OCT Phantoms Initiative

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https://doi.org/10.4224/21270495

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OCT Phantoms Initiative

Agrawal, Anant; Kennedy, Brendan; Lamouche, Guy; Tomlins, Pete; Mote, Bobby; Agrawal, Krishan

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OCT Phantoms Initiative

Anant Agrawal

1

_{, Brendan Kennedy}

2

_{, Guy Lamouche}

3

_,

Pete Tomlins

4

_{, Bobby Mote}

5

_{, Krishan Agrawal}

5

1. US Food and Drug Administration 2. The University of Western Australia 3. National Research Council Canada 4. Queen Mary University of London 5. Virginia State University

(3)

Outline

• Definition of the initiative

• Results of OCT phantoms survey

• Some available phantoms and test

targets to address OCT performance

characterization needs

– Review of phantoms developed

– Commercially-available test targets

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Definition of the Initiative

• What is the initiative?

– An effort to bring standardized tools for OCT system characterization and validation to the community

• Who are the current participants?

– Academic and government researchers – Experienced in OCT phantom development

– Previously or currently funded phantom development programs – Possess a variety of robust phantoms we can share with the OCT

community

• Our current goals

– Identify and prioritize most critical OCT performance characterization areas

• OCT Phantoms survey

– Identify and promote appropriate phantoms or test targets to address those areas

• Existing or to-be-developed phantoms

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OCT Phantoms Survey

• Posted online via OCTnews.org, Jan 2012

• 15 questions

– Respondent demographics

– Most important OCT system performance

characteristics

– Phantoms/test targets in use

– Issues with phantoms

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26% 11%

8%

55%

Laboratory research (non-clinical) Product development/Engineering Clinician/Clinical research Manager/Sales/Marketing

Demographics

Intravascular 12% Skin 20% Endoscopic 9% Non-medical 3% Other 20% Ophthalmic 36% Government 6% Device manufacturer 28% Research institution 50% Healthcare/Clinical 16% Type of institution Profession Application area

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Demographics

0% 10% 20% 30% 40% 50% 1 2 3 4 5

5-10

34%

>10

22%

< 5

44%

(8)

What’s the most important overall

performance factor of an OCT image?

1.5

1.7

1.9

1.4

1.9

1.8

1.6

2.1

2.6

2.5

Image quality, visibility of key structures Accuracy/precision of spatial dimensions/measurements Accuracy/precision of intensity-derived parameters (e.g., attenuation)

1=most important 3=least important

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What’s the most important overall

performance factor of an OCT image?

1.5

1.6

1.9

2.1

1.7

2.6

2.5

2.7

Image quality, visibility of key structures Accuracy/precision of spatial dimensions/measurements Accuracy/precision of intensity-derived parameters (e.g., attenuation)

1=most important 3=least important

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OCT System Parameters

• Axial resolution • Lateral resolution

• Thickness measurement accuracy • Lateral distance/area accuracy • Geometric image distortion

• Sensitivity – minimum value of true reflectance which can be detected • Linearity – relationship of signal intensity to true reflectance

• Dynamic range – ratio of maximum measurable reflectance (without

saturation) to minimum detectable reflectance

• Signal rolloff – reduction in intensity from a fixed reflectance sample with increasing sample depth

• Uniformity – variation in intensity laterally and/or axially across image • Contrast detectability – minimum difference in reflectance detectable

from adjacent sample regions

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0% 20% 40% 60% 80% 100% Axial Resolution Lateral resolution Thickness measurement accuracy Lateral distance/area accuracy Geometric image distortion

Sensitivity Linearity Dynamic range

Signal rolloff Uniformity Contrast detectability

Total (n=91) Ophthalmic (n=33) Intravascular (n=11) Skin (n=18) Endoscopic (n=8)

Relative Importance of Parameters

Axial res. Lateral res.* Sensitivity* Contrast det. Axial res. Lateral res. Thickness meas.* Sensitivity* Contrast det.* Axial res.

Geom. img distort.* Uniformity* Sensitivity* Axial res. Sensitivity Lateral res. Thickness meas. Axial res.* Lateral res.* Sensitivity* Dynamic range *Equal percentage

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Phantom Usage/Preferences

74% 26%

24% 76%

54% 46%

Using phantoms/calibration targets? Using commercially-available phantoms/calibration targets? Using self-made phantoms or calibration targets?

Yes No

1. Accuracy/precision of dimensions and properties 2. Similarity to biological tissue

3. Durability

4. Controllable mechanical properties 5. Biocompatibility

Application- independent Application- specific

Relative importance of phantom properties 59 % 69 % 43 % 41 % 31 % 57 %

All Lab PD/E

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Self-made phantoms and

calibration targets

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Additional comments from survey

• Measurement procedures and OCT signal

processing are important

• Wavelength range for which phantoms are

designed should be specified

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Some available phantoms and test

targets to address OCT

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Ophthalmic Phantoms

Rowe Technical Design phantom with custom eye model (commercially available) clinical OCT image of human retina

Commercially- available eye model (Ocular Instruments) Nanoparticle- embedded phantom for point spread function measurement Baxi et al, 8567-28 Sunday 8:15am, Room 305

Agrawal et al, Biomed Opt. Express (2012) de Kinkelder et al, J. Biophotonics (2012)

Parameters these phantoms can test:

Thickness measurement accuracy Axial resolution

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Intravascular Phantoms

Kawase Ultrasound Med Biol (2007 )

Non Uniform Rotational Distorsion phantom

Silicone phantoms

Layered restenosis

Polyvinyl alcohol cryogel phantoms

Bisaillon Proc. SPIE 7906 (2011) PVA also used by:

Ferencik Radiology (2006)

van Soest Proc. Biomed. Opt. (2006)

Flow phantoms

Munce Journal of Biomedical Optics (2010)

Geometric image distortion Uniformity

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Skin Phantoms

100 mm 100 mm

17

• Skin-like structures formed in silicone by sequential molding

• Positive replica of human skin

• Fibre embedded at depth ~0.5 mm

• Imaging artefacts caused by surface corrugations visible in image of fibre

• Real biological structure (the skin’s surface relief) is used to fabricate phantom.

Liew et al, J. Biomed. Opt. (2011)

Skin imaging artifacts phantom

de Bruin et al, J. Biomed. Opt. (2010)

Sensitivity

Thickness measurement accuracy

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Application-Independent Phantoms

3D bar chart phantoms

Gu et al, Biomed. Opt. Express (2012)

Axial/lateral resolution

Structured 3D phantom Curatolo et al, Opt. Express (2011)

Axial/lateral resolution Contrast detectability

Axial contrast transfer function phantoms Agrawal et al, Proc. SPIE (2011)

Axial resolution

Laser micro-inscription artifacts Tomlins et al, Biomed. Opt. Express (2011)

Axial/lateral resolution Sensitivity

Point spread function phantoms Wooliams et al, Meas. Sci. Technol. (2011)

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Commercially-Available Test

Targets

USAF 1951 resolution chart

Lateral resolution

Used by ~50% of respondents using commercially-available targets

Step height gage block (1, 2, 5, 10 mm)

Axial resolution

Schott Glass precision coverslip Type 1.5H

(170±5 mm, n=1.5255±0.0015)

Thickness measurement accuracy

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Conclusions

• Survey provided important insights into interests and

priorities of OCT community

– Broad range of users represented

– Trends among subgroups consistent with their specific priorities

– Many groups have creatively fulfilled their own needs – Interest in standardized phantom(s) is quite high (99%)

• A variety of phantoms and commercially-available

test targets already exist which address some of the

critical parameters

– Axial/lateral resolution, thickness accuracy appear to be covered

– Contrast detectability, sensitivity may need more development

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Next Steps

• Continue to solicit input from the OCT community

– More clearly identify problem areas in OCT (e.g., image artifacts)

– Correlate system performance parameters with clinical performance

– Harmonize with intravascular OCT standardization efforts

• Investigate and promote methods to

validate/standardize prototype phantoms

• Achieve consensus on particular phantom to address

specific system parameter(s)

– Starting point for more widespread and consistent OCT performance characterization

– Measurement and data analysis methods

– Incorporation into international standard (e.g., ISO)

• Develop pathways for dissemination in the

community

– Low-volume manufacturing (GMPs) – Commercialization

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Acknowledgements

• Eric Swanson, OCTnews.org

• Respondents of the OCT Phantoms

survey

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