Sheronda Statum

Metal-on-Metal Total Hip Arthroplasty: Do Symptoms Correlate with MR Imaging Findings?

PURPOSE To determine the prevalence of magnetic resonance (MR) imaging abnormalities after metal-on-metal total hip arthroplasty and to determine whether presence of symptoms correlates with findings at MR imaging. MATERIALS AND METHODS This HIPAA-compliant study was approved by the institutional review board, and informed consent was waived. MR imaging was performed with conventional sequences and a 1.5-T clinical imager in 192 hips (174 patients) evaluated during a 15-month period. Two observers retrospectively reviewed the images for the presence and size of pseudotumor, communication with the pseudocapsule, wall thickness, synovial hypertrophy, compartmentalization, solid components, foci of wall susceptibility, osteolysis, bone marrow edema, abductor muscle or tendon abnormality, and Anderson MR grade (normal, infection, or varying severity of metal-on-metal disease). These findings were compared between asymptomatic and symptomatic patients by using the Fisher exact test or the Wilcoxon-Mann-Whitney test, as appropriate. RESULTS Prevalence of pseudotumors per patient and per hip was 69% (120 of 174 patients, 132 of 192 hips). Bone marrow edema (present in six asymptomatic patients and 19 patients with pain, P < .01) and tendon tearing (present in five asymptomatic patients and 13 patients with pain, P < .05) were predictors of pain. Presence of symptoms was not correlated with presence (P = .4151) or size of pseudotumors. Anderson MR grade binarized into normal versus abnormal showed moderate agreement between readers (κ = 0.439) but was also not correlated with symptoms (P = .6648). CONCLUSION The presence of bone marrow edema and abductor tendon tears but not the presence or size of pseudotumor was associated with patient pain.

Ultrashort Echo Time MR Imaging of Osteochondral Junction of the Knee at 3 T: Identification of Anatomic Structures Contributing to Signal Intensity

PURPOSE To image cartilage-bone interfaces in naturally occurring and experimentally prepared human cartilage-bone specimens at 3 T by using ultrashort echo time (TE) (UTE) and conventional pulse sequences to (a) determine the appearance of the signal intensity patterns and (b) identify the structures contributing to signal intensity on the UTE MR images. MATERIALS AND METHODS This study was exempted by the institutional review board, and informed consent was not required. Five cadaveric (mean age, 86 years +/- 4) patellae were imaged by using proton density-weighted fat-suppressed (repetition time msec/TE msec, 2300/34), T1-weighted (700/10), and UTE (300/0.008, 6.6, with or without dual-inversion preparations at inversion time 1 = 135 msec and inversion time 2 = 95 msec) sequences. The UTE images were compared with proton density-weighted fat-suppressed and T1-weighted images and were evaluated by two radiologists. To identify the sources of signal on the UTE images, samples including specific combinations of tissues (uncalcified cartilage [UCC] only, calcified cartilage [CC] and subchondral bone [bone] [CC/bone], bone only; and UCC, CC, and bone [UCC/CC/bone]) were prepared and imaged by using the UTE sequence. RESULTS On the UTE MR images, all patellar sections exhibited a high-intensity linear signal near the osteochondral junction, which was not visible on protein density-weighted fat-suppressed or T1-weighted images. In some sections, focal regions of thickened or diminished signal intensity were also found. In the prepared samples, UCC only, CC/bone, and UCC/CC/bone samples exhibited high signal intensity on the UTE images, whereas bone-only samples did not. CONCLUSION These results show that the high signal intensity on UTE images of human articular joints originates from the CC and the deepest layer of the UCC, without a definite contribution from subchondral bone. UTE sequences may provide a way of evaluating abnormalities at or near the osteochondral junction. (c) RSNA, 2010.

Magic angle effect in magnetic resonance imaging of the Achilles tendon and enthesis.

Collagen fibers in tendons and entheses are highly ordered. The protons within the bound water are subject to dipolar interactions whose strength depends on the orientation of the fibers to the static magnetic field B(0). Clinical pulse sequences have been employed to investigate this magic angle effect of the Achilles tendon, but only limited to imaging appearance with a signal void at many angular orientations due to its short T2. Here we investigated the magic angle effect of the Achilles tendons and entheses on a clinical 3-T scanner using clinical sequences as well as an ultrashort TE sequence with a minimal TE of 8 micros. Qualitative and quantitative investigation of the angular-dependent imaging appearance, T1 and T2* values were performed on five ankle specimens. There was a significant increase in signal intensity for all pulse sequences near the magic angle. Mean T2* for tendon increased from 1.94+/-0.28 ms at 0 degrees relative to the B(0) field to 15.25+/-2.13 ms at 55 degrees, and mean T1 increased from 598+/-37 ms at 0 degrees to 621+/-44 ms at 55 degrees. There was less magic angle effect for enthesis whose mean T2* increased from 4.12+/-0.37 ms at 0 degrees to 12.46+/-1.78 ms at 55 degrees, and mean T1 increased from 685+/-41 ms at 0 degrees to 718+/-56 ms at 55 degrees.

Quantitative Characterization of the Achilles Tendon in Cadaveric Specimens: T1 and T2* Measurements Using Ultrashort-TE MRI at 3 T

OBJECTIVE The objective of our study was to provide a quantitative means of evaluating the intrinsic T1 and T2(*) values of the Achilles tendon through the measurement of T1 recovery and T2(*) relaxation times, respectively, using ultrashort-TE (UTE) MRI at 3 T with histologic correlation. MATERIALS AND METHODS Six cadaveric specimens underwent MRI at 3 T. The MRI protocol included standard MRI and UTE pulse sequences. For T1 measurement, a saturation recovery time method was applied (saturation recovery time range, 10-1,600 milliseconds), and for T2(*) measurements, a constant TR-varying TE method was used (TE, 100 microseconds-15 milliseconds). An analysis algorithm written in Matlab was executed offline on axial DICOM images for the T1 and T2(*) measurements in areas of normal tendon. The cadaveric specimens were subsequently frozen to -40 degrees C. They were sectioned with the slice thickness corresponding to the MR images. Anatomic sections were photographed and visually inspected. Specimens were then processed for histology. MR images, specimen photographs, and histology results were reviewed by two musculoskeletal radiologists and one pathologist. RESULTS Compared with histology results, the combination of UTE and standard MRI provided an accurate means of identifying normal tendon. The mean T1 measurement was 621 milliseconds and the mean T2(*) measurement was 2.18 milliseconds in histologically proven regions of normal tendon. CONCLUSION The UTE MR sequence offers structural information about and allows reproducible quantitative evaluation of tissues with short T2 components, such as tendons, that are inaccessible on conventional MRI. This technique showed T1 and T2(*) measurements in the normal Achilles tendon and allowed correlation with structural status by histology. Because of the small number of specimens, this is considered a feasibility study.

Morphology of the Cartilaginous Endplates in Human Intervertebral Disks with Ultrashort Echo Time MR Imaging

PURPOSE To image human disk-bone specimens by using conventional spin-echo (SE) and ultrashort echo time (TE) techniques, to describe the morphology at magnetic resonance (MR) imaging, and to identify tissue components contributing to high signal intensity near the cartilaginous endplates (CEPs). MATERIALS AND METHODS This study was exempt from institutional review board approval, and informed consent was not required. Five cadaveric lumbar spines (mean age, 61 years ± 11) were prepared into six sample types containing different combinations of disk, uncalcified CEP, calcified CEP, and subchondral bone components and were imaged with proton density-weighted SE (repetition time msec/TE msec, 2000/15) and ultrashort TE (300/0.008, 6.6, echo-subtraction) sequences. Images were evaluated to determine the presence of intermediate-to-high signal intensity in regions excluding the bone marrow. Logistic regression was used to determine which tissue components were significant predictors of the presence of signal intensity for each MR technique. RESULTS On ultrashort TE MR images, intact disk/uncalcified CEP/calcified CEP/bone samples exhibited bilaminar intermediate-to-high signal intensity in the region near the CEP, consistent with the histologic appearance of uncalcified and calcified CEPs. Conversely, proton density-weighted SE images exhibited low signal intensity in this region. Results of logistic regression suggested that the presence of uncalcified CEP (P = .023) and calcified CEP (P = .007) in the sample were strong predictors of the presence of signal intensity on ultrashort TE images, whereas the disk was the only predictor (P < .001) of signal intensity on proton density-weighted SE images. CONCLUSION Ultrashort TE imaging, unlike proton density-weighted SE imaging, enabled direct visualization of the uncalcified and calcified CEP. Evaluation of the morphology and identification of sources of signal intensity at ultrashort TE MR imaging provides opportunities to potentially aid in the understanding of degenerative disk disease.

Dual inversion recovery ultrashort echo time (DIR-UTE) imaging and quantification of the zone of calcified cartilage (ZCC)

OBJECTIVE To develop ultrashort echo time (UTE) magnetic resonance imaging (MRI) techniques to image the zone of calcified cartilage (ZCC), and quantify its T2*, T1 and T1ρ. DESIGN In this feasibility study a dual inversion recovery UTE (DIR-UTE) sequence was developed for high contrast imaging of the ZCC. T2* of the ZCC was measured with DIR-UTE acquisitions at progressively increasing TEs. T1 of the ZCC was measured with saturation recovery UTE acquisitions at progressively increasing saturation recovery times. T1ρ of the ZCC was measured with spin-locking prepared DIR-UTE acquisitions at progressively increasing spin-locking times. RESULTS The feasibility of the qualitative and quantitative DIR-UTE techniques was demonstrated on phantoms and in six cadaveric patellae using a clinical 3 T scanner. On average the ZCC has a short T2* ranging from 1.0 to 3.3 ms (mean ± standard deviation = 2.0 ± 1.2 ms), a short T1 ranging from 256 to 389 ms (mean ± standard deviation = 305 ± 45 ms), and a short T1ρ ranging from 2.2 to 4.6 ms (mean ± standard deviation = 3.6 ± 1.2 ms). CONCLUSION UTE MR based techniques have been developed for high resolution imaging of the ZCC and quantitative evaluation of its T2*, T1 and T1ρ relaxation times, providing non-invasive assessment of collagen orientation and proteoglycan content at the ZCC and the bone cartilage interface. These measurements may be useful for non-invasive assessment of the ZCC, including understanding the involvement of this tissue component in osteoarthritis.

Development of a Comprehensive Osteochondral Allograft MRI Scoring System (OCAMRISS) with Histopathologic, Micro-Computed Tomography, and Biomechanical Validation.

Objective: To describe and apply a semiquantitative MRI scoring system for multifeature analysis of cartilage defect repair in the knee by osteochondral allografts and to correlate this scoring system with histopathologic, micro–computed tomography (µCT), and biomechanical reference standards using a goat repair model. Design: Fourteen adult goats had 2 osteochondral allografts implanted into each knee: one in the medial femoral condyle and one in the lateral trochlea. At 12 months, goats were euthanized and MRI was performed. Two blinded radiologists independently rated 9 primary features for each graft, including cartilage signal, fill, edge integration, surface congruity, calcified cartilage integrity, subchondral bone plate congruity, subchondral bone marrow signal, osseous integration, and presence of cystic changes. Four ancillary features of the joint were also evaluated, including opposing cartilage, meniscal tears, synovitis, and fat-pad scarring. Comparison was made with histologic and µCT reference standards as well as biomechanical measures. Interobserver agreement and agreement with reference standards was assessed. Cohen’s κ, Spearman’s correlation, and Kruskal-Wallis tests were used as appropriate. Results: There was substantial agreement (κ > 0.6, P < 0.001) for each MRI feature and with comparison against reference standards, except for cartilage edge integration (κ = 0.6). There was a strong positive correlation between MRI and reference standard scores (ρ = 0.86, P < 0.01). Osteochondral allograft MRI scoring system was sensitive to differences in outcomes between the types of allografts. Conclusions: We have described a comprehensive MRI scoring system for osteochondral allografts and have validated this scoring system with histopathologic and µCT reference standards as well as biomechanical indentation testing.

Meniscal Calcifications: Morphologic and Quantitative Evaluation by using 2D Inversion-Recovery Ultrashort Echo Time and 3D Ultrashort Echo Time 3.0-T MR Imaging Techniques—Feasibility Study

PURPOSE To assess the ability of ultrashort echo time (UTE) magnetic resonance (MR) imaging techniques to enable morphologic assessment of different types of meniscal calcifications, to compare these sequences with standard clinical sequences, and to perform T2* measurements of meniscal calcifications. MATERIALS AND METHODS This study was exempted by the institutional review board, and informed consent was not required. Ten human cadaveric menisci were imaged with high-spatial-resolution radiography and 3.0-T MR imaging by using morphologic (T1-weighted fast spin-echo [FSE], T2-weighted FSE, proton density [PD]-weighted FSE, two-dimensional [2D] fast spoiled gradient-echo [FSPGR], three-dimensional [3D] FSPGR, and 3D UTE) and quantitative (2D inversion-recovery [IR] UTE and 3D UTE) sequences. The menisci were divided into thirds for regional analysis. Morphologic assessment was performed with MR imaging; MR imaging findings were correlated with radiographs. Calcifications were classified as punctate, linear, or globular. T2* measurements were performed by manual placement of regions of interest (ROIs) in calcifications and by automatically creating ROIs in the surrounding tissues. Mixed-effects linear regression was used to determine variations in T2* as a function of region, morphology, and tissue type. RESULTS The two globular calcifications were visualized with all sequences. For punctate (n=21) and linear (n=21) calcifications, respectively, visibility rates were as follows: 9.5% for both with the T1-weighted FSE sequence, 0% for both with the T2-weighted FSE sequence, 19.0% and 23.8% with the PD-weighted FSE sequence, 0% for both with the 2D IR UTE sequence, 100% for both with the 3D UTE sequence, and 100% for both with the 3D FSPGR sequence. T2* values were significantly lower for calcifications than for the surrounding meniscal tissue (P<.001). There was a trend of globular calcifications having lower T2* values than other morphologies (P=.08). With the 2D IR UTE technique, the T2* of the globular calcifications tended to be lower than with the 3D UTE technique (0.13-0.16 vs 1.32-3.03 msec) (P=.14, analysis of variance). CONCLUSION UTE MR imaging sequences may allow morphologic as well as quantitative evaluation of meniscal calcifications.

Effects of repetitive freeze–thawing cycles on T2 and T2* of the Achilles tendon

INTRODUCTION In this study we sought to evaluate the effects of multiple freezing and thawing cycles on two MR parameters to study Achilles tendon, T2 and T2. MATERIALS AND METHODS Four fresh Achilles tendons were imaged on a 3T clinical scanner and again after 1, 2, 4, and 5 freeze-thaw cycles with spin-echo (SE) and ultrashort echo time (UTE) sequences. Regions of interest were manually drawn over the entire Achilles tendon and mono-exponential curves were used to determine T2 and T2 relaxation times. RESULTS There was no statistically significant difference in mean T2 or T2 values between the fresh specimens and after subsequent cycles of freeze-thaw treatment (p>0.1). Linear regression between SE T2 values at baseline and after successive freeze-thaw cycles demonstrated moderate agreement (r=0.60) whereas UTE T2 values at baseline and after successive-freeze thaw cycles demonstrated strong agreement (r=0.92). CONCLUSION These findings suggest that changes between specimens seen in vitro are due to factors other than frozen storage. Furthermore, our results suggest that there is stronger agreement between baseline (fresh) and successive freeze-thaw T2 values of tendon obtained with the UTE technique in comparison to T2 values obtained with a conventional clinical CPMG technique.

Comparison of T1rho Measurements in Agarose Phantoms and Human Patellar Cartilage Using 2D Multislice Spiral and 3D Magnetization Prepared Partitioned k-Space Spoiled Gradient-Echo Snapshot Techniques at 3 T

OBJECTIVE The purpose of this article is to compare in vitro T1rho measurements in agarose phantoms and articular cartilage specimens using 2D multislice spiral and 3D magnetization prepared partitioned k-space spoiled gradient-echo snapshot MRI sequences. MATERIALS AND METHODS Six phantoms (agarose concentration, 2%, 3%, and 4%; n = 2 each) and 10 axially sliced patellar specimens from five cadaveric donors were scanned at 3 T. T1rho-weighted images were acquired using 2D spiral and 3D magnetization prepared partitioned k-space spoiled gradient-echo snapshot sequences. Regions of interest were analyzed to measure T1rho values centrally within phantoms, to evaluate effects of pulse sequence and agarose concentration. In patellar specimens, regions of interest were analyzed to measure T1rho values with respect to anatomic location (the medial and lateral facets and the median ridge in deep and superficial halves of the cartilage) as well as location that exhibited magic angle effect in proton density-weighted images, to evaluate the effects of pulse sequence, anatomic location, and magic angle. RESULTS In phantoms, T1rho values were similar (p = 0.9) between sequences but decreased significantly (p < 0.001), from ∼55 to ∼29 milliseconds, as agarose concentration increased from 2% to 4%. In cartilage specimens, T1rho values were also similar between sequences (p = 0.3) but were significantly higher (p < 0.001) in the superficial layer (95-120 milliseconds) compared with the deep layer (45-75 milliseconds). CONCLUSION T1rho measurements of human patellar cartilage specimens and agarose phantoms using 2D spiral and 3D magnetization prepared partitioned k-space spoiled gradient-echo snapshot sequences gave similar values. Lower T1rho values for phantoms with higher agarose concentrations and proteoglycan concentrations that are higher in deeper layers of cartilage than in superficial layers suggest that our method is sensitive to concentration of macromolecules in biologic tissues.