Mary Ann Riederer-Henderson

Correlation of tissue constituents with the acoustic properties of skin and wound

The purpose of this study was to compare measurements of ultrasound properties of skin and wound tissue with measurements of material properties such as total collagen concentration, acetic acid soluble collagen concentration, water concentration, and morphologic properties. Using a scanning laser acoustic microscope (SLAM), both ultrasonic speed and attenuation coefficient values were obtained for control skin (2-3 cm from the wound), for skin immediately adjacent to wounds (within 0.3 mm), as well as for wound tissue itself. The attenuation coefficient and speed measurements were lowest for wound tissue followed by adjacent skin and then control skin. As the wounds healed there appeared to be an increase in both speed and attenuation coefficient although the wound age at which these increases started and the length of time for which they continued varied from one dog to the next. The precision of duplicate sample measurement of wave speed was +/- 1.7% for control skin, whereas that for attenuation coefficient it was +/- 16%. Both ultrasonic speed and attenuation coefficient were directly correlated with tissue collagen concentration and inversely correlated with tissue water concentration (p less than 0.001). Attenuation coefficient correlated best (r = 0.73) with acetic acid soluble collagen concentration which reflects the changes in collagen taking place during the repair process. These attenuation measurements made at 100 MHz using the SLAM were compared for control skin and wound samples with measurements made at 10-40 MHz using backscatter acoustic techniques (BAT). The tissue samples analyzed by each ultrasound technique were from adjacent locations on the animals.

Ultrasonic assessment of skin and surgical wounds utilizing backscatter acoustic techniques to estimate attenuation

Backscatter acoustic techniques at high ultrasonic frequencies (10-40 MHz) were utilized to investigate the ultrasonic attenuation coefficient of normal skin and the relationship between attenuation and the healing of surgical wounds ranging in age from 9 to 49 days. The attenuation coefficient was calculated with measurements from depths of 0.5 and 1.0 mm, primarily in the reticular dermis. The values for control skin ranged from 6.0 Np cm-1 at 10 mHz to 19.6 Np cm-1 at 40 MHz and a corresponding slope of 0.45 Np cm-1 MHz-1. Wound attenuation initially increased with wound age from approximately 15% of control at day 9 to 30% of control at day 34 but did not continue to increase through day 49. During the same period, however, total collagen (as a percentage of wet weight) increased at a constant rate from approximately 45% of control at day 9 to 70% of control at day 49. Thus the attenuation coefficient in healing wounds over the time period studied may be sensitive to more than total collagen content in the tissue. It may be affected by other competing factors as wounds mature such as intermolecular cross-linking, collagen fiber bundle size, and structural arrangement of fiber bundles or other tissue constituents such as proteoglycans and elastin. The observations that wound integrated attenuation using backscatter techniques over the range of 10-40 MHz substantially increased in early wounds, did not increase beyond day 34, and remained significantly lower than control values over the entire healing period studied are in agreement with the results of an independent study of the same tissue using transmission techniques at 100 MHz.

Biochemical and acoustical parameters of normal canine skin

The scanning laser acoustic microscope (SLAM) at 100 MHz and backscattering acoustic technique (BAT) at 10-40 MHz were used to examine the normal canine skin. Skin specimens from four animals and from four locations on the animal were analyzed biochemically and morphologically as well as acoustically. At 100 MHz, the mean ultrasonic speed obtained with the SLAM was 1632+or-34 m/s and the mean attenuation coefficient at 25 MHz was 13+or-4 Np/cm. The biochemical analyses yielded a collagen concentration of 20+or-2% of the net weight or 65+or-12% of the dried defatted weight and a water concentration of 60+or-3% of the wet tissue.<<ETX>>

Measurement uncertainty assessment of the scanning laser acoustic microscope and application to canine skin and wound

Accuracy and precision were experimentally evaluated for the scanning laser acoustic microscope (SLAM) by measurements on homogeneous liquids of known ultrasonic properties. Using aqueous solutions of bovine serum albumin, the attenuation coefficient accuracy and precision are +or-12% and +or-15%, respectively. Using Dow Corning 710, a silicone oil, the speed accuracy and precision are +or-2.9% and +or-0.4%, respectively. Precision was assessed using duplicate samples of canine skin and wound tissue. The estimated precisions in the measurement of the attenuation coefficient and speed were +or-16% and +or-1.7%, respectively. >

Ultrasonic assessment of skin and wound with the scanning laser acoustic microscope

The ultrasonic attenuation coefficient and speed of canine wound tissue and adjacent skin have been studied at wound ages between 7 and 50 days with the scanning laser acoustic microscope at 100 MHz. Water, total collagen, and acid soluble collagen contents were determined for both wound and skin. Attenuation coefficient and speed were consistently greater for the skin than for the wound. Water content was generally higher and total collagen was generally lower in the wound tissue. Total collagen increased in the wound and its difference between wound and skin decreased with maturation. Attenuation coefficient (A in dB/mm) and speed (c in m/s) were highly significant with both total collagen and water. Mathematically, via least‐squares analysis, A = 1.67C + 6.3, A = − 1.77W + 154, c = 6.5C + 1460, and c = − 5.2W + 1923, where C is the total collagen (as percentage on a wet weight basis) and W is the percent water. [This work supported by NIH AM 21557 and CA 36029.]

Propagation of ultrasound in skin

The scanning laser acoustic microscope (SLAM) at 100 MHz and backscattering acoustic technique (BAT) at 10–40 MHz were used to examine canine skin. Specimens from four animals and from four locations on the animal were analyzed biochemically and morphologically as well as acoustically. The mean collagen and water concentrations were 20% ± 2% and 60% ± 3%, respectively. An analysis of variance of the SLAM data and the biochemical data showed significant animal to animal differences and some differences due to location on the animal. At 100 MHz the mean ultrasonic speed obtained with the SLAM was 1632 ± 34 m/s and the mean attenuation coefficient was 57 ± 10 dB/mm. Using BAT the mean integrated attenuation coefficient was 11 ± 3 dB/mm at 25 MHz (midfrequency range). While the speed values fall within the range of values previously reported for skin, the values for the attenuation coefficient using either SLAM or BAT are considerably higher than would be predicted from literature values at 1–10 MHz. Thus the...

Ultrasonic propagation properties of canine aorta at 100 MHz

A pilot study examining canine aorta investigated the ultrasonic propagation properties as a function of location and orientation along the aorta. Longitudinal, circumferential, intimal, and adventitial sections of canine aorta were taken at seven locations along the aorta from the aortic arch to the iliac bifurcation. Aortic media consists of circumferentially oriented elastin fibers interspersed with a randomly oriented network of fibrils. Over the distance from the heart to the abdomen, the elastin concentration decreases as the collagen concentration increases. The speed is shown to be statistically significant with respect to location and correlates strongly with orientation. The 28 speed values ranged from 1610–1859 m/s with the average being 1662 m/s. On the other hand, the attenuation coefficient is not shown to be statistically significant with respect to orientation but does correlate strongly with respect to location. The 27 attenuation coefficient values ranged from 48.5–131.8 dB/mm with an av...

Estimates of Acoustic Inhomogeneities in Skin from the Variation in Backscatter Efficiency at High Ultrasonic Frequencies

A high frequency pulsed ultrasonic system developed to interrogate skin is wtilized to study frequency dependent backscatter efficiency as a means of characterizing biological tissue. The statistical properties of such signals, windowinq artifacts related to signal processing techniques, and various scattering models are discussed in order present the possibilities and limitations of such measurements. It is shown that in order to detect frequency dependent backscatter fluctuations on the order of those expected from biological tissue, extreme care must be used in choosing a data window and in choosing the amount of variance reduction through averaging techniques. Backscatter from nearly monodisperse size distributions of polystyrene scatterers are analyzed to demonstrate the techniques.