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Magnetic resonance diffusion imaging detects structural damage in biological tissues upon hyperthermia
1Biophysics Laboratory, Department of Physics, Texas Tech University, Lubbock 79409.
Abstract:
The use of quantitative nuclear magnetic resonance (MR) imaging to investigate the extent and mechanism of hyperthermic damage in biological tissues has been studied. By using the multiple delay-multiple echo and pulsed-gradient spin echo MR imaging sequences, multiple frame MR images of freshly harvested rabbit tissues (brain, kidney, and muscle) and intact duck embryos in shells were obtained before and after heat treatment (45 degrees C for 30 min) using a clinical 1.5-Tesla whole-body superconducting MR scanner. Based on the relaxation and diffusion models, maps of the proton spin density, relaxation times, and various self-diffusion parameters of tissue water were generated from these multiple frame MR images. Our results indicated that the values of the diffusion barrier size and fractal parameter of the tissues and the self-diffusion coefficient of tissue water increased significantly, i.e., approached that of free water, after the heat treatment. In comparison, only slight changes in the spin density and relaxation times of the tissue water were found after the identical heat treatment. We concluded that the significant changes in the self-diffusive behavior of the tissue water are due to the denaturation of macromolecules (e.g., protein and fiber) within the tissues at elevated temperatures. We further suggested that MR diffusion imaging represents a powerful tool to investigate the extent and mechanism of heat damage of biological tissues in vivo and therefore bears important potential in the clinical assessment of the therapeutic efficacy of hyperthermia in cancer therapy.
Insights
Quantitative nuclear magnetic resonance (MR) imaging reveals heat-induced damage in tissues. Elevated temperatures alter water diffusion, indicating macromolecular denaturation and potential for hyperthermia therapy assessment.
Area of Science:
- Biophysics
- Medical Imaging
- Biomaterials
Background:
- Hyperthermia therapy uses heat to treat diseases, but understanding heat-induced tissue damage is crucial.
- Quantitative magnetic resonance (MR) imaging offers a non-invasive method to probe tissue properties.
Purpose of the Study:
- To investigate the extent and mechanism of hyperthermic damage in biological tissues using quantitative MR imaging.
- To assess the potential of MR diffusion imaging in evaluating heat-induced changes in tissues.
Main Methods:
- Utilized multiple delay-multiple echo and pulsed-gradient spin echo MR imaging sequences on rabbit tissues and duck embryos.
- Acquired MR images before and after heat treatment (45°C for 30 min) using a 1.5-Tesla scanner.
- Generated maps of proton spin density, relaxation times, and water self-diffusion parameters based on relaxation and diffusion models.
Main Results:
- Heat treatment significantly increased tissue water self-diffusion coefficients, diffusion barrier size, and fractal parameters, approaching free water values.
- Minimal changes were observed in spin density and relaxation times of tissue water post-heating.
- Quantitative MR imaging effectively detected alterations in tissue water diffusion.
Conclusions:
- Significant changes in water self-diffusion behavior are attributed to macromolecular denaturation (proteins, fibers) at elevated temperatures.
- MR diffusion imaging is a powerful tool for investigating heat damage mechanisms in biological tissues.
- This technique holds potential for clinical assessment of hyperthermia efficacy in cancer therapy.