The selection of well-vascularized tissue during DIEP flap harvest remains controversial. While several studies have elucidated cross-midline perfusion, further characterization of perfusion to the ipsilateral hemiabdomen is necessary for minimizing rates of fat necrosis or partial fat necrosis in bilateral DIEP flaps. Eighteen patients (29 flaps) underwent DIEP flap harvest using a prospectively designed protocol. Perforators were marked and imaged with a novel system for quantitatively measuring tissue oxygenation, the Digital Light Hyperspectral Imager. Images were then analyzed to determine if perforator selection influenced ipsilateral flap perfusion. Flaps based on a single lateral row perforator (SLRP) were found to have a higher level of hemoglobin oxygenation in Zone I (mean %HbO2 = 76.1) compared to single medial row perforator (SMRP) flaps (%HbO2 = 71.6). Perfusion of Zone III relative to Zone I was similar between SLRP and SMRP flaps (97.4% vs. 97.9%, respectively). These differences were not statistically significant (p>0.05). Perfusion to the lateral edge of the flap was slightly greater for SLRP flaps compared SMRP flaps (92.1% vs. 89.5%, respectively). SMRP flaps had superior perfusion travelling inferiorly compared to SLRP flaps (88.8% vs. 83.9%, respectively). Overall, it was observed that flaps were better perfused in the lateral direction than inferiorly. Significant differences in perfusion gradients directed inferiorly or laterally were observed, and perforator selection influenced perfusion in the most distal or inferior aspects of the flap. This suggests broader clinical implications for flap design that merit further investigation.
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.
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.
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.
Sara Best, Abhas Thapa, Michael Holzer, Neil Jackson, Saad Mir, Chester Donnally, Eleanor Wehner, Ganesh Raj, Edward Livingston, Jeffrey Cadeddu, Karel Zuzak
Digital Light Processing (DLP®) hyperspectral imaging (HsI) is a non-invasive method used to construct a highly
sensitive, real-time tissue oxygenation map through the measurement of the percentage of oxyhemoglobin. We have
demonstrated that this technology can detect the oxyhemoglobin in the blood vessels on the surface of the kidney and we
have used this to monitor renal perfusion during kidney cancer operations, where the blood supply to the kidney is
interrupted for a period of time. This technology may allow us to "personalize" surgery based on the oxygenation
profile.
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.
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.
Visible DLP® hyperspectral reflectance imaging in medical applications is limited by the lack of penetration of visible
light for visualization of deeper vessels and tissues. The longer, near infrared (NIR) wavelengths, capable of facilitating
chromophore and fluorophore visualization, penetrate deeper allowing visualization of anatomical structures in surgical
settings. Digital micromirror device (DMD) chips allow for digital programming of complex spectral illuminations with
bandwidths as low as 7nm. Furthermore, fluorescence can be maximized by programming the DMD chip to illuminate
with light precisely configured to contain excitation spectra. We have developed a "mid-range" system that extends from
the visible light range into the NIR (525nm - 1050nm) and has been characterized and configured for fluorescence of
indocyanine green (ICG). The DMD-based light source was found to be within the manufacturer's spectral specifications
and proved to be very versatile in both spectral behavior and application. Fluorescence of ICG was successfully
optimized by this system and demonstrated in capillary tubes and excised tissue.
Surgical technology advances slowly and only when there is overwhelming need for change. Change is
resisted by surgeons and is made hard by FDA rules that inhibit innovation. There is a pressing need to
improve surgeon's visualization of the operative field during laparoscopic surgery to minimize the risk
for significant injury that can occur when surgeons are operating around delicate, hidden structures. We
propose to use a Digital Light Processor-based hyperspectral imaging system to assist an operating
surgeon's ability to see through tissues and identify otherwise hidden structures such as bile ducts
during laparoscopic cholecystectomy.
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.
Surgeons often cannot see major vessels embedded in adipose tissue and inadvertently injure them. One such example occurs during surgical removal of the gallbladder, where injury of the nearby common bile duct leads to life-threatening complications. Near-infrared imaging of the intraoperative field may help surgeons localize such critical tissue-embedded vessels. We have investigated how continuous-wave (CW) imaging performs relative to time-gated wide-field imaging, presently a rather costly technology, under broad Gaussian beam-illumination conditions. We have studied the simplified case of an isolated cylinder having bile-duct optical properties, embedded at different depths within a 2-cm slab of adipose tissue. Monte Carlo simulations were preformed for both reflectance and transillumination geometries. The relative performance of CW versus time-gated imaging was compared in terms of spatial resolution and contrast-to-background ratio in the resulting simulated images. It was found that time-gated imaging offers superior spatial resolution and vessel-detection sensitivity in most cases, though CW transillumination measurements may also offer satisfactory performance for this tissue geometry at lower cost. Experiments were performed in reflectance geometry to validate simulation results, and potential challenges in the translation of this technology to the clinic are discussed.
We describe a novel digital light processing, DLP hyperspectral imaging system for visualizing chemical
composition of in vivo tissues during surgical procedures non-invasively and at near video rate. The novelty of the DLP
hyperspectral imaging system resides in (1) its ability to conform light to rapidly sweep through a series of preprogrammed
spectral illuminations as simple as a set of contiguous bandpasses to any number of complex spectra, and
(2) processing the reflected spectroscopic image data using unique supervised and unsupervised chemometric methods
that color encode molecular content of tissue at each image detector pixel providing an optical biopsy. Spectral
illumination of tissue is accomplished utilizing a DLP® based spectral illuminator incorporating a series of bandpass
spectra and measuring the reflectance image with a CCD array detector. Wavelength dependent images are post
processed with a multivariate least squares analysis method using known reference spectra of oxy- and deoxyhemoglobin.
Alternatively, illuminating with complex reference spectra reduces the number of spectral images required
for generating chemically relevant images color encoded for relative percentage of oxyhemoglobin are collected and
displayed in real time near-video rate, (3 to 4) frames per second (fps). As a proof of principle application, a kidney of
an anesthetized pig was imaged before and after renal vasculature occlusion showing the clamped kidney to be 61% of
the unclamped kidney percentage of oxyhemoglobin. Using the "3-Shot" spectral illumination method and gathering
data at (3 to 4) fps shows a non-linear exponential de-oxygenation of hemoglobin reaching steady state within 30
seconds post occlusion.
The clinical motivation for our work was to help surgeons see vessels through non-translucent intraoperative tissues
during laparoscopic removal of the gallbladder. Our main focus was to answer the question of how CW imaging
performs relative to ICCD (Intensified Charge-Coupled Device) based time-gated imaging, which is a lot more costly,
under broad Gaussian beam illumination conditions. We have studied the simplified case of an isolated bile duct
embedded at different depths within a 2 cm slab of adipose tissue. Monte Carlo simulations were preformed for both
reflectance and trans-illumination geometries. The relative performance of CW versus time-gated imaging was
compared in terms of spatial resolution and vessel detection sensitivity in the resulting simulated images. Experiments
were performed in reflectance geometry to validate simulation results. It was found that time-gated imaging offers
superior spatial resolution and vessel detection sensitivity in all cases though CW trans-illumination measurements may
also offer satisfactory performance for this tissue geometry at a lower cost.
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.
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