Quantitative Ultrashort Echo Time Magnetic Resonance Imaging Evaluation of Postoperative Menisci: a Pilot Study

Histological Findings and T2 Relaxation Time in Canine Menisci of Elderly Dogs—An Ex Vivo Study in Stifle Joints

Osteoarthritis is a chronic disease that often affects the canine stifle joint. Due to their biomechanical function, the menisci in the canine stifle play an important role in osteoarthritis. They compensate for the incongruence in the joint and distribute and minimize compressive loads, protecting the hyaline articular cartilage from damage. Meniscal degeneration favors the development and progression of stifle joint osteoarthritis. Qualitative magnetic resonance imaging (MRI) is the current golden standard for detecting meniscal changes, but it has limitations in detecting early signs of meniscal degeneration. A quantitative MRI offers new options for detecting early structural changes. T2 mapping can especially visualize structural changes such as altered collagen structures and water content, as well as deviations in proteoglycan content. This study evaluated T2 mapping and performed a histological scoring of menisci in elderly dogs that had no or only low radiographic osteoarthritis grades. A total of 16 stifles from 8 older dogs of different sex and breed underwent ex vivo magnet resonance imaging, including a T2 mapping pulse sequence with multiple echoes. A histological analysis of corresponding menisci was performed using a modified scoring system. The mean T2 relaxation time was 18.2 ms and the mean histological score was 4.25. Descriptive statistics did not reveal a correlation between T2 relaxation time and histological score. Ex vivo T2 mapping of canine menisci did not demonstrate histological changes, suggesting that early meniscal degeneration can be present in the absence of radiological signs of osteoarthritis, including no significant changes in T2 relaxation time.

Comparison of magnetic resonance imaging and computed tomography for bone assessment of neurogenic heterotopic ossification of the hip: a preliminary study

Background

Neurogenic heterotopic ossification (NHO) is a frequent complication, often involving the hip. The functional impact may require surgical management and pre-surgical imaging assessment is necessary, usually by computed tomography (CT). We aimed to compare the performances of magnetic resonance imaging (MRI) and CT for bone assessment on pre-surgical imaging of the heterotopic ossifications and their features in NHO of the hip.

Methods

This single-center prospective preliminary study included all patients who underwent surgery for NHO with joint limitation from July 2019 to March 2020. All patients had a CT after biphasic iodinated solution injection and an MRI including T1-weighted, STIR and ZTE sequences. Standardized reports were completed for both exams for each patient, evaluating location, implantation and fragmentation of NHO, relation to the joint capsule and bone mineralization, then were compared.

Results

Seven patients from 32 to 70 years old (mean = 50.2 ± 17.2 years) were evaluated. NHO were bilateral in 2 patients, for a total of nine hips: six right hips and three left hips. Observed concordance rates between MRI and CT were, respectively, 94.4% for location, 100% for circumferential extension, 87.3% for implantation 88.9% for fragmentation, 77.8% for relation to the joint capsule and 66.7% for bone mineralization. It was 100% for femoral neck fracture and osteonecrosis of the femoral head.

Conclusion

This preliminary study suggests that pre-surgical MRI imaging should be considered as effective as CT for bone assessment of NHO and their features.

Trial registration: ClinicalTrials.gov, NCT03832556. Registered February 6, 2019, https://clinicaltrials.gov/ct2/show/NCT03832556.

Zero echo time pediatric musculoskeletal magnetic resonance imaging: initial experience

BACKGROUND

Projection radiography (XR) is often supplemented by both CT (to evaluate osseous structures with ionizing radiation) and MRI (for marrow and soft-tissue assessment). Zero echo time (ZTE) MR imaging produces a "CT-like" osseous contrast that might obviate CT.

OBJECTIVE

This study investigated our institution's initial experience in implementing an isotropic ZTE MR imaging sequence for pediatric musculoskeletal examinations.

MATERIALS AND METHODS

Pediatric patients referred for extremity MRI at 3 tesla (T) underwent ZTE MR imaging to yield images with contrast similar to that of CT. A radiograph-like image was also created with ray-sum image processing. We assessed ZTE-CT/XR anatomical image quality (S_anat) from 0 (nondiagnostic) to 5 (outstanding). Further, we made image comparisons on a 5-point scale (S_comp) (range of -2 = conventional CT/XR greater anatomical delineation to +2 = ZTE-CT/XR greater anatomical delineation; 0=same) for three cohorts: (1) ZTE-XR to conventional radiography, (2) ZTE-CT to conventional CT and (3) pathological lesion assessment on ZTE-XR to conventional radiography. We measured cortical thickness of ZTE-XR and ZTE-CT and compared these with conventional imaging. We calculated confidence interval of proportions, Wilcoxon rank sum test and intraclass correlation coefficients for inter-reader agreement.

RESULTS

Cohorts 1, 2 and 3 consisted of 40, 20 and 35 cases, respectively (age range 0.6-23.0 years). ZTE-CT versus CT and ZTE-XR versus radiography of cortical thicknesses were not significantly different (P=0.55 and P=0.31, respectively). Cortical delineation was rated diagnostic or better (score of 3, 4 or 5) in all cases (confidence interval of proportions = 100%) for ZTE-CT/XR. Similarly, intramedullary cavity delineation was rated diagnostic or better in all cases for ZTE-CT, and ZTE-XR was at least diagnostic in 58-63% of cases. For cohort 2, cortex and intramedullary cavity S_comp for ZTE-CT was comparable to those of conventional CT, with confidence interval of proportion (sum of score of -1 to +2) of 93-100% and 95%, respectively. Pathology visualized on ZTE-CT/XR was comparable; S_comp confidence interval of proportions was 95%/97-100%, with improved delineation of non-displaced fractures on ZTE-XR. Readers had moderate to near-perfect intraclass correlation coefficient (range=0.60-0.93).

CONCLUSION

Implementation of a diagnostic-quality ZTE MRI sequence in the pediatric population is feasible and can be performed as a complementary pulse sequence to enhance musculoskeletal MRI studies. Compared to conventional CT, ZTE has comparable cortical delineation, intramedullary cavity and pathology visualization. While not intended as a replacement for conventional radiography, ZTE-XR provides similar visualization of pathology.

Evaluation of Meniscal Tissue after Meniscal Repair Using Ultrahigh Field MRI

The study evaluates the meniscal tissue after primary meniscal suturing using 7-Tesla (T) magnetic resonance imaging with T₂* mapping at 6 and 12 months after surgery to investigate the differences between repaired meniscal tissue and healthy meniscal tissue in the medial and lateral compartment. This prospective study included 11 patients (9m/2f) with a mean age of 30.6 years (standard deviation 9.0). Patients with a meniscal tear that was treated arthroscopically with meniscus suturing, using an all-inside technique, were included. All patients and seven healthy volunteers were imaged on a 7-T whole-body system. T2* mapping of the meniscus was applied on sagittal slices. Regions-of-interest were defined manually in the red and white zone of each medial and lateral meniscus to measure T2*-values. In the medial posterior and medial anterior horn similar T₂*-values were measured in the red and white zone at 6- and 12-month follow-up. Compared with the control group higher T₂*-values were found in the repaired medial meniscus. After 12-months T₂*-values decreased to normal values in the anterior horn and remained elevated in the posterior horn. In the red zone of the lateral posterior horn a significant decrease in the T₂*-values (from 8.2 milliseconds to 5.9 milliseconds) (p = 0.04), indicates successful repair; a tendency toward a decrease in the white zone between the 6 and 12 months follow-up was observed. In the red zone of the lateral anterior horn the T₂*-values decreased significantly during follow-up and in the white zone of the lateral anterior horn T₂*-values were comparable. In comparison to the control group higher T₂*-values were measured at 6-months; however, the T₂*-values showed comparable values in the repaired lateral meniscus after 12 months. The T2* mapping results of the current study indicated a better healing response of the red zone of the lateral posterior horn compared with the medial posterior horn.

3D MRI Models of the Musculoskeletal System

Computed tomography (CT) is most commonly used to produce three-dimensional (3D) models for evaluating bone and joint morphology in clinical practice. However, 3D models created from magnetic resonance imaging (MRI) data can be equally effective for comprehensive and accurate assessment of osseous and soft tissue structure morphology and pathology. The quality of 3D MRI models has steadily increased over time, with growing potential to replace 3D CT models in various musculoskeletal (MSK) applications. In practice, a single MRI examination for two-dimensional and 3D assessments can increase the value of MRI and simplify the pre- and postoperative imaging work-up. Multiple studies have shown excellent performance of 3D MRI models in shoulder injuries, in the hip in the setting of femoroacetabular impingement, and in the knee for the creation of bone surface models. Therefore, the utility of 3D MRI postprocessed models is expected to continue to rise and broaden in applications. Computer-based and artificial intelligence-assisted postprocessing techniques have tremendous potential to improve the efficiency of 3D model creation, opening many research avenues to validate the applicability of 3D MRI and establish 3D-specific quantitative assessment criteria. We provide a practice-focused overview of 3D MRI acquisition strategies, postprocessing techniques for 3D model creation, MSK applications of 3D MRI models, and an illustration of cases from our daily clinical practice.

A pilot study to assess the healing of meniscal tears in young adult goats

Meniscal tears are a common orthopedic injury, yet their healing is difficult to assess post-operatively. This impedes clinical decisions as the healing status of the meniscus cannot be accurately determined non-invasively. Thus, the objectives of this study were to explore the utility of a goat model and to use quantitative magnetic resonance imaging (MRI) techniques, histology, and biomechanical testing to assess the healing status of surgically induced meniscal tears. Adiabatic T1ρ, T2, and T2* relaxation times were quantified for both operated and control menisci ex vivo. Histology was used to assign healing status, assess compositional elements, and associate healing status with compositional elements. Biomechanical testing determined the failure load of healing lesions. Adiabatic T1ρ, T2, and T2* were able to quantitatively identify different healing states. Histology showed evidence of diminished proteoglycans and increased vascularity in both healed and non-healed menisci with surgically induced tears. Biomechanical results revealed that increased healing (as assessed histologically and on MRI) was associated with greater failure load. Our findings indicate increased healing is associated with greater meniscal strength and decreased signal differences (relative to contralateral controls) on MRI. This indicates that quantitative MRI may be a viable method to assess meniscal tears post-operatively.

Quantitative magnetic resonance imaging of meniscal pathology ex vivo

OBJECTIVE

To determine the ability of conventional spin echo (SE) T2 and ultrashort echo time (UTE) T2* relaxation times to characterize pathology in cadaveric meniscus samples.

MATERIALS AND METHODS

From 10 human donors, 54 triangular (radially cut) meniscus samples were harvested. Meniscal pathology was classified as normal (n = 17), intrasubstance degenerated (n = 33), or torn (n = 4) using a modified arthroscopic grading system. Using a 3-T MR system, SE T2 and UTE T2* values of the menisci were determined, followed by histopathology. Effect of meniscal pathology on relaxation times and histology scores were determined, along with correlation between relaxation times and histology scores.

RESULTS

Mean ± standard deviation UTE T2* values for normal, degenerated, and torn menisci were 3.6 ± 1.3 ms, 7.4 ± 2.5 ms, and 9.8 ± 5.7 ms, respectively, being significantly higher in degenerated (p < 0.0001) and torn (p = 0.0002) menisci compared to that in normal. In contrast, the respective mean SE T2 values were 27.7 ± 9.5 ms, 25.9 ± 7.0 ms, and 35.7 ± 10.4 ms, without significant differences between groups (all p > 0.14). In terms of histology, we found significant group-wise differences (each p < 0.05) in fiber organization and inner-tip surface integrity sub-scores, as well as the total score. Finally, we found a significant weak correlation between UTE T2* and histology total score (p = 0.007, R_s² = 0.19), unlike the correlation between SE T2 and histology (p = 0.09, R_s² = 0.05).

CONCLUSION

UTE T2* values were found to distinguish normal from both degenerated and torn menisci and correlated significantly with histopathology.

Magic angle effect on adiabatic T1ρ imaging of the Achilles tendon using 3D ultrashort echo time cones trajectory

The protons in collagen-rich musculoskeletal (MSK) tissues such as the Achilles tendon are subject to strong dipolar interactions which are modulated by the term (3cos² θ-1) where θ is the angle between the fiber orientation and the static magnetic field B₀ . The purpose of this study was to investigate the magic angle effect in three-dimensional ultrashort echo time Cones Adiabatic T_1ρ (3D UTE Cones-AdiabT_1ρ ) imaging of the Achilles tendon using a clinical 3 T scanner. The magic angle effect was investigated by Cones-AdiabT_1ρ imaging of five cadaveric human Achilles tendon samples at five angular orientations ranging from 0° to 90° relative to the B₀ field. Conventional Cones continuous wave T_1ρ (Cones-CW-T_1ρ ) and Cones T₂ * (Cones-T₂ *) sequences were also applied for comparison. On average, Cones-AdiabT_1ρ increased 3.6-fold from 13.6 ± 1.5 ms at 0° to 48.4 ± 5.4 ms at 55°, Cones-CW-T_1ρ increased 6.1-fold from 7.0 ± 1.1 ms at 0° to 42.6 ± 5.2 ms at 55°, and Cones-T2* increased 12.3-fold from 2.9 ± 0.5 ms at 0° to 35.8 ± 6.4 ms at 55°. Although Cones-AdiabT_1ρ is still subject to significant angular dependence, it shows a much-reduced magic angle effect compared to Cones-CW-T_1ρ and Cones-T₂ *, and may be used as a novel and potentially more effective approach for quantitative evaluation of the Achilles tendon and other MSK tissues.

Quantitative MRI UTE-T2* and T2* Show Progressive and Continued Graft Maturation Over 2 Years in Human Patients After Anterior Cruciate Ligament Reconstruction

Background:

Noninvasive quantitative magnetic resonance imaging (MRI) measures to assess anterior cruciate ligament (ACL) graft maturity are needed to help inform return to high-demand activities and to evaluate the effectiveness of new treatments to accelerate ACL graft maturation. Quantitative MRI ultrashort echo time T2* (UTE-T2*) and T2* mapping captures short T2 signals arising from collagen-associated water in dense regular connective tissues, such as tendon, ligament, and maturing grafts, which are invisible to conventional MRI.

Hypothesis:

Quantitative MRI UTE-T2* and T2* mapping is sensitive to ACL graft changes over the first 2 years after ACL reconstruction (ACLR).

Study Design:

Case series; Level of evidence, 4.

Methods:

A total of 32 patients (18 men; mean ± SD age, 30 ± 9 years) undergoing unilateral ACLR and 30 uninjured age-matched controls (18 men; age, 30 ± 9 years) underwent 3-T MRI examination. Patients who underwent ACLR were imaged at 6 weeks, 6 months, and 1 and 2 years postoperatively. Two separate ACLR cohorts were scanned with 2 MRI platforms at 2 institutions. Twelve ACLR knees were scanned with a 3-dimensional acquisition-weighted stack of spirals UTE sequence on a Siemens scanner, and 20 ACLR knees were scanned with a 3-dimensional Cones UTE sequence on a GE scanner. UTE-T2* or T2* maps were calculated for the intra-articular portion of the ACL graft.

Results:

Mean ACL graft UTE-T2* and T2* decreased from 1 to 2 years after ACLR. ACL graft T2* increased 25% to 30% during the first 6 months (P < .013) to a level not different from that of uninjured native ACL (P > .4), stabilized between 6 months and 1 year (P ≥ .999), and then decreased 19% between 1 and 2 years after ACLR (P = .027). At 6-month follow-up, ACL graft UTE-T2* differed from that of tendon (P < .02) but not uninjured native ACL (P > .7) and showed the greatest variability among patients.

Conclusion:

UTE-T2* mapping suggested substantial changes within the graft during the first 6 months postsurgery. T2* and UTE-T2* mapping showed relatively stable graft composition from 6 months to 1 year, consistent with remodeling, followed by decreases from 1 to 2 years, suggestive of continuing maturation. MRI UTE-T2* and T2* mapping demonstrated potential clinical utility as noninvasive quantitative imaging metrics for evaluation of human ACL grafts.

Knee Pathology in Young Adults After Pediatric Anterior Cruciate Ligament Injury: A Prospective Case Series of 47 Patients With a Mean 9.5-Year Follow-up

BACKGROUND

The rate of secondary knee injuries after pediatric anterior cruciate ligament (ACL) injury is uncertain, and previous studies are limited because of poor methodology.

PURPOSE

To evaluate the incidence of new meniscal injuries since the initial diagnostic magnetic resonance imaging (MRI) of young adults who sustained a pediatric ACL injury. In addition, to evaluate meniscal and cartilage injuries in the index knee and contralateral knee injuries on MRI at final follow-up (9.5 years). Furthermore, to assess leg length and alignment based on long-leg radiographs.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Study population at final follow-up included 47 young adults who sustained a pediatric ACL injury before age 13 years. They were followed prospectively since the time of injury for a mean 9.5 years at final follow-up. Imaging included diagnostic MRI of the index knee and 3.0-T MRI of both knees at 1-, 2-, and 9.5-year follow-up, in addition to long-leg radiographs at final follow-up. Forty-three patients underwent active rehabilitation without ACL reconstruction initially; 4 were treated with initial ACL reconstruction. At final follow-up, 27 (57%) had undergone ACL reconstruction.

RESULTS

Fourteen patients had meniscal tears in the index knee at final follow-up (prevalence, 30%). The majority of these were in the same location as previously repaired tears (n = 9). Between diagnostic MRI and final follow-up, 16 patients had sustained new meniscal tears to a healthy meniscus (incidence, 34%). At final follow-up, meniscal injuries recorded at baseline or during follow-up were no longer visible and appeared healed in 17 patients (20 tears). MRI at final follow-up showed cartilage injuries in the index knee of 13 patients (28%) and contralateral injuries in 8 patients (meniscus, n = 2; cartilage, n = 5; subchondral fracture, n = 1). Two patients had a leg-length difference >15 mm, and 3 had side-to-side difference in knee alignment >5°.

CONCLUSION

The incidence of new meniscal tears after pediatric ACL injury was 34% during a mean follow-up period of 9.5 years. At final follow-up, 27 patients (57%) had normal menisci, and none had developed knee osteoarthritis. Primary active rehabilitation, close follow-up, and delayed surgery if needed may be a viable and safe treatment option for some pediatric ACL injuries.

T2 mapping of the meniscus is a biomarker for early osteoarthritis

Purpose

To evaluate in vivo T₂ mapping as quantitative, imaging-based biomarker for meniscal degeneration in humans, by studying the correlation between T₂ relaxation time and degree of histological degeneration as reference standard.

Methods

In this prospective validation study, 13 menisci from seven patients with radiographic knee osteoarthritis (median age 67 years, three males) were included. Menisci were obtained during total knee replacement surgery. All patients underwent pre-operative magnetic resonance imaging using a 3-T MR scanner which included a T₂ mapping pulse sequence with multiple echoes. Histological analysis of the collected menisci was performed using the Pauli score, involving surface integrity, cellularity, matrix organization, and staining intensity. Mean T₂ relaxation times were calculated in meniscal regions of interest corresponding with the areas scored histologically, using a multi-slice multi-echo postprocessing algorithm. Correlation between T₂ mapping and histology was assessed using a generalized least squares model fit by maximum likelihood.

Results

The mean T₂ relaxation time was 22.4 ± 2.7 ms (range 18.5–27). The median histological score was 10, IQR 7–11 (range 4–13). A strong correlation between T₂ relaxation time and histological score was found (r_s = 0.84, CI 95% 0.64–0.93).

Conclusion

In vivo T₂ mapping of the human meniscus correlates strongly with histological degeneration, suggesting that T₂ mapping enables the detection and quantification of early compositional changes of the meniscus in knee OA.

Key Points

• Prospective histology-based study showed that in vivo T₂mapping of the human meniscus correlates strongly with histological degeneration.

• Meniscal T₂mapping allows detection and quantifying of compositional changes, without need for contrast or special MRI hardware.

• Meniscal T₂mapping provides a biomarker for early OA, potentially allowing early treatment strategies and prevention of OA progression.

Electronic supplementary material

The online version of this article (10.1007/s00330-019-06091-1) contains supplementary material, which is available to authorized users.

Magnetic resonance imaging of the zone of calcified cartilage in the knee joint using 3-dimensional ultrashort echo time cones sequences

Background:

The zone of calcified cartilage (ZCC) plays an important role in the pathogenesis of osteoarthritis (OA) but has never been imaged in vivo with magnetic resonance (MR) imaging techniques. We investigated the feasibility of direct imaging of the ZCC in both cadaveric whole knee specimens and in vivo healthy knees using a 3-dimensional ultrashort echo time cones (3D UTE-Cones) sequence on a clinical 3T scanner.

Methods:

In all, 12 cadaveric knee joints and 10 in vivo healthy were collected. At a 3T MR scanner with an 8-channel knee coil, a fat-saturated 3D dual-echo UTE-Cones sequence was used to image the ZCC, following with a short rectangular pulse excitation and 3D spiral sampling with conical view ordering. The regions of interests (ROIs) were delineated by a blinded observer. Single-component T2∗ and T2 values were calculated from fat-saturated 3D dual-echo UTE-Cones and a Carr-Purcell-Meiboom-Gill (T2 CPMG) data using a semi-automated MATLAB code.

Results:

The single-exponential fitting curve of ZCC was accurately obtained with R2 of 0.989. For keen joint samples, the ZCC has a short T2∗ ranging from 0.62 to 2.55 ms, with the mean ± standard deviation (SD) of 1.49 ± 0.66 ms, and with 95% confidence intervals (CI) of 1.20–1.78 ms. For volunteers, the short T2∗ ranges from 0.93 to 3.52 ms, with the mean ± SD of 2.09 ± 0.56 ms, and the 95% CI is 1.43 to 2.74 ms in ZCC.

Conclusions:

The high-resolution 3D UTE-Cones sequence might be used to directly image ZCC in the human knee joint on a clinical 3T scanner with a scan time of more than 10 min. Using this non-invasive technique, the T2∗ relaxation time of the ZCC can be further detected.

Ultrashort time-to-echo quantitative magnetic resonance imaging of the triangular fibrocartilage: differences in position

PURPOSE

To compare T2* values of the triangular fibrocartilage (TFC) obtained by ultrashort time-to-echo (UTE) techniques at the neutral position, ulnar flexion of the wrist, and pronation of the forearm.

MATERIALS AND METHODS

MR imaging was performed in ten healthy volunteers with a 3-T MR system by using an eight-channel knee coil. Coronal wrist T2* maps from three-dimensional cone UTE pulse sequences were obtained at the neutral, ulnar flexion, and pronation positions (TR: 19 ms, TE: 0.032 ms/4 ms/8 ms/12 ms, FOV: 18 cm, matrix: 430 × 430, section thickness: 1.5 mm, scan time: 8 min 31 s). UTE-T2* maps were calculated on a pixel-by-pixel basis for all structures of the wrist visualized in the coronal planes. The entire region of interest (ROI) for TFC was manually delineated, and the average T2* value was calculated for each ROI by three radiologists. The Kruskal-Wallis test, Wilcoxon signed-rank test, or intraclass correlation coefficients (ICC) were used for statistics.

RESULTS

The difference in the average T2* value among the three groups according to the forearm/wrist position was significant (p < 0.001). The T2* value of the TFC at pronation (mean ± 2 SD: 7.92 ± 1.37 ms) was significantly lower than those at the neutral (10.08 ± 1.90 ms) and ulnar flexion positions (9.15 ± 1.03 ms) (p < 0.017). The ICC showed a substantial interobserver agreement in the T2* value measurements of the TFC (ICC = 0.986).

CONCLUSION

T2* relaxation time measurement of the TFC using UTE may be useful for assessing the loading effect by the forearm/wrist position.

KEY POINTS

• The T2* value of the TFC may reflect the biomechanics of the wrist joint. • Acute loading at pronation results in a decrease in the T2* value of the TFC. • Quantitative wrist UTE MRI was successfully performed in vivo.

A pilot study of short T2* measurements with ultrashort echo time imaging at 0.35 T

PURPOSE

Ultrashort echo time (UTE) sequences play a key role in imaging and quantifying short T2 species. However, almost all of the relevant studies was conducted at relatively high fields. The purpose of this work was to further explore the feasibility of UTE imaging and T2* measurement for short T2 species at low fields.

METHODS

A 2D UTE sequence with an echo time (TE) of 0.37 ms was developed on a 0.35 T permanent magnet scanner. This sequence acquires multiecho images to fit the monoexponential signal decay model for quantitative T2* calculations. In the phantom experiments, MnCl₂ solutions with different T2* values were used to assess the curve fitting model in low fields. In the in vivo experiments, T2* measurements were performed on the Achilles tendon of five normal volunteers.

RESULTS

The phantom studies showed a significant linear relationship between the MnCl₂ solution concentration and R2* (1/T2*) values, which indicated the stability and accuracy of the T2* quantification model. The in vivo studies demonstrated that mean T2* value of Achilles tendon is 1.83 ± 0.21 ms, and the mean coefficient of determination (R-squared) was 0.996.

CONCLUSIONS

Both phantom and in vivo experiments showed that UTE imaging and quantification for short T2 components were feasible at low field 0.35 T scanner. This pilot study presents preliminary conclusions for future work.

New Techniques in MR Imaging of the Ankle and Foot

Foot and ankle disorders are common in everyday clinical practice. MR imaging is frequently required for diagnosis given the variety and complexity of foot and ankle anatomy. Although conventional MR imaging plays a significant role in diagnosis, contemporary management increasingly relies on advanced imaging for monitoring therapeutic response. There is an expanding need for identification of biomarkers for musculoskeletal tissues. Advanced imaging techniques capable of imaging these tissue substrates will be increasingly used in routine clinical practice. Radiologists should therefore become familiar with these innovative MR techniques. Many such techniques are already widely used in other organ systems.

Effects of fat saturation on short T2 quantification

Ultrashort TE (UTE) sequences have the capability to image tissues with very short T2s that typically appear as low signal in clinical sequences. UTE sequences can also be used in multi-echo acquisitions which allow assessment of the T2s of these tissues. Here we study the accuracy of such T2 measurements when combined with fat saturation (FS).

Advanced MRI Techniques for the Ankle

OBJECTIVE

The purposes of this article are to present a state-of-the-art routine protocol for MRI of the ankle, to provide problem-solving tools based on specific clinical indications, and to introduce principles for the implementation of ultrashort echo time MRI of the ankle, including morphologic and quantitative assessment.

CONCLUSION

Ankle injury is common among both athletes and the general population, and MRI is the established noninvasive means of evaluation. The design of an ankle protocol depends on various factors. Higher magnetic field improves signal-to-noise ratio but increases metal artifact. Specialized imaging planes are useful but prolong acquisition times. MR neurography is useful, but metal reduction techniques are needed whenever a metal prosthesis is present. An ultrashort echo time sequence is a valuable tool for both structural and quantitative evaluation.

Magnetic resonance imaging of the knee: An overview and update of conventional and state of the art imaging

Magnetic resonance imaging (MRI) has become the preferred modality for imaging the knee to show pathology and guide patient management and treatment. The knee is one of the most frequently injured joints, and knee pain is a pervasive difficulty that can affect all age groups. Due to the diverse pathology, complex anatomy, and a myriad of injury mechanisms of the knee, the MRI knee protocol and sequences should ensure detection of both soft tissue and osseous structures in detail and with accuracy. The knowledge of knee anatomy and the normal or injured MRI appearance of these key structures are critical for precise diagnosis. Advances in MRI technology provide the imaging necessary to obtain high-resolution images to evaluate menisci, ligaments, and tendons. Furthermore, recent advances in MRI techniques allow for improved imaging in the postoperative knee and metal artifact reduction, tumor imaging, cartilage evaluation, and visualization of nerves. As treatment and operative management techniques evolve, understanding the correct application of these advancements in MRI of the knee will prove to be valuable to clinical practice.

LEVEL OF EVIDENCE

5 J. MAGN. RESON. IMAGING 2017;45:1257-1275.

Meniscal biology in health and disease

The knee is a fascinating yet complex joint. Researchers and clinicians agree that the joint is an organ comprised of highly specialized intrinsic and extrinsic tissues contributing to both health and disease. Key to the function and movement of the knee are the menisci, exquisite fibrocartilage structures that are critical structures for maintaining biological and biomechanical integrity of the joint. The biological/physiological functions of the menisci must be understood at the tissue, cellular and even molecular levels in order to determine clinically relevant methods for assessing it and influencing it. By investigating normal and pathological functions at the basic science level, we can begin to translate data to patients. The objective of this article is to provide an overview of this translational pathway so that progression toward improved diagnostic, preventative, and therapeutic strategies can be effectively pursued. We have thoroughly examined the pathobiological, biomarker, and imaging aspects of meniscus research. This translational approach can be effective toward optimal diagnosis, prevention, and treatment for the millions of patients who suffer from meniscal disorders each year.