High resolution X-ray analysis of a proximal human femur with synchrotron radiation and an innovative linear detector

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High resolution X-ray analysis of a proximal
human femur with synchrotron radiation and an
innovative linear detector
IEEE NSS MIC, Rome 21st October 2004

• M.Bettuzzi, R. Brancaccio, F.Casali, S.
  Cornacchia, N.Lanconelli, A.Miceli, M. P.Morigi,
  A. Pasini, D. Romani, A.Rossi
• Department of Physics, University of Bologna
• and
• INFN, Section of Bologna

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Ostheoporosis Project
The experiment was carried out in the framework
of a project, powered by the University of
Bologna, concerning the characterization of the
human bone tissue by means of physical techniques

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Good results were already obtained with the 3D
micro-CT technique on small bone samples
With our micro-CT system we obtained images with
a pixel size from 20 to 30 microns (less than 20
microns with high magnification µfocus source)
A good agreement with results achieved by other
systems (i.e. Skyscan) was found
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However, such a technique allows to investigate
only small samples (1-2 cm maximum size), that
means you have to physically cut the bone into
slices and make out a carrot of one of them
The aim of the present experiment was to verify
the possibility of performing the same kind of
analysis over a complete human bone (i.e. a
femur) without altering its structure by any
mechanical treatment
Looking forward, this should be a first step
toward the hard task of building an X-ray CT
system for the structural bone analysis in vivo
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Trabeculae size in a human bone vary from 0.1 to
0.3 mm while spacing from 0.2 to 2 mm We had to
build a new detector with the proper spatial
resolution and a sufficiently wide field of
view The synchrotron radiation source was choose
because it provides a high flux of mono-energetic
photons Thus it is the best quality source for
this experiment, though its not the most
suitable one for routine analysis
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• A new linear intensified detector was designed at
  the University of Bologna ( EU patented )
• The detector is based on two main components
• a digital intensified CCD camera (the EBCCD)
• a special coherent fiber optics adapter

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The Electron Bombarded CCD camera Produced by
Geosphaera (Moscow)
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Scheme of the EBCCD tube
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The fiber-optics guide permits the conversion of
the geometry from linear to rectangular format
From 1024x512 to 5600x50 effective pixels
Realization
Concept
Produced by the Vavilov Institute (S.Petersburg)
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Detector assembly scheme
Scintillating screen stripe Gd2O2STb Fiber
optics light guide 1291.45 mm2 to 18.410.6 mm2
Multialkali input window 24.5 mm Back-thinned
frame transfer CCD 1024512 Intensifier tube
voltage 6 kV Image size
(multislice) 560050 pixel
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Mounted detector
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SPLINE interpolation of missing data into the
spacings between neighbouring FO ribbons
129 ???m
66 ?m
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Scheme of the CT system (microfocus source)
Fiber optics fan adapter
Microfocus X-ray tube
EBCCD
Controlled axis
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Radiograph of a calibrated bar-pattern direct
measurement of the spatial resolution
5 lp/mm (100 µm)
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Modulation Transfer Functionmicrofocus X-ray
tube measurements (focal spot 5 µm)
Spatial resolution of the detector (at 5
measured MTF value)
60 µm
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Noise and DQE
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Experiments at Elettra SRFin collaboration with
Rizzoli Institute, Bologna

• August 2003 - April 2004

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ELETTRA Syrmep Beamline
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Beam energy 34 keV max
Beam size width 120 mm (our detector is 130 mm
long) height 4 mm (our detector is 1.5 mm high)
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Experimental set-up at the SYRMEP beamline
beam
sample
proximal femur (pig)
detector
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Exposure Time 50 ms Number of averaged frames
16 Total exposure time for 500 projections
400 s Total CT time 8000 s (2 hours e 13
minutes)

• Proximal femur of a pig
• Maximum size 7,41 x 5,42 cm2
• CT parameters
• Energy 34 keV
• Number of projections 500
• Angle 180
• Voxel side 23 ?m

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The trabeculae structure becomes visible,
thought, spatial resolution is not enough at this
level to define it properly
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The use of a high resolution linear detector with
synchrotron light allowed the definition of the
trabecular structure in a CT slice of a complete
proximal femur bone of a pig
The image quality was too low and it was not
suitable for a proper segmentation and for the
calculation of the isomorphometric parameters of
the bone structure
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Improvements

• better alignment of the detector
• collection of a large number of projection
• recalibration and accurate reconstruction
• human femur analysis

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Human femur CT

• Parameters of the CT
• 1400 projections over 180 degrees
• 16 frame averaged for each projection
• 25 ms exposure time for each frame
• 2 hours 15 minutes total scanning time

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Radiography of a human femur
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A high resolution computed tomography of a
complete human femur was performed
The high quality of the images obtained after the
CT reconstruction allows the calculation of the
histomorphometric parameters of the bone
Thus, it is possible to study the trabeculae
structure of the complete human femur
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• Further steps
• Replicate the experiment with a microfocus X-ray
  tube
• Optimize the source-detector system
• Optimize the number of projections for a good
  image quality with a reduced dose

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THANK YOU FOR YOUR ATTENTION