A novel approach to produce axial echocardiographic images by three-dimensional transesophageal echocardiography: A step-by-step guide

Three-Dimensional (3-D) echocardiography is becoming increasingly used to diagnose and describe the spatial location of valvular pathologies and atrial septal defects during transesophageal echocardiography (TEE). The role of 3D-TEE is not well established in diagnosing other congenital heart diseases like partial anomalous pulmonary venous drainage (PAPVD) and coronary anomalous. We propose a step by step approach to producing computed tomography-simulated axial images from 3-D TEE to simplify TEE interpretation and diagnosis of cardiac abnormalities.     

Two distinct overstretched DNA structures revealed by single-molecule thermodynamics measurements

Double-stranded DNA is a dynamic molecule whose structure can change depending on conditions. While there is consensus in the literature about many structures DNA can have, the state of highly-stretched DNA is still not clear. Several groups have shown that DNA in the torsion-unconstrained B-form undergoes an “overstretching” transition at a stretching force of around 65 pN, which leads to approximately 1.7-fold elongation of the DNA contour length. Recent experiments have revealed that two distinct structural transitions are involved in the overstretching process: (i) a hysteretic “peeling” off one strand from its complementary strand, and (ii) a nonhysteretic transition that leads to an undetermined DNA structure. We report the first simultaneous determination of the entropy (ΔS) and enthalpy changes (ΔH) pertaining to these respective transitions. For the hysteretic peeling transition, we determined ΔS ∼ 20 cal/(K.mol) and ΔH ∼ 7 kcal/mol. In the case of the nonhysteretic transition, ΔS ∼ -3 cal/(K.mol) and ΔH ∼ 1 kcal/mol. Furthermore, the response of the transition force to salt concentration implies that the two DNA strands are spatially separated after the hysteretic peeling transition. In contrast, the corresponding response after the nonhysteretic transition indicated that the strands remained in close proximity. The selection between the two transitions depends on DNA base-pair stability, and it can be illustrated by a multidimensional phase diagram. Our results provide important insights into the thermodynamics of DNA overstretching and conformational structures of overstretched DNA that may play an important role in vivo.     

Morphological analysis of aortic root in eccentric aortic regurgitation using anyplane two-dimensional images produced by transesophageal three-dimensional echocardiography

BACKGROUND AND AIM OF THE STUDY: Evaluation of leaflet dysfunction in aortic valve repair is important. In eccentric aortic regurgitation (AR), it is unclear whether leaflet dysfunction other than prolapse exists. The study aim was to validate the hypothesis that eccentric AR correlates with leaflet dysfunction. METHODS: Both anyplane 2-D images produced by a 3-D reconstruction system and surgical views for 21 patients with eccentric AR (11 with aortic valve prolapse, group A; 10 without prolapse, group B) were analyzed prospectively. Vertical height from annulus to coaptation point (termed AC), and distance from coaptation point to sinotubular junction (CS) were measured at early diastole. RESULTS: For group A, AC and CS values were 1.3 +/- 2.2 mm and 25.9 +/- 3.4 mm respectively for leaflets of eccentric AR jet origin, and 3.8 +/- 0.4 mm and 22.7 +/- 2.1 mm for other leaflets. For group B, AC and CS values were 4.7 +/- 0.9 mm and 39.8 +/- 7.0 mm for leaflets of eccentric AR jet origin, and 7.8 +/- 0.9 mm and 31.9 +/- 5.7 mm for other leaflets. The AC for leaflets of eccentric AR jet origin was smaller than AC for other leaflets (p < 0.01) between both groups. There was no difference between CS for leaflets of eccentric AR jet origin and other leaflets in group A, but CS for leaflets of eccentric AR jet origin was larger than for other leaflets in group B (p <0.01). AC and CS values for leaflets of eccentric AR jet origin in group B were larger than those for group A. Leaflets of eccentric AR jet origin were always shifted toward the direction of the base in the anyplane images, and elongated in the surgical view. CONCLUSION: Anyplane 2-D images obtained by 3-D echocardiography showed that aortic leaflets of eccentric AR jet origin shifted towards the direction of the base with or without prolapse, and were accompanied by dysfunction. Color flow Doppler determination of the eccentricity of AR jet origin was useful in predicting aortic valve dysfunction.     

A new anatomical approach to congenital valve diseases by three-dimensional echocardiography]

Congenital valvular heart disease in childhood is often complex. Conventional echocardiography provides two-dimensional views which require mental reconstruction for three-dimensional assessment. This problem may be solved by the use of three-dimensional (3D) echocardiography which obtains images of valves comparable to those seen at surgery. This was confirmed by 4 cases of congenital valvular heart disease studied by 3D echocardiography: stenotic bicuspid aortic valve disease, parachute mitral valve and two cases of mitral regurgitation in patients with atrioventricular canal. The 3D views of the aortic valve showed the commissural opening after percutaneous balloon valvuloplasty of the bicuspid valve. The surface of the aortic orifice and the surface of the two mitral leaflets were measured from 3D reconstructions. The longitudinal 3D view analysed the extension of the single obstructive mitral papillary muscle of the parachute malformation. The 3D ventricular views allowed assessment of the extension of the cleft and the surface of the three mitral leaflets of the 2 cases of atrioventricular canal. In one of these cases, the results of surgical valvuloplasty were evaluated after 3D reconstruction of the valve. 3D echocardiography is not only a diagnostic tool for congenital heart disease but also a very useful complementary investigation for accurate evaluation of congenital valvular lesions to optimise possible valve repair.     

Interpreting three-dimensional structures from two-dimensional images: a web-based interactive 3D teaching model of surgical liver anatomy

Background:

Given the increasing number of indications for liver surgery and the growing complexity of operations, many trainees in surgical, imaging and related subspecialties require a good working knowledge of the complex intrahepatic anatomy. Computed tomography (CT), the most commonly used liver imaging modality, enhances our understanding of liver anatomy, but comprises a two-dimensional (2D) representation of a complex 3D organ. It is challenging for trainees to acquire the necessary skills for converting these 2D images into 3D mental reconstructions because learning opportunities are limited and internal hepatic anatomy is complicated, asymmetrical and variable. We have created a website that uses interactive 3D models of the liver to assist trainees in understanding the complex spatial anatomy of the liver and to help them create a 3D mental interpretation of this anatomy when viewing CT scans.

Methods:

Computed tomography scans were imported into DICOM imaging software (OsiriX™) to obtain 3D surface renderings of the liver and its internal structures. Using these 3D renderings as a reference, 3D models of the liver surface and the intrahepatic structures, portal veins, hepatic veins, hepatic arteries and the biliary system were created using 3D modelling software (Cinema 4D™).

Results:

Using current best practices for creating multimedia tools, a unique, freely available, online learning resource has been developed, entitled Visual Interactive Resource for Teaching, Understanding And Learning Liver Anatomy (VIRTUAL Liver) (http://pie.med.utoronto.ca/VLiver). This website uses interactive 3D models to provide trainees with a constructive resource for learning common liver anatomy and liver segmentation, and facilitates the development of the skills required to mentally reconstruct a 3D version of this anatomy from 2D CT scans.

Discussion:

Although the intended audience for VIRTUAL Liver consists of residents in various medical and surgical specialties, the website will also be useful for other health care professionals (i.e. radiologists, nurses, hepatologists, radiation oncologists, family doctors) and educators because it provides a comprehensive resource for teaching liver anatomy.     

An approach to crystallizing proteins by synthetic symmetrization

Previous studies of symmetry preferences in protein crystals suggest that symmetric proteins, such as homodimers, might crystallize more readily on average than asymmetric, monomeric proteins. Proteins that are naturally monomeric can be made homodimeric artificially by forming disulfide bonds between individual cysteine residues introduced by mutagenesis. Furthermore, by creating a variety of single-cysteine mutants, a series of distinct synthetic dimers can be generated for a given protein of interest, with each expected to gain advantage from its added symmetry and to exhibit a crystallization behavior distinct from the other constructs. This strategy was tested on phage T4 lysozyme, a protein whose crystallization as a monomer has been studied exhaustively. Experiments on three single-cysteine mutants, each prepared in dimeric form, yielded numerous novel crystal forms that cannot be realized by monomeric lysozyme. Six new crystal forms have been characterized. The results suggest that synthetic symmetrization may be a useful approach for enlarging the search space for crystallizing proteins.     

Direct single-molecule observation of a protein living in two opposed native structures

Biological activity in proteins requires them to share the energy landscape for folding and global conformational motions, 2 key determinants of function. Although most structural studies to date have focused on fluctuations around a single structural basin, we directly observe the coexistence of 2 symmetrically opposed conformations for a mutant of the Rop-homodimer (Repressor of Primer) in single-molecule fluorescence resonance energy transfer (smFRET) measurements. We find that mild denaturing conditions can affect the sensitive balance between the conformations, generating an equilibrium ensemble consisting of 2 equally occupied structural basins. Despite the need for large-scale conformational rearrangement, both native structures are dynamically and reversibly adopted for the same paired molecules without separation of the constituent monomers. Such an ability of some proteins or protein complexes to switch between conformations by thermal fluctuations and/or minor environmental changes could be central to their ability to control biological function.     

Route to three-dimensional fragments using diversity-oriented synthesis

Fragment-based drug discovery (FBDD) has proven to be an effective means of producing high-quality chemical ligands as starting points for drug-discovery pursuits. The increasing number of clinical candidate drugs developed using FBDD approaches is a testament of the efficacy of this approach. The success of fragment-based methods is highly dependent on the identity of the fragment library used for screening. The vast majority of FBDD has centered on the use of sp(2)-rich aromatic compounds. An expanded set of fragments that possess more 3D character would provide access to a larger chemical space of fragments than those currently used. Diversity-oriented synthesis (DOS) aims to efficiently generate a set of molecules diverse in skeletal and stereochemical properties. Molecules derived from DOS have also displayed significant success in the modulation of function of various "difficult" targets. Herein, we describe the application of DOS toward the construction of a unique set of fragments containing highly sp(3)-rich skeletons for fragment-based screening. Using cheminformatic analysis, we quantified the shapes and physical properties of the new 3D fragments and compared them with a database containing known fragment-like molecules.     

Transthoracic real-time three-dimensional echocardiography using the rotational scanning approach for data acquisition

Transthoracic real-time three-dimensional echocardiography using the rational scanning approach for data acquisition became a feasible modality for cardiac imaging during the last 4 years. Several attempts for reconstruction of the heart have been made using different methods. In this study we evaluate the data acquisition using the rotational approach from the transthoracic window. Thirty-five children with congenital heart disease were enrolled in the study. All of them underwent complete two-dimensional and Doppler echocardiogram followed by three-dimensional reconstruction using rotational image acquisition. The rotational approach enabled us to acquire good data from subcostal, apical, and suprasternal notch positions by rotating the transducer from 0 degrees-180 degrees. Novel views of the atrioventricular valve, semilunar valve, atrial, and ventricular septi were established by spatial plane imaging from the three-dimensional echocardiography. This reconstruction enables spatial imaging of cardiac structures and deficiencies. Three-dimensional echocardiography will enhance the understanding of complex congenital heart disease.     

Unified three-dimensional images of myocardial perfusion and coronary angiography

INTRODUCTION AND OBJECTIVES: In everyday clinical practice, the cardiologist needs to integrate anatomical and functional information from patients with coronary artery disease. The aim of this study is to present a way to unify, in three-dimensional images, anatomical information from coronary angiography with physiological information from myocardial perfusion scintigraphy. METHODS: Three patients with one vessel disease (left anterior descending, right coronary and left circumflex arteries, respectively) scheduled for percutaneous coronary revascularization were selected. Two-dimensional angiographic images were obtained before and after revascularization. 99mTc-tetrofosmin was administered during coronary occlusion and tomographic images corresponding to the occlusion were detected after coronary dilatation. Control rest scintigraphic images were obtained after two days. The three-dimensional coronary tree from coronary angiography was superposed on the epicardial contours of the myocardial perfusion images following a method of our own. RESULTS: A correct three-dimensional reconstruction of myocardial contour and coronary tree was achieved for each patient. The three-dimensional unified images showed excellent concordance between the extent of perfusion defects and the anatomic distribution of the occluded vessel. CONCLUSIONS: Three-dimensional unification of myocardial perfusion images and coronary angiography is technically possible. This technology integrates anatomical and functional information to facilitate the cardiologist's decision-making and so improve coronary patient management.     

Quantitative assessment of diffuse coronary artery disease using a three-dimensional reconstruction method compared with intravascular ultrasound images

BACKGROUND: It can be difficult to estimate the degree of stenosis in patients with diffuse coronary artery disease (CAD), because of the lack of a normal reference segment. If the size of normal coronary lumen has a direct relation to size of distal myocardial bed, it could be used to estimate the 'normal' cross-sectional area of coronary lumen. Accordingly, we could estimate the degree of stenosis of coronary arteries with diffuse disease by comparing them with calculated 'normal' areas of lumen. OBJECTIVE: To assess the validity of the above hypothesis. METHOD: Fourteen subjects without coronary atherosclerosis (group A) and 16 patients with CAD (group B) underwent simultaneous bidirectional coronary arteriography. Using these coronary arteriograms, we determined the relationship between cross-sectional area of coronary lumen measured by using a computerized edge-detection system and summed distal branch length calculated by using our computerized three-dimensional reconstruction method. RESULTS: For group A, we found a close correlation between area of lumen and branch length (r= 0.948). However, for group B, there were some segments for which the measured area of lumen was clearly smaller than that expected from the relationship for group A. From this relationship for group A, we calculated the stenosis ratios of 22 segments and, to confirm their accuracy, we compared the stenotic ratios with those measured on intravascular ultrasound images. The stenotic ratio of each segment of stenotic coronary artery calculated by our method agreed significantly well with the results obtained from the ultrasound measurements (r= 0.980). CONCLUSIONS: These observations validate a novel approach to quantifying diffuse CAD using clinical arteriograms.     

An automatic approach to the analysis, quantitation and review of perfusion and function from myocardial perfusion SPECT images

We have developed a software suite that automatically selects, analyses, quantitates and displays all the key image data in a myocardial perfusion SPECT study. Methods: The files automatically selected (upon specification of the patient name) are rest and stress projections, rest and stress short axis and gated short axis files, and all snapshot files. The projection data sets are presented in cine mode for evaluation of patient motion, while the lung/heart ratio at rest and stress is calculated from regions of interest (ROIs) that are automatically derived and overlayed on the LAO 45 images. Left ventricular (LV) cavity volumes at rest and stress are calculated from the short axis data sets, and the related transient ischemic dilation (TID) ratio derived and displayed. Quantitative measurements of global (ejection fraction) and regional function parameters are performed from the gated short axis dataset. All algorithms use the C++, X-Windows and OSF-Motif standards. The overall suite executes in less than 1 minute on a SunSPARC5 with 32 Mb of RAM and no proprietary hardware. Results: The software was validated on 144 patients (118 rest²⁰¹ Tl/post-stress ^99mTc-sestamibi, 18 post-stress ^99mTc-sestamibi, 8 rest ²⁰¹Tl) acquired on a 90° dual detector (ADAC Vertex, 91 patients) and a triple detector camera (Picker Prism 3000, 53 patients). Overall, the individual algorithms for the analysis of projection, short axis and gated short axis images were successful in 622/660 (94.2%) of the images. In 80.5% of the patients (73/91+43/53) all algorithms executed successfully, without significant difference in success rates for²⁰¹ Tl versus ^99mTc-sestamibi images. Conclusion: Our automated approach to myocardial perfusion SPECT analysis and review is highly successful, intrinsically reproducible, and can produce time and cost savings while improving accuracy in a clinical or teleradiology-type environment.     

Detection of single-molecule interactions using correlated thermal diffusion

Observation of discrete, single-molecule binding events allows one to bypass assumptions required to infer single-molecule properties from studies of ensembles of molecules. Optically trapped beads and glass microneedles have been applied to detect single-molecule binding events, but it remains difficult to identify signs of binding events given the large displacements induced by thermal forces. Here, we exploit thermal diffusion by using correlation between motion of optically trapped beads attached to both ends of a single actin filament to track binding events of individual myosin molecules. We use correlated diffusion to measure the stiffness of a single myosin molecule and estimate its thermal fluctuation in a poststroke state as comparable in amplitude to the measured stroke distance. The use of correlated diffusion to measure kinetics of single-molecule interactions and the stiffness of the interacting moieties should be applicable to any pair of interacting molecules, and not limited to biological motors.     

Imaging whole Escherichia coli bacteria by using single-particle x-ray diffraction

We report the first experimental recording, to our knowledge, of the diffraction pattern from intact Escherichia coli bacteria using coherent x-rays with a wavelength of 2 A. By using the oversampling phasing method, a real space image at a resolution of 30 nm was directly reconstructed from the diffraction pattern. An R factor used for characterizing the quality of the reconstruction was in the range of 5%, which demonstrated the reliability of the reconstruction process. The distribution of proteins inside the bacteria labeled with manganese oxide has been identified and this distribution confirmed by fluorescence microscopy images. Compared with lens-based microscopy, this diffraction-based imaging approach can examine thicker samples, such as whole cultured cells, in three dimensions with resolution limited only by radiation damage. Looking forward, the successful recording and reconstruction of diffraction patterns from biological samples reported here represent an important step toward the potential of imaging single biomolecules at near-atomic resolution by combining single-particle diffraction with x-ray free electron lasers.     

An approach to the multiple-minima problem by relaxing dimensionality.

A method is presented for starting from a very-low-energy high-dimensional conformation and obtaining a low-energy three-dimensional structure by gradual contraction of the dimensionality. The contraction in dimensionality is achieved by use of Cayley-Menger determinants, of which a simplified form is derived here. Preliminary results are presented for a virtual-bond pentapeptide and for full-atom representations of several terminally blocked amino acids.