title: Assessment of critical renal ischemia with real-time infrared imaging.
abstract: BACKGROUND
  Currently visual and tactile clues such as color, mottling, and tissue turgor are used in the operating room for subjective assessments of organ ischemia. Studies have demonstrated that infrared (IR) imaging is a reliable tool to identify perfusion of brain tumors and kidneys during human surgery. Intraoperative IR imaging has the potential for more objective real-time detection and quantitative assessment of organ viability including early ischemia. We hypothesize, by detecting variations of the IR signal, we can assess the degree to which renal surface temperature reflects underlying renal ischemia. To address this hypothesis, IR imaging-derived temperature fluctuations were evaluated during laparotomy in a porcine model (n = 15). These temperature profiles then underwent spectral (frequency) analysis to assess their relationship to well-described oscillations of the microcirculation.
  
  
  METHODS
  An IR camera was positioned 30-60 cm above the exposed kidneys. Images (3-5 mum wavelength) were collected (1.0/s) at baseline, during warm renal ischemia, and during reperfusion. Dominant frequency (DF) of the tissue temperature fluctuations were determined by a Fourier transformation (spectral) analysis.
  
  
  RESULTS
  IR images immediately showed which segments of the kidney were ischemic. DF at approximately 0.008 Hz that corresponds to blood flow oscillations was observed in thermal profiles. The oscillations were diminished or disappeared after 25 min of warm ischemia and were recovered with reperfusion in a time-dependent fashion. Oscillations were attenuated substantially in ischemic segments, but not in perfused segments of the kidney.
  
  
  CONCLUSIONS
  The described oscillations can be measured noninvasively using IR imaging in the operating room, as represented by the DF, and may be an early marker of critical renal ischemia.
authors.affiliation: Laboratory of Bioengineering and Physical Science, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Gorbach
authors.forename: Hengliang
authors.initials: H
authors.lastname: Wang
authors.forename: Nadeem N
authors.initials: NN
authors.lastname: Dhanani
authors.forename: Fred A
authors.initials: FA
authors.lastname: Gage
authors.forename: Peter A
authors.initials: PA
authors.lastname: Pinto
authors.forename: Paul D
authors.initials: PD
authors.lastname: Smith
authors.forename: Allan D
authors.initials: AD
authors.lastname: Kirk
authors.forename: Eric A
authors.initials: EA
authors.lastname: Elster
mesh_terms: D058186:Acute Kidney Injury / Q000175:diagnosis*; D000818:Animals; D005260:Female; D005583:Fourier Analysis; D006940:Hyperemia / Q000175:diagnosis; D007511:Ischemia / Q000175:diagnosis*; D007668:Kidney / Q000473:pathology*; D008297:Male; D015424:Reperfusion; D013552:Swine; D013817:Thermography; D014022:Tissue Survival