Search PubMed⌕ Search

Biomedical subjects

T N Hangartner

Publications and source records attributed to T N Hangartner.

12 recordsLinked to original sources
PubMed1996

Osteopenia in children: CT assessment.

PURPOSE: To assess the value of computed tomographic (CT) measurements of cortical bone in children with osteopenia. MATERIALS AND METHODS: The area and density of cortical bone in the midshaft of the femur were measured with CT in 37 children with osteopenia. Twenty had osteoporosis in one leg, nine had osteogenesis imperfecta (IO), and eight had vitamin D-resistant rickets. Comparisons were made between the CT measurements of the normal and abnormal extremities and between patients with OI or rickets and a group of 17 healthy, matched children. RESULTS: Sex, age, height, and weight did not influence cortical bone density; values were similar for the 17 control subjects. Children with osteoporosis and IO had reduced bone area but normal bone density. Compared with control subjects, patients with rickets had similar bone area but reduced bone density (869 mg/cm3 K2HPO4 +/- 79 [standard deviation] vs 1,132 mg/cm3 K2HPO4 +/- 41). CONCLUSION: CT measurements of area and density of cortical bone aided the differentiation of the various disorders that cause osteopenia in children.

Adolescent↗
PubMed1994

A variable-resolution rotate-only computed tomography scanner.

The Rotoscan is a computed tomography scanner that combines the advantages of variable geometric resolution and adjustable size of measurement diameter of translate-rotate scanners with the improved speed of rotate-only scanners. Because of the small number of only 26 detectors used for this scanner, a special data collection scheme of multiple rotations with interleaved detector positions was employed. In order to avoid angular data interpolation after reordering of the projections from the fan- to a parallel-beam geometry, the detectors were incrementally moved at a right angle to the centerline of the fan rather than rotated about the source. The measurement time of 40 s for one cross-section is comparable to that of second-generation systems. However, for longer measurement diameters, the measurement time for second-generation systems increases, whereas that of the Rotoscan remains constant.

Algorithms↗
PubMed1994

Tibial bone density loss in spinal cord injured patients: effects of FES exercise.

A group of 37 spinal cord injured (SCI) patients underwent bone density measurements at the distal and proximal end of the tibia by a special computed tomography scanner, the OsteoQuant. Fifteen of these patients had follow-up measurements while enrolled in a lower-limb exercise training program with functional electrical stimulation (FES). The pre-exercise measurements revealed a strong correlation (0.88 < or = r < or = 0.90) of trabecular, subcortical, and cortical bone density between the distal and proximal ends of the tibia. The expected bone density loss during the first two years post injury (as calculated from the regression lines of bone density vs. time post injury) amounted to 51.5% for trabecular, 44.2% for subcortical, and 32.7% for cortical bone. No major bone density loss was calculated after 7 years post injury. Analysis of the bone density data during the FES exercise program revealed various degrees of loss. However, the rate of bone loss for this FES exercise group was less than expected from the regression lines. The reduction of bone loss was between 0.2 and 3.3% per year, and was significant (p < 0.05) for all bone parameters at the distal end and for trabecular bone density at the proximal end of the tibia. These bone density measurements revealed a potentially positive effect of FES exercise intervention for the rehabilitation of SCI patients.

Adult↗
PubMed1992

Changes in the linear attenuation coefficient of canine appendicular bone following intravenous infusion of strontium lactate, measured using gamma-ray computed tomography.

Changes in the average linear attenuation coefficient (LAC) within a fixed measurement volume in the proximal end of the dog tibia, which contains trabecular bone and associated soft tissues (the trabecular bone "space"), were monitored continuously using gamma-ray computed tomography (gamma-CT) prior to, during, and following intravenous infusion of strontium (Sr) lactate. An infusion of 1.3-4.7 g of Sr over a period of 110-160 minutes into 20-kg dogs resulted, within 6-8 hours, in an increase of 0.019-0.045 cm-1 (P less than 0.002) in the LAC. Calibration of the gamma-CT system showed that 0.44 mg/cm3 of Sr produced a change of 0.01 cm-1 in the LAC. Using this conversion factor, the Sr concentration in the trabecular bone space resulting from infusion, as measured by flame atomic absorption spectroscopy, agreed with that predicted by the change observed in the LAC. Sr present in the serum and urine was consistent with the changes observed in the LAC over the study period. Control dogs infused with mineral-free solutions showed no change in LAC. Calcium equivalents required to give the changes observed in the LAC using Sr indicate that variations in skeletal turnover in man can be monitored in the peripheral skeleton using gamma-CT.

Animals↗
PubMed1990

Influence of fat on bone measurements with dual-energy absorptiometry.

In order to investigate the influence of fat on bone in dual-energy absorptiometry measurements, we evaluated a special phantom on the three scanners: Lunar DP3, Lunar DPX and Hologic QDR-1000. The phantom employed hydroxyapatite blocks of various thicknesses to simulate bone, water to simulate muscle and lucite to simulate fat. The lucite plates were arranged in one and two layers in three different configurations: over the whole measurement area, over the hydroxyapatite blocks only and at both sides of the hydroxyapatite blocks. For all scanners, no influence of fat could be demonstrated if it was homogeneously distributed over the whole measurement area. However, changes in area bone-density were observed if fat was distributed inhomogeneously over the measurement area. Fat over only the bone area reduced the measured bone values by 0.051 g/cm2 per cm fat layer. Fat over only the soft-tissue area increased the measured bone values by the same amount. These results apply to the Lunar DPX scanner. The results for the Lunar DP-3 scanner are similar; those for the Hologic QDR-1000 show a slightly smaller fat dependence of 0.044 g/cm2 per cm fat layer. The fat influences are not dependent on the amount of bone and only minimally on the soft-tissue thickness. A change of 50% in the fat content of the bone marrow will change the measured area bone-density of an averaged sized vertebra by 5-6% depending on scanner model. Inhomogeneous fat distribution in soft tissue, resulting in a difference of 2 cm fat layer between soft-tissue area and bone area, will influence the measured area bone-density by 9-10%.

Absorptiometry, Photon↗
PubMed1990

A special purpose x-ray fan-beam CT scanner for trabecular bone density measurement in the appendicular skeleton.

A special purpose x-ray CT scanner with the capability of scanning objects 75-220 mm in diameter with constant relative geometrical resolution has been developed. The data collection scheme for the scanner uses multiple rotations of a linearly shifted, asymmetric fan beam permitting user-defined variable resolution. Details of hardware and the calibration procedures for the scanner are described and the methods used to measure trabecular bone density (TBD) in the peripheral skeleton are outlined. The standard error of estimate (SEE) of a calibration line of pixel value as a function of K2HPO4 concentration was determined to be 0.07%. The short-term, in vivo precision of the TBD determination, by repeated measurements of a volunteer with repositioning between each measurement, was +/- 0.67% (coefficient of variation (CV] with a 50s scan time and a radiation dose of less than 20 mR per slice.

Bone Density↗
PubMed1987

Performance evaluation of density measurements of axial and peripheral bone with x-ray and gamma-ray computed tomography.

We examined sources of error in bone measurements made with computed tomography (CT) using a whole-body scanner (GE 8800) and a peripheral-bone CT scanner (developed at the University of Alberta). We investigated the influence of various factors on trabecular bone density: homogeneity and noise in the image plane, linearity of calibration, body size, effects of cortical bone, and the image analysis procedure. With the GE 8800 scanner, the precision (SD) of measurements of a single vertebra is expected to be +/- 1.65% (noise: +/- 0.22%, calibration: +/- 1.3%, analysis: +/- 1%); the accuracy, excluding consideration of marrow fat, varied between -2.7 and +7.3% (compact-bone thickness: 2-5%, body size: -2.5 - +1.5%, calibration: -0.47 - +0.77%). With the peripheral-bone CT scanner, the total precision error (+/- 0.53%) was dominated by noise, with only a minor contribution from the analysis procedure (+/- 0.04%); accuracy varied between -0.6 and +3.4% (effect of cortical bone: up to 3.0%; changes in size of object: -0.59 - +0.4%). The magnitude of these errors was determined under 'ideal' conditions, mostly through phantom measurements; therefore, the errors represent optimistic lower limits in clinical application. Furthermore, measurements of density of cortical bone were not reliable for bone thicknesses of less than about 4 mm with the GE 8800 scanner and less than about 1.5 mm with the peripheral scanner.

Absorptiometry, Photon↗
PubMed1985

Skeletal challenge: an experimental study of pharmacologically induced changes in bone density in the distal radius, using gamma-ray computed tomography.

Bone density (BD) at the distal end of the radius was measured serially with gamma-ray computed tomography (gamma-CT) in five groups of healthy postmenopausal women. One group comprised untreated controls; women in the other groups were subjected to pharmacologic challenge with putative activators and/or depressors of bone remodeling. The challenge agents, taken orally, were ergocalciferol (vitamin D2) alone and followed by calcium; calcitriol (1,25(OH)2D3), and prednisone. All of the subjects showed changes in BD following challenge; these changes were significant (P less than 0.05) for the groups receiving vitamin D2 and vitamin D2 plus calcium. Responses to ergocalciferol, calcitriol, and prednisone were similar within groups, whereas the group receiving ergocalciferol then calcium comprised two distinct subgroups: bone density transiently increased in one and decreased in the other. For all five groups, the direction of change in bone density in response to the challenge, and its duration and magnitude, were consistent with reported histomorphometric data. We conclude that gamma-CT assessment of change in bone density after pharmacologic challenge provides a useful noninvasive approach to skeletal investigation.

Aged↗
PubMed1982

Quantitative measurement of bone density using gamma-ray computed tomography.

A special purpose gamma-ray computed tomography scanner has been developed for precise measurements of bone density in the human appendicular skeleton. Details of the scanner's hardware and of the software organization for system control and data analysis are given, together with an outline of the theoretical basis for conversion of measured linear attenuation coefficients to physical bone densities. Performance of the system was evaluated on bone-like phantoms. Clinically, a precision of +/- 0.5% is obtained for bone density determinations. This device is being used in experimental studies and clinical investigations.

Bone Resorption↗
PubMedDate not supplied

Correction of scatter in computed tomography images of bone.

A cylindrical aluminum/Plexiglas phantom representing trabecular bone surrounded by various amounts of cortical bone was constructed. Measurements of this phantom using a computed tomography scanner with a 125I photon source demonstrated errors of 0% to 28% in the density of trabecular bone. Two contributing factors are identified: scatter and exponential edge-gradient effect. A simple first-order correction is developed to correct for the scatter-induced error. Relative to the exponential edge-gradient effect, which contributes up to 3.4% error over the range of cortical thicknesses measured, the correction procedure reduces the scatter-induced error to a level of -0.66% to +0.61%. The consistency of the optimized correction parameters with the physical model as well as the effect of scatter measured by the same phantom on a GE 8800 scanner are shown.

Bone and Bones↗
PubMedDate not supplied

The OsteoQuant: an isotope-based CT scanner for precise measurement of bone density.

OBJECTIVE: We attempted to design and construct a computed tomography scanner with an in vivo precision of better than 0.5% for trabecular bone density of the radius. MATERIALS AND METHODS: A number of considerations involving physical limitations, stability of the system, and cost led to the development of the OsteoQuant, an isotope-based computed tomography scanner working on the translate-rotate principle. With 16 detectors providing a total of 128 projections and 256 data points per projection, the measurement time for one cross section is typically 90 s. Optimal for bone measurements in arms and legs, 125I was chosen as the photon source. The detectors are photomultipliers with Nal(TI) crystals employed in the counting mode. Usually, six to ten slices are measured at a given site, 2 mm apart from each other, and bone density is calculated for trabecular, subcompact, and compact bone. For repeat measurements, the evaluation sites are carefully matched, and the same volume of bone is analyzed at each measurement occasion. RESULTS: The long-term precision of the scanner, measured with a water cylinder, is 0.03%. This error includes the performance of the scanner hardware, calibration of the photon count rates, and reconstruction process. In vivo precision is influenced by additional factors such as slice positioning, patient cooperation, and bone contour detection. At the distal end of the tibia, trabecular bone density can be measured with a precision of 0.1%. The error for trabecular bone density in the radius is 0.3%. CONCLUSION: The OsteoQuant surpasses the design goals and represents an ideal instrument to assess small changes in bone density over time.

Bone Density↗