Ankle: isotropic MR imaging with 3D-FSE-cube--initial experience in healthy volunteers

Presurgical and Postsurgical MRI Evaluation of Osteochondral Lesions of the Foot and Ankle: A Primer

The gold standard diagnostic imaging tool for ankle OCLs is magnetic resonance imaging, which allows precise evaluation of the articular cartilage and assessment of the surrounding soft tissue structures. Post-operative morphologic MRI assessment via MOCART scores provide semi-quantitative analysis of the repair tissue, but mixed evidence exists regarding its association with post-operative outcomes. Post-operative biochemical MRIs allow assessment of the collagen network of the articular cartilage via T2-mapping and T2∗ mapping, and assessment of the articular glycosaminoglycan content via delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T1rho mapping and sodium imaging.

Multiaxial 3D MRI of the Ankle: Advanced High-Resolution Visualization of Ligaments, Tendons, and Articular Cartilage

MRI is a valuable tool for diagnosing a broad spectrum of acute and chronic ankle disorders, including ligament tears, tendinopathy, and osteochondral lesions. Traditional two-dimensional (2D) MRI provides a high image signal and contrast of anatomic structures for accurately characterizing articular cartilage, bone marrow, synovium, ligaments, tendons, and nerves. However, 2D MRI limitations are thick slices and fixed slice orientations. In clinical practice, 2D MRI is limited to 2 to 3 mm slice thickness, which can cause blurred contours of oblique structures due to volume averaging effects within the image slice. In addition, image plane orientations are fixated and cannot be changed after the scan, resulting in 2D MRI lacking multiplanar and multiaxial reformation abilities for individualized image plane orientations along oblique and curved anatomic structures, such as ankle ligaments and tendons. In contrast, three-dimensional (3D) MRI is a newer, clinically available MRI technique capable of acquiring high-resolution ankle MRI data sets with isotropic voxel size. The inherently high spatial resolution of 3D MRI permits up to five times thinner (0.5 mm) image slices. In addition, 3D MRI can be acquired image voxel with the same edge length in all three space dimensions (isotropism), permitting unrestricted multiplanar and multiaxial image reformation and postprocessing after the MRI scan. Clinical 3D MRI of the ankle with 0.5 to 0.7 mm isotropic voxel size resolves the smallest anatomic ankle structures and abnormalities of ligament and tendon fibers, osteochondral lesions, and nerves. After acquiring the images, operators can align image planes individually along any anatomic structure of interest, such as ligaments and tendons segments. In addition, curved multiplanar image reformations can unfold the entire course of multiaxially curved structures, such as perimalleolar tendons, into one image plane. We recommend adding 3D MRI pulse sequences to traditional 2D MRI protocols to visualize small and curved ankle structures to better advantage. This article provides an overview of the clinical application of 3D MRI of the ankle, compares diagnostic performances of 2D and 3D MRI for diagnosing ankle abnormalities, and illustrates clinical 3D ankle MRI applications.

A hypertrophic distal fascicle of the anterior tibiofibular ligament is associated with a high rate of osteochondral lesions of the talus

PURPOSE

The purpose of this retrospective review was to determine the prevalence of osteochondral lesions (OCLs) of the lateral talar dome in patients with anterior ankle impingement with an associated hypertrophic distal fascicle of the anterior tibio-fibular ligament.

METHODS

Retrospective chart review identified 40 patients who underwent anterior ankle arthroscopy for the management of anterior ankle impingement. Clinical outcomes assessed included pre- and postoperative foot and ankle outcome score (FAOS), visual analogue scale (VAS), complications, failures, secondary surgical procedures, return-to-work data and return-to-sport data.

RESULTS

Thirty-two patients with a mean follow-up time of 29.3 ± 10.4 months were included. The hypertrophic distal fascicle of the anterior tibio-fibular ligament was hypertrophic in 29 patients (90.6%), with a mean thickness of 2.5 ± 0.4 mm on MRI. There were 22 OCLs of the lateral talar dome (75.9%) with an associated hypertrophic distal fascicle of the anterior tibio-fibular ligament visualized during arthroscopy. The international cartilage repair society gradings of the lesions included 3 (13.6%) grade I lesions, 15 (68.1%) grade II lesions, 3 (13.6%) grade III lesions, and 1 (4.6%) grade IV lesion. There was a statistically significant improvement in mean FAOS and VAS scores from preoperative to postoperative (p < 0.001). No cases of syndesmotic instability were observed following resection of hypertrophic distal fascicle of the anterior tibio-fibular ligament.

CONCLUSION

This retrospective case series demonstrated that a hypertrophic distal fascicle of the anterior tibio-fibular ligament was associated with an OCL of the lateral talar dome identified during arthroscopic evaluation. In addition, preoperative MRI demonstrated poor sensitivity for the detection of these OCLs. Heightened awareness is warranted for potential lateral talar dome OCLs in patients presenting with anterolateral ankle impingement with a hypertrophic ATiFLdf identified on preoperative MRI in the absence of an associated OCLs.

LEVEL OF EVIDENCE

Level IV, Retrospective case series.

Evaluating the Efficacy of Volume Isotropic Turbo Spin Echo Acquisition Versus T2-Weighted Turbo Spin Echo Imaging in the Diagnosis of Nerve Root and Perineuronal Pathologies in Spinal Disorders

Background While two-dimensional (2D) turbo spin echo (TSE) sequences offer better through-plane resolution than three-dimensional (3D) isotropic TSE sequences images, with a narrower thickness of the slice, 3D isotropic TSE sequences are known to have a weaker in-plane resolution as well as blurring of the image. These elements may make it more difficult to distinguish between nearby structures that may affect nerve roots and small nerve roots during spinal imaging. This study aimed to analyze the accuracy of T2 TSE sequence and volumetric isotropic TSE acquisition in determining the indentation of nerve roots and perineural diseases such as nerve sheath tumors and Tarlov cysts. Methods Fifty patients who attended the Department of Radiodiagnosis for magnetic resonance (MR) spine participated in this prospective study. Routine MR lumbosacral (LS) spine sequences, such as survey, coronal T2 short-tau inversion recovery (STIR), sagittal T2 TSE, sagittal T1 TSE, and axial T2 TSE, were carried out after a localizer was acquired. More sequences from volume isotropic turbo spin echo acquisition (VISTA) were acquired. For both 2D and 3D sequences, the visibility ratings for perineural cysts, spinal canal stenosis, and nerve root indentation were evaluated. Visibility ratings ranged from zero to four. Results In the cases of perineural cyst, spinal canal stenosis, and nerve root impingement, the mean difference between the VISTA and T2 TSE visibility scores was 0.04, 0.54, and 0.56, respectively. The VISTA and T2 TS had standard deviation differences of 0.006, 0.026, and 0.06, respectively. The "t" values for nerve root impingement, spinal canal stenosis, and perineural cysts were, in order, 50, 180, and 70. Because the p-value was <0.01, a statistically significant variation has been observed. Conclusion In the diagnosis of neural and perineuronal disorders, the visibility scores for 3D T2 TSE (VISTA) were considerably better than those for 2D T2 TSE in identifying perineural cysts, spinal canal stenosis, and nerve root indentation.

3D isotropic MRI of ankle: review of literature with comparison to 2D MRI

The ankle joint has complex anatomy with different tissue structures and is commonly involved in traumatic injuries. Magnetic resonance imaging (MRI) is the primary imaging modality used to assess the soft tissue structures around the ankle joint including the ligaments, tendons, and articular cartilage. Two-dimensional (2D) fast spin echo/turbo spin echo (FSE/TSE) sequences are routinely used for ankle joint imaging. While the 2D sequences provide a good signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) with high spatial resolution, there are some limitations to their use owing to the thick slices, interslice gaps leading to partial volume effects, limited fluid contrast, and the need to acquire separate images in different orthogonal planes. The 3D MR imaging can overcome these limitations and recent advances have led to technical improvements that enable its widespread clinical use in acceptable time periods. The volume imaging renders the advantage of reconstructing into thin continuous slices with isotropic voxels enabling multiplanar reconstructions that helps in visualizing complex anatomy of the structure of interest throughout their course with improved sharpness, definition of anatomic variants, and fluid conspicuity of lesions and injuries. Recent advances have also reduced the acquisition time of the 3D datasets making it more efficient than 2D sequences. This article reviews the recent technical developments in the domain 3D MRI, compares imaging with 3D versus 2D sequences, and demonstrates the use-case scenarios with interesting cases, and benefits of 3D MRI in evaluating various ankle joint components and their lesions.

Presurgical and Postsurgical MRI Evaluation of Osteochondral Lesions of the Foot and Ankle: A Primer

The gold standard diagnostic imaging tool for ankle OCLs is magnetic resonance imaging, which allows precise evaluation of the articular cartilage and assessment of the surrounding soft tissue structures. Post-operative morphologic MRI assessment via MOCART scores provide semi-quantitative analysis of the repair tissue, but mixed evidence exists regarding its association with post-operative outcomes. Post-operative biochemical MRIs allow assessment of the collagen network of the articular cartilage via T2-mapping and T2∗ mapping, and assessment of the articular glycosaminoglycan content via delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T1rho mapping and sodium imaging.

Multiaxial 3D MRI of the Ankle: Advanced High-Resolution Visualization of Ligaments, Tendons, and Articular Cartilage

MRI is a valuable tool for diagnosing a broad spectrum of acute and chronic ankle disorders, including ligament tears, tendinopathy, and osteochondral lesions. Traditional two-dimensional (2D) MRI provides a high image signal and contrast of anatomic structures for accurately characterizing articular cartilage, bone marrow, synovium, ligaments, tendons, and nerves. However, 2D MRI limitations are thick slices and fixed slice orientations. In clinical practice, 2D MRI is limited to 2 to 3 mm slice thickness, which can cause blurred contours of oblique structures due to volume averaging effects within the image slice. In addition, image plane orientations are fixated and cannot be changed after the scan, resulting in 2D MRI lacking multiplanar and multiaxial reformation abilities for individualized image plane orientations along oblique and curved anatomic structures, such as ankle ligaments and tendons. In contrast, three-dimensional (3D) MRI is a newer, clinically available MRI technique capable of acquiring high-resolution ankle MRI data sets with isotropic voxel size. The inherently high spatial resolution of 3D MRI permits up to five times thinner (0.5 mm) image slices. In addition, 3D MRI can be acquired image voxel with the same edge length in all three space dimensions (isotropism), permitting unrestricted multiplanar and multiaxial image reformation and postprocessing after the MRI scan. Clinical 3D MRI of the ankle with 0.5 to 0.7 mm isotropic voxel size resolves the smallest anatomic ankle structures and abnormalities of ligament and tendon fibers, osteochondral lesions, and nerves. After acquiring the images, operators can align image planes individually along any anatomic structure of interest, such as ligaments and tendons segments. In addition, curved multiplanar image reformations can unfold the entire course of multiaxially curved structures, such as perimalleolar tendons, into one image plane. We recommend adding 3D MRI pulse sequences to traditional 2D MRI protocols to visualize small and curved ankle structures to better advantage. This article provides an overview of the clinical application of 3D MRI of the ankle, compares diagnostic performances of 2D and 3D MRI for diagnosing ankle abnormalities, and illustrates clinical 3D ankle MRI applications.

Model-based image reconstruction with wavelet sparsity regularization for through-plane resolution restoration in T2 -weighted spin-echo prostate MRI

PURPOSE

The purpose is to develop a model-based image-reconstruction method using wavelet sparsity regularization for maintaining restoration of through-plane resolution but with improved retention of SNR versus linear reconstruction using Tikhonov (TK) regularization in high through-plane resolution (1 mm) T2 -weighted spin-echo (T2SE) images of the prostate.

METHODS

A wavelet sparsity (WS)-regularized image reconstruction was developed that takes as input a set of ≈80 overlapped 3-mm-thick slices acquired using a T2SE multislice scan and typically 30 coil elements. After testing in contrast and resolution phantoms and calibration in 6 subjects, the WS reconstruction was evaluated in 16 consecutive prostate T2SE MRI exams. Results reconstructed with nominal 1-mm thickness were compared with those from the TK reconstruction with the same raw data. Results were evaluated radiologically. The ratio of magnitude of prostate signal to periprostatic muscle signal was used to assess the presence of noise reduction. Technical performance was also compared with a commercial 3D-T2SE sequence.

RESULTS

The new WS reconstruction was assessed as superior statistically to TK for overall SNR, contrast, and multiple evaluation criteria related to sharpness while retaining the high (1 mm) through-plane resolution. Wavelet sparsity tended to provide improved overall diagnostic quality versus TK, but not significantly so. In all 16 studies, the prostate-to-muscle signal ratio increased.

CONCLUSIONS

Model-based WS-regularized reconstruction consistently provides improved SNR in high (1 mm) through-plane resolution images of prostate T2SE MRI versus linear reconstruction using TK regularization.

The anterior talofibular ligament: A thin-slice three-dimensional magnetic resonance imaging study

PURPOSE

The aim of this study was to provide an accurate and improved understanding of anterior talofibular ligament (ATFL) anatomy, and to determine the exact positioning and diameter of the bony tunnel during ATFL repair and/or reconstruction surgery.

METHOD

A total of 58 healthy asymptomatic volunteers were examined, wherein 38 underwent bilateral ankle 3D MRI, and 20 underwent unilateral ankle 3D MRI (10 left and 10 right ankles). Data from a total of 96 MRI datasets were collected. The MRI data from these cases were exported into Mimics to enable reconstruction of 3D ATFL models. The resulting image quality was evaluated using a 5-point subjective scoring system. In addition, the length, width, thickness, and positioning of each ATFL and the area of the ATFL footprints were identified within the 3D model using Mimics and SolidWorks.

RESULTS

The image quality score was 4.48 ± 0.50. The ATFL formed one (65.6%), two (31.3%), or three (3.1%) bundles forms. The footprint area was 31.25 ± 6.29 mm² on the fibular side, and 17.48 ± 4.49 mm² on the talar side.

CONCLUSION

Thin-slice 3D MRI aids in the reconstruction of the 3D ATFL model, and it provides reference for the accurate anatomy of the area and location of the ATFL. This technology will facilitate diagnosis of ATFL injuries and choice of surgical methods.

LEVEL OF EVIDENCE

level IV.

Quantitative analysis of both lacrimal glands in unilateral primary acquired nasolacrimal duct obstruction, based on three-dimensional fast spin echo-Cube-Flex

OBJECTIVE

To investigate whether unilateral primary acquired nasolacrimal duct obstruction (PANDO) changes the volume and water fraction of both lacrimal glands, using three-dimensional fast spin echo (3D-FSE)-Cube-Flex images, and to identify whether the lacrimal gland is a target organ in this disease.

METHODS

3D-FSE-Cube-Flex images of both lacrimal glands in 25 healthy volunteers and 31 patients with unilateral PANDO were retrospectively reviewed. The differences in volume and water content in the lacrimal glands between the controls, non-PANDO side, and PANDO side groups were examined. Moreover, the associations between magnetic resonance imaging (MRI) parameters and disease duration were assessed with correlation analysis.

RESULTS

The lacrimal gland volumes were not significantly different between the PANDO and non-PANDO side groups, compared to the control group (P = 0.484). However, the gland volumes tended to be increased bilaterally in patients with PANDO. In contrast, the gland water fractions in the PANDO and non-PANDO side groups were significantly higher than those in the control group (P = 0.009 and P = 0.014, respectively), and similar between the non-PANDO and PANDO side groups (P = 0.897). No correlation was found between the disease duration and the gland MRI parameters (volume and water fraction).

CONCLUSIONS

Both lacrimal glands are affected by unilateral PANDO. A change in the water fraction of these glands appears to precede the change in volume and may be a sensitive early indicator.

Meniscal Root Tears: An Update Focused on Preoperative and Postoperative MRI Findings

Meniscal root tears represent radial tears or avulsions of the meniscal cartilage at the tibial attachment site that profoundly affect meniscal biomechanics and kinematics. Meniscal root tears have the functional effect of a total meniscectomy and can lead to rapid degenerative change with development of early knee osteoarthritis (OA). A growing range of arthroscopic surgical techniques have been developed to repair meniscal root tears with the aim of restoring joint kinematics and contact pressures and delaying the development of OA. With increased understanding of the anatomy and biomechanics of the meniscal root, meniscal root injury repair has become the treatment of choice in knees with nonadvanced OA. This article reviews the anatomy and biomechanics of the meniscal roots, clinical and imaging diagnostic criteria of meniscal root tears, correlation between arthroscopy and MRI in the diagnosis and classification of meniscal root tears, and expected and abnormal MRI findings after meniscal root repair. Familiarity with MRI signs and classifications of meniscal root tears, as well as with root repair surgical techniques, can aid radiologists in correctly reporting preoperative and postoperative MRI findings.

Space-Occupying Lesions of the Inner Ear Are Easily Misdiagnosed as Endolymphatic Hydrops in a Perilymph-Enhanced Sequence Without the Assistance of a Heavily T2-Weighted Sequence

OBJECTIVE

The aim of the study was to explore the value of T2-sampling perfection with application-optimized contrasts by using different flip angle evolutions (T2-SPACE) in identifying space-occupying lesions of the inner ear.

METHODS

We collected the T2-SPACE and 3-dimensional inversion-recovery sequence with real reconstruction (3D-real IR) images of 220 patients with inner ear symptoms, including 15 patients with inner ear space-occupying lesions. With T2-SPACE images hidden, a senior and junior radiologist made a diagnosis for all patients using only the 3D-real IR images. After 4 weeks the images were shuffled, and T2-SPACE images were made available to the 2 radiologists in addition to 3D-real IR to reconsider the diagnosis for all patients.

RESULTS

With the SPACE images hidden, the correct diagnosis rate of the space-occupying lesions was 8/15 (53.3%) for the senior radiologist, whereas it was only 2/15 (13.3%) for the junior radiologist. Without the SPACE images hidden, the correct diagnosis rate of the space-occupying lesions was 15/15 (100.0%) for the senior radiologist, whereas it was 13/15 (86.7%) for the junior radiologist. Of the 15 patients, 7 had only vestibular space-occupying lesions, 2 had only cochlear space-occupying lesions, and 6 had both. No semicircular canal space-occupying lesion was observed.

CONCLUSIONS

T2-SPACE can help identify space-occupying lesions of the inner ear that tend to be misdiagnosed as endolymphatic hydrops on 3D-real IR. The senior radiologist had a higher rate for the identification of space-occupying lesions than the junior radiologist when using only 3D-real IR, although the senior radiologist detection rate was still only 53.3%. With the addition of T2-SPACE, both the junior and senior radiologist achieved a high detection rate, which increased to 86.7% and 100%, respectively.

Effect of Ligament Mapping from Different Magnetic Resonance Image Quality on Joint Stability in a Personalized Dynamic Model of the Human Ankle Complex

Background. Mechanical models of the human ankle complex are used to study the stabilizing role of ligaments. Identification of ligament function may be improved via image-based personalized approach. The aim of this study is to compare the effect of the ligament origin and insertion site definitions obtained with different magnetic resonance imaging (MRI) modalities on the mechanical behaviour of a dynamic model of the ankle complex. Methods. MRI scans, both via 1.5 T and 3.0 T, were performed on a lower-limb specimen, free from anatomical defects, to obtain morphological information on ligament-to-bone attachment sites. This specimen was used previously to develop the dynamic model. A third ligament attachment site mapping scheme was based on anatomical dissection of the scanned specimen. Following morphological comparison of the ligament attachment sites, their effect on the mechanical behaviour of the ankle complex, expressed by three-dimensional load–displacement properties, was assessed through the model. Results. Large differences were observed in the subtalar ligament attachment sites between those obtained through the two MRI scanning modalities. The 3.0 T MRI mapping was more consistent with dissection than the 1.5 T MRI. Load–displacement curves showed similar mechanical behaviours between the three mappings in the frontal plane, but those obtained from the 3.0 T MRI mapping were closer to those obtained from dissection. Conclusions. The state-of-the-art 3.0 T MRI image analysis resulted in more realistic mapping of ligament fibre origin and insertion site definitions; corresponding load–displacement predictions from a subject-specific model of the ankle complex showed a mechanical behaviour more similar to that using direct ligament attachment observations.

Comparison between T2-weighted two-dimensional and three-dimensional fast spin-echo MRI sequences for characterizing thoracolumbar intervertebral disc disease in small-breed dogs

Magnetic resonance imaging (MRI) is a standard test for diagnosis and treatment planning in dogs with degenerative thoracolumbar intervertebral disc disease (IVDD). However, published studies evaluating three-dimensional fast-spin echo (3D-FSE) pulse sequences for dogs with IVDD are currently limited. Aims of this retrospective, observational study were to compare findings from T2-weighted two- and three-dimensional fast spin-echo sequences (2D- and 3D-FSE, respectively) for a group of small breed dogs with thoracolumbar IVDD. Inclusion criteria were dogs with IVDD that underwent 1.5-Tesla MRI using both 2D-FSE and 3D-FSE sequences. For each dog and sequence, five pathologic indices were recorded: epidural fat discontinuation, vertebral canal compromise, spinal cord signal change, disc degeneration, and nerve root compression. Two independent investigators also scored visibility of the facet joint, intervertebral foramen, nerve roots, spinal cord grey-white matter differentiation, intervertebral discs, and epidural fat. The Wilcoxon signed-rank test was used to evaluate the between-sequence differences in pathologic indices and visibility scores. Interobserver agreement was measured using Cohen's weighted kappa along with 95% confidence intervals. A total of 21 dogs were sampled. The 3D-FSE sequences had higher pathologic indices of vertebral canal compromise (P = 0.020) and spinal cord signal change (P = 0.046) than 2D-FSE sequences. Furthermore, 3D-FSE sequences had higher visibility scores for the facet joint, intervertebral foramen, and nerve root structures (P < 0.001). Findings from the current supported the use of 3D-FSE sequences over 2D-FSE sequences for the evaluation of IVDD and visualization of spinal structures in small breed dogs.

Feasibility of MRI for the evaluation of interosseous ligament vertical segment via subtalar arthroscopy correlation: comparison of 2D and 3D MR images

Background

Interosseous ligament vertical segment (IOLV) and calcaneofibular ligament (CFL) have been reported to be important in stabilizing the subtalar joint. Unlike CFL, there is not much information regarding the comparison of MRI results with surgical evaluation of IOLV and the comparison between 2D and 3D MRI on IOLV evaluation. The feasibility of MRI in IOLV evaluation has yet to be reported. The purpose of this study was to evaluate the validity and reliability of MRI in IOLV tear detection via correlation with arthroscopic results. We also compared the diagnostic performance of 2D and 3D MR images.

Methods

In this retrospective study, 52 patients who underwent subtalar arthroscopy after ankle MRI were enrolled. Arthroscopic results confirmed IOLV tear in 25 cases and intact IOLV in 27 cases. Two radiologists independently evaluated the IOLV tears using only conventional 2D images, followed by isotropic 3D images, and comparison with arthroscopic results.

Results

Only the 2D sequences interpreted by two readers showed a sensitivity of 64.0–96.0%, a specificity of 29.6–44.4%, a positive predictive value of 51.6–56.4%, and a negative predictive value of 57.1–88.9%. Addition of isotropic 3D sequences changed the sensitivity to 60.0–80.0%, specificity to 63.0–77.8%, positive predictive value to 64.3–76.9%, and negative predictive value to 66.7–80.8%. The overall diagnostic performance of isotropic 3D sequences (AUC values: 0.679–0.816) was higher than that of 2D sequences (AUC values: 0.568–0.647). Inter-observer and intra-observer agreement between the two readers was moderate-to-good for both 2D and 3D sequences. The diagnostic accuracy in 19 patients with tarsal sinus fat obliteration tended to increase from 26.3–42.1% to 57.9–73.7% with isotropic 3D sequences compared with 2D sequences.

Conclusions

Isotropic 3D MRI was feasible for the assessment of IOLV tear prior to subtalar arthroscopy. Additional 3D sequences showed higher diagnostic accuracy compared with conventional 2D sequences in IOLV evaluation. Isotropic 3D sequences may be more valuable in detecting IOLV tear in case of tarsal sinus fat obliteration.

3D MRI of the Ankle: A Concise State-of-the-Art Review

Magnetic resonance imaging (MRI) is a powerful imaging modality for visualizing a wide range of ankle disorders that affect ligaments, tendons, and articular cartilage. Standard two-dimensional (2D) fast spin-echo (FSE) and turbo spin-echo (TSE) pulse sequences offer high signal-to-noise and contrast-to-noise ratios, but slice thickness limitations create partial volume effects. Modern three-dimensional (3D) FSE/TSE pulse sequences with isotropic voxel dimensions can achieve higher spatial resolution and similar contrast resolutions in ≤ 5 minutes of acquisition time. Advanced acceleration schemes have reduced the blurring effects of 3D FSE/TSE pulse sequences by affording shorter echo train lengths. The ability for thin-slice partitions and multiplanar reformation capabilities eliminate relevant partial volume effects and render modern 3D FSE/TSE pulse sequences excellently suited for MRI visualization of several oblique and curved structures around the ankle. Clinical efficiency gains can be achieved by replacing two or three 2D FSE/TSE sequences within an ankle protocol with a single isotropic 3D FSE/TSE pulse sequence. In this article, we review technical pulse sequence properties for 3D MRI of the ankle, discuss practical considerations for clinical implementation and achieving the highest image quality, compare diagnostic performance metrics of 2D and 3D MRI for major ankle structures, and illustrate a broad spectrum of ankle abnormalities.

Comparison of CAIPIRINHA-accelerated 3D fat-saturated-SPACE MRI with 2D MRI sequences for the assessment of shoulder pathology

OBJECTIVES

To compare the performance of 6-min MRI with a fat-saturated 3D-controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) Sampling perfection with application-optimized contrast using different flip angle evolution (SPACE) TSE protocol with 10-min 2D TSE MRI protocol for assessment of abnormalities of the shoulder.

METHODS

Forty-nine subjects underwent both 3D fat-saturated-CAIPIRINHA SPACE and 2D TSE sequences of the shoulder on a 3.0-T system. Following randomization and anonymization, two musculoskeletal radiologists evaluated the 2D and 3D images independently for image quality and diagnostic capability. Descriptive statistics, inter-observer, and inter-method concordance were investigated. p values < 0.05 were considered significant.

RESULTS

For image quality assessment, 2D images were similar to 3D CAIPIRINHA SPACE images (p = 0.05). 3D had lower noise standard deviation (SD) and higher fluid CNR than 2D images (p = 0.00). For diagnostic capability assessment, using 2D TSE as a standard of reference, sensitivity, specificity, and accuracy of 3D SPACE were, respectively, 94.81%, 94.12%, and 94.39% for tendon abnormalities; 97.06%, 80.00%, and 91.84% for acromioclavicular joint abnormalities; 88.89%, 100.00%, and 93.89% for adjacent bone alterations; and 97.30%, 100%, and 97.96% for joint fluid/effusion assessment. The inter-method concordance was moderate to almost perfect. The inter-observer-concordance of the shoulder assessment was also moderate to almost perfect, with SSP lesions demonstrating the greatest concordance.

CONCLUSIONS

The performance of 6-min 3D fat-saturated-CAIPIRINHA SPACE MRI for shoulder MRI is similar to that of 10-min 2D TSE MRI. 3D fat-saturated-CAIPIRINHA SPACE MRI can be utilized to reduce scan time without degradation in image quality.

KEY POINTS

• CAIPIRINHA acceleration 3D fat-saturated-MRI of the shoulder is achievable in 6 min with high spatial resolution. • 3D fat-saturated CAIPIRINHA MRI is similar to 2D MRI in the shoulder assessment. • 3D CAIPIRINHA MRI images enable rapid diagnosis of shoulder abnormalities without image quality degradation.

Modified acquisition strategy for reduced motion artifact in super resolution T 2 FSE multislice MRI: Application to prostate

PURPOSE

To reduce slice-to-slice motion effects in multislice T 2 -weighted fast-spin-echo ( T 2 FSE) imaging, manifest as "scalloping" in reformats, by modification of the acquisition strategy and to show applicability in prostate MRI.

METHODS

T 2 FSE images of contiguous or overlapping slices are typically acquired using multiple passes in which each pass is comprised of multiple slices with slice-to-slice gaps. Combination of slices from all passes provides the desired sampling. For enhancement of through-plane resolution with super resolution or for reformatting into other orientations, subtle ≈1 mm motion between passes can cause objectionable "scalloping" artifact. Here we address this by subdivision of each pass into multiple segments. Interleaving of segments from the multiple passes causes all slices to be acquired over substantially the same time, reducing pass-to-pass motion effects. This was implemented in acquiring 78 overlapped T 2 FSE axial slices and studied in phantoms and in 14 prostate MRI patients. Super-resolution axial images and sagittal reformats from the original and new segmented acquisitions were evaluated by 3 uroradiologists.

RESULTS

For all criteria of sagittal reformats, the segmented acquisition was statistically superior to the original. For all sharpness criteria of axial images, although the trend preferred the original acquisition, the difference was not significant. For artifact in axial images, the segmented acquisition was significantly superior.

CONCLUSIONS

For prostate MRI the new segmented acquisition significantly reduces the scalloping motion artifact that can be present in reformats due to long time lags between the acquisition of adjacent or overlapped slices while retaining image sharpness in the acquired axial slices.

Quality comparison between three-dimensional T2-weighted SPACE and two-dimensional T2-weighted turbo spin echo magnetic resonance images for the brachytherapy planning evaluation of prostate and periprostatic anatomy

PURPOSE

The purpose of this study was to compare an isotropic three-dimensional (3D) T2-weighted sequence sampling perfection with application-optimized contrasts by using flip angle evolution (SPACE) with an axial two-dimensional T2-weighted turbo spin echo (TSE) sequence with regard to overall image quality and the delineation of normal prostate and periprostatic anatomy for low-dose-rate prostate cancer brachytherapy planning evaluation.

METHODS AND MATERIALS

Patients (n = 69) with prostate cancer who had pelvic magnetic resonance imaging (MRI) for low-dose-rate brachytherapy treatment planning were included. Three radiologists independently assessed the visibility of nine anatomic structures on each sequence by using a 5-point scale and overall image quality by using a 4-point scale. The significance of the differences in diagnostic performance was tested with a Wilcoxon signed rank test.

RESULTS

No significant intersequence differences were found for most (7/9) anatomical structures and overall image quality. The mean scores for visibility of anatomical structures on the 3D SPACE and 2D TSE sequences, respectively, were as follows: the zonal anatomy (3.7; 3.9, p = 0.05), prostate capsule (3.9; 4.0, p = 0.08), neurovascular bundle (2.9; 2.9, p = 0.9), rectoprostatic angle (3.8; 3.8, p = 0.35), rectum (4.2; 4.3, p = 0.26), urethra (3.8; 3.9, p = 0.12), urinary bladder (4.6; 4.6, p = 0.61), and overall image quality (2.9; 2.9, p = 0.33). 3D SPACE was superior for delineation of the genitourinary diaphragm (3.8; 3.6, p = 0.003), whereas 2D TSE was superior for delineation of the seminal vesicles (3.5; 4.0, p < 0.0001).

CONCLUSIONS

Anatomic delineation of the prostatic and periprostatic anatomy provided by the 3D SPACE sequence is as robust in quality as that provided by a conventional 2D TSE sequence with superior delineation of the genitourinary diaphragm. For MRI-based brachytherapy treatment planning, the 3D SPACE sequence with subcentimeter isotropic resolution can replace the 2D TSE sequence and be incorporated into standard MRI protocols.

Evaluation of the anterior inferior tibiofibular and anterior talofibular ligaments using 2D oblique coronal imaging and 3D isotropic resolution T2-weighted fast spin-echo sequences at 3.0 T: Is there additional diagnostic value?

INTRODUCTION

To compare diagnostic performance of additional two-dimensional (2D) oblique coronal view and three-dimensional (3D) T2-weighted fast spin-echo(FSE) images for diagnosing injury of the anterior inferior tibiofibular (AiTFL) and anterior talofibular ligaments (ATFL).

METHODS

This study included 48 patients with ankle sprain who had undergone MRI using standard protocol and two additional sequences with 2D oblique coronal and 3D isotropic images, followed by arthroscopic surgery. Ligament injuries was subdivided by intact tendon, partial or complete tear. Retrospectively, two musculoskeletal radiologists respectively reviewed three image sets of MR including 2D axial image only (set 1), 2D axial and oblique coronal images (set 2), and 2D axial with 3D-isotropic images (set 3). Using arthroscopic findings as reference standard, diagnostic performances of both methods were analysed by the area under the curve (AUC).

RESULTS

Arthroscopy confirmed 13 AiTFL and 41 ATFL injuries. For AiTFL, when set 1 and set 3 were compared, AUC value was significantly higher for set 3 (P < 0.05). However, there was no significant difference between AUC values for set 2 and set 3 sequences by either reader for either type of tear (P > 0.05). For ATFL, both readers found there was no significant difference in AUC values between set 1 and set 3 and between set 2 and set 3.

CONCLUSION

Additional oblique coronal sequence demonstrated better diagnostic performance for AiTFL injury than conventional and isotropic imaging did. This sequence showed as much diagnostic accuracy as isotropic sequence for evaluation of ATFL injury.

[Advanced cartilage imaging for detection of cartilage injuries and osteochondral lesions]

BACKGROUND

Osteochondral defects represent a main risk factor for osteoarthritis of the ankle.

OBJECTIVES

The aim of this article is to provide an overview of current optimal clinical cartilage imaging techniques of the foot and ankle and to show typical osteochondral injuries on imaging.

MATERIALS AND METHODS

A thorough literature search was performed and was supported by personal experience.

RESULTS

Cartilage imaging of the foot and ankle remains challenging. However, advanced morphological and quantitative magnetic resonance (MR) imaging techniques may provide useful clinical information, for example, concerning cartilage repair surgery. Compared to MRI, MR arthrography (MR-A) and CT arthrography (CT-A) have higher sensitivity with respect to detection of osteochondral defects. Regarding smaller joints of the foot, mainly advanced osteoarthritic changes are detected on conventional radiography; only in rare cases, MR and CT imaging of these smaller joints is of relevance.

CONCLUSIONS

While at the smaller joints of the foot cartilage imaging only plays a minor role, at the ankle joint cross-sectional cartilage imaging using CT and MRI becomes more and more important for clinicians due to emerging therapeutic options, such as different osteochondral repair techniques.

Use of kZ -space for high through-plane resolution in multislice MRI: Application to prostate

PURPOSE

The goal of this work is to demonstrate 1 mm through-plane resolution in multislice T2SE MRI using k Z -space processing of overlapping slices and show applicability in prostate MRI.

METHODS

Multiple overlapped slices are acquired and Fourier transformed in the slice-select direction. The slice profile is incorporated into a Tikhonov-regularized reconstruction. Through-plane resolution is tested in a resolution phantom. An anthropomorphic prostate phantom is used to study the SNR, and results are compared with theoretical prediction. The proposed method is tested in 16 patients indicated for clinical prostate MRI who gave written informed consent as overseen by our IRB. The "proposed" vs. "reference" multislice images are compared using multiple evaluation criteria for through-plane resolution.

RESULTS

The modulation transfer function (MTF) plots of the resolution phantom show good modulation at frequency 0.5 lp/mm, demonstrating 1 mm through-plane resolution restoration. The SNR measurements experimentally match the theoretically predicted values. The radiological evaluation shows that the proposed method is superior to the reference method for five criteria of sharpness but inferior with respect to artifacts.

CONCLUSIONS

In conjunction with overlapped slices a k Z -space-based reconstruction approach can be used to improve through-plane resolution in multislice T2SE MRI. 1 mm resolution is demonstrated from 3.2 mm thick slices. The in vivo results from prostate MRI show improved sharpness when compared to the standard multislice method.

Evaluation of diagnostic value and T2-weighted three-dimensional isotropic turbo spin-echo (3D-SPACE) image quality in comparison with T2-weighted two-dimensional turbo spin-echo (2D-TSE) sequences in lumbar spine MR imaging

Purpose

to evaluate diagnostic value and image quality of T2-weighted Three-dimensional isotropic turbo spin-echo (SPACE) in comparison with T2-weighted two-dimensional turbo spin-echo (TSE) sequences for comprehensive evaluation of lumbar spine pathologies.

Materials and methods

Thirty-five participants with lumbar discopathy were examined on a 1.5-T MRI system with both 2D TSE and 3D SPACE sequences. Obtained images were analyzed with synedra view personal (V 17.0.0.2) software in terms of calculating image quality factors such as signal to noise ratio (SNR) and contrast to noise ratio (CNR) for selected regions of interest. In addition, images were referred to radiologists to report their pathologic indexes. The visibility of anatomical structures in the 3D and 2D sequences was qualitatively assessed by two radiologists independently. Cohen's kappa (k) and Wilcoxon signed rank test was used for the statistical analysis.

Results

In this study, the 3D SPACE T2-weighted sequence showed significant higher SNR and CNR as well as visibility in all of the regions of interest except vertebrae and intervertebral discs (p-value < 0.05). Inter-observer agreement for visibility of regions of interest was substantial and perfect (k > 0.6). Also, inter-observer and inter-method agreements for pathologic indexes were substantial and perfect for all of the pathologic indexes (k > 0.6). Inter-observer agreement for 3D SPACE sequence was higher (k = 0.793) in comparison with 2D-TSE sequence (k = 0.603). 3D SPACE sequence and its multi-planar reconstructions (MPR) scan time were less (192 s) than 2D TSE in the sagittal, axial and coronal planes (209 s).

Conclusion

3D SPACE sequence for lumbar spine MRI proved to have higher SNR, CNR, and visibility for all regions of lumbar spine except vertebrae and disc. Inter-observer and inter-method agreements for pathologic indexes between 3D SPACE and 2D TSE sequences were substantial and 3D SPACE had a higher inter-observer agreement and less scan time. Therefore, T2 weighted 3D SPACE sequence, and its MPR might be an excellent alternative for 2D TSE in sagittal, axial, and coronal planes, especially for patients with abnormal curvature of the lumbar spine.

Combined application of isotropic three-dimensional fast spin echo (3D-FSE-Cube) with 2-point Dixon fat/water separation (FLEX) and 3D-FSE-cube in MR dacryocystography

Objective:

To evaluate the image quality of magnetic resonance dacryocystography (MRD) using three-dimesional fast spin-echo -Cube (3D-FSE-Cube) and 3D-FSE-Cube-Flex sequences to examine the lacrimal drainage system (LDS).

Methods:

21 healthy volunteers underwent 3D-FSE-Cube and 3D-FSE-Cube-Flex MRD after topical administration of compound sodium chloride eye drops. Two radiologists assessed LDS images in a blinded fashion. The signal-to-noise ratio of fluid-filling and the contrast-to-noise ratio of fluid-turbinate were compared between the two sequences. Overall image quality, sharpness, artefacts, visualization of anatomical structures, and visibility of LDS segments were also compared.

Results:

Overall image quality, visualization of anatomic structures, and artefact were significantly better on 3D-FSE-Cube-Flex MRD (p < 0.001, respectively). when compared to 3D-FSE-Cube. 3D-FSE-Cube showed lower fluid-filling signal-to-noise ratio and fluid-inferior turbinate CNR (all p < 0.001). In comparison with 3D-FSE-Cube-Flex, 3D-FSE-Cube produced superior visibility of the upper drainage segments (superior canaliculi, p = 0.003; common canaliculus, p = 0.033; inferior canaliculi, p < 0.001), but inferior in lower-LDS visibility (lacrimal sac, p = 0.001; nasolacrimal duct, p < 0.001). There was no difference in the total number of segments visualized per LDS between the two sequences (p = 0.068).

Conclusions:

3D-FSE-Cube-Flex demonstrated superior image quality and visibility of the lower LDS segments. 3D-FSE-Cube showed an advantage in visualizing the upper LDS segments. The combination of these sequences can improve LDS visibility.

Advances in knowledge:

3D-FSE-Cube-Flex provides robust water & fat separation and mitigates lower LDS-associated inhomogeneity artefacts. 3D-FSE-Cube shows optimal upper LDS visualization. The combined application of these sequences is a non-invasive and effective method for assessing LDS disease.

Super-resolution musculoskeletal MRI using deep learning

PURPOSE

To develop a super-resolution technique using convolutional neural networks for generating thin-slice knee MR images from thicker input slices, and compare this method with alternative through-plane interpolation methods.

METHODS

We implemented a 3D convolutional neural network entitled DeepResolve to learn residual-based transformations between high-resolution thin-slice images and lower-resolution thick-slice images at the same center locations. DeepResolve was trained using 124 double echo in steady-state (DESS) data sets with 0.7-mm slice thickness and tested on 17 patients. Ground-truth images were compared with DeepResolve, clinically used tricubic interpolation, and Fourier interpolation methods, along with state-of-the-art single-image sparse-coding super-resolution. Comparisons were performed using structural similarity, peak SNR, and RMS error image quality metrics for a multitude of thin-slice downsampling factors. Two musculoskeletal radiologists ranked the 3 data sets and reviewed the diagnostic quality of the DeepResolve, tricubic interpolation, and ground-truth images for sharpness, contrast, artifacts, SNR, and overall diagnostic quality. Mann-Whitney U tests evaluated differences among the quantitative image metrics, reader scores, and rankings. Cohen's Kappa (κ) evaluated interreader reliability.

RESULTS

DeepResolve had significantly better structural similarity, peak SNR, and RMS error than tricubic interpolation, Fourier interpolation, and sparse-coding super-resolution for all downsampling factors (p < .05, except 4 × and 8 × sparse-coding super-resolution downsampling factors). In the reader study, DeepResolve significantly outperformed (p < .01) tricubic interpolation in all image quality categories and overall image ranking. Both readers had substantial scoring agreement (κ = 0.73).

CONCLUSION

DeepResolve was capable of resolving high-resolution thin-slice knee MRI from lower-resolution thicker slices, achieving superior quantitative and qualitative diagnostic performance to both conventionally used and state-of-the-art methods.

Computation of exact g-factor maps in 3D GRAPPA reconstructions

PURPOSE

To characterize the noise distributions in 3D-MRI accelerated acquisitions reconstructed with GRAPPA using an exact noise propagation analysis that operates directly in k-space.

THEORY AND METHODS

We exploit the extensive symmetries and separability in the reconstruction steps to account for the correlation between all the acquired k-space samples. Monte Carlo simulations and multi-repetition phantom experiments were conducted to test both the accuracy and feasibility of the proposed method; a high-resolution in-vivo experiment was performed to assess the applicability of our method to clinical scenarios.

RESULTS

Our theoretical derivation shows that the direct k-space analysis renders an exact noise characterization under the assumptions of stationarity and uncorrelation in the original k-space. Simulations and phantom experiments provide empirical support to the theoretical proof. Finally, the high-resolution in-vivo experiment demonstrates the ability of the proposed method to assess the impact of the sub-sampling pattern on the overall noise behavior.

CONCLUSIONS

By operating directly in the k-space, the proposed method is able to provide an exact characterization of noise for any Cartesian pattern sub-sampled along the two phase-encoding directions. Exploitation of the symmetries and separability into independent blocks through the image reconstruction procedure allows us to overcome the computational challenges related to the very large size of the covariance matrices involved.

The rotating stretched curved planar reconstruction of 3D-FIESTA MR imaging for evaluating the anterior cruciate ligament of the knee joint

PURPOSE

To determine the feasibility of the rotating stretched curved planar reconstruction (CPR) of three-dimensional fast imaging with steady-state acquisition magnetic resonance imaging (3D-FIESTA MRI) for evaluating the anterior cruciate ligament of the knee joint.

MATERIALS AND METHODS

MRI of 40 knee joints in healthy volunteers was performed on a 3.0-T MR scanner and a phased-array extremity coil. The protocol consisted of oblique sagittal spin echo (SE) T1WI, coronal FS-PDWI, axial FS-FSE-T2WI, and 3D-FIESTA sequences. The rotating stretched curved planar reconstructions (CPR) of the ACL at angles of 0°, 30°, 60°, 90°, 120°, 150°, and 180° were generated from images of 3D-FIESTA sequences. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the 3D-FIESTA were compared with those of the oblique sagittal SE T1WI sequence. The presence of the tibial attachment, midportion, femoral attachment, and double bundles of the ACL on the oblique sagittal SE T1WI and CPR of 3D-FIESTA MR imaging were divided into two categories: visible and not visible.

RESULTS

The ACL SNR efficiency of 3D-FIESTA sequences was significantly higher than that of oblique sagittal SE T1WI sequence (P < 0.05). The 3D-FIESTA sequences produced images with a significantly higher CNR between ACL and synovial fluid than did the oblique sagittal SE T1WI sequence (P < 0.05). CPR of 3D-FIESTA MRI generated an excellent visualization of the ACL. The CPR of 3D-FIESTA MRI was rated superior to oblique sagittal SE T1WI sequence in 60% and 65% of cases with regard to the tibial attachment and midportion of ACL, respectively (P < 0.05). CPR of 3D-FIESTA MR imaging was rated superior to oblique sagittal SE T1WI sequence in 80% and 85% of cases with regard to femoral attachment and double bundles of ACL, respectively (P < 0.05).

CONCLUSION

The rotating stretched curved planar reconstruction of 3D-FIESTA sequences is significantly better than that of conventional 2D-MRI in evaluating the native ACL and its components, AM bundle and PL bundle, in healthy volunteers.

Differences Between Subtalar Instability and Lateral Ankle Instability Focusing on Subtalar Ligaments Based on Three Dimensional Isotropic Magnetic Resonance Imaging

OBJECTIVE

The purpose of this study was to assess the differences between subtalar instability (STI) and lateral ankle instability (LAI) focusing on subtalar ligaments using 3-dimensional (3D) isotropic magnetic resonance imaging (MRI).

METHODS

Preoperative MRIs of 10 patients with STI who failed nonoperative treatment and consequently underwent arthroscopic subtalar reconstruction were compared with preoperative MRIs of 23 patients with LAI who underwent ligament repair or reconstruction. Dimensions of anterior capsular ligament (ACL), interosseous talocalcaneal ligament (ITCL), calcaneofibular ligament (CFL), and anterior talofibular ligament (ATFL) were measured. Tears of ACL, ITCL, CFL, ATFL, cervical ligament, and inferior extensor retinaculum were analyzed.

RESULTS

Patients with subtalar instability had significantly lower ACL thickness and width than patients with LAI (thickness: 1.48 vs 2.12 mm, P = 0.045; width: 7.30 vs 8.64 mm, P = 0.029). An ACL thickness of 1.8 mm or less had sensitivity and specificity both at 75.0%, and an ACL width of 8 mm or less had sensitivity of 75.0% and specificity of 85.0% for discriminating STI from LAI. Absence or complete tear of ACL was more frequent in patients with STI than in patients with LAI (60.0% vs 13.0%, P = 0.010). The ATFL thickness was significantly greater in patients with LAI (P = 0.001). Complete tear of ATFL was more common in patients with LAI (P = 0.008). Complete tear of CFL was common in both the STI and LAI groups without significant difference (20.0% vs 21.7%). There was no significant difference in thickness and width of ITCL and in CFL thickness. Complete tear of ITCL, cervical ligament, and inferior extensor retinaculum were rare without significant difference.

CONCLUSION

In patients with STI, the ACL is thin and narrow and more commonly absent or torn compared with patients with LAI. Complete tear of ATFL was more common in patients with LAI. Complete tear of CFL was commonly encountered in both the STI and LAI groups.

Routine clinical knee MR reports: comparison of diagnostic performance at 1.5 T and 3.0 T for assessment of the articular cartilage

OBJECTIVE

Accurate assessment of knee articular cartilage is clinically important. Although 3.0 Tesla (T) MRI is reported to offer improved diagnostic performance, literature regarding the clinical impact of MRI field strength is lacking. The purpose of this study is to compare the diagnostic performance of clinical MRI reports for assessment of cartilage at 1.5 and 3.0 T in comparison to arthroscopy.

MATERIALS AND METHODS

This IRB-approved retrospective study consisted of 300 consecutive knees in 297 patients who had routine clinical MRI and arthroscopy. Descriptions of cartilage from MRI reports of 165 knees at 1.5 T and 135 at 3.0 T were compared with arthroscopy. The sensitivity, specificity, percent of articular surfaces graded concordantly, and percent of articular surfaces graded within one grade of the arthroscopic grading were calculated for each articular surface at 1.5 and 3.0 T. Agreement between MRI and arthroscopy was calculated with the weighted-kappa statistic. Significance testing was performed utilizing the z-test after bootstrapping to obtain the standard error.

RESULTS AND CONCLUSIONS

The sensitivity, specificity, percent of articular surfaces graded concordantly, and percent of articular surfaces graded within one grade were 61.4%, 82.7%, 62.2%, and 77.5% at 1.5 T and 61.8%, 80.6%, 59.5%, and 75.6% at 3.0 T, respectively. The weighted kappa statistic was 0.56 at 1.5 T and 0.55 at 3.0 T. There was no statistically significant difference in any of these parameters between 1.5 and 3.0 T. Factors potentially contributing to the lack of diagnostic advantage of 3.0 T MRI are discussed.

Is the Grafted Tendon Shifted Anteriorly in the Femoral Tunnel at the Postremodeling Phase After Anterior Cruciate Ligament Reconstruction? A Clinical MRI Study

BACKGROUND

Based on previous in vitro studies, it has been commonly believed that during anterior cruciate ligament (ACL) reconstruction with hamstring tendon, the grafted tendon is shifted anteriorly in the tunnel permanently after the graft is anchored to the tunnel wall. However, this has not been proven by in vivo studies.

HYPOTHESIS

At 1 year after anatomic double-bundle ACL reconstruction, the grafted tendons may not be shifted anteriorly in the femoral tunnel but anchored to the bony wall at the center of the tunnel.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Participants consisted of 40 patients who underwent anatomic double-bundle ACL reconstruction. The grafted tendons located in the femoral tunnel were examined 1 year after surgery using 2 different magnetic resonance imaging (MRI) protocols. In the first substudy, with 20 patients, the grafted tendon location was evaluated on an inclined sagittal multiplanar reconstruction (MPR) image taken using a standard T2-weighted protocol. In the second substudy with the remaining 20 patients, tendon location was evaluated on a pure axial MPR image taken using a VISTA (volume isotropic turbo spin echo acquisition) protocol.

RESULTS

On the inclined sagittal T2-weighted images of the anteromedial (AM) graft, the anterior width of the newly formed fibrous tissue, which surrounded the tendon graft, was significantly greater than the posterior width (P = .001). The center of the grafted tendon was slightly (mean, 2.5% of the tunnel diameter) but significantly (P = .0310) shifted posteriorly from the tunnel center. On the axial T2-VISTA images, the center of the AM graft was slightly but significantly shifted posteriorly (3.9%; P = .022) and medially (5.5%; P = .002) from the tunnel center. The center of the posterolateral (PL) graft was not significantly shifted to any direction from the center of the tunnel.

CONCLUSION

The grafted tendons were not shifted anteriorly in the femoral tunnel 1 year after anatomic double-bundle ACL reconstruction. The PL graft was located approximately at the center of the tunnel outlet, while the AM graft was slightly but significantly shifted posteriorly and proximally.

MR arthrography of the shoulder: evaluation of isotropic 3D intermediate-weighted FSE and hybrid GRE T1-weighted sequences

PURPOSE

To compare the diagnostic accuracy of three-dimensional (3D) fast spin echo (FSE) intermediate-weighed (IW-3D) and 3D hybrid double-echo steady-state T1-weighted sequences (Hy-3D) and two-dimensional (FSE) images (2D) at shoulder MR arthrography (MRA).

MATERIALS AND METHODS

Institutional review board approval was obtained and informed consent was waived for this retrospective study. From September 2011 to October 2014, 102 patients who had undergone 1.5 Tesla MRA of the shoulder, including conventional 2D-FSE and IW-3D and Hy-3D images were included in our study. The mean interval between MRA and surgery was 21 days (range 2-70 days). MR images were retrospectively and independently reviewed by two experienced radiologists blinded to the clinical and surgical data. Supraspinatus tendon (SST), infraspinatus tendon (IST) and subscapularis tendon (SCT) tears, as well as antero-inferior, superior and posterior labral lesions were assessed, using surgery as the reference standard. Each reader's performance in assessing rotator cuff and labrum abnormalities was evaluated using the area under the receiver operating characteristic curve (AUC) and 95% confidence intervals (CIs). The difference was evaluated using a univariate z test. The sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV) and accuracy (Acc) for all types of rotator cuff tears and labral lesions were calculated. A value of p < 0.05 was considered statistically significant. Inter-observer agreement was calculated using kappa statistics.

RESULTS

The difference of diagnostic accuracy achieved was not significant (p > 0.05). In particular, differences in AUC values ranged from 0.002 (p = 0.98) to 0.014 (p = 0.82) as regards the comparison between 2D and IW-3D images, from 0.002 (p = 0.98) to 0.034 (p = 0.08) concerning the comparison between 2D and Hy-3D images and from 0.010 (p = 0.82) to 0.032 (p = 0.09) when comparing Hy-3D to IW-3D images. Accuracy values in evaluating RC lesions and labral lesions were 95.1, 92.1, 91.2, 93.1, 93.1 and 94.1% by reading 2D, Hy-3D and IW-3D images, respectively. The difference of diagnostic accuracy achieved using the datasets analyzed was not significant (p > 0.05). Inter-observer agreement was very good for each of the datasets that were evaluated, with near-perfect agreement for 2D dataset (k = 0.86), Hy-3D (k = 0.81) and IW-3D (k = 0.83).

CONCLUSIONS

The accuracy of IW-3D and Hy-3D images was not significantly higher than the 2D sequences in evaluating RC and labral lesions.

Diagnostic performance of wrist magnetic resonance (MR) arthrography: comparison of three-dimensional isotropic T1 weighted fast spin-echo MR arthrography and two-dimensional MR arthrography

OBJECTIVE

To compare the diagnostic performance of direct wrist MR arthrography (D-MRA) with two-dimensional (2D) T₁ weighted fast spin-echo (FSE) and three-dimensional (3D) isotropic T₁ weighted FSE sequences for detecting triangular fibrocartilage (TFC) central perforations and scapholunate ligament (SLL) and lunotriquetral ligament (LTL) tears.

METHODS

26 patients who had undergone pre-operative wrist D-MRA with 2D and 3D isotropic T₁ weighted FSE sequences and subsequent arthroscopic surgeries were included. Each MRI sequence was independently evaluated and scored by two readers retrospectively for the presence of TFC central perforations and SLL and LTL tears. Arthroscopic findings were used as the reference standard. Diagnostic performance was evaluated by using the area under the receiver operating characteristic curve. The sensitivity, specificity and accuracy of both sequences for diagnosing the injuries were calculated.

RESULTS

Arthroscopic surgery revealed 21 TFC central perforations, 7 SLL tears and 3 LTL tears. The area under the receiver operating characteristic curve value of 2D and 3D for central perforations in TFC and tears in SLL and LTL was identical or similar (0.667-0.947). The sensitivity, specificity and accuracy of both sequences for diagnosing the injury of each structure were not significantly different (TFC, 90.5/80/88.5% for both readers/sequences; SLL, 100/89.5/92.3% for both readers' 2D and Reader A's 3D, and 85.7/89.5/88.5% for Reader B's 3D; LTL, 66.7/100/96.2% for both readers' 2D and 33.3/100/92.3% for both readers' 3D). Interobserver agreements were substantial to excellent.

CONCLUSION

In wrist D-MRA, the diagnostic performances of 3D isotropic and 2D T₁ weighted FSE sequences are comparable for TFC central perforations and SLL and LTL tears. Advances in knowledge: The diagnostic performance of 3D isotropic T₁ weighted FSE D-MRA and that of 2D T₁ weighted FSE D-MRA were not significantly different in the diagnosis of central perforations in the TFC and tears in the SLL and LTL. 3D isotropic T₁ weighted FSE D-MRA has potential for substituting 2D imaging.

Diagnosis of Nerve Root Compromise of the Lumbar Spine: Evaluation of the Performance of Three-dimensional Isotropic T2-weighted Turbo Spin-Echo SPACE Sequence at 3T

Objective

To explore the performance of three-dimensional (3D) isotropic T2-weighted turbo spin-echo (TSE) sampling perfection with application optimized contrasts using different flip angle evolution (SPACE) sequence on a 3T system, for the evaluation of nerve root compromise by disc herniation or stenosis from central to extraforaminal location of the lumbar spine, when used alone or in combination with conventional two-dimensional (2D) TSE sequence.

Materials and Methods

Thirty-seven patients who had undergone 3T spine MRI including 2D and 3D sequences, and had subsequent spine surgery for nerve root compromise at a total of 39 nerve levels, were analyzed. A total of 78 nerve roots (48 symptomatic and 30 asymptomatic sites) were graded (0 to 3) using different MRI sets of 2D, 3D (axial plus sagittal), 3D (all planes), and combination of 2D and 3D sequences, with respect to the nerve root compromise caused by posterior disc herniations, lateral recess stenoses, neural foraminal stenoses, or extraforaminal disc herniations; grading was done independently by two readers. Diagnostic performance was compared between different imaging sets using the receiver operating characteristics (ROC) curve analysis.

Results

There were no statistically significant differences (p = 0.203 to > 0.999) in the ROC curve area between the imaging sets for both readers 1 and 2, except for combined 2D and 3D (0.843) vs. 2D (0.802) for reader 1 (p = 0.035), and combined 2D and 3D (0.820) vs. 3D including all planes (0.765) for reader 2 (p = 0.049).

Conclusion

The performance of 3D isotropic T2-weighted TSE sequence of the lumbar spine, whether axial plus sagittal images, or all planes of images, was not significantly different from that of 2D TSE sequences, for the evaluation of nerve root compromise of the lumbar spine. Combining 2D and 3D might possibly improve the diagnostic accuracy compared with either one.

3D isotropic T2-weighted fast spin echo (VISTA) versus 2D T2-weighted fast spin echo in evaluation of the calcaneofibular ligament in the oblique coronal plane

AIM

To investigate whether the image quality of three-dimensional (3D) volume isotropic fast spin echo acquisition (VISTA) magnetic resonance imaging (MRI) of the calcaneofibular ligament (CFL) view is comparable to that of 2D fast spin echo T2-weighted images (2D T2 FSE) for the evaluation of the CFL, and whether 3D VISTA can replace 2D T2 FSE for the evaluation of CFL injuries.

MATERIALS AND METHODS

This retrospective study included 76 patients who underwent ankle MRI with CFL views of both 2D T2 FSE MRI and 3D VISTA. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of both techniques were measured. The anatomical identification score and diagnostic performances were evaluated by two readers independently. The diagnostic performances of 3D VISTA and 2D T2 FSE were analysed by sensitivity, specificity, and accuracy for diagnosing CFL injury with reference standards of surgically or clinically confirmed diagnoses. Surgical correlation was performed in 29% of the patients, and clinical examination was used in those who did not have surgery (71%).

RESULTS

The SNRs and CNRs of 3D VISTA were significantly higher than those of 2D T2 FSE. The anatomical identification scores on 3D VISTA were inferior to those on 2D T2 FSE, and the differences were statistically significant (p<0.05). There were no significant differences in diagnostic performance between the two sequences when diagnoses were classified as normal or abnormal.

CONCLUSION

Although the image quality of 3D VISTA MRI of the CFL view is not equal to that of 2D T2 FSE for the anatomical evaluation of CFL, 3D VISTA has a diagnostic performance comparable to that of 2D T2 FSE for the diagnosis of CFL injuries.

Three-dimensional isotropic T2-weighted fast spin-echo (VISTA) knee MRI at 3.0 T in the evaluation of the anterior cruciate ligament injury with additional views: comparison with two-dimensional fast spin-echo T2-weighted sequences

Background There has been no comparison study to assess the diagnostic efficacy of additional anterior cruciate ligament (ACL) views in three-dimensional (3D) volume isotropic turbo spin-echo acquisition (VISTA) and two-dimensional (2D) fast spin-echo (FSE) T2-weighted (T2W) images for the diagnosis of ACL tear. Purpose To compare the diagnostic performances of additional ACL views on VISTA with those on the 2D FSE T2W images. Material and Methods This retrospective study included 78 patients who were suspected to have ACL injury and underwent both 2D TSE T2W magnetic resonance imaging (MRI) and 3D VISTA MRI of the knee between November 2012 and March 2013. The diagnostic performance of each oblique sagittal and coronal view and the combined images was evaluated for sensitivity, specificity, and accuracy for diagnosing an ACL tear. The arthroscopically and clinically confirmed diagnoses were used as the reference standard. The values were statistically analyzed using the McNemar test. Results The inter-observer agreement between two readers of the additional ACL views on 3D VISTA and 2D FSE T2W images were substantial on 2D FSE images and nearly concurred on the VISTA image. When considering both views of the oblique sagittal and coronal images, the inter-observer agreement between readers nearly concurred. There were no statistically significant differences in the sensitivity, specificity, and accuracy between 2D FSE images and VISTA images. Conclusion The performance of the additional ACL view on 3D VISTA MRI is comparable to that of 2D FSE T2W MRI in the diagnosis of ACL tear though the image quality of the 3D VISTA MRI is not equal to that of 2D FSE MRI.

Knee imaging: Rapid three-dimensional fast spin-echo using compressed sensing

PURPOSE

To investigate the feasibility of using compressed sensing (CS) to accelerate three-dimensional fast spin-echo (3D-FSE) imaging of the knee.

MATERIALS AND METHODS

A 3D-FSE sequence was performed at 3T with CS (CUBE-CS with 3:16-minute scan time) and without CS (CUBE with 4:44-minute scan time) twice on the knees of 10 healthy volunteers to assess signal-to-noise ratio (SNR) using the addition-subtraction method and once on the knees of 50 symptomatic patients to assess diagnostic performance. SNR of cartilage, muscle, synovial fluid, and bone marrow on CUBE and CUBE-CS images were measured in the 10 healthy volunteers. The CUBE and CUBE-CS sequences of all 50 symptomatic patients were independently reviewed twice by two musculoskeletal radiologists. The radiologists used CUBE and CUBE-CS during each individual review to determine the presence or absence of knee joint pathology. Student's t-tests were used to compare SNR values between sequences, while the kappa statistic was used to determine agreement between sequences for detecting knee joint pathology. Sensitivity and specificity of CUBE and CUBE-CS for detecting knee joint pathology was also calculated in the 18 symptomatic patients who underwent subsequent arthroscopic knee surgery.

RESULTS

CUBE and CUBE-CS had similar SNR (P = 0.15-0.67) of cartilage, muscle, synovial fluid, and bone marrow. There was near-perfect to perfect agreement between CUBE and CUBE-CS for both radiologists for detecting cartilage and bone marrow edema lesions, medial and lateral meniscus tears, anterior cruciate ligament tears, effusions, and intra-articular bodies. CUBE and CUBE-CS had similar sensitivity (75.0-100%) and specificity (87.5-100%) for detecting 60 cartilage lesions, 20 meniscus tears, four anterior cruciate ligament tears, and four intra-articular bodies confirmed at surgery.

CONCLUSION

CS provided a 30% reduction in scan time for 3D-FSE imaging of the knee without a corresponding decrease in SNR or diagnostic performance.

LEVEL OF EVIDENCE

1 J. MAGN. RESON. IMAGING 2017;45:1712-1722.

Comparison of oblique coronal images in knee of three-dimensional isotropic T2-weighted turbo spin echo MRI versus two-dimensional fast spin echo T2-weighted sequences for evaluation of posterior cruciate ligament injury

OBJECTIVE

To compare image quality between three-dimensional volume isotropic turbo spin echo acquisition (3D VISTA) with the posterior cruciate ligament (PCL) view and two-dimensional (2D) fast spin echo (FSE) for evaluation of PCL injury.

METHODS

This retrospective study included 60 patients with clinical suspicion of PCL injury who underwent both 2D FSE and 3D VISTA of the knee between January 2015 and December 2015. The diagnostic performance of each oblique coronal view and the combined images was evaluated for sensitivity, specificity and accuracy for diagnosing a PCL tear. The arthroscopically confirmed diagnoses were used as the reference standard. Data were analyzed using the McNemar test.

RESULTS

The mean contrast-to-noise ratio was significantly higher for 3D VISTA than for 2D FSE. The two imaging modalities did not differ significantly in anatomical identification ability, with the exception of margin sharpness, which was inferior for 3D VISTA with Reader 2 (p = 0.038). When we classified the diagnoses of PCL injury as normal or abnormal, there were no significant differences in sensitivity, specificity or accuracy between the PCL view of 3D VISTA and 2D FSE images (p > 0.05).

CONCLUSION

3D VISTA had a superior contrast-to-noise ratio than 2D FSE and similar image quality in the evaluation of the PCL. The PCL view of 3D VISTA has the same diagnostic ability as 2D FSE in the diagnosis of PCL injury and can thus replace 2D FSE. Advances in knowledge: The oblique coronal view 3D VISTA MRI has similar diagnostic ability to 2D FSE in the diagnosis of PCL injury, and therefore 3D VISTA image can replace 2D FSE.

Magnetic Resonance Imaging of Articular Cartilage

The emergence of newer pharmacotherapeutic agents and surgical cartilage resurfacing techniques is driving the need for imaging modalities capable of early, accurate, and reproducible lesion detection. Magnetic resonance imaging (MRI) has emerged as a noninvasive tool for direct 2-dimensional (2D) and 3-dimensional (3D) assessment of the articular cartilage in both clinical and research settings. MRI has largely overcome the shortcomings of the current gold standard, radiography, by allowing for the detection of preclinical disease and subtle early abnormalities prior to the onset of radiographic disease, when damage is still reversible. Current MRI techniques are either morphological (2D/3D qualitative and quantitative techniques) or compositional (matrix-assessment techniques that detect macromolecular changes prior to morphological changes). MRI is evolving as a complete answer to our cartilage-imaging requirements of lesion description, treatment planning, and outcome measurement as well as in various research settings.

Magnetic Resonance Three-dimensional Cube Technique in the Measurement of Piglet Femoral Anteversion

BACKGROUND

The accurate measurement of the femoral anteversion (FA) angle is always a topic of much debate in the orthopedic surgery and radiology research. We aimed to explore a new FA measurement method to acquire accurate results without radiation damage using piglet model.

METHODS

A total of thirty piglets were assigned to two groups based on the age. Bilateral femora were imaged with 3.0-T magnetic resonance (MR) and 64-slice computed tomography (CT) examinations on all piglets. FA was measured on MR-three-dimensional (3D) postprocessing software with a four-step method: initial validation of the femoral condylar axis, validation of the condylar plane, validation of the femoral neck axis, and line-plane angle measurement of FA. After MR and CT examinations, all piglets were sacrificed and their degree of FA was measured using their excised, dried femora. MR, CT, and dried-femur measurement results were analyzed statistically; MR and CT measurements were compared for accuracy against each other and against the gold standard dried femur measurement.

RESULTS

In both groups, the mean FA value measured by MR was lower than that measured by CT. A statistically significant difference was observed between CT- and dried-femur measurements but not between MR- and dried-femur measurements. A higher correlation (0.783 vs. 0.408) and a higher consistency (0.863 vs. 0.578) with dried-femur measurement results were seen for MR measurements than CT measurements in the 1-week age group. However, in the 8-week age group, similar correlations (0.707 vs. 0.669) and consistencies (0.864 vs. 0.821) were observed.

CONCLUSIONS

Noninvasive MR-3D-Cube reconstruction was able to accurately measure FA in piglets. Particularly in the 1-week age group with a larger proportion of cartilaginous structures, the correlation and consistency between MR- and dried-femur measurement results were higher than those between CT- and dried-femur measurements, suggesting that MR may be a new useful examination tool for FA-related diseases in children.

MRI of the anterior talofibular ligament, talar cartilage and os subfibulare: Comparison of isotropic resolution 3D and conventional 2D T2-weighted fast spin-echo sequences at 3.0 T

PURPOSE

To determine the accuracy of a three-dimensional (3D) T2-weighted fast spin-echo (FSE) magnetic resonance (MR) sequence compared with two-dimensional (2D) sequence for diagnosing anterior talofibular ligament (ATFL) tears, chondral lesion of the talus (CLT) and os subfibulare/avulsion fracture of the distal fibula (OSF).

MATERIALS AND METHODS

Thirty-five patients were included, who had undergone ankle MRI with 3D T2-weighted FSE and 2D T2-weighted FSE sequences, as well as subsequent ankle arthroscopy, between November 2013 and July 2014. Each MR imaging sequence was independently scored by two readers retrospectively for the presence of ATFL tears, CLT and OSF. The area under the receiver operating curve (AUC) was compared to determine the discriminatory power of the two image sequences. Interobserver agreement was expressed as unweighted kappa value.

RESULTS

Arthroscopic findings confirmed 21 complete tears of the ATFL, 14 partial tears of the ATFL, 17 CLTs and 7 OSFs. There were no significant differences in the diagnoses of ATFL tears (p = 0.074-0.501), CLT (p = 0.090-0.450) and OSF (p = 0.317) obtained from the 2D and 3D sequences by either reader. The interobserver agreement rates between two readers using the 3D T2-weighted FSE sequence versus those obtained with the 2D sequence were substantial (κ = 0.659) versus moderate (κ = 0.553) for ATFL tears, moderate (κ = 0.499) versus substantial (κ = 0.676) for CLT and substantial (κ = 0.621) versus substantial (κ = 0.689) for OSF.

CONCLUSION

Three-dimensional isotropic T2-weighted FSE MRI of the ankle resulted in no statistically significant difference in diagnostic performance compared to two-dimensional T2-weighted FSE MRI in the evaluation of ATFL tears, CLTs and OSFs.

Three-Dimensional Isotropic MRI of the Cervical Spine: A Diagnostic Comparison With Conventional MRI

STUDY DESIGN

Retrospective diagnostic trial.

OBJECTIVE

To determine the diagnostic performance of 3-dimensional turbo spin-echo (3D-TSE) isotropic magnetic resonance imaging (MRI) in the assessment of cervical spine pathology.

SUMMARY OF BACKGROUND DATA

MRI is the imaging modality of choice for many cervical spine pathologies. However, axial imaging may be suboptimal if the image plane is oriented differently than the plane of interest, due to lordosis, kyphosis, or deformity. 3D-TSE isotropic MRI is a promising novel technology that bypasses this limitation by enabling dynamic image reformation in any desired orientation.

METHODS

Forty-eight patients who underwent 3D-TSE and conventional 2-dimensional fast spin-echo (2D-FSE) T2-weighted cervical spine MRI at our institution were randomly selected. 3D-TSE and 2D-FSE sequences from each subject were independently evaluated by 2 orthopedic spine surgeons and 4 musculoskeletal radiologists. Images were assessed using specific pilot-tested criteria for stenosis, herniation, and degenerative changes. Intermethod, interrater, and intrarater agreements for 3D-TSE and 2D-FSE, and Fleiss κ coefficients were determined.

RESULTS

The overall intermethod agreement was 80.7%. The interrater agreement was 75.9% for 3D-TSE and 75.7% for 2D-FSE (P=0.47). The intrarater agreement was 82.2% for 3D-TSE and 81.5% for 2D-FSE (P=0.71). Fleiss κ coefficients were 0.42 for 3D-TSE and 0.43 for 2D-FSE (P=0.62), indicating moderate interrater reliability. The intermethod agreement and the 2D-FSE intrarater agreement were statistically similar (P=0.49).

CONCLUSIONS

There is a high degree of agreement between 3D-TSE and 2D-FSE MRI in assessing the cervical spine. The intermethod variability was statistically similar to the intrinsic intrarater variability of 2D-FSE MRI. This study demonstrates that 3D-TSE yields at least equivalent diagnostic information as conventional 2D-FSE in the cervical spine. In addition, reviewers noted subjective advantages of 3D-TSE image reprocessing, especially when evaluating greater pathology or deformity, with a simplified image acquisition process.