Background Ultrasonic backscatter demonstrates a cardiac cycle–dependent modulation. The exact mechanism of the modulation is under debate. The objective of the present study was to test the hypothesis that a change in size and configuration of myofilaments from systole to diastole alters acoustic propagation properties and backscatter. 

Methods and Results In vivo measurements were made of integrated backscatter at 5 MHz (IBR5), followed by in vitro measurements of ultrasonic attenuation, speed, and heterogeneity index using a scanning laser acoustic microscope at 100 MHz. Studies were performed in canine hearts (16) arrested in systole (8) with calcium chloride or arrested in diastole (8) with potassium chloride. Sarcomere length was measured with a calibrated eyepiece on a Ziess microscope. Wall thickness was measured with calipers. The attenuation coefficient of 220±34 dB/cm during systole was significantly higher than the coefficient of 189±24 dB/cm during diastole ( P <.01); the IBR5 of −44.7±1.2 dB during systole was significantly greater than the IBR5 of −47.0±1.0 dB during diastole ( P <.01); the ultrasonic speed of 1591±11 m/s during systole was higher than the speed of 1575±4.2 m/s during diastole ( P <.01); and the heterogeneity index of 7.4±1.8 m/s during systole was significantly lower than the index of 9.0±2.0 m/s during diastole ( P <.02). The sarcomere length of 1.804±0.142 μm during diastole was significantly higher than the length of 1.075±0.177 μm during systole ( P <.01). Wall thickness was significantly greater during systole than during diastole (20±3 versus 9±3 mm, P <.01). 

Conclusions Ultrasonic backscatter and propagation properties are directly related to sarcomere length and myocardial thickness and may be responsible for cardiac cycle–dependent variation in backscatter.

Relation of Ultrasonic Backscatter and Acoustic Propagation Properties to Myofibrillar Length and Myocardial Thickness

A new system and method for characterizing biological tissues in vitro and liquids in the VHF and UHF ranges is described. Bulk acoustic properties such as the sound velocity, attenuation, acoustic impedance, and density are determined in reflection and transmission modes, with the biological tissue/liquid specimen sandwiched between the parallel surfaces of synthetic silica glass buffer rods having ZnO piezoelectric film transducers on their opposite ends. The method is an ultrasonic transmission line comparison method wherein the reference medium is distilled water, for which all acoustic properties are known. Measurement errors due to diffraction losses in the acoustic media and to mode conversion at the buffer/sample interfaces are corrected. Special techniques for achieving precise parallelism between the two rod surfaces, for movement to adjust the gap distance, and for signal processing are employed in order to obtain high measurement accuracy. Attenuation and reflection coefficients are determined using the gated pulse echo method. The sound velocity is determined with the gated pulse interference method by sweeping the ultrasonic frequency, or by changing the gap distance. Results of measurements on castor oil, cottonseed oil, silicone oil, and bovine liver, in the frequency range from 10 to 500 MHz, are presented and compared with results of earlier reports.

VHF/UHF range bioultrasonic spectroscopy system and method

Background Identification of viable but stunned myocardium remains a major problem. Since stunned myocardium results in impairment of myocardial function without any structural damage and infarcted myocardium causes major structural disruption, we postulated that acoustic properties could distinguish between the two insults. 

Methods and Results Anesthetized open-chest dogs underwent a total occlusion of the left anterior descending coronary artery for 15 minutes (stunned, n=7) and 90 minutes (infarcted, n=8), followed by reperfusion for 3 hours. Circumflex coronary artery perfusion territory (n=15) served as normal control tissue. Regions of myocardium were quantitatively evaluated with a scanning laser acoustic microscope operating at 100 MHz and a research ultrasound system operating at 4 to 7 MHz. Four ultrasonic parameters were determined: attenuation coefficient (an index of loss per unit distance), speed of propagation, a spatial variation of propagation speed called the heterogeneity index (HI), and ultrasonic backscatter at 5 MHz (IBR5). Myocardial water, lipid, and protein contents of normal, stunned, and infarcted myocardium were also determined. The attenuation coefficient of normal myocardium (179±20 dB/cm) was significantly greater than that of stunned (136±7 dB/cm, P <.001) and infarcted (130±8 dB/cm, P <.001) myocardium. The propagation speed of normal myocardium (1597±6 m/s) was similar to that of stunned (1600±6 m/s) and significantly higher than that of infarcted (1575±7 m/s, P <.001) myocardium. The HI for specimen thicknesses of 75 to 100 μm showed an increase of 33% between normal (5.0±0.8 m/s) and stunned (7.5±2.3 m/s, P <.05) myocardium. However, for the infarcted myocardium (5.8±2.0 m/s), the HI was essentially the same as that of the normal myocardium (5.0±0.8 m/s). The IBR5 of normal (−47.1±1.0 dB) was not significantly different from that of stunned myocardium (−46.8±0.9 dB). The IBR5 of infarcted myocardium (−42.4±1.0 dB) was significantly greater than that of normal myocardium. Myocardial water and protein contents were similar in the normal and stunned myocardium. Water content in the infarcted myocardium (80.8±2%) was significantly greater ( P <.05) than in the normal (72.7±1.3%), and protein content of 18.5±0.7% was significantly lower ( P <.05) than the normal (21.4±0.8%). Lipid content was increased in the stunned (8.5±0.5%) and virtually absent in the infarcted myocardium (0.8±0.3%) compared with normal (5.5±0.6%). 

Conclusions We conclude that acoustic propagation properties can identify stunned and infarcted myocardium and may be related to biochemical/morphological differences.

Acoustic Propagation Properties of Normal, Stunned, and Infarcted Myocardium Morphological and Biochemical Determinants

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 < 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.

/pdf/correlation-of-tissue-constituents-with-the-acoustic-263j9lhl79.pdf

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

Ultrasonic assessment of skin and wounds with the scanning laser acoustic microscope.

Abstmct-An important ultrasonic propagation property for tissue characterization is the speed of sound. The scanning laser acoustic microscope (SLAM) provides the capacity to determine the speed of sound in tissue specimens or portions of specimens on the submillimeter scale. This capability potentially can be utilized to develop indices that quantify the spatial gradient of the tissue’s speed of sound. An automated technique for determining the speed of sound using the SLAM has been developed. It is now possible to study quantitatively the degree of tissue heterogeneity from SLAM measurements of the speed of sound distribution. T

Spatial Distribution of the Speed of Sound in Biological Materials with the Scanning Laser Acoustic Microscope

The fundamental examination of biological tissue with ultrasound can lead to important diagnostic capabilities. In order to quantify tissue characteristics with ultrasound, the ultrasonic propagation properties of normal and pathological tissues must be characterized and cataloged. An important ultrasonic property is the speed of sound for characterizing tissue [1]. In this work, the Scanning Laser Acoustic Microscope (SLAM) is used to measure the spatial variation of the speed of sound in tissue, thereby providing a quantitative ultrasonic parameter for tissue characterization.

P. M. Embree

Papers

Spatial Distribution of the Speed of Sound in Biological Materials with the Scanning Laser Acoustic Microscope

Ultrasonic velocity spatial distribution analysis of biological materials with the scanning laser acoustic microscope.