Advantages of Low-Field Scanners
Most magnets sold today are high-field superconducting. Why would anyone want to buy a lower field strength scanner?
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Although superconducting magnets of field strength 1.5T and higher dominate the MR marketplace, lower field scanners do often certain advantages.
1) Open design. The use of permanent and resistive magnets allow for these scanners to have a smaller physical footprints, wider bores, and a variety of configurations to maximize patient comfort and minimize claustrophobia. Open design also permits access to the patient for interventional MRI procedures.
2) Lower initial purchase price. As a rule scanner purchase price increases with field strength. The relationship is not linear, but a 0.35T permanent magnet system might cost only one-third to one-half that of a 1.5T superconducting unit.
3) Lower operational costs. Lower field permanent magnet scanners do not require liquid helium or special maintenance. (Resistive electromagnet scanners, however, consume large amounts of energy to produce the field and cool the coils during scanning and have relatively high operational costs.)
4) Lower fringe field. This means it is easier (and cheaper) to site and shield the magnet within a hospital or imaging center. Projectile risks to patients and personnel are reduced. Anesthesia and monitoring equipment may be brought closer to a low-field scanner.
5) Reduction of certain MR artifacts. Chemical shift, susceptibility, and flow/motion artifacts are often less apparent on images from lower field scanners. The biggest advantage may be for scanning patients with metal hardware, where susceptibility-induced spatial distortions and signal loss are typically much reduced compared to those obtained at high-fields.
6) Lower energy deposition in tissues. The amount of energy deposited in tissues by radiofrequency pulses (called the Specific Absorption Rate or SAR) is proportional to the square of the magnetic field strength. High SAR can cause dangerous heating in infants and sick/elderly patients who cannot regulate their body temperatures, so lower field scanners hold an advantage here.
7) Portability. In 2020 the world's first portable MR scanner, the Hyperfine Swoop™, began commercial sales in the US, made possible by innovative design and ultra-low field (0.064T).
1) Open design. The use of permanent and resistive magnets allow for these scanners to have a smaller physical footprints, wider bores, and a variety of configurations to maximize patient comfort and minimize claustrophobia. Open design also permits access to the patient for interventional MRI procedures.
2) Lower initial purchase price. As a rule scanner purchase price increases with field strength. The relationship is not linear, but a 0.35T permanent magnet system might cost only one-third to one-half that of a 1.5T superconducting unit.
3) Lower operational costs. Lower field permanent magnet scanners do not require liquid helium or special maintenance. (Resistive electromagnet scanners, however, consume large amounts of energy to produce the field and cool the coils during scanning and have relatively high operational costs.)
4) Lower fringe field. This means it is easier (and cheaper) to site and shield the magnet within a hospital or imaging center. Projectile risks to patients and personnel are reduced. Anesthesia and monitoring equipment may be brought closer to a low-field scanner.
5) Reduction of certain MR artifacts. Chemical shift, susceptibility, and flow/motion artifacts are often less apparent on images from lower field scanners. The biggest advantage may be for scanning patients with metal hardware, where susceptibility-induced spatial distortions and signal loss are typically much reduced compared to those obtained at high-fields.
6) Lower energy deposition in tissues. The amount of energy deposited in tissues by radiofrequency pulses (called the Specific Absorption Rate or SAR) is proportional to the square of the magnetic field strength. High SAR can cause dangerous heating in infants and sick/elderly patients who cannot regulate their body temperatures, so lower field scanners hold an advantage here.
7) Portability. In 2020 the world's first portable MR scanner, the Hyperfine Swoop™, began commercial sales in the US, made possible by innovative design and ultra-low field (0.064T).
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