A new approach based on bidirectional scanning improves the imaging performance of optoacoustic imaging to quasi-isotropic transverse resolution.
Optoacoustic imaging, also called photoacoustic imaging, is an imaging technology based on the photoacoustic effect. It enables high-resolution visualization of optical absorbers in biological tissue at depths beyond the operational limits of optical microscopy. The technique is often performed with one-dimensional transducer arrays, in analogy to ultrasound imaging.
Optoacoustic imaging using linear arrays offers ease of implementation but comes with several performance drawbacks, in particular poor elevation resolution, i.e. the resolution along the axis perpendicular to the focal plane. German researchers now propose a bidirectional scanning approach using linear arrays that can improve the imaging performance to quasi-isotropic transverse resolution.
The new approach consists of performing two linear scans of the same region in perpendicular directions, multiplication of the volumes and taking the square root thereof. The team from Technische Universität München and Helmholtz Zentrum München, German Research Center for Environment and Health in Neuherberg, Germany theoretically derived that the proposed method yields a significantly improved resolution in elevation direction with minor losses in lateral resolution and confirmed this behavior in simulation and experiment.
Comparing the novel method with simple addition of the two scans (2lsA mode) showed that taking the product t-norm of the data is the important step for achieving quasi-isotropic resolution. Multiplication improves the resolution because it suppresses those voxels that do not coincide in the reconstructed volumes of the perpendicular scans.
Besides the significant improvement of the transverse resolution when using the proposed reconstruction technique, the noise is suppressed by the multiplication method. Since noise is uncorrelated in independent datasets it is less likely for noise structures to coincide in both datasets of the bi-directional scan. In addition, arc artifacts, a common issue in backprojection algorithms, are reduced. The novel ability to achieve quasi-isotropic resolution in a planar scanning geometry utilizing rather big detector elements might be of great importance in clinical imaging scenarios where SNR is a crucial factor.
