Introduction

Optical absorption reveals both angiogenesis and

hypermetabolism, both of which are hallmarks of cancer. Near

infrared (NIR) imaging relies mainly on the absorption of

hemoglobin for the source of image contrast, and is highly

sensitive to the oxygen saturation of hemoglobin (SO2). [1-4]. We

recently developed a paired-wavelength spectral approach to

quantify the oxygen saturation of the hemoglobin in breast tumors

[5]. The basic idea is that an appropriate choice of a pair of

wavelengths (λ1, λ2), which depends on the oxygenation level of

the tumor and on the optical properties of the background healthy

breast tissue, leads to a measurement of the tumor oxygenation

that is largely independent of the tumor size, shape, and location

inside the breast [5].

Here, we present the scanning system and experimental results to

show the performance of our new system.

Yang Yu, Ning Liu, Angelo Sassaroli, and Sergio Fantini

Tufts University, Department of Biomedical Engineering, 4 Colby Street, Medford, MA 02155, USA

Abstract

A tunable band-pass(500nm to 1000nm) Xenon arc lamp is

coupled to a source fiber which delivers the light to the sample.

The light transmitted through the sample is sent through a

detector fiber to a spectrograph and then spatially dispersed onto

the charged-coupled device(CCD) array. The source and detector

fibers are collinear to each other and perform a tandem 2D scan.

The spatial sampling rate is controlled by changing the speed of

stepper motors and CCD acquisition time in a LabVIEW program.

We are optimizing the system in terms of signal-to-noise

ratio(SNR) at different wavelengths under the condition that the

maximum scanning time is 5 minutes for a typical breast scanning.

Fundamental tests are performed by using homogenous diffusive

media with optical properties similar to breast tissue. Incorporated

with the novel pair-wavelength approach, our breast imaging

system can provide relevant oxygenation information that can

ultimately result in a higher specificity for tumor detection or more

efficient follow-up to treatment.

Block Diagram for Block Diagram for

Optical Mammography InstrumentOptical Mammography Instrument

Essential Components corresponding to the Block Diagram

5-phase step motor –(adjust scanning speed (starting from 1cm/s))

Xenon Arc lamp (maximum output power 350W, provide broadband light

from 500nm to 1000nm after UV-filtering, )

Charged-coupled device detector(record spectral information at each

detection point with 1024*1024 pixel array)

LabVIEW program (control the scanning and data acquisition process)

Spectrograph (spectral dispersion 20nm/mm)

Optical fibers (deliver and receive photons with internal diameter: 4mm,

radiation exposure measured after the fiber attenuation)

SIEMENS scanning platform (adjustable height to accommodate various

subjects with parallel glass to achieve mild compression. equipped with gliding

scanner and detector where the optic fibers are embedded)

DAQ board (interface where analog trigger and TTL pulse signals are sent

and received)

Mammography instrumentation picture

corresponding to block diagram

The cooling system for the Arc Lamp and CCD camera, which is critical to

reduce the electronic noise generated inside the detector and source, does

not show in the figure above.

Spectrograph

CCD

Computer

Filters (500nm-

1000nm)

Xenon Arc

Lamp

Illumination

fiber bundleCollection fiber

bundle

6.3cm

30.4cm14.3cm

10cm

1cm diameter,

12cm long

cylindrical hole

6cm

Solid phantomSolid phantomSolid phantom

Shot Noise Description--- Poisson Distribution

Signal is the mean value of data points from one specific location

Noise is the standard deviation of data points from the same location

As a result, the detected signal level should be maximized in order to

achieve the optimal SNR with the regulation of CIE S 009: 2002.

CCD exposure time, which is limited by the maximum scanning time, is

another critical parameter that can affect the detected signal level.

Preliminary experiment setup Preliminary experiment setup

on solid phantomon solid phantom

Discussion

Noise can be characterized into three categories:

� Electronic Noise stems from the CCD dark current, readout noise and

amplifier noise. It is independent upon the signal level and its effect can

be significantly reduced by background acquisition in dark ambience.

� Structural noise comes from the slight misalignment between scanner and

detector, and different scratches among different glass positions. To sum

up, the structural noise is due to the instrumentation inhomogeneity.

Currently we are correcting this noise by flat-field method.

� After all the correction methods, the shot noise is the dominant noise

source to concern about. According to the definition of Poisson

Distribution, ANSI stardards, the light intensity should be increased to the

largest extent with the compliance to the current ANSI standards. Under

the 5-minute maximum scanning time, the CCD exposure time should be

increased given specific pixel size and subject breast size.

Conclusions

We have built a mammography spectral imaging system that provides a

large flexibility in terms of pixel size (in the order of millimeters), scanning

speed (starting from 1.0cm/s) and light radiance.

We are planning to assess the robustness of the pair-wavelength method

on human subjects and make comparisons with other spectral methods.

Combining with this newly-developed instrument we will measure the

oxygen saturation of hemoglobin in human breast tumors on patients from

different races.

Acknowledgments

This research is supported by the National Institutes of Health (Grant

CA95885), and by the National Science Foundation (Award BES-

93840).

References

[1] B. W. Pogue, S. Jiang, H. Dehghani, C. Kogel, S. Soho, S.

Srinivasan, X. Song, T. D. Tosteson, S. P. Poplack, and

K. D. Paulsen, “Characterization of hemoglobin, water, and NIR

scattering in breast tissue: analysis of intersubject variability and

menstrual cycle changes,” J. Biomed. Opt. 9, 541-552 (2004).

[2] Shah N, Cerussi AE, Jakubowski D, Hsiang D, Butler J, Tromberg BJ,

“Spatial variations in optical and physiological properties of healthy

breast tissue,” J. Biomed Opt. 9(3), 534-40, (2004)

[3] Pifferi A, Swartling J, Chikoidze E, Torricelli A, Taroni P, Bassi A,

Andersson-Engels, Cubeddu R., “Spectroscopic time-resolved diffuse

reflectance and transmittance measurements of the female breast at

different interfiber distances,” J. Biomed Opt. 9(6), 1143-51, (2004)

[4] Rinneberg H, Grosenick D, Moesta KT, Mucke J, Gebauer B,

Stroszczynski C, Wabnitz H, Moeller M, Wassermann B, Schlag PM,

“Scanning time-domain optical mammography: detection and

characterization of breast tumors in vivo,” Technol Cancer Res. Treat,

4(5), 483-96, (2005).

[5] E. L. Heffer and S. Fantini, “Quantitative oximetry of breast tumors: a

near-infrared method that identifies two optimal wavelengths for each

tumor,” Appl. Opt. 41, 3827-3839, (2002).

Design and Performance of a NearDesign and Performance of a Near--Infrared, Spectral Imaging SystemInfrared, Spectral Imaging System

For Optical MammographyFor Optical Mammography

0 2 4 6 8 10 12 14 16 18 200

50

100

150

200

250

x /cm

y/ summed C

CD intensity along column

S umm ed O ne S c ann ing line o f U n iform P han tom

X : 82

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uniform phantom iamge with

optical properties

similar to human breast

(Pixel size: 2.0mm×2.0mm;

Contrast-to-Noise Ratio: 8.4)

the averaged intensity for one scanning line

The two valleys here correspond

to inhomogeneity in the phantom which

is represented by dark parts in the left image

Key Experiment Parameters0 . 0 1 5 0 . 0 2 0 . 0 2 5 0 . 0 3 0 . 0 3 5 0 . 0 4 0 . 0 4 5

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The Square of SNR

S N R h a s a l i n e a r i t y r e l a t i o n s h i p w i t h C C D e x p o s u r e t i m e

2 4 6 8 10 12 14 16 18 20

2

4

6

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14

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x/cm

y/cm

Uniform Phantom Scanning3(Apr 27,2007)

0

50

100

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( )

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