Editors' ChoiceOPTICAL DIAGNOSTICS

Photoacoustic imaging sounds the alarm on liver fibrosis

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Science Translational Medicine  23 Nov 2016:
Vol. 8, Issue 366, pp. 366ec186
DOI: 10.1126/scitranslmed.aal2794

Liver fibrosis is a "silent" disease. Repeated liver injury can develop without symptoms for decades before detection. This progressive scarring can be caused by inflammatory processes related to hepatitis B or C infections, obesity, and long-term alcohol abuse. Although short-term inflammatory injuries to the liver are largely reversible, long-term chronic conditions can drive liver fibrosis toward cirrhosis or even liver failure. Blood tests alone are not reliable for detecting the disease, leaving biopsies as the gold standard for diagnosis. An inexpensive, noninvasive screening method that could be carried out in a physician's office would revolutionize the detection and prevention of liver fibrosis and advanced liver disease. Now, van den Berg et al. describe point-of-care imaging technology that might one day find utility in the clinical diagnosis of liver fibrosis.

The research team made use of the molecular imaging tool known as photoacoustic (PA) imaging to visualize and detect fibrotic conditions. In the PA process, light absorbed by endogenous chromophores, such as hemoglobin, triggers the generation of acoustic waves at ultrasonic frequencies. These waves can be detected using ultrasound (US) transducers to build three-dimensional images. The same transducer can be operated alongside PA for combined standard US imaging.

The authors created an inexpensive handheld PA/US tool based on pulsed light emitting diodes (LEDs), a significant simplification over the standard pulsed laser systems found in most laboratories. Using a mouse model of chronic liver injury, the authors were able to follow the remodeling of the liver tissue and correlate their PA/US findings with gold standard histological parameters of liver fibrosis. This finding proves the potential for such a device in the preclinical setting and hopefully sets the stage for future clinical instruments in the future. Several hurdles will need to be overcome to scale this technology to humans, including improving the delivery of light to the liver and building registration methods to revisit liver locations for long-term monitoring.

P. J. van den Berg et al., Preclinical detection of liver fibrosis using dual-modality photoacoustic/ultrasound system. Biomed. Opt. Express 7, 5081–5091 (2016). [Full Text]

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