Xiaoqi Li

Design and evaluation of a hybrid photoacoustic tomography and diffuse optical tomography system for breast cancer detection

PURPOSE The authors present the design and evaluation of a second-generation (G2) hybrid photoacoustic tomography (PAT) and diffuse optical tomography (DOT) imaging system for detection of breast cancer. The combined PAT/DOT system takes full advantages of two different modalities to provide complementary information and most accurate recovery of tissue optical properties. METHODS This system was designed to produce cross-section images of breast tissue with a ring-shaped home-made array of 64 wideband acoustic transducers combined with an array of 16/16 source/detector optical fiber bundles. A scanning light delivery system was built to illuminate a large area of breast tissue for optimized tissue penetration. Finite element reconstruction methods for quantitative PAT and DOT were utilized to recover absorption and scattering coefficients of tissue-mimicking phantoms and ex vivo tumor tissue. RESULTS Performances of the acoustic transducer array and the PAT/DOT system were investigated in detail. Frequency response of the transducers is from 380 kHz to 1.48 MHz and maximum frequency response is up to 2 MHz. Directivity of a single element in the array is ±30°. The PAT/DOT system offers a spatial resolution of ∼0.5 mm for PAT and of ∼4.0 mm for DOT. Quantitatively accurate absorption and scattering coefficients were obtained from both the phantom and ex vivo experiments. CONCLUSIONS The PAT/DOT system provided better PAT images when the targets were smaller in size and located near the center of the background phantom, while better DOT images were obtained when the targets were larger in size and located away from the center of the background. The successful results obtained from both the phantom and ex vivo experiments will allow us to test the hybrid system in humans with breast cancer in the near future.

Integrated diffuse optical tomography and photoacoustic tomography: phantom validations

We designed, fabricated and tested a novel imaging system that fuses diffuse optical tomography (DOT) and photoacoustic tomography (PAT) in a single platform. This platform takes advantages of both DOT and PAT, and can potentially provide dual-modality two dimensional functional and cellular images of the breast quantitatively. Here we describe this integrated platform along with initial tissue phantom validations.

Variable-thickness multilayered polyvinylidene fluoride transducer with improved sensitivity and bandwidth for photoacoustic imaging

The performance of photoacoustic imaging (PAI) is critically dependent on the sensitivity and bandwidth of the transducer. Here, we report the design and fabrication of a polyvinylidene fluoride ultrasonic transducer with variable-thickness layers that demonstrates significantly improved sensitivity and bandwidth. We show that the multilayered transducer provides more than 2-fold increase in sensitivity and more than 65% improvement in bandwidth compared with the conventional single-layer transducer. Photoacoustic imaging of mouse brain with the intact skull and scalp is conducted to demonstrate the power of the multilayered transducer for resolving brain structure in an in vivo setting.

High resolution functional photoacoustic tomography of breast cancer.

PURPOSE To evaluate the feasibility of functional photoacoustic tomography (fPAT) for high resolution detection and characterization of breast cancer and to demonstrate for the first time quantitative hemoglobin concentration and oxygen saturation images of breasts that were formed with model-based reconstruction of tomographic photoacoustic data. METHODS The study was HIPAA compliant and was approved by the university institutional review board. Written informed consents were obtained from all the participants. Ten cases, including six cancer and four healthy (mean age = 50 yr; age range = 41-66 yr), were examined. Functional images of breast tissue including absolute total hemoglobin concentration (HbT) and oxygen saturation (StO2%) were obtained by fPAT and cross validated with magnetic resonance imaging (MRI) readings and/or histopathology. RESULTS HbT and StO2% maps from all six pathology-confirmed cancer cases (60%) show clear detection of tumor, while MR images indicate clear detection of tumor for five of six cancer cases; one small tumor was read as near-complete-resolution by MRI. The average HbT and StO2% value of suspicious lesion area for the cancer cases was 61.6 ± 18.9 μM/l and 67.5% ± 5.2% compared to 25.6 ± 7.4 μM/l and 65.2% ± 3.8% for background normal tissue. CONCLUSIONS fPAT has the potential to be a significant add-on in breast cancer detection and characterization as it provides submillimeter resolution functional images of breast lesions.

Impact of inhomogeneous optical scattering coefficient distribution on recovery of optical absorption coefficient maps using tomographic photoacoustic data

We present a study through extensive simulation that considers the impact of inhomogeneous optical scattering coefficient distribution on recovery of optical absorption coefficient maps using tomographic photoacoustic data collected from media mimicking breast tissue. We found that while the impact of scattering heterogeneities/targets is modest on photoacoustic recovery of optical absorption coefficients, the impact of scattering contrast caused by adipose tissue, a layer of normal tissue along the boundary of the breast, is dramatic on reconstruction of optical absorption coefficients using photoacoustic data-up to 25.8% relative error in recovering the absorption coefficient is estimated in such cases. To overcome this problem, we propose a new method to enhance photoacoustic recovery of the optical absorption coefficient in heterogeneous media by considering inhomogeneous scattering coefficient distribution provided by diffuse optical tomography (DOT). Results from extensive simulations show that photoacoustic recovery of absorption coefficient maps can be improved considerably with a priori scattering information from DOT.

Morphologic tomography of nonspherical particles using multispectral diffusing light measurements.

A series of phantom experiments are conducted to demonstrate the ability of a T-matrix-based inverse algorithm for tomographic recovery of morphologic characteristics of nonspherical particles embedded in heterogeneous turbid media. Diffusely scattered light at several wavelengths along the boundary of the phantom are collected and analyzed to allow for simultaneous extraction of the size, concentration, and aspect ratio of the spheroidal particles.

Functional photoacoustic tomography of breast cancer: Pilot clinical results

A pilot clinical study for breast cancer diagnosis and neoadjuvant chemotherapy monitoring using quantitative multispectral photoacoustic tomography with absolute total hemoglobin concentration and oxygen saturation maps compared with MRI and biopsy.

Monitoring neoadjuvant chemotherapy in breast cancer using quantitative photoacoustic tomography

Quantitative photoacoustic tomography effectively monitor tumor response to neoadjuvant chemotherapy in breast cancer is presented. Recovered absolute total hemoglobin concentration and oxygen saturation maps are strongly correlated with MRI and ultrasound images.

Spatially variant total variation minimization improves photoacoustic tomography

A new method that can enhance quantitative recovery of optical absorption coefficient in heterogeneous media from noisy photoacoustic data by incorporating spatially variant information into total variation minimization with finite element method.