Biomedical subjects

Thomas A Krouskop

Publications and source records attributed to Thomas A Krouskop.

11 recordsLinked to original sources

PubMed2006

Signal-to-noise ratio, contrast-to-noise ratio and their trade-offs with resolution in axial-shear strain elastography.

In axial-shear strain elastography, the local axial-shear strain resulting from the application of quasi-static axial compression to an inhomogeneous material is imaged. In this paper, we investigated the image quality of the axial-shear strain estimates in terms of the signal-to-noise ratio (SNR(asse)) and contrast-to-noise ratio (CNR(asse)) using simulations and experiments. Specifically, we investigated the influence of the system parameters (beamwidth, transducer element pitch and bandwidth), signal processing parameters (correlation window length and axial window shift) and mechanical parameters (Young's modulus contrast, applied axial strain) on the SNR(asse) and CNR(asse). The results of the study show that the CNR(asse) (SNR(asse)) is maximum for axial-shear strain values in the range of 0.005-0.03. For the inclusion/background modulus contrast range considered in this study (<10), the CNR(asse) (SNR(asse)) is maximum for applied axial compressive strain values in the range of 0.005%-0.03%. This suggests that the RF data acquired during axial elastography can be used to obtain axial-shear strain elastograms, since this range is typically used in axial elastography as well. The CNR(asse) (SNR(asse)) remains almost constant with an increase in the beamwidth while it increases as the pitch increases. As expected, the axial shift had only a weak influence on the CNR(asse) (SNR(asse)) of the axial-shear strain estimates. We observed that the differential estimates of the axial-shear strain involve a trade-off between the CNR(asse) (SNR(asse)) and the spatial resolution only with respect to pitch and not with respect to signal processing parameters. Simulation studies were performed to confirm such an observation. The results demonstrate a trade-off between CNR(asse) and the resolution with respect to pitch.

Acoustics↗

PubMed2006

Resolution of axial shear strain elastography.

The technique of mapping the local axial component of the shear strain due to quasi-static axial compression is defined as axial shear strain elastography. In this paper, the spatial resolution of axial shear strain elastography is investigated through simulations, using an elastically stiff cylindrical lesion embedded in a homogeneously softer background. Resolution was defined as the smallest size of the inclusion for which the strain value at the inclusion/background interface was greater than the average of the axial shear strain values at the interface and inside the inclusion. The resolution was measured from the axial shear strain profile oriented at 45 degrees to the axis of beam propagation, due to the absence of axial shear strain along the normal directions. The effects of the ultrasound system parameters such as bandwidth, beamwidth and transducer element pitch along with signal processing parameters such as correlation window length (W) and axial shift (DeltaW) on the estimated resolution were investigated. The results show that the resolution (at 45 degrees orientation) is determined by the bandwidth and the beamwidth. However, the upper bound on the resolution is limited by the larger of the beamwidth and the window length, which is scaled inversely to the bandwidth. The results also show that the resolution is proportional to the pitch and not significantly affected by the axial window shift.

Algorithms↗

PubMed2005

A method for generating permeability elastograms and Poisson's ratio time-constant elastograms.

The feasibility of imaging the permeability and Poisson's ratio time-constant of porous media was investigated. The study involved the following steps. First, poroelastograms were generated from porous tofu phantoms under sustained compression. The sample materials used for the experiments were previously characterized through independent mechanical measurements. Second, corresponding Poisson's ratio time-constant elastograms were generated by calculating and displaying the decay time-constants of the local Poisson's ratios over the time interval in which the poroelastograms were acquired. Finally, for homogeneous samples, permeability elastograms were generated using the poroelastograms in combination with a previously proposed biphasic theoretical model, under very specific conditions. A comparison between the results obtained using poroelastography and those obtained through independent mechanical measurements suggests that poroelastography may be used for imaging the local time-dependent behavior of poroelastic media.

Computer Simulation↗

PubMed2005

Noise performance and signal-to-noise ratio of shear strain elastograms.

In this paper, we develop a theoretical expression for the signal-to-noise ratio (SNR) of shear strain elastograms. The previously-developed ideas for the axial strain filter (ASF) and lateral strain filter (LSF) are extended to define the concept of the shear strain filter (SSF). Some of our theoretical results are verified using simulations and phantom experiments. The results indicate that the signal-to-noise ratio of shear-strain elastograms (SNRsse) improves with increasing shear strain and with improvements in system parameters such as the sonographic signal-to-noise ratio (SNRs) beamwidth, center frequency and fractional bandwidth. The results also indicate that the amount of axial strain present along with the shear strain is an important parameter that determines the upper bound on SNRsse. The SNRsse will be higher in the absence of additional deformation due to axial strain.

Computer Simulation↗

PubMed2005

A new method for generating poroelastograms in noisy environments.

Poroelastography has been recently introduced as a new elastographic technique that may be used to describe the spatial and temporal behavior of poroelastic materials. The experimental methodology proposed thus far for phantoms and tissues in vitro requires the acquisition of a precompression rf frame, the application of a unit step strain compression to the sample and the acquisition of subsequent post-compression frames from the material. Elastograms and poroelastograms are generated by cross-correlating the sequentially-acquired postcompression frames with the reference precompression frame. The application of poroelastography to tissues in vivo must address the echo decorrelation problems that are encountered due to uncontrolled tissue motion, which may become significant shortly after the acquisition of the precompression frame. In this paper, we investigate the feasibility of performing poroelastography experiments using an alternative experimental scheme. In the proposed experimental methodology, the reference precompression frame is continuously moved while the time interval between the frames that are correlated is kept short. This allows long data acquisition times with simultaneous minimization of the decorrelation due to undesired tissue motion in vivo. We validated this new method using both a step and a ramp compression functions. We performed poroelastographic simulations and experiments in phantoms and in tissues in vivo. The results were compared to those obtained using the traditional acquisition methodology. This study shows that the two methods yield similar results in vitro and suggests that the new method may be more robust to decorrelation noise in applications in vivo.

Arm↗

PubMed2004

The feasibility of using elastography for imaging the Poisson's ratio in porous media.

The feasibility of using elastography for experimentally estimating and imaging the Poisson's ratio of porous media under drained and undrained conditions was investigated. Using standard elastographic procedures, static and time-sequenced poroelastograms (strain ratio images) of homogeneous cylindrical gelatin and commercially available tofu samples were generated under sustained applied axial strain. The experimental data show similar trends to those that were observed in finite-elements simulations, and to those that were calculated from classical theoretical models proposed for biphasic materials with similar mechanical properties. To demonstrate the applicability of elastography to monitor time-dependent changes in nonhomogeneous porous structures as well, preliminary time-sequenced poroelastograms were obtained from two-layer porous phantoms and porcine muscle samples in vitro. The results suggest that elastography may have significant potential for quantitatively mapping the time-dependent mechanical behavior of poroelastic media, which is related to the dynamics of fluid flow and to the elasticity and permeability parameters of the media.

Animals↗

PubMed2004

Telerehabilitation for veterans with a lower-limb amputation or ulcer: Technical acceptability of data.

A study was undertaken to determine the technical acceptability of information available via a customized telerehabilitation system regarding patients with lower-limb ulcers or recent lower-limb amputations receiving care at a Veterans Affairs Medical Center. Among the 54 participants, 57 wounds (39 ulcers, 19 amputation incisions) were evaluated by means of still photographs and skin temperature data sent via ordinary telephone lines. Three experienced clinicians served as raters. Intrarater agreements and McNemar chi(2) tests were assessed between decisions made after telerehabilitation sessions and decisions made by the same rater after in-person sessions. Interrater agreements and kappa coefficients were assessed between two raters for both telerehabilitation and in-person sessions. The intrarater agreement on 57 wounds for the primary rater was 93%, and the McNemar test indicated no significant difference in the ratings (p < 0.63). Interrater agreement on 18 wounds was 78% (kappa = 0.55, p < 0.02) for the telerehabilitation sessions and 89% (kappa = 0.77, p < 0.001) for the in-person sessions. Most qualitative comments by three clinicians on picture quality (54/63 = 86%) and temperature data (39/44 = 88%) were favorable (good to excellent). The information yielded from this study provides evidence that the telerehabilitation system has the potential to present sufficient information to experienced clinicians so they can make informed decisions regarding wound management. The next phase of the study will include in-home trials and improvements in the technology.

Adult↗

PubMed2003

Differences in the compressive stress-strain response of infiltrating ductal carcinomas with and without lobular features--implications for mammography and elastography.

In a previous study, it was noted that in some cases when compressive strains greater than about 5% were applied to tumors removed from the breast, there was an abrupt and irreversible change in the tissue stiffness. The data from that study were further analyzed and infiltrating ductal carcinomas with and without lobular features were selected for additional testing to explore their behavior under compressive strains from 0-10%. Fresh tumor samples were tested using a servo-hydraulic Instron testing machine to apply ramp type displacement loads to the samples. The results show that when strains greater than 5% are applied to the tumor tissue without lobular features, there is an irreversible decrease in the stiffness of the tissue while no such change is noted in the other tumor tissue. The implications for this behavior in making mammographic and elastographic images of the breast were then explored using finite element simulations to determine under what compression conditions could the critical strain threshold be reached in the tumor tissue.

Breast Neoplasms↗

PubMed2003

Under the surface.

Explore the source record for details and available documents.

Bedding and Linens↗

PubMed2002

Comparison of interface pressures in the pediatric population among various support surfaces.

OBJECTIVE: The purpose of this study was to evaluate the interface pressures under the bony prominences of children on several support surfaces to evaluate benefit, in terms of the lowest interface pressures, and cost-effectiveness. DESIGN: A descriptive study design was used. SETTING/SUBJECTS: A convenience sample of 54 healthy children from the community ranging in age from infancy through 16 years was enrolled through advertisements in the hospital newsletter. The study was conducted in the General Clinical Research Center located within Texas Children's Hospital, Houston, Texas. INSTRUMENTS: The instrument used to measure the interface pressures was the Mini-Texas Interface Pressure Evaluator. METHODS: A comparison was done to evaluate interface pressures under the occiput for infants to children younger than 6 years of age and under the occiput, coccyx, and heel for 6- to 18-year-olds. Five surface combinations were used for measurements: a standard hospital bed or crib mattress; mattress with Delta foam overlay; a mattress with a Gel-E-Donut pillow; a mattress with a Delta foam overlay plus Gel-E-Donut pillow; and an Efica low-air-loss bed. RESULTS: The standard hospital mattress yielded the highest interface pressures. The Delta Foam overlay alone or in combination with the Gel-E-Donut pillow produced the lowest occipital pressures in all age groups. The Delta foam overlay produced comparable pressures to the Efica low-air-loss bed when measuring the coccyx and heel interface pressures. CONCLUSIONS: The Delta Foam overlay alone or in combination with the Gel-E-Donut pillow is a cost-effective and therapeutic choice for pressure reduction as demonstrated in this study of healthy children.

Adolescent↗

PubMedDate not supplied

A noncontact wound measurement system.

The instrument described in this manuscript was developed to perform objective, quantitative measurements of wound healing, which will enable service providers to assess, improve, and individualize the treatment given to each wound patient. It was designed to produce measures that will enable the care provider to assess the current state of the wound as well as gain insight into the time course of the wound healing by comparing the series of wound data collected over time. The record provided by the instrument could also assist in legal defense; a need that, unfortunately, cannot be ignored. The system uses a structured lighting pattern captured on a digital photograph of a wound to calculate the area and volume of debrided wounds. We used plaster molds with spherical indentations to represent various wounds to evaluate the precision of the system. Results indicate that when at least 144 of the data points in the picture lie within the wound borders, the surface area and wound volume are repeatable and the precision is within +/-3% of the calculated values based on the geometry of the spherical indentation.

Anthropometry↗