Effects of prosthetic valve placement on mitral annular dynamics and the left ventricular base.

Insertion of a rigid mitral prosthesis impairs the function of the mitral annulus and induces systolic narrowing of the left ventricular outflow tract (LVOT). To study this mechanism, we investigated dynamic changes in the left ventricular (LV) base, which consists of the mitral annulus and LVOT orifice. In seven patients with mechanical mitral valve prostheses and eight normal subjects, the image of the LV base was reconstructed three-dimensionally and its dynamic change during systole was studied. In the patients, the rigid prosthetic valve (=mitral annulus) tilted toward the left ventricle with a hinge point at the posterior mitral annulus during systole. The left ventricular base exhibited contraction, but the size of the prosthetic valve was constant. As a consequence, the prosthetic valve occupied more of the left ventricular base, which resulted in narrowing of the LVOT. In the normal subjects, the mitral annulus did not interfere with the region of the LVOT orifice during systole as the mitral annulus underwent both dorsiflexion and contraction. Thus, fixation of the mitral annulus induces an anti-physiologic motion of the annulus. Conscious preservation of annular flexibility in mitral valve surgery is important in avoiding potential dynamic LVOT obstruction.

A system for computer-assisted design of stent-grafts for aortic aneurysms using 3-D morphological models.

A three-dimensional model was constructed from helical CT images for abdominal aortic aneurysm (AAA) and thoracic aortic aneurysm (TAA). A stent-graft was designed and positioned endoluminally on the computer. One hundred and nine stent-grafts for 101 patients were designed by this method and deployed well in all patients. The design time was reduced from 4 to 0.5 hr.

Detailed motion analysis of the left ventricular myocardium using an MR tagging method with a dense grid.

Detailed analysis of myocardial deformation through a whole cardiac cycle was accomplished using a tagging method with a high-density grid. Four sets of tagged images with a 4-mm-spacing grid were measured by generating four tagging pulses arranged at regular intervals in the cardiac cycle. Through each set of images, tag intersections were tracked semi-automatically. The estimated motions of tag intersections were concatenated so that sequential positions of myocardium were connected through a whole cardiac cycle. In vitro evaluation of the precision of this technique showed that the mean error of tracked 4-mm tag intersections was less than 0.47 +/- 0.17 mm, even on the quite low-contrast images, and the concatenation error caused by double concatenation was comparable to the interpolation error in the subendocardial area obtained with 8-mm tag intersection motion. The small difference between the two mean distance curves of the in vivo evaluation indicated that the method is useful for analyzing heart wall abnormalities. Magn Reson Med 44:73-82, 2000.

Three-dimensional thoracic modeling for an anatomical compatibility study of the implantable total artificial heart.

Anatomical compatibility with the thoracic cavity is important in developing a completely implantable total artificial heart (TAH). The purpose of this study was to examine the optimal morphology of our TAH and to develop a computer implantation simulation environment for preoperational discussion. As the first stage, we constructed a prototype simulation system by creating a 3-D surface model of a thoracic cavity and one of a TAH. In this system, the thoracic surface model, composed of the aorta, pulmonary artery, ventricle resected heart, diaphragm, and thoracic wall, was created based on the organ contours extracted from electrocardiogram (ECG)-synchronized ultrafast computer tomographic images. The accuracy of the thoracic model was discussed using a phantom. The fitting study can be performed on the computer with the model of the thorax and that of the TAH. In the future, construction of a database for the thoracic cavities of heart failure patients is planned to improve the morphology of the TAH.

A rapid matching algorithm for cerebral 3D images using 1D projection.

A rapid image matching algorithm for cerebral three-dimensional (3D) images is described. Fully automatic 3D image matching between images acquired the same modality and this was realized by applying the following sequential processes: (1) the calculation of one-dimensional (1D) projection patterns from both reference and input 3D images; (2) the matching between the two sets of 1D patterns; and (3) the transformation of input 3D image according to the pattern matching result. The 3D morphological variations among images due to shift and linear/non-linear scaling along projection axes were recovered, as well as compensation for mismatching due to image rotation and partial deficit of image data. The computation time of this method was quite short compared to that of the conventional 3D pattern matching method.

Medical applications with synchrotron radiation in Japan.

In Japan, various medical applications of synchrotron X-ray imaging, such as angiography, monochromatic X-ray computed tomography (CT), radiography and radiation therapy, are being developed. In particular, coronary arteriography (CAG) is quite an important clinical application of synchrotron radiation. Using a two-dimensional imaging method, the first human intravenous CAG was carried out at KEK in May 1996; however, further improvements of image quality are required in clinical practice. On the other hand, two-dimensional aortographic CAG revealed canine coronary arteries as clearly as those on selective CAG, and coronary arteries less than 0.2 mm in diameter. Among applications of synchrotron radiation to X-ray CT, phase-contrast X-ray CT and fluorescent X-ray CT are expected to be very interesting future applications of synchrotron radiation. For actual clinical applications of synchrotron radiation, a medical beamline and a laboratory are now being constructed at SPring-8 in Harima.

The relationship between the mitral annulus and left ventricular outflow tract.

Mitral annular inflexibility due to rigid prostheses (ring or valve) has long been considered to contribute to the mechanism of dynamic left ventricular outflow tract (LVOT) obstruction after mitral repair or replacement. In clarifying the geometric relationship between LVOT orifice and mitral valve annulus (MVA) in eight normal subjects, the authors have endeavored to show how that a rigid mitral prosthesis might obstruct the LVOT based on the assumption that any rigid prosthesis necessarily follows the motion of the posterior half of the MVA (MVApost) in the course of every heart beat. During systole, the relationship between the MVApost and the approximated plane of the LVOT orifice was constant. However, with the respect to the relationship between the LVOT orifice and the approximated plane of the MVApost (PI-MVApost), the intersection between the two shifted toward the apex during systole. Assuming the prosthesis is aligned on the MVApost with the same orientation as the PI-MvApost, this shift implies a reduction in the effective size of the LVOT orifice due to the prosthesis. The calculated obstruction rate was 24.9% (0 ms), 30.9% (100 ms), 35.5% (200 ms), and 45.4% (300 ms). These results indicate the importance of maintaining the flexibility of the MVA after mitral valve surgery.

Dynamic change in the left ventricular base with or without a rigid mitral valve prosthesis.

To evaluate the narrowing of the left ventricular outflow tract (LVOT) during systole caused by a rigid mitral prosthesis, the geometric relationship between the prosthesis (or the mitral annulus) and the left ventricular base (LVB) was studied in five patients with mechanical mitral valve prostheses and eight normal subjects. The images of the mitral valve annulus (MVA) and the LVOT orifice reconstructed in three dimensions were projected on the plane of the LV base. Calculating the areas of these projected images (i.e., those for MVA [Sm], LVOT orifice [So], the LVB [Sb; Sb = Sm + So]), the MVA-LVB ratio (Sm/Sb) was determined. In the normal subject, the MVA-LVB ratio was nearly constant during systole (59 +/- 5% at 0 msec and 62 +/- 7% at 300 msec, respectively), whereas in the patients with prostheses, the ratio increased from 61 +/- 4% (0 msec) to 69 +/- 4% (300 msec). The increase in MVA-LVB ratio reduces the proportionate share of LVOT orifice in relation to the total LVB. The ideal mitral valve prosthesis should be flexible at the annulus to attain good performance in LVB dynamics.

Imaging of the orifice of the left ventricular outflow tract: technique and initial results.

The mechanism of left ventricular outflow tract (LVOT) obstruction in the patient after mitral valve replacement or repair was examined with the aid of 2D echocardiography. For the interpretation of the spatial relationship between the aortic root and mitral annulus, however, the 2D display is sometimes inadequate since it may not simultaneously capture these structures in each center. We developed a method to clarify this relationship in 3D based on magnetic resonance images. We defined the office of the left ventricular outflow tract (LVOT orifice), consisting of, in turn, a muscular region, i.e., edge of the interventricular septum, and an annular region, i.e., the annulus of the anterior mitral leaflet. In this paper we present image data obtained from one of eight normal subjects examined and compare this with data of one of two patients who preoperatively suffered degenerative mitral regurgitation and subsequently underwent chordal-preserving mitral valve replacement, in which anterior chordae were reattached to the anterior annulus. In the normal subject, the mitral annulus exhibited a flexible change in shape during the systole, maintaining sufficient LVOT orifice size. In the patient, the prosthetic valve exhibited translational motion during systole, resulting in dynamic LVOT obstruction. This phenomenon was also observed in one other case. Furthermore, the lateral view of the LVOT orifice revealed a projection of the prosthetic valve into the LVOT, causing mechanical LVOT obstruction. The finding that translational motion of the prosthetic valve with an inflexible mitral annulus results in dynamic LVOT obstruction may support the hypothesis that annular rigidity causes dynamic LVOT obstruction after mitral valve repair with a rigid prosthetic ring.

An improved computer method to prepare 3D magnetic resonance images of thoracic structures.

The mediastinal and cardiovascular anatomy is complex. We have developed a three-dimensional (3D) reconstruction system for the major mediastinal structures using magnetic resonance imaging data on a NeXT workstation. The program uses a combination of automatic and manual procedures to determine the contours of the cardiac structures. The geometric centers of the contours are connected by a 3D space curve, and the central axis of each cardiac structures is determined. The contours are projected on the perpendicular plane to the central axis and semiautomatically processed until the contours of one pixel are obtained. Then the surface rendering with transparency is performed. Compositing combines two images so that both appear in the composite, superimposed on each other. Demonstration of the various mediastinal lines and cardiovascular diseases by the composits of the partly transparent 3D images has promoted a better understanding of the complex mediastinal and cardiovascular anatomy and diseases.

Mitral annular flexibility.

An analysis of three-dimensional movement of the mitral valve annulus (MVA) may address the question of geometrical change after mitral valve repair to preserve mitral annular function. Conventionally, annular contraction has been studied for this purpose. We investigated this geometrical change occurring in the anterior half of the MVA and discuss its clinical significance. Three-dimensional images of the MVA during systole were reconstructed from magnetic resonance images of eight normal subjects. The posterior half of the MVA exhibited translational motion. We assume that this portion, exhibiting translational motion as well as contraction, purely follows the motion of the left ventricular contraction. Compensating for the discrepancy between the motion of the aortic root and that of the posterior half of the MVA, the anterior half exhibited a flexible change in shape during systole, thus maintaining a sufficient left ventricular outflow tract (LVOT). The increase in the extent of displacement of the anterior MVA from the posterior half of the MVA during systole, which was 3.6 +/- 1.0 mm (mean +/- SD), indicates the annular flexibility. The preservation of annular flexibility may prevent LVOT obstruction. Further geometrical analysis of patients after mitral repair will clarify annular function as presented in this article.

Set-up, improvement, and evaluation of an electrohydraulic total artificial heart with a separately placed energy converter.

The authors have been developing an electrohydraulic total artificial heart (TAH) system with a separately placed electrohydraulic energy converter to minimize anatomic constraints in the pericardial space. Improvements to the system and current status of the development are reported. The energy converter was miniaturized to improve implantability, and its thickness was reduced to 54 mm. System efficiency was increased by suppressing rush current at the time of motor reversal. Maximum cardiac output of the TAH system was 9 L/min, and maximum system efficiency increased to 10%. The blood pump system was implanted easily in the body of a 57 kg calf, and no significant temperature rise on the energy converter surface was observed. As the next step, main components were integrated into a total system. The transcutaneous energy transfer system could supply power to the TAH without a decline in pump performance, and the internal battery could support the system at 6.5 L/min of cardiac output for 1 hour without a decrease in cardiac output. The authors consider the TAH system with a separately placed energy converter the most promising approach to development of a TAH for smaller sized patients.

The inflexible mitral annulus after valve prosthesis. Inherent risk of dynamic left ventricular outflow tract obstruction.

Although chordal preserving mitral valve replacement is beneficial to cardiac function, the loss of flexibility of the annulus and consequent translational motion of the valve prosthesis during systole may cause potential left ventricular outflow tract (LVOT) obstruction after surgery. The extent of the flexibility of the mitral valve annulus (MVA) necessary for the prosthetic valve to prevent potential LVOT obstruction was determined. The three dimensional images of the MVA at 0, 100, 200, and 300 msec delay from the electrocardiogram R wave were reconstructed from cine-mode magnetic resonance images in eight normal subjects. In the lateral view of the MVA, the dorsal flexion angle (DFA) was defined. This angle implies the extent of the flexion of the anterior half of the MVA in relation to the posterior half. The data (mean +/- SD) for the DFA were 31.7 +/- 5.4 degrees (0 msec), 36.4 +/- 4.5 degrees (100 msec), 39.0 +/- 3.8 degrees (200 msec), and 43.6 +/- 2.6 degrees (300 msec), whereas the systolic increase in DFA was 11.9 +/- 3.2 degrees. The flexibility observed in normal mitral annuli is relevant to prosthetic mitral valves.

Development of an electrohydraulic total artificial heart at the National Cardiovascular Center, Osaka, Japan.

The authors have been developing an electrohydraulic total artificial heart with a basic concept placing the blood pumps and an electrohydraulic energy converter separately, in the thorax and the abdominal region, respectively, to minimize anatomic constraints. Major problems of the system were a high energy consumption of 56 W at 6 L/min output and an insufficient maximum output of 6.7 L/min. The energy converter was redesigned to overcome these problems. A three phase, 4 pole brushless DC motor, which has maximum efficiency of 79% at a motor rotation of 2500 rpm with a load of 0.1 Nm, was developed for the new energy converter. Flow-channel design of the regenerative oil pump was optimized, which resulted in increasing the maximum flow rate at one directional motor rotation from 18 to 29 L/min. In vitro performance of the electrohydraulic total artificial heart was evaluated in a mock circulation with physiologic pressure conditions. Maximum output was increased to 10.7 L/min at a pump rate of 120 bpm and energy consumption of the motor at 6 L/min output was reduced to 18 W. Based upon these favorable results, the system is now being assembled for chronic animal implantation.

Study of cardiac structures in relation to the pericardial cavity for total artificial heart implantation.

To enhance the design of the completely implantable total artificial heart (TAH), we developed a coordinate system that expresses the geometry of the heart, including that at the interface with the TAH and that of the pericardial cavity. This coordinate system (ventricular coordinate system) was developed using 3D images of the heart which were obtained from magnetic resonance images. The origin is located on the centroid of the mitral annulus at 25 ms delay from the ECG R wave (M0), and the y axis is the axis from M0 to the apex at 25 ms delay (Apex0). The x-y plane includes M0, Apex0, and the centroid of the tricuspid annulus at 25 ms delay. Since the y axis expresses the apical orientation of the heart, data using this coordinate system are not affected by individual variation in heart orientation. Heart geometry data were obtained in 5 normal subjects. Compared with that using the coordinate system based on the thoracic wall, the expression of the data of interface geometry for the heart and the TAH is simplified when the ventricular coordinate system is used. A method of expressing the geometry of the pericardial cavity using the ventricular coordinate system is also proposed. These methods may be applicable in obtaining data in patients suffering from cardiomyopathy.

Mitral annular function assessed by 3D imaging for mitral valve surgery.

We developed a surgical technique for mitral valve reconstruction without a prosthetic ring. This procedure may have two advantages. One is avoidance of the potential thrombogenicity of the prosthetic ring, and the other is that this procedure may maintain the normal function of mitral annulus. To clarify the latter advantage, we defined a method for 3D assessment of the heart, especially for the dynamic changes of the mitral annulus. 3D images of the heart, including both mitral and tricuspid annuli in eight phases during the cardiac cycle, were reconstructed from magnetic resonance images of seven normal subjects, and used for this study. To depict the changes in the annular shape, we determined the following parameters of the annular function: (a) annular excursion, (b) direction of motion (direction cosine) and (c) orientation of the annulus (direction cosine) for the annular motion, (d) annular area and (e) displacement of the anterior portion from the approximated plane of the annulus. The data for the systolic annular motion indicate that the mitral annulus moves towards the apex with slight caudal deviation, with the excursion of 12.1 mm. The change in annular orientation indicates that the mitral annulus shows translational motion during systole. The mitral area was reduced by 25.6% (n = 5) from mid-diastole to mid-or late systole. Displacement at the anterior portion of the annulus did not change markedly during systole. The results demonstrate the physiologic function of the mitral annulus in normal subjects. This method will be applied to the clinical study of mitral valve reconstruction surgery. Based on the differences in annular length in intact and excised states, we describe the intact state of the posterior leaflet as "natural redundancy." Restoration of this natural redundancy has been a hallmark of successful mitral repair for over 20 years.

[Clinical applications of synchrotron radiation X-ray].

Synchrotron Radiation X-ray (SR X-ray) is an extremely strong X-ray source with a photon number more than 10(4) compared with that of the current X-ray tube. X-rays obtained by monochromatizing SR X-ray have been applied to new techniques for medical diagnosis. Several studies are now being conducted at the beam site for medical use at the Accumulation Ring of the High Energy Physics Research Institute, Tsukuba. Applications being studied include (1) energy subtraction coronary angiography. (2) microdetection of metas in samples excised from subjects. (3) monochromatic X-ray computed tomography and so on. Energy subtraction coronary angiography might have a safety advantage over the current selective coronary angiography. Microdetection of mandatory metals and poisonous heavy metals in in vivo samples contributes to the development of pathologic knowledge and clinical treatment of cancer and heavy metal toxications. Monochromatic X-ray CT is expected to detect diseases in the early stage due to increased accuracy in CT values.

Estimation of 2-D blood flow velocity map from cine-angiograms: algorithm using overlapping block set and illustration of vortex flow in abdominal aneurysm.

To derive blood flow dynamics from cine-angiograms (CAGs), we have developed an image-processing algorithm to determine a two-dimensional blood flow velocity map projected on CAGs. Each image data of CAG is divided into a set of overlapping blocks, and it is assumed that the contrast medium in each block moves only to its 'adjacent blocks' between two serial frames. Based on this assumption, a 'fundamental equation' and the 'maximum flow constraints' are derived. These equations state the relationship between the volume of contrast medium in each block and the volume of contrast medium flowing from/to its 'adjacent blocks'. The volume of the flowing contrast medium is calculated using these relationships, boundary conditions and an additional 'smoothness constraint'. The blood flow velocities are estimated from the volume of the flowing contrast medium and are illustrated with a needle diagram. We applied our algorithm to an abdominal CAG (clinical data). The result showed a vortex flow in the abdominal aneurysm, which was consistent with visual inspection of the CAG movie and with the existence of thrombus in the aneurysm. Our algorithm may be a useful diagnostic tool to assess vascular disease.

Optimal sampling interval and edge detection algorithm for measurement of blood vessel diameter on a cineangiogram.

RATIONALE AND OBJECTIVES: The authors studied the effects of image magnification and the type of edge detection filter on the precision of measuring blood vessel diameters on coronary angiograms. METHOD: A blood vessel phantom containing five channels of various diameters filled with contrast medium was filmed. The magnifications examined were x4, x10, and x20, and the edge detection filters used were the first derivative, second derivative, composite, and entropy filters. The regression line y = a+bx was introduced, where x represents the nominal diameter and y the diameter measured by the edge-detection filters. Determination criteria were the offset, slope, and residual variance from the regression equation. RESULTS: The best value among three criteria was obtained with a magnification of x10 or x20. The entropy filter gave the best value of slope and residual variance. The composite filter gave the best value of offset. CONCLUSION: The most precise measurement is obtained when the entropy filter and a magnification of x10 or x20 are applied.

Three-dimensional imaging of mitral and tricuspid annuli for total artificial heart implantation.

The establishment of a method to clarify the three-dimensional interrelations among the mitral annulus, tricuspid annulus, ascending aorta, and main pulmonary artery, which constitute the interface between the human and total artificial heart (TAH), is essential to the design of the TAH. In a previous study based on transverse magnetic resonance (MR) images of a live human heart, reconstructed images of mitral and tricuspid annuli were found to be deformed. The present study of cadaver and beating hearts revealed that the optimal conditions for atrioventricular annular reconstruction of a beating heart with electrocardiogram-gated MR imaging include use of four-chamber imaging, 5 mm slice thickness, and a slice interval ranging from 5 to 7 mm. Under these conditions, the mitral and tricuspid annuli of 3 beating hearts were reconstructed successfully. It was recognized that during the systolic phase the mitral and tricuspid annuli move anteriorly, leftward and downward, and that in late systole the right lateral margin of the tricuspid annulus is close to the sternum.