Temperature distribution is a crucial factor in determining the outcome of laser phototherapy in cancer treatment. Magnetic resonance imaging (MRI) is an ideal method for 3-D noninvasive temperature measurement. A 7.1-T MRI was used to determine laser-induced high thermal gradient temperature distribution of target tissue with high spatial resolution. Using a proton density phase shift method, thermal mapping is validated for in vivo thermal measurement with light-absorbing enhancement dye. Tissue-simulating phantom gels, biological tissues, and tumor-bearing animals were used in the experiments. An 805-nm laser was used to irradiate the samples, with laser power in the range of 1 to 3 W. A clear temperature distribution matrix within the target and surrounding tissue was obtained with a specially developed processing algorithm. The temperature mapping showed that the selective laser photothermal effect could result in temperature elevation in a range of 10 to 45°C. The temperature resolution of the measurement was about 0.37°C with 0.4-mm spatial resolution. The results of this study provide in vivo thermal information and future reference for optimizing laser dosage and dye concentration in cancer treatment.
The 3-D, in vivo temperature distributions within tumor-bearing rats were measured using Magnetic
Resonance Imaging (MRI) technique. The in vivo thermal distributions of rats were measured using MRI
chemical shift of water proton density. DMBA-4 tumor bearing rats are treated using laser photothermal
therapy combined with immunoadjuvant under the observation of MRI. The thermal images and the
immunological responses were studied and their relationships were investigated. The study of thermal
distribution and correlation with the immunological response under laser treatment provided rich information
with potential guidance for thermal-immunological therapy.
KEYWORDS: Laser tissue interaction, Absorption, Temperature metrology, Tumors, Magnetic resonance imaging, Laser therapeutics, Laser irradiation, Optical spheres, Tissue optics, System on a chip
Tissue-simulating gel phantoms have been used in selective laser photothermal interaction. The
gelatin phantom provides a uniform tissue-simulating medium for analyzing thermal performance under laser
radiation. The gelatin phantom gel is used particularly in measurements of thermal reactions in laser
thermology. The gelatin phantom is made from gelatin and Liposyn. A special gel sphere with Indocyanine
Green (ICG) laser absorption enhancement dye is embedded in normal gel to simulate the dye-enhanced
tumor in normal tissue. The concentration of ICG within the dye sphere is optimized using simulation for
selective phototherapy. As a first attempt, the concentration of ICG and laser power density was optimized
using a temperature ratio of target tissue versus surrounding tissue. The gel thermal performance is also
monitored using MRI thermology imaging technology. The thermal imaging shows in vivo, 3D
temperature mapping inside the gel. The study of thermal distribution using gel phantom provides
information to guide the future selective laser photothermal thermal therapy.
KEYWORDS: Tumors, Tissues, Natural surfaces, Laser irradiation, Monte Carlo methods, Laser therapeutics, Temperature metrology, Thermography, Infrared cameras, Breast
An ideal cancer treatment method should not only cause primary tumor suppression but also induce an
antitumor immunity, which is essential for control of metastatic tumors. A combination therapy using a
laser, a laser-absorbing dye, and an immunoadjuvant guided by temperature measurement probes such as
magnetic resonance imaging thermometry (MRT) and infrared thermography (IRT) can be an ideal treatment
modality. Temperature distribution inside the target tissue is important in laser treatment. The surface
temperature often serves as an indicator of the treatment effect. However, real-time monitoring of surface
temperature during laser irradiation poses a great challenge. In this study, we investigated the surface
temperature distribution using direct measurement and theoretical simulation. The preliminary results of in
vitro and in vivo studies are presented. Gel phantom and chicken breast tissue were irradiated by an 805 nm
laser and the surface temperature distribution was obtained using an infrared thermal camera. EMT-6 breast
tumors in mice were treated using the 805 nm laser and with different dye and immunoadjuvant
combinations, including intratumor injections of indocyanine green (ICG) and glycated chitosan (GC).
Monte Carlo simulation for selective photothermal-tissue interaction was also performed for the surface
temperature distributions. Our results demonstrated that the tissue temperature can be accurately monitored
in real time and can be controlled by appropriate treatment parameters.
In cancer treatment and immune response enhancement research, Magnetic Resonance Imaging (MRI) is an
ideal method for non-invasive, three-dimensional temperature measurement. We used a 7.1-Tesla magnetic
resonance imager for ex vivo tissues and small animal to determine temperature distribution of target tissue
during laser irradiation. The feasibility of imaging is approved with high spatial resolution and high signal-noise-
ratio. Tissue-simulating gel phantom gel, biological tissues, and tumor-bearing animals were used in
the experiments for laser treatment and MR imaging. Thermal couple measurement of temperature in target
samples was used for system calibration. An 805-nm laser was used to irradiate the samples with a laser
power in the range of 1 to 2.5 watts. Using the MRI system and a specially developed processing algorithm,
a clear temperature distribution matrix in the target tissue and surrounding tissue was obtained. The
temperature profiles show that the selective laser photothermal effect could result in tissue temperature
elevation in a range of 10 to 45 °C. The temperature resolution of the measurement was about 0.37°C
including the total system error. The spatial resolution was 0.4 mm (128x128 pixels with field of view of
5.5x5.5 cm). The temperature distribution provided in vivo thermal information and future reference for
optimizing dye concentration and irradiation parameters to achieve optimal thermal effects in cancer
treatment.
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