This work presents initial findings from the first-in-the world clinical trial examining the feasibility of photoacoustic imaging for assessing the quality of kidney transplants.
In the kidney and liver, fibrosis is a powerful predictor of outcomes. Unfortunately, accurate fibrosis quantification cannot be done non-invasively. Photoacoustic (PA) imaging offers the potential for measuring collagen, the principal component of the fibrotic matrix. Here, we demonstrate the potential of PA imaging for fibrosis quantification in preclinical kidney and liver fibrosis models. To induce kidney fibrosis, the left ureter was obstructed for 0 (n = 5), 7 (n = 5) or 14 days (n =5). The right kidneys at each day (n = 15) served as controls. To induce liver fibrosis, carbon tetrachloride (CCl4) injections were given to mice (n = 31). Control mice (n = 12) received corn oil vehicle injections. A PA unmixing algorithm based on the use of the variance inflation coefficient for detecting the multicollinearity of collagen/oxy/deoxyhemoglobin was developed and validated against gold standard histology measurements. The VevoLAZR-X system was used in the 680-930 nm illumination range at 15 MHz. PA imaging revealed 4x more collagen by day 14 post ureteral obstruction compared to sham kidneys. Similarly, PA imaging suggested that fibrotic livers 6 weeks post-CCl4 injection contained about 125% more collagen than control livers. Comparisons with histological gold standards revealed a strong linear correlation (r = 0.89 – 0.99). This work demonstrates the potential of PA imaging to accurately and non-invasively assess fibrotic burden in livers and kidneys. We postulate that this technology will accelerate the preclinical assessment of antifibrotic drugs.
In this work, we present the first time use of photoacoustic imaging for assessing the quality of donor kidneys pre-transplantation. There is a pressing clinical need to quantify the fibrotic (scarring) burden in a non-invasive manner to give clinicians crucial information before they decide whether to accept a donor kidney. Our results in human kidneys show that photoacoustic imaging can be a robust tool for assessing the degree of scarring, an important predictor of post-transplantation clinical outcome.
Ischemic reperfusion injuries (IRIs) occur after blood returns to a tissue or organ after a period without oxygen or nutrients, which causes an inflammatory response leading to heterogeneous scarring of the nearby tissue and vasculature. This is associated with long-term decreases blood flow, and necrosis. Although most commonly associated with heart attacks and strokes, IRIs are also a side effect of organ transplants, when the organ is reperfused in the recipient’s body after being transported from the donor to the transplant hospital. Currently, the optimal method of monitoring for IRI is limited to biopsies, which are invasive and poorly monitor the spatial heterogeneity of the damage. To non-invasively identify changes in kidneys, the left renal artery in mice (n=3) was clamped for 45 minutes to create an IRI event. Both kidneys of each animal were monitored using photoacoustics (PA) with the VevoLAZR system (Fujifilm-VisualSonics, Toronto) three, four and eight weeks after surgery. IRI-treated kidneys show increased picosirius red staining, indicative of collagen (0.601 vs 0.042, p < 0.0001), decreased size as assessed by cross-sectional area (7.8 mm2 vs 35.9 mm2 , p < 0.0001), and decreased oxygen saturation (sO2; 62% vs 77%, p = 0.02). Analysis of the photoacoustic data shows that a two-point metric, the 715:930 nm ratio of the whole kidney (1.05 vs 0.57, p = 0.049) and the optical spectral slope (OSS) (0.8 * 10-3 vs 3.0 * 10-3, p = 0.013) are both able to differentiate between IRI-treated and healthy kidneys. These data suggest that photoacoustics can be used as a non-invasive method to observe in vivo changes in the kidney due to IRI.
Ischemic reperfusion injuries (IRIs) are caused by return of blood to a tissue or organ after a period without oxygen or nutrients. Damage in the microvasculature causes an inflammatory response and heterogeneous scarring, which is associated with an increase in collagen in the extracellular matrix. Although most often associated with heart attacks and strokes, IRI also occurs when blood reperfuses a transplanted organ. Currently, monitoring for IRI is limited to biopsies, which are invasive and sample a limited area. In this work, we explored photoacoustic (PA) biomarkers of scarring. IRI events were induced in mice (n=2) by clamping the left renal artery, then re-establishing flow. At 53 days post-surgery, kidneys were saline perfused and cut in half laterally. One half was immediately imaged with a VevoX system (Fujifilm-VisualSonics, Toronto) in two near infrared ranges - 680 to 970 nm (NIR), and 1200 to 1350 nm (NIR II). The other half was decellularized and then imaged at NIR and NIR II. Regions of interest were manually identified and analyzed for each kidney. For both cellularized and decellularized samples, the PA signal ratio based on irradiation wavelengths of 715:930 nm was higher in damaged kidneys than for undamaged kidneys (p < 0.0001 for both). Damaged kidneys had ROIs with spectra indicating the presence of collagen in the NIR II range, while healthy kidneys did not. Collagen rich spectra were more apparent in decellularized kidneys, suggesting that in the cellularized samples, other components may be contributing to the signal. PA imaging using spectral ratios associated with collagen signatures may provide a non-invasive tool to determine areas of tissue damage due to IRIs.
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