Quantitative magnetic resonance imaging of meniscal pathology ex vivo

OBJECTIVE To determine the ability of conventional spin echo (SE) T2 and ultrashort echo time (UTE) T2* relaxation times to characterize pathology in cadaveric meniscus samples. MATERIALS AND METHODS From 10 human donors, 54 triangular (radially cut) meniscus samples were harvested. Meniscal pathology was classified as normal (n = 17), intrasubstance degenerated (n = 33), or torn (n = 4) using a modified arthroscopic grading system. Using a 3-T MR system, SE T2 and UTE T2* values of the menisci were determined, followed by histopathology. Effect of meniscal pathology on relaxation times and histology scores were determined, along with correlation between relaxation times and histology scores. RESULTS Mean ± standard deviation UTE T2* values for normal, degenerated, and torn menisci were 3.6 ± 1.3 ms, 7.4 ± 2.5 ms, and 9.8 ± 5.7 ms, respectively, being significantly higher in degenerated (p  0.14). In terms of histology, we found significant group-wise differences (each p < 0.05) in fiber organization and inner-tip surface integrity sub-scores, as well as the total score. Finally, we found a significant weak correlation between UTE T2* and histology total score (p = 0.007, R$_{s}$$^{2}$ = 0.19), unlike the correlation between SE T2 and histology (p = 0.09, R$_{s}$$^{2}$ = 0.05). CONCLUSION UTE T2* values were found to distinguish normal from both degenerated and torn menisci and correlated significantly with histopathology

T1rho MR properties of human patellar cartilage: correlation with indentation stiffness and biochemical contents

ObjectiveCartilage degeneration involves structural, compositional, and biomechanical alterations that may be detected non-invasively using quantitative MRI. The goal of this study was to determine if topographical variation in T1rho values correlates with indentation stiffness and biochemical contents of human patellar cartilage.DesignCadaveric patellae from unilateral knees of 5 donors with moderate degeneration were imaged at 3-Telsa with spiral chopped magnetization preparation T1rho sequence. Indentation testing was performed, followed by biochemical analyses to determine water and sulfated glycosaminoglycan contents. T1rho values were compared to indentation stiffness, using semi-circular regions of interest (ROIs) of varying sizes at each indentation site. ROIs matching the resected tissues were analyzed, and univariate and multivariate regression analyses were performed to compare T1rho values to biochemical contents.ResultsGrossly, superficial degenerative change of the cartilage (i.e., roughened texture and erosion) corresponded with regions of high T1rho values. High T1rho values correlated with low indentation stiffness, and the strength of correlation varied slightly with the ROI size. Spatial variations in T1rho values correlated positively with that of the water content (R2 = 0.10, p &lt; 0.05) and negatively with the variations in the GAG content (R2 = 0.13, p &lt; 0.01). Multivariate correlation (R2 = 0.23, p &lt; 0.01) was stronger than either of the univariate correlations.ConclusionThese results demonstrate the sensitivity of T1rho values to spatially varying function and composition of cartilage and that the strength of correlation depends on the method of data analysis and consideration of multiple variables

Time-Resolved Noncontrast Magnetic Resonance Perfusion Imaging of Paraspinal Muscles.

BACKGROUND: While evaluation of blood perfusion in lumbar paraspinal muscles is of interest in low back pain, it has not been performed using noncontrast magnetic resonance (MR) techniques. PURPOSE: To introduce a novel application of a time-resolved, noncontrast MR perfusion technique for paraspinal muscles and demonstrate effect of exercise on perfusion parameters. STUDY TYPE: Longitudinal. SUBJECTS: Six healthy subjects (27-48 years old, two females) and two subjects with acute low back pain (46 and 65 years old females, one with diabetes/obesity). FIELD STRENGTH/SEQUENCE: 3-T, MR perfusion sequence. ASSESSMENT: Lumbar spines of healthy subjects were imaged axially at L3 level with a tag-on and tag-off alternating inversion recovery arterial spin labeling technique that suppresses background signal and acquires signal increase ratio (SIR) from the in-flow blood at varying inversion times (TI) from 0.12&nbsp;seconds to 3.5 seconds. SIR vs. TI data were fit to determine the perfusion metrics of peak height (PH), time to peak (TTP), mean transit time, apparent muscle blood volume (MBV), and apparent muscle blood flow (MBF) in iliocostal, longissimus, and multifidus. Imaging was repeated immediately after healthy subjects performed a 20-minute walk, to determine the effect of exercise. STATISTICAL TESTS: Repeated measures analysis of variance. RESULTS: SIR vs. TI data showed well-defined leading and trailing edges, with sharply increasing SIR to TI of approximately 500 msec subsiding quickly to near zero around TI of 1500 msec. After exercise, the mean SIR at every TI increased markedly, resulting in significantly higher PH, MBV, and MBF (each P &lt; 0.001 and F &gt; 28.9), and a lower TTP (P &lt; 0.05, F&nbsp;=&nbsp;4.5), regardless of the muscle. MBF increased 2- to 2.5-fold after exercise, similar to the expected increase in cardiac output, given the intensity of the exercise. DATA CONCLUSIONS: Feasibility of an MR perfusion technique for muscle perfusion imaging was demonstrated, successfully detecting significantly increased perfusion after exercise. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 1

Ultrashort time to echo magnetic resonance techniques for the musculoskeletal system

Magnetic resonance (MR) imaging has been widely implemented as a non-invasive modality to investigate musculoskeletal (MSK) tissue disease, injury, and pathology. Advancements in MR sequences provide not only enhanced morphologic contrast for soft tissues, but also quantitative biochemical evaluation. Ultrashort time to echo (UTE) sequence, in particular, enables novel morphologic and quantitative evaluation of previously unseen MSK tissues. By using short minimum echo times (TE) below 1 msec, the UTE sequence can unveil short T2 properties of tissues including the deepest layers of the articular cartilage, cartilaginous endplate at the discovertebral junction, the meniscus, and the cortical bone. This article will discuss the application of UTE to evaluate these MSK tissues, starting with tissue structure, MR imaging appearance on standard versus short and ultrashort TE sequences, and provide the range of quantitative MR values found in literature

Effects of Achilles tendon immersion in saline and perfluorochemicals on T2 and T2*.

PurposeTo determine if immersion of Achilles tendon segments into various solutions improved qualitative delineation of tendon and affected quantitative MR values of T2 and T2*.Materials and methodsSix Achilles tendons were dissected, sectioned (proximal, midportion, and distal tensile pieces) and imaged at 3T both at baseline in air and after immersion into saline, Fomblin, and perfluorooctyl bromide (PFOB), respectively, for 24 h. Blinded readers qualitatively assessed the delineation of tendon boundaries and quantitatively Carr-Purcell-Meiboom-Gill (CPMG) T2 and ultrashort echo time (UTE) T2* was calculated. Comparison between images obtained in air and in solution was made.ResultsOn qualitative evaluation, all images obtained in air had larger air-tissue susceptibility effects. Mean T2 values of saline, Fomblin, and PFOB groups were 16.1 ± 3.7, 16.6 ± 2.9, and 18.8 ± 2.6 ms at baseline in air, and 14.8 ± 4.6, 15.9 ± 3.0, and 17.7 ± 3.0 ms after immersion in the fluid, respectively. Mean T2* values of saline, Fomblin, and PFOB groups were 2.0 ± 0.8, 1.6 ± 0.5, and 1.5 ± 0.5 ms at baseline in air, and 2.1 ± 0.5, 1.6 ± 0.5, and 1.4 ± 0.5 ms after immersion in the fluid, respectively. There was no significant effect of immersion or fluid type on measured T2 or T2* (P &gt; 0.1).ConclusionThese results validate the continued use of these solutions to prevent tendon specimen dehydration and to minimize susceptibility effects

Quantitative bi-component T2* analysis of histologically normal Achilles tendons.

Introductionthe aim of this pilot study was to implement ultrashort echo time (UTE) MRI with bi-component analysis on grossly normal Achilles tendons with histologic correlation.Materials and methodssix tendon samples which were grossly normal on visual inspection and palpation were harvested. A 2D UTE pulse sequence was implemented on a 3T MR scanner and bi-component and single-component T2* analysis was performed. Tendon samples were histologically processed and evaluated.Resultsmean short T2* fraction was 79.2% (95% confidence interval [CI], 70.1 - 88.3%), mean short T2* was 1.8 ms (95% CI, 1.3 - 2.3 ms), mean long T2* fraction was 20.8% (95% CI, 11.7 - 29.9%), mean long T2* was 9.2 ms (95% CI, 5.1 - 13.3 ms), and mean single-component T2* was 2.5 ms (95% CI, 1.8 - 3.1 ms).Discussion2D UTE MRI with bi-component and single-component T2* analysis was successfully implemented. Inter-individual variation can be demonstrated in grossly and histologically normal Achilles tendons

Ultrashort Time to Echo Magnetic Resonance Evaluation of Calcium Pyrophosphate Crystal Deposition in Human Menisci.

OBJECTIVES In human menisci, we aimed to investigate whether calcium pyrophosphate crystal deposition (CPPD) affects biomechanical and quantitative MR properties, and their zonal distribution. MATERIALS AND METHODS From 9 cadaveric knees, sectioned triangular meniscus pieces were harvested. Samples were classified into "normal" or "CPPD" groups based upon visual inspection. Micro computed tomography scan verified CPPD. Using magnetic resonance imaging, ultrashort echo time (UTE) T2* and spin echo (SE) T2, quantitative values in 3 zones (red, red-white, and white) were determined. Using biomechanical test, indentation forces in the same zones were determined. Effects of CPPD and meniscal zone on indentation force and quantitative MR values were compared. RESULTS On UTE MRI scans, CPPD-affected menisci exhibited punctate dark regions, found mostly (92%) in avascular white and red-white zones. Indentation forces were significantly higher for CPPD samples in the red-white (all P 0.2). Similarly, UTE T2* red zone values were similar between both groups (~6.6 milliseconds, P = 0.8), whereas in the red-white and white zones, CPPD samples had significantly lower values (~5.1 milliseconds, P = 0.005 to 0.007). In contrast, SE T2 values showed no difference with CPPD (P = 0.12 to 0.16). UTE T2*, but not SE T2, correlated significantly with indentation force (R = -0.29, P = 0.009). CONCLUSIONS Dark CPP deposits were detectable on UTE images featuring high signal intensity from surrounding meniscal tissue. Preliminary results indicate that CPP deposits were almost exclusively found in the avascular zones. Compared with normal, CPPD menisci featured higher indentation stiffness and lower UTE T2* values in the affected zones

Quantitative magnetic resonance imaging of meniscal pathology ex vivo.

ObjectiveTo determine the ability of conventional spin echo (SE) T2 and ultrashort echo time (UTE) T2* relaxation times to characterize pathology in cadaveric meniscus samples.Materials and methodsFrom 10 human donors, 54 triangular (radially cut) meniscus samples were harvested. Meniscal pathology was classified as normal (n = 17), intrasubstance degenerated (n = 33), or torn (n = 4) using a modified arthroscopic grading system. Using a 3-T MR system, SE T2 and UTE T2* values of the menisci were determined, followed by histopathology. Effect of meniscal pathology on relaxation times and histology scores were determined, along with correlation between relaxation times and histology scores.ResultsMean ± standard deviation UTE T2* values for normal, degenerated, and torn menisci were 3.6 ± 1.3&nbsp;ms, 7.4 ± 2.5&nbsp;ms, and 9.8 ± 5.7&nbsp;ms, respectively, being significantly higher in degenerated (p &lt; 0.0001) and torn (p = 0.0002) menisci compared to that in normal. In contrast, the respective mean SE T2 values were 27.7 ± 9.5&nbsp;ms, 25.9 ± 7.0&nbsp;ms, and 35.7 ± 10.4&nbsp;ms, without significant differences between groups (all p &gt; 0.14). In terms of histology, we found significant group-wise differences (each p &lt; 0.05) in fiber organization and inner-tip surface integrity sub-scores, as well as the total score. Finally, we found a significant weak correlation between UTE T2* and histology total score (p = 0.007, Rs2 = 0.19), unlike the correlation between SE T2 and histology (p = 0.09, Rs2 = 0.05).ConclusionUTE T2* values were found to distinguish normal from both degenerated and torn menisci and correlated significantly with histopathology

Effects of Achilles tendon immersion in saline and perfluorochemicals on T2 and T2*.

PurposeTo determine if immersion of Achilles tendon segments into various solutions improved qualitative delineation of tendon and affected quantitative MR values of T2 and T2*.Materials and methodsSix Achilles tendons were dissected, sectioned (proximal, midportion, and distal tensile pieces) and imaged at 3T both at baseline in air and after immersion into saline, Fomblin, and perfluorooctyl bromide (PFOB), respectively, for 24 h. Blinded readers qualitatively assessed the delineation of tendon boundaries and quantitatively Carr-Purcell-Meiboom-Gill (CPMG) T2 and ultrashort echo time (UTE) T2* was calculated. Comparison between images obtained in air and in solution was made.ResultsOn qualitative evaluation, all images obtained in air had larger air-tissue susceptibility effects. Mean T2 values of saline, Fomblin, and PFOB groups were 16.1 ± 3.7, 16.6 ± 2.9, and 18.8 ± 2.6 ms at baseline in air, and 14.8 ± 4.6, 15.9 ± 3.0, and 17.7 ± 3.0 ms after immersion in the fluid, respectively. Mean T2* values of saline, Fomblin, and PFOB groups were 2.0 ± 0.8, 1.6 ± 0.5, and 1.5 ± 0.5 ms at baseline in air, and 2.1 ± 0.5, 1.6 ± 0.5, and 1.4 ± 0.5 ms after immersion in the fluid, respectively. There was no significant effect of immersion or fluid type on measured T2 or T2* (P &gt; 0.1).ConclusionThese results validate the continued use of these solutions to prevent tendon specimen dehydration and to minimize susceptibility effects