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

linear detector

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

IEEE NSS – MIC, Rome

21st October 2004

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

Ostheoporosis Project

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 µ–focus source)

A good agreement with results achieved by other systems (i.e. Skyscan) was found

micro-CT slice

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”

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 it’s not the most suitable one for routine analysis

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

The Electron Bombarded CCD camera

Produced by Geosphaera (Moscow)

Scheme of the EBCCD tube

The fiber-optics guide permits the conversion of the geometry from linear to rectangular format

Concept

Realization

From 1024x512 to 5600x50 effective pixels

Produced by the Vavilov Institute (S.Petersburg)

Scintillating screen stripe Gd2O2S:Tb Fiber optics light guide 129×1.45 mm2 to 18.4×10.6 mm2 Multialkali input window 24.5 mm Back-thinned frame transfer CCD 1024×512 Intensifier tube voltage

6 kV Image size (multislice)5600×50 pixel

Detector assembly scheme

Mounted detector

66 m 129 m

SPLINE interpolation of missing data into the spacings between neighbouring FO ribbons

Microfocus X-ray tube

Controlled axis

Fiber optics fan adapter

EBCCD

Scheme of the CT system (microfocus source)

Radiograph of a calibrated bar-patterndirect measurement of the spatial resolution

5 lp/mm

(100 µm)

Modulation Transfer Functionmicrofocus X-ray tube measurements (focal spot 5 µm)

0

0,2

0,4

0,6

0,8

1

0 1 2 3 4 5 6 7 8 9 10

lp/mm

MT

F

8,35 lp/mm

5% MTF

Spatial resolution of the detector (at 5% measured MTF value)

60 µm

Noise and DQE

Experiments at Elettra SRFin collaboration with

Rizzoli Institute, Bologna

August 2003 - April 2004

ELETTRA

Syrmep Beamline

Beam size

width: 120 mm

(our detector is 130 mm long)

height: 4 mm

(our detector is 1.5 mm high)

Beam energy

34 keV max

Experimental set-up at the SYRMEP beamline

beam

detector

sample

proximal femur (pig)

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

position of the CT slices

1

2

Each CT section is made of about 35 slices, one pixel thick (23 µm)

Original projections size

5600 x 35 pixel

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)

1

2

The trabeculae structure becomes visible, thought, spatial resolution is not enough at this level to define it properly

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

Improvements

• better alignment of the detector

• collection of a large number of projection

• recalibration and accurate reconstruction

• human femur analysis

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

Radiography of a human femur

Micro-CT slice

A high resolution computed tomography of a complete human femur was performed

Thus, it is possible to study the trabeculae structure of the complete human femur

The high quality of the images obtained after the CT reconstruction allows the calculation of the histomorphometric parameters of the bone

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

THANK YOU FOR YOUR ATTENTION