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Biomedical subjects

M C Ziskin

Publications and source records attributed to M C Ziskin.

At least 73 records · Page 4Linked to original sources
PubMed1986

Geometric and intensity distortion in echography.

Anatomic structures possessing varying sonic propagation velocities refract ultrasonic beams and create distortions in the sonographic image. The distortions consist of inaccurate positioning of echogenic locations (geometric distortions) and of inaccurate display of ultrasonic intensities (intensity distortions). Artifacts of both types occur in the region distal to a structure of circular cross section with an internal sonic propagation velocity lower than that of its surroundings. In an attempt to better understand these distortions, a model is developed from first principles of the production of sonograms of such a region. Assuming a uniform ultrasonic beam and uniform echogenicity of the surrounding tissue, a mathematical expression has been derived for the intensity of the sound arriving at each point and returning to the transducer. Computer simulations of the resulting sonographic image are provided for visualization. In spite of many simplifying assumptions, this model is shown to be consistent with several known artifacts, and provides insight into the mechanisms of their production.

Computer Simulation↗
PubMed1986

The retrolenticular afterglow: an echo enhancement artifact.

A mathematical model for a sonogram containing a circular object with a sonic speed less than that of its surroundings was constructed. The circular object acts as a lens to the ultrasound beam, which explains the refractive artifacts often observed. An unexpected artifact is also predicted, a region of increased echogenicity, which the authors named the retrolenticular afterglow, since it occurs behind a lens-like structure. An experiment was designed to show the appearance of this artifact occurring distal to an ethyl alcohol-filled cylindrical well in a tissue equivalent phantom.

Gallbladder↗
PubMed1986

Effect of WR-2721 on fetal development in the rat.

The radioprotector WR-2721 has been shown to radioprotect all tissues studied except the central nervous system. However, it has not yet been used to radioprotect the fetus. In this study we determined that [14C]WR-2721 injected into pregnant rats quickly passed the placenta and was concentrated by the fetus. In addition, we evaluated the toxicity of WR-2721 (2.5-600 mg/kg) to pregnant rats and their fetuses during the period of major organogenesis at Days 9, 11, and 14 postconception. Pregnant animals were only slightly more (10%) sensitive (LD50, 580 mg/kg) to WR-2721 than nonpregnant cohort animals (LD50, 640 mg/kg). At concentrations of 50 mg/kg or less there was a small but statistically significant increase in fetal deaths, while at doses greater than 300 mg/kg a larger degree of fetal mortality occurred. Maximal fetal weight loss, to about 84% of control, was found at 500 mg/kg. No changes in head dimensions or gross malformations of the surviving fetuses were detected at any time or concentration. Of all the parameters measured in this study none demonstrated a predilection for any specific period of major organogenesis. The results of this study indicate that while WR-2721 demonstrates a dose-related embryotoxicity it is not teratogenic.

Amifostine↗
PubMed1983

Effect of display format on detectability.

The effects of black-echo (black dots on white background) and white-echo (white dots on black background) display formats on detectability of a wire embedded in an echogenic test object were compared. Trained observers were asked to note the presence or absence of the wire on a randomized series of 528 B scans (264 black-echo and 264 white-echo images), half of which contained a wire. The scans not containing a wire were used as controls. The specificity of the white-echo display (75 per cent) exceeded that of the black-echo display (54 per cent), with statistical significance at the 99 per cent confidence level. There was no measurable difference in sensitivity. These results are explained in terms of principles of visual physiology.

Ultrasonography↗
PubMed1983

Clinical manifestations of the comet tail artifact.

The comet tail artifact appears as a dense tapering trail of echoes just distal to a strongly reflecting structure. This reverberation type of artifact occurs when there is a marked difference in acoustic impedances between an object and its surround. This paper presents a spectrum of comet tail artifacts seen in clinical practice and discusses their usefulness in decision making.

Foreign Bodies↗
PubMed1983

Growth of mammalian multicellular tumor spheroids.

The in vitro growth of small (0.05 to 3 mm diameter) avascular multicellular tumor spheroids from six rodent and two human tumor lines has been analyzed. Surprisingly, the radial increase of multicellular tumor spheroids is linear with time after a brief initial period of geometric growth. These multicellular tumor spheroids are shown to have a constant thickness of proliferative outer crust and of middle nonproliferative but viable mantle. An analytical model for their growth is developed which explains the growth pattern. This constant crust thickness model leads to a progressively diminishing growth fraction as radius increases and should be applicable to such early growth of micrometastases in vivo. The model also provides a procedure for determining cell cycle time.

Animals↗
PubMed1982

Frequency analysis approach to the origin of the first and second heart sounds.

Catheter-tipped micromanometers were used to simultaneously record left ventricular and aortic pressures, and left ventricular and aortic internal phonocardiograms in order to determine if they had a common mode of origin and propagation. Spectrographic analysis showed that even with high-pass filtration the phonocardiogram obtained with a commonly used system (Millar) contained large amounts of energy in the subaudible frequency range (below 40 Hz). It was possible to derive close facsimiles of the phonocardiograms by double differentiation of the corresponding pressure pulse and conversely to derive the pressure pulse by double integration of the phonocardiograms. The propagation velocities of the first heart sound, second heart sound, and the foot of the aortic pressure pulse were found to be similar and were respectively, 4.3 +/- 0.2, 4.6 +/- 0.3, and 4.2 +/- 0.2 m/sec (+/- SE). These data support the concept that the low frequency pressure variations produced by the heart, which predominate in the left ventricular and aortic pressure pulse waveforms, are generated and propagated in the same manner as the high frequency pressure variations, which are the first and second heart sounds.

Animals↗
PubMed1982

Helical fibers in myocardium of dogs change their pitch as they contract.

We have investigated the dynamic relationship between fiber structure and deformation of the epicardium in the canine right ventricle. We have reconstructed this deformation as the motion undergone by groups of three radiopaque markers implanted close together in small epicardial regions. As reported earlier, this motion has a stretch and a rotation component. The stretch relates to shortening in the epicardial segment, whereas the rotation describes how this segment changes orientation during the heart cycle. If one postulates this segment as attached to a myocardial spiral, then one can interpret the systolic shortening of the ventricular axis as a compression of the spiral with decrease in pitch and the diastolic lengthening as an extension with increase in pitch. If one further postulates that the epicardial segment is attached to a right-hand spiral, then decreases in pitch imply local clockwise segment rotations, and increases, local counterclockwise rotations. From the motion of the implanted markers, we have found that a small segment ion the midfree wall of the right ventricle twists first locally clockwise as the ventricular axis shortens and later counterclockwise as the axis lengthens. We conclude that deformation of the epicardium is the result of a helical fiber arrangement that is characteristic of the endocardial half of the wall. Near the apex we observed the segment rotation to be reversed: counterclockwise during systole and clockwise during diastole. This observation implies a left-hand helix, which is the path of the apical epicardial fibers, suggesting that the endocardial half of the wall is no longer predominant here.

Animals↗
PubMed1981

Ultrasonic effects on mammalian multicellular tumor spheroids.

Mammalian multicellular tumor spheroids (MTS), grown in liquid culture medium, 0.23 to 0.32 mm in diameter and consisting of 4,500 to 12,100 cells, were exposed to three ultrasonic machines: a clinical diagnostic device with an emitted intensity of 13 mW/cm2, a therapeutic machine with emitted intensities of 1 to 3.5 W/cm2, and a laboratory emitting 12 to 50 W/cm2. (All intensities are temporal and spatial average.) Four measures of ultrasonic effect on MTS were made: decrease in diameter after treatment, damage to subsequent growth outright kill, and number of cells detached from the MTS. There was no loss in MTS size from diagnostic or therapeutic exposures. None of the exposures from any of the three machines caused any damage to subsequent growth or survival. There was no significant detachment of cells from the MTS by any of the diagnostic exposures (at 13 mW/cm2, out of 40 minutes). With the laboratory machine, a significant number of cells were detached, about 0.02% of the MTS (approximately one cell per MTS) per W/cm2 in a ten-minute exposure. Cells detached by therapeutic exposure increased linearly with exposure. On the average, 1 W/cm2 detaches about 0.5 cells per minute, per MTS, or about 0.006% of the cells in the MTS.

Animals↗
PubMed1979

Radiation measurement with a solid-state-matrix camera.

A solid-state-matrix camera containing 32 X 32 photodiode array served as the output device on an image intensifier tube. The resulting images had poor spatial resolution but permitted precise measurement of x-ray intensity. Transmission differences of 1% were detectable.

Fluoroscopy↗
PubMed1976

Monomer addition as a mechanism of forming peptide cross-links in the cell-wall peptidoglycan of Streptococcus faecalis ATCC 9790.

The relative amounts of radioactively labelled disaccharide-peptide monomers and peptide-cross-linked dimers and trimers found in the peptidoglycan of Streptococcus faecalis ATCC 9790 were compared to the relative amounts to be expected from two different polymerization mechanisms (random condensation and monomer addition). Data from continuously-labeled, exponentially-growing cells are consistent with a monomer addition cross-linking process, not with a random condensation cross-linking mechanism. This conclusion was supported by data obtained from analyses of cells labeled during valine starvation (and wall thickening), recovery from valine starvation, and pulse and pulse-chase labeling of walls from exponentially-growing cultures.

Binding Sites↗
PubMed1975

Computer Diagnosis of Breast Thermograms.

A computer-based technique was developed for the automated diagnosis of breast thermogram. Eighty-five thermograms were digitized and analyzed, and 23 parameters computed for each thermogram. A statistical decision program, based on a linear discriminant analysis technique, classified the thermograms into normal and abnormal categories. The accuracy of classification was evaluated by several techniques and found to be comparable to that of trained thermographers.

Breast Neoplasms↗