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.

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 system's 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.

Characterization of renal ischemia using DLP hyperspectral imaging: a pilot study comparing artery-only occlusion versus artery and vein occlusion.

BACKGROUND AND PURPOSE: Renal artery-only (AO) occlusion, as opposed to artery and vein (AV) occlusion, has demonstrated some benefit in reducing renal insufficiency during warm ischemia. In this pilot study, we used digital light projection hyperspectral imaging (HSI) to construct a "real time" tissue oxygenation "map" to determine whether there are differences in renal tissue oxygenation during vascular occlusion with AO vs AV. MATERIALS AND METHODS: Renal vascular occlusion with either AO or AV was performed for 60 minutes in seven porcine renal units. Using HSI, the percentage of oxyhemoglobin (%HbO(2)) in the renal cortex was determined at 4-minute increments throughout the ischemic period and for 30 minutes after reperfusion. RESULTS: Average baseline %HbO(2) in all animals was approximately 70%. After vascular occlusion in both cohorts, %HbO(2) decreased by one third within 2 to 5 minutes, with a gradual decline in %HbO(2) over the remaining 55 minutes. Oxyhemoglobin profiles for AO and AV occlusion diverged significantly between 16 and 24 minutes after vascular occlusion (P = 0.0001 and 0.036, respectively), with a merging of the two curves occurring after approximately 36 minutes (P = 0.093). During reperfusion, average %HbO(2) improved to 72.4% after 25 to 30 minutes. CONCLUSION: In this pilot study, we demonstrate that renal tissue oxygenation drops rapidly after occlusion of the renal vasculature and returns to near baseline 30 minutes after reperfusion. In the porcine model, the %HbO(2) differs significantly between AO and AV occlusion for up to 35 minutes after ischemia onset, indicating a possible "ischemic window" in which AO occlusion may provide benefit over AV occlusion.