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.

• MeSH
• algoritmy MeSH
• design vybavení MeSH
• fantomy radiodiagnostické MeSH
• financování organizované MeSH
• kalibrace MeSH
• měniče MeSH
• počítačová simulace MeSH
• počítačové zpracování signálu MeSH
• reprodukovatelnost výsledků MeSH
• teoretické modely MeSH
• ultrasonografie normy   přístrojové vybavení   MeSH

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

The contribution presents some results obtained on the way to checking (and partly complementing) the standard reconstruction procedures in USCT by wave-equation based simulations. Mathematical models emerging from the transparent physical background for both the surrounding fluid and the object tissue are presented, followed by the present results of developing a realistic original finite-element-method based simulation. With respect to the need of comparison with the calibration measurements, a preliminary optimization of initial guesses to boundary conditions at the transducer array is discussed, based on a point-source model. The computational requirements of the procedures are also mentioned together with concrete examples of achieved results.

• MeSH
• automatizované zpracování dat MeSH
• financování organizované MeSH
• teoretické modely MeSH
• ultrasonografie MeSH

The contribution deals with the first step in using proper wave-equation based ultrasound propagation model in image reconstruction from the ultrasonic computed tomography data. Particularly, it compares the transducer calibration results obtained via direct measurement of the empty image field and consequential data processing based on a simple direct-propagation model with the simulation results obtained via solving the single-frequency wave equation under proper border conditions reflecting the realistic measurement geometry. The results show a reasonable qualitative agreement when a certain degree of phase-shifted coupling from the transmitting transducer elements to the neighbouring elements of the transducer field is admitted.

• MeSH
• algoritmy MeSH
• financování organizované MeSH
• interpretace obrazu počítačem metody   normy   MeSH
• kalibrace MeSH
• měniče MeSH
• radiační rozptyl MeSH
• reprodukovatelnost výsledků MeSH
• senzitivita a specificita MeSH
• ultrasonografie normy   přístrojové vybavení   MeSH
• vylepšení obrazu metody   normy   MeSH
• Publikační typ
• hodnotící studie MeSH
• srovnávací studie MeSH
• validační studie MeSH
• Geografické názvy
• Česká republika MeSH