MR Parametric Mapping as a Biomarker of Early Joint Degeneration

Abstract

Context: Osteoarthritis (OA) is a common, worldwide disorder. Magnetic resonance (MR) imaging can directly and noninvasively evaluate articular cartilage and has emerged as an essential tool in the study of OA.

Evidence acquisition: A PubMed search was performed using the keywords quantitative MRI and cartilage. No limits were set on the range of years searched. Articles were reviewed for relevance with an emphasis on in vivo studies performed at 3 tesla.

Study design: Clinical review.

Level of evidence: Level 4.

Results: T2, T2*, T1 (particularly when measured after exogenous contrast administration, such as with the delayed gadolinium-enhanced MR imaging of cartilage [dGEMRIC] technique), and T1ρ are among the most widely utilized quantitative MR imaging techniques to evaluate cartilage and have been implemented in various patient cohorts. Existing challenges include reproducibility of results, insufficient consensus regarding optimal sequences and parameters, and interpretation of values.

Conclusion: Quantitative assessment of cartilage using MR imaging techniques likely represents the best opportunity to identify early cartilage degeneration and to follow patients after treatment. Despite existing challenges, ongoing work and unique approaches have shown exciting and promising results.

Keywords: cartilage; osteoarthritis; parametric mapping; quantitative MRI.

Figure 1.

Magnetic resonance (MR) images (11.7 T) with 20-µm in-plane resolution. (A) The patella shows the perpendicular orientation of the deep and intermediate layers of cartilage. Note the high signal intensity superficial layer (arrows), which is due to the magic angle effect as the fibrils parallel the surface. (B) Tibial plateau with chondral fraying shows the orientation change at the superficial layer (arrows).

Figure 2.

Schematic of a magnetic resonance (MR) imaging machine. When inside the magnet, protons in the patient’s body will tend to align with the main magnetic axis, or z-direction in an exponential manner (characterized by T1). After radiofrequency waves are introduced, there is a net transverse magnetization vector in the x-y direction, which can be detected with specially positioned coils, decreasing in an exponential manner (characterized by T2 or T2*).

Figure 3.

T2 and T1 relaxation. (a) Illustrative magnetization decay curves in the x-y plane (M_xy) for diseased tissue (red curve) compared with normal tissue (black curve), with T2 times defined as the time required for 63% loss of magnetization. (b) Illustrative magnetization growth curve (M_Z) for diseased tissue (red curve) compared with normal tissue (black curve), with T1 times defined as the time required for magnetization to reach 63% of its maximum value.

Figure 4.

A 52-year-old woman with International Cartilage Repair Society (ICRS) grade 4 lesions measuring 2.5 × 3.5 cm at the medial femoral condyle and 2.0 × 2.5 cm at the medial tibial plateau who underwent arthroscopic subchondral drilling followed by postoperative intra-articular injections of bone marrow aspirate concentrate, platelet-rich plasma, and hyaluronic acid. (a and d) Coronal and sagittal fluid-sensitive magnetic resonance (MR) images show grade 4 lesions 2 days after surgery. (b and e) Coronal fluid-sensitive and sagittal intermediate-weighted MR images 18 months after surgery show impressive volume of cartilage repair tissue at both sites. (c and f) Coronal and sagittal T2 maps show that the repair tissue does not demonstrate normal stratification expected of hyaline cartilage. Case courtesy of Jeb Broyles, MD (Bone & Joint Clinic of Baton Rouge, Louisiana).

Figure 5.

dGEMRIC color overlays representing cartilage glycosaminoglycan (GAG) content. (a) Healthy, nonosteoarthritic knee with preserved GAG content and resultant reference T1 values in the mid to upper range of the scale (green arrows). (b) In a patient with medial compartment pain but without radiographic osteoarthritis (OA), contrast agent accumulates in cartilage resulting in decreased T1 values (red arrows) compared with the healthy control. This is due to decreased GAG content and is consistent with early OA. Case courtesy of Jasper van Tiel, MD, PhD, and Edwin Oei, MD, PhD (Erasmus MC Rotterdam, The Netherlands).

Figure 6.

A 30-year-old woman with anterior knee pain and surgically confirmed chondromalacia involving the entire lateral facet of the patella. (a) T1ρ map shows diffusely abnormal lateral facet, including an area of elevated values at the superior portion of the patella (arrow). (b) On the conventional intermediate-weighted magnetic resonance (MR) image, the superior portion was prospectively interpreted as normal.