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Short-TE projection reconstruction NMR microscopy of trabecular bone
Magnetic Resonance Imaging 19 (2001) 485– 486
Short-TE projection reconstruction NMR microscopy of trabecular bone Renato Toffanina,b,*, Vladimı´r Jellu´sˇc, Pavol Szomola´nyic, Franco Vittur* a
Department of Biochemistry, Biophysics and Macromolecular Chemistry, University of Trieste, Trieste, Italy b PROTOS Research Institute, Trieste, Italy c Institute of Measurement Science, Slovak Academy of Sciences, Bratislava, Slovakia
Abstract The aim of this study was to assess the potential of projection reconstruction (PR) NMR microscopy in the quantitative evaluation of trabecular bone architecture. Short-TE PR spin-echo microimages were acquired at 7.05 T on normal bone explants. The main structural parameters such as bone volume fraction (BVF), trabecular thickness (Tb.Th.) and trabecular separation (Tb.Sp.) were obtained from the 3D microimages using the method of directed secants. Quantitative structural data were then compared with those derived from conventional spin-echo microimages. Our study indicates that projection reconstruction NMR microscopy promises to be more accurate than the conventional FTI method in the analysis of trabecular bone. Keywords: NMR microscopy, projection reconstruction, trabecular bone
1. Introduction Two main different types of bone are present in the skeleton: cortical and trabecular bone. Cortical or compact bone serves primarily a mechanical function providing skeletal strength. Trabecular or spongy bone, in addition to providing mechanical and skeletal strength, plays important metabolic functions as, for example, calcium buffering. In healthy persons the trabecular thickness ranges from 0.1 to 0.2 mm. Bone disorders such as osteoporosis lead to alterations in the trabecular bone mass and microarchitecture. NMR microscopy may potentially be very useful in the ex vivo study of osteoporosis as non-destructive technique with the ability to provide three dimensional information of the trabecular bone microstructure [1,2,3,4]. However, as the difference in diamagnetic susceptibility between bone and marrow causes intravoxel phase dispersion, the trabecular width appears larger in conventional MR images. Such an effect can be minimized if the echo-time (TE) or voxel size are reduced. The purpose of our research was to develop new NMR microscopic imaging techniques that have a potential role in the assessment of trabecular bone microarchitecture. In this study we describe the use of short-TE * Corresponding author. Department of Biochemistry, Biophysics and Macromolecular Chemistry, University of Trieste, via L. Giorgieri 1, I-34127 Trieste, Italy. E-mail address: [email protected] (R. Toffanin).
projection reconstruction NMR microscopy for the quantitative characterization of trabecular bone explants. 2. Materials and methods Specimens consisting of cylindrical bone plugs (A ⫽ 4 mm) were excised from the same weight-bearing region of seven porcine humeral heads. The explants were examined at 7.05 Tesla using a Bruker AM300 WB instrument equipped with a microimaging accessory. Short-TE 3D spin-echo microimages (TE ⫽ 3.0 ms) were acquired according to the PR method with constant gradient step already described [5,6]. This method provided images with a final voxel resolution of 41 ⫻ 41 ⫻ 41 m3. PR microimages were then compared with spin-echo microimages (TE ⫽ 6.2 ms) obtained on the same explants by the standard FT imaging method. The main architectural parameters such as bone volume fraction (BVF), trabecular thickness (Tb.Th.) and trabecular separation (Tb.Sp.) were obtained from the 3D microimages using the method of directed secants [7]. Segmentation of the binary images was performed using a variable threshold. 3. Results and Discussion Short-TE projection reconstruction NMR microscopy allowed three dimensional representation and assessment of
0730-725X/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S 0 7 3 0 - 7 2 5 X ( 0 1 ) 0 0 2 7 3 - 9
486
R.T. Toffanin et al. / Magnetic Resonance Imaging 19 (2001) 485– 486
Table 1 Main architectural parameters obtained from 3D microimages of porcine trabecular bone explants. Tb.Th. and Tb.Sp. are expressed in mm BVF
Tb.Th.
Tb.Sp.
sample
SE
PR-SE
SE
PR-SE
SE
PR-SE
1 2 3 4 5 6 7 mean S.D.
0.635 0.522 0.655 0.590 0.450 0.516 0.570 0.563 0.072
0.601 0.608 0.585 0.581 0.644 0.559 0.500 0.583 0.045
0.235 0.189 0.223 0.252 0.192 0.184 0.164 0.206 0.032
0.218 0.190 0.185 0.195 0.203 0.175 0.168 0.191 0.017
0.135 0.173 0.117 0.175 0.234 0.172 0.124 0.161 0.040
0.145 0.123 0.131 0.141 0.112 0.138 0.167 0.137 0.018
the microstructure of isolated intact specimens of trabecular bone. By this method, the bone-marrow interface provides high contrast because marrow is bright and bone appears dark as a result of its very short T2. A 2D section of the 3D PR spin-echo microimage of a porcine trabecular bone explant is shown in Fig. 1. The main structural parameters such as bone volume fraction (BVF), trabecular thickness (Tb.Th.) and trabecular separation (Tb.Sp.) were obtained from the PR microimages of seven trabecular bone specimens. Quantitative structural data were then compared with those derived from conventional spin-echo microimages (Table 1). Our study indicates that short-TE projection reconstruction NMR microscopy promises to be more accurate than the conventional FTI method in the analysis of trabecular bone.
vivo evaluation of trabecular bone architecture. The described PR method can be, therefore, a contribution toward a better understanding of the role of bone architecture in determining the overall bone quality. Acknowledgments
4. Conclusions
This work was supported by grants of the Italian Ministry of University and Scientific and Technological Research (PRIN 97), of the University of Trieste, Italy, of the Commissariato del Governo nella Regione Friuli-Venezia Giulia (Fondo speciale per la Ricerca Scientifica e Tecnologica. Prog. 63–1997) and of the Slovak Academy of Sciences (VEGA 2/5087/99). We wish to thank Giulia Candido for calculating the bone structural parameters.
These results demonstrate that quantitative PR NMR microscopy can be used as a non-destructive tool for the ex
References
Fig. 1. 2D section taken from the 3D projection reconstruction spin-echo microimage of a porcine trabecular bone explant. The in-plane resolution is 41 m.
[1] Chung H, Chung H-S, Wehrli FW, Williams JL, Kugelmass S, Wehrli SL. Three-dimensional nuclear magnetic resonance microimaging of trabecular bone. J Bone Miner. Res. 10:1452– 61, 1995. [2] Hwang SN, Wehrli FW, Williams JL. Probability-based structural parameters from three-dimensional nuclear magnetic resonance images as predictors of trabecular bone strength. Med Phys 1997;24:1255– 61. [3] Majumdar S, Newitt D, Jergas M, Gies A, Chiu E, Osman D, Keltner J, Keyak J, Genant H. Evaluation of technical factors affecting the quantification of trabecular bone structure using magnetic resonance imaging. Bone 1995;17:417–30. [4] Majumdar S, Kothari M, Augat P, Newitt DC, Link TM, Lin JC, Lang T, Lu Y, Genant, HK. High-resolution magnetic resonance imaging: three-dimensional trabecular bone architecture and biomechanical properties. Bone 1998;22:445–54. [5] Jellu´sˇ V, Latta P, Budinsky L’, Szomolanyi P, Toffanin R, Jarh O, Vittur, F. Three-dimensional projection-reconstruction method with constant gradient step. MAG*MA 5 (Suppl. 1):163, 1997. [6] Toffanin R, Szomolanyi P, Jellu´sˇ V, Cova M, Pozzi-Mucelli, RS, Vittur F. Magnetic resonance microscopy of osteoporotic bone. In: M.S. El-Genk (Ed). Proceedings of the Space Technology and Applications International Forum –2000 (STAIF-2000). American Institute of Physics, 2000: pp. 295–99. [7] Hipp JA, Jansujwicz A, Simmons CA, Snyder, BD. Trabecular bone morphology from micro-magnetic resonance imaging. J Bone Miner Res 1996;11:286 –92.
Short-TE projection reconstruction NMR microscopy of trabecular bone Renato Toffanina,b,*, Vladimı´r Jellu´sˇc, Pavol Szomola´nyic, Franco Vittur* a
Department of Biochemistry, Biophysics and Macromolecular Chemistry, University of Trieste, Trieste, Italy b PROTOS Research Institute, Trieste, Italy c Institute of Measurement Science, Slovak Academy of Sciences, Bratislava, Slovakia
Abstract The aim of this study was to assess the potential of projection reconstruction (PR) NMR microscopy in the quantitative evaluation of trabecular bone architecture. Short-TE PR spin-echo microimages were acquired at 7.05 T on normal bone explants. The main structural parameters such as bone volume fraction (BVF), trabecular thickness (Tb.Th.) and trabecular separation (Tb.Sp.) were obtained from the 3D microimages using the method of directed secants. Quantitative structural data were then compared with those derived from conventional spin-echo microimages. Our study indicates that projection reconstruction NMR microscopy promises to be more accurate than the conventional FTI method in the analysis of trabecular bone. Keywords: NMR microscopy, projection reconstruction, trabecular bone
1. Introduction Two main different types of bone are present in the skeleton: cortical and trabecular bone. Cortical or compact bone serves primarily a mechanical function providing skeletal strength. Trabecular or spongy bone, in addition to providing mechanical and skeletal strength, plays important metabolic functions as, for example, calcium buffering. In healthy persons the trabecular thickness ranges from 0.1 to 0.2 mm. Bone disorders such as osteoporosis lead to alterations in the trabecular bone mass and microarchitecture. NMR microscopy may potentially be very useful in the ex vivo study of osteoporosis as non-destructive technique with the ability to provide three dimensional information of the trabecular bone microstructure [1,2,3,4]. However, as the difference in diamagnetic susceptibility between bone and marrow causes intravoxel phase dispersion, the trabecular width appears larger in conventional MR images. Such an effect can be minimized if the echo-time (TE) or voxel size are reduced. The purpose of our research was to develop new NMR microscopic imaging techniques that have a potential role in the assessment of trabecular bone microarchitecture. In this study we describe the use of short-TE * Corresponding author. Department of Biochemistry, Biophysics and Macromolecular Chemistry, University of Trieste, via L. Giorgieri 1, I-34127 Trieste, Italy. E-mail address: [email protected] (R. Toffanin).
projection reconstruction NMR microscopy for the quantitative characterization of trabecular bone explants. 2. Materials and methods Specimens consisting of cylindrical bone plugs (A ⫽ 4 mm) were excised from the same weight-bearing region of seven porcine humeral heads. The explants were examined at 7.05 Tesla using a Bruker AM300 WB instrument equipped with a microimaging accessory. Short-TE 3D spin-echo microimages (TE ⫽ 3.0 ms) were acquired according to the PR method with constant gradient step already described [5,6]. This method provided images with a final voxel resolution of 41 ⫻ 41 ⫻ 41 m3. PR microimages were then compared with spin-echo microimages (TE ⫽ 6.2 ms) obtained on the same explants by the standard FT imaging method. The main architectural parameters such as bone volume fraction (BVF), trabecular thickness (Tb.Th.) and trabecular separation (Tb.Sp.) were obtained from the 3D microimages using the method of directed secants [7]. Segmentation of the binary images was performed using a variable threshold. 3. Results and Discussion Short-TE projection reconstruction NMR microscopy allowed three dimensional representation and assessment of
0730-725X/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S 0 7 3 0 - 7 2 5 X ( 0 1 ) 0 0 2 7 3 - 9
486
R.T. Toffanin et al. / Magnetic Resonance Imaging 19 (2001) 485– 486
Table 1 Main architectural parameters obtained from 3D microimages of porcine trabecular bone explants. Tb.Th. and Tb.Sp. are expressed in mm BVF
Tb.Th.
Tb.Sp.
sample
SE
PR-SE
SE
PR-SE
SE
PR-SE
1 2 3 4 5 6 7 mean S.D.
0.635 0.522 0.655 0.590 0.450 0.516 0.570 0.563 0.072
0.601 0.608 0.585 0.581 0.644 0.559 0.500 0.583 0.045
0.235 0.189 0.223 0.252 0.192 0.184 0.164 0.206 0.032
0.218 0.190 0.185 0.195 0.203 0.175 0.168 0.191 0.017
0.135 0.173 0.117 0.175 0.234 0.172 0.124 0.161 0.040
0.145 0.123 0.131 0.141 0.112 0.138 0.167 0.137 0.018
the microstructure of isolated intact specimens of trabecular bone. By this method, the bone-marrow interface provides high contrast because marrow is bright and bone appears dark as a result of its very short T2. A 2D section of the 3D PR spin-echo microimage of a porcine trabecular bone explant is shown in Fig. 1. The main structural parameters such as bone volume fraction (BVF), trabecular thickness (Tb.Th.) and trabecular separation (Tb.Sp.) were obtained from the PR microimages of seven trabecular bone specimens. Quantitative structural data were then compared with those derived from conventional spin-echo microimages (Table 1). Our study indicates that short-TE projection reconstruction NMR microscopy promises to be more accurate than the conventional FTI method in the analysis of trabecular bone.
vivo evaluation of trabecular bone architecture. The described PR method can be, therefore, a contribution toward a better understanding of the role of bone architecture in determining the overall bone quality. Acknowledgments
4. Conclusions
This work was supported by grants of the Italian Ministry of University and Scientific and Technological Research (PRIN 97), of the University of Trieste, Italy, of the Commissariato del Governo nella Regione Friuli-Venezia Giulia (Fondo speciale per la Ricerca Scientifica e Tecnologica. Prog. 63–1997) and of the Slovak Academy of Sciences (VEGA 2/5087/99). We wish to thank Giulia Candido for calculating the bone structural parameters.
These results demonstrate that quantitative PR NMR microscopy can be used as a non-destructive tool for the ex
References
Fig. 1. 2D section taken from the 3D projection reconstruction spin-echo microimage of a porcine trabecular bone explant. The in-plane resolution is 41 m.
[1] Chung H, Chung H-S, Wehrli FW, Williams JL, Kugelmass S, Wehrli SL. Three-dimensional nuclear magnetic resonance microimaging of trabecular bone. J Bone Miner. Res. 10:1452– 61, 1995. [2] Hwang SN, Wehrli FW, Williams JL. Probability-based structural parameters from three-dimensional nuclear magnetic resonance images as predictors of trabecular bone strength. Med Phys 1997;24:1255– 61. [3] Majumdar S, Newitt D, Jergas M, Gies A, Chiu E, Osman D, Keltner J, Keyak J, Genant H. Evaluation of technical factors affecting the quantification of trabecular bone structure using magnetic resonance imaging. Bone 1995;17:417–30. [4] Majumdar S, Kothari M, Augat P, Newitt DC, Link TM, Lin JC, Lang T, Lu Y, Genant, HK. High-resolution magnetic resonance imaging: three-dimensional trabecular bone architecture and biomechanical properties. Bone 1998;22:445–54. [5] Jellu´sˇ V, Latta P, Budinsky L’, Szomolanyi P, Toffanin R, Jarh O, Vittur, F. Three-dimensional projection-reconstruction method with constant gradient step. MAG*MA 5 (Suppl. 1):163, 1997. [6] Toffanin R, Szomolanyi P, Jellu´sˇ V, Cova M, Pozzi-Mucelli, RS, Vittur F. Magnetic resonance microscopy of osteoporotic bone. In: M.S. El-Genk (Ed). Proceedings of the Space Technology and Applications International Forum –2000 (STAIF-2000). American Institute of Physics, 2000: pp. 295–99. [7] Hipp JA, Jansujwicz A, Simmons CA, Snyder, BD. Trabecular bone morphology from micro-magnetic resonance imaging. J Bone Miner Res 1996;11:286 –92.