We present a technique for modeling liver motion during the respiratory cycle using intensity-based nonrigid registration of gated magnetic resonance (MR) images. Three-dimensional MR images of the abdomens of four volunteers were acquired at end-inspiration, end-expiration, and eight time points in between using respiratory gating. The deformation fields between the images were computed using intensity-based rigid and nonrigid registration algorithms. Global motion is modeled by a rigid transformation while local motion is modeled by a free-form deformation based on B-splines. Much of the liver motion was cranial-caudal translation, which was captured by the rigid transformation. However, there was still substantial residual deformation (approximately 10 mm averaged over the entire liver in four volunteers, and 34 mm at one place in the liver of one volunteer). The computed organ motion model can potentially be used to determine an appropriate respiratory-gated radiotherapy window during which the position of the target is known within a specified excursion.

PURPOSE:To reconstruct three-dimensional (3D) myocardial deformations from orthogonal sets of parallel-tagged magnetic resonance (MR) images. MATERIALS AND METHODS:Displacement information in the direction normal to the undeformed tag planes was obtained at points along tag lines. Three independent sets of onedimensional displacement data were used to fit an analytical series expression to describe 3D displacement as a function of deformed position. The technique was demonstrated with computergenerated models of the deformed left ventricle with data from healthy human volunteers. RESULTS:Model deformations were reconstructed with a 3D tracking error of less than 0.3 mm. Error between estimated and observed one-dimensional displacements along the tags in 10 human subjects was 0.00 mm ± 0.36 (mean ± standard deviation). Robustness to noise in the tag displacement data was demonstrated by using a Monte Carlo simulation. CONCLUSION:The combination of rapidly acquired parallel-tagged MR images and field-fitting analysis is a valuable tool in cardiac mechanics research and in the clinical assessment of cardiac mechanical function. KeywordsHeart, function, 51.91; Magnetic resonance (MR), physics, 511.1214; Myocardium, MR, 511.1214 MAGNETIC resonance (MR) imaging tagging (1-7) and fast, breath-hold imaging (8,9) are promising tools for noninvasive study of the function of the heart wall in both research and clinical settings. The objective of this study was to measure noninvasively the threedimensional (3D) deformation field within the heart wall at many time points in the heart cycle.Myocandial tags are regions where the magnetization has been perturbed before imaging and that, therefore, produce a signal intensity difference relative to that of nontagged regions for a time proportional to T1. Because the tags result from perturbations of the magnetization of the tissue itself, the deformation of the tags accurately reflects the motion of the underlying tissue (10-12). Special techniques are needed to reconstruct the 3D motion of the heart from MR image planes that are fixed in space, because different sections of tissue are sampled at different times.Correspondence to: Elliot R. McVeigh.Address reprint requests to E.R.M.. NIH Public Access Author ManuscriptRadiology. Author manuscript; available in PMC 2008 May 26. Published in final edited form as:Radiology. 1995 June ; 195(3): 829-835. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptThe movement of the heart through short-axis image planes, known as cardiac through-plane motion, is typically 10 mm at the base of the left ventricle (13). (This was confirmed with the analysis of 10 healthy human subjects discussed in this article.) Correction for this is crucial, even for two-dimensional analysis of wall deformation (14). This correction was achieved by combining information from both long-and short-axis sets of tagged heart images into a unified expression for the 3D displacement field.Previously presented motion reconstruction sc...

Purpose: To demonstrate the efficacy of an automated three-dimensional (3D) template matching-based algorithm in detecting brain metastases on conventional MR scans and the potential of our algorithm to be developed into a computer-aided detection tool that will allow radiologists to maintain a high level of detection sensitivity while reducing image reading time. Materials and Methods:Spherical tumor appearance models were created to match the expected geometry of brain metastases while accounting for partial volume effects and offsets due to the cut of MRI sampling planes. A 3D normalized cross-correlation coefficient was calculated between the brain volume and spherical templates of varying radii using a fast frequency domain algorithm to identify likely positions of brain metastases.Results: Algorithm parameters were optimized on training datasets, and then data were collected on 22 patient datasets containing 79 total brain metastases producing a sensitivity of 89.9% with a false positive rate of 0.22 per image slice when restricted to the brain mass.Conclusion: Study results demonstrate that the 3D template matching-based method can be an effective, fast, and accurate approach that could serve as a useful tool for assisting radiologists in providing earlier and more definitive diagnoses of metastases within the brain.

All previous studies of residual strain in the ventricular wall have been based on one- or two-dimensional measurements. Transmural distributions of three-dimensional (3-D) residual strains were measured by biplane radiography of columns of lead beads implanted in the midanterior free wall of the canine left ventricle (LV). 3-D bead coordinates were reconstructed with the isolated arrested LV in the zero-pressure state and again after local residual stress had been relieved by excising a transmural block of tissue. Nonhomogeneous 3-D residual strains were computed by finite element analysis. Mean ± SD ( n = 8) circumferential residual strain indicated that the intact unloaded myocardium was prestretched at the epicardium (0.07 ± 0.06) and compressed in the subendocardium (−0.04 ± 0.05). Small but significant longitudinal shortening and torsional shear residual strains were also measured. Residual fiber strain was tensile at the epicardium (0.05 ± 0.06) and compressive in the subendocardium (−0.01 ± 0.04), with residual extension and shortening, respectively, along structural axes parallel and perpendicular to the laminar myocardial sheets. Relatively small residual shear strains with respect to the myofiber sheets suggest that prestretching in the plane of the myocardial laminae may be a primary mechanism of residual stress in the LV.