Biomedical subjects
F W Kremkau
Publications and source records attributed to F W Kremkau.
Doppler color imaging. Principles and instrumentation.
DCI acquires Doppler-shifted echoes from a cross-section of tissue scanned by an ultrasound beam. These echoes are then presented in color and superimposed on the gray-scale anatomic image of non-Doppler-shifted echoes received during the scan. The flow echoes are assigned colors according to the color map chosen. Usually red, yellow, or white indicates positive Doppler shifts (approaching flow) and blue, cyan, or white indicates negative shifts (receding flow). Green is added to indicate variance (disturbed or turbulent flow). Several pulses (the number is called the ensemble length) are needed to generate a color scan line. Linear, convex, phased, and annular arrays are used to acquire the gray-scale and color-flow information. Doppler color-flow instruments are pulsed-Doppler instruments and are subject to the same limitations, such as Doppler angle dependence and aliasing, as other Doppler instruments. Color controls include gain, TGC, map selection, variance on/off, persistence, ensemble length, color/gray priority. Nyquist limit (PRF), baseline shift, wall filter, and color window angle, location, and size. Doppler color-flow instruments generally have output intensities intermediate between those of gray-scale imaging and pulsed-Doppler duplex instruments. Although there is no known risk with the use of color-flow instruments, prudent practice dictates that they be used for medical indications and with the minimum exposure time and instrument output required to obtain the needed diagnostic information.
Introduction to transvaginal imaging.
Transvaginal sonography provides improved resolution and avoidance of intervening anatomic structures that can degrade the image. In this article, transvaginal transducers are described and compared with transabdominal transducers. The sagittal and coronal views used in transvaginal sonography are described. Advantages and disadvantages of transvaginal sonography are considered. Safety considerations of the decreased attenuation path to the fetus are dealt with.
Clinical benefit of higher acoustic output levels.
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Biomolecular absorption of ultrasound. III. Solvent interactions.
Absorption coefficients for several biomolecules have been measured to determine the role of solvent interactions in the absorption characteristics of biomolecules at neutral pH. The presence of phosphate buffer ions in aqueous solvent dramatically increases the absorption of small biomolecules (sugars and amino acids). These increases suggest the importance of solvent interactions in absorption. For large molecules (proteins and polysaccharides), buffer ion effects are lessened and the role of solvent interactions is not as clear. Absorptions of hemoglobin are essentially the same in each of five aqueous solvents and are greater in nonaqueous solvents. Solvation interactions may be inhibited by the tertiary structure of globular proteins. Solvation apparently does contribute to absorption in biomolecules along with other physicochemical processes.
Doppler shift frequency data.
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Interlaboratory comparison of ultrasonic attenuation and speed measurements.
A set of test samples, all containing ultrasonically equivalent tissue-mimicking material, was produced and measurements of ultrasonic speed and ultrasonic attenuation coefficients were made at seven laboratories using various techniques. The ultrasonic speed values agree well with one another, having a spread of about 0.3 per cent; thus, speed values for tissue parenchyma appearing in the literature are likely to be accurate. Values of ultrasonic attenuation coefficients agree fairly well with one another, with differences between individual values and the group mean of generally less than 20 per cent of the group mean.
Sonographic terminology: hypoechoic vs. sonolucent.
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Artifacts in ultrasound imaging.
Ultrasound imaging artifacts of acoustic origin relating to resolution, propagation path, and attenuation are reviewed. Lateral and axial resolution limitations are artifactual in nature since a failure to resolve means a loss of detail and two adjacent structures may be visualized as one. Apparent resolution close to the transducer (speckle) is not directly related to tissue texture but is a result of interference effects from the distribution of scatterers in the tissue. Reverberation produces a set of equally spaced artifactual echoes distal to the real reflectors. The mirror image artifact is the presentation of objects that are present on one side of a strong reflector, appearing on the other side as well. Shadowing and enhancement are useful artifacts for determining the nature of masses. Enhancement results from low attenuation objects in the sound path while shadowing results from strongly reflecting or strongly attenuating objects. Additional artifacts include section thickness, refraction, multipath, side lobe, grating lobe, focal enhancement, comet tail, ring down, speed error, and range ambiguity.
Biomolecular absorption of ultrasound: II. Molecular structure.
Measurements of absorption coefficients in several globular and linear proteins yield no correlations of absorption with alpha-helix content or with the number of polypeptide chains in the protein. Removal of all but the primary structure with denaturing agents that convert proteins to random chains causes only small changes in the absorption of globular proteins. Complete denaturing of linear muscle proteins results in large reductions in absorption. Therefore, it is concluded that absorption in globular proteins is insensitive to structural characteristics while in linear proteins it is dependent upon the amount of alpha-helix content. An alternative explanation of the results is that alpha-helix contributes to absorption in both globular and linear proteins but tertiary structure in globular proteins reduces absorption because of inhibited solvent interactions.
A comparison of sector and linear array scanners for the measurement of the fetal femur.
This study was designed to determine whether differences between sector and linear array scanners introduce variability in fetal femur length measurements, used to determine gestational age. Twenty transducers from 15 machines were tested with the manufacturers' approval. Machines were coded to maintain anonymity. Three different sized sections of plastic straws were scanned in a water bath. All measurements were made by the same investigator. Measurements were adjusted to compensate for the difference in sound velocity in water, which introduced a 3.36 per cent error in apparent depth of the image for linear array scanners, and a 3.36 per cent error in apparent depth and length for sector scanners. A large variation in measurements was obtained, although the differences were usually within acceptable limits (approximately 4 per cent). Linear array scanners were found to give similar readings as sector scanners.
Cancer therapy with ultrasound: a historical review.
The 45-year history of research in cancer therapy involving ultrasound may be divided into the four periods of initiation, enthusiasm, pessimism and revival. There have been three approaches to the subject: studies have sought to measure the effects on tumors of a) ultrasound alone; b) ultrasound in combination with radiotherapy, and c) ultrasound in combination with chemotherapy. With the first approach the results have varied. In some cases, decreased growth rates or regressions of tumors have been reported; in other cases, either no effect has been observed or growth has been increased. With the second approach, for some tumors, combined treatment has produced greater effects on tumors than has x-ray alone, whereas in other tumors the addition of ultrasound has produced no change. With the third approach, enhancement of the effects of drugs has been observed in melanoma and mouse tumor cells treated with ultrasound and several anticancer drugs. The mechanism of action in most (but not all) cases has appeared to be absorption heating. The potential of ultrasound to provide local tumor control and to enhance other therapy modes has motivated the current efforts by several groups to further study and understand it actions on malignancies.
Ultrasonic enhancement of cancer radiotherapy.
Ultrasound treatment (1.5 W/cm2, 1.9 MHz, C.W.) for 15 minutes either before or after x irradiation reduced the TCD50 of sarcoma-180 by approximately 40% while similar ultrasound treatment for up to 30 minutes did not reduce the TCD50 of the C3HBA mammary adenocarcinoma. Water bath heating (44.5 degrees C for 15 minutes) after x irradiation reduced the TCD50 of both tumors. Ultrasound alone for up to 30 minutes had no effect on growth or cure rate of either tumor.
Diagnostic ultrasound and its obstetric applications.
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Ultrasonic enhancement of nitrogen mustard cytotoxicity in mouse leukemia.
Mouse leukemia L1210 cells were exposed to continuous wave 2 MHz, 10 W/cm(2) ultrasound for 10 minutes while suspended in nitrogen mustard solution in vitro. Mice subsequently inoculated with these cells had longer survival times than control animals that received cells exposed to the drug but not ultrasound. Without the drug, ultrasound did not alter survival time. Tracer studies revealed increased cellular accumulation of drug under the influence of ultrasound.
Physical principles of ultrasound.
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Mitotic reduction in rat liver exposed to ultrasound.
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The influence of ovarian sonication on fetal development in the rat.
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