Imaging of the Achilles tendon in spondyloarthritis: a comparison of ultrasound and conventional, short and ultrashort echo time MRI with and without intravenous contrast

Imaging and Image Processing Techniques for High-Resolution Visualization of Connective Tissue with MRI: Application to Fascia, Aponeurosis, and Tendon

Recent interest in musculoskeletal connective tissues like tendons, aponeurosis, and deep fascia has led to a greater focus on in vivo medical imaging, particularly MRI. Given the rapid T2* decay of collagenous tissues, advanced ultra-short echo time (UTE) MRI sequences have proven useful in generating high-signal images of these tissues. To further these advances, we discuss the integration of UTE with Diffusion Tensor Imaging (DTI) and explore image processing techniques to enhance the localization, labeling, and modeling of connective tissues. These techniques are especially valuable for extracting features from thin tissues that may be difficult to distinguish. We present data from lower leg scans of 30 healthy subjects using a non-Cartesian MRI sequence to acquire axial 2D images to segment skeletal muscle and connective tissue. DTI helped differentiate aponeurosis from deep fascia by analyzing muscle fiber orientations. The dual echo imaging methods yielded high-resolution images of deep fascia, where in-plane spatial resolutions were between 0.3 × 0.3 mm to 0.5 × 0.5 mm with a slice thickness of 3-5 mm. Techniques such as K-Means clustering, FFT edge detection, and region-specific scaling were most effective in enhancing images of deep fascia, aponeurosis, and tendon to enable high-fidelity modeling of these tissues.

Changes to muscle and fascia tissue after eighteen days of ankle immobilization post-ankle sprain injury: an MRI case study

BACKGROUND

Ankle sprains often result in muscle atrophy and reduced range of motion, which can cause long-term ankle instabilities. Understanding the changes to muscle-such as atrophy-and concomitant changes to deep fascia-which may thicken alongside muscle loss-after ankle sprain injury is important to understanding structural changes about the joint and how they might contribute to longer-term impairments. Here, we employ advanced MRI to investigate skeletal muscle and fascial structural changes during the recovery period of one patient undergoing immobilization after ankle sprains.

MATERIAL AND METHODS

In this case study, a participant who suffered an ankle sprain underwent initial MRI scans and, after 21 days (18 of which included immobilization), a follow-up MRI. Techniques used included proton density, 3D stack of spirals, and diffusion tensor imaging to analyse muscle and fascia changes pre- and post-injury.

RESULTS

Results showed muscle atrophy in most shank muscles, with volume loss ranging from no change in the lateral gastrocnemius to 12.11% in the popliteus. Thigh muscles displayed hypertrophy of 6% in the hamstrings, while the quadriceps atrophied by 2.5%. Additionally, fascia thickness increased from 0.94 mm to 1.03 mm. Diffusion tensor imaging indicated that the biceps femoris experienced the most significant changes in physiological cross-sectional area, while the rectus femoris showed minimal change.

CONCLUSION

The findings highlight the variable responses of muscles and a notable thickening of deep fascia post-injury, underscoring its role in recovery from ankle sprains.

Characterization of Equine Chronic Tendon Lesions in Low- and High-Field Magnetic Resonance Imaging

In equine medicine, experience regarding MRI of chronic tendon lesions is limited, and evidence on the suitability of different sequences in 3 T high-field MRI is scarce. Therefore, macroscopically healthy and altered tendons were examined by histology and in 0.27 T low- and 3 T high-field MRI, focusing on T1-weighted (T1w) sequences to visualize chronic lesions. In high-field MRI, tendons were positioned parallel (horizontal) and perpendicular (vertical) to the magnetic field, acknowledging the possible impact of the magic angle effect. The images were evaluated qualitatively and signal intensities were measured for quantitative analysis. Qualitative evaluation was consistent with the quantitative results, yet there were differences in lesion detection between the sequences. The low-field T1w GRE sequence and high-field T1w FLASH sequence with vertically positioned tendons displayed all tendon lesions. However, the horizontally scanned high-field T1w SE sequence failed to detect chronic tendon lesions. The agreement regarding tendon signal intensities was higher between high-field sequences scanned in the same orientation (horizontal or vertical) than between the same types of sequence (SE or FLASH), demonstrating the impact of tendon positioning. Vertical scanning was superior for diagnosis of the tendon lesions, suggesting that the magic angle effect plays a major role in detecting chronic tendon disease.

Emerging quantitative MR imaging biomarkers in inflammatory arthritides

PURPOSE

To review quantitative magnetic resonance imaging (qMRI) methods for imaging inflammation in connective tissues and the skeleton in inflammatory arthritis. This review is designed for a broad audience including radiologists, imaging technologists, rheumatologists and other healthcare professionals.

METHODS

We discuss the use of qMRI for imaging skeletal inflammation from both technical and clinical perspectives. We consider how qMRI can be targeted to specific aspects of the pathological process in synovium, cartilage, bone, tendons and entheses. Evidence for the various techniques from studies of both adults and children with inflammatory arthritis is reviewed and critically appraised.

RESULTS

qMRI has the potential to objectively identify, characterize and quantify inflammation of the connective tissues and skeleton in both adult and pediatric patients. Measurements of tissue properties derived using qMRI methods can serve as imaging biomarkers, which are potentially more reproducible and informative than conventional MRI methods. Several qMRI methods are nearing transition into clinical practice and may inform diagnosis and treatment decisions, with the potential to improve patient outcomes.

CONCLUSIONS

qMRI enables specific assessment of inflammation in synovium, cartilage, bone, tendons and entheses, and can facilitate a more consistent, personalized approach to diagnosis, characterisation and monitoring of disease.

Ultrasound Characteristics of Foot and Ankle Structures in Healthy, Coper, and Chronically Unstable Ankles

OBJECTIVE

Ankle sprains constitute approximately 85% of all ankle injuries, and up to 70% of people experience residual symptoms. While the injury to ligaments is well understood, the potential role of other foot and ankle structures has not been explored. The objective was to characterize and compare selected ankle structures in participants with and without a history of lateral ankle sprain.

METHODS

A total of 71 participants were divided into 31 healthy, 20 coper, and 20 chronic ankle instability groups. Ultrasound images of the anterior talofibular and calcaneofibular ligaments, fibularis tendons and muscles, tibialis posterior, and Achilles tendon were obtained. Thickness, length, and cross-sectional areas were measured and compared among groups.

RESULTS

When under tension, the anterior talofibular ligament (ATFL) was longer in copers and chronic ankle instability groups compared to healthy participants (P < .001 and P = .001, respectively). The chronic ankle instability group had the thickest ATFL and calcaneofibular ligament among the 3 groups (p < 0.001). No significant differences (P > .05) in tendons and muscles were observed among the 3 groups.

CONCLUSIONS

The ultrasound protocol proved reliable and was used to evaluate the length, thickness, and cross-sectional areas of selected ankle structures. The length of the ATFL and the thickness of the ATFL and calcaneofibular ligament were longer and thicker in injured groups compared to healthy.

Validity and reliability of measurements of aponeurosis dimensions from magnetic resonance images

Muscle performance is closely related to the structure and function of tendons and aponeuroses, the sheet-like, intramuscular parts of tendons. The architecture of aponeuroses has been difficult to study with magnetic resonance imaging (MRI) because these thin, collagen-rich connective tissues have very short transverse relaxation (T2) times and therefore provide a weak signal with conventional MRI sequences. Here, we validated measurements of aponeurosis dimensions from two MRI sequences commonly used in muscle-tendon research (mDixon and T1-weighted images), and an ultrashort echo time (UTE) sequence designed for imaging tissues with short T2 times. MRI-based measurements of aponeurosis width, length, and area of 20 sheep leg muscles were compared to direct measurements made with three-dimensional (3D) quantitative microdissection. The errors in measurement of aponeurosis width relative to the mean width were 1.8% for UTE, 3.7% for T1, and 18.8% for mDixon. For aponeurosis length, the errors were 7.6% for UTE, 1.9% for T1, and 21.0% for mDixon. Measurements from T1 and UTE scans were unbiased, but mDixon scans systematically underestimated widths, lengths, and areas of the aponeuroses. Using the same methods, we then found high inter-rater reliability (intraclass correlation coefficients >0.92 for all measures) of measurements of the dimensions of the central aponeurosis of the human tibialis anterior muscle from T1-weighted scans. We conclude that valid and reliable measurements of aponeurosis dimensions can be obtained from UTE and from T1-weighted scans. When the goal is to study the macroscopic architecture of aponeuroses, UTE does not hold an advantage over T1-weighted imaging.

Three-dimensional ultrashort echo time (3D UTE) MRI of Achilles tendon at 4.7T MRI with comparison to conventional sequences in an experimental murine model of spondyloarthropathy

BACKGROUND

Due to the very short T₂ of its components, the normal anatomy of Achilles enthesis is impossible to define with "conventional" long echo time (TE) T₂ sequences. However, this is a common site affected by rheumatologic disease. Early abnormalities related to inflammatory processes are impossible to detect in this location.

PURPOSE

To assess the feasibility of a 3D-UTE (ultrashort echo time) sequence to evaluate normal and pathological Achilles entheses, determining both anterior fibrocartilaginous and posterior collagenic portions at 4.7T, in a rat model of spondyloarthropathy (SpA) with histological correlation. To assess whether this sequence detects SpA enthesopathy prior to long TE T₂ sequences, enabling disease monitoring.

STUDY TYPE

Prospective case-control study.

ANIMAL MODEL

Twelve immunocompetent Wistar male rats imaged before (controls); the model was induced in eight rats (16 tendons) imaged at day 6, day 13, and day 21 with regular sacrifice for ex vivo imaging and histological correlation.

FIELD STRENGTH

4.7T Bruker Biospec Systems. 3D balanced steady-state free precession (bSSFP) and 3D-UTE sequences, performed at baseline (day 0, n = 12 animals / 24 tendons), day 6 (n = 8/16), 13 (n = 4/8), and day 21 (n = 2/4).

ASSESSMENT

Visual analysis and signal intensity measurements (signal to noise ratio, SNR) of both bSSFP and UTE images were performed by two independent musculoskeletal radiologists at different locations of the Achilles enthesis and preinsertional area.

STATISTICAL TESTS

Normal and pathological rat values were compared by Wilcoxon signed-rank tests, as well as interobserver differences. MRI findings were compared against histological data.

RESULTS

The 3D-UTE sequence identified the anterior fibrocartilage and posterior collagenic areas of Achilles entheses in all cases. Visual analysis and signal intensity measurements distinguished SpA-affected entheses from healthy ones at days 6 and 13 (P = 0.002 and P = 0.006, respectively). Neither the normal anatomy of the enthesis nor its pathological pattern could be identified on T₂ bSSFP sequences.

DATA CONCLUSION

Unlike bSSFP T₂ sequences, 3D-UTE sequences enable visualization of normal enthesis anatomy and early detection of abnormalities in pathological conditions.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:127-135.

Quick water-selective excitation of fast relaxing tissues with 3D UTE sequences

PURPOSE

The aim of this study was to implement a time effective 1-1 double pulse water-selective excitation (WE) into a three-dimensional ultrashort echo time (UTE) sequence (WE-UTE) for visualization of short-T2 tissues with positive contrast and sufficient suppression of surrounding fat.

METHODS

First, an analytical description of magnetization components in the steady state applying WE-UTE was derived and results were compared with numerical simulations based on Bloch's equations. Parameters were optimized for best positive contrast between short-T2 tissues and fat under consideration of variable relaxation properties over a broad range. Maximal signal yield and signal efficiency of on-resonant protons were compared with UTE sequences with and without off-resonance fat saturation (FatSat). WE-UTE was exemplarily applied for in-vivo musculoskeletal imaging on a 3T whole-body MR unit.

RESULTS

Steady state magnetization of WE-UTE could be described analytically and showed excellent accordance with numerical simulations. Even for tissues with T2 = 1 ms WE-UTE resulted in 79% of maximal signal yield of UTE without FatSat and was more efficient regarding signal yield if compared with UTE with FatSat. Using WE-UTE in-vivo tendons and ligaments could be well delineated with positive contrast to surrounding fat.

CONCLUSION

WE-UTE provides a quick method for visualizing short-T2 tissues with positive contrast.

Off-resonance saturation ratio obtained with ultrashort echo time-magnetization transfer techniques is sensitive to changes in static tensile loading of tendons and degeneration

BACKGROUND

To determine if off-saturation ratio (OSR) measured with the ultrashort echo time magnetization transfer (UTE-MT) sequence could differentiate between tendons under different states of tensile load and to compare these changes between normal versus degenerated tendons.

METHODS

Fourteen tendons were imaged at 3 Tesla before and during the application of 0.5-1 kg tension. A two-dimensional (2D) -UTE-MT sequence with 1.5, 3, and 5 kHz frequency offsets was used on nine tendons and a 3D-UTE-MT sequence with 1.5 kHz frequency offset was used on five tendons. OSR was calculated and compared for each condition. Histologic correlation was performed using light microscopy.

RESULTS

In general, OSR increased after the application of tension. Mean increase of 2D OSR was 0.035 (95% confidence interval [CI], 0.013-0.056) at 1.5 kHz offset (P < 0.01), 0.031 (95% CI, 0.023-0.040) at 3 kHz offset (P < 0.01), and 0.013 (95% CI, -0.013-0.027) at 5 kHz offset (P = 0.07) from pre- to posttension states. Mean increase of 3D OSR was 0.026 (95% CI, 0.008-0.044) at a 1.5 kHz offset (P = 0.02) from pre- to posttension states. Mean decrease of 2D OSR at 1.5 kHz offset was 0.074-0.087 when comparing normal versus degenerated tendons (P < 0.01).

CONCLUSION

OSR as measured with 2D or 3D UTE-MT sequences can detect the changes in hydration seen when tendons are placed under two different states of tensile load, but these changes are smaller than those encountered when comparing between normal versus pathologic tendons. Lower off-resonance saturation frequencies (3 kHz or less) are more sensitive to these changes than higher off-resonance saturation frequencies.

Depiction of achilles tendon microstructure in vivo using high-resolution 3-dimensional ultrashort echo-time magnetic resonance imaging at 7 T

OBJECTIVES

The objective of this study was to demonstrate the feasibility of depicting the internal structure of the Achilles tendon in vivo using high-resolution 3-dimensional ultrashort echo-time (UTE) magnetic resonance imaging at 7 T.

MATERIALS AND METHODS

For our UTE imaging, a minimum-phase radiofrequency pulse and an anisotropic field-of-view 3-dimensional radial acquisition were used to minimize the echo time and scan time. A fat saturation pulse was applied every 8 spoke acquisitions to reduce blurring and chemical shift artifacts from fat and to improve the dynamic range of the tendon signal. Five healthy volunteers and 1 patient were scanned with an isotropic spatial resolution of up to 0.6 mm. Fat-suppressed UTE images were qualitatively evaluated and compared with non-fat-suppressed UTE images and longer echo-time images.

RESULTS

High-resolution UTE imaging was able to visualize the microstructure of the Achilles tendon. Fat suppression substantially improved the depiction of the internal structure. The UTE images revealed a fascicular pattern in the Achilles tendon and fibrocartilage at the tendon insertion. In a patient who had tendon elongation surgery after birth, there was a clear depiction of disrupted tendon structure.

CONCLUSIONS

High-resolution fat-suppressed 3-dimensional UTE imaging at 7 T allows for the evaluation of the Achilles tendon microstructure in vivo.

Tendon and ligament imaging

MRI and ultrasound are now widely used for the assessment of tendon and ligament abnormalities. Healthy tendons and ligaments contain high levels of collagen with a structured orientation, which gives rise to their characteristic normal imaging appearances as well as causing particular imaging artefacts. Changes to ligaments and tendons as a result of disease and injury can be demonstrated using both ultrasound and MRI. These have been validated against surgical and histological findings. Novel imaging techniques are being developed that may improve the ability of MRI and ultrasound to assess tendon and ligament disease.

Comparative study of MRI and power Doppler ultrasonography of the heel in patients with spondyloarthritis with and without heel pain and in controls

INTRODUCTION

Imaging of heel enthesopathy in spondyloarthritis (SpA) could potentially be useful for diagnosis and monitoring. The aim of this study was to assess the diagnostic capacities of MRI and power Doppler ultrasonography (PDUS) of the heel to distinguish patients with SpA from controls and to distinguish between patients with SpA with and without enthesopathy.

METHODS

A cross-sectional single-centre study was performed in 51 patients (102 heels) with definite SpA according to Amor's criteria. Patients with degenerative non-inflammatory low back pain (n=24, 48 heels) were included as controls. Bilateral heel MRI and PDUS were performed by two senior musculoskeletal radiologists blinded to the clinical and biological data on the same day as the clinical evaluation. The data were analysed by patient and by heel.

RESULTS

Neither MRI nor PDUS could discriminate between patients with SpA and controls; bone oedema on MRI was the only abnormality specific to SpA (94%), but with a poor sensitivity (22%). However, among patients with SpA, painful heels had more inflammatory abnormalities (81% by MRI, 58% by PDUS) than heels with no pain (56% at MRI, 17% at PDUS).

CONCLUSION

Heel MRI and PDUS frequently show inflammatory lesions in SpA, particularly in painful heels. However, they were also often abnormal in controls. These results suggest that heel MRI and PDUS cannot be used for the diagnosis of SpA. However, PDUS and MRI may be useful for the depiction and assessment of enthesis inflammatory lesions in patients with SpA with heel pain.

Comparison of two ultrashort echo time sequences for the quantification of T1 within phantom and human Achilles tendon at 3 T

Ultrashort echo time (UTE) techniques enable direct imaging of musculoskeletal tissues with short T2 allowing measurement of T1 relaxation times. This article presents comparison of optimized 3D variable flip angle UTE (VFA-UTE) and 2D saturation recovery UTE (SR-UTE) sequences to quantify T1 in agar phantoms and human Achilles tendon. Achilles tendon T1 values for asymptomatic volunteers were compared to Achilles tendon T1 values calculated from patients with clinical diagnoses of spondyloarthritis (SpA) and Achilles tendinopathy using an optimized VFA-UTE sequence. T1 values from phantom data for VFA- and SR-UTE compare well against calculated T1 values from an assumed gold standard inversion recovery spin echo sequence. Mean T1 values in asymptomatic Achilles tendon were found to be 725±42 ms and 698±54 ms for SR- and VFA-UTE, respectively. The patient group mean T1 value for Achilles tendon was found to be 957±173 ms (P<0.05) using an optimized VFA-UTE sequence with pulse repetition time of 6 ms and flip angles 4, 19, and 24°, taking a total 9 min acquisition time. The VFA-UTE technique appears clinically feasible for quantifying T1 in Achilles tendon. T1 measurements offer potential for detecting changes in Achilles tendon due to SpA without need for intravenous contrast agents.

Review. The Agfa Mayneord lecture: MRI of short and ultrashort T₂ and T₂* components of tissues, fluids and materials using clinical systems

A variety of techniques are now available to directly or indirectly detect signal from tissues, fluids and materials that have short, ultrashort or supershort T₂ or T₂* components. There are also methods of developing image contrast between tissues and fluids in the short T₂ or T₂* range that can provide visualisation of anatomy, which has not been previously seen with MRI. Magnetisation transfer methods can now be applied to previously invisible tissues, providing indirect access to supershort T₂ components. Particular methods have been developed to target susceptibility effects and quantify them after correcting for anatomical distortion. Specific methods have also been developed to image the effects of magnetic iron oxide particles with positive contrast. Major advances have been made in techniques designed to correct for loss of signal and gross image distortion near metal. These methods are likely to substantially increase the range of application for MRI.