Application of time-resolved autofluorescence to label-free in vivo optical mapping of changes in tissue matrix and metabolism associated with myocardial infarction and heart failure

Abstract

We investigate the potential of an instrument combining time-resolved spectrofluorometry and diffuse reflectance spectroscopy to measure structural and metabolic changes in cardiac tissue in vivo in a 16 week post-myocardial infarction heart failure model in rats. In the scar region, we observed changes in the fluorescence signal that can be explained by increased collagen content, which is in good agreement with histology. In areas remote from the scar tissue, we measured changes in the fluorescence signal (p < 0.001) that cannot be explained by differences in collagen content and we attribute this to altered metabolism within the myocardium. A linear discriminant analysis algorithm was applied to the measurements to predict the tissue disease state. When we combine all measurements, our results reveal high diagnostic accuracy in the infarcted area (100%) and border zone (94.44%) as well as in remote regions from the scar (> 77%). Overall, our results demonstrate the potential of our instrument to characterize structural and metabolic changes in a failing heart in vivo without using exogenous labels.

Real‐time fiber‐based fluorescence lifetime imaging with synchronous external illumination: A new path for clinical translation

“…The application of autofluorescence measurements in clinical research was boosted by advances in light delivery and collection via fiber‐optic systems, which facilitated the development of optical techniques for non‐ and minimally invasive measurements of tissues, including in endoscopic and catheter procedures . The clinical potential and feasibility of autofluorescence measurements for in vivo clinical diagnosis have been demonstrated in a number of studies, either employing steady‐state , and/or time‐resolved autofluorescence measurements . Steady‐state autofluorescence intensity or emission spectroscopy have been widely employed in clinical diagnostic research and are by far more intensively exploited compared to time‐resolved measurements, mainly due to the simplicity and typically lower cost of the instrumentation involved.…”

Autofluorescence Lifetime Reports Cartilage Damage in Osteoarthritis

“…Single-point time-resolved spectrofluorometer. AFL measurements of human samples were realised using a more compact fibre optic based time-resolved spectrofluorometer previously described elsewhere 22 . The instrument comprises two excitation sources, although for the measurements reported below we only used a 375 nm laser diode (LDH-P-C-375B, PicoQuant GmbH, Germany) that provides ~70 ps optical pulses.…”

Development of Low-Cost Instrumentation for Single Point Autofluorescence Lifetime Measurements

“…Short optical pulses were achieved by fine-tuning the DC current so that the laser diode current was only above threshold for a small fraction of the modulation period. The optical power at the sample was adjusted using neutral density filters in the excitation path and the beam was directed into a fibre-optic probe, identical to that described in a previous study [ 21 ], featuring three optical fibres used to deliver excitation light and fourteen optical fibres used to collect the fluorescence signal. A lens relay directed the emission light used to the photocathode of an uncooled photon counting PMT (PMH-100, Becker and Hickl, Germany) via a band-pass filter (FF03–525/50–25, Semrock, USA) to remove any residual excitation light and to restrict fluorescence detection to the range of wavelengths between 500 to 550 nm.…”

“…Further information can be obtained by fitting fluorescence decay profiles to more complex models [ 7 – 9 ] or using phasor analysis [ 10 , 11 ]. TRFS of autofluorescence has been shown to discriminate between healthy and diseased tissues in the case of different types of cancer [ 12 – 17 ], atherosclerosis [ 18 – 20 ], myocardial infarction [ 21 ] or cartilage degradation [ 22 ]. It may also be applied to engineered tissues [ 23 ] and could provide a useful monitor for bioreactors.…”