Mapping T2 relaxation time in the pediatric knee: feasibility with a clinical 1.5-T MR imaging system

T2 Relaxation Time Changes in the Distal Femoral Condylar Cartilage of Children and Young Adults with Discoid Meniscus

OBJECTIVE

To investigate compositional changes in the distal femoral condylar cartilage (FCC) of children and young adults with and without discoid meniscus by T2 relaxation time mapping.

DESIGN

We retrospectively reviewed knee magnetic resonance images including sagittal T2 maps of distal FCC performed in patients with or without discoid meniscus. Combined meniscal pathology such as degeneration or tears was also reviewed. Regions of interest were selected, and T2 relaxation time profiles were generated according to medial and lateral and FCC and according to weight-bearing and non-weight-bearing FCC. Nonparametric comparison tests using median values were performed.

RESULTS

Seventy-nine knees from 73 patients (2-20 years) including 45 knees with lateral discoid meniscus (discoid group) were studied. T2 values of FCC showed negative correlation with age in both the discoid and nondiscoid groups (P < 0.01), except for medial weight-bearing FCC. In the discoid group, T2 relaxation times of lateral weight-bearing FCC (median, 46.5 ms) were lower than those of lateral non-weight-bearing (median, 53.2 ms; P < 0.001) and medial weight-bearing (median, 50.5 ms; P = 0.012) FCC. Lateral weight-bearing FCC also showed lower T2 values than other areas in patients with meniscal pathology in the discoid group. However, T2 relaxation times did not differ between the discoid and nondiscoid groups in patients without meniscal pathology.

CONCLUSIONS

Children and young adults with discoid meniscus have lower T2 relaxation times in lateral weight-bearing FCC compared with non-weight-bearing or medial FCC, suggesting compositional changes have occurred in these patients.

T2 mapping of the acetabular cartilage in infants and children with developmental dysplasia of the hip

BACKGROUND

T2 mapping is useful for evaluating the cartilage matrix.

PURPOSE

To determine the variations in the acetabular cartilage T2 relaxation values between healthy individuals and those with developmental dysplasia of the hip (DDH).

MATERIAL AND METHODS

Thirty-three patients with unilateral DDH underwent 3-T magnetic resonance imaging (MRI) between January 2018 and February 2019. Fifteen volunteers (30 hips) were enrolled as controls. T2 values were measured with the T2 mapping sequence in all layers and were equally divided into three layers (deep, middle, and superficial) with equal thickness. We calculated the mean T2 relaxation values for the full thickness, deep, middle, and superficial layers and compared the values between the different groups. In addition, the inter- and intra-observer agreements were calculated.

RESULTS

The T2 relaxation values in the DDH arm were significantly lower in the middle, superficial, and full thickness layers compared with those of the volunteers and contralateral hips. The T2 relaxation values of the deep layers showed no significant difference between the different groups. The acetabular cartilage T2 relaxation values increased from the deep layer to the superficial layer in the control and contralateral groups. Both inter- and intra-observer agreements were good.

CONCLUSION

MRI T2 mapping may help to diagnose developmental disorders of the acetabular cartilage matrix in infants and children with DDH. Abnormal acetabular cartilage T2 relaxation values may be due to the extraordinary stress load of the femoral head.

Knee Cartilage Imaging

Articular cartilage injury and degeneration represent common causes of knee pain, which can be evaluated accurately and noninvasively using MRI. This review describes the structure of cartilage focusing on its histologic appearance to emphasize that structure will dictate patterns of tissue failure as well as MR appearance. In addition to identifying cartilage loss, MRI can demonstrate signal changes that correspond to intrinsic structural abnormalities which place the cartilage at risk for subsequent more serious injury or premature degeneration, allowing for earlier intervention and treatment of important causes of pain and morbidity.

Current status of MR imaging of juvenile idiopathic arthritis

Juvenile idiopathic arthritis (JIA) is the most common chronic arthropathy in the pediatric population. Although the diagnosis is essentially clinical for many affected joints, MR imaging has become an important tool for the assessment of joints that are difficult to evaluate clinically, such as temporomandibular and sacroiliac joints, and for screening of inflammatory changes in the entire body by whole body MRI (WBMRI) assessment. The utilization of MR imaging is challenging in the pediatric population given the need for discrimination between pathological and physiological changes in the growing skeleton. Several multicentric multidisciplinary organizations have made major efforts over the past decades to standardize, quantify, and validate scoring systems to measure joint changes both cross-sectionally and longitudinally according to rigorous methodological standards. In this paper, we (1) discuss current trends for the diagnosis and management of JIA, (2) review challenges for detecting real pathological changes in growing joints, (3) summarize the current status of standardization of MRI protocols for data acquisition and the quantification of joint pathology in JIA by means of scoring systems, and (4) outline novel MR imaging techniques for the evaluation of anatomy and function of joints in JIA. Optimizing the role of MRI as a robust biomarker and outcome measure remains a priority of future research in this field.

T1ρ-mapping for assessing knee joint cartilage in children with juvenile idiopathic arthritis - feasibility and repeatability

BACKGROUND

Ongoing arthritis in children with juvenile idiopathic arthritis (JIA) can result in cartilage damage.

OBJECTIVE

To study the feasibility and repeatability of T_1ρ for assessing knee cartilage in JIA and also to describe T_1ρ values and study correlation between T_1ρ and conventional MRI scores for disease activity.

MATERIALS AND METHODS

Thirteen children with JIA or suspected JIA underwent 3-tesla (T) knee MRI that included conventional sequences and a T_1ρ sequence. Segmentation of knee cartilage was carried out on T_1ρ images. We used intraclass correlation coefficient to study the repeatability of segmentation in a subset of five children. We used the juvenile arthritis MRI scoring system to discriminate inflamed from non-inflamed knees. The Mann-Whitney U and Spearman correlation compared T_1ρ between children with and without arthritis on MRI and correlated T_1ρ with the juvenile arthritis MRI score.

RESULTS

All children successfully completed the MRI examination. No images were excluded because of poor quality. Repeatability of T_1ρ measurement had an intraclass correlation coefficient (ICC) of 0.99 (P<0.001). We observed no structural cartilage damage and found no differences in T_1ρ between children with (n=7) and without (n=6) inflamed knees (37.8 ms vs. 31.7 ms, P=0.20). However, we observed a moderate correlation between T_1ρ values and the juvenile arthritis MRI synovitis score (r=0.59, P=0.04).

CONCLUSION

This pilot study suggests that T_1ρ is a feasible and repeatable quantitative imaging technique in children. T_1ρ values were associated with the juvenile arthritis MRI synovitis score.

Using Cartilage MRI T2-Mapping to Analyze Early Cartilage Degeneration in the Knee Joint of Young Professional Soccer Players

OBJECTIVE

To evaluate and characterize the appearance of articular cartilage in the tibiofemoral joint of young professional soccer players using T2-relaxation time evaluation on magnetic resonance imaging (MRI).

DESIGN

In this study, we included 57 male adolescents from the youth academy of a professional soccer team. The MRI scans were acquired of the knee joint of the supporting leg. An "early unloading" (minute 0) and "late unloading" (minute 28) T2-sequence was included in the set of images. Quantitative T2-analysis was performed in the femorotibial joint cartilage in 4 slices with each 10 regions of interest (ROIs). Statistical evaluation, using Wilcoxon signed-rank tests, was primarily performed to compare the T2 values of the "early unloading" and "late unloading."

RESULTS

When comparing "early unloading" with "late unloading," our findings showed a significant increase of T2-relaxation times in the weightbearing femoral cartilage of the medial (P < 0.001) and lateral (P < 0.001) compartment of the knee and in the tibial cartilage of the medial compartment (P < 0.001).

CONCLUSION

In this study, alterations of the cartilage were found with a maximum in the medial condyle where the biomechanical load of the knee joint is highest, as well as where most of the chronic cartilage lesions occur. To avoid chronic damage, special focus should be laid on this region.

Maturation-Related Changes in T2 Relaxation Times of Cartilage and Meniscus of the Pediatric Knee Joint at 3 T

OBJECTIVE

The objective of our study was to use a T2 mapping sequence performed at 3 T to investigate changes in the composition and microstructure of the cartilage and menisci of the pediatric knee joint during maturation.

MATERIALS AND METHODS

This retrospective study was performed of MRI examinations of 76 pediatric knees without internal derangement in 72 subjects (29 boys [mean age, 12.5 years] and 43 girls [mean age, 13.0 years]) who were evaluated with a sagittal T2 mapping sequence. T2 relaxation time values were quantitatively measured in eight cartilage subregions and in the medial and lateral menisci. Wilcoxon rank sum and Kruskal-Wallis tests were used to analyze the relationship between cartilage and meniscus T2 relaxation time values and sex and skeletal maturation, respectively. A multivariate linear regression model was used to investigate the independent association between cartilage T2 relaxation time values and age, weight, and body mass index (BMI [weight in kilograms divided by the square of height in meters]).

RESULTS

There were no significant sex differences (p = 0.26-0.91) in T2 relaxation time values for cartilage or meniscus. T2 relaxation time values in each individual cartilage subregion significantly decreased (p < 0.001) with progressive maturation. T2 relaxation time values in the lateral meniscus significantly increased (p = 0.001) with maturation, whereas T2 relaxation time values in the medial meniscus did not significantly change (p = 0.82). There was a significant association (p < 0.001) between cartilage T2 relaxation time values and age independent of weight and BMI, but no significant association between cartilage T2 relaxation time values and weight (p = 0.06) and BMI (p = 0.20) independent of age.

CONCLUSION

Cartilage T2 relaxation time values significantly decreased in all cartilage subregions and meniscus T2 relaxation time values significantly increased in the lateral meniscus during maturation. These changes in T2 relaxation time values reflect age-related changes in tissue composition and microstructure.

T2 mapping in dermatomyositis/polymyositis and correlation with clinical parameters

AIM

To explore the T2-mapping signal characteristics of the thigh muscles in patients with dermatomyositis/polymyositis (DM/PM) and to investigate the correlation between thigh muscle T2 values, clinical parameters, and serum creatinine kinase (CK).

MATERIALS AND METHODS

Forty-two patients with DM/PM proven by diagnostic criteria were enrolled in the study along with 13 healthy control subjects. Both T2-mapping and conventional magnetic resonance imaging (MRI) images were obtained in the thigh musculature of all subjects. The T2 values of thigh muscles were compared between the DM/PM patients and control groups. Thirty-one DM/PM patients were evaluated with manual muscle testing (MMT) and serum CK levels. A Spearman correlation coefficient model was used to correlate the mean T2 values and clinical assessments. The Kruskal-Wallis test and receiver operating characteristic (ROC) curves were also utilised. p-Values <0.05 reflected statistical significance.

RESULTS

The T2 value of all oedematous muscles was greater on average than that of the unaffected muscles of the DM/PM patients (p<0.05) and the muscles of healthy volunteers (p<0.05). The T2 value of unaffected muscles in DM/PM patients was also greater than that of the normal muscles in healthy volunteers (p<0.05). The area under the curves (AUCs) for T2 relaxation time values was 0.72 with respective sensitivity and specificity of 72.6% and 65.4%. The mean T2 relaxation time of the 31 patients group and the MMTs (p<0.05) was correlated without serum CK levels (p>0.05).

CONCLUSION

T2 mapping is not only quantitatively used for subclinical muscle involvement in DM/PM, but also be used to demonstrate severity of damaged muscles in DM/PM.

T2 mapping and post-contrast T1 (dGEMRIC) of the patellar cartilage: 12-year follow-up after patellar stabilizing surgery in childhood

Background

Cartilage degeneration has been reported after recurrent patellar dislocation. However, effects of surgical stabilization in childhood have not yet been described.

Purpose

To examine the cartilage quality in very young adults operated with a patellar stabilizing procedure due to recurrent patellar dislocation in childhood, and evaluate if cartilage quality correlates with clinical parameters and patient-reported outcomes.

Material and Methods

Seventeen patients were investigated ≥ 5 years (mean = 11.6 years) after patellar stabilizing surgery in childhood. Pre-contrast T2 relaxation times were analyzed in four superficial and four deep patellar cartilage regions of both knees. Two hours after 0.2 mM/kg Gd-DTPA² i.v., post-contrast T1 (T1(Gd)) was analyzed in the same regions. Patient-reported outcomes (KOOS, Kujala, and Tegner scores) and recurrence rates were evaluated.

Results

Comparing operated to healthy side, neither T2 nor dGEMRIC differed between the operated and the reference knee regarding the superficial half of the cartilage. In the deep half of the cartilage, T1(Gd) was shorter in the central part of the cartilage, whereas T2 was longer medially (P < 0.05). A low score in the KOOS subscales Symptom and Sports & Recreation, was correlated to the degenerative changes detected by T1(Gd) (r = 0.5, P = 0.041).

Conclusion

In general, our findings demonstrate good cartilage quality 12 years after patellar stabilizing surgery during childhood. The subtle changes in T2 and T1(Gd) in the deep cartilage layer may be a result of altered biomechanics, although very early degenerative changes cannot be excluded. The short T1(Gd) centrally may reflect lower glycosaminoglycan content, whereas the increase in T2 medially indicates increased cartilage hydration.

Femoral epiphyseal cartilage matrix changes at predilection sites of equine osteochondrosis: Quantitative MRI, second-harmonic microscopy, and histological findings

Osteochondrosis is an ischemic chondronecrosis of epiphyseal growth cartilage that results in focal failure of endochondral ossification and osteochondritis dissecans at specific sites in the epiphyses of humans and animals, including horses. The upstream events leading to the focal ischemia remain unknown. The epiphyseal growth cartilage matrix is composed of proteoglycan and collagen macromolecules and encases its vascular tree in canals. The matrix undergoes major dynamic changes in early life that could weaken it biomechanically and predispose it to focal trauma and vascular failure. Subregions in neonatal foal femoral epiphyses (n = 10 osteochondrosis predisposed; n = 6 control) were assessed for proteoglycan and collagen structure/content employing 3T quantitative MRI (3T qMRI: T1ρ and T2 maps). Site-matched validations were made with histology, immunohistochemistry, and second-harmonic microscopy. Growth cartilage T1ρ and T2 relaxation times were significantly increased (p < 0.002) within the proximal third of the trochlea, a site predisposed to osteochondrosis, when compared with other regions. However, this was observed in both control and osteochondrosis predisposed specimens. Microscopic evaluation of this region revealed an expansive area with low proteoglycan content and a hypertrophic-like appearance on second-harmonic microscopy. We speculate that this matrix structure and composition, though physiological, may weaken the epiphyseal growth cartilage biomechanically in focal regions and could enhance the risk of vascular failure with trauma leading to osteochondrosis. However, additional investigations are now required to confirm this. 3T qMRI will be useful for future non-invasive longitudinal studies to track the osteochondrosis disease trajectory in animals and humans. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1743-1752, 2016.

The influences of different spatial resolutions on the characteristics of T2 relaxation times in articular cartilage: A coarse-graining study of the microscopic magnetic resonance imaging data

Microscopic magnetic resonance imaging (µMRI) T2 data from canine cartilage at different tibial locations were analyzed to investigate the influences of spatial resolution and pixel position on the T2 sensitivity to osteoarthritis (OA). Five experimental factors were investigated: inaccurate pixel position, different pixel resolutions, different specimen orientations in the magnetic field, topographical variations over the tibial surface, and different OA stages. A number of significant trends were identified in this analysis, which shows the subtle but substantial influences to our abilities of detecting OA due to T2 changes. In particular, any deviation in locating the cartilage pixels may result in erratic values near the cartilage surface. Significant differences were found in T2 values between nearly any two comparison-groups under all resolutions both in the meniscus-covered and -uncovered areas, which were also showed interaction between the OA degradation stages. This multiresolution project should help to improve the detection sensitivities of MRI toward cartilage degeneration. Microsc. Res. Tech. 79:754-765, 2016. © 2016 Wiley Periodicals, Inc.

T2 Relaxation Time Mapping of the Cartilage Cap of Osteochondromas

Objective

Our aim was to evaluate the cartilage cap of osteochondromas using T2 maps and to compare these values to those of normal patellar cartilage, from age and gender matched controls.

Materials and Methods

This study was approved by the Institutional Review Board and request for informed consent was waived. Eleven children (ages 5-17 years) with osteochondromas underwent MR imaging, which included T2-weighted fat suppressed and T2 relaxation time mapping (echo time = 9-99/repetition time = 1500 msec) sequences. Lesion origins were femur (n = 5), tibia (n = 3), fibula (n = 2), and scapula (n = 1). Signal intensity of the cartilage cap, thickness, mean T2 relaxation times, and T2 spatial variation (mean T2 relaxation times as a function of distance) were evaluated. Findings were compared to those of patellar cartilage from a group of age and gender matched subjects.

Results

The cartilage caps showed a fluid-like high T2 signal, with mean thickness of 4.8 mm. The mean value of mean T2 relaxation times of the osteochondromas was 264.0 ± 80.4 msec (range, 151.0-366.0 msec). Mean T2 relaxation times were significantly longer than the values from patellar cartilage (39.0 msec) (p < 0.0001). These findings were observed with T2 spatial variation plots across the entire distance of the cartilage cap, with the most pronounced difference in the middle section of the cartilage.

Conclusion

Longer T2 relaxation times of the cartilage caps of osteochondromas should be considered as normal, and likely to reflect an increased water content, different microstructure and component.

T2 Relaxation time quantitation differs between pulse sequences in articular cartilage

BACKGROUND

To compare T2 relaxation time measurements between MR pulse sequences at 3 Tesla in agar phantoms and in vivo patellar, femoral, and tibial articular cartilage.

METHODS

T2 relaxation times were quantified in phantoms and knee articular cartilage of eight healthy individuals using a single echo spin echo (SE) as a reference standard and five other pulse sequences: multi-echo SE (MESE), fast SE (2D-FSE), magnetization-prepared spoiled gradient echo (3D-MAPSS), three-dimensional (3D) 3D-FSE with variable refocusing flip angle schedules (3D vfl-FSE), and quantitative double echo steady state (qDESS). Cartilage was manually segmented and average regional T2 relaxation times were obtained for each sequence. A regression analysis was carried out between each sequence and the reference standard, and root-mean-square error (RMSE) was calculated.

RESULTS

Phantom measurements from all sequences demonstrated strong fits (R(2)  > 0.8; P < 0.05). For in vivo cartilage measurements, R(2) values, slope, and RMSE were: MESE: 0.25/0.42/5.0 ms, 2D-FSE: 0.64/1.31/9.3 ms, 3D-MAPSS: 0.51/0.66/3.8 ms, 3D vfl-FSE: 0.30/0.414.2 ms, qDESS: 0.60/0.90/4.6 ms.

CONCLUSION

2D-FSE, qDESS, and 3D-MAPSS demonstrated the best fits with SE measurements as well as the greatest dynamic ranges. The 3D-MAPSS, 3D vfl-FSE, and qDESS demonstrated the closest average measurements to SE. Discrepancies in T2 relaxation time quantitation between sequences suggest that care should be taken when comparing results between studies.

Diffusion tensor imaging can detect the early stages of cartilage damage: a comparison study

BACKGROUND

In the present study, we measured damaged areas of cartilage with diffusion tensor (DT) imaging and T2 mapping, and investigated the extent to which cartilage damage could be determined using these techniques.

METHODS

Forty-one patients underwent arthroscopic knee surgery for osteoarthritis of the knee, a meniscus injury, or an anterior cruciate ligament injury. Preoperative magnetic resonance imaging of the knee was performed, including T2 mapping and diffusion tensor imaging. The presence of cartilage injury involving the medial and lateral femoral condyles and tibia plateau was assessed during surgery using the Outerbridge scale. The ADC, T2 values and fractional anisotropy of areas of cartilage injury were then retrospectively analysed.

RESULTS

The ADC results identified significant differences between Outerbridge grades 0 and 2 (P = 0.041); 0 and 3 (P < 0.001); 1 and 2 (P = 0.045); 1 and 3 (P < 0.001); and 2 and 3 (P = 0.028). The FA results identified significant differences between grades 0 and 1 (P < 0.001); 0 and 2 (P < 0.001); and 0 and 3 (P < 0.001). T2 mapping identified significant differences between Outerbridge grades 0 and 2 (P = 0.032); 0 and 3 (P < 0.001); 1 and 3 (P < 0.001); and 2 and 3 (P < 0.001). Both the T2 mapping (R(2) = 0.7883) and the ADC (R(2) = 0.9184) correlated significantly with the Outerbridge grade. The FA (R(2) = 0.6616) correlated slightly with the Outerbridge grade.

CONCLUSIONS

T2 mapping can be useful for detecting moderate or severe cartilage damage, and the ADC can be used to detect early stage cartilage damage. The FA can also distinguish normal from damaged cartilage.

Pre- and postcontrast T1 and T2 mapping of patellar cartilage in young adults with recurrent patellar dislocation

PURPOSE

To examine the cartilage quality in young adults with recurrent patellar dislocation in childhood using different magnetic resonance imaging parameters.

METHODS

Sixteen young adults with unilateral recurrent patellar dislocation were investigated ≥5 y (mean, 8.5 y) after the first dislocation. Pre- and postcontrast T1 and precontrast T2 relaxation times were analyzed in four superficial and four deep patellar cartilage regions of both knees. Two hours after intravenous injection of 0.2 mM/kg Gd-DTPA(2-), postcontrast T1 [T1(Gd)] and ΔR1 [1/T1 (precontrast) - 1/T1 (postcontrast)] were analyzed in the regions. Muscle performance and patient-reported outcome were evaluated.

RESULTS

When comparing the injured side with the noninjured side, differences were seen in the superficial half but not the deep half of the cartilage. T1(Gd) was shorter in the central part, whereas T2 was shorter in the periphery of the patellar cartilage (P < 0.05). ΔR1 demonstrated similar differences between healthy and diseased cartilage as T1(Gd) alone. The knee function was not correlated to the degenerative changes.

CONCLUSION

The short T1(Gd) centrally indicates degenerative cartilage changes consistent with loss of glycosaminoglycans. Precontrast and ΔR1 calculations may be excluded in clinical dGEMRIC, which simplifies the procedure. A decrease in T2 may be a very early sign of joint pathology but warrants further investigation.

Diffusion-tensor imaging of the growing ends of long bones: pilot demonstration of columnar structure in the physes and metaphyses of the knee

PURPOSE

To determine the feasibility of using in vivo diffusion-tensor imaging and tractography of the physis to examine changes related to rate of growth, location, and age.

MATERIALS AND METHODS

This retrospective study was institutional review board approved and HIPAA compliant and the requirement for informed consent was waived. Diffusion-tensor imaging of the knee was performed at 3.0 T in 31 subjects (nine boys and 22 girls) with a median age of 13.6 years. The mean ages of boys and girls were 14.7 years (range, 12.0-18.3 years) and 13.2 years (range, 7.0-18.6 years), respectively. Regions of interest were placed in the physis of the tibia and femur, and in the epiphyseal and articular cartilage of these bones. Tractography was performed by using a fractional anisotropic threshold of 0.15 and an angle threshold of 40°. The tractographic patterns were qualitatively evaluated and changes related to age were described. The tract-based apparent diffusion coefficient, fractional anistropy, tensor eigenvalues, and tract length were measured. Diffusion parameters were compared between the center and periphery of the physis, and between the distal femur and proximal tibia.

RESULTS

Tractography resulted in parallel tracts in the physis and the adjacent metaphysis. Tractographic pattern changed with age, with individuals approaching physeal closure having shorter tracts in a random arrangement. Patterns of tractography varied with age in the femur (P < .001) and tibia (P < .001). Femoral tracts (median length, 6.5 mm) were longer than tibial tracts (median length, 4.3 mm) (P < .001). Tracts in the periphery of the physes were longer than those in the center (femur, P = .005; tibia, P = .004). In the physis of the femur and tibia, a significant age-related decrease was observed in apparent diffusion coefficient (P < .001 for both), axial diffusion (femur, P = .001; tibia, P < .001), and transverse diffusion [P < .001 for both]), and an age-related increase was seen in fractional anistropy (P < .001, for both).

CONCLUSION

Diffusion-tensor imaging shows the columnar microstructure of the physis and adjacent metaphysis, and provides further insight into normal growth.

An in vitro comparative study of T2 and T2* mappings of human articular cartilage at 3-Tesla MRI using histology as the standard of reference

OBJECTIVE

The aim of this study was to evaluate the correlations between T2 value, T2* value, and histological grades of degenerated human articular cartilage.

MATERIALS AND METHODS

T2 mapping and T2* mapping of nine tibial osteochondral specimens were obtained using a 3-T MRI after total knee arthroplasty. A total of 94 ROIs were analyzed. Histological grades were assessed using the David-Vaudey scale. Spearman's rho correlation analysis and Pearson's correlation analysis were performed.

RESULTS

The mean relaxation values in T2 map with different histological grades (0, 1, 2) of the cartilage were 51.9 ± 9.2 ms, 55.8 ± 12.8 ms, and 59.6 ± 10.2 ms, respectively. The mean relaxation values in T2* map with different histological grades (0, 1, 2) of the cartilage were 20.3 ± 10.3 ms, 21.1 ± 12.4 ms, and 15.4 ± 8.5 ms, respectively. Spearman's rho correlation analysis confirmed a positive correlation between T2 value and histological grade (ρ = 0.313, p < 0.05). Pearson's correlation analysis revealed a significant negative correlation between T2 and T2* (r = -0.322, p < 0.05). Although T2* values showed a decreasing trend with an increase in cartilage degeneration, this correlation was not statistically significant in this study (ρ = -0.192, p = 0.129).

CONCLUSIONS

T2 mapping was correlated with histological degeneration, and it may be a good biomarker for osteoarthritis in human articular cartilage. However, the strength of the correlation was weak (ρ = 0.313). Although T2* values showed a decreasing trend with an increase in cartilage degeneration, the correlation was not statistically significant. Therefore, T2 mapping may be more appropriate for the initial diagnosis of articular cartilage degeneration in the knee joint. Further studies on T2* mapping are needed to confirm its reliability and mechanism in cartilage degeneration.

Spatial variation of T2 relaxation times of patellar cartilage and physeal patency: an in vivo study in children and young adults

OBJECTIVE

The purpose of this study was to determine whether the T2 spatial variation of patellar cartilage is different between children and young adults with open and closed physes.

MATERIALS AND METHODS

Fifty-two subjects in two age ranges were included; 13 girls and 13 boys from 5 to 11 years old, and 13 female young adults and 13 male young adults from 17 to 22 years old. T2 maps of patellar cartilage were generated at 1.5 T. Physeal patency and mean T2 relaxation times as a function of normalized distance (T2 spatial variation) were evaluated in each group and sex.

RESULTS

All the subjects from 5 to 11 years old had open physes and all the subjects from 17 to 22 years old had closed physes. Mean T2 relaxation times of patellar cartilage in the open physis group were significantly longer than in the closed physis group throughout all normalized distances across patellar cartilage (p<0.05). There were significant differences in T2 spatial variation between the two groups (p<0.05). The open physis group had longer mean T2 relaxation times at the osteochondral area and articular cartilage than in the central portion. The closed physis group had shorter mean T2 relaxation times in the osteochondral area, with a gradual increase to longer values at the articular surface. Differences in T2 spatial variation were greatest at the osteochondral junction (p<0.05). There was no statistically significant sex difference in T2 spatial variation in either group.

CONCLUSION

T2 spatial variation is different between skeletally immature and mature patellar cartilage. This difference is most prominent at the osteochondral junction and likely relates to the presence or absence of ongoing endochondral ossification.

Quantitative mapping of human cartilage at 3.0T: parallel changes in T₂, T₁ρ, and dGEMRIC

RATIONALE AND OBJECTIVES

The objectives of this study were to measure the parallel changes of transverse relaxation times (T₂), spin-lattice relaxation time in the rotating frame (T₁ρ), and the delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC)-T1 mapping of human knee cartilage in detecting cartilage degeneration at 3.0T.

MATERIALS AND METHODS

Healthy volunteers (n = 10, mean age 35.6 years) and patients (n = 10, mean age 65 years) with early knee osteoarthritis (OA) were scanned at 3.0T MR using an 8-channel phased array knee coil (transmit-receive). Quantitative assessment of T₂, T₁ρ, and dGEMRIC-T₁ values (global and regional) were correlated between asymptomatic subjects and patients with OA.

RESULTS

The average T₂ (39 ± 2 milliseconds [mean ± standard deviation] vs. 47 ± 6 milliseconds, P < .0007) and T₁ρ (48 ± 3 vs. 62 ± 8 milliseconds, P < .0002) values were all markedly increased in all patients with OA when compared to healthy volunteers. The average dGEMRIC-T₁ (1244 ± 134 vs. 643 ± 227 milliseconds, P < .000002) value was sharply decreased after intravenous administration of gadolinium contrast agent in all patients with OA.

CONCLUSIONS

The research results showed that all the T₂, T₁ρ, and dGEMRIC-T₁ relaxation times varied with the cartilage degeneration. The dGEMRIC-T₁ and T₁ρ relaxation times seem to be more sensitive than T₂ in detecting early cartilage degeneration. The preliminary study demonstrated that the early biochemical changes in knee osteoarthritic patients could be detected noninvasively in in vivo using T₁ρ and dGEMRIC-T₁ mapping.

Objective measurement of minimal fat in normal skeletal muscles of healthy children using T2 relaxation time mapping (T2 maps) and MR spectroscopy

BACKGROUND

Various skeletal muscle diseases result in fatty infiltration, making it important to develop noninvasive biomarkers to objectively measure muscular fat.

OBJECTIVE

We compared T2 relaxation time mapping (T2 maps) and magnetic resonance spectroscopy (MRS) with physical characteristics previously correlated with intramuscular fat to validate T2 maps and MRS as objective measures of skeletal muscle fat.

MATERIALS AND METHODS

We evaluated gluteus maximus muscles in 30 healthy boys (ages 5-19 years) at 3 T with T1-weighted images, T2-W images with fat saturation, T2 maps with and without fat saturation, and MR spectroscopy. We calculated body surface area (BSA), body mass index (BMI) and BMI percentile (BMI %). We performed fat and inflammation grading on T1-W imaging and fat-saturated T2-W imaging, respectively. Mean T2 values from T2 maps with fat saturation were subtracted from T2 maps without fat saturation to determine T2 fat values. We obtained lipid-to-water ratios by MR spectroscopy. Pearson correlation was used to assess relationships between BSA, BMI, BMI %, T2 fat values, and lipid-to-water ratios for each boy.

RESULTS

Twenty-four boys completed all exams; 21 showed minimal and 3 showed no fatty infiltration. None showed muscle inflammation. There was correlation between BSA, BMI, and BMI %, and T2 fat values (P < 0.05), and between BMI and BMI %, and lipid-to-water ratios (P < 0.05). There was strong correlation between T2 fat values and lipid-to-water ratios (P < 0.0001, r = 0.83).

CONCLUSION

T2 maps and MR spectroscopy correlate with physical characteristics associated with fatty infiltration of skeletal muscles, even in microscopic amounts, and validate each other. Both techniques might enable detection of minimal pathological fatty infiltration in children with skeletal muscle disorders.

Biochemical analysis of the articular disc of the temporomandibular joint with magnetic resonance T2 mapping: a feasibility study

OBJECTIVES

Symptoms of temporomandibular joint (TMJ) dysfunction can seriously compromise patients' quality of life. The aim of our study was to use magnetic resonance imaging (MRI) T2 mapping of the articular disc to determine whether T2 mapping of the TMJ disc is feasible in routine clinical imaging and to assess the normal T2 relaxation time distribution within the TMJ.

METHODS

Included were ten asymptomatic volunteers without pain, any mouth-opening limitations, or any clicking phenomena. MR imaging was performed on a 3-T MR scanner using a flexible, dedicated, eight-channel multielement coil. T2 mapping was performed in the oblique sagittal plane. The regions of interest (ROIs) for the T2 relaxation time maps of the disc were selected manually.

RESULTS

The mean values for ROIs ranged between 22.4 and 28.8 ms, and the mean for all ROIs was 26.0 ± 5.0 ms. Intraclass correlation (ICC) for interobserver variability was 0.698, and ICC for intraobserver variability was 0.861. There was no statistically significant difference between raters (p = 0.091) or sides (p = 0.810).

CONCLUSION

The T2 mapping technique enables ultrastructural analysis of the composition of TMJ disc. This biochemical technique is feasible in vivo, as shown in our study, when a high-field (3 T) MR and a dedicated TMJ coil are used.

CLINICAL RELEVANCE

T2 mapping as a biochemical technique, together with morphological MRI, may help to gain more insights into the physiology and into the pathophysiology of the articular disc in the TMJ noninvasively and in vivo.

Repair tissue quality after arthroscopic autologous collagen-induced chondrogenesis (ACIC) assessed via T2* mapping

OBJECTIVE

A novel single-stage approach using arthroscopic microdrilling and atelocollagen/fibrin-gel application is employed for cartilage repair of the knee. The purpose of our study was to investigate the morphological and biochemical MRI outcome after this technique.

MATERIALS AND METHODS

A retrospective case series of ten patients (mean age 45 years) with symptomatic chondral defects in the knee who were treated arthroscopically with microdrilling and atelocollagen application was analyzed. All defects were ICRS grade III or IV and the sizes were 2-8 cm(2) intra-operatively. All patients underwent morphological MRI and T2-star mapping at 1.5 T at 1-year follow-up. The magnetic resonance observation of cartilage repair tissue (MOCART) score was assessed. T2* relaxation time values of repair tissue and a healthy native cartilage area was assessed by means of region of interest analysis on the T2* maps.

RESULTS

The mean MOCART score at 1-year follow-up was 71.7 ± 21.0 ranging from 25 to 95. The mean T2* relaxation times were 30.6 ± 11.3 ms and 28.8 ± 6.8 ms for the repair tissue and surrounding native cartilage, respectively. The T2* ratio between the repair tissue and native cartilage was 105%  ± 30%, indicating repair tissue properties similar to native cartilage.

CONCLUSIONS

An arthroscopic single-stage procedure using microdrilling in combination with atelocollagen gel and fibrin-glue can provide satisfactory MRI results at 1-year follow-up, with good cartilage defect filling. The T2* values in the repair tissue achieved similar values compared to normal hyaline cartilage.

Cartilage imaging in children: current indications, magnetic resonance imaging techniques, and imaging findings

Evaluation of hyaline cartilage in pediatric patients requires in-depth understanding of normal physiologic changes in the developing skeleton. Magnetic resonance (MR) imaging is a powerful tool for morphologic and functional imaging of the cartilage. In this review article, current imaging indications for cartilage evaluation pertinent to the pediatric population are described. In particular, novel surgical techniques for cartilage repair and MR classification of cartilage injuries are summarized. The authors also provide a review of the normal anatomy and a concise description of the advances in quantitative cartilage imaging (ie, T2 mapping, delayed gadolinium-enhanced MR imaging of cartilage, and T1rho).

Magnetic resonance imaging of pediatric muscular disorders: recent advances and clinical applications

This review describes various quantitative magnetic resonance imaging techniques that can be used to objectively analyze the composition (T2 relaxation time mapping, Dixon imaging, and diffusion-weighted imaging), architecture (diffusion tensor imaging), mechanical properties (magnetic resonance elastography), and function (magnetic resonance spectroscopy) of normal and pathologic skeletal muscle in the pediatric population.

MR imaging of articular cartilage physiology

The newer magnetic resonance (MR) imaging methods can give insights into the initiation, progression, and eventual treatment of osteoarthritis. Sodium imaging is specific for changes in proteoglycan (PG) content without the need for an exogenous contrast agent. T1ρ imaging is sensitive to early PG depletion. Delayed gadolinium-enhanced MR imaging has high resolution and sensitivity. T2 mapping is straightforward and is sensitive to changes in collagen and water content. Ultrashort echo time MR imaging examines the osteochondral junction. Magnetization transfer provides improved contrast between cartilage and fluid. Diffusion-weighted imaging may be a valuable tool in postoperative imaging.

[T2 and T1rho values of the knee joint cartilage]

Measurement of T(2) and T(1)ρ relaxation time is a quantitative evaluation technique that uses magnetic resonance imaging. This study aimed to evaluate T(2) and T(1)ρ relaxation time considering the load on the knee. 14 healthy volunteers were studied at 3 T. Four main compartments were defined for cartilage analysis in the knee joint: lateral femoral condyle (LFC), medial femoral condyle (MFC), and lateral and medial tibia (LT and MT). Femur cartilage was partitioned into anterior, middle, and posterior nonweight-bearing (a-NWB, m-NWB, p-NWB) portions and weight-bearing (WB) portions. T(2) and T(1)ρ values between the medial side and lateral side indicated a nonsignificant difference. T(2) and T(1)ρ values of NWB portions were higher than those of WB portions. The measured value rate of extension of NWB to WB was more remarkable in the T(1)ρ value than in the T(2) value. Therefore, evaluating cartilaginous injuries and damages using the T(1)ρ value seems to more effectively describe them.

T2 relaxation time changes in distal femoral articular cartilage in children with juvenile idiopathic arthritis: a 3-year longitudinal study

OBJECTIVE

Increased cartilage T2 relaxation time is thought to be an early marker of disease progression in juvenile idiopathic arthritis, because it can identify microstructural changes before damage becomes visible. The purpose of this study was to investigate longitudinal changes in T2 relaxation time mapping (i.e., T2 map) in children with early juvenile idiopathic arthritis and to compare with changes in clinical assessments.

SUBJECTS AND METHODS

Twenty children (age range, 6.4-16 years) with early juvenile idiopathic arthritis completed at least four evaluations with T2 maps and clinical assessments: at enrollment, at 3 months, and at 1, 2, and 3 years. Sagittal T2 maps of distal femoral cartilage were generated, a region of interest was selected, and a T2 relaxation time profile was generated. The area under the curve from the T2 profile (i.e., T2 value) was correlated with patient age and sex and the following clinical assessments: total knee score, Childhood Health Assessment Questionnaire, physician global assessment, parent global assessment, and total number of active joints.

RESULTS

There was a significant increase in mean T2 values from 3 months to 2 years (p < 0.05). There was a significant decrease in mean Childhood Health Assessment Questionnaire values between enrollment and 2 years (p < 0.05) and a significant decrease in parent global assessment, physician global assessment, total number of active joints, and total knee score values between enrollment and 1 year (p < 0.05). There were no statistically significant correlations between T2 values and patient age, sex, or clinical assessments.

CONCLUSION

In patients with early juvenile idiopathic arthritis, T2 maps showed increased T2 values from the 3-month to 2-year follow-up, during which time the clinical assessments improved. This increase likely represents progressive microstructural changes, even though clinical symptoms improved with treatment.

T2 mapping in Duchenne muscular dystrophy: distribution of disease activity and correlation with clinical assessments

PURPOSE

To analyze T2 maps of pelvic and thigh muscles in Duchenne muscular dystrophy (DMD), to identify the most severely affected muscle, and to correlate the T2 of muscle with the grade of fatty infiltration at nonquantitative magnetic resonance (MR) imaging and results of clinical assessment.

MATERIALS AND METHODS

This prospective study was HIPAA compliant and was approved by the institutional review board; written consent was obtained from all participants' parents or guardians. Thirty-four boys with DMD (mean age, 8.4 years) were evaluated clinically (age, clinical function score, timed Gower score, time to run 30 feet, and serum creatine kinase [CK] level) and with nonquantitative MR imaging and axial T2 mapping from the iliac crest to the mid thigh. The T2 maps and mean T2 of 18 muscles in the pelvis and thighs were analyzed to identify the most severely involved muscle. The amount of fatty infiltration was assigned a grade of zero to four for all pelvic and thigh muscles by using T1-weighted nonquantitative MR images. The Spearman correlation coefficients model was used to correlate the mean T2, nonquantitative MR imaging score and clinical assessments.

RESULTS

The gluteus maximus muscle had the highest T2. The mean T2 for this muscle showed a significant correlation with the nonquantitative MR imaging score for fatty infiltration (P < .001) and with all clinical assessments except CK level.

CONCLUSION

Gluteus maximus muscles are most severely affected in patients with DMD. The T2 of the gluteus maximus muscle can be used as a quantitative and objective measure of disease severity.

Longitudinal analysis of MRI T(2) knee cartilage laminar organization in a subset of patients from the osteoarthritis initiative

The purpose of this pilot study was to longitudinally quantify the T(2) laminar integrity of knee cartilage in a subset of subjects with osteoarthritis from the Osteoarthritis Initiative at baseline, 1-year follow-up, and 2-year follow-up. Cartilage from 13 subjects was divided into six compartments and subdivided into deep and superficial layers. At each time point, mean T(2) values in superficial and deep layers were compared. Longitudinal analysis included full-thickness mean T(2), mean deep T(2), mean superficial T(2), mean T(2) laminar difference, mean percentage T(2) laminar difference, and two-dimensional measures of cartilage thickness. More compartments showed significantly higher superficial T(2) than deep T(2) values at baseline and 1-year follow-up compared to 2-year follow-up. No significant longitudinal changes of full-thickness mean T(2) and superficial T(2) values were observed. Significant longitudinal changes were observed in the deep T(2) values, T(2) laminar difference, and percentage T(2) laminar difference. Cartilage thickness had no influence on T(2) analysis. Results of this study suggest that laminar analysis may improve the sensitivity to detect longitudinal T(2) changes and that disruption of the T(2) laminar organization of knee cartilage may be present in knee osteoarthritis progressors. Further investigation is warranted to evaluate the potential of the presented methodology to better characterize evolution and pathophysiology of osteoarthritis.

Spatial analysis of magnetic resonance T1rho and T2 relaxation times improves classification between subjects with and without osteoarthritis

PURPOSE

Studies have shown that functional analysis of knee cartilage based on magnetic resonance (MR) relaxation times is a valuable tool in the understanding of osteoarthritis (OA). In this work, the regional spatial distribution of knee cartilage T1rho, and T2 relaxation times based on texture and laminar analyses was studied to investigate if they provide additional insight compared to global mean values in the study of OA.

METHODS

Knee cartilage of 36 subjects, 19 healthy controls and 17 with mild OA, was divided into 16 compartments. T1rho and T2 relaxation times were studied with first order statistics, eight texture parameters with four different orientations using gray-level co-occurrence matrices and by subdividing each compartment into two different layers: Deep and superficial. Receiver operating characteristic curve analysis was performed to evaluate the potential of each technique to correctly classify the populations.

RESULTS

Although the deep and superficial cartilage layers had in general significantly different T1rho and T2 relaxation times, they performed similarly in terms of subject discrimination. The subdivision of lateral and medial femoral compartments into weight-bearing and non-weight-bearing regions did not improve discrimination. Also it was found that the most sensitive region was the patella and that T1rho discriminated better than T2. The most important finding was that with respect to global mean values, laminar and texture analyses improved subject discrimination.

CONCLUSIONS

Results of this study suggest that spatially assessing MR images of the knee cartilage relaxation times using laminar and texture analyses could lead to better and probably earlier identification of cartilage matrix abnormalities in subjects with OA.

T2 mapping of articular cartilage of glenohumeral joint with routine MRI correlation--initial experience

The evaluation of articular cartilage currently relies primarily on the identification of morphological alterations of the articular cartilage. Unlike anatomic imaging, T2 mapping is sensitive to changes in the chemical composition and structure of the cartilage. Clinical evaluation of T2 mapping of the glenohumeral joint has not been previously reported. The objectives of this study were to evaluate the feasibility of magnetic resonance T2 mapping of the glenohumeral joint in routine clinical imaging, to assess the normal T2 mapping appearance of the glenohumeral joint, and to compare the findings on T2 maps to conventional MR pulse sequences. Magnetic resonance imaging (MRI) examinations of 27 shoulders were performed in a routine clinical setting. All studies included acquisition of T2 mapping using a dedicated software. The T2 maps were analyzed along with the routine MR exam and correlation of cartilage appearance on T2 map and on conventional MR sequences. T2 imaging maps were obtained successfully in all patients. T2 maps and routine MRI correlated in cases of normal cartilage and prolonged T2 values and cartilage defects. In four cases, increased T2 relaxation times in the cartilage and cartilage defects were more apparent on T2 maps. Acquisition of T2 maps at the time of routine MRI scanning is feasible and not time-consuming.

Relationship between trabecular bone structure and articular cartilage morphology and relaxation times in early OA of the knee joint using parallel MRI at 3 T

OBJECTIVE

To evaluate trabecular bone structure in relationship with cartilage parameters in distal femur and proximal tibia of the human knee at 3Tesla (3T) using high-resolution magnetic resonance imaging (MRI) with parallel imaging.

METHOD

Sixteen healthy controls and 16 patients with mild osteoarthritis (OA) were studied using a 3T magnetic resonance (MR) scanner and an eight-channel phased-array knee coil. Axial 3D GeneRalized Autocalibrating Partially Parallel Acquisition (GRAPPA)-based phase cycled Fast Imaging Employing Steady State Acquisition (FIESTA-c) images were acquired in order to quantify the trabecular bone structure. For assessing cartilage morphology (thickness, volume), sagittal high-resolution 3D spoiled gradient echo (SPGR) images were acquired. In a subset of the subjects, sagittal images were acquired for measuring T1rho and T2 relaxation times, using 3D T1rho and T2 mapping techniques.

RESULTS

Good measurement reproducibility was observed for bone parameters, the coefficients of variations (CVs) ranging from 1.8% for trabecular number (app. Tb.N) to 5.5% for trabecular separation (app. Tb.Sp). Significant differences between control and OA groups were found for bone volume fraction bone volume over total volume (app. BV/TV) and app. Tb.Sp in all compartments. Significantly increased values in T1rho and T2 were demonstrated in OA patients compared with controls at the femur, but not at the tibia. T1rho was negatively correlated with app. BV/TV, app. Tb.N and app. Tb.Sp both at the medial femoral condyle (MFC) and lateral tibia (LT), while T2 was only correlated at the LT. Also, medial tibia (MT) T1rho was negatively correlated with app. BV/TV (R(2)=-0.49, P<0.05) and app. Tb.N (R(2)=-0.42, P<0.05) from the opposite side of lateral femoral condyle (LFC). Significant correlations were found between trabecular bone parameters and cartilage thickness and normalized volume, mainly at LT, tibia (T) and femur (F).

CONCLUSION

At this early stage of OA, an overall decrease in bone structure parameters and an increase in cartilage parameters (T1rho, T2) were noticed in patients. Trabecular bone structure correlated with articular cartilage parameters suggesting that loss of mineralized bone is associated with cartilage degeneration.

In vivo T(1rho) mapping in cartilage using 3D magnetization-prepared angle-modulated partitioned k-space spoiled gradient echo snapshots (3D MAPSS)

For T(1rho) quantification, a three-dimensional (3D) acquisition is desired to obtain high-resolution images. Current 3D methods that use steady-state spoiled gradient-echo (SPGR) imaging suffer from high SAR, low signal-to-noise ratio (SNR), and the need for retrospective correction of contaminating T(1) effects. In this study, a novel 3D acquisition scheme-magnetization-prepared angle-modulated partitioned-k-space SPGR snapshots (3D MAPSS)-was developed and used to obtain in vivo T(1rho) maps. Transient signal evolving towards the steady-state were acquired in an interleaved segmented elliptical centric phase encoding order immediately after a T(1rho) magnetization preparation sequence. RF cycling was applied to eliminate the adverse impact of longitudinal relaxation on quantitative accuracy. A variable flip angle train was designed to provide a flat signal response to eliminate the filtering effect in k-space caused by transient signal evolution. Experiments in phantoms agreed well with results from simulation. The T(1rho) values were 42.4 +/- 5.2 ms in overall cartilage of healthy volunteers. The average coefficient-of-variation (CV) of mean T(1rho) values (N = 4) for overall cartilage was 1.6%, with regional CV ranging from 1.7% to 8.7%. The fitting errors using MAPSS were significantly lower (P < 0.05) than those using sequences without RF cycling and variable flip angles.

In vivo T(1rho) and T(2) mapping of articular cartilage in osteoarthritis of the knee using 3 T MRI

OBJECTIVE

Evaluation and treatment of patients with early stages of osteoarthritis (OA) is dependent upon an accurate assessment of the cartilage lesions. However, standard cartilage dedicated magnetic resonance (MR) techniques are inconclusive in quantifying early degenerative changes. The objective of this study was to determine the ability of MR T1rho (T(1rho)) and T(2) mapping to detect cartilage matrix degeneration between normal and early OA patients.

METHOD

Sixteen healthy volunteers (mean age 41.3) without clinical or radiological evidence of OA and 10 patients (mean age 55.9) with OA were scanned using a 3Tesla (3T) MR scanner. Cartilage volume and thickness, and T(1rho) and T(2) values were compared between normal and OA patients. The relationship between T(1rho) and T(2) values, and Kellgren-Lawrence scores based on plain radiographs and the cartilage lesion grading based on MR images were studied.

RESULTS

The average T(1rho) and T(2) values were significantly increased in OA patients compared with controls (52.04+/-2.97ms vs 45.53+/-3.28ms with P=0.0002 for T(1rho), and 39.63+/-2.69ms vs 34.74+/-2.48ms with P=0.001 for T(2)). Increased T(1rho) and T(2) values were correlated with increased severity in radiographic and MR grading of OA. T(1rho) has a larger range and higher effect size than T(2), 3.7 vs 3.0.

CONCLUSION

Our results suggest that both in vivo T(1rho) and T(2) relaxation times increase with the degree of cartilage degeneration. T(1rho) relaxation time may be a more sensitive indicator for early cartilage degeneration than T(2). The ability to detect early cartilage degeneration prior to morphologic changes may allow us to critically monitor the course of OA and injury progression, and to evaluate the success of treatment to patients with early stages of OA.

T(2) relaxation time mapping reveals age- and species-related diversity of collagen network architecture in articular cartilage

OBJECTIVE

The magnetic resonance imaging (MRI) parameter T(2) relaxation time has been shown to be sensitive to the collagen network architecture of articular cartilage. The aim of the study was to investigate the agreement of T(2) relaxation time mapping and polarized light microscopy (PLM) for the determination of histological properties (i.e., zone and fibril organization) of articular cartilage.

METHODS

T(2) relaxation time was determined at 9.4 T field strength in healthy adult human, juvenile bovine and juvenile porcine patellar cartilage, and related to collagen anisotropy and fibril angle as measured by quantitative PLM.

RESULTS

Both T(2) and PLM revealed a mutually consistent but varying number of collagen-associated laminae (3, 3-5 or 3-7 laminae in human, porcine and bovine cartilage, respectively). Up to 44% of the depth-wise variation in T(2) was accounted for by the changing anisotropy of collagen fibrils, confirming that T(2) contrast of articular cartilage is strongly affected by the collagen fibril anisotropy. A good correspondence was observed between the thickness of T(2)-laminae and collagenous zones as determined from PLM anisotropy measurements (r=0.91, r=0.95 and r=0.91 for human, bovine and porcine specimens, respectively).

CONCLUSIONS

According to the present results, T(2) mapping is capable of detecting histological differences in cartilage collagen architecture among species, likely to be strongly related to the differences in maturation of the tissue. This diversity in the MRI appearance of healthy articular cartilage should also be recognized when using juvenile animal tissue as a model for mature human cartilage in experimental studies.

Risk-Benefit Analysis of X-Ray Exposure Associated with Lung Cancer Screening in the Italung-CT Trial

OBJECTIVE

Prior analyses of X-ray exposures in lung cancer screening with CT considered the basic acquisition technique in single-detector scanners and the effects of a lifetime screening regimen, whereas the potential benefit in terms of lives saved was not addressed.

MATERIALS AND METHODS

We determined the total-body effective dose of different acquisition techniques for one single-detector and one MDCT scanner and made projections about the cumulative radiation exposure to smokers undergoing four annual CT examinations on the same scanners in the Italung-CT Trial. Combining these data with estimates of radiation-induced fatal cancer and of the benefit of screening, we calculated the risk-benefit ratio for participants in the trial, ex-smokers, and never-smokers.

RESULTS

The cumulative effective doses per 1,000 subjects were 3.3 Sv using an MDCT scanner and 5.8 or 7.1 Sv using a single-detector scanner. Potential fatal cancers associated with radiation exposure were 0.11 per 1,000 subjects for MDCT scanners and 0.20 or 0.24 for single-detector scanners, which is about 10-100 times lower than the number of expected lives saved by screening assuming a 20-30% lung cancer-specific mortality reduction in current smokers. They were, however, of similar magnitude to the lives saved by screening in never-smokers and former smokers assuming a 10% efficacy of screening.

CONCLUSION

MDCT is associated with lower radiation doses than single-detector CT technology. The risk of radiation dose in the Italung-CT Trial is compensated for by the expected benefit. CT screening for lung cancer should not be offered to never-smokers, whereas its recommendation in former smokers is debatable.

3T MR Imaging of the Musculoskeletal System (Part II): Clinical Applications

The gain in SNR that is afforded by 3T MR imaging systems has tremendous clinical applications in the musculoskeletal system. The potential for demonstrating and enhancing the visibility of normal osseous, tendinous, cartilaginous, and ligamentous structures is exciting. Furthermore, harnessing this added signal to increase spatial resolution may improve our diagnostic abilities in various joints dramatically. Radiologists have enjoyed great success in assessing joint disease with current MR imaging field strengths; however, many intrinsic joint structures remain poorly evaluated, which leads to a golden opportunity for 3T MR imaging. The articular cartilage of the knee, the glenoid labrum of the shoulder, the intrinsic ligaments and TFC of the wrist, the collateral ligaments of the elbow, the labrum and articular cartilage of the hip, and the collateral ligaments of the ankle have been evaluated suboptimally on 1 .5T systems using routine nonarthrographic MR images. Because of the enhanced SNR, the higher spatial resolution, and the greater CNR of intrinsic joint structures at higher field strengths, 3T MR imaging has the potential to improve diagnostic abilities in the musculoskeletal system vastly, which translates into better patient care and management. The author's 2 years of clinical experience with musculoskeletal MR imaging on 3T systems has met and exceeded his expectations, and has bolstered the confidence of his orthopedic surgeons in his diagnoses. As coil technology advances and as the use of parallel imaging becomes more available in the extremities, the author expects to see even more dramatic improvements in image quality.

New techniques for cartilage imaging: T2 relaxation time and diffusion-weighted MR imaging

In view of recent therapeutic approaches to cartilage damage in osteoarthritis, it is necessary to develop and further refine noninvasive quantitative tools for specific diagnosis and follow-up studies. There is considerable experimental and some clinical experience with T2 relaxation time measurements. Motivation for diffusion-weighted imaging and diffusion-tensor imaging as comparably new techniques for cartilage imaging is to obtain directly additional three-dimensional architectural and directional information about the cartilage matrix.

Effect of Proteoglycan Depletion on T2 Mapping in Rat Patellar Cartilage

PURPOSE

To evaluate experimentally the sensitivity of T2 mapping with magnetic resonance (MR) imaging at 8.5 T in depicting variations in proteoglycan content and concurrent extracellular matrix of rat patellar cartilage.

MATERIALS AND METHODS

The study was performed in 36 immature (age, 5 weeks) and 36 mature (age, 10 weeks) Wistar rats. Maintenance and care of the rats were conducted in accordance with National Institutes of Health guidelines. Fifty-six rats underwent T2 mapping in 28 right patellae degraded with hyaluronidase for 1 and 6 hours and in 28 undegraded age-matched patellae that served as controls. After MR mapping, the rats were sacrificed, and the patellae were studied histologically to evaluate proteoglycan and collagen content and collagen network organization in cartilage. Biochemical analysis was performed in 88 patellae to quantify sulfated glycosaminoglycan and hydroxyproline content. Effects of age and/or degree of degradation were evaluated after rank transformation of continuous data by using rank analysis of variance (ANOVA). Associations between continuous variables were assessed with the Spearman rank correlation coefficient.

RESULTS

Results of histologic analysis showed proteoglycan loss after hyaluronidase degradation without alteration of collagen network. No significant variation in hydroxyproline sulfate content was observed with depletion of proteoglycan. Proteoglycan losses of 19% and 13%, found after 1-hour degradation in immature and mature groups, respectively, were associated with significantly increased global T2 values (ANOVA, P < .001). Six-hour degradation resulted in more severe proteoglycan losses of 45% and 53% in immature and mature groups, respectively, inducing significant increases in global T2 values in immature and mature groups (ANOVA, P < .001). Variations in T2 values between superficial and deep cartilage zones were not affected by proteoglycan depletion.

CONCLUSION

In rat patellar cartilage, T2 mapping permits detection of slight or severe proteoglycan depletion and concurrent changes of extracellular matrix when age-matched samples are compared.

T2 Mapping of Human Femorotibial Cartilage with Turbo Mixed MR Imaging at 1.5 T: Feasibility

The feasibility of a high-spatial-resolution technique for mapping T1 and T2 in articular cartilage in the human knee was evaluated. The technique, turbo mixed magnetic resonance (MR) imaging, is based on a pulse sequence in which inversion-recovery and spin-echo measurements are interleaved. The sequence was first validated in a phantom experiment in which T1 and T2 values obtained with an accepted spectroscopic technique were correlated with those obtained by using a clinical magnetic resonance imager with the turbo mixed technique. T2 maps were obtained with turbo mixed imaging in 25 volunteers (17 men, eight women; mean age, 30.8 years; range, 23-45 years). A high correlation (r = 0.99) was found between T1 and T2 values obtained at spectroscopy and those obtained at turbo mixed imaging. Relative differences in the range of cartilage relaxation times between the two techniques were less than 20%. Turbo mixed imaging in human volunteers showed T2 cartilage relaxation times that corresponded with previously published data. Turbo mixed imaging, thus, is feasible for T2 mapping of cartilage.

Skeletal development in fetal pig specimens: MR imaging of femur with histologic comparison

PURPOSE

To evaluate the magnetic resonance (MR) imaging features of the developing femur in fetal pig specimens.

MATERIALS AND METHODS

MR images of 15 fetal pig femurs, which were categorized into three groups of specimens representing each third of the gestational period, were used to compare increasing femoral length (as an indication of gestational age) with epiphyseal growth in multiple dimensions by using Pearson product moment correlation. Physeal-epiphyseal demarcation, visibility of the secondary ossification center and its physis, prominence of the perichondrial structures (ie, groove of Ranvier and bone bark), metaphyseal undulation, and corticomedullary differences were evaluated qualitatively. These features were also evaluated on histologic sections.

RESULTS

With femoral length measurements used as indications of gestational age, there were three, five, and seven fetal pig specimens in each gestation group. During fetal development, the cartilaginous epiphysis of the distal femur transformed from an oval to a bicondylar structure, with most of the growth occurring sagittally (P < .001). Physeal-epiphyseal demarcation, visibility of the secondary ossification center and its physis, and metaphyseal undulation increased later in gestation. Detection of perichondrial structures, however, was greatest during the middle third of gestation and decreased thereafter. During the fetal period, the perichondrial groove of Ranvier and the bone bark were easily identifiable at MR imaging. Marrow cavitation increased with gestation.

CONCLUSION

MR imaging depicts fetal pig skeletal features that can be confirmed histologically and that may prove to be useful at human prenatal skeletal imaging.

Interphalangeal joint cartilage: high-spatial-resolution in vivo MR T2 mapping--a feasibility study

The purpose of this study was to evaluate feasibility of magnetic resonance (MR) T2 mapping of the proximal interphalangeal joint of the index finger. Cartilage T2 maps with an in-plane resolution of 39 microm were obtained from five asymptomatic subjects-four men and one woman, aged 24-45 years-by using a 3.0-T MR imager. Image acquisition time was 9.6 minutes. All cartilage T2 maps demonstrated spatial variation similar to that reported previously for knee cartilage, with T2 values increasing toward the articular surface. These results demonstrate the feasibility of acquiring cartilage T2 maps of small joints in the hand. Application of T2 mapping techniques to non-weight-bearing joints may provide a means for differentiation of local biomechanical and systemic factors that can affect cartilage T2 values.

Diffraction enhanced imaging of articular cartilage and comparison with micro-computed tomography of the underlying bone structure

The goal of this study was to explore the role of diffraction enhanced X-ray imaging (DEI) for assessing changes in osteoarthritic cartilage and correlating the findings with concurrent changes in the underlying bone imaged using micro-computed tomography (microCT). DEI was used to image femoral head specimens at various beam energies. DEI utilizes a monochromatic, highly collimated beam, with an analyzer crystal that selectively weights out photons according to the angle they have been deviated with respect to the original direction. This provides images of very high contrast, with the rejection of X-ray scatter. The underlying bone was imaged using microCT and measures quantifying the bone structure were derived. Confirmation of cartilage degeneration was obtained from histology and polarized light microscopy. DEI allowed the visualization of articular cartilage and reflected the fibrillations and fissures in tissues from degenerated joints. The trabecular bone underlying the most degenerated articular cartilage showed increased bone volume fraction and more plate-like characteristics, compared with that underlying normal appearing cartilage. The histology and polarized light microscopy images reflected the DEI based features of cartilage architecture. These data reflect the ability of X-ray based emerging technologies to depict cartilage-bone interactions in joint degeneration.