In vivo safety study using radiation at wavelengths and dosages relevant to intravascular imaging.

Intravascular photoacoustic (IVPA) imaging can identify native lipid in atherosclerotic plaques in vivo. However, the large number of laser pulses required to produce 3D images is a safety concern that has not been fully addressed. We aim to evaluate if irradiation at wavelengths and dosages relevant to IVPA imaging causes target vessel damage. We irradiate the carotid artery of swine at one of several energy dosages using radiation at 1064 or 1720 nm and use histological evaluation by a pathologist to identify dose-dependent damage. Media necrosis was the only dose-dependent form of injury. Damage was present at a cumulative fluence of 50  J  /  cm2 when using 1720 nm light. Damage was more equivocally identified at 700  J  /  cm2 using 1064 nm. In prior work, IVPA imaging of native lipid in swine has been successfully conducted below the damage thresholds identified. This indicates that it will be possible to use IVPA imaging in a clinical setting without damaging vessel tissue. Future work should determine if irradiation causes an increase in blood thrombogenicity and confirm whether damaged tissue will heal over longer time points.