Operating principle and scanner design
The method is based on the physical phenomenon of nuclear magnetic resonance (NMR). During the procedure, the absorbed high-frequency signal is re-emitted by the protons and (or) neutrons of the patient's tissues while situated in a strong magnetic field.
The scanner hardware is a complex system that includes the following key components:
- Main magnet.
- Radiofrequency coils (performing the functions of signal transmitter and receiver).
- Gradient coils.
- Computer workstation with high-capacity storage for reconstructing the acquired data.
Advantages of MRI in musculoskeletal imaging
Tomography is ideally suited for evaluating orthopedic pathologies due to the high difference in signals originating from various tissues. This provides the specialist with a detailed picture of the injury site.
Key capabilities of the method:
- Excellent soft tissue differentiation: The scanner clearly visualizes ligaments, tendons, muscles, hyaline cartilage, as well as adjacent blood vessels and nerves.
- Evaluation of bone structures: The method allows for reliable differentiation between cortical and trabecular bone.
- Detection of occult injury: MRI is capable of detecting contusions and trabecular bone microfractures. These injuries often accompany complex ligament tears, but are completely undetectable on standard radiographs and computed tomography.
- Diagnosis of joints and spine: To date, MRI is the most informative method in this field. It provides targeted assessment of the spinal cord, spinal nerve roots, and intervertebral discs.
Why choose MRI over CT or ultrasound for ligaments?
In injuries of the tendon-ligament apparatus, it is crucial to choose the correct diagnostic imaging method while understanding the limitations of alternative technologies:
- Ultrasound imaging (US): Ultrasound is also actively used to assess soft tissues and tendons (especially the Achilles tendon). Its main advantages are the absence of ionizing radiation, relatively low cost, equipment mobility, and the ability to immediately compare the injured limb with the healthy (contralateral) one. Ultrasound effectively detects joint effusion and meniscal injuries; however, MRI provides a deeper, higher-contrast, and more detailed spatial picture.
- Computed tomography (CT): Although CT is capable of producing ultra-thin slices (from 0.1 to 11 mm) and building excellent 3D bone models, it has poor soft tissue differentiation. CT is indispensable for complex comminuted fractures (pelvis, facial bones, ankle), but the ligamentous apparatus is poorly visualized on it. Furthermore, the presence of metal implants (plates, screws, rods, joint replacements) causes severe artifacts that drastically reduce image quality, and the scan itself involves a high radiation dose.
Additional protocols: contrast enhancement and angiography
In complex clinical cases, tendon and joint examinations can be expanded using additional techniques:
- Contrast administration: Intravenous or intra-articular contrast enhancement is used to better highlight pathological processes and injury boundaries.
- MR angiography: Allows visualization of blood vessels in any plane and creation of three-dimensional (3D) models of the vascular bed. This mode is critical for assessing blood supply in severe limb trauma, as well as for analyzing the vascularity of detected soft tissue neoplasms.
Class and exam questions
Why is MRI prescribed instead of computed tomography for a ligament tear?
Computed tomography (CT) has poor soft tissue differentiation and is primarily intended for evaluating bones and bone fragments. MRI, on the other hand, provides high signal contrast from ligaments, tendons, and muscles, allowing for a detailed examination of their structure.
Can ultrasound (US) replace MRI in a tendon injury?
In a number of cases, yes. Ultrasound is highly informative for examining superficial structures, such as the Achilles tendon. The method is less expensive, uses no radiation, and provides the opportunity to immediately compare the injured area with the healthy symmetrical side.
Does MRI show bone damage?
Yes, the method excellently differentiates cortical and trabecular bone. Moreover, MRI visualizes occult contusions and trabecular bone microfractures that are completely undetectable on standard radiographs or CT scans.
Is a contrast agent used in joint and ligament MRI?
Yes, the capabilities of the method allow for the use of both intravenous and specific intra-articular contrast enhancement for a more accurate diagnosis.
What else to study on this topic
- Diagnosis of occult injuries: visualization of contusions and trabecular bone microfractures.
- MR angiography: assessment of the vascular bed and blood circulation in limb trauma.
- Comparison of radiation exposure and metal artifact interference in CT and MRI.
- Capabilities of ultrasound in orthopedics: diagnosis of pathologies of the Achilles tendon, menisci, and popliteal cysts.
- The role of MRI in diagnosing spinal disorders: evaluation of intervertebral discs and spinal nerve roots.
Master the entire topic in the "Diagnostic Radiology" course
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- Complete study guide on "MRI of tendons and ligaments" and 2,199 more pages on the subject
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