Power Doppler imaging as a basis for automated endocardial border detection during left ventricular contrast enhancement

Echocardiographic evaluation of left ventricular (LV) systolic function relies on endocardial visualization, which can be improved when necessary using contrast enhancement. However, there is no method to automatically detect the endocardial boundary from contrast-enhanced images. We hypothesized that this could be achieved using harmonic power Doppler imaging. Twenty-two patients were studied in two protocols: (1) 11 patients with poorly visualized endocardium (> 3 contiguous segments not visualized) and (2) 11 consecutive patients referred for dobutamine stress echocardiography who were studied at rest and at peak dobutamine infusion. Patients were imaged in the apical four-chamber view using harmonic power Doppler mode (HP SONOS 5500) during LV contrast enhancement (Optison or Definity DMP115). Digital images were analyzed using custom software designed to automatically extract the endocardial boundary from power Doppler color overlays. LV cavity area was automatically measured frame-by-frame throughout the cardiac cycle, and fractional area change calculated and compared with those obtained by manually tracing the endocardial boundary in end-systolic and end-diastolic gray scale images. Successful border detection and tracking throughout the cardiac cycle was possible in 9 of 11 patients with poor endocardial definition and in 10 of 11 unselected patients undergoing dobutamine stress testing. Fractional area change obtained from power Doppler images correlated well with manually traced area changes (r = 0.82 and r = 0.97, in protocols 1 and 2, respectively). Harmonic power Doppler imaging with contrast may provide a simple method for semi-automated border detection and thus facilitate the objective evaluation of LV function both at rest and under conditions of stress testing. This methodology may prove to be particularly useful in patients with poorly visualized endocardium.

Immortalization of human corneal endothelial cells using electroporation protocol optimized for human corneal endothelial and human retinal pigment epithelial cells

PURPOSE

In this study we established a protocol for transfection of human corneal endothelial and human retinal pigment epithelial cells. This protocol was used for immortalization of human corneal endothelial cells.

METHODS

Transfection was performed by means of electroporation. For immortalization a plasmid encoding large and small SV40 T-antigen was used.

RESULTS

The established electroporation protocol was suitable for both cell types. This protocol was used for transfection of human corneal endothelial cells with a plasmid containing the early region of SV40. The transfected cultures exhibited an increased life-span before they entered crisis. One culture recovered from crisis and was cultivated for 300 population doublings. The cells exhibited an in vivo-like morphology usually lost during cell culture.

CONCLUSIONS

We describe for the first time a culture of SV40 transfected human corneal endothelial cells which recovered from crisis and can therefore be regarded as immortalized.

Effect of perfluorodecalin on human retinal pigment epithelium and human corneal endothelium in vitro

BACKGROUND

Perfluorocarbon liquids are useful intraoperative tools in complicated vitreoretinal surgery. They are usually removed at the end of the procedure, but small amounts may remain in the eye. Recently, contradictory results have been reported on the damage in association with residual perfluorocarbon liquids in the eye. This study examined the effects of perfluorodecalin on human retinal pigment epithelium and corneal endothelium in vitro.

METHODS

Vitality and proliferative capacity of cell cultures were measured after incubation with perfluorodecalin. Vitality of cell cultures were measured using the Life-Dead assay. Cell proliferation was determined by measuring incorporation of 5-bromo-2'-deoxyuridine into cellular DNA. Furthermore, endothelium of organ-cultured human corneas was examined after incubation with perfluorodecalin by photodocumentation.

RESULTS

Both cell types showed less extinctions in the Life-Dead assay after incubation with perfluorodecalin. After removing perfluorodecalin from the cultures, cells showed the same capacity of proliferation as the control cells. Compared to control corneas, perfluorodecalin induced a decrease in endothelial cell density. In four corneas, endothelial cell necrosis was observed.

CONCLUSION

Decreasing extinctions in the Life-Dead assay after incubation with perfluorodecalin can be interpreted as showing a decreasing amount of vital cells. Because cell proliferation showed no significant changes the results suggest that perfluorodecalin may not be directly toxic to cells in vitro. It may exert an indirect or mechanical effect on cell function by impeding the normal metabolic exchange between endothelium and medium. Based on these results perfluorodecalin should be completely removed after operation.

The role of echocardiographic harmonic imaging and contrast enhancement for improvement of endocardial border delineation

Despite advances in imaging technology, many myocardial segments remain poorly visualized with echocardiography; however, both contrast enhancement and harmonic imaging have shown promise for improving endocardial definition. Fifty subjects with technically limited echocardiograms were studied with fundamental and harmonic imaging as well as during echocardiographic contrast injection. Overall endocardial visualization scores improved with both techniques compared with fundamental imaging. Harmonic imaging improved endocardial visualization in 43% of all segments and in 57% of segments nonvisualized with fundamental imaging. The benefit of harmonic imaging was seen in all segments. Contrast echocardiography had similar overall improvements in visualization (42% of all segments, 67% of segments nonvisualized with fundamental imaging) but was not helpful in all regions. Harmonic imaging outperformed contrast in 9 of 22 segments, whereas contrast was superior in 4 of 22. In a subgroup of patients with very poor images, contrast enhancement was superior, with a greater increase in overall score and a higher salvage rate than harmonic (68% vs 40%).

Three-dimensional echocardiography in adult patients: comparison between transthoracic and transesophageal reconstructions

BACKGROUND

Three-dimensional (3D) echocardiography is a relatively new technique typically implemented with transesophageal imaging with multiplane transducers.

OBJECTIVES

The goals of this study were (1) to test the feasibility of 3D reconstruction with a new transthoracic multiplane transducer in adult subjects with excellent quality of 2-dimensional images and (2) to compare these reconstructions with those obtained in the same patients with the transesophageal approach.

METHODS

Transthoracic multiplane image acquisition was performed in 37 patients who were selected on the basis of the quality of their 2-dimensional images. In addition, transesophageal acquisition was also performed in 19 of 37 patients. Three-dimensional reconstruction of mitral and aortic valves was performed. Three-dimensional images were reviewed, and the visualization of various anatomic features was graded.

RESULTS

The reconstruction of 25 mitral valves and 16 aortic valves, normal and pathologic, was feasible and resulted in visualization of anatomic detail. Score indexes of all valvular characteristics studied were not significantly different when transthoracic and transesophageal reconstructions were compared.

CONCLUSIONS

Transthoracic 3D echocardiography with a multiplane transducer in adult patients with good acoustic windows is feasible. This technique will allow easy noninvasive serial assessment of valvular pathophysiologic characteristics.

Morphological and functional analysis of immortalized human corneal endothelial cells after transplantation

Approximately 50% of donor corneas are unsuitable for keratoplasty due to an unacceptably low endothelial cell count. One way of overcoming this problem and minimizing wastage of donor corneas may be to transplant cultured human corneal endothelial cells onto these. In this study, we examined the morphological characteristics and functional attributes of endothelial layers formed after the transplantation of immortalized cells in vitro. Cultured human corneal endothelial cells, immortalized by transfection with a plasmid encoding SV40 T-antigen, were seeded onto human corneas denuded of their own endothelium. Seven days after transplantation the newly established monolayers were examined by light, confocal and scanning electron microscopy. Endothelial pump function was gauged by monitoring changes in corneal thickness during perfusion of the endothelial face. The endothelia formed from transplanted immortalized cells had a cobblestone-like appearance, being composed of polygonal units joined by junctional complexes. The stromal hydration state of corneas bearing such endothelial layers could be controlled during perfusion. This was an active process achieved via the Na(+)/K(+)-ATPase-dependent endothelial pump, as demonstrated by inhibiting the enzyme with ouabain. Transplantation of immortalized human corneal endothelial cells onto recipient corneas led to the establishment of new monolayers which had the morphology of the native ones in organ-cultured corneas. This model provides us with a means of studying the formation and function of corneal endothelial layers in vitro.

[Endothelial cell transplantation and growth behavior of the human corneal endothelium]

BACKGROUND

The human corneal endothelium has a limited proliferative capacity in vivo. Until now it has only been possible to replace damaged endothelium by transplantation of a donor cornea. After establishing methods for the isolation and in vitro cultivation of human corneal endothelial cells, transplantation of these cells my be an alternative therapeutic option.

MATERIALS AND METHODS

In this review methods for the in vitro cultivation of human corneal endothelial cells and their transplantation on the Descemet membrane of donor corneas are described.

RESULTS

In vitro proliferation of human adult corneal endothelial cells was achieved by the development of defined cell culture conditions, including supplementation of culture medium with specified growth factors and substances. Dependent on the culture conditions, as well as independent of them, in vitro cultured endothelial cells showed phenotypic changes and different proliferative behavior. Thus, molecular biological examinations revealed a different expression pattern of growth factor receptors in fibroblast-like endothelial cells (dedifferentiated) compared to typical endothelial cells (differentiated). Moreover, the proliferative capacity of the cells differed, dependent on their corneal location. Cells isolated from the peripheral part of donor corneas have a higher proliferative capacity than cells obtained from the central part. The propagation of corneal endothelial cells in vitro offered the possibility of their transplantation on donor corneas in an in vitro model. After transplantation, these cells formed a monolayer whose morphology and cell density depended on the differentiation of the cells. DNA synthesis was predominantly detectable in cells of the corneal periphery.

CONCLUSIONS

Our findings are the basis of the following hypothesis: the periphery of the cornea represents a regenerative zone of the corneal endothelium. The fact that early after transplantation corneal endothelial cells form a monolayer on the natural extracellular matrix (ECM), which shows contact inhibition, suggests that inhibitory factors are released by the Descemet membrane that influence the proliferation of the cells. Further studies on the regulation of the proliferation and differentiation of human corneal endothelial cells in vitro and after transplantation might offer the possibility to establish a selective procedure for the treatment of corneal endothelial cell loss in the near future.

Objective evaluation of regional left ventricular wall motion during dobutamine stress echocardiographic studies using segmental analysis of color kinesis images

OBJECTIVES

To test the feasibility of objective and automated evaluation of echocardiographic stress tests, we studied the ability of segmental analysis of color kinesis (CK) images to detect dobutamine-induced wall motion abnormalities and compared this technique with inexperienced reviewers of conventional gray-scale images.

BACKGROUND

Conventional interpretation of stress echocardiographic studies is subjective and experience dependent.

METHODS

CK images were obtained in 89 of 104 consecutive patients undergoing clinical dobutamine stress studies and were analyzed using custom software to calculate regional fractional area change in 22 segments in four standard views. Each patient's data obtained at rest was used as a control for automated detection of dobutamine-induced wall motion abnormalities. Independently, studies were reviewed without CK overlays by two inexperienced readers who classified each segment's response to dobutamine. A consensus reading of two experienced reviewers was used as the gold standard for comparisons. In a subgroup of 16 patients, these consensus readings and CK detection of wall motion abnormalities were compared with coronary angiography.

RESULTS

The consensus reading detected ischemic response to dobutamine in 43 of 1958 segments in 23 of 89 patients. Automated detection of stress-induced wall motion abnormalities correlated more closely with the standard technique than the inexperienced reviewers (sensitivity 0.76 vs. 0.55, specificity 0.98 vs. 0.94 and accuracy 0.97 vs. 0.92). When compared with coronary angiography in a subgroup of patients, analysis of CK images differentiated between normal and abnormal wall motion more accurately than expert readers of gray-scale images (accuracy of 0.93 vs. 0.82).

CONCLUSIONS

Analysis of CK images allows fast, objective and automated evaluation of regional wall motion, sensitive enough for clinical dobutamine stress data and more accurate than inexperienced readers. This method may result in a valuable adjunct to conventional visual interpretation of dobutamine stress echocardiography.

Quantitative assessment of regional right ventricular function with color kinesis

We used color kinesis, a recent echocardiographic technique that provides regional information on the magnitude and timing of endocardial wall motion, to quantitatively assess regional right ventricular (RV) systolic and diastolic properties in 76 subjects who were divided into five groups, as follows: normal (n = 20), heart failure (n = 15), pressure/volume overload (n = 14), pressure overload (n = 12), and RV hypertrophy (n = 15). Quantitative segmental analysis of color kinesis images was used to obtain regional fractional area change (RFAC), which was displayed in the form of stacked histograms to determine patterns of endocardial wall motion. Time curves of integrated RFAC were used to objectively identify asynchrony of diastolic endocardial motion. When compared with normal subjects, patients with pressure overload or heart failure exhibited significantly decreased endocardial motion along the RV free wall. In the presence of mixed pressure/volume overload, the markedly increased ventricular septal motion compensated for decreased RV free wall motion. Diastolic endocardial wall motion was delayed in 17 of 72 segments (24%) in patients with RV pressure overload, and in 31 of 90 segments (34%) in patients with RV hypertrophy. Asynchrony of diastolic endocardial wall motion was greater in the latter group than in normal subjects (16% versus 10%: p < 0.01). Segmental analysis of color kinesis images allows quantitative assessment of regional RV systolic and diastolic properties.

Use of harmonic imaging without echocardiographic contrast to improve two-dimensional image quality

The aim of this study was to determine whether harmonic imaging (HI) improves endocardial visualization during 2-dimensional echocardiography without echocardiographic contrast. HI differs from fundamental imaging (FI) by transmitting ultrasound at one frequency and receiving at twice the transmitted frequency. This technique has been used in conjunction with contrast echocardiography to enhance myocardial contrast visualization. HI and FI were sequentially performed in 20 patients. Images were digitally stored and subsequently reviewed by 2 observers for the quality of endocardial visualization. In addition, acoustic quantification was performed in both FI and HI modes and endocardial tracking qualitatively judged. HI was compared with FI during dobutamine stress echocardiography in 17 patients who were imaged at baseline and peak stress. Overall, the harmonic images had less clutter and better myocardial blood contrast. Individual segments were better visualized with HI in 30% to 73% of cases. The acoustic quantification endocardial tracking was rated better with HI in 67% of short-axis views and in 58% of apical 4-chamber views. During dobutamine stress testing the overall number of interpretable segments improved from 64% for FI to 84% with HI. Many segments traditionally difficult to image were improved with HI. HI without the use of contrast agents improved endocardial visualization during routine 2-dimensional echocardiography. This improved endocardial visualization led to better endocardial tracking with acoustic quantification and to more segments being clinically interpretable during dobutamine stress testing.

Assessment of small-diameter aortic mechanical prostheses: physiological relevance of the Doppler gradient, utility of flow augmentation, and limitations of orifice area estimation

BACKGROUND

Noninvasive assessment of functionally stenotic small-diameter aortic mechanical prostheses is complicated by theoretical constraints relating to the hemodynamic relevance of Doppler-derived transprosthetic gradients. To establish the utility of Doppler echocardiography for evaluation of these valves, 20-mm Medtronic Hall and 19-mm St Jude prostheses were studied in vitro and in vivo.

METHODS AND RESULTS

Relations between the orifice transprosthetic gradient (equivalent to Doppler), the downstream gradient in the zone of recovered pressure (equivalent to catheter), and fluid mechanical energy losses were examined in vitro. Pressure-flow relations across the 2 prostheses were evaluated by Doppler echocardiography in vivo. For both types of prosthesis in vitro, the orifice was higher than the downstream gradient (P<0.001), and fluid mechanical energy losses were as strongly correlated with orifice as with downstream pressure gradients (r2=0.99 for both). Orifice and downstream gradients were higher and fluid mechanical energy losses were larger for the St Jude than the Medtronic Hall valve (all P<0.001). Whereas estimated effective orifice areas for the 2 valves in vivo were not significantly different, model-independent dynamic analysis of pressure-flow relations revealed higher gradients for the St Jude than the Medtronic Hall valve at a given flow rate (P<0.05).

CONCLUSIONS

Even in the presence of significant pressure recovery, the Doppler-derived gradient across small-diameter aortic mechanical prostheses does have hemodynamic relevance insofar as it reflects myocardial energy expenditure. Small differences in function between stenotic aortic mechanical prostheses, undetectable by conventional orifice area estimations, can be identified by dynamic Doppler echocardiographic analysis of pressure-flow relations.

Different characteristics of endothelial cells from central and peripheral human cornea in primary culture and after subculture

Several methods for isolation and cultivation of human corneal endothelial cells have been described during the last few decades. In contrast to the situation in vivo, the cultured cells show mitogenic activity but often lose their typical morphological appearance. In this paper, we describe a technique to isolate and cultivate morphologically unchanged endothelium from the human cornea. This method revealed different characteristics of endothelial cells according to their position within the human cornea. Endothelial cells isolated from the central part have a morphology similar to that of cells in vivo (i.e., they are densely packed and show no mitogenic activity). In contrast, endothelial cells derived from the peripheral part of the cornea are characterized by mitogenic activity but their cell-to-cell attachment seems to be less tight than in vivo. The significance of these two different endothelial cell types for wound healing in the human cornea is discussed.

Comparative study on the effects of different growth factors on migration of bovine corneal endothelial cells during wound healing

PURPOSE

In a comparative study we investigated the effects of epidermal growth factor, acidic and basic fibroblast growth factor, transforming growth factor-beta1, and vascular endothelial growth factor on proliferation and migration of cultured bovine corneal endothelial cells during wound healing.

METHODS

Cell proliferation was determined by incorporation of 5-bromo-2'-deoxy-uridine and by cell counting. To investigate cell migration, we established a method to produce identically shaped cell-free areas in monolayers of cultured cells and documented the wound-healing process.

RESULTS

Concerning the five tested growth factors, only epidermal growth factor as well as basic and acidic fibroblast growth factor stimulated DNA synthesis, cell proliferation, and migration during wound healing. Vascular endothelial growth factor stimulated migration during wound healing without influencing DNA synthesis or cell proliferation.

CONCLUSION

Whereas epidermal growth factor and the basic and acidic forms of fibroblast growth factor enhance proliferation as well as migration during wound healing, vascular endothelial growth factor seems to be a stimulatory agent specific for corneal endothelial cell migration.

Differences in proliferation and migration of corneal endothelial cells [correction of epithelial cells] after cell transplantation in vitro

For regular function the human cornea requires an intact endothelial cell layer with a sufficiently high cell density. One approach used to compensate endothelial cell loss is transplantation of cultured corneal endothelial cells. Using a previously described transplantation protocol, we observed topographic differences after transplantation of cultured human corneal endothelial cells to recipient corneas previously denuded of their own endothelium. The results presented in this paper suggest different interactions of the transplanted endothelial cells with the central or the peripheral part of the corneal matrix, respectively. Furthermore, cells isolated from the center of a human cornea differ from those isolated from the periphery in terms of their mitogenic capacity. The significance of these observations for corneal endothelial cell transplantation is discussed.

[Effect of differentiation on expression of genes for growth factors and growth factor receptors in human corneal endothelial cells]

In earlier publications we described a method for the isolation and long-term cultivation of human corneal endothelial cells. In several cultures we observed dedifferentiation of these cells, shown by loss of their normal polygonal shape and assumption of a fibroblastlike morphology. To reveal the role of growth factors for this dedifferentiation we analyzed the expression of genes encoding growth factors and growth factor receptors by differentiated and dedifferentiated human corneal endothelial cells. By means of northern blot analysis we demonstrated expression of the genes encoding basic fibroblast growth factor (bFGF), transforming growth factor beta (TGF beta 1), vascular endothelial growth factor (VEGF), FGF receptor-1 (flg-type) and epidermal growth factor receptor (EGF receptor) by both differentiated and dedifferentiated human corneal endothelial cells. In addition, expression of VEGF was stimulated by supplementation of growth medium by bFGF. In contrast, expression of the gene encoding flt-1, a receptor for VEGF, was only observed in dedifferentiated and not in differentiated human corneal endothelial cells. Despite this expression of flt-1, the dedifferentiated cells showed no mitogenic response to VEGF. The role of growth factors for dedifferentiation of human corneal endothelial cells is discussed.

Echocardiographic quantification of regional left ventricular wall motion with color kinesis

BACKGROUND

Color kinesis is a new technology for the echocardiographic assessment of left ventricular wall motion based on acoustic quantification. This technique automatically detects endocardial motion in real time by using integrated backscatter data to identify pixel transitions from blood to tissue during systole on a frame-by-frame basis. In this study, we evaluated the feasibility and accuracy of quantitative segmental analysis of color kinesis images to provide objective evaluation of regional systolic endocardial motion.

METHODS AND RESULTS

Two-dimensional echocardiograms were obtained in the short-axis and apical four-chamber views in 20 normal subjects and 40 patients with regional wall motion abnormalities. End-systolic color overlays superimposed on the gray scale images were obtained with color kinesis to color encode left ventricular endocardial motion throughout systole on a frame-by-frame basis. These color-encoded images were divided into segments by use of custom software. In each segment, pixels of different colors were counted and displayed as stacked histograms reflecting the magnitude and timing of regional endocardial excursion. In normal subjects, histograms were found to be highly consistent and reproducible. The patterns of contraction obtained in normal subjects were used as a reference for the objective automated interpretation of regional wall motion abnormalities, defined as deviations from this pattern. The variability in the echocardiographic interpretation of wall motion between two experienced readers was similar to the diagnostic variability between the consensus of the two readers and the automated interpretation.

CONCLUSIONS

Color kinesis is a promising new tool that may be used clinically to improve the qualitative and quantitative evaluation of spatial and temporal aspects of global and regional wall motion. In this initial study, segmental analysis of color kinesis images provided accurate, automated, and quantitative diagnosis of regional wall motion abnormalities.

Influence of vascular endothelial growth factor on bovine corneal endothelial cells in a wound-healing model

In this study we determined the influence of vascular endothelial growth factor (VEGF) on bovine corneal endothelial cell proliferation and wound healing. Proliferation was determined by measurement of DNA replication as well as by counting of the number of cells present after a defined growth period. In a wound-healing model, reproducible cell-free areas were created within monolayers of cultured bovine corneal endothelial cells and the migration of the cells into these areas was analyzed. The DNA replication and cell proliferation of bovine corneal endothelial cells were not influenced by VEGF. In contrast, in the wound-healing model, VEGF supplementation at concentrations of 1 and 10 ng/ml increased the cell density of the wounded area by 20% and 50%, respectively, as compared with the cell density of wounds left untreated by VEGF. Furthermore, no increase in DNA replication was found in cells involved in wound healing. Our results demonstrate that healing of bovine corneal endothelial cell layers after wounding is predominantly performed by cell migration rather than by proliferation. This migration can be stimulated by the addition of exogenous VEGF.