Modern low-field MRI

Abstract

This narrative review explores recent advancements and applications of modern low-field (≤ 1 Tesla) magnetic resonance imaging (MRI) in musculoskeletal radiology. Historically, high-field MRI systems (1.5 T and 3 T) have been the standard in clinical practice due to superior image resolution and signal-to-noise ratio. However, recent technological advancements in low-field MRI offer promising avenues for musculoskeletal imaging. General principles of low-field MRI systems are being introduced, highlighting their strengths and limitations compared to high-field counterparts. Emphasis is placed on advancements in hardware design, including novel magnet configurations, gradient systems, and radiofrequency coils, which have improved image quality and reduced susceptibility artifacts particularly in musculoskeletal imaging. Different clinical applications of modern low-field MRI in musculoskeletal radiology are being discussed. The diagnostic performance of low-field MRI in diagnosing various musculoskeletal pathologies, such as ligament and tendon injuries, osteoarthritis, and cartilage lesions, is being presented. Moreover, the discussion encompasses the cost-effectiveness and accessibility of low-field MRI systems, making them viable options for imaging centers with limited resources or specific patient populations. From a scientific standpoint, the amount of available data regarding musculoskeletal imaging at low-field strengths is limited and often several decades old. This review will give an insight to the existing literature and summarize our own experiences with a modern low-field MRI system over the last 3 years. In conclusion, the narrative review highlights the potential clinical utility, challenges, and future directions of modern low-field MRI, offering valuable insights for radiologists and healthcare professionals seeking to leverage these advancements in their practice.

Keywords: 0.55 Tesla; Field strength; Joints; Knee; Low-field; MRI; Musculoskeletal radiology.

Fig. 1

MRI at 0.55 T of the lumbar spine of a 32-year-old patient with non-radiating lower back pain. A T2-weighted sagittal image shows a subligamental disc herniation L4/5 inferiorly protruded (arrow). B Corresponding axial T2-weighted image at the level of the intervertebral space shows median disc protrusion without recessal obstruction (arrow). Acquisition time (TA): 02:48 min (A), 03:35 min (B)

Fig. 2

MRI at 0.55 T of the elbow of a 44-year-old patient with lateral elbow pain for the last 4 months. Coronal proton density-weighted image with spectral fat saturation shows increased intratendinous signal at the origin of the common extensor tendon group consistent with epicondylopathy (arrow). B Corresponding axial proton density-weighted image shows a small insertional defect consistent with a circumscribed partial rupture (arrow). TA: 01:49 min (A), 03:32 min (B)

Fig. 3

MRI at 0.55 T of the hand of a 77-year old patient with suspected late-onset rheumatoid arthritis. Coronal T1-weighted (A) image shows erosions at the 2nd metacarpophalangeal joint (arrows). In addition, osteophytes are depicted at the 2nd and 4th distal interphalangeal joints (arrowheads). B Corresponding STIR image shows synovitis at the metacarpophalangeal joints 2 and 3, and at the proximal interphalangeal joint 4 (arrows). TA: 03:20 min (A), 05:11 min (B)

Fig. 4

0.55-T MRI of the knee of a 13-year-old girl after knee transient first-time patellar dislocation. A Sagittal proton density-weighted image with spectral fat saturation shows a traumatic bone contusion in the anterior-central lateral femoral condyle (arrows) and joint effusion (asterisk). B Axial proton density-weighted image with spectral fat saturation shows a rupture of the medial patellofemoral ligament at the patellar attachment (arrow). TA: 04:00 min (A), 05:42 min (B)

Fig. 5

Comparison of a 1.0-T small-bore extremity system with a standard 1.5 T large-bore MRI for assessment of knee osteoarthritis. A Standard 1.5-T proton density-weighted fat-suppressed image shows small subchondral bone marrow lesions (BMLs) at the central medial femur and the anterior medial tibia (arrows). In addition, there is a horizontal oblique degenerative tear of the posterior horn of the medial meniscus (arrowhead). B At 1.0-T extremity MRI, BMLs (arrows) and tear (arrowhead) are visualized with similar image quality. C Axial 1.5-T proton density-weighted fat-suppressed image shows a small BML at the lateral patella (arrow) and joint effusion (asterisk). D Axial 1.0-T image shows BML (arrow) and effusion (asterisk) in similar fashion. In addition, there is a small medial patellar plica (arrowhead). TA: 3:53 min (A), 4:44 min (B), 2:45 min (C), 2:59 min (D)

Fig. 6

MRI at 0.55 T of the ankle of a 14-year-old patient after ankle sprain. A Axial proton density-weighted image shows a complete rupture of the anterior talofibular ligament (arrow). B Parasagittal proton density-weighted image demonstrates that the anterior and posterior tibiofibular ligaments are intact (arrows). C Small-bore dedicated 1.0-T extremity MRI allows for assessment of the ankle joint, but depending on size of the patient usually plantar flexion is applied as shown in this T1-weighted spin echo image. Note circular field of view of magnet system. TA: 03:07 min (A), 05:26 min (B), 04:21 min (C)

Fig. 7

0.55-T MRI of the temporomandibular joint of a 55-year-old patient with chronic pain. A Sagittal proton density-weighted image with closed mouth shows a normal disc morphology and position without degenerative changes of the temporomandibular joint (arrows). B The open mouth position also shows a normal morphology and position of the disc (arrows). TA: 02:48 min (A), 02:48 min (B)