In the diagnosis and therapy of prostate cancer, it is critical to measure the volume of the prostate and locate its boundary. Three-dimensional transrectal ultrasound (3D TRUS) imaging has been demonstrated to be a useful technique to perform such a task. Due to image speckle as well as low contrast in ultrasound images, segmentation of the prostate in 3D US images is challenging. In this paper, we report on the development of an improved slice-based 3D prostate segmentation method. First, we imposed a continuity constraint for the end points of the prostate boundaries in a cross-sectional plane so that a smooth prostate boundary in 2D is obtained. Then, in each 2D slice, we inserted the end points into the vertex list of the initial contour to obtain a new contour, which forces the evolving contour to be driven to the boundary of the prostate. Evaluation demonstrated that our method could segment the prostate in 3D TRUS images more quickly and accurately.
Background: Micro-computed tomography offers numerous advantages for small animal imaging, including the ability to monitor the same animals throughout a longitudinal study. However, concerns are often raised regarding the effects of x-ray dose accumulated over the course of the experiment. In this study, we scan C57BL/6 mice multiple times per week for six weeks, to determine the effect of the cumulative dose on pulmonary tissue at the end of the study. Methods/Results: C57BL/6 male mice were split into two groups (irradiated group=10, control group=10). The irradiated group was scanned (80kVp/50mA) each week for 6 weeks; the weekly scan session had three scans. This resulted in a weekly dose of 0.84 Gy, and a total study dose of 5.04 Gy. The control group was scanned on the final week. Scans from weeks 1 and 6 were reconstructed and analyzed: overall, there was no significant difference in lung volume or lung density between the control group and the irradiated group. Similarly, there were no significant differences between the week 1 and week 6 scans in the irradiated group. Histological samples taken from excised lung tissue also showed no evidence of inflammation or fibrosis in the irradiated group. Conclusion: This study demonstrates that a 5 Gy x-ray dose accumulated over six weeks during a longitudinal micro-CT study has no significant effects on the pulmonary tissue of C57BL/6 mice. As a result, the many advantages of micro- CT imaging, including rapid acquisition of high-resolution, isotropic images in free-breathing mice, can be taken advantage of in longitudinal studies without concern for negative dose-related effects.
Sensitivity to phase deviations in MRI forms the basis of a variety of techniques, including magnetic susceptibility weighted imaging and chemical shift imaging. Current phase processing techniques fall into two families: those which process the complex image data with magnitude and phase coupled, and phase unwrapping-based techniques that first linearize the phase topology across the image. However, issues, such as low signal and the existence of phase poles, can lead both methods to experience error. Cyclic continuous max-flow (CCMF) phase processing uses primal-dual-variational optimization over a cylindrical manifold, which represent the inherent topology of phase images, increasing its robustness to these issues. CCMF represents a third distinct paradigm in phase processing, being the only technique equipped with the inherent topology of phase. CCMF is robust and efficient with at least comparable accuracy as the prior paradigms.
We have constructed a table-top CT system with high spatial resolution in all three dimensions which can be used to analyze excised tissue samples in vitro. Our system uses an x-ray image intensifier, optically coupled to a time delay integration (ThI) CCD to obtain low-noise, low-scatter projection radiographs of the sample volume. Rather than collecting one projection line at a time (as in conventional CT scanners), the architecture of the TDI-CCD allows us to collect 96 image lines simultaneously. The digital radiograph is formed by scanning a slot-beam of radiation across the sample, reducing the detection of scattered radiation without excessive x-ray tube heat loading. Objects to be imaged are placed on a computer-controlled stage and projections are obtained as the sample is rotated. A water bath surrounds the sample to equalize the exposure to the image intensifier, thereby reducing the dynamic range of the input signal. CT reconstruction of this data results in a 512 volume image with 0.13 x 0.13 mm pixels in the transverse plane and a slice thickness of 0.15 mm. This table-top CTscanner has been used to investigate the properties of intact, excised human arterial samples as part of our research into the development of vascular disease.
Advances in nanotechnology have led to the development of blood-pool contrast agents for micro-computed tomography (micro-CT). Although long-circulating nanoparticle-based agents exist for micro-CT, they are predominantly based on iodine, which has a low atomic number. Micro-CT contrast increases when using elements with higher atomic numbers (i.e. lanthanides), particularly at higher energies. The purpose of our work was to develop and evaluate a lanthanide-based blood-pool contrast agent that is suitable for in vivo micro-CT. We synthesized a contrast agent in the form of polymer-encapsulated Gd nanoparticles and evaluated its stability in vitro. The synthesized nanoparticles were shown to have an average diameter of 127 ± 6 nm, with good size dispersity. Particle size distribution -- evaluated by dynamic light scattering over the period of two days -- demonstrated no change in size of the contrast agent in water and saline. Additionally, our contrast agent was stable in a mouse serum mimic for up to 30 minutes. CT images of the synthesized contrast agent (containing 27 mg/mL of Gd) demonstrated an attenuation of over 1000 Hounsfield Units. This approach to synthesizing a Gd-based blood-pool contrast agent promises to enhance the capabilities of micro-CT imaging.
We have developed an interactive geometric method for 3D reconstruction of the coronary arteries using multiple single‐plane angiographic views with arbitrary orientations. Epipolar planes and epipolar lines are employed to trace corresponding vessel segments on these views. These points are utilized to reconstruct 3D vessel centerlines. The accuracy of the reconstruction is assessed using: (1) near‐intersection distances of the rays that connect x‐ray sources with projected points, (2) distances between traced and projected centerlines. These same two measures enter into a fitness function for a genetic search algorithm (GA) employed to orient the angiographic image planes automatically in 3D avoiding local minima in the search for optimized parameters. Furthermore, the GA utilizes traced vessel shapes (as opposed to isolated anchor points) to assist the optimization process. Differences between two‐view and multiview reconstructions are evaluated. Vessel radii are measured and used to render the coronary tree in 3D as a surface. Reconstruction fidelity is demonstrated via (1) virtual phantom, (2) real phantom, and (3) patient data sets, the latter two of which utilize the GA. These simulated and measured angiograms illustrate that the vessel centerlines are reconstructed in 3D with accuracy below . The reconstruction method is thus accurate compared to typical vessel dimensions of . The methods presented should enable a combined interpretation of the severity of coronary artery stenoses and the hemodynamic impact on myocardial perfusion in patients with coronary artery disease.
