Biomedical subjects

Ziji Wu

Publications and source records attributed to Ziji Wu.

5 recordsLinked to original sources

PubMed2005

Comparative evaluation of strain-based and model-based modulus elastography.

Elastography based on strain imaging currently endures mechanical artefacts and limited contrast transfer efficiency. Solving the inverse elasticity problem (IEP) should obviate these difficulties; however, this approach to elastography is often fraught with problems because of the ill-posed nature of the IEP. The aim of the present study was to determine how the quality of modulus elastograms computed by solving the IEP compared with those produced using standard strain imaging methodology. Strain-based modulus elastograms (i.e., modulus elastograms computed by simply inverting strain elastograms based on the assumption of stress uniformity) and model-based modulus elastograms (i.e., modulus elastograms computed by solving the IEP) were computed from a common cohort of simulated and gelatin-based phantoms that contained inclusions of varying size and modulus contrast. The ensuing elastograms were evaluated by employing the contrast-to-noise ratio (CNR(e)) and the contrast transfer efficiency (CTE(e)) performance metrics. The results demonstrated that, at a fixed spatial resolution, the CNR(e) of strain-based modulus elastograms was statistically equivalent to those computed by solving the IEP. At low modulus contrast, the CTE(e) of both elastographic imaging approaches was comparable; however, at high modulus, the CTE(e) of model-based modulus elastograms was superior.

Algorithms↗

PubMed2005

Adaptive model initialization and deformation for automatic segmentation of T1-weighted brain MRI data.

A fully automatic, two-step, T1-weighted brain magnetic resonance imaging (MRI) segmentation method is presented. A preliminary mask of parenchyma is first estimated through adaptive image intensity analysis and mathematical morphological operations. It serves as the initial model and probability reference for a level-set algorithm in the second step, which finalizes the segmentation based on both image intensity and geometric information. The Dice coefficient and Euclidean distance between boundaries of automatic results and the corresponding references are reported for both phantom and clinical MR data. For the 28 patient scans acquired at our institution, the average Dice coefficient was 98.2% and the mean Euclidean surface distance measure was 0.074 mm. The entire segmentation for either a simulated or a clinical image volume finishes within 2 min on a modern PC system. The accuracy and speed of this technique allow us to automatically create patient-specific finite element models within the operating room on a timely basis for application in image-guided updating of preoperative scans.

Algorithms↗

PubMed2005

Stereopsis-guided brain shift compensation.

Brain deformation models have proven to be a powerful tool in compensating for soft tissue deformation during image-guided neurosurgery. The accuracy of these models can be improved by incorporating intraoperative measurements of brain motion. We have designed and implemented a passive intraoperative stereo vision system capable of estimating the three-dimensional shape of the surgical scene in near real-time. This intraoperative shape is compared with the cortical surface in the co-registered preoperative magnetic resonance (MR) volume for the estimation of the cortical motion resulting from the open cranial surgery. The estimated cortical motion is then used to guide a full brain model, which updates a preoperative MR volume. We have found that the stereo vision system is accurate to within approximately 1 mm. Based on data from two representative clinical cases, we show that stereopsis guidance improves the accuracy of brain shift compensation both at and below the cortical surface.

Algorithms↗

PubMed2005

Cortical surface tracking using a stereoscopic operating microscope.

OBJECTIVE: To measure and compensate for soft tissue deformation during image-guided neurosurgery, we have developed a novel approach to estimate the three-dimensional (3-D) topology of the cortical surface and track its motion over time. METHODS: We use stereopsis to estimate the 3-D cortical topology during neurosurgical procedures. To facilitate this process, two charge-coupled device cameras have been attached to the binocular optics of a stereoscopic operating microscope. Before surgery, this stereo imaging system is calibrated to obtain the extrinsic and intrinsic camera parameters. During surgery, the 3-D shape of the cortical surface is automatically estimated from a stereo pair of images and registered to the preoperative image volume to provide navigational guidance. This estimation requires robust matching of features between the images, which, when combined with the camera calibration, yields the desired 3-D coordinates. After the 3-D cortical surface has been estimated from stereo pairs, its motion is tracked by comparing the current surface with its previous locations. RESULTS: We are able to estimate the 3-D topology of the cortical surface with an average error of less than 1.2 mm. Executing on a 1.1-GHz Pentium machine, the 3-D estimation from a stereo pair of 1024 x 768 resolution images requires approximately 60 seconds of computation. By applying stereopsis over time, we are able to track the motion of the cortical surface, including the pulsatile movement of the cortical surface, gravitational sag, tissue bulge as a result of increased intracranial pressure, and the parenchymal shape changes associated with tissue resection. The results from 10 surgical patients are reported. CONCLUSION: We have demonstrated that a stereo vision system coupled to the operating microscope can be used to efficiently estimate the dynamic topology of the cortical surface during surgery. The 3-D surface can be coregistered to the preoperative image volume. This unique intraoperative imaging technique expands the capability of the current navigational system in the operating room and increases the accuracy of anatomic correspondence with preoperative images through compensation for brain deformation.

Adult↗

PubMed2004

Activation of neural pathways associated with sexual arousal in non-human primates.

PURPOSE: To evaluate brain activity associated with sexual arousal, fully conscious male marmoset monkeys were imaged during presentation of odors that naturally elicit high levels of sexual activity and sexual motivation. MATERIAL AND METHODS: Male monkeys were lightly anesthetized, secured in a head and body restrainer with a built-in birdcage resonator and positioned in a 9.4-Tesla spectrometer. When fully conscious, monkeys were presented with the odors of a novel receptive female or an ovariectomized monkey. Both odors were presented during an imaging trial and the presentation of odors was counterbalanced. Significant changes in both positive and negative BOLD signal were mapped and averaged. RESULTS: Periovulatory odors significantly increased positive BOLD signal in several cortical areas: the striatum, hippocampus, septum, periaqueductal gray, and cerebellum, in comparison with odors from ovariectomized monkeys. Conversely, negative BOLD signal was significantly increased in the temporal cortex, cingulate cortex, putamen, hippocampus, substantia nigra, medial preoptic area, and cerebellum with presentation of odors from ovariectomized marmosets as compared to periovulatory odors. A common neural circuit comprising the temporal and cingulate cortices, putamen, hippocampus, medial preoptic area, and cerebellum shared both the positive BOLD response to periovulatory odors and the negative BOLD response to odors of ovariectomized females. CONCLUSION: These data suggest the odor-driven enhancement and suppression of sexual arousal affect neuronal activity in many of the same general brain areas. These areas included not only those associated with sexual activity, but also areas involved in emotional processing and reward.

Animals↗