Karel J. Zuzak

Intraoperative bile duct visualization using near-infrared hyperspectral video imaging

BACKGROUND Current methodologies for imaging the biliary system during cholecystectomy are cumbersome and do not eliminate the risk of bile duct injury. We describe an approach to intraoperative biliary imaging that will enable surgeons to see through the hepatoduodenal ligament and visualize the anteriorly placed biliary system. METHODS A laparoscopic-capable, near-infrared, hyperspectral imaging system was built. Reflected light passes through a liquid crystal filter that is continuously tunable in the near-infrared spectrum (650-1,100 nm). Spectroscopic image data are collected from laparoscopic surgery images onto array detectors formatted into a 3-dimensional hyperspectral data cube having spatially resolved images in the x-y plane and wavelength data in the z plane. Deconvoluting and color-coding the spatial and spectral information provides an image representative of inherent chemical properties to the imaged tissue. RESULTS Images of porcine biliary structures were obtained. The common duct-reflected spectra displayed a characteristic lipid shoulder at 930 nm and a strong water peak at 970 nm. Venous structures had absorption peaks at 760 nm (deoxyhemoglobin), 800 nm (oxyhemoglobin), and 970 nm (water). Arterial vessels had absorption peaks at 800 nm and 970 nm that would be expected for oxyhemoglobin and water. CONCLUSIONS We have designed and constructed a device to significantly enhance intraoperative biliary imaging. This system should enable surgeons to see through the hepatoduodenal ligament and image the anteriorly placed biliary system without the need for dissection of the cystic duct, as is needed with intraoperative cholangiography. Because the biliary system can be seen before any dissection is performed, this dimensional imaging technology has the potential for eradicating bile duct injury.

Minimal arterial in-flow protects renal oxygenation and function during porcine partial nephrectomy: Confirmation by hyperspectral imaging

OBJECTIVES To examine the potential for renal protection through incomplete renal artery (RA) occlusion with both assessments of creatinine changes and the use of hyperspectral imaging to monitor tissue oxygenation. Renal ischemia during partial nephrectomy can have adverse consequences on renal function. METHODS Fourteen pigs with a solitary kidney underwent open partial nephrectomy with warm ischemia. The RA flow was measured and reduced to 25%, 10%, and 0% of baseline for 60 minutes. Hyperspectral imaging was used to assess the percentage of oxyhemoglobin (%HbO(2)) at baseline, during ischemia, and during reperfusion. The %HbO(2) and change in the serum creatinine level from baseline were compared. RESULTS The baseline RA flow and %HbO(2) were similar in all groups, and, as expected, RA occlusion resulted in decreasing %HbO(2). The reduction of RA flow to 25% and 10% improved the nadir tissue oxygenation compared with 0% flow (P = .01 and P = .04, respectively) and 25% flow also appeared to prolong the interval to reach the nadir %HbO(2). Reperfusion resulted in a swift return to the baseline %HbO(2) in all 3 groups. The change in the serum creatinine from baseline to postoperative day 7 showed significantly improved renal preservation in the 25% RA flow group. CONCLUSIONS Incomplete RA occlusion during porcine partial nephrectomy resulted in favorable renal oxygenation profiles with as little as 10% blood flow and appeared to be renoprotective when 25% of the baseline RA flow is preserved. Hyperspectral imaging is a sensitive, noninvasive tool for real-time monitoring of renal oxygenation and, thereby, blood flow, which could facilitate intraoperative decision-making to protect 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 retinal imaging with a spectrally tunable light source

Hyperspectral retinal imaging can measure oxygenation and identify areas of ischemia in human patients, but the devices used by current researchers are inflexible in spatial and spectral resolution. We have developed a flexible research prototype consisting of a DLP®-based spectrally tunable light source coupled to a fundus camera to quickly explore the effects of spatial resolution, spectral resolution, and spectral range on hyperspectral imaging of the retina. The goal of this prototype is to (1) identify spectral and spatial regions of interest for early diagnosis of diseases such as glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy (DR); and (2) define required specifications for commercial products. In this paper, we describe the challenges and advantages of using a spectrally tunable light source for hyperspectral retinal imaging, present clinical results of initial imaging sessions, and describe how this research can be leveraged into specifying a commercial product.

Dynamically programmable digital tissue phantoms

As optical imaging modalities gain acceptance for medical diagnostics and become common in clinical applications, standardized protocols to quantitatively assess optical sensor performance are required to ensure commonality in measurements and to validate system performance. The current emphasis is on the development of 3-dimensional, tissue-simulating artifacts with optical scattering and absorption properties designed to closely mimic biological systems. These artifacts, commonly known as tissue phantoms, can be fairly complex and are tailored for each specific application. In this work, we describe a conceptually simpler, 2-dimensional digital analog to the 3-dimensional tissue phantoms that we call Digital Tissue Phantoms. The Digital Tissue Phantoms are complex, realistic, calibrated, optical projections of medically relevant images with known spectral and spatial content. By generating a defined set of Digital Tissue Phantoms, the radiometric performance of the optical imaging sensor can be quantified, based on the accuracy of measurements of the projected images. The system is dynamically programmable, which means that the same system can be used with different sets of Digital Tissue Phantoms for sensor performance metrics covering a wide range of optical medical diagnostics, from cancer and tumor detection to burn quantification.

A Multimodal Reflectance Hyperspectral Imaging System for Monitoring Wound Healing in Below Knee Amputations

The multimodal reflectance hyperspectral imaging system presented here was developed in the Laboratory of Biomedical Imaging, at the University of Texas at Arlington, UTA. This system is an extension of the visible hyperspectral imaging prototype developed at the National Institutes of Health, NIH. It uses visible and near-infrared, NIR, light and electro-optical components to obtain spectroscopic images, thereby rendering the name multimodal. The goal of this research plan is to fabricate and utilize this system for monitoring wound healing in below the knee amputations. The system illuminates the amputation area with a cold broadband light source, collects a series of spectroscopic images spanning the visible and NIR, in parallel, deconvolutes the acquisitioned hyperspectral data using chemometric methods for imaging the spatial distribution of inherent chromophores. This technique is non-invasive, eliminates the use of contrast dye injection. The images produced visualize changes in the deeper larger blood vessels, provided by the NIR component and the superficial microvascular capillaries, provided by the visible component.

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.