Magnetic resonance imaging (MRI) systems require a cooling close to the absolute zero point. This is necessary to avoid thermal losses due to the extremely high currents in the coils of the electromagnet used to gener...Magnetic resonance imaging (MRI) systems require a cooling close to the absolute zero point. This is necessary to avoid thermal losses due to the extremely high currents in the coils of the electromagnet used to generate the static magnetic field. The cooling is usually achieved using helium based refrigerating machine. The coldhead is an important and critical mechanical component in this system. An inefficient or failed coldhead can lead to severe damages to the MRI system or to the loss of helium. Hence, a continuous and reliable monitoring of this system component is necessary but not always available. To tackle this problem, we propose a monitoring system by means of analyzing the structure-borne noises caused by the mechanical activities of the coldhead. For this purpose, a measurement system based on piezoelectric elements was designed and implemented. Vibrations were measured at various locations at the MRI scanner with and without MR imaging. In all positions, the function of the coldhead could be detected. Hence, the developed system is suitable for monitoring an MRI’s coldhead without directly accessing the MR scanner’s hardware or software. For a future long-term monitoring, the aim is to predict a failure of the MRI’s coldhead based on changes in the vibrations signals.展开更多
Selective Internal Radiation Therapy (SIRT) is used as a treatment option for unresectable liver tumors. In SIRT, microspheres, which have a radioactive substance as an integral component, are placed via image guided ...Selective Internal Radiation Therapy (SIRT) is used as a treatment option for unresectable liver tumors. In SIRT, microspheres, which have a radioactive substance as an integral component, are placed via image guided catheters into the hepatic artery. The ionizing radiation is directly delivered to the tumor. Currently used commercially available microspheres are based on Yttrium 90, a β-emitter, which has been shown to be safe and to produce good clinical results. The technical features of Y90, their applications and their limitations are presented. Image guidance and intraoperative depiction of Yttrium 90 microspheres are restricted, which is currently one of the main limitations in SIRT. Therapy planning and control is currently based on pre- and post-operative images to evaluate the placement of the microspheres respectively. Holmium 166, another possible nuclide integrated into the microspheres emits a higher amount of secondary γ-radiation (Bremsstrahlung) than Yttrium 90. This enables an improved depiction of the microspheres inside the patient during and immediately after application, but comes with other shortfalls. Imaging of delivery and verification of the microsphere placement could solve many of the identified problems with SIRT. The different technologies are reviewed and an outlook in future developments is given particularly on image guidance and therapy control.展开更多
文摘Magnetic resonance imaging (MRI) systems require a cooling close to the absolute zero point. This is necessary to avoid thermal losses due to the extremely high currents in the coils of the electromagnet used to generate the static magnetic field. The cooling is usually achieved using helium based refrigerating machine. The coldhead is an important and critical mechanical component in this system. An inefficient or failed coldhead can lead to severe damages to the MRI system or to the loss of helium. Hence, a continuous and reliable monitoring of this system component is necessary but not always available. To tackle this problem, we propose a monitoring system by means of analyzing the structure-borne noises caused by the mechanical activities of the coldhead. For this purpose, a measurement system based on piezoelectric elements was designed and implemented. Vibrations were measured at various locations at the MRI scanner with and without MR imaging. In all positions, the function of the coldhead could be detected. Hence, the developed system is suitable for monitoring an MRI’s coldhead without directly accessing the MR scanner’s hardware or software. For a future long-term monitoring, the aim is to predict a failure of the MRI’s coldhead based on changes in the vibrations signals.
文摘Selective Internal Radiation Therapy (SIRT) is used as a treatment option for unresectable liver tumors. In SIRT, microspheres, which have a radioactive substance as an integral component, are placed via image guided catheters into the hepatic artery. The ionizing radiation is directly delivered to the tumor. Currently used commercially available microspheres are based on Yttrium 90, a β-emitter, which has been shown to be safe and to produce good clinical results. The technical features of Y90, their applications and their limitations are presented. Image guidance and intraoperative depiction of Yttrium 90 microspheres are restricted, which is currently one of the main limitations in SIRT. Therapy planning and control is currently based on pre- and post-operative images to evaluate the placement of the microspheres respectively. Holmium 166, another possible nuclide integrated into the microspheres emits a higher amount of secondary γ-radiation (Bremsstrahlung) than Yttrium 90. This enables an improved depiction of the microspheres inside the patient during and immediately after application, but comes with other shortfalls. Imaging of delivery and verification of the microsphere placement could solve many of the identified problems with SIRT. The different technologies are reviewed and an outlook in future developments is given particularly on image guidance and therapy control.
