Hyperspectral image-based analysis of thermal damage in living liver undergoing laser ablation

Abstract

Laser ablation (LA) is a minimally invasive procedure based on light/tissue interaction aimed to induce a controlled tumor necrosis by increasing tissue temperature. Given the relationship between tissue damage and produced heat, LA needs a fine control of evolving thermal effects in order to evaluate and control procedure outcome. This study relies on biomedical optics principles for non-invasive diagnostic tools development, and presents a contactless approach based on hyperspectral imaging (HSI) to monitor thermal damage during in vivo porcine LA. By collecting relative pixel-by-pixel reflectance/absorbance of a wide range spectrum (500-1000nm), HSI can track molecular structure modifications caused by the thermoablative procedure. Indeed, these modifications alter tissue light scattering and absorption. In order to investigate tissue spectrum change by increasing temperature, HSI was collected at fixed maximum temperatures (37, 60, 70, 80, 90, 100, 110 °C) and immediately after LA (1, 2, 3, 4, and 5 minutes). Tissue spectral response for two tests was analyzed also relying on the ablated area considered. Regions of Interest of different dimensions (16, 77, and 170 pixels) were placed in the images after applying a motion correction. Obtained spectra show noticeable variations once a specific temperature threshold has been reached (80-100 °C). Specifically, the measured absorbance variation for selected wavelengths (630, 760, 960nm, for methemoglobin, deoxyhemoglobin, and water respectively) confirms tissue optical behavior dependence with its thermal state. This preliminary investigation discloses the potential of HSI measurement to characterize LA damage, encouraging future studies to standardize this novel technique.

Hyperspectral Imagery for Assessing Laser-Induced Thermal State Change in Liver

“…For example, the 800–995 nm was set as a single range even though hemoglobin, water and lipid demonstrate optical contributions, especially in the case of fatty live tissues. Nevertheless, a previous work [ 24 ] showed a similar trend for the 800–995 nm thus proving not consistent loss of information in combining the overall data included in the range. This point has been partially confirmed by observing for the global Hgb, W and L range a behavior close to the single water peak measured at 960 nm [ 24 ]: here, the spectral value in the range drops with temperature, and is maintained until the end of the procedure.…”

“…Nevertheless, a previous work [ 24 ] showed a similar trend for the 800–995 nm thus proving not consistent loss of information in combining the overall data included in the range. This point has been partially confirmed by observing for the global Hgb, W and L range a behavior close to the single water peak measured at 960 nm [ 24 ]: here, the spectral value in the range drops with temperature, and is maintained until the end of the procedure. This result is probably attesting the dominance of the water variation in this range during thermal therapy.…”

“…Indeed, previous studies showed changes in optical properties mainly for hemoglobin and water chromophores with temperature increase [ 19 ], thus confirming an insubstantial change for the lipid content. Moreover, the necessity to attempt a more robust analysis based on optical information extracted from multiple wavelengths aimed at minimizing the potential errors was associated with a single wavelength [ 24 ]. Furthermore, considering only four spectral information limits the band number for the analysis.…”

“…Tissue chromophores such as oxyhemoglobin (HbO 2 ), deoxyhemoglobin (Hb), and water (H 2 O) [ 19 ] are sensitive to the temperature of the environment, thus monitoring their spectral variation has the potential to be the basis for design a therapeutic supportive-tool, which can indicate the thermal tissue state [ 20 , 21 ]. In this scenario, hyperspectral imaging (HSI) holds the potentiality of combining spectral and spatial information of the thermal state of the tissue [ 22 , 23 , 24 , 25 ]. The use of HSI is rapidly increasing in the biomedical field, where HSI is devoted to “see the invisible” in several diagnostic and therapeutic applications [ 26 , 27 ].…”

Prospective study for commercial and low-cost hyperspectral imaging systems to evaluate thermal tissue effect on bovine liver samples

“…The experimental outcome shows that the methemoglobin absorption in the thermal region was 40 % more than in the non-ablated regions. 42,43 R.P. Singh-Moon et al developed a near infrared (NIR) spectroscopic catheter for real-time monitoring of tissue reflection during RFA.…”