2 and 3).

CONCLUSION

This study demonstrates that coronary vasa vasorum neovascularization occurs within the first weeks of experimental hypercholesterolemia and prior to the development of endothelial dysfunction of the host vessel, suggesting a role for vasa vasorum neovascularization in the initial stage of atherosclerotic vascular disease.

An integrated approach to assess structure-to-function relationships in the skeleton

In general, the disciplines of biomechanics, morphology, densitometry, biochemistry, cell biology and molecular biology have advanced independently of one another. In spite of this fragmentation, there have been incremental increases in our understanding of the organization, mechanical properties, growth, remodeling and repair of the tissues comprising the skeleton. As a practical application, this increased knowledge has greatly improved our capabilities for early diagnosis of bone loss and has proven similarly useful in determining the efficacy of interventions to prevent osteoporosis. This approach, however, has been much less successful in countering several other important musculoskeletal disorders, including arthritis. In the immediate future, a major emphasis will be placed on tissue regeneration (engineering) to restore lost mechanical function to a compromised skeleton. To accomplish this goal, it will be necessary to employ much more sophisticated approaches toward evaluating the structure-to-function relationships, ones which will include integration of the respective contributions of gene expression, cell number and activity, matrix composition and architecture to achieve adequate tissue function.

Measurement and display of regional myocardial motion during post infarct treatment

Quantitative assessment of 3-D regional heart motion has significant potential to provide more specific diagnosis of cardiac malfunction than currently possible. Using functional parametric mapping, regional myocardial motion during a cardiac cycle can be color-mapped onto a deformable heart model to provide better understanding of the structure-to-function relationships in the myocardium, including regional patterns of akinesis or dyskinesis associated with ischemia or infarction. In this study, 3-D reconstructions of human hearts were obtained from Electron-Beam Computed Tomography [1] (EB-CT), comparing stages of treatment after myocardial infarction.

Quantitative assessment of the rat intrahepatic biliary system by three-dimensional reconstruction

The anatomical details of the biliary tree architecture of normal rats and rats in whom selective proliferation was induced by feeding alpha-naphthylisothiocyanate (ANIT) were reconstructed in three dimension using a microscopic-computed tomography scanner. The intrahepatic biliary tree was filled with a silicone polymer through the common bile duct and each liver lobe embedded in Bioplastic; specimens were then scanned by a microscopic-computed tomography scanner and modified Feldkamp cone beam backprojection algorithm applied to generate three-dimensional images. Quantitative analysis of bile duct geometry was performed using a customized software program. The diameter of the bile duct segments of normal and ANIT-fed rats progressively decreased with increasing length of the biliary tree. Diameter of bile ducts from ANIT-fed rats (range, 21 to 264 microm) was similar to that of normal rats (22 to 279 microm). In contrast, the number of bile duct segments along the major branch reproducibly doubled, the length of the bile duct segments decreased twofold, and the length of the biliary tree remained unchanged after ANIT feeding. Moreover, the total volume of the biliary tree of ANIT-fed rats was significantly greater (855 microl) than in normal rats (47 microl). Compared with normal rats, the total surface area of the biliary tree increased 26 times after ANIT-induced bile duct proliferation. Taken together, these observations quantitate the anatomical remodeling after selective cholangiocyte proliferation and strongly suggest that the proliferative process involves sprouting of new side branches. Our results may be relevant to the mechanisms by which ducts proliferate in response to hepatic injury and to the hypercholeresis that occurs after experimentally induced bile duct proliferation.

Corporeal structural and vascular micro architecture with X-ray micro computerized tomography in normal and diabetic rabbits: histopathological correlation

PURPOSE

The pathophysiology of diabetes mellitus induced erectile dysfunction is poorly understood. In patients with diffuse venous leakage structural changes in the corpora cavernosa have correlated with failure of the veno-occlusive mechanism. Three-dimensional (D) micro computerized tomography (CT) has proved to be an important imaging technique for the intact kidney, heart, liver and bone. We examined control and diabetic rabbit penises by 3-D micro CT and quantified any structural changes.

MATERIALS AND METHODS

Male white New Zealand rabbits were treated with alloxan to induce diabetes or used as normal controls. Via aortic access at laparotomy the penile vascular tree was vasodilated with papaverine and perfused with radiopaque silicone rubber. X-ray micro CT was then performed at 21 microm. resolution and images were analyzed in 3-D using custom software.

RESULTS

Nine diabetic rabbits with blood glucose greater than 400 mg./dl. and 9 control animals were used for micro CT analysis. Significant decreases (p <0.05) were observed in the mean sinusoidal and vascular volume fraction plus or minus standard error of mean of the corpus cavernosum in the diabetic (323.7 +/- 43.1 mm.3 and 37.9 +/- 2.0%, respectively) and control (510.1 +/- 47.4 mm.3 and 53.1 +/- 3.80%, respectively) groups. Also, the mean left and right cavernous artery luminal cross-sectional area in diabetics (0.15 +/- 0.02 and 0.16 +/- 0.01 mm.2, respectively) versus controls (0.2 +/- 0.01 and 0.2 +/- 0.01 mm.2, respectively) was significantly decreased (p <0.05). Furthermore, the mean left and right total cavernous artery luminal volume in diabetics (0.4 +/- 0.07 and 0.4 +/- 0.09 mm.3, respectively) versus controls (1.0 +/- 0.13 and 0.9 +/- 0.11 mm.3, respectively) was significantly decreased (p <0.05).

CONCLUSIONS

Diabetic rabbit penises showed a significant decrease in corporeal vascular volume as well as decreased cavernous artery diameter and luminal volume compared to controls. This finding correlated well with the mean decrease in trabecular smooth muscle in control and severely diabetic rabbits on histopathological studies (42.2% +/- 1.5% versus 35.8% +/- 1.5%). This combination of potential arterial insufficiency as well as an increase in diffuse connective tissue may contribute to the overall pathophysiology of diabetic erectile dysfunction. These results suggest that 3-D x-ray micro CT with molecular analysis may be a powerful tool for examining the pathophysiology of diabetic erectile dysfunction.

Minimally invasive evaluation of coronary microvascular function by electron beam computed tomography

BACKGROUND

We previously demonstrated that in vivo electron-beam computed tomography (EBCT)-based indicator-dilution methods provide an estimate of intramyocardial blood volume (BV) and perfusion (F), which relate as BV=aF+b radicalF, where a characterizes the recruitable (exchange) and b the nonrecruitable (conduit) component of the myocardial microcirculation. In the present study, we compared BV and F with intracoronary Doppler ultrasound-based coronary blood flow (CBF) as a method for detecting and quantifying differential responses of these microvascular components to vasoactive drugs in normal (control) and hypercholesterolemic (HC) pigs.

METHODS AND RESULTS

BV and F values were obtained from contrast-enhanced EBCT studies in 14 HC and 14 control pigs. BV, F, and CBF values were obtained at baseline (intracoronary infusion of saline) and after 5 minutes each of intracoronary infusion of adenosine (100 microgram. kg(-1). min(-1)) and nitroglycerin (40 microgram/min). BV and CBF reserves in response to adenosine were attenuated in HC pigs compared with controls (90+/-36% versus 127+/-42%, P<0.03, and 485+/-182% versus 688+/-160%, P<0.01, respectively). The relationship between BV and F showed consistently lower recruitable BV in HC versus control pigs. Nonrecruitable BV reserve in response to adenosine was attenuated in HC compared with controls (77+/-20% versus 135+/-28%, P<0.001). Our findings are consistent with HC-induced impairment of intramyocardial resistance vessel function.

CONCLUSIONS

EBCT technology allows minimally invasive evaluation of intramyocardial microcirculatory function and permits assessment of microvascular BV distribution in different functional components. This method may be of value in evaluating the coronary microcirculation in pathophysiological states such as hypercholesterolemia.

Altered myocardial microvascular 3D architecture in experimental hypercholesterolemia

BACKGROUND

Experimental hypercholesterolemia (HC) impairs intramyocardial microvascular function. However, whether this is associated with alterations in microvascular architecture remained unknown. Using a novel 3D micro-CT scanner, we tested the hypothesis that HC is associated with an alteration in the microvascular architecture.

METHODS AND RESULTS

Pigs were euthanized after 12 weeks of either normal (n=6) or 2% HC (n=6) diet. The hearts were excised and the coronary arteries injected with a radiopaque contrast material. Myocardial samples were scanned with micro-CT, and 3D images were reconstructed with 21-microm cubic voxels. The myocardium was tomographically subdivided into subepicardium and subendocardium, and microvessels (<500 microm in diameter) were counted in situ within each region. In the subendocardium of HC pigs, the intramyocardial density of microvessels was significantly higher than in normal animals (1221.4+/-199.7 versus 758.3+/-90.8 vessels/cm(3), P:<0.05) because of an increase in the number of microvessels <200 microm in diameter (1214.4+/-199.7 versus 746. 6+/-101.5 vessels/cm(3), P:<0.05). The subepicardial vascular density was similar in both groups.

CONCLUSIONS

-HC has differential effects on the spatial density of the subendocardial microvasculature that may play a role in regulation and/or spatial distribution of myocardial blood flow. This study also demonstrates the feasibility of studying myocardial microvascular architecture with micro-CT in pathophysiological states.

Microcomputed tomography of kidneys following chronic bile duct ligation

BACKGROUND

In hepatic cirrhosis, renal sodium and water retention can occur prior to decreases in renal blood flow (RBF). This may be explained in part by redistribution of the intrarenal microcirculation toward the juxtamedullary nephrons. To appreciate this three-dimensional spatial redistribution better, we examined the intrarenal microcirculatory changes using microcomputed tomography (micro-CT) in rats subjected to chronic bile duct ligation (CBDL).

METHODS

Six kidneys from control rats and eight kidneys from rats that had undergone CBDL for 21 days were perfusion fixed in situ at physiological pressure, perfused with silicon-based Microfil containing lead chromate, embedded in plastic, and scanned by micro-CT. The microvasculature in the reconstructed three-dimensional renal images was studied using computerized image-analysis techniques. To determine the physiological condition of the rats, parallel experiments were conducted on six control and six CBDL rats to measure mean arterial pressure (MAP), RBF, glomerular filtration rate (GFR), urine flow (UF) rate, and sodium excretion by conventional methods.

RESULTS

The percentage of vasculature in the renal cortex from CBDL rats was significantly decreased (10.8 +/- 0.4% vs. 16.8 +/- 2.7% control values). However, the vascular volume fractions of the medullary tissues were not significantly altered. There were no significant differences in the number of glomeruli between groups (36,430 +/- 1908 CBDLs, 36,609 +/- 3167 controls). The CBDL rats had a similar GFR than the controls but a reduced MAP, RBF, UF, and sodium excretion.

CONCLUSIONS

The results indicate that after CBDL, there is a selective decrease in cortical vascular filling, which may contribute to the salt and water retention that accompanies cirrhosis.

Extraction of the hepatic vasculature in rats using 3-D micro-CT images

High-resolution micro-computed tomography (CT) scanners now exist for imaging small animals. In particular, such a scanner can generate very large three-dimensional (3-D) digital images of the rat's hepatic vasculature. These images provide data on the overall structure and function of such complex vascular trees. Unfortunately, human operators have extreme difficulty in extracting the extensive vasculature contained in the images. Also, no suitable tree representation exists that permits straight-forward structural analysis and information retrieval. This work proposes an automatic procedure for extracting and representing such a vascular tree. The procedure is both computation and memory efficient and runs on current PCs. As the results demonstrate, the procedure faithfully follows human-defined measurements and provides far more information than can be defined interactively.

Imaging Angiogenesis with Three-Dimensional Microscopic Computed Tomography

An increasing number of patients with advanced coronary artery disease remain symptomatic, despite maximal interventional or medical treatment. A high demand exists for alternative anti-anginal therapies and ways to improve survival. One of the most intriguing new approaches to increase blood flow to ischemic myocardium is therapeutic angiogenesis, the induction of new vessel growth. Current methods involve local angiogenic growth factor administration, transfection of genes expressing angiogenic proteins, or direct myocardial revascularization. These new therapeutics are undergoing intensive basic and clinical investigation.

A systematic analysis of factors which may impact upon tomographic perfusion imaging measurements: implications for the use of Tc-99m sestamibi in acute myocardial infarction

BACKGROUND

The use of acute Tc-99m sestamibi imaging has provided a valuable methodology to assess myocardium at risk and collateral blood flow.

OBJECTIVE

The purpose of this study was to determine the impact of physical, physiologic, and reconstruction factors on the extent and severity of Tc-99m sestamibi images in a porcine model of coronary occlusion and reperfusion.

METHODS AND RESULTS

Eleven pigs underwent 40 min of coronary occlusion using a balloon catheter followed by reperfusion. Radiolabeled microspheres were injected during occlusion for blood flow determination and 20-30 mCi of Tc-99m sestamibi was injected intravenously for cardiac imaging. Each animal underwent four modes of gamma camera imaging: a cardiac and respiratory gated SPECT study, an ungated SPECT study, a post-mortem SPECT study and an ex-situ study where the heart was sliced into five short axis slices and directly imaged. All animals had extensive wall motion abnormalities at the time of imaging. Myocardial risk area by ex-situ imaging was 32 +/- 9% LV and did not significantly change with the addition of a chest cavity and tomographic reconstruction (post-mortem and gated imaging) or cardiac and respiratory motion (ungated imaging). Defect severity was significantly underestimated with the addition of a chest cavity and tomographic reconstruction but was unaltered by cardiac and respiratory motion.

CONCLUSIONS

The assessment of risk area acutely by SPECT Tc-99m sestamibi imaging is unaffected by cardiac motion obviating the necessity for gated imaging. Estimated defect severity (which has been used as a measure of collateral flow) is significantly reduced by the chest wall and tomographic acquisition and reconstruction suggesting a role for scatter and attenuation algorithms for this measure.

Effects of acute and chronic angiotensin receptor blockade on myocardial vascular blood volume and perfusion in a pig model of coronary microembolization

Based on the reduction of ischemic cardiac events in clinical trials and experimental observations, inhibition of the effects of angiotensin II on coronary microcirculatory function may afford myocardial protection after injury. The immediate effects of intracoronary AT1 receptor blockade with irbesartan were examined in a pig model in the healthy myocardium and in acute ischemia induced by injection of 30-microm microspheres into the left anterior descending coronary artery (LAD). Electron-beam computed tomography was performed for in-vivo quantitative measurements of regional intramyocardial vascular blood volume (V(B)) and perfusion (F(M)), as well as left ventricular ejection fraction (LVEF) and muscle mass. Ratios of V(B) and F(M) in the anterior (LAD-supplied)/ inferior (control) myocardium were generated. At baseline, 0.2 mg/kg irbesartan injected into the LAD increased V(B) and F(M) ratios significantly by 27 +/- 8% and 51 +/- 13%, respectively. After anterior coronary microembolization, V(B) and F(M) ratios were 0.60 +/- 0.05 and 0.51 +/- 0.05, respectively, and were significantly increased by irbesartan (by 24 +/- 10% and by 36 +/- 11%, respectively). After 4 weeks of treatment with oral irbesartan (n = 7) or placebo (n = 7), an improved LVEF (56 +/- 4% v 44 +/- 4%, P = .046) was observed in irbesartan-treated animals, but no difference in LV end-diastolic volumes or muscle mass. Resting V(B) (0.95 +/- 0.06 v 0.76 +/- 0.06; P = .047) and F(M) (0.84 +/- 0.05 v 0.64 +/- 0.04; P = .016) ratios were significantly greater in irbesartan-treated animals. Using adenosine, there was a trend for higher V(B) and F(M) ratios in irbesartan- v placebo-treated animals. Therefore, in a pig model of acute myocardial ischemia, AT1 receptor blockade by irbesartan induced microvascular vasodilation and, ostensibly, conveyed myocardial protection. Long-term treatment with irbesartan resulted in moderate enhancements of resting V(B) and F(M) compared with placebo, suggesting a role for coronary microcirculatory effects of chronic AT1 receptor blockade in preserving LVEF.

The effect of collateral flow and myocardial viability on the distribution of technetium-99m sestamibi in a closed-chest model of coronary occlusion and reperfusion

Myocardial uptake of technetium-99m sestamibi at low coronary flow rates overestimates blood flow, but the relative impact of flow and viability on 99mTc-sestamibi kinetics is unclear. The objective of this study was to determine the effect of myocardial viability and the degree of collateral blood flow on the uptake and retention of 99mTc-sestamibi by examining three animal models of coronary occlusion and reperfusion, each reflecting a different state of viability and collateral blood flow. Three closed-chest animal models were studied: canine (high collateral flow, preserved viability), porcine (low collateral flow, absent viability) and porcine with slowly occlusive coronary stents producing infarction and enhanced collateral blood flow (high collateral flow, absent viability). There were seven dogs, seven pigs and six pigs, respectively, in each animal model. Animals from all three models were subjected to a 40-min total left anterior descending artery (LAD) occlusion followed by 2 h of reperfusion. 99mTc-sestamibi and radiolabelled microspheres were injected during LAD occlusion 10 min prior to reperfusion. Animals were sacrificed after 2 h of reperfusion flow. Ex situ heart slice imaging to determine risk area was followed by viability staining to determine infarct size. Slices were subsequently sectioned into equally sized radial segments and placed in a gamma well counter. Risk area as determined by ex situ 99mTc-sestamibi imaging was not significantly different by model. Pathological infarct size differed significantly by model [canine = 1%+/-1% of the left ventricle (LV); porcine = 13%+/-8% LV; porcine with stent = 14%+/-7% LV; P = 0.002)]. Collateral blood flow by microspheres during occlusion tended to differ among models (overall P = 0.08), with the canine and porcine with stent models having relatively high flow rates compared with the acute porcine model. 99mTc-sestamibi activity correlated with microsphere blood flow in all three models, with r values for individual animals (n = 20) ranging from 0.86 to 0.96 (all P<0.0001). There was a significant difference in the regression line intercepts (P<0.0001) and slopes (P<0.01) among the three models comparing 99mTc-sestamibi uptake with myocardial blood flow. 99mTc-sestamibi uptake overestimated blood flow to a greater extent in the canine model (high flow with viability) than in the porcine model (low flow, absent viability). Despite enhanced collateral flow, there was significantly less overestimation of flow in the porcine stent model (high flow, absent viability). In conclusion, at low flow rates 99mTc-sestamibi activity overestimates myocardial blood flow. This effect is most pronounced in myocardium with significant collateral flow and preserved viability, consistent with over-extraction or redistribution of the tracer. The effect is markedly decreased in non-viable myocardium regardless of blood flow.

Restoration of bone mass in the severely osteopenic senescent rat

Studies in humans and rats suggest that age impairs the ability to form bone. This impairment may be due to a depletion or deficit in osteoprogenitor stem cells. Such a deficit would be expected to reduce the ability of the skeleton to respond to therapy designed to restore lost bone. This study evaluated whether severely osteopenic senescent rats are capable of responding to a potent anabolic factor in bone, prostaglandin E2 (PGE). Growing female Sprague Dawley rats were ovariectomized at 3 months and aged until the start of treatment at 23 months. Rats were treated daily with PGE (3 mg/kg sc) or vehicle for 56 days. Tibiae were harvested for bone histomorphometry and femora were obtained for mRNA analysis of bone matrix proteins. The cancellous bone area was fivefold greater in PGE-treated rats than in vehicle-treated controls and not different from age-matched ovary-intact rats. PGE approximately doubled the bone-forming surface and the mineral apposition rate and increased the bone formation rate fourfold. The increased cancellous bone area in PGE-treated rats was primarily due to an increase in osteoblasts over osteoclasts. One hundred percent of the endocortical surface and 72 +/- 9% of the periosteal surface of cortical bone was undergoing mineralization in PGE-treated rats, whereas no mineratization was evident in vehicle-treated rats. An architectural analysis of cancellous bone indicates that trabecular number and thickness were increased and separation decreased in the treated rats. Imaging by microcomputed tomography further revealed that with PGE treatment, trabeculae in the medial plane of the proximal tibial metaphysis were more robust and continuous with the endocortical surface. PGE also significantly induced message levels for the prepro-alpha (I) subunit of type I collagen (collagen), osteonectin, and osteocalcin. In summary, bone mass can be restored to severely osteopenic senescent rats, suggesting that aging does not necessarily diminish the capacity of the skeleton to form bone.

Contrast-enhanced 3D MR breathhold imaging of porcine coronary arteries using fluoroscopic localization and bolus triggering

The purpose of this study was to develop cardiac-gated contrast-enhanced 3D MRA for imaging the coronary arteries of pigs. Each major coronary artery was imaged individually in a single 3D slab in one breathhold. To permit acquisition within a breathhold, a limited number of partitions (12-16) were collected in a single, oblique, thin 3D slab. Typical resolution of the acquisition was 0.8 (X) x 1.6 (Y) x 1.6 (Z) mm. MR fluoroscopic localization was used to establish the 3D double-oblique orientation. Real-time MR fluoroscopy was also used to instantaneously trigger the 3D scan after detection in the aortic root of the intravenously administered contrast bolus. Six pigs were used in the study. Each pig was scanned on two separate days. Images routinely show the majority of the length of the three principal coronary arteries. Magn Reson Med 42:1159-1165, 1999.

Evaluation of microvascular anatomy by micro-CT

Observations indicate that adventitial vasa vasorum may play a role in the development and/or the progression of coronary atherosclerosis. There is a lack of information regarding the spatial three-dimensional pattern of the vasa vasorum in the coronary artery. This is due to the technical difficulties in visualizing the course of this fine vascular network with histologic methods. Microscopic computed tomography (micro-CT) is a novel technique that allows three-dimensional views of the entire microvascular structure. The current review summarizes our current advances in using this technique in visualization of the coronary circulation.

Percutaneous transmyocardial revascularization induces angiogenesis: a histologic and 3-dimensional micro computed tomography study

The purpose of this study was to visualize the spatial patterns and connection of channels created after percutaneous transmyocardial revascularization (PTMR) in normal porcine hearts, and to estimate the relative contributions of transmyocardial and coronary perfusion. Six pigs underwent PTMR creating channels using radiofrequency ablative energy. Three-dimensional computed tomography imaging of channels 1 hr after PTMR showed the direct connection of PTMR channels to the myocardial capillary network and to epicardial coronary vessels. In the heart, examined 28 day after PTMR, there was a fine, extensive, network of microvessels originating from the site of the original PTMR channel, also connecting the left ventricular cavity to myocardial capillaries. Histopathologic examination of the 1-hr specimens showed numerous regions of myocardial hemorrhage and associated inflammatory cell infiltration. In the 28-day specimens, newly developed new vascular network suggested neovascularization within the core of these channel remnants. The immunoreactivity for basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) were intense within myocardium and neovascular structure surrounding PTMR channel remnants. The vascular connections occur by direct communication with existing myocardial vasculature acutely, and angiogenesis in these channel remnant chronically.

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.

Cardiac production of angiotensin II and its pharmacologic inhibition: effects on the coronary circulation

Angiotensin II (AII), produced systemically as well as locally in the heart, affects the coronary circulation, as do consequences of its pharmacologic inhibition. AII is a powerful vasoconstrictor directly acting on vascular smooth muscle cells, modulating sympathetic innervation and calcium ion influx, and releasing other vasoconstrictor factors. In addition to these immediate actions, AII has longer-term biologic actions that influence cardiac endothelial function, vascular smooth muscle cell phenotype expression, and fibroblast proliferation. Moreover, the production of AII is interrelated with the vasodilator substances bradykinin, nitric oxide, and prostaglandins E2 and I2 (prostacyclin). Circulating hormonal actions of AII include fluid retention, direct vasoconstriction, and sympathetic neuromodulation, all resulting in increased left ventricular preload and afterload. Because of these local and hormonal characteristics, AII can immediately affect the myocardial balance of metabolic demand and supply and long term can induce structural vascular and myocardial alterations. Pharmacologic inhibition of AII production likely conveys myocardial and vascular protection in situations of acute myocardial oxygen debt. In the long term, inhibition of AII may attenuate structural changes in the coronary microcirculation related to various cardiomyopathies or acute tissue injury, and direct antiatherogenic effects may also occur.

Micro-CT imaging of structure-to-function relationship of bone microstructure and associated vascular involvement

We are exploring methods of quantitating the 3D microstructure of bone in a way that will provide quantitative information about the functional status of the bone. The basic strategy is to image the spatial distribution of a selected, local, marker of function (e.g., material properties or new bone formation) and relate this to the simultaneously imaged 3D anatomic microstructure. Many of these approaches are extensions of well-established 2D imaging techniques (e.g., use of fluorophores and autoradiography) to 3D micro-CT. Local stresses throughout the microstructure can be estimated from the 3D geometry (and change in that geometry in response to stress applied to the outside of the bones) and correlated to the local function. In addition to study of bone, we are also exploring calcification of arterial walls, both within the bone and outside the bone, such as coronary arteries. Arterial calcification in ovariectomised rats has been observed.

Adventitial vasa vasorum in balloon-injured coronary arteries: visualization and quantitation by a microscopic three-dimensional computed tomography technique

OBJECTIVES

The objective of this study was to examine the quantitative response of the adventitial vasa vasorum to balloon-induced coronary injury.

BACKGROUND

Recent attention has focused on the role of vasa vasorum in atherosclerotic and restenotic coronary artery disease. However, the three-dimensional anatomy of these complex vessels is largely unknown, especially after angioplasty injury. The purpose of this study was to visualize and quantitate three-dimensional spatial patterns of vasa vasorum in normal and balloon injured porcine coronary arteries. We also studied the spatial growth of vasa vasorum in regions of neointimal formation. A novel imaging technique, microscopic computed tomography, was used for these studies.

METHODS

Four pigs were killed 28 d after coronary balloon injury, and four pigs with uninjured coronary arteries served as normal controls. The coronary arteries were injected with a low-viscosity, radiopaque liquid polymer compound. Normal and injured coronary segments were scanned using a microscopic computed tomography technique. Three-dimensional reconstructed maximum intensity projection and voxel gradient shading images were displayed at different angles and voxel threshold values, using image analysis software. For quantitation, seven to 10 cross-sectional images (40 normal and 32 balloon injured cross-sections) were captured from each specimen at a voxel size of 21 microm.

RESULTS

Normal vasa vasorum originated from the coronary artery lumen, principally at large branch points. Two different types of vasa were found and classified as first-order or second-order according to location and direction. In balloon-injured coronary arteries, adventitial vasa vasorum density was increased (3.16+/-0.17/mm2 vs. 1.90+/-0.06/mm2, p = 0.0001; respectively), suggesting neovascularization by 28 d after vessel injury. Also, in these injured arteries, the vasa spatial distribution was disrupted compared with normal vessels, with proportionally more second-order vasa vasorum. The diameters of first-order and second-order vasa were smaller in normal compared with balloon-treated coronary arteries (p = 0.012 first-order; p < 0.001, second-order; respectively). The density of newly formed vasa vasorum was proportional to vessel stenosis (r = 0.81, p = 0.0001). Although the total number of vasa was increased after injury, the total vascular area comprised of vasa was significantly reduced in injured vessels compared with normals (3.83+/-0.20% to 5.42+/-0.56%, p = 0.0185).

CONCLUSIONS

Adventitial neovascularization occurs after balloon injury. The number of new vessels is proportional to vessel stenosis. These findings may hold substantial implications for the therapy of vascular disease and restenosis.

Three-dimensional imaging of vasculature and parenchyma in intact rodent organs with X-ray micro-CT

A microcomputed tomography (micro-CT) scanner, which generates three-dimensional (3-D) images consisting of up to a billion cubic voxels, each 5-25 micron on a side, and which has isotropic spatial resolution, is described. Its main components are a spectroscopic X-ray source that produces selectable primary emission peaks at approximately 9, 18, or 25 keV and a fluorescing thin crystal plate that is imaged (at selectable magnification) with a lens onto a 2.5 x 2.5-cm, 1,024 x 1,024-pixel, charge-coupled device (CCD) detector array. The specimen is positioned close to the crystal and is rotated in 721 equiangular steps around 360 degrees between each X-ray exposure and its CCD recording. Tomographic reconstruction algorithms, applied to these recorded images, are used to generate 3-D images of the specimen. The system is used to scan isolated, intact, fixed rodent organs (e.g., heart or kidney) with the image contrast of vessel lumens enhanced with contrast medium. 3-D image display and analysis are used to address physiological questions about the internal structure-to-function relationships of the organs.

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.

The effect of nitrous oxide on chest wall function in humans and dogs

The purpose of this study was to determine the effects of nitrous oxide (N2O) on the chest wall of anesthetized humans and dogs. Six human subjects and six mongrel dogs were studied during 1 minimum alveolar anesthetic concentration halothane anesthesia before and during the substitution of 70% N2O for 70% N2 in the inspired gas mixture. On a separate occasion, measurements also were made in pentobarbital-anesthetized dogs. Respiratory muscle activity was measured using electromyographic (EMG) electrodes. Chest wall configuration was determined by using fast three-dimensional computed tomography in dogs and by using respiratory impedance plethysmography in humans. N2O consistently decreased inspiratory ribcage displacement, a decrease attributable in dogs to decreased inspiratory activation of parasternal intercostal muscles; parasternal intercostal activity was not present in anesthetized humans. The decrease in ribcage motion decreased the tidal volume in humans, but not in dogs, because displacement of the diaphragm was better preserved in dogs, in association with changes in diaphragm EMG activation. N2O significantly increased phasic expiratory muscle activity in halothane-anesthetized humans and pentobarbital-anesthetized dogs. Thus, as has been demonstrated for other anesthetics, the actions of N2O are caused by alterations in the distribution and timing of neural drive to the respiratory muscles, rather than by a global depression of respiratory motoneuron drive.

IMPLICATIONS

In this study, we examined the effects of nitrous oxide on breathing in halothane-anesthetized dogs and humans. Nitrous oxide affected breathing by changing the distribution and timing of neural drive to the respiratory muscles in a species-dependent manner, rather than by causing a global depression of their activity.

Enhanced coronary vasa vasorum neovascularization in experimental hypercholesterolemia

Coronary arteries contain a network of vasa vasorum in the adventitia. The three-dimensional anatomy of the vasa vasorum in early coronary atherosclerosis is unknown. This study was designed to visualize and quantitate the three-dimensional spatial pattern of vasa vasorum in normal and experimental hypercholesterolemic porcine coronary arteries, using a novel computed tomography technique. Animals were killed after being fed either a high cholesterol diet (n = 4) or a control diet (n = 4) for 12 wk. The proximal left anterior descending coronary artery was removed from the heart, scanned, and reconstructed, and quantitation of vasa vasorum density was performed. Two different types of vasa vasorum were defined: first-order vasa vasorum ran longitudinally parallel to the vessel and second-order originated from first-order vasa circumferentially around the vessel wall. Compared with controls in hypercholesterolemic coronary arteries, there was a significant increase in the area of the vessel wall (3.86+/-0.22 vs. 8.07+/-0.45 mm2, respectively, P < 0.01) and in the density of vasa vasorum (1. 84+/-0.05/mm2 vs. 4.73+/-0.24/mm2; respectively, P = 0.0001). This occurred especially by an increase of second-order vasa vasorum and disorientation of normal vasa vasorum spatial pattern. This study suggests that adventitial neovascularization of vasa vasorum occurs in experimental hypercholesterolemic coronary arteries and may be a part of the early atherosclerotic remodeling process.