Nicholas B. MacKinnon

Automated image analysis of digital colposcopy for the detection of cervical neoplasia

Digital colposcopy is a promising technology for the detection of cervical intraepithelial neoplasia. Automated analysis of colposcopic images could provide an inexpensive alternative to existing screening tools. Our goal is to develop a diagnostic tool that can automatically identify neoplastic tissue from digital images. A multispectral digital colposcope (MDC) is used to acquire reflectance images of the cervix with white light before and after acetic-acid application in 29 patients. A diagnostic image analysis tool is developed to identify neoplasia in the digital images. The digital image analysis is performed in two steps. First, similar optical patterns are clustered together. Second, classification algorithms are used to determine the probability that these regions contain neoplastic tissue. The classification results of each patients images are assessed relative to the gold standard of histopathology. Acetic acid induces changes in the intensity of reflected light as well as the ratio of green to red reflected light. These changes are used to differentiate high-grade squamous intraepithelial (HGSIL) and cancerous lesions from normal or low-grade squamous intraepithelial (LGSIL) tissue. We report diagnostic performance with a sensitivity of 79% and a specificity of 88%. We show that diagnostically useful digital images of the cervix can be obtained using a simple and inexpensive device, and that automated image analysis algorithms show a potential to identify histologically neoplastic tissue areas.

Spectrally programmable light engine for in vitro or in vivo molecular imaging and spectroscopy

A spectrally and temporally programmable light engine can create any spectral profile for hyperspectral, fluorescence, or principal-component imaging or with medical photonics devices employing spectroscopy, microscopy, and endoscopy. Multispectral imaging feasibility was demonstrated by capturing nine images at wavelengths from 450 to 650 mm (25-nm FWHM) with a CCD-camera-equipped bronchoscope coupled to the light engine. Selected wavelength regions were combined to produce a color endoscopy image.

New Method for Detection of Heart Allograft Rejection Validation of Sensitivity and Reliability in a Rat Heterotopic Allograft Model

BACKGROUND Patients with inflammatory heart muscle diseases would benefit from a safe, convenient, rapidly performed diagnostic technique with real-time results not involving tissue removal. We have performed a detailed evaluation of detection of heart allograft rejection by autofluorescence in a heterotopic abdominal rat heart allograft model ex vivo. METHODS AND RESULTS Recipient rats with allograft (Lewis to Fisher 344; n=71) and isograft (Lewis to Lewis; n=33) hearts, treated with cyclosporine or untreated, were killed at days 2, 4, 7, 14, 21, 28, and 56 after transplant. Nontransplant controls with (n=24) or without (n=24) immunosuppressive therapy were also studied. When the rats were killed, autofluorescence spectra were acquired under blue-light excitation from midtransverse ventricular sections of native and transplanted hearts. Corresponding sections were then evaluated pathologically by a modified International Society for Heart and Lung Transplantation (ISHLT) grading schema. The spectral differences between rejecting and nonrejecting hearts were quantified by linear discriminant functions, producing scores that decreased progressively with increasing severity of tissue rejection. Mean+/-SD discriminant function scores were 2.9+/-1.6, 1.8+/-2.2, -0.1+/-2.8, -1.2+/-2.3, and -2.3+/-3.0 for isografts and allograft ISHLT grades 0, I, II, and III, respectively (Spearman rank-order correlation -0.6; P<0.001, test for trend). Cyclosporine had no detectable effect on the spectra. CONCLUSIONS The correlation between changes in autofluorescence spectra and ISHLT rejection grade strongly supports the possibility of catheter-based, fluorescence-guided surveillance of rejection.

Review of the potential of optical technologies for cancer diagnosis in neurosurgery: a step toward intraoperative neurophotonics.

Abstract. Advances in image-guided therapy enable physicians to obtain real-time information on neurological disorders such as brain tumors to improve resection accuracy. Image guidance data include the location, size, shape, type, and extent of tumors. Recent technological advances in neurophotonic engineering have enabled the development of techniques for minimally invasive neurosurgery. Incorporation of these methods in intraoperative imaging decreases surgical procedure time and allows neurosurgeons to find remaining or hidden tumor or epileptic lesions. This facilitates more complete resection and improved topology information for postsurgical therapy (i.e., radiation). We review the clinical application of recent advances in neurophotonic technologies including Raman spectroscopy, thermal imaging, optical coherence tomography, and fluorescence spectroscopy, highlighting the importance of these technologies in live intraoperative tissue mapping during neurosurgery. While these technologies need further validation in larger clinical trials, they show remarkable promise in their ability to help surgeons to better visualize the areas of abnormality and enable safe and successful removal of malignancies.

Multicenter clinical trials of in vivo fluorescence: are the measurements equivalent?

With the development of fluorescence spectroscopy, multicenter clinical trials are becoming more common both in the academic and commercial arenas. To ensure the quality of quantitative and device independent results, standardization of the tissue spectra is essential for the comparison of data from various groups. An added concern is the potential degradation of instrumentation during a trial which may affect the instruments ability to accurately represent the tissue spectra. Our group has recently completed a Phase II clinical trial for the detection of cervical neoplasia using two different generations of spectroscopic devices at multiple sites. Both positive and negative optical standards were used to calibrate the tissue spectra as well as aid in the diagnosis of potential instrumentation problems during the trial. We have also conducted a cross validation study of fiber optic probes, spectroscopic devices, and optical standards for the latest generation of devices. The spectroscopic data of optical standards were analyzed for both the clinical trial and cross validation studies. Results demonstrated perceptible differences in optical standards data between the two generations of spectroscopy devices in the clinical trial, as well as the cross validation study with multiple devices of the same generation. Although the spectra were unexpectedly different, tissue spectra measured with the different systems can be empirically corrected by use of the various optical standards. Device performance during the clinical trial also was a concern; however, with the use of optical calibration standards, instrumentation problems were easily identified. To eliminate the problems associated with instrumentation, we have recently developed real-time quality assurance software to assess the optical calibration standards immediately after acquisition.

Melanoma detection using smartphone and multimode hyperspectral imaging

This projects goal is to determine how to effectively implement a technology continuum from a low cost, remotely deployable imaging device to a more sophisticated multimode imaging system within a standard clinical practice. In this work a smartphone is used in conjunction with an optical attachment to capture cross-polarized and collinear color images of a nevus that are analyzed to quantify chromophore distribution. The nevus is also imaged by a multimode hyperspectral system, our proprietary SkinSpect™ device. Relative accuracy and biological plausibility of the two systems algorithms are compared to assess aspects of feasibility of in-home or primary care practitioner smartphone screening prior to rigorous clinical analysis via the SkinSpect.

Separating melanin from hemodynamics in nevi using multimode hyperspectral dermoscopy and spatial frequency domain spectroscopy

Abstract. Changes in the pattern and distribution of both melanocytes (pigment producing) and vasculature (hemoglobin containing) are important in distinguishing melanocytic proliferations. The ability to accurately measure melanin distribution at different depths and to distinguish it from hemoglobin is clearly important when assessing pigmented lesions (benign versus malignant). We have developed a multimode hyperspectral dermoscope (SkinSpect™) able to more accurately image both melanin and hemoglobin distribution in skin. SkinSpect uses both hyperspectral and polarization-sensitive measurements. SkinSpect’s higher accuracy has been obtained by correcting for the effect of melanin absorption on hemoglobin absorption in measurements of melanocytic nevi. In vivo human skin pigmented nevi (N=20) were evaluated with the SkinSpect, and measured melanin and hemoglobin concentrations were compared with spatial frequency domain spectroscopy (SFDS) measurements. We confirm that both systems show low correlation of hemoglobin concentrations with regions containing different melanin concentrations (R=0.13 for SFDS, R=0.07 for SkinSpect).

Toward in vivo diagnosis of skin cancer using multimode imaging dermoscopy: (II) molecular mapping of highly pigmented lesions

We have developed a multimode imaging dermoscope that combines polarization and hyperspectral imaging with a computationally rapid analytical model. This approach employs specific spectral ranges of visible and near infrared wavelengths for mapping the distribution of specific skin bio-molecules. This corrects for the melanin-hemoglobin misestimation common to other systems, without resorting to complex and computationally intensive tissue optical models that are prone to inaccuracies due to over-modeling. Various human skin measurements including a melanocytic nevus, and venous occlusion conditions were investigated and compared with other ratiometric spectral imaging approaches. Access to the broad range of hyperspectral data in the visible and near-infrared range allows our algorithm to flexibly use different wavelength ranges for chromophore estimation while minimizing melanin-hemoglobin optical signature cross-talk.

In vivo skin chromophore mapping using a multimode imaging dermoscope (SkinSpec)

We introduce a multimode dermoscope (SkinSpectTM) we developed for early detection of melanoma by combining fluorescence, polarization and hyperspectral imaging. Acquired reflection image datacubes were input to a wavelength-dependent linear model to extract the relative contributions of skin chromophores at every pixel. The oxy-hemoglobin, deoxy hemoglobin, melanin concentrations, and hemoglobin oxygen saturation by the single step linear least square fitting and Kubelka-Munk tissue model using cross polarization data cubes were presented. The comprehensive data obtained by SkinSpect can be utilized to improve the accuracy of skin chromophore decomposition algorithm with less computation cost. As an example in this work, the deoxy-hemoglobin over-estimation error in highly pigmented lesion due to melanin and deoxy hemoglobin spectral cross talk were analyzed and corrected using two-step linear least square fitting procedure at different wavelength ranges. The proposed method also tested in skin with underlying vein area for validating the proof of concept.

Multimode optical dermoscopy (SkinSpect) analysis for skin with melanocytic nevus

We have developed a multimode dermoscope (SkinSpect™) capable of illuminating human skin samples in-vivo with spectrally-programmable linearly-polarized light at 33 wavelengths between 468nm and 857 nm. Diffusely reflected photons are separated into collinear and cross-polarized image paths and images captured for each illumination wavelength. In vivo human skin nevi (N = 20) were evaluated with the multimode dermoscope and melanin and hemoglobin concentrations were compared with Spatially Modulated Quantitative Spectroscopy (SMoQS) measurements. Both systems show low correlation between their melanin and hemoglobin concentrations, demonstrating the ability of the SkinSpect™ to separate these molecular signatures and thus act as a biologically plausible device capable of early onset melanoma detection.