In vivo nerve identification in head and neck surgery using diffuse reflectance spectroscopy

Background

Careful identification of nerves during head and neck surgery is essential to prevent nerve damage. Currently, nerves are identified based on anatomy and appearance, optionally combined with electromyography (EMG). In challenging cases, nerve damage is reported in up to 50%. Recently, optical techniques, like diffuse reflectance spectroscopy (DRS) and fluorescence spectroscopy (FS) show potential to improve nerve identification.

Methods

212 intra‐operative DRS/FS measurements were performed. Small nerve branches (1–3 mm), on near‐nerve adipose tissue, muscle and subcutaneous fat were measured during 11 surgical procedures. Tissue identification was based on quantified concentrations of optical absorbers and scattering parameters.

Results

Clinically comprehensive parameters showed significant differences (<0.05) between the tissues. Classification using k‐Nearest Neighbor resulted in 100% sensitivity and a specificity of 83% (accuracy 91%), for the identification of nerve against surrounding tissues.

Conclusions

DRS/FS is a potentially useful intraoperative tool for identification of nerves from adjacent tissues.

Level of Evidence

Observational proof of principle study.

Correlation of breast tissue histology and optical signatures to improve margin assessment techniques

Optical spectroscopy is sensitive to morphological composition and has potential applications in intraoperative margin assessment. Here, we evaluate ex vivo breast tissue and corresponding quantified hematoxylin & eosin images to correlate optical scattering signatures to tissue composition stratified by patient characteristics. Adipose sites (213) were characterized by their cell area and density. All other benign and malignant sites (181) were quantified using a grid method to determine composition. The relationships between mean reduced scattering coefficient (〈μs′〉), and % adipose, % collagen, % glands, adipocyte cell area, and adipocyte density were investigated. These relationships were further stratified by age, menopausal status, body mass index (BMI), and breast density. We identified a positive correlation between 〈μs′〉 and % collagen and a negative correlation between 〈μs′〉 and age and BMI. Increased collagen corresponded to increased 〈μs′〉 variability. In postmenopausal women, 〈μs′〉 was similar regardless of fibroglandular content. Contributions from collagen and glands to 〈μs′〉 were independent and equivalent in benign sites; glands showed a stronger positive correlation than collagen to 〈μs′〉 in malignant sites. Our data suggest that scattering could differentiate highly scattering malignant from benign tissues in postmenopausal women. The relationship between scattering and tissue composition will support improved scattering models and technologies to enhance intraoperative optical margin assessment.

Optical breast cancer margin assessment: an observational study of the effects of tissue heterogeneity on optical contrast

Introduction

Residual cancer following breast conserving surgery increases the risk of local recurrence and mortality. Margin assessment presents an unmet clinical need. Breast tissue is markedly heterogeneous, which makes distinguishing small foci of cancer within the spectrum of normal tissue potentially challenging. This is further complicated by the heterogeneity as a function of menopausal status. Optical spectroscopy can provide surgeons with intra-operative diagnostic tools. Here, we evaluate ex-vivo breast tissue and determine which sources of optical contrast have the potential to detect malignancy at the margins in women of differing breast composition.

Methods

Diffuse reflectance spectra were measured from 595 normal and 38 malignant sites from the margins of 104 partial mastectomy patients. All statistical tests were performed using Wilcoxon Rank-Sum tests. Normal and malignant sites were compared before stratifying the data by tissue type and depth and computing statistical differences. The frequencies of the normal tissue types were separated by menopausal status and compared to the corresponding optical properties.

Results

The mean reduced scattering coefficient, < μ_s' >, and concentration of total hemoglobin, [THb]), showed statistical differences between malignant (< μ_s' > : 8.96 cm^-1 ± 2.24_MAD, [THb]: 42.70 μM ± 29.31_MAD) compared to normal sites (< μ_s' > : 7.29 cm^-1 ± 2.15_MAD, [THb]: 32.09 μM ± 16.73_MAD) (P < 0.05). The sites stratified according to normal tissue type (fibro-glandular (FG), fibro-adipose (FA), and adipose (A)) or disease type (invasive ductal carcinoma (IDC) and ductal carcinoma in situ (DCIS)) showed that FG exhibited increased < μ_s' > and A showed increased [β-carotene] within normal tissues. Scattering differentiated between most malignant sites, DCIS (9.46 cm^-1 ± 1.06_MAD) and IDC (8.00 cm^-1 ± 1.81_MAD), versus A (6.50 cm^-1 ± 1.95_MAD). [β-carotene] showed marginal differences between DCIS (19.00 μM ± 6.93_MAD, and FG (15.30 μM ± 5.64_MAD). [THb] exhibited statistical differences between positive sites (92.57 μM ± 18.46_MAD) and FG (34.12 μM ± 22.77_MAD), FA (28.63 μM ± 14.19_MAD), and A (30.36 μM ± 14.86_MAD). The diagnostic ability of the optical parameters was affected by distance of tumor from the margin as well as menopausal status. Due to decreased fibrous content and increased adipose content, normal sites in post-menopausal patients exhibited lower < μ_s' >, but higher [β-carotene] than pre-menopausal patients.

Conclusions

The data indicate that the ability of an optical parameter to differentiate benign from malignant breast tissues may be dictated by patient demographics. Scattering differentiated between malignant and adipose sites and would be most effective in post-menopausal women. [β-carotene] or [THb] may be more applicable in pre-menopausal women to differentiate malignant from fibrous sites. Patient demographics are therefore an important component to incorporate into optical characterization of breast specimens.

Rapid Optical Imaging of Breast Tumor Margins: Final Results from a 100-Patient Clinical Study

Background: Increasing attention has been given to the surgical margin status in primary breast conserving therapy (BCT) due to reports which indicate that 20-70% of patients undergoing BCT must undergo multiple surgeries for complete tumor resection. For the past 4 years, our multidisciplinary group has been working to address this clinical need via the development of an optically-based intraoperative breast tumor margin assessment device. This device, based on diffuse reflectance spectroscopy, is sensitive to biochemical and morphological changes associated with cancer and has a sensing depth of 1-2 mm which is compatible with widely used criteria for cancer-free margins. The device is capable of surveying the entire specimen surface intraoperatively in imaging mode. Here we report the results of a non-significant-risk study of the device in over 100 patients at Duke University Medical Center.Materials and Methods: Under an institutionally-approved protocol, we tested our device on consented patients undergoing a partial mastectomy at DukeUniversity Medical Center for invasive or in situ malignancies. Optical spectral images of tumor margins were recorded within 20 minutes of excision and converted into tissue compositional parameter maps that reflect the vascular density, fat content and cell density in the tissue. The pathologic status of the imaged margins was collected from standard post-operative surgical pathology reports. Intraoperative frozen section and touch prep analysis was not performed on these specimens. Margins were considered positive if residual malignancy was found within 2 mm of the tissue surface.Results and Discussion: BCT specimens from 121 patients have been imaged with the optical device. One to four margins were imaged on each BCT specimen. Data from 112 patients were retained for analysis (51 negative margins, and 47 margins containing cancer within 1mm). Images of negative margins from patients with at least one positive margin (9 patients) elsewhere on the specimen were excluded from analysis due to the potential for presence of margin positivity that was not identified pathologically. For each margin, a set of 8 tissue composition maps were generated, from which a set of 36 image-descriptive variables were obtained. Wilcoxon rank-sum tests were used to determine which of the variables best separated negative from positive margins. A predictive model was developed using conditional inference trees to identify the optimal partitions from all 36 image-descriptive variables. The model selected variables related to the light scattering properties, total hemoglobin content, and β-carotene content of the underlying tissue, which are related to tissue density and morphology, vascular volume, and fat content, respectively. This model resulted in a sensitivity of 80% for detecting cancer at the margin, a sensitivity of 73% for detecting residual disease within 1mm of the margin, and a specificity of 65%. These results are promising and a prospective validation trial of the device is under development.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5017.

Diffuse reflectance spectroscopy with a self-calibrating fiber optic probe

Calibration of the diffuse reflectance spectrum for instrument response and time-dependent fluctuation as well as interdevice variations is complicated, time consuming, and potentially inaccurate. We describe a novel fiber optic probe with a real-time self-calibration capability that can be used for tissue optical spectroscopy. The probe was tested in a number of liquid phantoms over a relevant range of tissue optical properties. Absorption and scattering coefficients are extracted with an average absolute error and standard deviation of 6.9%+/-7.2% and 3.5%+/-1.5%, respectively.