Method for Improving the Lateral Resolution of Near-Infrared (NIR) Single Optods: Application to Subcutaneous Vein Detection and Localization

doi:10.4236/opj.2012.24044

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Optics and Photonics Journal, 2012, 2, 352-357

http://dx.doi.org/10.4236/opj.2012.24044 Published Online December 2012 (http://www.SciRP.org/journal/opj)

Method for Improving the Lateral Resolution of

Near-Infrared (NIR) Single Optods: Application to

Subcutaneous Vein Detection and Localization

Yasser S. Fawzy1,2

1Inovia Technologies Ltd., Vancouver, Canada

2National Laser Institute, Cairo University, Cairo, Egypt

Email: [email protected]

Received September 11, 2012; revised October 13, 2012; accepted October 24, 2012

ABSTRACT

NIR backscattering measurements using single source-detector optical probe (optods) can detect absorption areas within

deep tissue layer. However, such optods, are characterized by large separation distance between the source and detec-

tors (>2 cm) and poor lateral resolution (>1 cm), which limits its usage for the localization of small absorption volumes

embedded deep within the tissue such as subcutaneous veins. In this work a method to improve the accuracy of locating

such absorption volumes (areas) using backscattered NIR measurements is suggested and investigated with the aim of

developing an optical sensor for detecting and localizing large subcutaneous veins. The method is based on measuring

the differential signal from three overlapping source-detector pairs arranged within the prob e such that the total photon

sensitivity profile of the probe is maximized along a narrow width area (within the central of the probe) an d minimized

along its sides. The location of th e absorption areas is th en determined when a peak maximum of the measured signal is

detected. Monte Carlo simulation and light transport modeling was used to determine the optimum arrangement of each

source-detector pair within the probe to create the required spatial sensitivity p rofile and demonstrate the validity of the

method. The results showed that the differential optode has more than two times improvement in the lateral resolution

compared to the standard optode. The result also showed that the differential probe can locate subcutaneous veins with

diameter ~5 mm and embedded at ~1.5 cm depth. The method could have a potential for designing and developing an

optical backscattering sensors for detecting and localizing large subcutaneous veins embedded <2 cm depths.

Keywords: Reflectance Measurements; Photon Migration; Optical Diagnosis; Fiber Probe Design

1. Introduction

NIR diffuse reflectance measurements and spectroscopy

is simple and portable optical diagnostic technique that

can be used to detect and to monitor the alteration in tis-

sue physiology and/or pathology, by measuring the

change in absorption coefficient related to such alteratio n.

Several different types of NIR instruments in the CW

domain [1], frequency-domain [2], and time-domain [3]

have been developed over the past 20 years to measure

changes in tissue oxygenation, perfusion, and brain ac-

tivity [4-7]. Depending on the source-detector sep aration,

among other parameters, NIR reflectance measurements

can detect absorption changes from areas or volumes that

are 2 - 3 centimeters deep within the tissues [8,9]. How-

ever the lateral spatial resolution for such single source-

detector arrangement is typically larger than 1 cm for

absorption areas lo cated within such depths [10,11]. This

would limit the application of such probes in the ap-

plications that require detecting as well as localizing the

lateral position of the measured absorption areas within

deep tissue layers.

The aim of this work is to develop a method of reflec-

tance probe design and measurement that could improve

the lateral spatial resolution to the detected NIR diffuse

reflectance signal obtained from large depths within the

tissue. For that respect we have investigated th e possibil-

ity of using multiple source-detector pairs arranged in

certain design such that the spatial sensitivity profile of

the measured signal is maximized along certain localized

area (volume) within the tissue. We have also presented a

method of measurement for using such probe, referred

here as differential probe, to localize the position within

which the absorption changes have occurred. Monte

Carlo simulation was used to determine the optimum

distances to produce the required spatial sensitivity pro-

file and to verify the improvement in the spatial resolu-

tion using simul at e d dat a.

Y. S. FAWZY 353

2. Method

2.1. Probe Design Method

Our design method is based on measuring the differential

signal obtained using multiple overlapping source-de-

tector pairs interrogate common area (or volume) within

the tissue. The multiple source-detector pairs were ar-

ranged such that the probe photon sensitivity profile is

maximized within a narrow area (volume) along the cen-

ter of the probe. In particular, we have used in this design,

three source-detector pairs arranged such that one pair in

the probe center and the other two arranged at symmetri-

cal distance from the probe center as shown in Figure

1(b). The two detectors at the side of probe are assumed

to have a similar distance (d) from the center of the probe.

The differential probe signal Idiff is equal to





13 2

II where I1, I

2, I

3 are the intensity meas-

ured by the first, second (central) and third source-de-

-tector pairs respectively. Monte Carlo simulation, de-

scribed below, was used to calculate the spatial sensitiv-

ity profile [12,13] of this differential detection sequence.

The photon sensitivity profile was calculated for different

distances (d) to find the optimum distance (d) that produce

the smallest (width) area with maximum photon density

along the center of the probe. The width of this high pho-

ton density area obtained from such arrangement should

determine the lateral resolution of the designed probe.

2.2. Measured Method

The method of measurement is based on scanning the

tissue with the probe, and measur es the change in attenu-

ated light over the scanned area. The position of the ab-

sorber is localized when it falls within the central of the

probe which has the maximum photon density (maximum

probe sensitivity). In terms of reflectance measurements,

this will corresponds to a peak maximum during the

measurement scan. We have verified the measurement

method using a Monte Carlo simulation by modeling the

total diffuse reflectance measured by the differential

probe from a scattering media contains two subcutaneous

veins (diameter ~5 mm each) separated by ~5 mm dis-

tance as shown in Figure 2. The absorption coefficient of

the subcutaneous veins was chosen to simulate realistic

conditions of the subcutaneous veins embed de d wi thi n f at

3 2 1 3 2 1

Figure 1. (a) Standard probe; (b) Differential probe. Detec-

tor (framed circle), source (solid black).

Probe Scan Measurement

Turbid Media

Absorption rods

Figure 2. Schematic diagram of the measurement method.

and muscle layers (~8 folds increase). To model the

scanning measurements of the probe we have acquired

different measurements at interval distances in the radial

direction





0,4 cm,0.5 mm.rr dr  The radial dis-

tance is referenced to the position of the maximum sensi-

tivity point in each probe (probe center).

2.3. Monte Carlo Simulation

Monte Carlo simulations were performed using custom-

ized software based on the algorithm s and technique s used

by Phral et al. [14]. In particular, the Monte Carlo simu-

lation has been customized to estimate the spatial sensi-

tivity profile (photon density distribution) and the total

diffuse reflectance measured from the differential probe.

The meas ured diffuse reflectance signal wa s calculated by

recording the photons that hit the detectors when it escape

the sample and propagate to any of the three detectors

plane with an angle, to the surface normal, less than the

NA cone of the fiber detector. A detector fiber with 400

µm diameter and NA ~ 0.4 was used for the simulated

reflectance probes. The spatial sensitiv ity profile calcula-

tions required to keep track of the escaped photons in

three dimensions. To simulate differential probe detection,

the photon is reco rded to hit the probe when the weighted

intensity of the photon detected by the second (central)

detector is larger than the half su m of the weighted in ten-

sities detected by the two other detectors in the side. This

would be corresponding to detecting the signal only when

(Idiff > 0).

3. Results

Figure 3 shows the spatial sensitivity (photon density)

profile of the single standard probe and the triple differ-

ential probe. As shown in the figure the photon density of

the differential probe has an overall increase within the

central of the probe while it was reduced along the side

of the probe. Also, the width of the area with increased

photon density was significantly reduced compared to

Y. S. FAWZY

354

-3

-2

-1

02015 -10 -505101520

-Max

-Min

(a)

-3

-2

-1

02015-10-50510 15 20

-Max

-Min

(b)

Figure 3. Photon Sensitivity Profile for (a) Single source-detector probe and (b) Differential triple source-detector probe

(units in 0.5*cm).

Figure 5 shows the radial sensitivity profile (at depth

~10 mm) of the differential probe in comparison to the

single probe. The radial sen sitivity profile was calculated

by recording all the radial position of the photons de-

tected by the probe detectors from depths between 10 -

12 mm. As shown in Figure 5, the width of the radial

sensitivity profile was reduced more than two times

compared to the standard probe. This would result in

improving the localization accuracy of an absorption

structure by two times.

that of the single source-detector probe.

The distance between the source-detectors pairs de-

termine the resultant sensitivity pr ofile of the probe. Dis-

tance (d) between the center of the detector on the side

(detector 1 or 3) and the probe center was varied and the

width of the resultant sensitivity profile (wi), defined

here as the area with photon sensitivity >75% of the

maximum, was calculated. Figure 4 shows the width of

the sensitivity profile calculated for a range of distances

(d) between –8 mm to 8 mm. As shown in the figure, the

width of the sensitivity p rofile (wi) is minimized to 4mm

along distances (d) between (0 - 3 mm). The figure also

shows that the optimum distance range for minimizing

the sensitivity profile width depends on the background

optical properties of the tissu e being investigated.

The depth sensitivity profile was also calculated for

each probe by recording all the photons that hit the probe

detectors with intensity larger than 1/e of the maximum

detected photon intensity. Figure 6, shows that both the

ifferential probe and the standard probe interrogate d

Y. S. FAWZY 355

Figure 4. Design optimization for improving the lateral resolution for turbid media with different optical scattering proper-

ties (µa = 0.01 mm–1).

Sensitivity

Figure 5. Radial sensitivity profile at 10 mm depth for the total diffuse reflectance collected by the standard probe and the

differential probe.

similar depths (up to 2 cm) when measuring the diffuse

reflectance signal from the same tissue optical properties.

The result of the virtual scanning measurements is

shown in Figure 7. For such measurement the back-

ground optical properties was (µs’ = 1.5 mm–1, µa = 0.01

mm–1) and the two absorption rods was assumed to have

a diameter of 5 mm and µa = 0. 08 mm–1. As shown in

figure the measured signal detected using the differential

probe measurement has two remarkable peak minimum

corresponding to the position of the absorption rods. The

figure also shows the diffuse reflectance measured during

the virtual scanning (along different distances) using the

standard probe measurement. The differential signal

plotted in the figure is equal to (Idiff + 0.4). As shown in

the figure the position of the two absorption rods are not

differentiated using the standard probe measurements.

4. Discussion

Improving the lateral resolution of NIR reflectance

measurement could be of great benefit for a number of

applications that require a method fo r detecting as well as

localizing the position of absorption volume within deep

tissue layers. A potential application is the detection and

localization of subcutaneous veins (for example internal

jugular vein) for accurate puncturing positioning [15,16].

Also such probes could be sed to monitor tissue oxy- u

Y. S. FAWZY

356

Sensitivity

Figure 6. Depth sensitivity profile for the total diffuse reflectance measured by the standard probe and the diffe re ntial probe .

Figure 7. Results of the virtual scanning measurements, using Monte Carlo simulation, showing the total diffuse reflectance

measured using the differential and the standard reflectance probes. The two rectangles on the bottom of the graph indicate

the actual position of the two absorption rods.

genation from deep veins by localizing the area or the

volume from where the signal is measured [17].

Our results showed that the differential probe can de-

tect and localize the attenuation changes from area

(volume) with diameter ~5 mm at depths ~1.5 cm. Com-

pared to the standard probe with the same source-detec-

tor distance, the designed probe has at least two folds

improvement in the lateral reso lution and consequently in

the localization accuracy of the small absorption volume

embedded deep within the tissue. This improvement in

the spatial resolution is the resultant of the differential

measurements of the signals detected by multiple sour ce-

detector pairs interrogating common area or volume.

The design analysis for the optimum source-detector

arrangement and spacing within the differential probe

showed that the optical properties of the investigated

tissue should be taken into consideration when calculat-

ing the optimum source-detector distances that would

improve the spatial sensitivity of the probe. Thus, a pri-

ori information about the range of the tissue optical

properties being investigated would be needed to make

use of this method in practice. It should be noted also

that finer lateral resolution could be achieved using the

above approach but with more complex fiber arrange-

Y. S. FAWZY 357

ments and with a priori knowledge about the optical

properties range of the tissue being investigated. Never-

theless, the objective of this work is mainly to illustrate

the validity of the proposed method and the concept for

designing diffuse reflectance probes that have improved

lateral resolution (<5 mm) and yet interrogate d eep tissue

layers within ~1.5 cm depth.

In addition, the proposed method is not li mited to CW

measurements and could be used with other types of NIR

instruments including time-resolved and frequency mo-

dulated reflectance measurements. However, other de-

sign parameters such as detectors SNR, dynamic range,

source-detector pairs switching, and tissue background

optical properties, need to be investigated before devel-

oping an experimental differential probe that could lo-

calize deep small absorption changes from different

modes of reflectance measurements.

5. Conclusion

We have proposed and investigated a new method for

improving the lateral resolution of the optical back-scat-

tering (reflectance) measurements. The method could

have potential for improving the accuracy of the locating

absorption structure (such as vein) embedded deep within

the biological tissue. Future work will involve develop-

ing an optical probe based the suggested method and

verifying the validity of this approach using experimental

measurements on tissue simulating phantoms.

REFERENCES

[1] T. Vaithianathan, I. D. Tullis, N. Everdell, T Leung, A.

Gibson, J. Meek and D. T. Delpy, “Design of a Portable

Near-Infrared System for Topographic Imaging of the

Brain in Babies,” Review of Scientific Instruments, Vol.

75, No. 10, 2004, p. 3276. doi:10.1063/1.1775314

[2] M. A. O’Leary, D. A. Boas and B. Chance, “Experimen-

tal Images of Heterogeneous Turbid Media by Fre-

quency-Domain Diffusing-Photon Tomography,” Optics

Letters, Vol. 20, No. 5, 1995, pp. 426-428.

doi:10.1364/OL.20.000426

[3] H. Eda, I. Oda, Y. Ito, Y. Wada, Y. Oikawa, Y. Tsuna-

zawa, M. Takada, Y. Tsuchiya, Y. Yamashita, M. Oda, A.

Sassaroli, Y. Yamada and M. Tamura, “Multichannel Time-

Resolved Optical Tomographic Imaging System,” Review

of Scientific Instruments, Vol. 70, No. 9, 1999, p. 3595.

doi:10.1063/1.1149965

[4] J. M. Murkin and M. Arango, “Near-Infrared Spectros-

copy as an Index of Brain and Tissue Oxygenation,” Brit-

ish Journal of Anaesthesia, Vol. 103, Suppl. 1, 2009, pp.

3-13. doi:10.1093/bja/aep299

[5] N. Subhash, J. R. Mallia, S. S. Thomas, A. Mathews, P.

Sebastian and J. Madhavan, “Oral Cancer Detection Us-

ing Diffuse Reflectance Spectral Ratio R540/R575 of

Oxygenated Hemoglobin Bands,” Journal of Biomedical

Optics, Vol. 11, No. 1, 2006, Article ID: 014018.

doi:10.1117/1.2165184

[6] M. L. Flexman, M. A. Khalil, R. Al Abdi, H. K. Kim, C. J.

Fong, E. Desperito, D. L. Hershman, R. L. Barbour and A.

H. Hielscher, “Digital Optical Tomography System for

Dynamic Brea st Imaging,” Journal of Biomedical Optics,

Vol. 16, No. 7, 2011, Article ID: 076014.

doi:10.1117/1.3599955

[7] M. Ferrari, V. Cettolo and V. Quaresima, “Light Source-

Detector Spacing of Near-Infrared-Based Tissue Oxime-

ters and the Influence of Skin Blood Flow,” Journal of

Applied Physiology, Vol. 100, No. 4, 2006, pp. 1426-

1427. doi:10.1152/japplphysiol.01207.2005

[8] M. S. Patterson, S. Anderson, B. C. Wilson and E. K.

Osei, “Absorption Spectroscopy in Tissue-Simulating Ma-

terials: A Theoretical and Experimental Study of Photon

Paths,” Applied Optics, Vol. 34, No. 1, 1995, pp. 22-30.

doi:10.1364/AO.34.000022

[9] E. Okada, M. Firbank and D. T. Delpy, “The Effect of

Overlying Tissue on the Spatial Sensitivity Profile of Near-

Infrared Spectroscopy,” Physics in Medicine and Biology,

Vol. 40, No. 12, 1995, pp. 2093-2108.

doi:10.1088/0031-9155/40/12/007

[10] D. A. Boas, K. Chen, D. Grebert and M. A. Franceschini,

“Improving the Diffuse Optical Imaging Spatial Resolu-

tion of the Cerebral Hemodynamic Response to Brain

Activation in Humans,” Optics Letters, Vol. 29, No. 13,

2004, pp. 1506-1508.

[11] H. Kawaguchi and E. Okada, “Evaluation of Image Re-

construction Algorithm for Near-Infrared Topography by

Virtual Head Phantom,” Progress in Bimedical Optics

and Imaging, Vol. 10, 2007, pp. 1-662906.

[12] J. C. Schotland, J. C. Haselgrove and J. S. Leigh, “Photon

Hitting Density,” Applied Optics, 32, 1993, pp. 448-453.

doi:10.1364/AO.32.000448

[13] Y. Fawzy, A. Youssef, M. El-Batanony and Y. Kadah,

“Determination of the Optical Properties of A Two-Layer

Tissue Model by Detecting Photons Migrating at Pro-

gressively Increasing Depths,” Applied Optics, Vol. 42,

No. 31, 2003, pp. 6398-6411.

doi:10.1364/AO.42.006398

[14] M. Keijzer, S. L. Jacques, S. A. Prahl and A. J. Welch,

“Light Distributions in Artery Tissue: Monte Carlo Simu-

lations for Finite-Diameter Lasers Beams,” Lasers in

Medicine and Surgery, Vol. 9, No. 2, 1989, pp. 148-154.

doi:10.1002/lsm.1900090210

[15] B. Lin, C. Kong, D. Tarng, T. Huang and G. Tang, “Ana-

tomical Variation of the Internal Jugular Vein and Its Im-

pact on Temporary Haemodialysis Vascular Access: An

Ultra-Sonographic Survey in Uraemic Patients,” Ne-

phrology Dialysis Transplantation, Vol. 13, No. 1, 1998,

pp. 134-138. doi:10.1093/ndt/13.1.134

[16] V. Zharov, S. Ferguson, J. Eidt, P. Howard, L. Fink and

M. Waner, “Infrared Imaging of Subcutaneous Veins,”

Laser in Surgery and Medicine, Vol. 34, No. 1, 2006, pp.

56-61. doi:10.1002/lsm.10248

[17] H. P. Brecht, D. S. Prough, Y. Y. Petrov, I. Patrikeev, I.

Y. Petrova, D. J. Deyo, I. Cicenaite and R. O. Esenaliev,

“In Vivo Monitoring of Blood Oxygenation in Large

Veins with a Triple-Wavelength Optoacoustic System,”

Optics Express, Vol. 15, No. 24, 2007, pp. 16261-16269.

doi:10.1364/OE.15.016261