[show abstract][hide abstract] ABSTRACT: The authors' purpose was to develop a magnetic resonance (MR) imaging technique for examining the hip joint of a rabbit with a clinical MR imager.
Fourteen hips of 10 male New Zealand white rabbits were examined on a 1.5-T MR imager with a specially designed surface coil. Field of view was 3-8 cm, matrix was 256-512 x 192-256, section thickness was 0.9-2.0 mm, and spacing was 0.3-0.5 mm. The hips were sectioned and evaluated by means of light microscopy. Measurements of cartilage thickness from MR images were correlated with those from histologic specimens.
The resolution obtainable with a 1.5-T imager was adequate for imaging articular cartilage when a débrided rabbit hip specimen was placed in the center of a 3.5-cm single-loop coil. Rabbit hip cartilage had a trilaminar appearance on MR images. The coefficient of correlation between cartilage-thickness measurements was .81.
MR imaging of rabbit hip cartilage can be performed on 1.5-T clinical MR imaging unit. Limitations due to the field strength can be overcome with efficiently designed surface coils.
[show abstract][hide abstract] ABSTRACT: The 3D visual presentation of biodynamic events of human joints is a challenging task. Although the 3D reconstruction of high contrast structures from CT data has been widely explored, then there is much less experience in reconstructing the small low contrast soft tissue structures from inhomogeneous and sometimes noisy MR data. Further, there are no algorithms for tracking the motion of moving anatomic structures through MR data. We represent a comprehensive approach to 3D musculoskeletal imagery that addresses these challenges. Specific imaging protocols, segmentation algorithms and rendering techniques are developed and applied to render complex 3D musculoskeletal systems for their 4D visual presentation. Applications of our approach include analysis of rotational motion of the shoulder, the knee flexion, and other complex musculoskeletal motions, and the development of interactive virtual human joints.
Studies in health technology and informatics 02/1998; 50:27-33.
[show abstract][hide abstract] ABSTRACT: In magnetic resonance imaging (MRI), it is well-known that patient motion plays a significant role in the degradation of image quality. Although the case of translational in-plane motion (x-y-motion) has been studied by several researchers, the effect of rigid, translational out-of-plane motion (z-motion) has not yet been completely analyzed due to its more complex nature. Out-of-plane motion introduces blurring along the slice-selection direction in addition to motion artifacts. Here, the authors present a model to represent the effect of out-of-plane motion on multislice MR data. The inversion of this model not only results in the correction of the artifacts due to out-of-plane motion, but also reduces blurring in the slice-selection direction, yielding higher resolution images. Because of the shift-varying nature of the authors' model, they propose to use a nonlinear postprocessing method, projection onto convex sets (POCS), for its inversion, provided that the motion kernel and the slice-selection profile are known. The proposed method has been tested on simulated data and then applied to actual MR data to demonstrate the feasibility of the technique in real imaging situations.
IEEE Transactions on Medical Imaging 02/1995; 14(3):464-70. · 4.03 Impact Factor
[show abstract][hide abstract] ABSTRACT: Donors routinely undergo preoperative conventional arteriography to evaluate the renal arteries before nephrectomy. The purpose of this study was to assess the capability of three-dimensional phase-contrast MR angiograms postprocessed with maximum-intensity-projection and surface-rendering techniques to show the renal arteries of potential donors.
Postprocessed three-dimensional phase-contrast MR angiograms of 17 patients were retrospectively reviewed by two experienced radiologists for the number and length of renal arteries visualized. Conventional arteriograms were used as the reference standard. Coronal maximum-intensity-projection and surface-rendered MR angiograms were also compared with each other with regard to the delineation of renal arteries from overlapping vessels.
MR angiograms showed all 34 single or dominant renal arteries but only eight of 10 accessory arteries seen on conventional arteriograms. One of the nonvisualized accessory arteries was located within the imaged volume, and the other one arose from the distal aorta beyond the imaged regions. Five of six arterial branches arising from the proximal 30-mm portions of the renal arteries were seen on MR angiograms. Postprocessing with either maximum-intensity projection or surface-rendering showed the same number of renal arteries, although surface rendering separated overlapping veins from the renal arteries better than the maximum-intensity-projection technique.
These results suggest that three-dimensional MR angiography is a reliable method of imaging single or dominant renal arteries, but not for showing all accessory renal arteries and small arterial branches. Surface rendering may provide specific advantages over maximum-intensity-projection in delineating renal arteries from overlapping vessels.
American Journal of Roentgenology 02/1995; 164(1):117-21. · 2.90 Impact Factor
[show abstract][hide abstract] ABSTRACT: Flow- and motion-related artifacts are problematic in clinical MR imaging. In this paper we discuss the utility of a phase-corrected real reconstruction to reduce flow artifacts. This technique is particularly useful when flow-compensation pulse sequences may not be possible, such as when a very short echo delay or small field-of-view is desired. We will demonstrate that the phase-corrected real reconstruction provides superior results to the magnitude reconstruction either used alone or in conjunction with existing flow-compensation techniques.
Magnetic Resonance in Medicine 01/1994; 30(6):724-31. · 3.27 Impact Factor