Magnetic resonance imaging (MRI) is one of the most important medical imaging techniques today. It utilizes strong magnetic fields and radiofrequency pulses to non-invasively acquire high-resolution cross-sectional images of human tissues, playing a crucial role in diagnosing many diseases. However, traditional MRI scanners have an enclosed tubular structure, forcing patients to lie still in a narrow tunnel during scans. This creates tremendous mental stress, especially for children, elders, and patients with claustrophobia, as lying inside an enclosed tunnel can be extremely uncomfortable. Moreover, loud noise is generated continuously during MRI scans, further adding to patient discomfort. Open MRI scanners were thus developed to significantly improve patient experience.
The biggest feature of open MRI is its C-shaped or O-shaped magnet that creates an open access on both sides of the bore. Patients are positioned in the opening so that they can see the outside environment instead of being enclosed in a narrow space. This greatly alleviates patient anxiety and feelings of confinement. In addition, open access MRI generates only around 70 decibels of noise, a 40% reduction from the 110 decibels of traditional enclosed MRI scanners, allowing for a more comfortable scanning process.
C-shaped
O-shaped
In terms of system components, open MRI retains the core parts of a standard MRI scanner, including the main magnet that produces a strong static magnetic field, gradient coils that generate gradient fields, and RF coils for excitation and signal detection. The field strength of the main magnet in open MRI can still reach 0.2 to 3 Tesla, on par with conventional MRI. Open MRI also incorporates additional patient support structures and docking mechanisms to accommodate the open configuration and patient positioning requirements. Overall, while improving patient experience, open MRI retains the fundamental principles of magnetic resonance imaging and can still provide high quality images of human tissues.
Compared to traditional enclosed MRI, open MRI has the following main advantages:
1. Greatly reduces claustrophobic fears. The open design ensures patients do not feel confined inside a narrow tunnel, providing a calming environment especially for children, elderly, or claustrophobic patients. This improves compliance and allows for acquisition of high-quality scans.
2. Significantly reduced noise, allowing for more comfortable scans. Open MRI noise levels are about 40% lower than enclosed systems. The reduced noise minimizes patient anxiety, allowing longer scan times and more detailed imaging acquisition.
3. More flexible and accessible for all patients. The open access and reduced noise makes screening easier for wheelchair users, stretcher patients, or those with mobility difficulties. Open MRI scanners can scan patients directly without physically and psychologically stressful transfers.
4. Enables interventional applications. The open design provides easy access to patients during scans, facilitating MRI-guided intervention procedures. Doctors can operate on patients real-time while continuously imaging the treatment area.
There are some limitations of open MRI compared to enclosed systems:
1. Image quality may be slightly lower, especially in soft tissue contrast and resolution. The open design means the magnetic field is more inhomogeneous than traditional enclosed cylinders, leading to degraded gradient linearity and lower final image resolution. This is especially prominent on weaker low-field open MRI scanners. Stronger 1.5T or 3T open scanners can compensate for field inhomogeneity with advanced shimming and pulse sequence design. But theoretically, enclosed cylinders always enable more optimized and homogeneous fields.
2. Inferior imaging performance for obese patients due to more inhomogeneous magnetic fields. Obese patients have a larger body volume, and the open design struggles to maintain homogeneous magnetic field coverage over them. Traditional enclosed MRI scanners only need to optimize field homogeneity over a small cylindrical tunnel space, achieving better results for large patients. But open MRI vendors are working on customized solutions like wider patient openings and stronger field strengths to address this limitation.
3. More complex structure leading to higher cost of purchase and maintenance. The open design requires more complicated magnet and gradient coil geometries, along with customized patient handling systems. This increased construction complexity translates to higher initial cost compared to enclosed cylindrical magnets of equivalent field strength. Moreover, the unconventional shape of open MRI magnets makes them difficult to site within existing hospital infrastructures designed for enclosed MRI bores. Long-term maintenance and helium refills are also costlier due to the custom nature of open MRI systems. But for patients who highly benefit from the open design, these extra costs may be justified.
In summary, open architecture MRI scanners overcome the weaknesses of traditional enclosed MR systems and significantly enhance patient comfort and acceptance. They provide a friendly scanning environment benefiting more patients. With continued advances, open MRI will find wider clinical utilization, especially for anxious, pediatric, elderly, and immobilized patients.
