Showing papers by "Michael W. Vannier published in 1997"

Subgenual prefrontal cortex abnormalities in mood disorders

Abstract: Pathological disturbances of mood may follow a 'bipolar' course, in which normal moods alternate with both depression and mania, or a 'unipolar' course, in which only depression occurs. Both bipolar and unipolar disorders can be heritable illnesses associated with neurochemical, neuroendocrine and autonomic abnormalities. The neurobiological basis for these abnormalities has not been established. Using positron emission tomographic (PET) images of cerebral blood flow and rate of glucose metabolism to measure brain activity, we have now localized an area of abnormally decreased activity in the prefrontal cortex ventral to the genu of the corpus callosum in both familial bipolar depressives and familial unipolar depressives. This decrement in activity was at least partly explained by a corresponding reduction in cortical volume, as magnetic resonance imaging (MRI) demonstrated reductions in the mean grey matter volume in the same area of 39 and 48% in the bipolar and unipolar samples, respectively. This region has previously been implicated in the mediation of emotional and autonomic responses to socially significant or provocative stimuli, and in the modulation of the neurotransmitter systems targeted by antidepressant drugs.

Three-dimensional hippocampal MR morphometry with high-dimensional transformation of a neuroanatomic atlas.

Abstract: PURPOSE: To test automated three-dimensional magnetic resonance (MR) imaging morphometry of the human hippocampus, to determine the potential gain in precision compared with conventional manual morphometry. MATERIAL AND METHODS: A canonical three-dimensional MR image atlas was used as a deformable template and automatically matched to three-dimensional MR images of 10 individuals (five healthy and five schizophrenic subjects). A subvolume containing the hippocampus was defined by using 16 landmarks that constrained the automated search for hippocampal boundaries. Transformation of the hippocampus template was automatically performed by using global pattern matching through a sequence of low-then high-dimensional translations, rotations, and scalings. RESULTS: The average test-retest volume difference measured with the automatic method was 3.1%, compared with the manual test-retest difference of 7.1%. Correlation between automated and manually determined volumes demonstrated the validity of the automated t...

Total hip prosthesis metal-artifact suppression using iterative deblurring reconstruction.

Abstract: Purpose: CT of total joint prostheses is limited by metal artifact produced mainly by missing projection data. Iterative deblurring reconstruction is less sensitive to missing projection data than filtered backprojection. A software CT simulator was used to compare total hip prosthesis images reconstructed using standard filtered backprojection, filtered backprojection after linear interpolation of missing data, and iterative deblurring. Method: Unilateral and bilateral total hip replacements with metal-backed or all-polyethylene acetabular prostheses were simulated using bone, metal, and polyethylene annuli and circles of metal and water (soft tissue). Material attenuation properties were taken from the literature. The simulation assumed that no X-rays penetrated the metal. Simulated projection data were reconstructed using filtered backprojection, filtered backprojection after linear interpolation of missing data, and iterative deblurring. Visual observations and objective region-of-interest analyses were made. Results: Even with no X-rays penetrating the metal, iterative deblurring produced almost no visible artifact within the bone or soft tissues. Bone edge detection and sizing were more easily and accurately done from the iterative deblurring images. All reconstruction techniques underestimated bone and water CT attenuation values. Metal artifact was worse for the bilateral or metal-backed prostheses. Conclusion: Iterative deblurring generated nearly metal-artifact-free images in this simulation. Filtered backprojection, even after linear interpolation, produced typical clinical metal-artifact images.

Iterative process for reconstructing cone-beam tomographic images

Abstract: In the present invention, an iterative process is provided for cone-beam tomography (parallel-beam and fan-beam geometries are considered as its special cases), and applied to metal artifact reduction and local reconstruction from truncated data, as well as image noise reduction. In different embodiments, these iterative processes may be based upon the emission computerized tomography (CT) expectation maximization (EM) formula and/or the algebraic reconstruction technique (ART). In one embodiment, generation of a projection mask and computation of a 3D spatially varying relaxation factor are utilized to compensate for beam divergence, data inconsistence and incompleteness.

Three-dimensional dental imaging by spiral CT: A progress report

Abstract: Objective. To demonstrate the feasibility of using spiral computed tomographic data for three-dimensional image acquisition, display, and segmentation of dental structures and lesions and to demonstrate the feasibility of metal artifact suppression. Study design. Isolated extracted teeth, a dry mandible, cadaver mandible, and cadaver head were scanned and reconstructed using spiral computed tomography data. Algorithms for metal artifact reduction including extended attenuation range and interpolation of missing projections were applied. Volumetric rendering was performed to synthesize images comparable to conventional intraoral dental radiographs. Serial examinations were obtained by spiral computed tomographic tomography, registered by surface matching, and interval change determined by three-dimensional subtraction. Results. Metal artifact reduction was successful in markedly reducing the streaks and star patterns that usually accompany metallic restorations and intraoral appliances. Voxel sum images were comparable to dental radiographs. Image segmentation could successfully isolate dental structures, and simulated lesions could be detected through three-dimensional subtraction. Conclusion. The results demonstrate the feasibility of spiral volumetric computed tomography for quantitative study of oral hard tissues in the presence of metal restorations.

Attachment loss with postmenopausal age and smoking

Abstract: To determine whether postmenopausal bone loss and factors associated with osteoporosis affect tooth retention, we examined vertebral and proximal femoral (postcranial) bone mineral density in relation to tooth loss and attachment loss in a cross-sectional study of 135 postmenopausal women (age range 41-70 yr). Women had at least 10 teeth and no evidence of moderate or severe periodontal disease. Full-mouth attachment loss measurements were made using a pressure-sensitive probe, and bone density was determined by dual-energy X-ray absorptiometry. Attachment loss was correlated with tooth loss (number of remaining teeth, radiologically determined), but not with vertebral or proximal femur bone density. Multivariate analysis showed current smoking (p = 0.01), years since menopause (p = 0.02) and the interaction of age and current smoking (p < 0.01), to be statistically significant predictors of attachment loss in our study population.

Relationship between bone and muscles of mastication in hemifacial microsomia

Abstract: The relationship between the bone and muscles of mastication in hemifacial microsomia was studied using three-dimensional volumetric computed tomography scans and image processing techniques. High resolution head computed tomography scans were obtained from 31 patients with unilateral hemifacial microsomia and eight normal patients. Using three-dimensional volume renderings of bone, mandibular deformities in patients with hemifacial microsomia were classified using the Pruzansky system. For each patient, specific craniofacial bones (temporal bone, maxilla mandible) and the muscles of mastication (masseter, temporalis and lateral and medial pterygoid) were segmented bilaterally from the image volume for independent display and volume measurement. Volumes were expressed as the ratio of the affected: unaffected sides. For the masseter and temporalis, the relationship between muscular hypoplasia and osseous hypoplasia in its origin and insertion was studied by plotting affected:unaffected bone volume as a function of affected:unaffected muscle volume for each muscle, bone of origin, bone of insertion triplet. The volumes of the pterygoid muscles were compared with hemimandibular volumes. The precision of object segmentations was examined by repetitive definition tasks, whereas the accuracy of volume measurement was tested by scanning custom-made phantom objects and comparing digital to physical object volume measurements. Volume measurements performed using these techniques were both accurate and precise. In hemifacial microsomia, the extent of hypoplasia of specific muscles of mastication predicted the extent of dysplasia in their osseous origin and insertion. However, the reverse was not true. The extent of hypoplasia of the facial bones did not necessarily predict the extent of hypoplasia in the attached muscles of mastication. Pruzansky grade of the mandible described the degree of mandibular hypoplasia on the affected side, but was inconsistent in its prediction of volume decrease of the other facial bones.

Visualization of colorectal polyps with spiral CT colography: evaluation of processing parameters with perspective volume rendering.

Abstract: PURPOSE: To evaluate two key processing steps for detection of colon polyps with spiral computed tomographic (CT) colography with perspective volume rendering (PVR): image reconstruction and opacity assignment of the attenuation data. MATERIALS AND METHODS: Spiral CT was performed in 10 patients with known polyps confirmed at colonoscopy, and detailed quantitative analyses were performed of data obtained in four. First, anatomic fidelity of three-dimensional (3D) images generated from two-dimensional (2D) source images with equal voxel dimensions (87%-90% overlap) was compared with 3D images generated from 2D source images with unequal voxel dimensions (0%-80% overlap). Next, the relative dimensions of colorectal polyps to adjacent structures were evaluated for various opacity threshold settings. Then, step and sigmoidal opacity functions were compared with respect to image smoothness and edge sharpness. RESULTS: PVR images generated after interpolation of image data reconstructed with at least 60% overla...

Optimal pitch in spiral computed tomography

Abstract: The focus of this paper is to analytically optimize spiral/helical computed tomography (CT) protocols based on a simplified imaging model. Spiral CT was approximately modeled as follows: Using the half-scan raw data interpolation method, the variance of the spiral CT slice sensitivity profile is equal to the sum of squared detector collimation divided by 12 and squared table increment divided by 24. Image noise variance is inversely proportional to tube current and detector collimation. The maximum continuous scanning time is inversely proportional to tube current. Slice thickness, image noise, and signal-to-noise ratio were, respectively, optimized for a given scanning coverage, consistently resulting in pitch of square root of 2. To avoid longitudinal aliasing, at least 2-3 transverse slices should be reconstructed per collimation. When the simplified spiral CT model is valid and a scanning range specified, 1.4 pitch is required for optimal image quality. The method can be applied to more accurate spiral CT models.

A comparison of the response of storage phosphor and film radiography to small variations in X-ray exposure.

Abstract: OBJECTIVES To determine the response to small repeated variations in X-ray exposure of storage phosphor (SP) plates compared with Ektaspeed Plus dental film. METHODS Exposure of SP plates and Ektaspeed Plus dental film was varied within a small range [8.62 microC kg-1 to 9.03 microC kg-1, (5%)]. Radiographs were digitized and SP plates read with a laser-based scanner. Nested analysis of variance, analysis of covariance, and regression analysis were used to test the relationship between exposure and the resulting signal. RESULTS The relationship between exposure and signal for digital images of film radiographs was not significant whereas the corresponding relationship for SP images was highly significant (P < 0.001, R2 = 0.44). CONCLUSIONS Over the narrow range of X-ray exposures studied there was a significant direct linear relationship between exposure and digital gray-scale values for SP images but not for digital images of Ektaspeed Plus films.

Low-contrast resolution in volumetric x-ray CT—Analytical comparison between conventional and spiral CT

Abstract: Spiral/helical computed tomography (CT) was introduced to scan an anatomical volume in a single breath-hold for better temporal resolution as compared to conventional CT. Recently, it was established that given an x-ray dose, spiral CT also allows better longitudinal high-contrast resolution due to retrospective reconstruction. In spiral CT, full scan with interpolation (FI) and half-scan with interpolation (HI) are limited by the degraded slice sensitivity profile and increased image noise, respectively. We combined these two interpolation methods for a desirable balance. This new interpolation method, FI + HI, was shown to produce 4% lower image noise standard deviation than conventional CT, without loss of longitudinal bandwidth according to one-tenth-cutoff and mean-square-root measures. The analytic model of image noise was validated in a water phantom experiment. Our findings suggest the superiority of spiral CT over conventional CT in terms of both low-contrast resolution and high-contrast resolution.

Visualization of prosthesis fit in lower-limb amputees

Abstract: Lower-limb prosthesis quality-of-fit assessment is purely subjective in routine clinical practice, relying on patient reports of discomfort, erythema (localized pain), and palpation. Wide variations in residual limb physical characteristics and conditions preclude a rigid approach to prosthesis prescription. With relatively long life expectancy for many lower-limb amputees, clinicians measure outcome in terms of return to work and quality of life, which have important social and economic consequences. An objective quantitative metric of fit that predicts functional outcome has not been described to date. Volumetric CT scanning provides in situ static 3D determination of residual limb soft tissue changes caused by the prosthesis socket. This mapping aids in prosthesis design and evaluation.

Three-Dimensional Lower-Extremity Residua Measurement Systems Error Analysis

Abstract: Accurate and reproducible geometric measurement of lower-extremity residua is required for custom prosthetic socket design. The authors compared three-dimensional electromagnetic point digitizer, spiral X-ray computed tomography (SXCT) and three-dimensional optical surface scanning (OSS) with caliper measurements and evaluated the precision and accuracy of each system. Digitizer, SXCT and OSS were used to measure lower-limb residuum geometry of 13 transtibial adult amputees. Six markers were placed on each subject's residuum and corresponding positive plaster models, and distance measurements were taken to determine precision and accuracy for each system. The digitizer, SXCT and OSS measurements were precise within 1 percent in vivo and 0.5 percent on positive plaster models. When compared with caliper measures, these measures were within 2 percent in vivo and 1 percent on positive plaster models. SXCT and three-dimensional optical surface-imaging systems, which are feasible for capturing the comprehensive three-dimensional surface geometry of transtibial residua, provide distance measurements statistically equivalent to calipers. In addition, SXCT can readily distinguish internal soft tissue and bony structure of the residuum.

Osteochondral allografts with an intramedullary muscle flap in rabbits

Abstract: A model for hemijoint reconstruction using partially demineralized and lyophilized osteochondral allografts combined with an intramedullary muscle flap is described. The proximal 2/3 of the humerus was resected in 10 rabbits. The remaining defect was reconstructed with either a control lyophilized osteochondral allograft or a lyophilized allograft with a muscle flap filling the marrow cavity. Graft healing was followed by serial radiographs and magnetic resonance imaging. The grafts were harvested at 5 weeks for histologic analysis. By 5 weeks, 4 of 5 control allografts had fractured. In contrast, only 1 allograft with an intramedullary muscle flap showed evidence of a cortical break. Magnetic resonance imaging of control allografts showed a persistent large dead space within the marrow cavity and callus formation only at the outer cortical surface. Magnetic resonance imaging of allografts with an intramedullary muscle flap showed muscle obliterating the marrow cavity and areas of callus formation at both the outer and inner cortical surfaces. Histologically, graft incorporation was occurring at the outer cortical surface of the control allografts. In contrast, graft incorporation was occurring at both the outer and inner cortical surfaces of the allografts with an intramedullary muscle flap. The articular surface of the control allografts was severely degenerated. In allografts with an intramedullary muscle flap, the articular surface was smoother. Joints reconstructed with allografts with an intramedullary muscle flap had a significantly better range of motion at 5 weeks compared with control allografts. These results suggest that an intramedullary muscle flap can improve the functional results of joints reconstructed with partially demineralized and lyophilized osteochondral allografts by providing both vascularity and an increased population of mesenchymal stem cells capable of responding to bone morphogenetic proteins that reside in the partially demineralized allograft.