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.

MRI biomarkers such as T₂ , T₂ * and T_1rho have been widely used, but are confounded by the magic angle effect. The purpose of this study is to investigate the use of the two-dimensional ultrashort echo time magnetization transfer (UTE-MT) sequence for potential magic angle independent MR biomarkers. Magnetization transfer was investigated in cadaveric Achilles tendon samples using the UTE-MT sequence at five MT powers and five frequency offsets ranging from 2 to 50 kHz. The protocol was applied at five sample orientations ranging from 0 to 90° relative to the B₀ field. The results were analyzed with a two-pool quantitative MT model. Multiple T_E data were also acquired and mono-exponential T₂ * was calculated for each orientation. Macromolecular proton fractions and exchange rates derived from UTE-MT modeling did not appreciably change between the various orientations, whereas the T₂ * relaxation time demonstrated up to a sixfold increase from 0° to 55°. The UTE-MT technique with two-pool modeling shows promise as a clinically compatible technique that is resistant to the magic angle effect. This method provides information on the macromolecular proton pool that cannot be directly obtained by other methods, including regular UTE techniques.

Tissues, such as bone, tendon, and ligaments, contain a high fraction of components with "short" and "ultrashort" transverse relaxation times and therefore have short mean transverse relaxation times. With conventional magnetic resonance imaging (MRI) sequences that employ relatively long echo times (TEs), there is no opportunity to encode the decaying signal of short and ultrashort T2 /T2 * tissues before it has reached zero or near zero. The clinically compatible ultrashort TE (UTE) sequence has been increasingly used to study the musculoskeletal system. This article reviews the UTE sequence as well as various modifications that have been implemented since its introduction. These modifications have been used to improve efficiency or contrast as well as provide quantitative analysis. This article reviews several clinical musculoskeletal applications of UTE.

Purpose

To investigate quantitative 2D ultrashort echo time magnetization transfer (UTE-MT) imaging in ex vivo bovine cortical bone and in vivo human tibial cortical bone.

Methods

Data were acquired from five fresh bovine cortical bone samples and five healthy volunteer tibial cortical bones using a 2D UTE-MT sequence on a clinical 3T scanner. The 2D UTE-MT sequence used four or five MT powers with five frequency offsets. Results were analyzed with a two-pool quantitative MT model, providing measurements of macromolecular fraction (f), macromolecular proton transverse relaxation times (T_2m ), proton exchange rates from water/macromolecular to the macromolecular/water pool (RM_0m /RM_0w ), and spin-lattice relaxation rate of water pool (R_1w ). A sequential air-drying study for a small bovine cortical bone chip was used to investigate whether above MT modeling parameters were sensitive to the water loss.

Results

Mean fresh bovine cortical bone values for f, T_2m , R_1w , RM_0m , and RM_0w were 59.9 ± 7.3%, 14.6 ± 0.3 μs, 9.9 ± 2.4 s^-1 , 17.9 ± 3.6 s^-1 , and 11.8 ± 2.0 s^-1 , respectively. Mean in vivo human cortical bone values for f, T_2m , R_1w , RM_0m and RM_0w were 54.5 ± 4.9%, 15.4 ± 0.6 μs, 8.9 ± 1.1 s^-1 , 11.5 ± 3.5 s^-1 , and 9.5 ± 1.9 s^-1 , respectively. The sequential air-drying study shows that f, RM_0m , and R_1w were increased with longer drying time.

Conclusion

UTE-MT two-pool modeling provides novel and useful quantitative information for cortical bone. Magn Reson Med 79:1941-1949, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Purpose

To accelerate the quantitative ultrashort echo time imaging using a time-efficient 3D multispoke Cones sequence with magnetization transfer (3D UTE-Cones-MT) and signal modeling.

Theory and methods

A 3D UTE-Cones-MT acquisition scheme with multispoke per MT preparation and a modified rectangular pulse (RP) approximation was developed for two-pool MT modeling of macromolecular and water components including their relative fractions, relaxation times and exchange rates. Numerical simulation and cadaveric specimens, including human Achilles tendon and bovine cortical bone, were investigated using a clinical 3T scanner.

Results

Numerical simulation showed that the modified RP model provided accurate estimation of MT parameters when multispokes were acquired per MT preparation. For the experiment with the Achilles tendon and cortical bone samples, the macromolecular fractions were 20.4 ± 2.0% and 59.4 ± 5.3%, respectively.

Conclusion

The 3D multispoke UTE-Cones-MT sequence can be used for fast volumetric assessment of macromolecular and water components in short T₂ tissues. Magn Reson Med 79:692-700, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Posterolateral (PLC) and posteromedial (PMC) corners of the knee represent complex anatomic regions because of intricate soft tissue and osseous relationships in small areas. Concise knowledge of these relationships is necessary before approaching their evaluation at imaging. Magnetic resonance imaging offers an accurate imaging diagnostic tool to establish normal anatomy and diagnose and characterize soft tissue and osseous injury. It is important to carefully evaluate the PLC and PMC structures on magnetic resonance imaging before planned surgical intervention to avoid potential complications resulting from occult injury.

Purpose

To develop a 3D adiabatic T_1ρ prepared ultrashort echo time cones (3D AdiabT_1ρ UTE-Cones) sequence for whole knee imaging on a clinical 3T scanner.

Methods

A train of adiabatic full passage pulses were used for spin locking, followed by time-efficient multispoke UTE acquisition to detect signals from both short and long T₂ tissues in the whole knee joint. A modified signal model was proposed for multispoke UTE data fitting. The feasibility of this 3D AdiabT_1ρ UTE-Cones technique was demonstrated through numerical simulation, phantom, and ex vivo knee sample studies. The 3D AdiabT_1ρ UTE-Cones technique was then applied to 6 in vivo knee joints of healthy volunteers to measure T_1ρ values of quadriceps tendon, patellar tendon, anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), meniscus, patellar cartilage, and muscle.

Results

Numerical simulation, phantom and ex vivo knee sample studies demonstrated the feasibility of whole knee imaging using the proposed multispoke 3D AdiabT_1ρ UTE-Cones sequence. The healthy volunteer knee study demonstrated an averaged T_1ρ of 13.9 ± 0.7 ms for the quadriceps tendon, 9.7 ± 0.8 ms for the patellar tendon, 34.9 ± 2.8 ms for the ACL, 21.6 ± 1.4 ms for the PCL, 22.5 ± 1.9 ms for the meniscus, 44.5 ± 2.4 ms for the patellar cartilage, and 43.2 ± 1.1 ms for the muscle.

Conclusion

The 3D AdiabT_1ρ UTE-Cones sequence allows volumetric T_1ρ assessment of both short and long T₂ tissues in the knee joint on a clinical 3T scanner.

Objective

To correlate training habits of Taekwondo (TKD) athletes to risk for injury.

Background

TKD is a Korean marital art that has been growing in popularity, with nearly 2 million individuals practicing the sport in the United States. Because of the combative nature of the sport, injuries are an inherent risk. However, data on proper training habits, types of injuries sustained during training, and recommendations for athletes to avoid injury are lacking. Frequently, studies of TKD evaluate athletes' injuries during tournaments, but most do not evaluate athletes in training.

Hypothesis

Increased training would potentially create more injuries secondary to increased exposure.

Methods

This is a cross-sectional observational survey of 72 collegiate TKD athletes from the Pacific West Sanctioned Taekwondo Tournaments in the 2008-2009 season. Variables analyzed during training and competitions were training sessions per week, workout habits, belt level, years of experience, and characteristics of injury (location, type, mechanism, situation, treatment, and days missed).

Results

TKD training habits of individuals who practiced four or more times per week (odds ratio [OR], 4.5; P=0.005) or sparred for more than 2 hours (OR, 8.7; P=0.003) were associated with significantly increased odds (risk) of sustaining an injury. Those who had more than 3 years of tournament experience were more likely to sustain an injury (OR, 0.198; P=0.020).

Conclusion

Increased risk for injury with more frequent practice and longer sparring should remind coaches and trainers that monitoring and adjusting the athletes' training schedules and exposure time could decrease the chance of injury. An athlete that has spent more years in tournaments along with high-frequency and long-duration training was associated with greater risk for injuries. Prevention and education about the risk for exposure to injury may may help athletes and trainers promote prevention strategies and adjust an athletes' training and tournament schedules to decrease the risk for injury.

Osteoarthritis is a common chronic degenerative disease that causes pain and disability with increasing incidence worldwide. The osteochondral junction is a dynamic region of the joint that is associated with the early development and progression of osteoarthritis. Despite the substantial advances achieved in the imaging of cartilage and application to osteoarthritis in recent years, the osteochondral junction has received limited attention. This is primarily related to technical limitations encountered with conventional MR sequences that are relatively insensitive to short T2 tissues and the rapid signal decay that characterizes these tissues. MR sequences with ultrashort echo time (UTE) are of great interest because they can provide images of high resolution and contrast in this region. Here, we briefly review the anatomy and function of cartilage, focusing on the osteochondral junction. We also review basic concepts and recent applications of UTE MR sequences focusing on the osteochondral junction.

Synovial chondromatosis is a rare disease that causes disability and dysfunction of the involved synovial joint. We describe the second case in the literature of intraligamentous synovial chondromatosis involving the anterior cruciate ligament, confirmed by pathology after arthroscopic removal of the chondral bodies. We also describe associated magnetic resonance imaging findings which may be helpful for diagnosis of this very rare entity.