In the previous paper [11], a method for geometrical and transducer-time-delay auto-calibration of an ultrasonic computed tomography (USCT) system has been described, aiming at calibration of individual ultrasonic (US) transducer positions. The present contribution describes a novel modification of the method utilizing the particular USCT system concept: the exactly known spatial relations among transducers grouped in each of the transducer array systems (TASes). The algorithms used for the calibration remain based on the principles similar to the global positioning system (GPS) navigation, however, the positions and orientations of complete TASes are calibrated, rather than individual positions of transducers. This way, the number of unknowns is substantially reduced while the number of available equations remains unchanged. Consequently, a solution substantially more robust with respect to measurement noise can be obtained based on this highly overdetermined equation system. The method is capable of calibrating the individual positions of all ultrasonic transducers via their positions in TASes as well as their individual time delays at once during sc. empty measurement, without a need for any particular arrangements, e.g. calibration phantoms.
The contribution presents further results in developing the exact means for simulating the realistic situation in the USCT (ultrasonic computed tomography) imaging system, aiming both at evaluating the approximations used in the existing USCT image reconstruction methods as to their precision and also (in a longer perspective) at iterative improvement of the obtained images via continuum mechanics based feedback. The mathematical models, generalised in comparison with [1], emerging from the transparent physical background, are presented for inhomogeneous media incorporating both the object tissue and the surrounding fluid. The equations are already general enough to employ complex nonlinear phenomena in three-dimensional space; and linearised 3D simulations (giving rise to wave equation, WE) have been performed enabling first conclusions on the feasibility of this approach with respect to the available computing resources. Some of the results of the numerical solution of the WE in 3D by means of the finite-element method show in local detail the diffraction phenomena on acoustic-impedance inhomogeneities. The spatial extent of the simulations is basically limited only by the available computing resources. The hardware requirements and related practical limitations are mentioned together with a few examples of presently available results. Together with conclusions, further perspectives of this branch of the USCT research are suggested.
- MeSH
- algoritmy MeSH
- biologické modely MeSH
- financování organizované MeSH
- interpretace obrazu počítačem metody MeSH
- počítačová simulace MeSH
- refraktometrie metody MeSH
- reprodukovatelnost výsledků MeSH
- senzitivita a specificita MeSH
- tomografie metody MeSH
- ultrasonografie metody MeSH
- vylepšení obrazu metody MeSH
- zobrazování trojrozměrné metody MeSH
This paper presents a method for geometrical and time-delay auto-calibration of an ultrasonic computed tomography (USCT) system. The algorithms used for the calibration are based on the principles similar to the global positioning system (GPS) navigation. Ultrasonic transmitters and receivers in USCT can be viewed like satellite transmitters and mobile receiver units in GPS. However, unlike in GPS, none of the positions of the transmitters or receivers in USCT are assumed to be known and all are the to-be-calibrated unknowns. The presented method is capable of calibrating the positions of all ultrasonic transducers and their individual time delays at once. No calibration phantoms are necessary.
- MeSH
- algoritmy MeSH
- časové faktory MeSH
- design vybavení MeSH
- financování organizované MeSH
- kalibrace MeSH
- počítačová rentgenová tomografie metody přístrojové vybavení MeSH
- počítačová simulace MeSH
- počítačové zpracování signálu MeSH
- reprodukovatelnost výsledků MeSH
- rozpoznávání automatizované MeSH
- statistické modely MeSH
- teoretické modely MeSH
- ultrasonografie metody přístrojové vybavení MeSH
- ultrazvuk MeSH
- zobrazování trojrozměrné metody MeSH
