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Electromagnetic Heating of Breast Tumors in Interventional Radiology: In Vitro and in Vivo Studies in Human Cadavers and Mice¹

¹ From the Institutes of Diagnostic and Interventional Radiology (I.H., W.A.K.) and Animal Research (H.S.), Clinics of Friederich Schiller University Jena, Bachstrasse 18, D-07740 Jena, Germany; and the Institute of Physical High Technology, Jena, Germany (W.A., R. Hergt, R. Hiergeist). From the 1999 RSNA scientific assembly. Received November 28, 1999; revision requested January 11, 2000; final revision received May 30; accepted June 9. Address correspondence to W.A.K. (e-mail: Werner.Kaiser@med.uni-jena.de).

View larger version (87K): [in a new window]   Figure 1. Radiograph of breast tissue sample shows the in vitro experimental setup. C = magnetic field applicator coil, B = breast tissue sample containing iron oxides (I) (ie, magnetite), T = thermocouple.

View larger version (82K): [in a new window]   Figure 2. Radiograph of a recumbent mouse shows the in vivo experimental setup. C = magnetic field applicator coil, T = thermocouple.

View larger version (20K): [in a new window]   Figure 3. Graph of calculated (line) and experimental () values of temperature elevation as a function of magnetite mass in breast tissue after an exposure time of 2 minutes. The functional dependency for sample 6 magnetite masses of up to 28 mg is calculated as follows: T = 2.31 · M, with r2 = 0.97, where M is the mass of magnetite and T is the temperature elevation. The data, which are based on an alternating current magnetic field with a 400-kHz frequency and 6.5-kA/m amplitude, show that the temperature elevation as a function of magnetite mass increases linearly (r2 = 0.97) with a mass of up to about 28 mg; at higher masses, the temperature elevation saturates. The vertical error bars represent the SD from the mean temperature elevations. Experiments were performed in triplicate.

View larger version (16K): [in a new window]   Figure 4. Graph of calculated (line) and experimental () values of temperature elevation as a function of magnetic field amplitude in breast tissue after an exposure time of 2 minutes. The functional dependency is calculated as follows: T = 0.26°C/(kA/m)3 · H3, with r2 = 0.95, where T is the temperature elevation and H is the magnetic field amplitude. The data, which are based on an alternating current magnetic field with a 400-kHz frequency and a magnetite mass (sample 6) of 28 mg, show that the relationship between temperature elevation and magnetic field amplitude is described by a third-order power law of dependency. The vertical error bars represent the SD from the mean temperature elevations. Experiments were performed in triplicate.

View larger version (36K): [in a new window]   Figure 5. Graph of intratumoral and rectal temperature courses during exposure of 10 tumor-bearing mice to an alternating magnetic field (frequency, 400 kHz; amplitude, 6.5 kA/m) for 242 seconds after intratumoral injection of 21 mg ± 9 of magnetite (sample 6) per 299 mm3 of tissue. The intratumoral temperature, which began at 26°C ± 1, increased to 71°C ± 8 at the end of treatment (242 seconds). No substantial increase in rectal temperature was observed.  = mean intratumoral temperature data,  = mean rectal temperature data. The vertical error bars represent the SD from the mean temperature.

View larger version (98K): [in a new window]   Figure 6a. Radiographs of a recumbent mouse show the macroscopic tumor (arrow) (a) before and (b) after magnetic thermoablation.

View larger version (102K): [in a new window]   Figure 6b. Radiographs of a recumbent mouse show the macroscopic tumor (arrow) (a) before and (b) after magnetic thermoablation.

View larger version (150K): [in a new window]   Figure 7a. Histologic sections (4 µm; with Azure II stain) show human breast adenocarcinoma cells (a) before and (b) after magnetic thermoablation. In contrast to findings in the nonheated tumor cells with normal nuclear morphology (a), substantial nuclear degeneration effects, such as chromatin margination along the nuclear envelope (arrows) and nuclear pyknosis (arrowheads), can be observed in the heated cells (b). In a and b, the horizontal line in the bottom right corner represents a length of 50 µm.

View larger version (169K): [in a new window]   Figure 7b. Histologic sections (4 µm; with Azure II stain) show human breast adenocarcinoma cells (a) before and (b) after magnetic thermoablation. In contrast to findings in the nonheated tumor cells with normal nuclear morphology (a), substantial nuclear degeneration effects, such as chromatin margination along the nuclear envelope (arrows) and nuclear pyknosis (arrowheads), can be observed in the heated cells (b). In a and b, the horizontal line in the bottom right corner represents a length of 50 µm.