China
Africa
Explore chapters and articles related to this topic
Magnetic Resonance Imaging Physics
Published in Debbie Peet, Emma Chung, Practical Medical Physics, 2021
MRI involves several hazards, including strong magnetic fields, the use of liquid helium, contrast agent side-effects and potential hazards to hearing. Trainee Clinical Scientists need to develop expertise in all aspects of MRI safety, which includes reading and familiarising themselves with relevant guidelines, local rules and standard operating procedures (SOP). A key role of the Clinical Scientist is to review MR local rules and SOPs, providing necessary recommendations for updating these safety documents.
Safety Considerations on Siting and Shielding
Published in Bertil R. R. Persson, Freddy Ståhlberg, Health and Safety of Clinical NMR Examinations, 2019
Bertil R. R. Persson, Freddy Ståhlberg
To maintain the superconducting conditions, the magnet must be filled with liquid cryogens which are usually transferred into the cryostat from transport vessels (dewar) using routine top-pressure methods. During this operation one must put the cryogens in the correct inlets and not blow warm helium gas onto the magnet. These mistakes could result in a magnet quench. Liquid nitrogen consumption will be of the order of 200 to 250 ℓ/week and can be obtained from bulk storage either directly by a fixed, insulated transfer pipe or transport dewar of suitable capacity. The cryostat capacity of liquid helium is 200 to 450ℓ and typical consumption is between 50 to 100 ℓ/week with a monthly refill period. The costs of cryogens vary considerably but are in the order of 6 U.S. dollars/ℓ of liquid helium and 0.7 U.S. dollars/ℓ of liquid nitrogen. In order to reduce the cost it may be effective to install a helium recovery system. Physical data for the cryogenics are given in Table 1.
History of Brain Mapping and Neurophotonics
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
Babak Kateb, Frank Boehm, Alexandra Jalali, Vassiliy Tsytsarev, Vicky Yamamoto, Bahram Jalali, Derek Backer, Brian Pikul, Parham Yashar, Yu Chen
The integration of a flashpoint (LED-based) navigational strategy (Flashpoint, integrated technologies, Boulder, CO) enables the capacity for 3D tracking at the central axis of the magnet, which facilitates a spherical imaging area of Ø30 cm (Moriarty et al., 1996; Lipson et al., 2001; Albayrak et al., 2004). Increased patient access was made possible via the enhanced cooling of the magnetic coils through the use of niobium tin, and thermal shielding that incorporated a dual-stage cryocooler, which negated the necessity for liquid helium baths. A customized vertically positioned microscope and a range of MR-safe surgical instrumentation and integrated anesthesia ventilators and monitors were developed to be accommodated by this system. Further, a number of LCD screens were arranged in close proximity to the surgeons to allow easy viewing of the acquired imagery (single-plane imagery is typically acquired within 60–120 s) (Albayrak et al., 2004).
Anaesthesia in the MRI suite
Published in Southern African Journal of Anaesthesia and Analgesia, 2018
Reinier Swart, William Ian Duncombe Rae
The superconducting magnets are cooled to below 4.2 Kelvin by super-cooled liquids or cryogens, with liquid helium being the most commonly used agent.1 Quenching is the process through which the liquid is rapidly boiled off and large volumes of gas are produced, which are generally vented into the atmosphere outside the building. Subsequently, the magnets lose their superconducting ability and the magnetic field is deactivated. This process may be initiated manually by means of an emergency switch generally located in the chamber, or may occur because of an error of installation or service.3 This process rapidly cools the gases in the MRI chamber if the vent is exposed to the environment and may lead to condensation of liquid oxygen. The descending vapour cloud may be harmful to the patient and staff, as it may create a hypoxic environment in the MRI suite. As a result of this possibility, oxygen sensors should be present in the MRI suite to alert the operators when a hypoxic environment develops.6 The implications of this process should also caution the anaesthetic care provider not to view quenching as a first-line option in the event of an emergency. It is, however, imperative that quenching be reserved for dire emergencies only, for example, in the case of impingement of a person to the magnet by another object. Each unit should have a quenching policy that is readily available.