Breast density quantification using structured-light-based diffuse optical tomography simulations

Medium-adaptive compressive diffuse optical tomography

The low spatial resolution of diffuse optical tomography (DOT) has motivated the development of high-density DOT systems utilizing spatially-encoded illumination and detection strategies. Data compression methods, through the application of Fourier or Hadamard patterns, have been commonly explored for both illumination and detection but were largely limited to pre-determined patterns regardless of imaging targets. Here, we show that target-optimized detection patterns can yield significantly improved DOT reconstructions in both in silico and experimental tests. Applying reciprocity, we can further iteratively optimize both illumination and detection patterns and show that these simultaneously optimized source/detection patterns outperform predetermined patterns in simulation settings. In addition, we show media-adaptive measurement data compression methods enable wide-field DOT systems to recover highly complex inclusions inside optically-thick media with reduced background artifacts. Furthermore, using truncated optimized patterns shows an improvement of 2-4× in increased speed of data acquisition and reconstruction without significantly losing image quality. The proposed method can be readily extended for additional data dimensions such as spectrum and time.

Photothermal Effects of High-Energy Photobiomodulation Therapies: An In Vitro Investigation

The purpose of this study was to investigate photothermal aspects of photobiomodulation therapies (PBMT) in vitro to assist in the development of safe clinical parameters with respect to higher-power devices with large surface applicators. Laser wavelengths in the range of 650 nm-1064 nm were investigated using a thermal camera. Thermographic measures of surface and sub-surface temperature variations of similar lean porcine muscle tissue samples were recorded for a series of calibrated experiments. A thermal comparison was then made between Flat-top and Gaussian beam spatial distribution devices. Outcome data were subjected to statistical analysis using an ANOVA model. Results acquired at similar parameters of irradiance indicated that the application of the 980 nm wavelength was associated with the highest rise in temperature, which decreased with other wavelengths in the order 980 > 1064 ≈ 650 >>> 810 nm (p < 5 × 10^-20). All wavelengths assessed were associated with a significant temperature increase, and with the exception of 810 nm, all exceeded the threshold of a 6 °C rise within the prescribed parameter limits. Optical scanning by movement of the applied source over a relevant area was found to offer effective mitigation of these temperature increases. An extended discussion is presented, analysing the clinical significance of the study outcomes. Recommendations are made within the limits of this in vitro study in order to assist future clinical investigations.

Development of a theranostic preclinical fluorescence molecular tomography/cone beam CT-guided irradiator platform

Image-guided small animal radiation research platforms allow more precise radiation treatment. Commercially available small animal X-ray irradiators are often equipped with a CT/cone-beam CT (CBCT) component for target guidance. Besides having poor soft-tissue contrast, CBCT unfortunately cannot provide molecular information due to its low sensitivity. Hence, there are extensive efforts to incorporate a molecular imaging component besides CBCT on these radiation therapy platforms. As an extension of these efforts, here we present a theranostic fluorescence tomography/CBCT-guided irradiator platform that provides both anatomical and molecular guidance, which can overcome the limitations of stand-alone CBCT. The performance of our hybrid system is validated using both tissue-like phantoms and mice ex vivo. Both studies show that fluorescence tomography can provide much more accurate quantitative results when CBCT-derived structural information is used to constrain the inverse problem. The error in the recovered fluorescence absorbance reduces nearly 10-fold for all cases, from approximately 60% down to 6%. This is very significant since high quantitative accuracy in molecular information is crucial to the correct assessment of the changes in tumor microenvironment related to radiation therapy.

Multiwavelength photo-magnetic imaging algorithm improved for direct chromophore concentration recovery using spectral constraints

Multiwavelength photo-magnetic imaging (PMI) is a novel combination of diffuse optics and magnetic resonance imaging, to the best of our knowledge, that yields tissue chromophore concentration maps with high resolution and quantitative accuracy. Here, we present the first experimental results, to the best of our knowledge, obtained using a spectrally constrained PMI image reconstruction method, where chromophore concentration maps are directly recovered, unlike the conventional two-step approach that requires an intermediate step of reconstructing wavelength-dependent absorption coefficient maps. The imposition of the prior spectral information into the PMI inverse problem improves the reconstructed image quality and allows recovery of highly quantitative concentration maps, which are crucial for effective cancer detection and characterization. The obtained results demonstrate the higher performance of the direct reconstruction method. Indeed, the reconstructed concentration maps are not only of higher quality but also obtained approximately 2 times faster than the conventional method.

Multi-Wavelength Photo-Magnetic Imaging System for Photothermal Therapy Guidance

BACKGROUND AND OBJECTIVES

In photothermal therapy, cancerous tissue is treated by the heat generated from absorbed light energy. For effective photothermal therapy, the parameters affecting the induced temperature should be determined before the treatment by modeling the increase in temperature via numerical simulations. However, accurate simulations can only be achieved when utilizing the accurate optical, thermal, and physiological properties of the treated tissue. Here, we propose a multi-wavelength photo-magnetic imaging (PMI) technique that provides quantitative and spatially resolved tissue optical absorption maps at any wavelength within the near-infrared (NIR) window to assist accurate photothermal therapy planning.

STUDY DESIGN/MATERIALS AND METHODS

The study was conducted using our recently developed multi-wavelength PMI system, which operates at four laser wavelengths (760, 808, 860, and 980 nm). An agar tissue-simulating phantom containing water, lipid, and ink was illuminated using these wavelengths, and the slight internal laser-induced temperature rise was measured using magnetic resonance thermometry (MRT). The phantom optical absorption was recovered at the used wavelengths using our dedicated PMI image reconstruction algorithm. These absorption maps were then used to resolve the concentration of the tissue chromophores, and thus deduce its optical absorption spectrum in the NIR region based on the Beer-Lambert law.

RESULTS

The optical absorption of the phantom was successfully recovered at the used four wavelengths with an average error of ~1.9%. The recovered absorption coefficient was then used to simulate temperature variations inside the phantom. A comparison between the modeled temperature maps and the MRT measured ones showed that these maps are in a good agreement with an average pseudo R2 statistic of 0.992. These absorption values were used to successfully recover the concentration of the used chromophores. Finally, these concentrations are used to accurately calculate the total absorption spectrum of the phantom in the NIR spectral window with an average error as low as ~2.3%.

CONCLUSIONS

Multi-wavelength PMI demonstrated a great ability to assess the distribution of tissue chromophores, thus providing its total absorption at any wavelength within the NIR spectral range. Therefore, applications of photothermal therapy applied at NIR wavelengths can benefit from the absorption spectrum recovered by PMI to determine important parameters such as laser power as well as the laser exposure time needed to attain a specific increase in temperature prior to treatment. Lasers Surg. Med. 00:00-00, 2020. © 2020 Wiley Periodicals LLC.

Resolving tissue chromophore concentration at MRI resolution using multi-wavelength photo-magnetic imaging

Photo-magnetic imaging (PMI) is an emerging optical imaging modality that showed great performance on providing absorption maps with high resolution and quantitative accuracy. As a multi-modality technology, PMI warms up the imaged object using a near infrared laser while temperature variation is measured using magnetic resonance imaging. By probing tissue at multiple wavelengths, concentration of the main tissue chromophores such as oxy- and deoxy-hemoglobin, lipid, and water are obtained then used to derive functional parameters such as total hemoglobin concentration and relative oxygen saturation. In this paper, we present a multi-wavelength PMI system that was custom-built to host five different laser wavelengths. After recovering the high-resolution absorption maps, a least-squared minimization process was used to resolve the different chromophore concentration. The performance of the system was experimentally tested on a phantom with two different dyes. Their concentrations were successfully assessed with high spatial resolution and average accuracy of nearly 80%.

Automatic cancer tissue detection using multispectral photoacoustic imaging

PURPOSE

In the case of multispecimen study to locate cancer regions, such as in thyroidectomy and prostatectomy, a significant labor-intensive processing is required at a high cost. Pathology diagnosis is usually done by a pathologist observing tissue-stained glass slide under a microscope.

METHOD

Multispectral photoacoustic (MPA) specimen imaging has proven successful in differentiating photoacoustic (PA) signal characteristics between a histopathology-defined cancer region and normal tissue. This is mainly due to its ability to efficiently map oxyhemoglobin and deoxyhemoglobin contents from MPA images and key features for cancer detection. A fully automated deep learning algorithm is purposed, which learns to detect the presence of malignant tissue in freshly excised ex vivo human thyroid and prostate tissue specimens using the three-dimensional MPA dataset. The proposed automated deep learning model consisted of the convolutional neural network architecture, which extracts spatially colocated features, and a softmax function, which detects thyroid and prostate cancer tissue at once. This is one of the first deep learning models, to the best of our knowledge, to detect the presence of cancer in excised thyroid and prostate tissue of humans at once based on PA imaging.

RESULT

The area under the curve (AUC) was used as a metric to evaluate the predictive performance of the classifier. The proposed model detected the cancer tissue with the AUC of 0.96, which is very promising.

CONCLUSION

This model is an improvement over the previous work using machine learning and deep learning algorithms. This model may have immediate application in cancer screening of the numerous sliced specimens that result from thyroidectomy and prostatectomy. Since the instrument that was used to capture the ex vivo PA images is now being developed for in vivo use, this model may also prove to be a starting point for in vivo PA image analysis for cancer diagnosis.

Diffuse optical tomography of the breast: a potential modifiable biomarker of breast cancer risk with neoadjuvant chemotherapy

The purpose of this study is to evaluate whether a diffuse optical tomography breast imaging system (DOTBIS) can provide a comparable optical-based image index of mammographic breast density, an established biomarker of breast cancer risk. Oxyhemoglobin concentration (ctO₂Hb) measured by DOTBIS was collected from 40 patients with stage II-III breast cancer. The tumor-free contralateral breast was used for this evaluation. We observed a moderate positive correlation between the patient's mammogram density classification and ctO₂Hb, r_s = 0.486 (p = 0.001). In addition, significant reduction in ctO₂Hb levels were noted during neoadjuvant chemotherapy treatment (p = 0.017). This observation indicates that ctO₂Hb levels measured by DOTBIS could be a novel modifiable imaging biomarker of breast cancer risk and warrants further investigation.

Profile measurement adopting binocular active vision with normalization object of vector orthogonality

Active-vision-based measurement plays an important role in the profile inspection study. The binocular vision, a passive vision, is employed in the active vision system to contribute the benefits of them. The laser plane is calibrated by two 2D targets without texture initially. Then, an L target with feature points is designed to construct the orthogonality object of two vectors. In order to accurately model the binocular-active-vision system, the feature points on the L target are built by two cameras and parameterized by the laser plane. Different from the optimization methods on the basis of the distance object, the laser plane is further refined by the distance-angle object. Thus, an optimization function is created considering both the norms and angles of the vectors. However, the scale of the distance is diverse from the scale of the angle. Therefore, the optimization function is enhanced by the normalization process to balance the different scales. The comparison experiments show that the binocular active vision with the normalization object of vector orthogonality achieves the decreasing distance errors of 25%, 22%, 13% and 4%, as well as the decreasing angle errors of 23%, 20%, 14% and 4%, which indicates an accurate measurement to reconstruct the object profile.