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Title: Bone-composition imaging using coherent-scatter computed tomography: Assessing bone health beyond bone mineral density

Abstract

Quantitative analysis of bone composition is necessary for the accurate diagnosis and monitoring of metabolic bone diseases. Accurate assessment of the bone mineralization state is the first requirement for a comprehensive analysis. In diagnostic imaging, x-ray coherent scatter depends upon the molecular structure of tissues. Coherent-scatter computed tomography (CSCT) exploits this feature to identify tissue types in composite biological specimens. We have used CSCT to map the distributions of tissues relevant to bone disease (fat, soft tissue, collagen, and mineral) within bone-tissue phantoms and an excised cadaveric bone sample. Using a purpose-built scanner, we have measured hydroxyapatite (bone mineral) concentrations based on coherent-scatter patterns from a series of samples with varying hydroxyapatite content. The measured scatter intensity is proportional to mineral density in true g/cm{sup 3}. Repeated measurements of the hydroxyapatite concentration in each sample were within, at most, 2% of each other, revealing an excellent precision in determining hydroxyapatite concentration. All measurements were also found to be accurate to within 3% of the known values. Phantoms simulating normal, over-, and under-mineralized bone were created by mixing known masses of pure collagen and hydroxyapatite. An analysis of the composite scatter patterns gave the density of each material. For each composite,more » the densities were within 2% of the known values. Collagen and hydroxyapatite concentrations were also examined in a bone-mimicking phantom, incorporating other bone constituents (fat, soft tissue). Tomographic maps of the coherent-scatter properties of each specimen were reconstructed, from which material-specific images were generated. Each tissue was clearly distinguished and the collagen-mineral ratio determined from this phantom was also within 2% of the known value. Existing bone analysis techniques cannot determine the collagen-mineral ratio in intact specimens. Finally, to demonstrate the in situ potential of this technique, the mineralization state of an excised normal cadaveric radius was examined. The average collagen-mineral ratio of the cortical bone derived from material-specific images of the radius was 0.53{+-}0.04, which is in agreement with the expected value of 0.55 for healthy bones.« less

Authors:
; ; ;  [1];  [2];  [3]
  1. Imaging Research Laboratories, Roberts Research Institute, London, Ontario, N6A 5K8 (Canada) and Department of Medical Biophysics, University of Western Ontario, London, Ontario, N6A 5C1 (Canada)
  2. (Canada)
  3. (Canada) and Department of Medical Biophysics, The University of Western Ontario, London, Ontario, N6A 5C1 (Canada)
Publication Date:
OSTI Identifier:
20775128
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 33; Journal Issue: 4; Other Information: DOI: 10.1118/1.2179151; (c) 2006 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; BIOCHEMISTRY; BONE TISSUES; COLLAGEN; COMPUTERIZED TOMOGRAPHY; DIAGNOSIS; FATS; IMAGES; MINERALIZATION; MINERALS; PHANTOMS; SKELETAL DISEASES; SKELETON; X RADIATION

Citation Formats

Batchelar, Deidre L., Davidson, Melanie T.M., Dabrowski, Waldemar, Cunningham, Ian A., Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5K8, and Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5K8. Bone-composition imaging using coherent-scatter computed tomography: Assessing bone health beyond bone mineral density. United States: N. p., 2006. Web. doi:10.1118/1.2179151.
Batchelar, Deidre L., Davidson, Melanie T.M., Dabrowski, Waldemar, Cunningham, Ian A., Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5K8, & Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5K8. Bone-composition imaging using coherent-scatter computed tomography: Assessing bone health beyond bone mineral density. United States. doi:10.1118/1.2179151.
Batchelar, Deidre L., Davidson, Melanie T.M., Dabrowski, Waldemar, Cunningham, Ian A., Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5K8, and Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5K8. Sat . "Bone-composition imaging using coherent-scatter computed tomography: Assessing bone health beyond bone mineral density". United States. doi:10.1118/1.2179151.
@article{osti_20775128,
title = {Bone-composition imaging using coherent-scatter computed tomography: Assessing bone health beyond bone mineral density},
author = {Batchelar, Deidre L. and Davidson, Melanie T.M. and Dabrowski, Waldemar and Cunningham, Ian A. and Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5K8 and Imaging Research Laboratories, Robarts Research Institute, London, Ontario, N6A 5K8},
abstractNote = {Quantitative analysis of bone composition is necessary for the accurate diagnosis and monitoring of metabolic bone diseases. Accurate assessment of the bone mineralization state is the first requirement for a comprehensive analysis. In diagnostic imaging, x-ray coherent scatter depends upon the molecular structure of tissues. Coherent-scatter computed tomography (CSCT) exploits this feature to identify tissue types in composite biological specimens. We have used CSCT to map the distributions of tissues relevant to bone disease (fat, soft tissue, collagen, and mineral) within bone-tissue phantoms and an excised cadaveric bone sample. Using a purpose-built scanner, we have measured hydroxyapatite (bone mineral) concentrations based on coherent-scatter patterns from a series of samples with varying hydroxyapatite content. The measured scatter intensity is proportional to mineral density in true g/cm{sup 3}. Repeated measurements of the hydroxyapatite concentration in each sample were within, at most, 2% of each other, revealing an excellent precision in determining hydroxyapatite concentration. All measurements were also found to be accurate to within 3% of the known values. Phantoms simulating normal, over-, and under-mineralized bone were created by mixing known masses of pure collagen and hydroxyapatite. An analysis of the composite scatter patterns gave the density of each material. For each composite, the densities were within 2% of the known values. Collagen and hydroxyapatite concentrations were also examined in a bone-mimicking phantom, incorporating other bone constituents (fat, soft tissue). Tomographic maps of the coherent-scatter properties of each specimen were reconstructed, from which material-specific images were generated. Each tissue was clearly distinguished and the collagen-mineral ratio determined from this phantom was also within 2% of the known value. Existing bone analysis techniques cannot determine the collagen-mineral ratio in intact specimens. Finally, to demonstrate the in situ potential of this technique, the mineralization state of an excised normal cadaveric radius was examined. The average collagen-mineral ratio of the cortical bone derived from material-specific images of the radius was 0.53{+-}0.04, which is in agreement with the expected value of 0.55 for healthy bones.},
doi = {10.1118/1.2179151},
journal = {Medical Physics},
number = 4,
volume = 33,
place = {United States},
year = {Sat Apr 15 00:00:00 EDT 2006},
month = {Sat Apr 15 00:00:00 EDT 2006}
}
  • Coherent-scatter computed tomography (CSCT) is a method of ''composition'' imaging based on measurements of diffraction patterns from tissues. Use of an x-ray tube degrades scatter pattern angular resolution due to the x-ray spectral width, making it difficult to uniquely identify some materials. The use of two transmission filters with similar atomic numbers (balanced ''Ross filters'') to generate pseudomonoenergetic scatter patterns is described as it applies to CSCT. An analysis of angular-blur mechanisms reveals that focal spot size and beam width are the most important factors determining Bragg-peak width when Er-Tm filters are used. A relative RMS spectral width of 1%more » can be achieved in the difference spectrum and a Bragg-peak RMS angular width of approximately 0.14 deg. (relative width of 3% at 5 deg. scatter angle) can be achieved with an effective energy of 58 keV.« less
  • Plug density phantoms were constructed in accordance to CT density phantom model 062M CIRS using binderless, pre-treated and tannin-based Rhizophora Spp. particleboards. The Rhizophora Spp. plug phantoms were scanned along with the CT density phantom using Siemens Somatom Definition AS CT scanner at three CT energies of 80, 120 and 140 kVp. 15 slices of images with 1.0 mm thickness each were taken from the central axis of CT density phantom for CT number and CT density profile analysis. The values were compared to water substitute plug phantom from the CT density phantom. The tannin-based Rhizophora Spp. gave the nearest valuemore » of CT number to water substitute at 80 and 120 kVp CT energies with χ{sup 2} value of 0.011 and 0.014 respectively while the binderless Rhizphora Spp. gave the nearest CT number to water substitute at 140 kVp CT energy with χ{sup 2} value of 0.023. The tannin-based Rhizophora Spp. gave the nearest CT density profile to water substitute at all CT energies. This study indicated the suitability of Rhizophora Spp. particleboard as phantom material for the use in CT imaging studies.« less
  • 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.
  • Purpose: Microcomputed tomography (micro-CT) is increasingly used as a nondestructive alternative to ashing for measuring bone mineral content. Phantoms are utilized to calibrate the measured x-ray attenuation to discrete levels of mineral density, typically including levels up to 1000 mg HA/cm{sup 3}, which encompasses levels of bone mineral density (BMD) observed in trabecular bone. However, levels of BMD observed in cortical bone and levels of tissue mineral density (TMD) in both cortical and trabecular bone typically exceed 1000 mg HA/cm{sup 3}, requiring extrapolation of the calibration regression, which may result in error. Therefore, the objectives of this study were tomore » investigate (1) the relationship between x-ray attenuation and an expanded range of hydroxyapatite (HA) density in a less attenuating polymer matrix and (2) the effects of the calibration on the accuracy of subsequent measurements of mineralization in human cortical bone specimens. Methods: A novel HA-polymer composite phantom was prepared comprising a less attenuating polymer phase (polyethylene) and an expanded range of HA density (0-1860 mg HA/cm{sup 3}) inclusive of characteristic levels of BMD in cortical bone or TMD in cortical and trabecular bone. The BMD and TMD of cortical bone specimens measured using the new HA-polymer calibration phantom were compared to measurements using a conventional HA-polymer phantom comprising 0-800 mg HA/cm{sup 3} and the corresponding ash density measurements on the same specimens. Results: The HA-polymer composite phantom exhibited a nonlinear relationship between x-ray attenuation and HA density, rather than the linear relationship typically employed a priori, and obviated the need for extrapolation, when calibrating the measured x-ray attenuation to high levels of mineral density. The BMD and TMD of cortical bone specimens measured using the conventional phantom was significantly lower than the measured ash density by 19% (p<0.001, ANCOVA) and 33% (p<0.05, Tukey's HSD), on average, respectively. The BMD and TMD of cortical bone specimens measured using the HA-polymer phantom with an expanded range of HA density was significantly lower than the measured ash density by 8% (p<0.001, ANCOVA) and 10% (p<0.05, Tukey's HSD), on average, respectively. Conclusions: The new HA-polymer calibration phantom with a less attenuating polymer and an expanded range of HA density resulted in a more accurate measurement of micro-CT equivalent BMD and TMD in human cortical bone specimens compared to a conventional phantom, as verified by ash density measurements on the same specimens.« less
  • Application of computed tomography (CT) to the study of bone structure and density was explored and developed. A review of bone mineral densitometry (BMD) methodology and general principles of quantitative CT (QCT) are presented. A method for QCT of the spine was developed using a flexible tissue equivalent reference placed adjacent to the patient. A methodology for the development and production of tissue equivalent materials is also presented. Patient equivalent phantoms were used to characterize the method, and phantom studies were performed at five clinical sites. A protocol is defined for measuring the inside diameter of the lumbar pedicular canal.more » Data generated from this study has proven invaluable in the planning for lumbar fusion surgery when screws are to be used for immobilization. Pedicular canal data from 33 patients is presented. QCT was also used to quantify several parameters of the femoral shaft for use in hip replacement surgical planning. Parameters studied include inside diameter, BMD, endosteal BMD and proximal shaft morphology. The structure and trabecular BMD of the proximal femur was extensively studied using QCT. A large variation was found in the fat content of marrow within the proximal femur, and phantom studies were performed to quantify the effect of fat on trabecular QCT BMD. Cadaveric trabecular bone samples with marrow were analyzed physically to determine water, fat, non-fat soft tissue, and ash content. Multiple thin-slice CT studies were performed on cadaveric femurs. A structural model of the proximal femur was developed in which the structural support is provided primarily by trabecular bone. This model may have profound implications in the study of femoral fractures and prosthetic hardware design.« less