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T Krouskop

Publications and source records attributed to T Krouskop.

11 recordsLinked to original sources
PubMed2006

Elastographic image quality vs. tissue motion in vivo.

Elastography is a noninvasive method of imaging tissue elasticity using standard ultrasound equipment. In conventional elastography, axial strain elastograms are generated by cross-correlating pre- and postcompression digitized radio frequency (RF) echo frames acquired from the tissue before and after a small uniaxial compression, respectively. The time elapsed between the pre- and the postcompression frames is referred to as the interframe interval. For in vivo elastography, the interframe interval is critical because uncontrolled physiologic motion such as heartbeat, muscle motion, respiration and blood flow introduce interframe decorrelation that reduces the quality of elastograms. To obtain a measure of this decorrelation, in vivo experimental data (from human livers and thyroids) at various interframe intervals were obtained from 20 healthy subjects. To further examine the effect of the different interframe intervals on the elastographic image quality, the experimental data were also used in combination with elastographic simulation data. The deterioration of elastographic image quality was objectively evaluated by computing the area under the strain filter (SF) at a given resolution. The experimental results of this study demonstrate a statistical exponential behavior of the temporal decay of the echo signal cross-correlation amplitudes from the in vivo tissues due to uncontrollable motion. The results also indicate that the dynamic range and height of the SF are reduced at increased interframe intervals, suggesting that good objective image quality may be achieved provided only that a high frame rate is maintained in elastographic applications.

Acoustics↗
PubMed2004

Comparing elastographic strain images with modulus images obtained using nanoindentation: preliminary results using phantoms and tissue samples.

Conventional elastography involves quasistatic mechanical compression (external or internal) of the tissue under ultrasonic insonification to obtain radiofrequency (RF) A-lines before and after compression. Cross-correlation of the pre- and postcompression A-lines results in displacement images with axial gradients that produce the strain images (strain elastograms). Though the strain elastograms show structural similarities to the modulus images, they are not related in a simple way to the modulus images because the strains depend on both modulus and geometry of the materials being deformed. Therefore, a quantification of the similarities between the strain and modulus images may enhance the interpretation confidence of strain elastograms in depicting tissue structure. To demonstrate similarities between modulus images and strain elastograms, a feasibility study of using nanoindentation to obtain modulus images of thin slices of tissue and tissue-mimicking phantoms (agar-gelatin mixtures) was performed first, with encouraging results. This was followed by a comparison of modulus images and strain elastograms obtained from the same sample slices. The experimental results indicated that, under certain experimental conditions, it is feasible to perform quantitative comparisons between strain images (using elastography) and modulus images. A good visual, as well as quantitative, correspondence between structures in the modulus and strain images could be obtained at a 3-mm scale.

Agar↗
PubMed2004

A quantitative comparison of modulus images obtained using nanoindentation with strain elastograms.

Tissue stiffness is generally known to be associated with pathologic changes. Ultrasound (US) elastography, on the other hand, is capable of imaging tissue strain, which may or may not be well-correlated with tissue stiffness. Hence, a quantitative comparison between the elastographic tissue strain images and the corresponding tissue modulus images needed to be performed to evaluate the usefulness of elastography in imaging tissue stiffnesss properties. Simulations were performed to demonstrate and quantify the similarities between modulus images and strain elastograms. This was followed by comparing nanoindenter-based modulus images with strain elastograms of thin slices of tissue-mimicking phantoms. Finally, some beef slices, canine prostates, ovine kidneys and breast cancers grown in mice were used to demonstrate the qualitative correspondence between modulus images and strain elastograms. The simulations and the experiments indicated that it is feasible to perform quantitative comparisons between strain images (using elastography) and modulus images on certain tissue structures and geometries. A good quantitative correspondence (correlation values of greater than 0.8) between structures in the modulus and strain images could be obtained at scales equal to or larger than 20 Qlambda (where Q is the quality factor defined as the ratio of the center frequency over the band width and lambda is the wavelength of the US system) modulus contrasts larger than 5, applied strains between 0.5% and 3% and window lengths for computing strain elastograms between 3 Qlambda and 5 Qlambda. The gelatin-phantom experiments showed lower values of correlation (values around 0.5) than with theory and simulations. The decrease in correlation was attributed to the presence of measurement noise in both strain elastography and modulus imaging, an increase of dimensionality of the problem (from 2-D to 3-D), local anisotropy, heterogeneity and nonstationarity. Experiments on real tissue slices showed further decrease in the correlation to around 0.3, possibly due to additional confounding factors such as time-dependent mechanical properties and geometrical distortions in the tissue during imaging. The work presented in this paper demonstrates that there is an intrinsic relationship between strain elastograms and the actual distribution of soft tissue elastic moduli, and bodes well for continued work in the area of elastography.

Algorithms↗
PubMed1999

Elastography: ultrasonic estimation and imaging of the elastic properties of tissues.

The basic principles of using sonographic techniques for imaging the elastic properties of tissues are described, with particular emphasis on elastography. After some preliminaries that describe some basic tissue stiffness measurements and some contrast transfer limitations of strain images are presented, four types of elastograms are described, which include axial strain, lateral strain, modulus and Poisson's ratio elastograms. The strain filter formalism and its utility in understanding the noise performance of the elastographic process is then given, as well as its use for various image improvements. After discussing some main classes of elastographic artefacts, the paper concludes with recent results of tissue elastography in vitro and in vivo.

Animals↗
PubMed1998

Elastographic imaging of low-contrast elastic modulus distributions in tissue.

Elastography is a new ultrasonic imaging technique that produces images of the strain distribution in compliant tissues. This strain distribution is derived from ultrasonically estimated longitudinal internal motion induced by an external compression of the tissue. The displayed two-dimensional (2-D) images are called elastograms. In this paper, it is demonstrated that, when signal-to-noise ratio-enhancing techniques are used, elastography is capable of imaging low-contrast elastic modulus tissue structures with high contrast-to-noise ratios. This is demonstrated using both computer simulations and data obtained from 3 days postmortem ovine kidneys in vitro. The elastograms of such organs suggest that the modulus slowly decays from the renal cortex (RC) to the interior of the renal sinus (RS). Such modulus variation is corroborated by independent measurements of the Young's moduli. It is found that the RC is approximately twice as hard as the interior of the RS. We invoke our previous results on elastographic contrast-transfer efficiency to demonstrate that, at low contrast, the elastogram may be interpreted as a quantitative image of the relative Young's modulus distribution.

Animals↗
PubMed1992

Applying robotic technology to aid people with severe disabilities.

Researchers at Rice University and the Baylor College of Medicine in Houston have developed a prototype robotic aid for people with severe disabilities, with emphasis on low cost, versatility, and ease of use. Using custom software written for the Macintosh¿ line of personal computers and a custom input device that emulates a mouse, a user can command a modified HERO 2000¿ robot to perform simple fetch and carry tasks in a structured indoor environment. Further interaction with the environment is possible using a household appliance controller that is also interfaced to the computer.

Computers↗
PubMed1988

Supine interface pressure in children.

The effectiveness of using 2-inch and 4-inch convoluted foam overlays to protect children from developing pressure sores was investigated in 13 healthy children ranging in age from ten weeks to 13.5 years. Interface pressures were measured under the occipital, sacral, and scapular areas of children as they lay on a standard mattress, then on 2-inch and 4-inch foam overlays. The differences in pressures between the occiput and scapula, occiput and sacrum, and scapula and sacrum were significant (p less than .001), with the highest pressures recorded under the occipital area. Occipital pressures decreased from 45.7mmHg on the standard mattress to 22.3mmHg on the 4-inch overlay in ages 0 to 2, 54.3mmHg to 30.5mmHg in ages 2 to 10, and 78.0mmHg to 42.4mmHg in ages 10 to 14. Sacral pressures were highest in older and larger children, increasing from 17mm Hg in ages 0 to 2 to 34mmHg in ages 10 to 14, and when body surface area was greater than 1m2. These results indicate that the site of greatest pressure changes with increasing age from the occipital area to the sacral area. Therefore, different pressure relief considerations are necessary in treating pediatric patients than in managing pressure under adults.

Adolescent↗
PubMed1987

Salvage of amputation stumps by secondary reconstruction utilizing microsurgical free-tissue transfer.

During a 2-year period, 15 lower and upper extremity amputees were treated by microsurgical free-tissue transfer in an effort to salvage their amputation stumps. Salvage of length and restoration of contour to aid in prosthetic rehabilitation were the two main indications for reconstruction. Included in the 15 transfers were 3 scapular free flaps, 11 latissimus dorsi musculocutaneous flaps, and 1 groin flap. Thirteen of the patients in this group were refitted with prostheses following reconstruction and did well with no pain or skin breakdown of the resurfaced stumps. The follow-up period on these patients averaged 16 months. One patient, in whom the flap succeeded, underwent stump soft-tissue revision and myodesis. One patient, in whom the flap failed, continued to develop recurrent ulceration in his stump. This clinical experience followed an extensive laboratory study of 12 above-knee amputation patients using noninvasive Doppler ultrasound measurements to determine weight-loading and interface-pressure distribution between the stump and the socket of the prostheses and their relation to stump length and circumference.

Adolescent↗
PubMedDate not supplied

Standardizing performance-based criteria for support surfaces.

Due to the sparsity of prospective, controlled, clinical studies on the efficacy of and the lack of standardized information about support surfaces, current literature does not clearly define how these surfaces address patient needs. Standardization would help healthcare professionals make better informed decisions about the use of support surfaces. Standardization would also help researchers design and implement controlled, clinical studies by defining characteristics of surface evaluation, making it possible to replicate research activities. The first step toward standardization is to develop a performance-based set of criteria for classifying these surfaces. With respect to the three purposes identified: comfort, postural control and pressure management, only parameters that can be measured noninvasively, have been considered. The nine parameters are life expectancy of the surface, skin moisture control, skin temperature control, redistribution of pressure, product service requirements, fail safety, infection, flammability, and patient/product friction. Specific guidelines for each of these nine parameters are discussed in depth. With testing and evaluation of support surfaces standardized, clinicians will be able to choose a surface to meet the needs of patients the same way they make other treatment decisions: based on outcomes and the results of controlled, clinical studies.

Beds↗