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Circulation. 1995;91:154-160

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(Circulation. 1995;91:154-160.)
© 1995 American Heart Association, Inc.

Articles

Acoustic Propagation Properties of Normal, Stunned, and Infarcted Myocardium

Morphological and Biochemical Determinants

William D. O'Brien, Jr, PhD; Kiran B. Sagar, MD; David C. Warltier, MD, PhD; Theodore L. Rhyne, SCD

From the Department of Electrical and Computer Engineering, University of Illinois, Urbana (W.O'B.); the Division of Cardiology (K.B.S.) and Division of Anesthesia (D.C.W.), Medical College of Wisconsin, Milwaukee; and General Electric Medical Systems Division, Milwaukee, Wis (T.L.R.).

Correspondence to Kiran B. Sagar, MD, Medical College of Wisconsin, Department of Medicine, Division of Cardiology, 8700 West Wisconsin Ave, Box 123, Milwaukee, WI 53226.


*    Abstract
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 *Abstract
down arrowIntroduction
 down arrowMethods
down arrowResults
down arrowDiscussion
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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.


Key Words: ultrasonics • ischemia • myocardium


*    Introduction
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 up arrowAbstract
 *Introduction
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Postischemic ventricular dysfunction, or myocardial stunning, is the mechanical dysfunction that persists after reperfusion despite the absence of irreversible damage. This postischemic dysfunction is a fully reversible abnormality.1 In contrast, postischemic ventricular dysfunction secondary to myocardial infarction or cell death is completely irreversible.2

Identification of viable but stunned myocardium remains a major problem. Ultrasonic tissue characterization analyses are based on the hypothesis that pathological changes of myocardial structure and function result in alterations in the fundamental physical properties of tissue, which can be quantified with ultrasonic propagation property indexes of ultrasonic backscatter, propagation speed, and attenuation. We and others have shown that ultrasonic backscatter can characterize structural and functional abnormalities associated with myocardial ischemic injury and necrosis.3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Characterization of myocardial ultrasonic propagation properties has permitted quantitative delineation of the effects of the duration of ischemia and subsequent reperfusion on the time course of recovery of myocardial contractile function.15 19 20 Ultrasonic propagation properties of a tissue are determined by structural integrity and biochemical constituents such as water, protein, and fat contents of that tissue.21 22 Ultrasonic attenuation, an index of energy loss per unit distance, is dependent on relative concentration of tissue collagen and water. Propagation speed, a measure of the rate at which ultrasound travels through a tissue, is determined principally by the amount of water content. The heterogeneity index (HI), which is a marker for ultrasonic backscatter, reflects spatial variation of ultrasonic speed: the more homogeneous the tissue, the lower the HI and the lower the backscatter. Integrated Backscatter Rayleigh 5 (IBR5), the integrated backscatter Rayleigh spectral intensity measurement, is a measure of the ultrasonic backscatter from the structural components of a tissue and its structural integrity.

Since stunned myocardium is characterized by minimal structural and biochemical abnormalities and infarcted myocardium is associated with cellular disruption and biochemical changes, we postulated that ultrasonic propagation properties will distinguish the two syndromes. This study was designed to determine ultrasonic propagation properties of normal, stunned, and infarcted myocardium and to establish a relation with biochemical constituents and structure of the tissue.


*    Methods
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 *Methods
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General Preparation
Adult mongrel dogs of either sex weighing 15 to 25 kg were anesthetized with pentobarbital sodium (30 mg/kg supplemented with 5 mg · kg-1 · h-1 IV) and ventilated with a respirator (Harvard model 607, Harvard Apparatus). Atelectasis was prevented by maintaining an end-expiratory pressure of 5 to 7 cm water. In eight experiments, induction was achieved with thiamylal sodium (10 mg/kg IV), and anesthesia was maintained with halothane (2.0%) in oxygen (2 L/min) by way of a ventilator (Monoghan model 300 D/M, Monoghan Co). Throughout the experimental procedure, PO2, PCO2, and pH were maintained at physiological levels. Body temperature was controlled at 38°C with a heating pad and servomechanical controller. All procedures were in accordance with institutional guidelines.

Left ventricular pressure was monitored by a pressure transducer–tipped catheter (Millar PC 380, 8F, Millar Instruments) inserted into the left ventricle by way of the left carotid artery. The left ventricular pressure pulse was electronically differentiated to obtain peak positive left ventricular dP/dt. The differentiator was calibrated by means of a triangular waveform of known slope. Phasic and mean aortic blood pressures were recorded by means of a catheter inserted into the right femoral artery, advanced to the ascending thoracic aorta, and connected to a strain-gauge pressure transducer (Statham P50, Gould-Spectromed). The right femoral vein was cannulated for drug administration. A thoracotomy was performed in the left fifth intercostal space, and the lungs were gently retracted. The heart was suspended in a pericardial cradle. The ECG (limb lead II) was monitored, and all hemodynamic variables were continuously recorded on a Grass (model 7) polygraph (Grass Instruments Co).

Regional myocardial contractile function was assessed in the perfusion territories of the left anterior descending (LAD) and left circumflex (LCx) coronary arteries. Percent segment shortening was measured with piezoelectric crystals, details of which have been described previously.23 24

Ultrasonic Backscatter Instrumentation and Data Analysis
Ultrasonic backscatter was measured in vivo with a research instrument used in previous studies.14 24 The myocardium was examined with a water-filled fixture that contained an unfocused circular transducer, 6 mm in diameter, which was maintained {approx}18 mm from the epicardial surface. The specular echoes at the endocardial and epicardial surfaces were avoided by range-gating the echoes at the midmyocardium. The prototype obtained echo signals having a 0.5-µs resolution and a uniform spectrum over a bandwidth extending from 4.0 to 6.5 MHz. The data were synchronized with the QRS complex by a digitized ECG waveform. Backscatter echoes were obtained at evenly spaced intervals within the cardiac cycle over 16 cardiac cycles, and data were stored for later analysis.

According to previous methods,14 24 the echoes were adjusted by use of transducer calibration data25 and further adjusted for the frequency effects of tissue absorption, diffraction, and power-law scattering, resulting in measurements of absolute reflectivity integrated over the frequency spectrum from 4.0 to 6.5 MHz. This is the IBR5, referred to 5 MHz, and represents an absolute measure of the backscatter in square centimeters of reflecting surface per cubic centimeter of volume.26 The IBR5 was calculated for selected ranges and expressed in decibels per centimeter.

Scanning Laser Acoustic Microscope
A scanning laser acoustic microscope (SLAM) (Sonomicroscope 100, Sonoscan, Inc), operating at an ultrasonic frequency of 100 MHz, was used to determine the attenuation coefficient, propagation speed, and HI of the specimen. Operational details of the SLAM have been published previously.26 27 28 29 30 31 The SLAM produces an acoustic image, from which the attenuation coefficient is determined; an interference image, from which the speed and HI are determined; and an optical image for reference purposes. All three images are displayed in real time on a standard television monitor representing a specimen area approximately 3 mm horizontally by 2 mm vertically (typically x100).

Attenuation Coefficient
An insertion loss procedure is used to estimate the attenuation coefficient, which is a measure of energy loss per unit distance (dB/cm). The insertion loss procedure compares the received signal amplitude of the specimen of known thickness in the sound path with that of the reference medium, normal saline,12 15 within a subimage area of approximately 400x250 µm (96 pixels horizontally by 32 pixels vertically). The signals received from the subimage area are digitized to yield an average amplitude value (V). A minimum of five V values are recorded for normal saline, the reference medium. The specimen is then moved into the subimage area, and a minimum of three values of V are recorded at each of five separate specimen locations. An insertion loss (IL) value, in decibels, is estimated from the difference between the average of the V values recorded from normal saline and the individual V values from the specimen. This process yields five IL values for each specimen thickness. Eight specimen thicknesses ranging from 75 to 400 µm are used, and the slope of IL versus specimen thickness, via a linear least-squares fit (using all 40 IL-thickness values), yields the attenuation coefficient.

Speed
The propagation speed, in meters per second, is estimated by the horizontal shift of the fringe lines relative to where the fringe lines would be without the specimen, that is, relative to the reference medium (known speed value).28 30 From the interference image, basically each interference line is digitized and processed, yielding a vertical (relative to the image orientation) speed profile. For each sample, eight specimen thicknesses are analyzed, each group of eight yielding a mean speed value from the speed profile region within the specimen. The individual mean speed values are then averaged to yield the ultrasonic speed of that sample.

Heterogeneity Index
The HI represents an estimate of the spatial distribution of the ultrasonic speed.27 Specifically, the SD of the spatial speed distribution is the estimate of the HI of the specimen at the specified thickness. The values of the HI possess an inverse function of the thickness. Therefore, two separate HI values are reported, one that averages the 75- and 100-µm HI values and another that averages the 200- and 250-µm HI values, which are denoted "HI <75-100 µm>" and "HI <200-250 µm>," respectively.

Reproducibility
The uncertainty of the estimates of attenuation coefficient and speed from the SLAM have been assessed for solutions of known acoustic properties and duplicate samples of skin and healing wound tissue.30 With a homogeneous medium, the accuracy (proximity to the true value) was ±2.9% and the precision (reproducibility of successive independent measurements) was ±0.4% for speed; and for attenuation coefficient, accuracy and precision were ±12% and ±15%, respectively. With heterogeneous samples of normal canine skin and wound tissue, the speed and attenuation coefficient precision were ±1.7% and ±16%, respectively. It is important to note that there are no known independent standards for attenuation coefficient of biological materials at 100 MHz.

Experimental Design
Experiments were performed in two groups of dogs. In group 1 (n=7), reversible myocardial ischemia was produced by total occlusion of the LAD for 15 minutes followed by 180 minutes of reperfusion. In group 2 (n=8), irreversible myocardial ischemic injury was produced by total LAD occlusion for 90 minutes followed by 180 minutes of reperfusion. A catheter was inserted in the LAD distal to the occlusion to drain collateral blood flow. Additionally, small vessels in the vicinity were tied to ensure production of an infarct. Measurements of hemodynamics, segment length, and ultrasonic backscatter were made before, during, and after coronary occlusion from the areas perfused by the LAD and LCx. The latter perfusion territory served as a control. Regions of ultrasonic measurement were marked with ink. Presence of myocardial infarction was confirmed by electron microscopic examination and histochemical staining.32 33

At the end of each experiment, the dog was killed, and tissue specimens (5x5 mm) from the subendocardium of the LAD and LCx perfusion territories (corresponding to epicardial ink marks) were obtained for SLAM evaluation. The acoustic microscope samples were mounted on a circular cork (22 mm in diameter, 3 mm thick) with Ames Tissue-Tek OCT (optimal cutting temperature), a polyvinyl alcohol, benzalkonium chloride, and polyethylene glycol gel used as an embedding medium for frozen tissue specimens; frozen in liquid nitrogen; placed in Ziploc bags; and shipped on dry ice from the Medical College of Wisconsin to the Bioacoustics Research Laboratory at the University of Illinois for storage at -70°C before analysis. Specific orientation of the endocardial and epicardial surfaces, as well as apex and base orientations within the left ventricle, were carefully marked on the corks. Immediately before SLAM analysis, each tissue specimen was removed from the freezer, and the corks were mounted on an object disk of a Lipshaw cryostat (maintained at -35°C). Approximately 100 µm of the upper surface of the specimen was sectioned and discarded to provide a flat, even surface for subsequent sections. This procedure ensured that all specimens remained frozen between the time of initial freezing and the acoustic microscope analysis. Previous studies have shown that rapid freezing in liquid nitrogen has no effect on the ultrasonic impedance and other mechanical properties of several different tissues,34 35 including rat myocardium (this laboratory, unpublished data).

Eight sections of known thickness (75, 100, 150, 200, 250, 300, 350, and 400 µm) were evaluated on the acoustic microscope. Each was sectioned and mounted on a 2.5-cm2 sheet of Mylar (25 µm thick), and the position of the endocardium was always known.

Biochemical Analysis
Total lipid was determined by the technique of Folch et al,36 and total protein was determined by a modified Lowry procedure,37 38 39 each starting with a small portion (<0.5 g) of myocardium. Water concentration was determined gravimetrically with a small portion (0.15 to 0.35 g) of myocardium. Samples, which were assayed in triplicate, were weighed before and after being placed in a 90°C oven for 24 hours.

Electron Microscopic Analysis
Myocardial tissue specimens from normal, stunned, and infarcted myocardium were processed by standard electron microscopic techniques using glutaraldehyde fixation. Specimens were examined for ultrastructural evidence of myocardial ischemia, including the presence or absence of glycogen granules and membrane and organelle integrity (ie, the presence of mitochondrial swelling and disruption).

Statistical Analysis
An ANOVA was used to determine the probability that the means of several treatment groups of scores deviated from one another merely by sampling error. All statistical tests were performed with SAS software. Scheffé's test was used after the ANOVA to determine which pairs of means were significantly different. Results were considered statistically significant when the probability of error was P<.05.


*    Results
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 up arrowAbstract
 up arrowIntroduction
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*Results
down arrowDiscussion
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Ultrasonic attenuation coefficient, speed, HI, IBR5, and segment shortening were measured in 15 dogs. A total of 15 dogs yielded control (LCx) data, while 7 dogs provided stunned (LAD/15) and 8 dogs provided infarcted data (LAD/90). Additionally, water content, protein content, and lipid content were obtained in 9 specimens from 3 dogs.

The acoustic data for the normal, stunned, and infarcted regions are presented in Fig 1Down and Table 1Down. The most remarkable difference between normal and stunned myocardium occurred in the attenuation coefficient and to a lesser extent in the HI. The attenuation coefficient of the control myocardium, 179±20 dB/cm, was significantly greater (P<.001) than that of the stunned, 136±7 dB/cm, and the infarcted, 130±8 dB/cm, as seen previously.26 The HI for thin sections (75 to 100 µm) of control myocardium, 5.0±0.8 m/s, was significantly smaller than the 7.5±2.3 m/s value for stunned (P<.05) and not different from the infarcted value at 5.8±2.0 m/s. Ultrasonic tissue properties that did not change significantly in the stunned myocardium are the speed, from a control of 1597±6 m/s to 1600±6 m/s, and the IBR5, from -47.1±1.0 to -46.8±0.9 dB. Both of these properties exhibited, with infarction, a reduction to 1575±7 m/s and increase to -42.4±1.0 dB, respectively, which is consistent with a previous study.26 Segment shortening was affected in a manner characteristic of ischemia/infarction by becoming progressively weaker from the control, 13±2.5%, to stunned, 0.7±3.4%, and finally to infarcted, -6.7±1.9%.



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  		Figure 1. Bar graphs showing acoustic microscope, backscatter, and segment shortening parameters of control, stunned, and infarcted myocardium. Vertical bars represent SD. *P<.001. IBR5 indicates integrated backscatter Rayleigh spectral intensity measurement referred to 5 MHz; LAD/15, data for stunned myocardium; LAD/90, data for infarcted myocardium; and CCX, control data (left circumflex artery).


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  		Table 1. Mean±SD of Dependent Variables

The HI demonstrated a very striking dependence on the thickness of the specimen, as shown in Fig 2Down, in which the HI is plotted separately for control (LCx), stunned (LAD/15), and infarcted (LAD/90) myocardium. There is a distinct difference in the shapes of the three curves, with the control appearing to be linear with thickness. By contrast, the stunned and infarcted are curved, starting at higher values than the control curve, becoming weaker at a thickness of 150 µm, and ultimately becoming identical to the control for thicknesses >300 µm. To provide a means by which the HI can be quantitatively evaluated, the HI analyses are reported separately in terms of HI <75-100 µm> and HI <200-250 µm>, the respective mean values.



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  		Figure 2. Graph showing heterogeneity index as a function of specimen thickness of control, stunned, and infarcted myocardium. Values below figure represent ranges for single, double, and multiple scattering. LAD/15 indicates data for stunned myocardium; LAD/90, data for infarcted myocardium; and CCX, control data (left circumflex artery).

Biochemical data from normal, stunned, and infarcted myocardium are outlined in Table 2Down. Water and protein contents were similar in normal and stunned myocardium. Myocardial water content was significantly increased and protein and lipid contents were significantly decreased in the infarcted myocardium. Lipid content was increased in the stunned (8.5±0.5%) and decreased in the infarcted (0.8±0.3%) myocardium compared with the normal (5.5±0.6%). Electron microscopic examination demonstrated diminished glycogen granules, with intact structural integrity in the stunned myocardium. Infarcted myocardium showed a marked swelling of both myofibrils and mitochondria, loss of mitochondrial cristae, disruption of sarcolemma, and absence of glycogen granules.


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  		Table 2. Biochemical Data From Normal, Stunned, and Infarcted Myocardium


*    Discussion
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*Discussion
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The most striking results of this study are that the acoustic propagation properties, specifically attenuation coefficient and HI, of the stunned myocardium were abnormal despite a normal IBR5 and normal myocardial structure. The only abnormality in the stunned myocardium was an increased lipid content. Ultrasonic speed and HI of thick myocardial specimens were similar to those of the normal myocardium. The infarcted myocardium demonstrated alterations in attenuation coefficient, speed, and HI in accord with our previous study.26 A total occlusion of the LAD for 5 hours resulted in a decrease in attenuation coefficient, ultrasonic speed, and HI (for the thicker specimens) and an increase in IBR5. Compared with that study, however, the attenuation coefficient data reported here present a grossly different scale factor, on the order of 2 to 3. The explanations for the marked differences are that this study used more specimens (8 versus 30) over a larger range of specimen thicknesses (75 to 400 versus 100 to 150 µm), and the subimage area was greater (250x400 versus {approx}100x100 µm), thus possibly resulting in a more accurate estimate of attenuation coefficient for this study. At the time of the previous study, it had not been determined that the HI was a function of thickness (see Fig 2Up); additionally, we have gained much more experience in conducting these difficult experimental procedures. In the previous study, the reported value for HI of 14±8 m/s for normal myocardium falls slightly above the range of the HI for some of the thinner samples in this study. However, the relative comparisons between the control, stunned, and infarcted results reported in this study are valid because the same experimental procedures by the same SLAM operator were consistently applied in analyzing these data.

IBR5 was sensitive in distinguishing stunned from infarcted myocardium but insensitive in differentiating stunned from normal myocardium. Acoustic propagation properties were superior to IBR5 in distinguishing between normal, stunned, and infarcted myocardium. Echocardiographic images are created from backscattered ultrasound, typically in the frequency range from 2.5 to 7.5 MHz. The quantitative SLAM technology is a through-transmission technique operating in the frequency range near 100 MHz. Although SLAM is not applicable as a clinical imaging system, it is quite valuable in identifying fundamental ultrasonic features of tissue that might be clinically imaged. Tissue attenuation is thought to arise from myocyte relaxation processes, as well as loss of energy from the beam. These mechanisms are expected to be more pronounced as frequency increases, especially over the 20-fold difference in frequency considered here. On the other hand, scattering of ultrasound should be more consistent over this frequency range, since it arises at the surface impedance discontinuities of structures within the tissue,40 which are known to be small compared with the 100-MHz wavelength of 16 µm. Similarly, the ultrasonic speed should depend only weakly on frequency, since it is generally determined by the average density and compressibility of the media.

The IBR5 reported here is similar to integrated backscatter used by Miller's group.3 In the latter case, several frequency bands of data are combined using the spectrum of echoes from a highly reflective block to correct the various frequency bands. Similarly, IBR5 is constructed from echoes whose spectra are corrected by the backscatter spectrum of a calibrated suspension of microspheres in water. With this correction, the IBR5 becomes an absolute measurement related to a Rayleigh backscattering spectrum at the chosen reference frequency of 5 MHz.25 Both measures integrate the power spectra of the random backscatter and will track each other with changes in the backscatter. The measures differ in the use of the absolute calibration and a statistically lower measurement variance in the case of IBR5.41

Of particular interest is the reduction in attenuation coefficient between control and stunned myocardium. Attenuation coefficient in various tissues is dependent on protein and water content.22 As protein content increases or water content decreases, the attenuation coefficient increases. Thus, tendon has a low water content and high protein content and has the highest attenuation coefficient for any tissue except bone.38 Lipids have similarly high attenuation compared with water. A reduction in attenuation coefficient was observed in both stunned and infarcted myocardium. Water content was increased in infarcted myocardium. Protein content appeared to be unchanged in the stunned and progressed to a decreased value in the infarcted myocardium. Moreover, lipid content increased from control to stunned and was nearly absent in the infarcted myocardium. These findings are consistent with established mechanisms of response to ischemia leading to infarction. Thus, the overall effect in stunned myocardium may have been an increase in the lipid content and other energy-containing constituents, with an increase in intercellular water. In ultrastructural studies, glycogen is observed to be diminished in the stunned and infarcted states. As the ischemia progressed to infarction, there may have been continuing dilution of protein content and increasing water, resulting in a reduction of attenuation coefficient. This is supported by observations that edematous adult brain and infarcted brain, which has higher water content, have lower attenuation coefficients.42 In infarcted myocardium, the observed increased water content may have decreased the attenuation coefficient further.

Backscatter and HI are related to morphological and structural alterations in the tissue, whereas attenuation and speed are related to biochemical constituents of the tissue. Stunned myocardium presented a normal structure and a normal IBR5, as does HI at the upper range of thicknesses studied. Conversely, ultrasonic speed was not significantly altered in stunned myocardium but dropped significantly once the biochemical constituents had significantly altered with infarction, most notably with an increase in water and decreases in lipid and protein content. Jennings and coworkers43 demonstrated that changes in myocardial electrolytes and gross ultrastructure induced by 15 minutes of coronary occlusion returned to normal within 20 minutes of reperfusion. A longer-term effect of the occlusion was the apparent depression of ATP, ADP, and AMP levels together with the remaining constituents of normal cellular metabolism. Most significantly for this study, they also found that total tissue water remained elevated by about 10%, plus the appearance of occasional mitochondrial disruption and the near absence of glycogen. We speculate that the observed reduction in ultrasonic absorption coefficient in the infarcted state may well be associated with total tissue water, mitochondrial disruption, and apparent reduction in glycogen as well as reduction in the energy-containing constituents (ATP, ADP, AMP, etc) of normal cellular metabolism. On the other hand, it appears that structural alteration of the ultrastructure is necessary to effect the observed alterations in IBR5, so that its effects are not seen until true infarction has taken place.

It is of interest that the HI for the thinner sections studied, <75-100 µm>, demonstrated an almost statistically significant increase from control to stunned, whereas the HI from thicker slices, <200-250 µm>, showed a less significant decrease. Moreover, the data in Fig 2Up demonstrate that the HI varies depending on the specimen thickness. HI, as determined by SLAM, is a measure of the spatial variation of ultrasonic speed in a tissue, which also indicates acoustic mismatch.

Sehgal and Greenleaf44 45 46 proposed a model of ultrasonic propagation in tissues in which velocity fluctuations and absorption arise from multiple scattering among small scattering regions. Indeed, a test they apply from optics states that the order of the scattering may be judged by the total one-way attenuation seen in a specimen. The transition from single to double scattering occurs at 0.43-dB loss, while the transition from double- to multiple-order scattering occurs at 1.3-dB loss. Applying this test to the attenuation data of Table 1Up, control data showing 179 dB/cm correspond to specimen loss ranging from 1.3 to 7.0 dB for sample thicknesses from 75 to 400 µm, respectively. Similarly, for the stunned/infarcted data, a loss of 130 dB/cm corresponds to a specimen loss ranging from 1.0 to 5.2 dB for sample thicknesses from 75 to 400 µm, respectively. These data indicate that the HI data in Fig 2Up represent the transition from low-order scattering (at, for example, 75 to 150 µm) to multiple-order scattering (at, for example, 150 to 400 µm).

By Sehgal and Greenleaf's test, the thinner HI measurements, <75-100 µm>, represent low-order scattering, whereas the thicker HI measurements, <200-250 µm>, represent higher-order scattering. This difference in ultrasonic propagation mechanisms may account for the apparent sensitivity of HI <75-100 µm> to stunned myocardium. Low-order scattering implies that changes in the tissue may be expressed more directly as spatial variations, whereas in multiple-order scattering, a greater spatial homogeneity is seen because of relatively greater mixing of the multiply scattered ultrasonic waves. The significance of these SLAM observations to clinical measurements made at lower frequencies (from 2.5 to 7.5 MHz) is not yet clear. The possibility that scattering (on the order of two or more) occurs within a 75-µm specimen implies that the basis of backscattered echoes lies at a resolution of <37 µm. Also, demonstration of sensitivity to stunned versus control myocardium for low-order scattering may motivate a method for direct clinical determination of stunned but salvageable myocardium.


*    Acknowledgments
 
This work was supported by grants HL-39104 and CA-09067 from the National Institutes of Health. We would like to thank Jeanne Howard, Kathi Annous, and Sandra Wilton for technical assistance and Mary Frescura and Cindy Ketola for preparing the manuscript.

Received June 15, 1994; accepted August 9, 1994.


*    References
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 up arrowAbstract
 up arrowIntroduction
 up arrowMethods
up arrowResults
up arrowDiscussion
*References
 

  1. Braunwald E, Kloner RA. The stunned myocardium: prolonged, postischemic ventricular dysfunction. Circulation. 1982;6:1146-1149.
  2. Jennings RB, Reimer KA. Factors involved in salvaging ischemic myocardium: effects of reperfusion of arterial blood. Circulation. 1983;68(suppl I):I-25-I-36.
  3. Miller JG, Perez JE, Madaras EI, Mottley JG, Johnston PH, Blodgett ED, Thomas LJ III, Sobel BE. Myocardial tissue characterization: an approach based on quantitative backscatter and attenuation. Proc 1983 IEEE Ultrasonics Symposium. 1983;83CH1947-1:782-793.
  4. Miller JG, Perez JE, Sobel BE. Ultrasonic characterization of myocardium. Prog Cardiovasc Dis. 1985;28:85-110. [Medline] [Order article via Infotrieve]
  5. Perez JE, Miller JG, Barsilai B, Wickline SA, Mohr GA, Wear KA, Vered Z, Sobel BE. Progress in quantitative ultrasonic characterization of myocardium: from the laboratory to the bedside. J Am Soc Echocardiogr. 1988;1:294-305. [Medline] [Order article via Infotrieve]
  6. Parisi AF, Nieminen M, O'Boyle JE, Moynihan PF, Khuri S, Kloner RA, Folland ED, Shoen FJ. Enhanced detection of the evolution of tissue changes after acute myocardial infarction using color-encoded two-dimensional echocardiography. Circulation. 1982;66:764-770. [Abstract/Free Full Text]
  7. Skorton DA, Melton HE, Pandian NG, Nichols J, Koyanagi S, Marcus ML, Collins SM, Kerber RE. Detection of acute myocardial infarction in closed-chest dogs by analysis of regional two-dimensional echocardiographic gray level distributions. Circ Res. 1983;52:36-44. [Abstract/Free Full Text]
  8. Barzilai B, Madaras EI, Sobel BE, Miller JG, Perez JE. Effects of myocardial contraction on ultrasonic backscatter before and after ischemia. Am J Physiol. 1984;247:H478-H483.
  9. Glueck RM, Mottley JG, Miller JG, Sobel BE, Perez JE. Effects of coronary artery occlusion and reperfusion on cardiac cycle-dependent variation of myocardial ultrasonic backscatter. Circ Res. 1985;56:683-689. [Abstract/Free Full Text]
  10. Schnittger IA, Vieli A, Heiserman JE, Director BE, Billingham ME, Ellis SE, Kernoff RS, Takamoto T, Popp RL. Ultrasonic tissue characterization: detection of acute myocardial ischemia in dogs. Circulation. 1985;72:193-199. [Abstract/Free Full Text]
  11. Shaw TRD, Logan-Sinclair RB, Surin C, McAnulty RJ, Heard B, Laurent GJ, Gibson DJ. Relation between regional echo intensity and myocardial connective tissue in chronic left ventricular disease. Br Heart J. 1984;51:46-53. [Abstract/Free Full Text]
  12. Chandraratna PAN, Ulene R, Nimalasuriya A, Reid CL, Kawinishi D, Rahimtoola SH. Differentiation between acute and healing myocardial infarction by signal averaging and color encoding two-dimensional echocardiography. Am J Cardiol. 1985;56:381-384. [Medline] [Order article via Infotrieve]
  13. Tanaka M, Nitta S, Nitta K, Sogo Y, Yamamoto A, Katahira Y, Sato N, Ohkawai H, Tezuka F. Non-invasive estimation by cross sectional echocardiography of myocardial damage in cardiomyopathy. Br Heart J. 1985;53:137-152. [Abstract/Free Full Text]
  14. Sagar KB, Rhyne TL, Warltier DC, Pelc L, Wann S. Intramyocardial variability in integrated backscatter: effects of coronary occlusion and reperfusion. Circulation. 1987;75:436-442. [Abstract/Free Full Text]
  15. Fitzgerald PJ, McDaniel MD, Rolett EL, Strohben JW, James DH. Two-dimensional ultrasonic tissue characterization: backscatter power, endocardial motion, and their phase relationship for normal, ischemic, and infarcted myocardium. Circulation. 1987;76:850-859. [Abstract/Free Full Text]
  16. Vered Z, Barsilai B, Mohr GA, Thomas LJ III, Genton R, Sobel BE, Shoup TA, Melton HE, Miller JG, Perez JE. Quantitative ultrasonic tissue characterization with real-time integrated backscatter imaging in normal human subjects and in patients with dilated cardiomyopathy. Circulation. 1987;76:1067-1073. [Abstract/Free Full Text]
  17. Vered Z, Mohr GA, Gessler CJ, Wickline SA, Barzilai B, Wear KA, Shoup TA, Weiss AN, Sobel BE, Miller JG, Perez JE. Ultrasound integrated backscatter tissue characterization of remote myocardial infarction in human subjects. J Am Coll Cardiol. 1989;13:84-91. [Abstract]
  18. Wear KA, Milunski MR, Wickline SA, Perez JE, Sobel BE, Miller JG. Discrimination between acutely ischemic myocardium and remote infarct in dogs on the basis of frequency dependent backscatter. J Acoust Soc Am. 1988;86:1067-1072.
  19. Wickline SA, Thomas LJ III, Miller JG, Sobel BE, Perez JE. Sensitive detection of the effects of reperfusion on myocardium by ultrasonic tissue characterization with integrated backscatter. Circulation. 1986;74:389-400. [Abstract/Free Full Text]
  20. Milunski MR, Mohr GA, Wear KA, Sobel BE, Miller JG, Wickline SA. Early detection with ultrasonic integrated backscatter of viable but stunned myocardium in dogs. J Am Coll Cardiol. 1989;14:462-471. [Abstract]
  21. Bamber JC, Fry JJ, Hill CR, Dunn F. Ultrasonic attenuation and backscatter by mammalian organs as a function of time after excision. Ultrasound Med Biol. 1977;3:15-17. [Medline] [Order article via Infotrieve]
  22. Pohlhammer J, O'Brien WD Jr. The relationship between ultrasonic attenuation and speed in tissues and constituents: water, collagen, protein and fat. In: Fullerton GD, Zagzebski JA, eds. Medical Physics of CT and Ultrasound: Tissue Imaging and Characterization. New York, NY: 1980:409-435.
  23. Theroux P, Franklin D, Ross J, Kemper WS. Regional myocardial function during acute coronary occlusion and modification by pharmacologic agents in the dog. Circ Res. 1974;35:896-902. [Abstract/Free Full Text]
  24. Sagar KB, Pelc LE, Rhyne TL, Wann LS, Warltier DC. Influence of heart rate, preload, afterload, and inotropic state on myocardial ultrasonic backscatter. Circulation. 1988;77:478-483. [Abstract/Free Full Text]
  25. Rhyne TL, Sagar KB, Wann SL, Haasler G. The myocardial signature: absolute backscatter, cyclic variation, frequency variation and statistics. Ultrason Imaging. 1986;6:107-120.
  26. Sagar KB, Agemura DH, O'Brien WD Jr, Pelc LR, Rhyne TL, Wann LS, Komorowski RA, Warltier DC. Quantitative ultrasonic assessment of normal and ischaemic myocardium with an acoustic microscope: relationship to integrated backscatter. Cardiovasc Res. 1990;24:447-455. [Abstract/Free Full Text]
  27. Embree PM, Tervola KMU, Foster SG, O'Brien WD Jr. Spatial distribution of the speed of sound in biological materials with the scanning laser acoustic microscope. IEEE Trans Sonics Ultrason. 1985;SU-32:341-350.
  28. Tervola KMU, Foster SC, O'Brien WD Jr. Attenuation coefficient measurement technique at 100 MHz with the scanning laser acoustic microscope. IEEE Trans Sonics Ultrason. 1985;SU-32:259-265.
  29. Olerud JE, O'Brien WD Jr, Reiderer-Henderson MA, Steiger DL, Forster FK, Daly C, Ketterer DJ, Odland GF. Ultrasonic assessment of skin and wounds with the scanning laser acoustic microscope. J Invest Dermatol. 1987;88:615-623. [Medline] [Order article via Infotrieve]
  30. Steiger DL, O'Brien WD Jr, Olerud JE, Reiderer-Henderson MA, Odland GF. Measurement uncertainty assessment of the scanning laser acoustic microscope and application to canine skin and wound. IEEE Trans Ultrason, Ferroelectrics, Frequency Control. 1988;35:741-748. [Medline] [Order article via Infotrieve]
  31. Tervola KMU, O'Brien WD Jr. Spatial frequency domain technique: an approach for analyzing the scanning laser acoustic microscope interferogram images. IEEE Trans Sonics Ultrason. 1985;SU-32:544-554.
  32. Nachlas MM, Shitlaka TK. Macroscopic identification of early myocardial infarct by alteration in dehydrogenase activity. Am J Pathol. 1963;42:379-405.
  33. Warltier DC, Zyvoloski MG, Gross GH, Brooks HL. Determination of experimental myocardial infarct size. J Pharmacol Methods. 1981;6:199-210. [Medline] [Order article via Infotrieve]
  34. Marangore RD, Glaser AA, Must JS, Brody GS, Beckwith TH, Walker GR, White WL. Effect of storage and handling techniques on skin tissue properties. Ann N Y Acad Sci. 1966;136:439-454.
  35. Gellski JV, Shung KK. Studies on acoustic impedance of major bovine blood vessel walls. J Acoust Soc Am. 1982;71:467-470.[Medline] [Order article via Infotrieve]
  36. Folch JM, Lees K, Sloan-Stanley GH. A simple method for the isolation and purification of total lipids from animal tissues. J Biol Chem. 1957;226:497-509. [Free Full Text]
  37. Clark JM Jr, Switzer RL. Experimental Biochemistry. 2nd ed. San Francisco, Calif: Freeman; 12.
  38. O'Brien WD Jr. The relationship between collagen and ultrasonic attenuation and velocity in tissue. In: Proceedings of the Ultrasonic International. Guildford, UK: IPC Sciences and Technology Press; 1977:194-205.
  39. Peterson GL. A simplification of the protein assay method of Lowry et al which is more generally applicable. Anal Biochem. 1977;83:346-356. [Medline] [Order article via Infotrieve]
  40. O'Donnell M, Mimbs JW, Miller JG. Relationship between collagen and ultrasonic backscatter in myocardial tissue. J Acoust Soc Am. 1981;62:580-588.
  41. Rhyne TL, Sagar KB. IBR5: An optimal measurement of integrated backscatter and cyclic variation of integrated backscatter. Ultrason Imaging. 1990;12:189-204. [Medline] [Order article via Infotrieve]
  42. Goss SA, Frizzell LA, Dunn F, Dines RA. Dependence of the ultrasonic properties of biological tissue on constituent proteins. J Acoust Soc Am. 1980;67:1041-1044.
  43. Jennings RB, Schaper J, Hill ML, Steenbergen C Jr, Reimer KA. Effect of reperfusion late in the phase of reversible ischemic injury. Circ Res. 1985;56:262-278. [Abstract/Free Full Text]
  44. Sehgal CM, Greenleaf JF. Ultrasonic absorption and dispersion in biological media: a postulated model. J Acoust Soc Am. 1982;72:1711-1718.
  45. Sehgal CM, Greenleaf JF. Diffraction of ultrasound by soft tissue: the inhomogeneous continuous model. In: Kaveh M, Mueller RK, Greenleaf JF, eds. Acoustical Imaging. New York, NY: 1984:163-178.
  46. Sehgal CM, Greenleaf JF. Scattering of ultrasound by tissues. Ultrason Imaging. 1984;6:60-80.[Medline] [Order article via Infotrieve]



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