Eleanor Wehner

Active DLP hyperspectral illumination: a noninvasive, in vivo, system characterization visualizing tissue oxygenation at near video rates.

We report use of a novel hyperspectral imaging system utilizing digital light processing (DLP) technology to noninvasively visualize in vivo tissue oxygenation during surgical procedures. The systems novelty resides in its method of illuminating tissue with precisely predetermined continuous complex spectra. The Texas Instruments digital micromirror device, DMD, chip consisting of 768 by 1024 mirrors, each 16 μm square, can be switched between two positions at 12.5 kHz. Switching the appropriate mirrors controls the intensity of light illuminating the tissue as a function of wavelength, active spectral illumination. Meaning, the tissue can be illuminated with a different spectrum of light within 80 μs. Precisely, predetermined spectral illumination penetrates into patient tissue, its chemical composition augments the spectral properties of the light, and its reflected spectra are detected and digitized at each pixel detector of a silicon charge-coupled device, CCD. Using complex spectral illumination, digital signal processing and chemometric methods produce chemically relevant images at near video rates. Specific to this work, tissue is illuminated spectrally with light spanning the visible electromagnetic spectrum (380 to 780 nm). Spectrophotometric images are detected and processed visualizing the percentage of oxyhemoglobin at each pixel detector and presented continuously, in real time, at 3 images per second. As a proof of principle application, kidneys of four live anesthetized pigs were imaged before, during, and after renal vascular occlusion. DLP Hyperspectral Imaging with active spectral illumination detected a 64.73 ± 1.5% drop in the oxygenation of hemoglobin within 30 s of renal arterial occlusion. Producing chemically encoded images at near video rate, time-resolved hyperspectral imaging facilitates monitoring renal blood flow during animal surgery and holds considerable promise for doing the same during human surgical interventions.

First Place: Renal Oxygenation During Robot-Assisted Laparoscopic Partial Nephrectomy: Characterization Using Laparoscopic Digital Light Processing Hyperspectral Imaging

UNLABELLED Abstract Background and Purpose: Digital light processing-based hyperspectral imaging (DLP(®)-HSI) was adapted for use during laparoscopic surgery by coupling the spectral illumination source with a conventional laparoscopic light guide and incorporating a customized digital charge-coupled device camera for image acquisition. The system was used to characterize renal oxygenation during robot-assisted laparoscopic partial nephrectomy (RALPN) in humans. PATIENTS AND METHODS After Institutional Review Board approval, laparoscopic DLP-HSI was performed in consecutive patients undergoing RALPN at our institution. Time trends in relative tissue oxygen saturation (%HbO2) were descriptively analyzed. Associations between %HbO2 and patient age, comorbidities, and estimated glomerular filtration rate (eGFR) were investigated using the Kendall tau test. RESULTS Laparoscopic DLP-HSI was performed in 18 patients between May 2011 and February 2012. Median (interquartile range; IQR) age was 55.9 (49-67.5) years. Of the patients, 10/18 (56%) were men and 12/18 (66.7%) had a history of hypertension, diabetes, and/or tobacco use. Median (IQR) %HbO2 before, during, and after ischemia was 60.8% (57.9-68.2%), 53.6% (46.8-55.1%), and 61.5% (54.9-67.6%), respectively. Baseline %HbO2 was inversely associated with preoperative eGFR (τ=-0.38; P=0.036), and eGFR at most recent follow-up (τ=-0.38; P=0.036). Baseline or ischemic %HbO2 did not correlate with hypertension, diabetes, and/or tobacco history. Younger patients (<56 years) had a lower median baseline %HbO2 (P=0.07) and a higher median preoperative eGFR (P=0.038), than their older counterparts. CONCLUSION The laparoscopic HSI system successfully characterized dynamic changes in renal oxygenation during RALPN. Intraoperative laparoscopic HSI outcomes have the potential to predict postoperative individual kidney function.

Hyperspectral imaging utilizing LCTF and DLP technology for surgical and clinical applications

Two different, already characterized, hyperspectral imaging systems created for visualizing the spatial distribution of tissue oxygenation non-invasively for in vivo clinical use are described. Individual components of both liquid crystal tunable filter (LCTF) and digital light processing (DLP) systems were characterized, calibrated, and found to be well within manufacturer specifications. Coupling LCTF with charge coupled device (CCD) technology and acquiring images at multiple, contiguous wavelengths and at narrow bandwidths are formatted into a hyperspectral data cube consisting of one spectral and two spatial dimensions. DLP® technology has the novel ability to conform light to any desired spectral illumination scheme. Subsequently the collected multispectral data are processed into chemically relevant images that are color encoded at each pixel detector for the relative percentage of oxyhemoglobin. Using spectral illumination methods unique to the DLP hyperspectral imager results in producing chemically relevant images at near video rate; 4 frames per second. As an example, both systems are used to collect spectral data from a 27.22 kg porcine kidney whose renal artery has been occluded for 60 minutes. Both systems return nearly identical spectra collected from the surface of the kidney, with a root mean square deviation between the two spectra of 0.02.

NIR DLP hyperspectral imaging system for medical applications

DLP® hyperspectral reflectance imaging in the visible range has been previously shown to quantify hemoglobin oxygenation in subsurface tissues, 1 mm to 2 mm deep. Extending the spectral range into the near infrared reflects biochemical information from deeper subsurface tissues. Unlike any other illumination method, the digital micro-mirror device, DMD, chip is programmable, allowing the user to actively illuminate with precisely predetermined spectra of illumination with a minimum bandpass of approximately 10 nm. It is possible to construct active spectral-based illumination that includes but is not limited to containing sharp cutoffs to act as filters or forming complex spectra, varying the intensity of light at discrete wavelengths. We have characterized and tested a pure NIR, 760 nm to 1600 nm, DLP hyperspectral reflectance imaging system. In its simplest application, the NIR system can be used to quantify the percentage of water in a subject, enabling edema visualization. It can also be used to map vein structure in a patient in real time. During gall bladder surgery, this system could be invaluable in imaging bile through fatty tissue, aiding surgeons in locating the common bile duct in real time without injecting any contrast agents.

The robustness of DLP hyperspectral imaging for clinical and surgical utility

Utilizing seed funding from Texas Instruments, a DLP (R)Hyperspectral Imaging system was developed by integrating a focal-plane array, FPA, detector with a DLP based spectrally tunable illumination source. Software is used to synchronize FPA with DLP hardware for collecting spectroscopic images as well as running novel illumination schemes and chemometric deconvolution methods for producing gray scale or color encoded images visualizing molecular constituents at video rate. Optical spectra and spectroscopic image data of a variety of live human organs and diseased tissue collected from patients during surgical procedures and clinical visits being cataloged for a database will be presented.

Hyperspectral image projection of a pig kidney for the evaluation of imagers used for oximetry

Hyperspectral image projection applied to optical medical imaging can provide a means to evaluate imager performance. This allows repeated viewing of unique surgical scenes without the need for costly experiments on patients. Additionally, the generated scene can be well characterized and used repeatedly as a standard for many different imagers at different times and locations. This paper describes the use of a hyperspectral image of a pig kidney. The scene of the kidney is projected with the full spectral content allowing the oxygenation status of the tissue to be observed and evaluated spatially.

Calibration and Validation Scheme for In Vivo Spectroscopic Imaging of Tissue Oxygenation

The determination of the level of oxygenation in optically accessible tissues using multispectral or hyperspectral imaging (HSI) of oxy- and deoxyhemoglobin has special appeal in clinical work due to its noninvasiveness, ease of use, and capability of providing molecular and anatomical information at near video rates during surgery. In this paper we refer to an example of the use of HSI in monitoring oxygenation of kidneys during partial nephrectomy. In a study using porcine models, it was found that artery-only clamping left the kidney better oxygenated, as opposed to simultaneously clamping the artery and the vein. A subsequent study correlates gradations in blood flow by partial clamping during the surgical procedure with postoperative renal function via assessment of creatinine level. We discuss the various contributions to the uncertainty of the oxygen saturation measured by this remote-sensing imaging technique in medical application.

An examination of spectral diversity of medical scenes for hyperspectral projection

There are numerous medical conditions which may benefit from hyperspectral imaging. The imagers used for these conditions will need to have the performance validated to ensure consistency, gain acceptance and clear regulatory hurdles. NIST has been developing a Digital Light Processing (DLP)-based Hyperspectral Image Projector (HIP) for providing scenes with full spectral content in order to evaluate multispectral and hyperspectral imagers. In order for the scene to be projected, a dimensionality reduction is performed in order to project spectra efficiently. The number of eigenspectra needed to best represent a scene is an important part in the recombining of the image. This paper studies the spectral diversity between different medical scenes collected by a DLP based hyperspectral imager. Knowledge gained from this study will help guide the methods used for hyperspectral image projection of medical scenes in the future.

Spectral light source distribution variations to enhance discrimination of the common bile duct from surroundings in reflectance hyperspectral images

The classification of anatomical features using hyperspectral imaging has been a common goal in biomedical hyperspectral imaging. Identification and location of the common bile duct is critical in cholecystectomies, one of the most common surgical procedures. In this study, surgical images where the common bile duct is visible to the surgeon during open surgeries of patients with normal bile ducts were acquired. The effect of the spectral distribution of simulated light sources on the scene color are explored with the objective of providing the optimum spectral light distribution that can enhance contrast between the common bile duct and surrounding tissue through luminance and color differences.

Hyperspectral image segmentation of the common bile duct

Over the course of the last several years hyperspectral imaging (HSI) has seen increased usage in biomedicine. Within the medical field in particular HSI has been recognized as having the potential to make an immediate impact by reducing the risks and complications associated with laparotomies (surgical procedures involving large incisions into the abdominal wall) and related procedures. There are several ongoing studies focused on such applications. Hyperspectral images were acquired during pancreatoduodenectomies (commonly referred to as Whipple procedures), a surgical procedure done to remove cancerous tumors involving the pancreas and gallbladder. As a result of the complexity of the local anatomy, identifying where the common bile duct (CBD) is can be difficult, resulting in comparatively high incidents of injury to the CBD and associated complications. It is here that HSI has the potential to help reduce the risk of such events from happening. Because the bile contained within the CBD exhibits a unique spectral signature, we are able to utilize HSI segmentation algorithms to help in identifying where the CBD is. In the work presented here we discuss approaches to this segmentation problem and present the results.