A quantitative evaluation of the three dimensional reconstruction of patients' coronary arteries.

BACKGROUND: Through extensive training and experience angiographers learn to mentally reconstruct the three dimensional (3D) relationships of the coronary arterial branches. Graphic computer technology can assist angiographers to more quickly visualize the coronary 3D structure from limited initial views and then help to determine additional helpful views by predicting subsequent angiograms before they are obtained. METHODS: A new computer method for facilitating 3D reconstruction and visualization of human coronary arteries was evaluated by reconstructing biplane left coronary angiograms from 30 patients. The accuracy of the reconstruction was assessed in two ways: 1) by comparing the vessel's centerlines of the actual angiograms with the centerlines of a 2D projection of the 3D model projected into the exact angle of the actual angiogram; and 2) by comparing two 3D models generated by different simultaneous pairs on angiograms. The inter- and intraobserver variability of reconstruction were evaluated by mathematically comparing the 3D model centerlines of repeated reconstructions. RESULTS: The average absolute corrected displacement of 14,662 vessel centerline points in 2D from 30 patients was 1.64 +/- 2.26 mm. The average corrected absolute displacement of 3D models generated from different biplane pairs was 7.08 +/- 3.21 mm. The intraobserver variability of absolute 3D corrected displacement was 5.22 +/- 3.39 mm. The interobserver variability was 6.6 +/- 3.1 mm. CONCLUSIONS: The centerline analyses show that the reconstruction algorithm is mathematically accurate and reproducible. The figures presented in this report put these measurement errors into clinical perspective showing that they yield an accurate representation of the clinically relevant information seen on the actual angiograms. These data show that this technique can be clinically useful by accurately displaying in three dimensions the complex relationships of the branches of the coronary arterial tree.

Applied virtual reality for simulation of endoscopic retrograde cholangio-pancreatography (ERCP).

Researchers from the Georgia Institute of Technology and the Medical College of Georgia (GIT/MCG) have developed an interactive computer simulation of Endoscopic Retrograde Cholangio-Pancreatography (ERCP). ERCP is a minimally invasive technique for evaluating and treating pathologic conditions of the biliary and pancreatic ducts. While ERCP provides the patient with substantial advantages over traditional methods, ERCP requires advanced skills and extensive experience to minimize the risk of complications. Computer simulation offers many advantages for efficiently and safely training physicians in ERCP. The GIT/MCG proof of concept simulation provides realistic training with both visual and force feedback while an endoscopist practices the ERCP procedure.

Three-dimensional displays of left ventricular epicardial surface from standard cardiac SPECT perfusion quantification techniques.

UNLABELLED: Two methods for generating left ventricular epicardial surface from SPECT perfusion tomograms are described and validated. Both methods use the locations of the maximal reconstructed count values determined from a perfusion quantification procedure as a basis for generating surfaces. METHODS: The first method fits circular contours, which are perpendicular to the long-axis, to the points obtained from perfusion quantification. The second method applies median and linear filters to the points to remove noise but maintain the basic shape of the surface. Both models are validated against an automatic technique and against the user-traced surfaces of both the perfusion image and an MR image of the same patient. RESULTS: The median-filtered model was found to be closer to the standard surfaces than the circular model in all cases, and 85% of the points on the median-filtered surfaces were within one SPECT pixel length of the hand-traced MR surfaces. CONCLUSION: Accurate, three-dimensional left ventricular epicardial surfaces can be generated quickly and easily from already existing perfusion quantification software. The resulting images may be useful for realistic displays of ventricular size, shape and the three-dimensional distribution of perfusion.

Computer-simulated eye surgery. A novel teaching method for residents and practitioners.

PURPOSE: To describe an eye surgery simulator that uses a computerized graphic display to allow ophthalmic surgeons of all experience levels to enhance their surgical skills. METHODS: The eye surgery simulation environment consists of a high-speed computer graphics workstation, a stereo operating system, a wrist rest, and a position tracking stylus connected to force feedback motors. The surgeon views computer-generated images of the eye and surgical instruments through the stereo operating system and controls the position and orientation of the chosen surgical instrument by moving the stylus. During the simulated instrument-tissue interactions, three feedback motors generate component force feedback along three orthogonal axes connected by thin rigid bars to the tip of the stylus. RESULTS: The current proof-of-concept system provides a method for rapid learning experiences in a living eye simulation. Procedures can be recorded for playback and analysis, as well as for examination of techniques from different viewpoints (e.g., from inside the eye). Four simulated surgical instruments are available for use (scalpel, forceps, scissors, and phacoemulsifier). CONCLUSION: Eye surgery simulation offers both beginning and experienced ophthalmic surgeons an opportunity to learn new techniques and skills and achieve a satisfactory level of proficiency before use of that procedure in the operating room. When fully developed, this system should shorten the learning curve for new surgeons (i.e., residents) and offer an opportunity for practice before doing a difficult case or development of new techniques by experienced surgeons. The goal of replacement of current standard training methods for surgeons awaits further refinement and adjustment of the model.

Three-dimensional coronary angiography.

For at least two decades coronary cine-angiograms have been reviewed on film projectors. The cardiologist most often reviews the multiple two-dimensional projections of the coronary arterial tree on a screen, and then mentally create a three-dimensional (3-D) model of the patient's arteries. The ability to synthesize this data and grasp the three-dimensionality of a patient's specific anatomy is quite difficult and requires extensive training and experience to perfect. Fortunately, with advances in computer hardware and software, cardiologists, with all levels of experience, will have assistance with this difficult task. It is now possible, with the use of computers, to reconstruct and display a patient's coronary angiogram in 3-D, allowing the cardiologist to review this data in ways not previously available. In the near future, enhancements in the technique will allow this technology to be placed on-line, directly in the cardiac catheterization laboratory, greatly facilitating the ability to diagnose abnormalities and more appropriately plan treatment strategies.

Computer modeling of the abdominal aorta using magnetic resonance images.

An approach is described for creating a 3-D computer model of the abdominal aorta from just two projective images. The aorta is modeled by conical segments connecting circular cross sections. Accuracy of this technique is within 1 mm. From the 3-D computer model, quantitative measurements of vessel diameter, length, and position are available for any subset of the arterial structure. Visualization is enhanced by displaying the computer model rather than a direct set of images obtained from different perspectives. Ambiguities from overlapping branches can be resolved by rotating the model or by eliminating the interfering structures. This approach has been applied in both phantom studies, in which quantitative comparisons were made, and in vivo studies, in which qualitative evaluations were made.

Evaluation of magnetic resonance velocimetry for steady flow.

Whole body magnetic resonance (MR) imaging has recently become an important diagnostic tool for cardiovascular diseases. The technique of magnetic resonance phase velocity encoding allows the quantitative measurement of velocity for an arbitrary component direction. A study was initiated to determine the ability and accuracy of MR velocimetry to measure a wide range of flow conditions including flow separation, three-dimensional secondary flow, high velocity gradients, and turbulence. A steady flow system pumped water doped with manganese chloride through a variety of test sections. Images were produced using gradient echo sequences on test sections including a straight tube, a curved tube, a smoothly converging-diverging nozzle, and an orifice. Magnetic resonance measurements of laminar and turbulent flows were depicted as cross-sectional velocity profiles. MR velocity measurements revealed such flow behavior as spatially varying velocity, recirculation and secondary flows over a wide range of conditions. Comparisons made with published experimental laser Doppler anemometry measurements and theoretical calculations for similar flow conditions revealed excellent accuracy and precision levels. The successful measurement of velocity profiles for a variety of flow conditions and geometries indicate that magnetic resonance imaging is an accurate, non-contacting velocimeter.

Visualization of multimodality cardiac imagery.

A large number of clinically important and medically difficult decisions in diagnostic radiology involve interpreting the information derived from multiple imaging modalities. This is especially true in the assessment of heart disease, wherein at least two types of image information are generally required prior to deciding on the course of action: structural information describing coronary vessel anatomy and functional information related to heart muscle physiology. This paper will present and discuss the methods and results associated with a research program aimed at quantifying and visualizing the unified anatomic and physiologic information obtained from these complementary imaging modalities. The discussions will emphasize the reconstruction, processing, and visualization of three-dimensional cardiovascular structure, including the procedures and results obtained from phantom and patient studies.