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Biomedical subjects

B Krasner

Publications and source records attributed to B Krasner.

11 recordsLinked to original sources
PubMed1993

Vector quantization distortion of medical ultrasound features.

Pruned-tree structured vectored quantization (PTSVQ) was applied to the lower five gray scale remapped bits of normal and fatty ultrasound liver images. The upper bits were compressed reversibly. This combination of techniques is termed PTSVQ with splitting. The effect of the compression on the difference in texture between normal and fatty liver images was studied at different compression rates and distortions. The changes in texture were measured by changes in the principal components of the covariance matrix of image vectors. The vectors were the same size as those used in the compression technique. There were clear differences in the components of normal and fatty liver images. These differences were largely removed by the PTSVQ with splitting technique even at average single pixel distortions several times smaller than the image noise. These results suggest that the effect of compression on second order statistics should be measured when evaluating algorithms in addition to the first order average distortion.

Fatty Liver↗
PubMed1992

A comparison of case retrieval times: film versus picture archiving and communications systems.

One of the advantages that a picture archiving and communications system (PACS) is supposed to provide over a film-based operation is improved performance in retrieving images. Although it seems self-evident that this should be so, this experiment was intended to verify this and to provide some time comparisons for the two methods. The experiment consisted of randomly selecting ultrasound and computed tomography cases and determining how long it took to retrieve files at a PACS workstation or in person from the file room. To simulate actual retrieval volumes, a total of 40 cases from current to 6 months old, 20 cases from the past year, and 10 cases more than 1 year old was selected. Results indicate that PACS retrieval can indeed be faster than file room retrieval. However, the difference is less for recent cases than for older cases. For cases 6 or fewer months old, the workstation retrieval was approximately 2.5 minutes faster per case than the film file room. This time difference increased markedly when extended to the 1-year and older-than-1-year groups. This report details the results of this study and provides information about the reliability of the two archives.

Filing↗
PubMed1984

The relationship between ATP hydrolysis and active force in compressed and swollen skinned muscle fibers of the rabbit.

We investigated whether the inhibition of force generation observed in compressed muscle fibers is accompanied by a coupled reduction in hydrolytic activity. Isometric force and rates of ATP hydrolysis (ATPase) were measured as functions of the relative width of chemically skinned skeletal muscle fiber segments immersed in relaxing (pCa greater than 8) and activating (pCa 4.9) salt solutions. Osmotic radial compression of the fiber segment was produced (with little or no affect on striation spacing) by adding Dextran T500 to the bathing media. ADP as a product of ATP hydrolysis in fibers undergoing 10-15 min contractions was measured using high pressure liquid chromatography. Compression of the (initially swollen) fiber segment with dextran produced a slight (4%) increase in average active force and then, with further compression, a sharp decrease (with maximum around in situ width). With compression, the average ATPase of the fiber decreased monotonically, and with extreme compression (with 0.22 g dextran per ml), ATPase fell to a fifth of its level determined in dextran-free solution while force was abolished. The time course of active force development was described by the sum of two exponential functions, the faster of which characterized the rate of rise. Fiber compression (0.14 g dextran per ml) reduced the rate of rise of force ten-fold compared to that in dextran-free solution. Hindrance of cross movement is proposed to account for the inhibition of active force generation and (coupled) ATPase in compressed fibers.

Adenosine Triphosphatases↗
PubMed1982

Force and ATPase rate in skinned skeletal muscle fibers.

Measurements of ATPase, force, and their ratio in chemically and mechanically skinned segments of muscle fibers provide a measure of steady-state kinetics of actomyosin interactions under force-generating conditions and thereby provide unique chemomechanical information. Preparations in which nonactomyosin ATPases are inhibited are available. The ratio of steady-state ATPase to steady-state isometric force (tension cost) was not altered significantly at different degrees of activation of contraction by Ca2+ or by shrinking the fiber lattice progressively to reduce force to zero. A fivefold decrease in tension cost was measured at low MgATP concentrations; data indicate either a decreased cross-bridge cycling time or an increased force per cross-bridge.

Actomyosin↗
PubMed1979

Nonparallel isometric tension response of rabbit soleus skinned muscle fibers to magnesium adenosine triphosphate and magnesium inosine triphosphate.

The isometric tension response of single "skinned' rabbit soleus muscle fibers to MgATP and McITP in the absence of calcium was studied. [MgATP] or [MgITP] was varied in solutions of ionic strength 0.30 and temperature 20 degrees C. Steady-state tension that developed in MgATP or MgITP solutions was a biphasic bell-shaped function of log [MgATP] or log [MgITP] which increased from zero to maximum tension and then declined again to zero. Analysis of the data showed that, under comparable ionic conditions, percent tension vs. log [MgATP] and percent tension vs. log [MgITP] curves are not parallel. Instead, the percent tension vs. log [MgITP] curve is much broader. Additionally, under comparable ionic conditions maximum tension in MgITP solutions was higher than in MgATP solutions. In addition, in MgATP solutions, pH, [K+], and excess ATP were varied. Raising pH from 7 to 8, [K+] from 46 mM to 200 mM, or decreasing excess ATP from 2 to 0.5 mM all increased maximum tension. None of these factors, however, influenced the shape or position of the percent tension vs. log [MgATP] curve.

Adenosine Triphosphate↗
PubMed1975

Disruption of the sarcolemma of mammalian skeletal muscle fibers by homogenization.

A new method has been developed for mechanically disrupting the sarcolemma of mammalian sketletal muscle fibers (sarcolemma nonfunctional). Single fibers were produced from small pieces of the soleus muscle of the rabbit by gentle homogenization in a relaxing solution in a tissue homogenizer. These fibers were found to be longitudinally intact, with a sarcomere spacing of approximately 2.1 mum, permeable to large molecules of 10,000 MW, sensitive to the chemical stimuli that cause Ca2+ to be released from the sarcoplasmic reticulum, and responsive to Ca2+ in the same manner as frog fibers skinned in the traditional manner. The single fibers were mounted in a tension transducer and steady-state tensions were recorded in test solutions of different Ca2+ concentrations. The data did not differ statistically from data similarly obtained in identically prepared fibers that, in addition, we had longitudinally split in half to ensure disruption of the sarcolemmal barrier to the diffusion of ions.

Animals↗
PubMedDate not supplied

MR imaging using a rampable system.

A series of cranial images obtained at three magnetic field strengths in a volunteer on a fast ramp magnetic resonance system is presented. This study was undertaken in the space of 5 h.

Brain↗