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The stabilities of the cation radicals of veratryl alcohol, 3,4-dimethoxytoluene and 1,4-dimethoxy-benzene were compared by monitoring the formation of dimeric products during the oxidation of these substrates by lignin peroxidase (LiP). LiP oxidized veratryl alcohol to generate veratraldehyde as the major product. Several other monomeric products were obtained in low yield. Dimeric products resulting from the coupling of two cation radicals, or a cation radical with a neutral molecule, were obtained only in trace amounts or not at all. This suggests that the cation radical of veratryl alcohol rapidly loses a benzylic proton to form a benzylic radical which undergoes further reactions to form veratraldehyde. In contrast, the LiP oxidation of 3,4-dimethoxytoluene generated the dimeric product 3-(2,3-dimethoxy-6- methylphenyl)-4-methyl-1,2-benzoquinone as the major product. Several other monomeric and dimeric products were produced in lower yields. The generation of these dimeric products indicates that the cation radical of 3,4-dimethoxytoluene is considerably more stable than that of veratryl alcohol. This suggests that the electronegative benzylic oxygen of veratryl alcohol increases the acidity of the benzylic protons, destabilizing the veratryl alcohol cation radical. LiP oxidized 1,4-dimethoxybenzene to generate 1,4- benzoquinone and 2-(2,5-dimethoxyphenyl)-1,4-benzoquinone as the major products. The formation of these products indicates that the cation radical of 1,4-dimethoxybenzene also is relatively stable, as previously demonstrated by ESR. All of these results indicate that the veratryl alcohol cation radical generated by LiP oxidation is unstable, suggesting that it would not act as a diffusible radical mediator in LiP-catalyzed reactions. [ABSTRACT FROM AUTHOR]

The absorption and speed of ultrasound in mammalian tissues are discussed in relation to the fractional protein content. To a first approximation, biological tissues are shown to correspond to composite materials whose ultrasonic propagation properties are determined by the individual ultrasound properties of their globular and structural protein contents. [ABSTRACT FROM AUTHOR]

Radiographic density is considered an important feature in the evaluation of noncalcified breast masses, yet no studies assessing its value have been published. The radiographic densities of 91 biopsy-proved, nonfatty, noncalcified breast masses were evaluated by three mammographers. The density determinations made by each observer were compared with the histologic outcome for the 51 benign and 40 malignant lesions. With the kappa statistic, interobserver agreement was relatively poor (0.22 to 0.49), and intraobserver agreement for one expert mammographer was 0.50. When the majority opinion of the mammographers was used, sensitivity was 48%, specificity was 80%, and both positive and negative predictive values were 66%. As a solitary feature in lesion analysis, mammographic density is difficult to assess and is of limited value for the prediction of the benign or malignant nature of noncalcified breast masses.

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.

High intensity focused ultrasound was employed to modify the permeability of the normal feline and canine blood-brain barrier (BBB) to a circulating vital dye--Evans blue (EB). The threshold doses (W sec/cm2) for focally increasing the permeability of the BBB in white matter (WM) and gray matter (GM) were as follows: internal capsule (WM)--340 to 680; thalamus (GM)--approximately 1326; and caudate nucleus (GM)--2284 to 2952. In the presence of supralesioning doses of ultrasound, the cross sectional area occupied by the EB was consistently greater than that of the attendant nonhemorrhagic lesion--thus suggesting that BBB changes may be inducible at sublesioning doses. These findings, in conjunction with those of others, suggest that high intensity focused ultrasound may have a role in the treatment of brain tumors based on cell destruction by two mechanisms: (a) direct, by the ultrasound and (b) indirect, by an antineoplastic agent which is delivered via an ultrasonically modified BBB.

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).

The ultrasonic absorption coefficient of freshly-excised rat liver is measured as a function of intensity in a 1 MHz focused field. The 7 cm diameter source has a geometric focus of 20 cm and a half-intensity linear focal beamwidth of 4.65 mm. Free-field harmonic content and radiation force measurements within the focal region indicate that quasilinear shock (sigma = 1) is attained in the intensity range of 225 W cm-2 to 275 W cm-2 SPTP intensity. Radiometric measurements of focal beamwidth and intensity response (focal intensity versus transducer input voltage squared) demonstrated beam narrowing up to 700 W cm-2 and focal intensities greater than would be expected from linear theory. This nonlinear acoustic field is employed to measure the absorption coefficient of liver at the beam focus. The pressure absorption coefficient, measured via the transient thermoelectric technique, was 0.038 Np cm-1 at low intensities (below 100 W cm-2 SPTP) and rose to approximately 0.117 Np cm-1 at 750 W cm-2 SPTP intensity. The absorption predicted using spherically converging beam theory is in agreement with the experimental data at the lower (below 200 W cm-2) and the higher (above 650 W cm-2) intensities. Gaussian theory provided a poor fit to the experimental data even after deficiencies in the model were considered.

Computed sonographic transmission tomograms of infant and adult human cadaver heads are presented and compared with sonographic pulse-echo and x-ray tomograms of the same horizontal planes. The sonographic attenuation tomograms were reconstructed from broadband transmission data obtained using the rotate/translate axial scan mode in much the same way as x-ray tomography is performed. The formalin-fixed infant cadaver head was scanned through the anterior fontanelle using pulse-echo and in a horizontal plane (3.3 cm superior to the Frankfort plane) using both pulse-echo (3.5 MHz and 5 MHz) and transmission sonography (5 MHz). The computed sonographic transmission tomogram revealed superior anatomic detail as compared with the pulse-echo images obtained in the horizontal plane and compared favorably with x-ray scans. The quantitative, noninvasive nature of sonographic tomography shows promise for clinical applicability in the infant. In the adult human cadaver, sonographic tomograms at 750 kHz are presented in both the transskull and excised brain conditions. These scans also offer promise for the possible clinical exploration of the method.