Quantitative assessment of burn injury in porcine skin with high-frequency ultrasonic imaging.

Early excision and grafting of full thickness burns has been shown to decrease morbidity and mortality. Errors made in assessing acute burn depth are common and result in prolonged hospitalization in expectant healing of full-thickness burns and in unnecessary excision and grafting of potentially regenerative partial-thickness burns. High-frequency ultrasonic imaging may be a noninvasive, convenient means of quantitating burn depth. A depth analysis system for imaging burned skin was developed using a high-frequency 18.5 MHz (nominal 25 MHz) pulse-echo ultrasound system with a longitudinal resolution of 86 mu. Five adult mini-swine (15 kg) were burned with a temperature-(190 degrees C) and pressure-controlled (236 g/cm2) burning iron. A series of burn durations (1-45 seconds) was used to inflict partial- and full-thickness burns of various depths. Ultrasonic scans of the acutely excised burns were performed across the lateral margin of the burn, including adjacent normal skin to serve as control. Direct histologic comparison was made with each scan plane. Average burn and normal skin depth measurements were made by independent observers for 34 scans and corresponding histologic sections. A significant correlation was achieved between burn depth and percent burn (burn depth/adjacent normal skin depth) as measured by ultrasound and histology (R = 0.90, t = 11.2, P less than .001).

Acute effects of ultrasound on skeletal muscle oxygen tension, blood flow and capillary density.

The acute effects of pulsed (5 kHz, PRF) ultrasound (2.5 and 5 W/cm2 SPTA at 1 MHz) on the microvasculature of the rat cremaster were examined. Tissue blood flow, capillary density and PO2 were measured in both normally perfused and ischemic tissue. Exposure to 2.5 W/cm2 produced no significant changes in either blood flow or capillary density, however, oxygen tension was significantly reduced in normal tissue at this intensity. Capillary density was significantly diminished in ischemic tissue following exposure to 5 W/cm2 as was PO2 in normally perfused tissue. Blood flow was decreased only in the normoxic tissue at 5 W/cm2. These data suggest that ultrasound at the intensities and frequency employed is capable of producing at least an acute reduction in tissue PO2.

Absorption in liver at the focus of an ultrasonic shock wave field.

This experimental study is an extension of a previous investigation of finite amplitude ultrasound absorption at 1 MHz fundamental frequency in freshly excised rat liver at 37 degrees C (Fry et al. 1989). The work reported here includes measurements of the absorption as a function of intensity under a variety of conditions (temperature, pressure, and tissue state). The maximum intensity employed in the investigation (700 W/cm-2) corresponds to a shock parameter of approximately 1.7 based on previous characterization of the acoustic field which established that shock (sigma = 1) occurred in the range 225 W/cm-2 to 275 W/cm-2 (Fry et al. 1989). Of the three temperatures chosen for the thermal study (30 degrees C, 37 degrees C, and 41 degrees C), the only statistically significant differences (p less than 0.05) in absorption were between the 30 degrees C and 41 degrees C data in the intensity range just above sigma = 1 (300-500 W/cm-2). The intensity-dependent absorption coefficient was also determined for excised liver under hyperbaric conditions and for liver in situ at 37 degrees C. At a pressure of 350 psi, the absorption was generally less than at atmospheric pressure. In situ liver at 37 degrees C had a lower absorption above 200 W/cm-2 than freshly excised liver, but the difference was only significant between 200 and 300 W/cm-2 and between 600 and 700 W/cm-2.

Evaluation of high-intensity therapeutic ultrasound irradiation in the treatment of experimental hepatoma.

A study evaluating the efficacy of high-intensity therapeutic ultrasound (HITU) as a treatment modality in experimental hepatoma is reported. Morris hepatoma (3924) 1 x 10(6) cells were transferred subcutaneously into 40 male ACI rats (weight, 150 to 200 g). Animals were divided into four experimental groups: group 1 (n = 10) consisted of untreated controls; group 2 (n = 10) received intraperitoneal cyclophosphamide 50 mg/kg as a single dose; group 3 (n = 10) underwent HITU only; and group 4 (n = 10) received both chemotherapy (as in group 2) and HITU (as in group 3). HITU was administered with a 5.5-cm diameter 4-MHz quartz transducer creating a continuous wave with 400 W/cm2 focal intensity. The entire tumor was irradiated in 1-mm increments (horizontal and vertical) using treatment cycles of 4 seconds on and 11 seconds off. Total body weight and tumor volume were measured on the day of treatment, and 4 weeks later. At 4 weeks, the animals were killed, the tumor was excised and weighed, and tumor volume was determined. Tumor volume in all treated animals (groups 2, 3 and 4) was significantly smaller than in controls (P less than .001) at 4 weeks, and tumor volume for animals in group 4 was significantly smaller than for those in groups 2 and 3 (P less than .01). These data indicate that HITU significantly reduces tumor size when compared with control rats with Morris hepatoma. A synergistic effect of chemotherapy and HITU was observed and resulted in an enhanced tumor response and reduction of tumor size.(ABSTRACT TRUNCATED AT 250 WORDS)