Biomedical subjects

D D Cody

Publications and source records attributed to D D Cody.

At least 19 recordsLinked to original sources

PubMed2005

A Monte Carlo based method to estimate radiation dose from multidetector CT (MDCT): cylindrical and anthropomorphic phantoms.

The purpose of this work was to extend the verification of Monte Carlo based methods for estimating radiation dose in computed tomography (CT) exams beyond a single CT scanner to a multidetector CT (MDCT) scanner, and from cylindrical CTDI phantom measurements to both cylindrical and physical anthropomorphic phantoms. Both cylindrical and physical anthropomorphic phantoms were scanned on an MDCT under the specified conditions. A pencil ionization chamber was used to record exposure for the cylindrical phantom, while MOSFET (metal oxide semiconductor field effect transistor) detectors were used to record exposure at the surface of the anthropomorphic phantom. Reference measurements were made in air at isocentre using the pencil ionization chamber under the specified conditions. Detailed Monte Carlo models were developed for the MDCT scanner to describe the x-ray source (spectra, bowtie filter, etc) and geometry factors (distance from focal spot to isocentre, source movement due to axial or helical scanning, etc). Models for the cylindrical (CTDI) phantoms were available from the previous work. For the anthropomorphic phantom, CT image data were used to create a detailed voxelized model of the phantom's geometry. Anthropomorphic phantom material compositions were provided by the manufacturer. A simulation of the physical scan was performed using the mathematical models of the scanner, phantom and specified scan parameters. Tallies were recorded at specific voxel locations corresponding to the MOSFET physical measurements. Simulations of air scans were performed to obtain normalization factors to convert results to absolute dose values. For the CTDI body (32 cm) phantom, measurements and simulation results agreed to within 3.5% across all conditions. For the anthropomorphic phantom, measured surface dose values from a contiguous axial scan showed significant variation and ranged from 8 mGy/100 mAs to 16 mGy/100 mAs. Results from helical scans of overlapping pitch (0.9375) and extended pitch (1.375) were also obtained. Comparisons between the MOSFET measurements and the absolute dose value derived from the Monte Carlo simulations demonstrate agreement in terms of absolute dose values as well as the spatially varying characteristics. This work demonstrates the ability to extend models from a single detector scanner using cylindrical phantoms to an MDCT scanner using both cylindrical and anthropomorphic phantoms. Future work will be extended to voxelized patient models of different sizes and to other MDCT scanners.

Body Burden↗

PubMed2004

Using cartilage to repair bone: an alternative approach in tissue engineering.

Materials and techniques currently used for bone replacement/repair conform to the current paradigm, relying on bone or bone products to produce bone or induce bone formation. Yet, nature forms and heals most of the skeleton by ossification of a cartilaginous model. In this study, we cultured aggregates of E10.5 or E12 mouse embryonic limb cells in the bioreactor for 3 weeks, determined the stages of cartilage differentiation attained, and assessed the ossification and bone healing potential of the spheroids by implantation adjacent to, or directly in, a skull defect. Cultured spheroids had large cartilaginous areas, sometimes with cellular arrangements characteristic of growth plate zones. Aggregates implanted for 2 weeks adjacent to a defect mineralized and ossified (histology, micro-CT). Defects with implants had a central mass of differentiated and differentiating bone, with osteoclast activity, filling the defect. Controls had considerable remodeling on the bone edges demarcating the still present defect. This study shows that cartilage, grown in the bioreactor for 3 weeks, ossified when implanted adjacent to a bone defect, and when implanted directly in a defect, contributed to its healing. Our ability to grow differentiated bone-forming cartilage for implantation is an alternative approach in the field of bone repair.

Animals↗

PubMed2000

Femoral structure and stiffness in patients with femoral neck fracture.

Bone morphological characteristics may relate to the risk of hip fracture. We applied finite element modeling to radiologic data for two groups of women in vivo to address two questions: (a) Do individuals who have just sustained a femoral neck fracture exhibit reduced three-dimensional structural stiffness? and (b) Are victims of hip fracture disproportionately more susceptible to loads sustained in a fall than to stance-type loads? Ten white women (age: 64-76 years) who had just sustained a femoral neck fracture and 18 female volunteers (age: 65-76 years), matched as groups for race, age. and body mass index, were evaluated. From quantitative computed tomography scans, femoral morphometric and volumetric cancellous density measurements were obtained and a finite element model was constructed. Two load conditions were simulated: single-stance phase and lateral fall. Global stiffness values were determined for each model. The cancellous bone density was significantly lower at the femoral neck and the femoral neck and head diameters were significantly larger in the women in the fracture group than in those in the control group. The stiffness of the proximal femur did not differ significantly between the groups for either load condition. An apparently linear relationship was found for stiffness at stance load compared with stiffness at fall load (r = 0.84, p < 0.001). and slopes did not differ significantly between the groups. Although cancellous density was reduced at the fracture site in patients with femoral neck fractures. this did not result in a reduction in the predicted bone stiffness. Previous studies have established a very strong relationship between the stiffness and strength of bone. Since these modeling methods were thoroughly validated ex vivo, we conclude that although decreased bone density at the femoral neck may predict where fracture initiates, the risk of hip fracture per se may be more strongly dependent on issues such as the risk of falling and fall biomechanics than on the structural characteristics of bone.

Accidental Falls↗

PubMed2000

Bone density distribution and gender dominate femoral neck fracture risk predictors.

OBJECTIVE: To determine whether regional characteristics of the proximal femur could discriminate between a group of patients who had just sustained a first low-trauma femoral neck fracture (n=50) from a group of healthy volunteers (n=123). DESIGN: The application of an integral bone measurement (dual-energy X-ray absorptiometry) in conjunction with a volumetric cancellous bone density measurement (quantitative computed tomography) to the proximal femur in vivo provided an estimate of the contribution of the spatial distribution of bone density to hip fracture risk prediction. RESULTS: The primary finding of this study was a significant difference between male and female hip fracture risk predictor variables. In men with femoral neck fracture, a significant decrease in bone density throughout the proximal femur was observed. In women with femoral neck fracture, a combination of local bone deficits (significant decrease in cancellous bone at the site of fracture, and a decrease in cortical bone at the site of impact) and significantly larger proximal femur dimensions (femoral neck and head widths) was evident. CONCLUSIONS: These results imply that effective hip fracture prevention strategies may require separate approaches for men and women. Screening programs for diminished bone density at the proximal femur have proved effective in previous studies. An approach which includes examining these local bone characteristics may further improve our ability to accurately determine hip fracture risk in vivo.

Absorptiometry, Photon↗

PubMed2000

Short term in vivo precision of proximal femoral finite element modeling.

As more therapies are introduced to treat osteoporosis, precise in vivo methods are needed to monitor response to therapy and to estimate the gains in bone strength that result from treatment. A method for evaluating the strength of the proximal femur was developed and its short term reproducibility, or precision, was determined in vivo. Ten volunteer subjects aged 51-62 years (mean 55.6 years), eight women and two men, were examined using a quantitative computed tomography (QCT) protocol. They were positioned, scanned, repositioned and re-scanned. The QCT images were registered in three-dimensional space, and finite element (FE) models were generated and processed to simulate a stance phase load configuration. Stiffness was computed from each FE model, and strength was computed using a regression equation between FE stiffness and fracture load for a small set (n = 6) of experimental specimens. The coefficients of variation (COV) and repeatability (COR= 2.23* 42*COV) were determined. The COV for the FE fracture load computed was 1.85%, and the detectable limit (coefficient of repeatability) for serial measurements was 5.85%. That is, if a change of 5.85% or more in computed FE fracture load is observed, it will be too large to be consistent with measurement variation, but instead can be interpreted as a real change in the strength of the bone. The detectable limit of this method makes it suitable for serial research studies on changes in femoral bone strength in vivo.

Biomechanical Phenomena↗

PubMed1999

Hearing loss as a complication of Paget's disease of bone.

Hearing loss has long been known to be a complication of Paget's disease of bone. Older ideas about the mechanisms of hearing loss are being replaced by a new view based on experimental evidence from patients. Studies reviewed show no evidence of auditory nerve dysfunction and confirm a cochlear site of lesion. A loss of bone mineral density in the cochlear capsule is associated with both a high-tone hearing loss and a low-tone air-bone gap.

Aged↗

PubMed1999

Femoral strength is better predicted by finite element models than QCT and DXA.

Clinicians and patients would benefit if accurate methods of predicting and monitoring bone strength in-vivo were available. A group of 51 human femurs (age range 21-93; 23 females, 28 males) were evaluated for bone density and geometry using quantitative computed tomography (QCT) and dual energy X-ray absorptiometry (DXA). Regional bone density and dimensions obtained from QCT and DXA were used to develop statistical models to predict femoral strength ex vivo. The QCT data also formed the basis of a three-dimensional finite element (FE) models to predict structural stiffness. The femurs were separated into two groups; a model training set (n = 25) was used to develop statistical models to predict ultimate load, and a test set (n = 26) was used to validate these models. The main goal of this study was to test the ability of DXA, QCT and FE techniques to predict fracture load non-invasively, in a simple load configuration which produces predominantly femoral neck fractures. The load configuration simulated the single stance phase portion of normal gait; in 87% of the specimens, clinical appearing sub-capital fractures were produced. The training/test study design provided a tool to validate that the predictive models were reliable when used on specimens with "unknown" strength characteristics. The FE method explained at least 20% more of the variance in strength than the DXA models. Planned refinements of the FE technique are expected to further improve these results. Three-dimensional FE models are a promising method for predicting fracture load, and may be useful in monitoring strength changes in vivo.

Absorptiometry, Photon↗

PubMed1999

Premature partial closure and other deformities of the growth plate: MR imaging and three-dimensional modeling.

PURPOSE: To examine growth plates of the distal femur and tibia with magnetic resonance (MR) imaging to detect bone bridges and other deformities in children. MATERIALS AND METHODS: Thirteen children (nine boys and four girls, aged 5-13 years; mean age, 9.8 years) were referred because of suspected or known bone bridging of the growth plate. Among the 13 patients, 10 had Salter-Harris fractures of the knee or ankle, two had Blount disease, and one had neonatal sepsis. Fat-saturated spoiled gradient-recalled images enabled reconstruction of a three-dimensional model of the growth plate. Patients underwent one to four MR examinations. RESULTS: Nine patients had bone bridging of less than 1% to 39% of the area of the growth plate. On MR images obtained in the growth plate of five patients, a stripe of low signal intensity indicated fracture. On MR images obtained in three patients, intrusions of growth plate cartilage into the metaphysis were seen to increase in depth over time. MR images obtained in four patients showed no bridges. In the two patients who underwent surgery, excellent correspondence was found between MR findings and surgical observations. CONCLUSION: Marked undulation or splitting of the growth plate may occur with fixation of some cartilage in the metaphysis or epiphysis while growth continues. The configuration of the growth plate and bone bridges can be accurately mapped with MR imaging. Treatment planning is facilitated.

Adolescent↗

PubMed1999

Evaluation of intraoperative nerve-monitoring during insertion of an iliosacral implant in an animal model.

BACKGROUND: The use of continuous electromyographic and somatosensory-evoked-potential monitoring systems has been advocated to assist in avoiding nerve-root injury during operations on the pelvic ring. More recently, it was suggested that stimulus-evoked electromyographic monitoring may further decrease the risk of iatrogenic nerve-root injury during posterior pelvic fixation by enabling the surgeon to determine the actual distance of an implant from a nerve root. The purpose of the current study was to evaluate the relative efficacy of these three methods of monitoring for minimizing the risk of neural injury during the placement of iliosacral implants. METHODS: While the function of the first sacral nerve root was monitored with the use of stimulus-evoked electromyographic, continuous electromyographic, and somatosensory-evoked-potential monitoring techniques, a 2.0-millimeter stainless-steel Kirschner wire was progressively inserted, guided by a high-speed computerized tomographic scanner, into the first sacral body of seventeen hemipelves in nine dogs. The end point was contact with the nerve as demonstrated by the computerized tomographic images. It was expected that this end point would be heralded by a burst of spontaneous electromyographic activity and an abnormal somatosensory-evoked-potential signal. Anatomical dissection at the completion of the study documented the final position of the Kirschner wire. RESULTS: Anatomical dissection demonstrated compression or penetration of the nerve root in sixteen of the seventeen specimens. A spontaneous burst of electromyographic activity was not recorded for any specimen on continuous electromyographic monitoring; this finding was significantly different from what had been expected (p<0.001). Because of technical problems, somatosensory evoked potentials could be recorded for only twelve hemipelves that had nerve-root compression or penetration, and abnormal somatosensory evoked potentials were recorded for only one of the twelve; this finding was significantly different from what had been expected (p<0.001). A total of 113 stimulus-evoked electromyographic data points were obtained. The correlation coefficient for the relationship between the current threshold recorded with stimulus-evoked electromyographic monitoring and the distance of the wire from the nerve was 0.801 (p<0.001). The actual measured current thresholds were of an observed proportion not different from what had been expected (p = 0.48). CONCLUSIONS: Continuous electromyographic and somatosensory-evoked-potential monitoring techniques failed to indicate contact with the nerve root reliably in this animal model. However, stimulus-evoked electromyographic monitoring consistently provided reliable information indicating the proximity of the implant to the nerve root.

Animals↗

PubMed1997

Decrease in canine proximal femoral ultimate strength and stiffness due to fatigue damage.

Fractures of the proximal femur represent a significant health concern especially in the elderly. Fatigue damage and microfractures have been implicated in the etiology of hip fractures; however, the extent to which these factors are sufficient to bring about significant reductions in proximal femur strength and stiffness is unknown. This study examined the hypothesis that fatigue loading of the proximal femur results in highly correlated decreases in bone stiffness and strength through the accumulation of bone microdamage. One canine femur from each of 10 pairs was monotonically loaded to failure to determine the ultimate strength. The contralateral femur was then cyclically loaded at 50% of the ultimate load value for either 3600 cycles or until a 40% reduction in stiffness was achieved. This femur was then monotonically loaded to failure. For two additional femur pairs, the fatigued femur was histologically processed to reveal bone microdamage. In support of the hypothesis, the data demonstrated a linear relationship between strength loss and stiffness loss (Adj. R2 = 0.79, p < 0.0004) with significant decreases in residual whole bone strength (p < 0.004) following cyclic loading. In addition, damage (microcracks) in the cortical bone and broken trabeculae were observed in the neck and head region of the femur fatigued until its stiffness was reduced by 40% but not fractured subsequent to cyclic loading.

Animals↗

PubMed1997

Segmentation of acoustic neuromas with magnetic resonance imaging and Eigen image filtering.

OBJECTIVE: This study aimed to determine whether magnetic resonance imaging with Eigen image filtering can segment acoustic neuromas as a preliminary requirement to the development and validation of a volumetric method of measuring tumor size and growth using Eigen image filtering. STUDY DESIGN: This was an observational study. SETTING: The study was performed in an academic, comprehensive multi-specialty group practice. PATIENTS: Patients were a convenience sample of adults of both sexes who had acoustic neuromas identified by magnetic resonance imaging. Tumors ranged widely in size. INTERVENTION: Magnetic resonance imaging with digital image analysis using Eigen image filtering was the intervention. MAIN OUTCOME MEASURE: Observation and analysis of magnetic resonance images was the main outcome measure. RESULTS: The ability of magnetic resonance imaging with Eigen image filtering to segment acoustic neuromas of various sizes and shapes is illustrated. CONCLUSIONS: Magnetic resonance imaging with digital image analysis using Eigen image filtering is a promising method for volumetric measurement of acoustic neuroma size and growth. The potential for acoustic neuromas to grow may be underestimated by linear methods because of their relative lack of precision and of the geometric error that occurs in representing the volumetric growth of a three-dimensional tumor as a linear diameter.

Adult↗

PubMed1996

Predictive value of proximal femoral bone densitometry in determining local orthogonal material properties.

Models which are based on non-invasive bone measurements may in the future be able to successfully identify individual subjects at an increased risk for hip fracture; thus, we designed a study to determine the usefulness of dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) in predicting the local material properties of human proximal femoral cancellous bone. There has been some disagreement in the scientific literature regarding appropriate predictive models for local material properties of cancellous bone. We sought to confirm that density-mechanical property relationships were consistent from subject to subject, and that three-dimensional QCT measurements were stronger predictors of mechanical properties than two-dimensional DXA results. Linear and power fit relationships between these densitometric measures and material properties were also examined to determine which were more appropriate. Bone cubes from specific regions of highly oriented trabeculae were analyzed separately to determine if cube orientation had an effect on mechanical properties independent of bone density. Ten pairs of ex vivo femurs (five male, five female; age 30-93, mean age 62) were prepared such that specific anatomic planes were visible radiographically. Both QCT and DXA measurements were made on all 20 femurs. Cancellous bone cubes were obtained proceeding along two distinct directions from the proximal end of each femur pair. Unexpectedly, the density-modulus relationships among these ten donors were found to be significantly different at p <0.01 (83 percent of the tests were different at p <0.0001). Density-strength regressions were also significantly different at p <0.01, but this effect was not as consistent nor as statistically significant. In general, the QCT method did not produce predictions of local cancellous bone material properties superior to the DXA method. The linear and power fit models appeared to produce consistent results, with neither being obviously more advantageous. These density measurements explained at best 30-40 percent of the variance in modulus and 50-60 percent of the variance in ultimate stress. The orientation of cancellous cubes in the principal compressive trabeculae region was a significant contributor to mechanical properties (p= 0.0001) independent of bone density. This finding was not as dramatic in the femoral neck cancellous bone region.

Absorptiometry, Photon↗

PubMed1995

Static and fatigue failure properties of thoracic and lumbar vertebral bodies and their relation to regional density.

This study investigated (1) whether a characterization of the macroscopic architecture within the vertebral centrum would improve predictions of vertebral strength, (2) if regions in the centrum where least bone loss with age occurs are more predictive of vertebral strength, and (3) whether different patterns of the macroscopic architecture are predictive of static as compared to fatigue strength. To characterize the vertebral macroscopic architecture, a regional bone mineral density (rBMD) technique was used that estimated the cancellous density distribution (in 18 specific regions of the vertebral centrum) for vertebrae T7-L4, from spines of 20 female cadavers. Static and fatigue failure properties of whole vertebrae were obtained, and predictive models of static and fatigue failure properties of whole vertebrae were examined. We found that (1) vertebral failure properties were better predicted by combinations of vertebral regional cancellous density (multiple linear regressions) rather than by any individual region of cancellous density alone (simple linear regressions); (2) models using regions of density that demonstrated minimum decline with age [from the data of Flynn and Cody (Calcif. Tissue Int. 53, S170-S175 (1993))] resulted in better correlations with ex vivo vertebral static failure properties than models using density regions that showed maximum decline with age, and (3) static and fatigue characteristics required different density regions to reach significance. (A comparison of models predictive of static and fatigue failure properties revealed that anterior density regions were most often included in predictive models of the static properties while posterior regions were more predictive of the fatigue properties).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Hearing loss in Paget's disease of bone: the relationship between pure-tone thresholds and mineral density of the cochlear capsule.

We have developed a unique method of quantitative computed tomography (QCT) that enables measurement of the density of the cochlear capsule in vivo. We performed pure-tone audiometry and QCT on 67 ears from 35 subjects with radiographically confirmed Paget's disease of the skull and on 40 ears from twenty volunteer subjects. The Pearson product-moment correlation coefficients (age- and sex-adjusted) in the group affected by Paget's disease were -0.63 for left ears and -0.73 for right ears for high-frequency air conduction pure-tone thresholds (mean of 1, 2, and 4 kHz) versus cochlear capsule density. Correlation coefficients (age- and sex-adjusted) between cochlear capsule density and air-bone gap (mean at 0.5 and 1 kHz) for the affected group were -0.67 for left ears and -0.63 for right ears. All correlations between hearing thresholds and cochlear capsule density in pagetic subjects were significant at p < 0.001. The regressions were consistent throughout the ranges of hearing level. There were no significant correlations between cochlear capsule mean density and hearing level in the volunteer subjects. These findings demonstrate the feasibility of precise and accurate density measurements in the temporal bone in vivo and support the use of the mean cochlear capsule density as a marker of disease effect. Alteration of cochlear capsule bone density may be related to the mechanisms of hearing loss in Paget's disease of bone.

Adult↗

PubMed1995

Hearing loss in Paget's disease of bone: evidence of auditory nerve integrity.

Auditory brainstem responses (ABRs) were recorded in 64 ears with radiographically confirmed Paget's disease involving the skull. Responses were absent in eight ears, all of which had elevated high pure-tone thresholds. Auditory brainstem responses were interpreted as normal in 56 ears; none were abnormal. Computed tomography and digital image analysis were used to quantify internal auditory canal (IAC) dimensions. The midlength diameter and minimum diameter of the IAC of 68 temporal bones from subjects with Paget's disease were found to have no statistically significant relation to hearing thresholds. Increased IAC length showed a limited relation to reduced hearing level in pagetic subjects, possibly consistent with bossing adjacent to the porus acusticus. Findings support the principle that hearing loss in Paget's disease of bone is generally associated with intact auditory nerve function and also support a cochlear site of lesion.

Audiometry, Pure-Tone↗

PubMed1994

Application of quantitative computed tomography to Paget's disease of bone.

Serial evaluation of pagetic lesions is handicapped by the inability of conventional methods to reproduce precisely the positioning of the area of interest. A computed tomography method that provides visual and quantitative comparisons between data sets acquired at different times has been developed. The utility of this method is illustrated with an example of serial examinations that demonstrate the effect of treatment on small lytic lesions in the lumbar spine. A further demonstration is made of the ability of this method to identify and quantify lytic changes within the cochlear capsule.

Aged↗

PubMed1993

The assessment of vertebral bone macroarchitecture with X-ray computed tomography.

On a macroscopic scale, the structural characteristics of whole bone are likely dependent on the distribution of typically applied loads to the bone surface, the full bone shape, the thickness of the cortex at the various surface positions, and the distribution of cancellous bone material. X-ray computed tomography is presently the best available method for assessing the macroarchitecture of bone in-vivo. Fine detail, three-dimensional CT methods are available to measure regional bone mineral density (rBMD) in contiguously spaced small volumes and have been applied to the assessment of macroarchitecture in vertebrae. The more detailed rBMD methods produce radiation exposures to the subject similar to lumbar radiography and substantially higher than traditional QCT. The cancellous bone within lumbar vertebral bodies has been found in cross-sectional studies to have increased density in the inferior, posterior and lateral regions. Notably, regions with higher density at age 40 have a larger decline with age. The vertebral body cortex declines with age at a slower rate than observed for cancellous bone; however, the decline with age of cortical bone appears to vary substantially amongst subjects. The amount of cortical bone in the anterior portion of the body is less than in the lateral portion, which may explain previous discrepancies in assessing the fraction of vertebral body bone in the cortex.

Adult↗

PubMed1993

Measurement of regional bone mineral density: a new technique for the evaluation of the temporal bone.

The measurement of regional bone mineral density (rBMD) is a new method of evaluation of the human temporal bone in vitro or in vivo. Modified computed tomography (CT) enables us to collect a three-dimensional array of precise, reproducible bone density values, as well as high-quality CT images. Measurements are calibrated using phantoms of known composition and density. Conventional CT provides density information that is relative, qualitative, and lacks precise reproducibility over time. The rBMD technique provides precise numeric density measurements. Additional image processing capabilities are described. In vivo data from six normal temporal bones and from two patients with Paget's disease involving the temporal bone are presented to demonstrate the technique.

Aged↗