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118. Phantom-based image quality test methods for photoacoustic imaging systems.

Author

Vogt, William C., Congxian Jia, Wear, Keith A., Garra, Brian S., and Pfefer, T. Joshua

Subjects
ACOUSTIC imaging, IMAGE quality analysis, COMPUTED tomography, MAMMOGRAMS, MAGNETIC resonance imaging
Abstract

As photoacoustic imaging (PAI) technologies advance and applications arise, there is increasing need for standardized approaches to provide objective, quantitative performance assessment at various stages of the product development and clinical translation process. We have developed a set of performance test methods for PAI systems based on breast-mimicking tissue phantoms containing embedded inclusions. Performance standards for mature imaging modalities [magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound] were used to guide selection of critical PAI image quality characteristics and experimental methods. Specifically, the tests were designed to address axial, lateral, and elevational spatial resolution, signal uniformity, penetration depth, sensitivity, spatial measurement accuracy, and PAI-ultrasound coregistration. As an initial demonstration of the utility of these test methods, we characterized the performance of a modular, bimodal PAI-ultrasound system using four clinical ultrasound transducers with varying design specifications. Results helped to inform optimization of acquisition and data processing procedures while providing quantitative elucidation of transducer-dependent differences in image quality. Comparison of solid, tissue-mimicking polymer phantoms with those based on Intralipid indicated the superiority of the former approach in simulating realworld conditions for PAI. This work provides a critical foundation for the establishment of well-validated test methods that will facilitate the maturation of PAI as a medical imaging technology. [ABSTRACT FROM AUTHOR]

Published
2017
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139. Modeling laser treatment of port wine stains with a computer-reconstructed biopsy

Author

Pfefer, T. J., Barton, J. K., Smithies, D. J., Milner, T. E., Nelson, J. S., van Gemert, M. J., Welch, A. J., and Other departments

Abstract

The efficacy of laser treatment of port wine stains (PWS) has been shown to be highly dependent on patient-specific vasculature. The effect of tissue structure on optical and thermal mechanisms was investigated for different pulse durations by using a novel theoretical model that incorporates tissue morphology reconstructed tomographically from a PWS biopsy. An optical-thermal numerical model capable of simulating arbitrarily complex, three-dimensional tissue geometries was developed. The model is comprised of (1) a voxel-based Monte Carlo optical model, (2) a finite difference thermal model, and (3) an Arrhenius rate process calculation to predict the distribution of thermal damage. Simulations based on previous computer-based reconstruction of a series of 6 microm sections from a PWS biopsy were performed for laser pulse durations (taup) of 0.5, 5.0, and 10.0 ms at a wavelength of 585 nm. Energy deposition rate in the blood vessels was primarily a function of vessel depth in skin, although shading effects were evident. Thermal confinement and selectivity of damage were seen to be inversely proportional to pulse duration. The model predicted blood-specific damage for taup = 0.5 ms, vascular and perivascular damage for taup = 5 ms, and widespread damage in superficial regions for taup = 10 ms. The effect of energy deposition in the epidermis was most pronounced for longer pulse durations, resulting in increased temperature and extent of damage. Pulse durations between 0.5 and 5 ms are likely optimal for the PWS analyzed. The incorporation of a tomographically reconstructed PWS biopsy into an optical-thermal model represents a significant advance in numerical modeling of laser-tissue interaction

Published
1999

140. Diffuse optical spectroscopy of melanoma-simulating silicone phantoms

Author

Grant, Alexander M., Sry, Kelly, Saager, Rolf B., Ayers, Frederick, Pfefer, T. Joshua, Kelly, Kristen M., Tseng, Sheng-Hao, Durkin, Anthony J., Grant, Alexander M., Sry, Kelly, Saager, Rolf B., Ayers, Frederick, Pfefer, T. Joshua, Kelly, Kristen M., Tseng, Sheng-Hao, and Durkin, Anthony J.

Abstract

Currently the only method for positively identifying malignant melanoma involves invasive and often undesirable biopsy procedures. Available ex-vivo data indicates increased vascularization in the lower regions of excised melanoma, as compared to dysplastic nevi. The ability to interrogate this region of tissue in-vivo could lead to useful diagnostic information. Using a newly developed fiber based superficial probe in conjunction with a steady-state frequency-domain photon migration (SSFDPM) system, we can probe the upper 1-2 mm of tissue, extracting functional information in the near infrared (650-1000 nm) range. To test the resolution and detection range of the superficial probe in this context, deformable silicone phantoms have been fabricated that simulate normal skin with melanocytic lesions. These phantoms consist of a two-layered matrix with the optical properties of normal light skin, containing several cylindrical inclusions that simulate highly absorbing pigmented lesions such as melanoma. These inclusions are varied in depth, diameter, and optical properties in order to fully test the probe's detection capabilities. It was found that, depending on absorption, we can typically probe to a depth of 1.0-1.5 mm in an inclusion, likely reaching the site of angiogenesis in an early-stage melanoma. Additionally, we can successfully interrogate normal tissue below lesions 1.5mm deep when absorption is about 0.4/mm or less. This data indicates that the superficial probe shows great promise for non-invasive diagnosis of pigmented lesions.

Published
2009
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