Towards a field-compatible optical spectroscopic device for cervical cancer screening in resource-limited settings: effects of calibration and pressure

Epidemiology of Cervical Cancer in the Caribbean

Cervical cancer (CvC) is considered a preventable disease; however, in the Caribbean, it is still one of the fourth most common causes of death in women. Efforts to overcome obstacles to the treatment and control of this preventable disease are being made by several countries within the Caribbean. However, no health issue can be readily managed without first acquiring an understanding of the dynamics relating to its severity of impact reaching the target population, its clinical pathology, and the availability of treatment and/or preventative measures to control or halt its progression. To assess the status of CvC in the Caribbean, a review of the literature was conducted using PubMed. The Caribbean was defined in the review as comprising nations and islands whose coastlines are touched by the Caribbean Sea. This led to an assessment of the available literature on CvC for 33 Caribbean territories. The review showed a lack of published information on CvC and highlights the need for greater research. This also serves as a template for subsequent investigations.

A Clinical Study to Assess Diffuse Reflectance Spectroscopy with an Auto-Calibrated, Pressure-Sensing Optical Probe in Head and Neck Cancer

Diffuse reflectance spectroscopy (DRS) is a powerful tool for quantifying optical and physiological tissue properties such as hemoglobin oxygen saturation and vascularity. DRS is increasingly used clinically for distinguishing cancerous lesions from normal tissue. However, its widespread clinical acceptance is still limited due to uncontrolled probe–tissue interface pressure that influences reproducibility and introduces operator-dependent results. In this clinical study, we assessed and validated a pressure-sensing and automatic self-calibration DRS in patients with suspected head and neck squamous cell carcinoma (HNSCC). The clinical study enrolled nineteen patients undergoing HNSCC surgical biopsy procedures. Patients consented to evaluation of this improved DRS system during surgery. For each patient, we obtained 10 repeated measurements on one tumor site and one distant normal location. Using a Monte Carlo-based model, we extracted the hemoglobin saturation data along with total hemoglobin content and scattering properties. A total of twelve cancer tissue samples from HNSCC patients and fourteen normal tissues were analyzed. A linear mixed effects model tested for significance between repeated measurements and compared tumor versus normal tissue. These results demonstrate that cancerous tissues have a significantly lower hemoglobin saturation compared to normal controls (p < 0.001), which may be reflective of tumor hypoxia. In addition, there were minimal changes over time upon probe placement and repeated measurement, indicating that the pressure-induced changes were minimal and repeated measurements did not differ significantly from the initial value. This study demonstrates the feasibility of conducting optical spectroscopy measurements on intact lesions prior to removal during HNSCC procedures, and established that this probe provides diagnostically-relevant physiologic information that may impact further treatment.

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.

Assessing effects of pressure on tumor and normal tissue physiology using an automated self-calibrated, pressure-sensing probe for diffuse reflectance spectroscopy

Diffuse reflectance spectroscopy (DRS) represents a quantitative, noninvasive, nondestructive means of assessing vascular oxygenation, vascularity, and structural properties. However, it is known that such measurements can be influenced by the effects of pressure, which is a major concern for reproducible and operator-independent assessment of tissues. Second, regular calibration is a necessary component of quantitative DRS to account for factors such as lamp decay and fiber bending. Without a means of reliably controlling for these factors, the accuracy of any such assessments will be reduced, and potentially biased. To address these issues, a self-calibrating, pressure-controlled DRS system is described and applied to both a patient-derived xenograft glioma model, as well as a set of healthy volunteers for assessments of oral mucosal tissues. It was shown that pressure had a significant effect on the derived optical parameters, and that the effects on the optical parameters were magnified with increasing time and pressure levels. These findings indicate that not only is it critical to integrate a pressure sensor into a DRS device, but that it is also important to do so in an automated way to trigger a measurement as soon as possible after probe contact is made to minimize the perturbation to the tissue site.

Noninvasive optical spectroscopy for identification of non-melanoma skin cancer: Pilot study

OBJECTIVE

Optical spectroscopy offers a noninvasive alternative to biopsy as a first-line screening tool for suspicious skin lesions. This study sought to define several optical parameters across malignant and benign tissue types.

STUDY DESIGN

Prospective pilot trial utilizing the Zenalux IM1 optical spectroscopy device from April 2016 to February 2017. For each skin lesion, provider pre-biopsy probability of malignancy was compared to histolopathologic diagnosis. Optical data were characterized across basal cell carcinoma (BCC; n = 9), squamous cell carcinoma (SCC; n = 5), actinic keratosis (AK; n = 4), scar tissue (n = 6), nevus (n = 2), and neurofibroma (NF; n = 1). Across all patients, agreement was determined between control measurements collected adjacent to the lesion and from the upper extremity.

METHODS

Prospective single center pilot study. The optical properties of 27 cutaneous lesions were collected from 18 adult patients presenting to Otolaryngology and Dermatology clinics with suspicious skin lesions warranting biopsy. Spectroscopy measurements were recorded for each lesion: two at the lesion site, two at an adjacent site (internal control), and one at the central medial upper extremity (arm control). Variables of interest included absolute oxygenated hemoglobin (Hb), Hb saturation, total Hb concentration, and Eumelanin concentration. For each lesion, internal control averages were subtracted from lesion averages to provide delta parameter values, and lesion averages were divided by internal control averages to provide ratio parameter values.

RESULTS

Mean percent difference between pre-biopsy probability of malignancy and histology was 29%, with a difference of 75% or greater seen in 5 of 25 lesions. Mean values for BCC, SCC, AK, and scar tissue varied most between extracted mean reduced scatter estimate (μa'; cm- ) delta values (BCC: -2.2 ± 3.8; SCC: -3.9 ± 2.0; AK: -3.3 ± 4.2, Scar: -1.7 ± 1.2) and total Hb (µM) ratio (BCC: 2.0 ± 3.3; SCC: 3.0 ± 1.3; AK: 1.1 ± 0.6; Scar: 1.4 ± 1.1). Agreement between local and arm controls was poor.

CONCLUSION

This pilot trial utilizes optical spectroscopy as a noninvasive method for determining cutaneous lesion histology. Effect sizes observed across optical parameters for benign and malignant tissue types will guide larger prospective studies that may ultimately lead to prediction of lesional histology without need for invasive biopsy. Lasers Surg. Med. 50:246-252, 2018. © 2018 Wiley Periodicals, Inc.

Optical techniques for cervical neoplasia detection

This paper provides an overview of the current research in the field of optical techniques for cervical neoplasia detection and covers a wide range of the existing and emerging technologies. Using colposcopy, a visual inspection of the uterine cervix with a colposcope (a binocular microscope with 3- to 15-fold magnification), has proven to be an efficient approach for the detection of invasive cancer. Nevertheless, the development of a reliable and cost-effective technique for the identification of precancerous lesions, confined to the epithelium (cervical intraepithelial neoplasia) still remains a challenging problem. It is known that even at early stages the neoplastic transformations of cervical tissue induce complex changes and modify both structural and biochemical properties of tissues. The different methods, including spectroscopic (diffuse reflectance spectroscopy, induced fluorescence and autofluorescence spectroscopy, Raman spectroscopy) and imaging techniques (confocal microscopy, optical coherence tomography, Mueller matrix imaging polarimetry, photoacoustic imaging), probe different tissue properties that may serve as optical biomarkers for diagnosis. Both the advantages and drawbacks of these techniques for the diagnosis of cervical precancerous lesions are discussed and compared.

Properties of contact pressure induced by manually operated fiber-optic probes

We assess the properties of contact pressure applied by manually operated fiber-optic probes as a function of the operator, probe contact area, and sample stiffness. First, the mechanical properties of human skin sites with different skin structures, thicknesses, and underlying tissues were studied by in vivo indentation tests. According to the obtained results, three different homogeneous silicone skin phantoms were created to encompass the observed range of mechanical properties. The silicon phantoms were subsequently used to characterize the properties of the contact pressure by 10 experienced probe operators employing fiber-optic probes with different contact areas. A custom measurement system was used to collect the time-lapse of diffuse reflectance and applied contact pressure. The measurements were characterized by a set of features describing the transient and steady-state properties of the contact pressure and diffuse reflectance in terms of rise time, optical coupling, average value, and variability. The average applied contact pressure and contact pressure variability were found to significantly depend on the probe operator, probe contact area, and surprisingly also on the sample stiffness. Based on the presented results, we propose a set of practical guidelines for operators of manual probes.

Diffuse reflectance spectroscopy of epithelial tissue with a smart fiber-optic probe

Diffuse reflectance spectroscopy (DRS) with a fiber-optic probe can noninvasively quantify the optical properties of epithelial tissues and has shown the potential as a cost-effective, fast and sensitive tool for diagnosis of early precancerous changes in the cervix and oral cavity. However, current DRS systems are susceptible to several sources of systematic and random errors, such as uncontrolled probe-to-tissue pressure and lack of a real-time calibration that can significantly impair the measurement accuracy, reliability and validity of this technology as well as its clinical utility. In addition, such systems use bulky, high power and expensive optical components which impede their widespread use in low- and middle-income countries (LMICs) where epithelial cancer related death is disproportionately high. In this paper we report a portable, easy-to-use and low cost, yet accurate and reliable DRS device that can aid in the screening and diagnosis of oral and cervical cancer. The device uses an innovative smart fiber-optic probe to eliminate operator bias, state-of-the-art photonics components to reduce size and power consumption, and automated software to reduce the need of operator training. The device showed a mean error of 1.4 ± 0.5% and 6.8 ± 1.7% for extraction of phantom absorption and reduced scattering coefficients, respectively. A clinical study on healthy volunteers indicated that a pressure below 1.0 psi is desired for oral mucosal tissues to minimize the probe effects on tissue physiology and morphology.

Hemoglobin parameters from diffuse reflectance data

Tissue vasculature is altered when cancer develops. Consequently, noninvasive methods of monitoring blood vessel size, density, and oxygenation would be valuable. Simple spectroscopy employing fiber optic probes to measure backscattering can potentially determine hemoglobin parameters. However, heterogeneity of blood distribution, the dependence of the tissue-volume-sampled on scattering and absorption, and the potential compression of tissue all hinder the accurate determination of hemoglobin parameters. We address each of these issues. A simple derivation of a correction factor for the absorption coefficient, μa, is presented. This correction factor depends not only on the vessel size, as others have shown, but also on the density of blood vessels. Monte Carlo simulations were used to determine the dependence of an effective pathlength of light through tissue which is parameterized as a ninth-order polynomial function of μa. The hemoglobin bands of backscattering spectra of cervical tissue are fit using these expressions to obtain effective blood vessel size and density, tissue hemoglobin concentration, and oxygenation. Hemoglobin concentration and vessel density were found to depend on the pressure applied during in vivo acquisition of the spectra. It is also shown that determined vessel size depends on the blood hemoglobin concentration used.

Evaluating and improving the quality of time-dependent, diffuse reflectance spectroscopic signals measured from in vivo brain during craniotomy

BACKGROUND

Optical spectroscopy can be used to assess the pathophysiological characteristics of diseased and injured biological tissue in vivo in a non-destructive way. It is often used in conjunction with a contact optical probe for the purposes of operating and sensing in a sterile field. Since the probe is often held by the hand of an investigator during data acquisition, any hand instability can affect the quality of acquired data and, hence, degrade the accuracy of diagnosis. This study was designed to quantitatively characterize these artifacts, and then propose an effective engineering solution to remove them.

METHODS

Time-dependent diffuse reflectance spectra (Rd(λ,t)) were acquired from the normal cortex region of pediatric patients undergoing epilepsy surgery. They were acquired at a rate of 33 Hz, and their range was 400 and 900 nm. Two distinct ways of collecting data were tested: one with the fiber optical probe held by the surgeon's hand during data acquisition, and the other with the probe held by a specially designed probe holder. The probe holder was designed and constructed to minimize the variations in probe contact pressure and contact point for the full duration of any given investigation. Spectral data acquired using versus not using the probe holder were characterized and compared in the time, wavelength, and frequency domains, using both descriptive and inferential statistics.

RESULTS

Hand motion manifested as strong random variations in Rd(λ,t) which impacted temporal and frequency characteristics of Rd(λ,t). The percentage standard deviation %STD of Rd(λ,t) acquired without probe holder could be as high as 60%, and they are significantly higher than those with probe holder at all wavelengths. This difference is especially prominent between 400 and 600 nm. Rd(λ,t) acquired without the probe holder also processed a higher spectral power energy in the frequency domain than those with the probe holder. The correlation analysis revealed that the hand motions induced synchronistic variations in Rd(λ,t) between 600 and 800 nm, but this synchronicity is not obvious between 400 and 600 nm.

CONCLUSION

The results of this investigation demonstrate the nature and the magnitude of hand motion induced artifacts in in vivo diffuse reflectance spectra and propose one potential solution (i.e., a probe holder) to remove them. These findings allow us to improve the quality of time-dependent, diffuse reflectance signals acquired to study the dynamic characteristics of biological tissues, like brain, in vivo.

Method of detecting tissue contact for fiber-optic probes to automate data acquisition without hardware modification

We present a novel algorithm to detect contact with tissue and automate data acquisition. Contact fiber-optic probe systems are useful in noninvasive applications and real-time analysis of tissue properties. However, applications of these technologies are limited to procedures with visualization to ensure probe-tissue contact and individual user techniques can introduce variability. The software design exploits the system previously designed by our group as an optical method to automatically detect tissue contact and trigger acquisition. This method detected tissue contact with 91% accuracy, detected removal from tissue with 83% accuracy and reduced user variability by > 8%. Without the need for additional hardware, this software algorithm can easily integrate into any fiber-optic system and expands applications where visualization is difficult.