Development of an Add-on 23Na-MRI Radiofrequency Platform for a 1H-MRI System Using a Crossband Repeater: Proof-of-concept.

23Na-MRI provides information on Na+ content, and its application in the medical field has been highly anticipated. However, for existing clinical 1H-MRI systems, its implementation requires an additional broadband RF transmitter, dedicated transceivers, and RF coils for Na+ imaging. However, a standard medical MRI system cannot often be modified to perform 23Na imaging. We have developed an add-on crossband RF repeater system that enables 23Na-MRI simply by inserting it into the magnet bore of an existing 1H MRI. The three axis gradient fields controlled by the 1H-MRI system were directly used for 23Na imaging without any deformation. A crossband repeater is a common technique used for amateur radio. This concept was proven by a saline solution phantom and in vivo mouse experiments. This add-on RF platform is applicable to medical 1H MRI systems and can enhance the application of 23Na-MRI in clinical usage.

Development of a Car-mounted Mobile MR Imaging System for Diagnosis of Sports-related Wrist Injury.

Portable MRI scanners, in which a permanent magnet with a low magnetic field is mounted on a small car, have enabled the performance of MRI examinations in various remote environments. Here, we have modified the portable MRI system to enable the early diagnosis of wrist sports injuries among tennis players. A RF probe specifically designed for the human wrist was developed, and a power supply scheme using a small generator was introduced. The portable MRI system was located at a tennis school and imaging of the wrists of junior tennis players was performed. To demonstrate clinical feasibility, image quality was assessed by a radiologist and clinical evaluations were performed. In most cases, the image quality was sufficient for diagnosis, and triangular fibrocartilage complex damage could be detected. The results indicated that the modified portable MRI system could be applied for an early diagnosis of wrist injuries.

Use of a Small Car-Mounted Magnetic Resonance Imaging System for On-Field Screening for Osteochondritis Dissecans of the Humeral Capitellum.

Mobile magnetic resonance imaging (MRI) using a car is a recent advancement in imaging technology. Specifically, a car-mounted mobile MRI system is expected to be used for medical check-ups; however, this is still in the research stage. This study demonstrated the practicality of a small car-mounted mobile MRI in on-field screening for osteochondritis dissecans (OCD) of the humeral capitellum. In the primary check-up, we screened the throwing elbows of 151 young baseball players using mobile MRI and ultrasonography. We definitively diagnosed OCD at the secondary check-up using X-ray photography and computed tomography or MRI. We investigated the sensitivity and specificity of mobile MRI and ultrasonography for OCD. Six patients were diagnosed with OCD. The sensitivity was 83.3% for mobile MRI and 66.7% for ultrasonography, with specificity of 99.3% vs. 100%, respectively. One patient was detected using ultrasonography but was missed by mobile MRI due to poor imaging quality at the first medical check-up. Following this false-negative case, we replaced a damaged radio frequency coil to improve the image quality, and the mobile MRI could detect all subsequent OCD cases. Two patients were diagnosed by mobile MRI only; ultrasonography missed cases lacking subchondral bone irregularity, such as a healing case, and an early-stage case. Mobile MRI could screen for OCD from the very early stages through the healing process and is therefore a practical tool for on-field screening.

Development of a small car-mounted magnetic resonance imaging system for human elbows using a 0.2 T permanent magnet.

Portable magnetic resonance imaging (MRI) scanners can provide opportunities for mobile operation in many environments including disease screening and primary care suites. Here, we develop a new, compact transportable MRI system for imaging small joints of the extremities using a 0.2 T, 200 kg permanent magnet. The whole system, including the magnet, gradient coils, RF probes, and MRI consoles (80 kg in weight) was installed in a standard-size minivan-style vehicle. The use of the open-geometry magnet enables easy patient positioning within the limited space of the vehicle. We show that our portable MRI system provides clinically relevant images of screening for elbow injuries induced by overuse of overhand throwing. This transportable system is deployable during sport events or in environments with poor access to MRI systems, and could be applicable for mass screening, early diagnosis, and case finding.