Objective, real-time, intraoperative assessment of renal perfusion using infrared imaging

Protocol description and initial experience in kidney graft perfusion using infrared thermography

PURPOSE

Protocol description for renal perfusion study using thermographic technology and description of the thermographic and clinical behavior of the transplanted kidneys before and after unclamping.

METHODS

Infrared thermographic images of renal grafts are obtained before kidney reperfusion, 10 min after and just before closing the surgical wound. Thermographic data is evaluated together with the type of graft and donor, cold ischemia time, hypovascularized areas determined by the surgeon during surgical intervention, alterations in vascular flow in postoperative echo-Doppler, time at the beginning of graft function and serum creatinine monitoring during postoperative follow-up.

RESULTS

17 grafts were studied. The mean temperature of the grafts before reperfusion, 10 min after and at the end of the surgery were 18.7 °C (SD 6.27), 32.36 °C (SD1.47) and 32.07 °C (SD1.78) respectively. 4 grafts presented hypoperfused areas after reperfusion. These areas presented a lower temperature compared to the well perfused parenchyma surface using thermographic images.

CONCLUSION

The study of the usefulness and applicability of thermography can allow the development of tools that provide additional objective information on organ perfusion in real time and non-invasive manner. Our protocol and initial results can contribute to provide new evidence. Further analyses should be developed to shed light on the role of this technology.

Radial artery pulse wave velocity: a new characterization technique and the instabilities associated with the respiratory phase and breath-holding

Objective. Pulse wave velocity (PWV) is a key diagnostic parameter of the cardiovascular system's state. However, approaches aimed at PWV characterization often suffer from inevitable drawbacks. Statistical results demonstrating how closely PWV in the radial artery (RA) and the respiration phase correlate, as well as RA PWV evolution during breath-holding (BH), have not yet been presented in the literature. The aims of this study are (a) to propose a simple robust technique for measuring RA PWV, (b) to reveal the phase relation between the RA PWV and spontaneous breathing, and (c) to disclose the influence of BH on the RA PWV.Approach.The high-resolution remote breathing monitoring method Sorption-Enhanced Infrared Thermography (SEIRT) and the new technique aimed at measuring RA PWV described in this paper were used synchronously, and their measurement data were processed simultaneously.Main results. Spontaneous breathing leaves a synchronous 'trace' on the RA PWV. The close linear correlation of the respiration phase and the phase of concomitant RA PWV changes is statistically confirmed in five tested people (Pearson's r is of the order of 0.5-0.8, P < 0.05). The BH appreciably affects the RA PWV. A phenomenon showing that the RA PWV is not indifferent to hypoxia is observed for the first time.Significance.The proposed technique for RA PWV characterization has high prospects in biomedical diagnostics. The presented pilot study deserves attention in the context of the mutual interplay between respiratory and cardiovascular systems. It may also be useful in cases where peripheral pulse wave propagation helps assess respiratory function.

Lung thermography during the initial reperfusion period to assess pulmonary function in cellular ex vivo lung perfusion

BACKGROUND

Thermography is a non-invasive technology to detect low temperatures in poorly circulated areas. In ex vivo lung perfusion (EVLP), lungs are rewarmed to body temperature during the initial 1 h. Currently, the effect of graft thermal changes during the rewarming phase on pulmonary function is unknown. In this study, we evaluated the correlation of lung surface temperature with physiological parameters, wet/dry ratio, and transplant suitability in Lund-type EVLP.

METHODS

Fifteen pigs were divided into three groups: control group (no warm ischemia) or donation after circulatory death groups with 60 or 90 min of warm ischemia (n = 5, each). Thermal images of the lower lobes were continuously collected from the bottom of organ chamber using infrared thermography throughout EVLP.

RESULTS

At 8 min, lung surface temperatures of non-suitable cases were significantly lower than in suitable cases (25.1 ± 0.6 vs. 27.8 ± 1.2°C, P < 0.001), while there was no difference in lung surface temperature between the two groups at 0-4 min and 12-120 min. There was a significant negative correlation between lung surface temperature at 8 min and wet/dry ratio at 2 h in the lower lobes (R = -0.769, P < 0.001, cut-off = 26°C, Area under the curve = 1.0). A lung surface temperature of < 26°C was significantly correlated with poor pulmonary function and transplant non-suitability.

CONCLUSION

A lung surface temperature of ≥ 26°C at 8 min is a good early predictor of transplant suitability in cellular EVLP and might be applicable in clinical EVLP.

Modeling of pre-transplantation liver viability with spatial-temporal smooth variable selection

BACKGROUND AND OBJECTIVE

Liver viability assessment plays a critical role in liver transplantation, and the accuracy of the assessment directly determines the success of the transplantation surgery and patient's outcomes. With various factors that affect liver viability, including pre-existing medical conditions of donors, the procurement process, and preservation conditions, liver viability assessment is typically subjective, invasive or inconsistent in results among different surgeons and pathologists. Motivated by these challenges, we aimed to create a non-invasive statistical model utilizing spatial-temporal infrared image (IR) data to predict the binary liver viability (acceptable/unacceptable) during the preservation.

METHODS

The spatial-temporal features of liver surface temperature, monitored by IR thermography, are significantly correlated with the liver viability. A spatial-temporal smooth variable selection (STSVS) method is proposed to define the smoothness of model parameters corresponding to different liver surface regions at different times.

RESULTS

A case study, using porcine livers, has been performed to validate the efficacy of the STSVS method. The comparison results show that STSVS has the better overall prediction performance compared to the past state-of-the-art predictive models, including generalized linear model (GLM), support vector machine (SVM), LASSO, and Fused LASSO. Moreover, the significant predictors identified by the STSVS method indicate the importance of edges of lobes in predicting liver viability during the pre-transplantation preservation.

CONCLUSIONS

The proposed method has the best performance in predicting liver viability. This 'real-time' prediction method may increase the utilization of donors' livers without damaging tissues and time-consuming, yet imprecise feature assessment.

Real-time kidney graft perfusion monitoring using infrared imaging during pediatric kidney transplantation

INTRODUCTION

Ischemia times in kidney transplantation have shown to be predictive for future graft function. Preservation solutions and anticoagulation protocols have improved the management of pediatric kidney transplantation. Nonetheless, there is no current tool for intra-operative graft monitoring. The aim of this project is to present a novel technique for intra-operative real-time assessment of graft perfusion using a non-invasive infrared camera.

METHODS

Prospectively, the authors included 10 pediatric patients. Surgical procedure followed their institutional protocol. Infrared imaging was captured at graft preparation, vascular anastomosis, unclamping, and at 30 s, 1, 5, and 10 min after unclamping. Analyzed variables included type of transplant, ischemia and procedure times, type of anastomosis, and results of doppler/ultrasound. Postoperative variables included creatinine levels during first 72 h. Any complications were also recorded. Delta analysis was calculated to establish the variation of temperature after unclamping.

RESULTS

Average age at transplant was 9.9 years. Five cases were living donor transplants. Mean overall ischemia time was 395.6 (SD 64.4 min). Two patients had poor graft perfusion after unclamping. Of those, one had torsion of the arterial anastomosis and the other was a graft from a donor that required cardiopulmonary resuscitation for 45 min. Thermal imaging showed a correlation of 0.318 between graft temperature change and creatinine decrease. Cut-off delta for temperature for good reperfusion was above 0.2 at 1 min CONCLUSION: Real-time infrared imaging shows to be a promising option for non-invasive graft perfusion monitoring. Initial results show good correlation between intra-operative temperature changes, graft perfusion, and postoperative graft function.

Comparison between near-infrared fluorescence imaging with indocyanine green and infrared imaging: on-bench trial for kidney perfusion analysis. A project of the ESUT-YAUWP group

BACKGROUND

Infrared thermography (IRT) imaging technology is able to measure surface temperatures in real-time. The aim of our study is to understand whether IRT imaging is a reliable technology for the assessment of kidney-parenchyma perfusion with warm fluids.

METHODS

We used three porcine kidneys as a sample. IRT was compared to Near-infrared fluorescence (NIRF) technology with Indocyanine Green (ICG), X-rays with Contrast medium was used as a benchmark. Each kidney, placed inside an incubator, was perfused with contrast medium by a vascular 6-Fr catheter, to preview the perfusable parenchymal area. 100 mL of saline solution at 45 °C was then administered along a five-minutes time, followed by a second administration of 2/10 diluted ICG solution. A FLIR© C2 IR camera was used to acquire thermal data. During ICG administration, image acquisition was obtained with FireFly technology, with a 0° endoscopic camera. Quantitative variables are described using median and quartiles.

RESULTS

Real-time evaluation by IRT showed that, after five minutes of perfusion, it was possible to highlight the same parenchymal areas as visualized by X-ray. The IR images showed that surface temperature rise was directly reflecting local perfusion with heated saline solution. Analysis of NIRF technology and ICG showed an overlap between the two technologies. In addition to the compared technology, IR provided separate temperature measurement for each pixel in real time. Our findings were replicable on all the three kidneys examined. Higher resolution IR-cameras could provide even more detailed information.

CONCLUSIONS

Although NIRF technology with ICG is providing more image detail, we demonstrated that IRT is capable of detecting kidney parenchyma perfusion with warm fluids. Further studies will show its feasibility in graft re-perfusion assessment during kidney transplant or similar applications.

Reconstruction of Thermographic Signals to Map Perforator Vessels in Humans

Thermal representations on the surface of a human forearm of underlying perforator vessels have previously been mapped via recovery-enhanced infrared imaging, which is performed as skin blood flow recovers to baseline levels following cooling of the forearm. We noted that the same vessels could also be observed during reactive hyperaemia tests after complete 5-min occlusion of the forearm by an inflatable cuff. However, not all subjects showed vessels with acceptable contrast. Therefore, we applied a thermographic signal reconstruction algorithm to reactive hyperaemia testing, which substantially enhanced signal-to-noise ratios between perforator vessels and their surroundings, thereby enabling their mapping with higher accuracy and a shorter occlusion period.

Real-time assessment of renal cortical microvascular perfusion heterogeneities using near-infrared laser speckle imaging

Laser speckle imaging (LSI) is able to provide full-field perfusion maps of the renal cortex and allows quantification of the average LSI perfusion within an arbitrarily set region of interest and the recovery of LSI perfusion histograms within this region. The aim of the present study was to evaluate the use of LSI for mapping renal cortical microvascular perfusion and to demonstrate the capability of LSI to assess renal perfusion heterogeneities. The main findings were that: 1) full-field LSI measurements of renal microvascular perfusion were highly correlated to single-point LDV measurements; 2) LSI is able to detect differences in reperfusion dynamics following different durations of ischemia; and 3) renal microvascular perfusion heterogeneities can be quantitatively assessed by recovering LSI perfusion histograms.

Biological modulation of renal ischemia-reperfusion injury

PURPOSE OF REVIEW

Biological modulation of renal ischemia-reperfusion injury holds the potential to reduce the incidence of early graft dysfunction and to safely expand the donor pool with kidneys that have suffered prolonged ischemic injury before organ recovery.

RECENT FINDINGS

In the current review, we will discuss clinical studies that compare kidney transplant recipients with and without early graft dysfunction in order to elucidate the pathophysiology of ischemic acute allograft injury. We will specifically review the mechanisms leading to depression of the glomerular filtration rate and activation of the innate immune system in response to tissue injury.

SUMMARY

We conclude that the pathophysiology of delayed graft function after kidney transplantation is complex and shares broad similarity with rodent models of ischemic acute kidney injury. Given the lack of specific therapies to prevent delayed graft function in transplant recipients, comprehensive efforts should be initiated to translate the promising findings obtained in small animal models into clinical interventions that attenuate ischemic acute kidney injury after transplantation.

Modified spectrometry (O2C device) of intraoperative microperfusion predicts organ function after kidney transplantation: a pilot study

BACKGROUND

Delayed graft function (DGF) is defined as posttransplantation dialysis within 1 week, which might be associated with impaired long-term graft survival. The aim of our pilot study was to establish the ability of intraoperative spectrometry of allograft microperfusion to predict DGF.

METHODS

Twenty human kidney allografts transplanted from deceased donors were evaluated intraoperatively after reperfusion using modified organ spectrometry (O2C device). We examined hemoglobin oxygen saturation, intravascular amount of hemoglobin, and microperfusion flow/velocity.

RESULTS

Retrospectively, 10/20 (50%) allografts with measurable impairment of cortical hemoglobin oxygen saturation and microperfusion flow/velocity developed DGF. Retrospectively, we found that if the intravascular amount of hemoglobin was increased upon intraoperative measurement, the kidney was prone to develop DGF.

CONCLUSIONS

Spectrometry data predicted DGF. Our results supported the thesis that impaired microperfusion is the key to DGF and might be related to postcapillary endothelial damage or intravascular sludge.

WITHDRAWN: Endothelium in the allograft

The paper entitled "Endothelium in the allograft" by Bryan N Becker et al, which was published online on 9 September 2009, has been withdrawn at the authors' request. Kidney International advance online publication, 9 September 2009; doi:10.1038/ki.2009.333.

Assessment of cadaveric organ viability during pulsatile perfusion using infrared imaging

Assessment of pulsatile perfusion (PP) is limited to measurements of flow (V) and resistance (R). We investigated infrared (IR) imaging during PP as a means for precise organ assessment. IR was used to monitor 10 porcine kidneys during 18 hr of PP in an uncontrolled Donation after Cardiac Death model. An IR camera (Lockheed Martin) was focused on the anterior surfaces of the kidneys. The degree of temperature homogeneity was compared with standard measurements of V and R. IR thermal images correlated with V and R (R=0.92, P<0.001). IR detected an increase in homogeneity during PP by comparing standard deviation differences before and after PP (P=0.002), which was not evident by standard measurements of V and R. Finally, IR assessment allowed for measurement of dynamic changes in perfusion.

Infrared thermal imaging: a review of the literature and case report

Intraoperative Thermal Imaging (ITI) is a novel neuroimaging technique that can potentially locate the margins of primary and metastatic brain tumors. As a result, the additional real-time anatomical and pathophysiological information may significantly contribute to an improved extent of tumor resection. Our objectives in this article are i) to briefly discuss the current status of intraoperative imaging modalities including ITI and ii) to present a case report that evaluates the usefulness of ITI in detection of brain tumor and its margins. In this case report, ITI was used in a patient with a metastatic intracortical melanoma. The thermal profile of the tumor and surrounding normal cerebral cortex were mapped with a ThermaCAM P60 (TCP60) infrared camera by FLIR Systems. The data obtained by TCP60, intra-operatively, revealed a clear demarcation of tumor with significant temperature differences, up to 3.3 degrees C, between the tumor core (36.4 degrees C) and the surrounding normal tissue (33.1 degrees C). Ultrasound and pre-resection MR and CT confirmed the position and size of the metastasis. The volume of the tumor was preoperatively calculated using the CyberKnife software and postoperative volumetric measurement of the tumor residual was calculated by the Gamma Knife software. Our result, along with previously published results of others, suggests that thermal imaging could be used to provide a rapid, non-invasive, and real-time intra-operative imaging.

Thermal oscillations in rat kidneys: an infrared imaging study

A high-resolution infrared (IR) camera was used to assess rhythmicity in localized renal blood flow, including the extent of regions containing nephrons with spontaneous oscillations in their individual blood flow. The IR imaging was able to follow changes in rat renal perfusion during baseline conditions, during occlusion of the main renal artery and during the administration of either saline or papaverine. Concurrent recordings were made of tubular pressure in superficial nephrons. Spontaneous vascular oscillations centred around 0.02-0.05 Hz and approximately 0.01 Hz could be detected reproducibly by IR imaging. Their spectral characteristics and their response to papaverine were in line with tubular pressure measurements. The intensity of and synchrony between thermal signals from different local areas of the kidney may allow, after surgical exposure, non-invasive imaging of functional clusters involved in renal cortical blood flow. Through visualization of the spatial extent of thermal oscillations, IR imaging holds promise in assessing kidney autoregulatory mechanisms.

Renal ischemia in rats: mitochondria function and laser autofluorescence

Ischemia-reperfusion injury is the major cause of organ dysfunction or even nonfunction following transplantation. It can attenuate the long-term survival of transplanted organs. To evaluate the severity of renal ischemia injury determined by histology, we applied laser- (442 nm and 532 nm) induced fluorescence (LIF), mitochondria respiration, and membrane swelling to evaluate 28 Wistar rats that underwent left kidney warm ischemia for 20, 40, 60, or 80 minutes. LIF performed before ischemia (control) was repeated at 20, 40, 60, and 80 minutes thereafter. We harvested left kidney tissue samples immediately after LIF determination for histology and mitochondrial analyses: state 3 and 4 respiration, respiration control rate (RCR), and membrane swelling. The association of optic spectroscopy with histological damage showed: LIF, 442 nm (r2 = 0.39, P < .001) and 532 nm, (r2 = 0.18, P = .003); reflecting laser/fluorescence-induced, 442 nm (r2 = 0.20, P = .002) and 532 nm (r2 = 0.004, P = .67). The associations between mitochondria function and tissue damage were: state 3 respiration (r2 = 0.43, P = .0004), state 4 respiration (r2 = 0.03, P = 0.38), RCR (r2 = 0.28, P = .007), and membrane swelling (r2 = 0.02, P = .43). The intensity of fluorescence emitted by tissue excited by laser, especially at a wave length of 442 nm, was determined in real time. Mitochondrial state 3 respiration and respiratory control ratio also exhibited good correlations with the grade of ischemic tissue damage.

Quantification of in vivo autofluorescence dynamics during renal ischemia and reperfusion under 355 nm excitation

We explore a method to quantitatively assess the ability of in vivo autofluorescence as a means to quantify the progression of longer periods of renal warm ischemia and reperfusion in a rat model. The method employs in vivo monitoring of tissue autofluorescence arising mainly from NADH as a means to probe the organ's function and response to reperfusion. Clinically relevant conditions are employed that include exposure of the kidney to ischemia on the order of tens of minutes to hours. The temporal profile during the reperfusion phase of the autofluorescence intensity averaged over an area as large as possible was modeled as the product of two independent exponential functions. Time constants were extracted from fits to the experimental data and their average values were found to increase with injury time.

Diagnostic Tools for Monitoring Kidney Transplant Recipients

Recent advancements in immunobiology have introduced several new diagnostic tools for monitoring kidney transplant recipients. These have been added to more established tests that, although imperfect, remain important benchmarks of diagnostic utility. Both new and old tests can be characterized with regard to their practicality, and as to whether they detect aberrant function or define the cause of dysfunction. Unfortunately, no current test is both practical and specific to a particular disease entity. Accordingly, the diagnosis of graft dysfunction remains dependent on the proper use and interpretation of many studies. This article reviews the current assays that have been evaluated in the clinic for the diagnosis of renal allograft-related diseases. These are limited to assays based on routinely obtainable samples such as blood, biopsy tissue, and urine. Newer studies are presented, along with more mundane assays, to highlight the practical use of studies regardless of their degree of mechanistic sophistication.

Spectroscopic imaging for detection of ischemic injury in rat kidneys by use of changes in intrinsic optical properties

It is currently impossible to consistently predict kidney graft viability and function before and after transplantation. We explored optical spectroscopy to assess the degree of ischemic damage in kidney tissue. Tunable UV laser excitation was used to record autofluorescence images, at different spectral ranges, of injured and contralateral control rat kidneys to reveal the excitation conditions that offered optimal contrast. Autofluorescence and near-infrared cross-polarized light-scattering imaging were both used to monitor changes in intensity and spectral characteristics, as a function of exposure time to ischemic injury. These two modalities provided different temporal behaviors, arguably arising from two different mechanisms providing direct correlation of intrinsic optical signatures to ischemic injury time.

Assessment of renal ischemia by optical spectroscopy1,2

INTRODUCTION

No reliable method currently exists for quantifying the degree of warm ischemia in kidney grafts before transplantation. We describe a method for evaluating pretransplant warm ischemia time using optical spectroscopic methods.

METHODS

Lewis rat kidney vascular pedicles were clamped unilaterally in vivo for 0, 5, 10, 20, 30, 60, 90, or 120 min; eight animals were studied at each time point. Injured and contralateral control kidneys were then flushed with Euro-Collins solution, resected, and placed on ice. 335 nm excitation autofluorescence as well as cross-polarized light scattering images were then taken of each injured and control kidney using filters of various wavelengths. The intensity ratio of the injured to normal kidneys was compared to ischemia time.

RESULTS

Autofluorescence intensity ratios through a 450-nm filter and light scattering intensity ratios through an 800-nm filter both decreased significantly with increasing ischemia time (P < 0.0001 for each method, one-way analysis of variance). All adjacent and nonadjacent time points between 0 and 90 min were distinguishable using one of these two modalities by Fisher's protected least significant difference.

CONCLUSIONS

Optical spectroscopic methods correlate with warm ischemia time in kidneys that have been subsequently hypothermically preserved. Further studies are needed to correlate results with physiological damage and posttransplant performance.