![Multispectral photoacoustic images of the human placenta. (A)Photograph of the human twin placenta. Ultrasound and photoacoustic imaging were performed at the location indicated with a white dashed line in (A). An ultrasound image of the placenta together with the image outlines are shown in (C and B). Co-registered Photoacoustic images at wavelength of 750 nm and 850 nm are shown in (E) and (F). Photoacoustic images corresponded well to the ultrasound images. Two major blood vessels [v1 and v2 in (B) and (C)] were clearly visible in photoacoustic images. Average photoacoustic amplitudes for regions of interest (v1: ROI v1; v2: ROI v2; background noise: ROI n) indicated in (E)-(F) are compared with the absorption spectra of oxygenated and deoxygenated blood in (D) for wavelengths from 750 nm to 900 nm. The oxygenated and deoxygenated blood spectra are normalized to the measured average photoacoustic amplitudes at 750 nm for comparison. The photoacoustic signal amplitudes are averaged over 15 image frames, the error bars represent standard deviations.](http://wp1.cs.ucl.ac.uk/gift-surg-intranet/wp-content/uploads/sites/14/2015/05/g15944.png)
the human twin placenta. Ultrasound and photoacoustic imaging were performed at the
location indicated with a white dashed line in (A). An ultrasound image of the placenta together with the image outlines are shown in (C and B). Co-registered Photoacoustic images at wavelength of 750 nm and 850 nm are shown in (E) and (F). Photoacoustic images
corresponded well to the ultrasound images. Two major blood vessels [v1 and v2 in (B) and (C)] were clearly visible in photoacoustic images. Average photoacoustic amplitudes for regions of interest (v1: ROI v1; v2: ROI v2; background noise: ROI n) indicated in
(E)-(F) are compared with the absorption spectra of oxygenated and deoxygenated blood in (D) for wavelengths from 750 nm to 900 nm. The oxygenated and deoxygenated blood
spectra are normalized to the measured average photoacoustic amplitudes at 750 nm for comparison. The photoacoustic signal amplitudes are averaged over 15 image frames, the
error bars represent standard deviations.
May 2015
Image guidance plays a central role in minimally invasive fetal surgery, such as photocoagulation of inter-twin placental anastomosing vessels to treat twin-to-twin transfusion syndrome (TTTS). Fetoscopic guidance provides insufficient sensitivity for imaging the vasculature that lies beneath the fetal placental surface due to strong light scattering in biological tissues. Incomplete photocoagulation of anastamoses is associated with postoperative complications and higher perinatal mortality. In this study, we investigated the use of multi-spectral photoacoustic (PA) imaging for better visualization of the placental vasculature. Excitation light was delivered with an optical ber with dimensions that are compatible with the working channel of a fetoscope.
Imaging was performed on an ex-vivo normal term human placenta collected at Caesarean section birth, with the umbilical cord vessels clamped to prevent blood loss. The photoacoustically-generated ultrasound signals were received by an external clinical linear array ultrasound imaging probe. A vein under illumination on the fetal placenta surface was visualized with PA, and good correspondence was obtained between the measured PA spectrum and the optical absorption spectrum of deoxygenated blood.
Wenfeng Xia