Knowledge of the positions of ultrasound transducer elements in a photoacoustic computed tomography (PACT) system is essential for reconstructing high-quality images. Errors in these positions, typically due to manufacturing defects, can degrade the reconstructed image quality perceivably. To overcome this, we present a calibration method for the ultrasound transducer array geometry that is based on the times-of-arrival of point source signals at the array elements. We pose the problem in terms of the speed of sound, the transducer positions, and the point source positions. We reformulate the problem as a linear problem in the transducer coordinates by obtaining the other unknowns using surrogate methods. Finally, we estimate the transducer coordinates using the pseudoinverse solution and characterize the estimation error in the coordinates. We use our method for calibrating an experimental PACT system, which results in an improvement in the contrast-to-noise ratio and resolution of point source reconstructions. Additionally, we reconstruct the images of a healthy human breast and show that the calibrated image reveals vasculatures that were previously not visible.
We present photoacoustic computed tomography through an ergodic relay (PACTER), a method for single-shot 3D imaging of hemodynamics using a single-element detector. Our approach allows for ultrafast volumetric imaging at kilohertz rates without the need for numerous detector elements. We demonstrate PACTER in both human and small animal subjects, emphasizing its potential utility in early detection and monitoring of peripheral vascular diseases. Our single-element detector design aims to offer a more convenient and potentially affordable option, while the concept could also be relevant to other imaging technologies, contributing to various applications in medical imaging.
At present, there is no reliable non-invasive imaging modality accepted as the routine method to assess response to neoadjuvant chemotherapy (NAC). Using photoacoustic computed tomography (PACT), we imaged breast cancer patients at three time points: before, during, and after NAC. We measured the tumor size, blood vascular density, and irregularity in the distribution and morphology of the blood vessels on PACT. We used these measurements to accurately identify response to NAC as confirmed by the histopathological diagnosis. We demonstrate PACT’s near-term potential as a diagnostic tool for assessing breast cancer response to systemic treatment by non-invasively measuring the changes in cancer-associated angiogenesis.
We introduce a three-dimensional photoacoustic computed tomography (3D-PACT) system with unparalleled imaging depth, clarity, and speed, and demonstrate that the imaged structural and functional optical contrast provide a unique tool for preclinical research and an appealing prototype for clinical translation. 3D-PACT allows for multipurpose imaging of biological tissues ranging from the rodent brain to the human breast. In the rat brain, we visualized whole brain vasculatures, oxygenation dynamics, intrinsic functional connectivity, and electrical-stimulation-induced hemodynamics. In the human breast, an in vivo imaging depth of 4 cm has been achieved by scanning the breast within a single breath hold of 10 seconds. 3D-PACT holds a high reliability to reproducibly generate detailed images with a contrast similar to that provided by contrast enhanced magnetic resonance imaging, yet with higher spatiotemporal resolution and without using exogenous contrast agents.
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