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Research on Temperature Measurement Based Chemical Shifting of Proton Resonance Frequency at Low Field

Author: MoJiJiang
Tutor: FengYanQiu；ChenWuFan
School: Southern Medical University,
Course: Biomedical Engineering
Keywords: Magnetic resonance imaging Non-invasive temperature measurement Proton resonance frequency Sparse sampling Compressed Sensing
CLC: R310
Type: Master's thesis
Year: 2011
Downloads: 56
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Abstract

Magnetic resonance imaging may be provided under the conditions of the non-invasive imaging of the structure and function of the internal organization of the human body or organism compared to CT and other imaging techniques, it has a multi-parameter imaging the human body without ionizing radiation, etc., so its clinical been widely used, and to become one of the most important method in the field of medical diagnostics. In recent years, minimally invasive and non-invasive surgical techniques continue development of thermal ablation for prostate cancer and uterine fibroids greatly concerned by people. Minimally invasive techniques in the treatment of malignant lesions do not cause or minimize damage to normal tissue around the lesion. Surgery in the patient's body, and reduce the cost of surgery to reduce the morbidity and mortality. The basic principle of thermal ablation: the rise and kill diseased tissue temperature by heating. Meanwhile, it must ensure that the surrounding healthy tissue, the cell temperature is maintained within a safe range. Therefore, how to quickly and accurately measure the temperature change has become the focus of people's studies of lesions during treatment. Only by the temperature measurement feedback information, the doctor can understand the treatment effects, predict the necrotic area and modify the treatment plan in a timely manner and to avoid injury lesion area surrounding healthy tissue. Imaging methods and monitoring thermal ablation process, mainly three types: CT imaging, ultrasound imaging, and MR imaging. Compared with the other two technologies, the MR temperature measurement techniques are not only for precise positioning of the target area, but also a temperature change in the treatment process to measure quantitatively, even be possible to predict the necrotic area. MR temperature measurements are non-invasive temperature measurement techniques, the use of certain imaging parameters of temperature sensitivity. MR method of measuring temperature proton resonance frequency (Proton Resonance Frequency PRF), depending on the use of temperature-sensitive parameters, the spin-lattice relaxation time T1, the diffusion coefficient of water molecules, 3D-MRSI several. Currently the most widely used in the low-field environment is the method of spin-lattice relaxation time T1, but because of the different organizations T1 sensitive to temperature coefficient, the T1 temperature sensitive correction is more difficult, the clinical application of this method is not good. PRF method to a linear relationship between their resonance frequency variation and temperature variation within a certain range, the sensitivity coefficient of the temperature thereof is very little difference for different organizations except (fat), close to the pure water PRF temperature sensitivity coefficient (-0.01ppm / ℃), and can achieve near real-time temperature measurement, people pay attention. However, due to the the PRF method of temperature sensitivity and is proportional to the field strength, so the more the applied high field strength of the superconducting environment, while the low-field application rarely. Sparse magnetic resonance imaging technology to shorten the time of the data collection of this pathway by reducing the amount of K-space data acquisition. Reduce the amount of data acquisition, so that the collected data is no longer satisfy the sampling theorem, the image reconstructed using these data there are serious artifacts. However, sparse theory of magnetic resonance imaging shows that if the use of down-sampled at random, similar to noise and artifacts caused by the down-sampling in the performance of the image in a transform domain (such as the wavelet transform), as long as to be reconstructed image in the transform The domain has a sparse and a suitable method of nonlinear reconstruction reconstruction can still be accurately reconstructed image. Sparse magnetic resonance acquisition mode can further improve the time resolution of the temperature measurement. This article attempts to low field permanent environment, the use of the experimental study: (1) based on the chemical shift of the proton resonance frequency (PRF) thermometry method for permanent in the low-field magnetic resonance environment based on proton resonance frequency chemical shift the feasibility of the method of temperature measurement. Permanent magnet devices XGY Oper-0.4T In this paper, the choice of the temperature measurement method based on the chemical shift of the proton resonance frequency, using the FLASH sequence capture agar gel cooling process data and measurement results were compared with the glass thermometer. The MRI thermometry experimental results reached: a head coil ± 1.5 ° C, precision a body coil ± 2 ° C; each scan time, the time resolution MRI thermometry for 6s. Thus proving that, in the low-field proton resonance frequency chemical shift thermometry method accuracy and time resolution to meet the clinical requirements. (2) the introduction of magnetic resonance images of the sparse reconstruction ideas to the temperature measurement, and a full matrix scanning the agar cool experimental data simulation generates a sparse collection of data to be verified. The experimental results show that the set of sparse data generated by the temperature change is still relatively accurate information.

Research on Temperature Measurement Based Chemical Shifting of Proton Resonance Frequency at Low Field

Abstract

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