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Biomedical subjects

J Delannoy

Publications and source records attributed to J Delannoy.

6 recordsLinked to original sources
PubMed1991

Noninvasive temperature imaging using diffusion MRI.

Efficacy and safety considerations for cancer therapy with hyperthermia require accurate temperature measurements throughout the heated volume. We report the use of molecular diffusion, whose temperature dependence is well known. A dedicated hyperthermia applicator was built, combining a MRI gradient coil and a rf coil. Diffusion and derived temperature images were obtained with a 1 x 2 mm pixel size on a polyacrylamide gel phantom using a clinical 1.5-T whole body MRI system. Temperatures determined from these images using 1 cm2 regions of interest were found to be within 0.2 degrees C of those recorded from the thermocouples and fiber-optic probes placed inside the gel.

Body Temperature↗
PubMed1989

Temperature mapping with MR imaging of molecular diffusion: application to hyperthermia.

Efficacy and safety considerations for hyperthermia (HT) cancer therapy require accurate temperature measurements throughout the heated volume. Noninvasive thermometry methods have been proposed, including magnetic resonance (MR) imaging based on the temperature dependence of the relaxation time T1. However, the temperature accuracy achieved to date with T1 measurements does not fulfill the HT requirements (1 degree C/cm). The authors propose to use molecular diffusion, for which temperature dependence is well known. Molecular diffusion is more sensitive than T1 and can be determined with high accuracy with MR imaging. Diffusion and derived temperature images were obtained with a 2 X 2-mm pixel size in a polyacrylamide gel phantom heated inside the head coil of a clinical 0.5-T whole-body MR imaging system by means of a modified clinical HT device made compatible with the system. Temperatures determined from these images with 0.8-cm2 regions of interest were found to be within 0.5 degrees C of those recorded with thermocouples placed inside the gel. The utility of this method in clinical hyperthermia is enhanced by its potential to also help monitor blood perfusion.

Diffusion↗
PubMedDate not supplied

Hyperthermia system combined with a magnetic resonance imaging unit.

Magnetic resonance imaging (MRI) has recently been proposed as a method to monitor, noninvasively, temperature, blood flow, and cell metabolism during oncologic hyperthermia (HT). To heat and "image" simultaneously, it is necessary to combine a HT device and a MRI unit. As a demonstrative example of the problems associated with implementing such a system, a mini-annular phased array hyperthermia applicator was combined with a 0.5-T whole body MRI unit. With the aid of filters, baluns, and switches, the HT applicator and the MRI unit were made compatible. The overall system was tested using a muscle-equivalent, cylindrically shaped polyacrylamide gel phantom. No interference between the HT device and the MRI unit was observed. Noninvasive temperature images, with a resolution better than 1 degree C/cm, were obtained from images of molecular diffusion recorded before and during heating.

Humans↗
PubMedDate not supplied

Measurements of effective thermal conductivity during hyperthermia: a comparison of experimental and clinical results.

Temperature and effective thermal conductivity (including the convective effects due to tissue blood flow) profiles have been mapped both within a perfused phantom model containing a differentially perfused pseudo-tumour and in patients undergoing microwave (915 MHz) hyperthermia. These measurements demonstrate the influence of differential thermal characteristics of tumour vs. normal tissue on the temperature distributions obtained during hyperthermia. Effective thermal conductivity was measured using a self-heated thermistor probe, and temperature profiles were measured by means of conventional thermocouples and fibre-optic temperature probes. Measurements of effective thermal conductivity obtained in patients prior to microwave hyperthermia, and temperature profiles obtained once steady-state treatment conditions had been attained, show a strong relation between the effective thermal conductivity profile and the ability to obtain therapeutic temperatures without excessive heating of intervening tissues. These observations were confirmed in phantom experiments, demonstrating that this perfused phantom is a more realistic physical model than the conventional unperfused gels usually employed as physical models for hyperthermia experiments. These results demonstrate that tissue thermal clearance is an important determinant of treatment temperature fields, independent of and in addition to the SAR distribution of the particular applicator. Effective thermal conductivity measurements of the different tissues constituting the volume to be heated could be an important index in the planning and optimization of treatment strategies.

Clinical Protocols↗