MR microimaging of articular cartilage and contrast enhancement by manganese ions

Rat mandibular condyle and fossa grew separately then unified as a single joint at 20 days old, which was the weaning age

Magnetic resonance imaging (MRI) was used to observe growth of the mandibular condyle, mandibular fossa, and articular disc as a single unit. Changes in each component's relative position and size were observed using 7-tesla MRI. Mandibular condyle chondrocytes' growth was evaluated with immunohistochemistry, using the expression of zinc transporter ZIP13. Three-dimensional T₁-weighted (T_1w) MRI was used to obtain images of the TMJ of Sprague Dawley rats at 4-78 days old (P4-78) with a voxel resolution of 65 μm. Two-dimensional T_1w MR images were acquired after a subcutaneous injection of the contrast reagent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The T_1w MR images showed that the mandibular condyle was located posterior to the mandibular fossa until P20; however, it then moved to a location underneath the mandibular fossa. In the Gd-DTPA enhanced images, the articular disc was identified as a region with lower signal intensity from P20. The number of ZIP13-positive chondrocytes at P6 was larger than the number at P24. In conclusion, the mandibular condyle with cartilage and disc grows on the posterior side of the mandibular fossa until P20, which was the weaning age. Then, the condyle fit into the mandibular fossa and completed the functional unit.

Observation of sGAG content of human hip joint cartilage in different old age groups based on EPIC micro-CT

OBJECTIVES

To observe the age-related changes of sulfated glycosaminoglycan (sGAG) content of hip joint cartilage of elderly people based on Equilibrium Partitioning of an Ionic Contrast Agent (EPIC) micro-CT.

METHODS

Seventy human hip cartilage-bone samples were collected from hip-fracture patients (ages 51-96) and divided into five groups (10 years in an age group). They were first immersed in 20% concentration of the contrast agent Meglumine Diatrizoate (MD) for 6 h at 37 °C, and then scanned by micro-CT. Following scanning, samples were stained for sGAG with toluidine blue. The X-ray attenuation and sGAG optical density were calculated by image processing. The correlation between X-ray attenuation and sGAG optical density was then analyzed.

RESULTS

The X-ray mean attenuation of the cartilage increased by 18.81% from the 50-80 age groups (p < 0.01), but decreased by 7.15% in the 90 age group compared to the 80 age group. The X-ray mean attenuation of the superficial layer and middle layer increased by 31.60 % and 44.68% from the 50-80 age groups, respectively (p < 0.01), but reduced by 4.67% and 6.05% separately in the 90 age group. However, the deep layer showed no significant change with aging. The sGAG optical density showed a linear correlation (r = -0.91, p < 0.01) with the X-ray attenuation.

CONCLUSION

The sGAG content of hip joint cartilage varied with aging in elderly people. The changes in superficial layer and middle layer were more evident than deep layer.

Selective visualization of rabbit knee cartilage using MR imaging with a double-contrast agent

PURPOSE

To establish a reliable method and efficient contrast agent for selective MR imaging of articular cartilage to improve the diagnosis of cartilage disorders.

MATERIALS AND METHODS

A standard trace element replenisher (Mineric), which includes manganese chloride, cupric sulfate (both positive MR contrast agents), and colloidal ferric chloride (a negative contrast agent), was evaluated in comparison with gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) as a potential contrast agent. Normal saline was used as a control. The agents were injected into bilateral knee joints, and the entire joint block was dissected. Coronal images of femorotibial joints were obtained at 7.05 Tesla. Signal intensity ratios (SIRs) of cartilage to joint fluid were calculated for T1 and T2 values. The side effects of the agents were also investigated. Finally, histological evaluations were performed.

RESULTS

SIRs were significantly increased in the Mineric treatment group compared with the Gd-DTPA and saline treatment groups. The T1 values of cartilage and fluid were significantly decreased in the Gd-DTPA and Mineric treatment groups. The T2 values of fluid were significantly decreased in the Mineric treatment group. No apparent side effects or degenerative changes in the joints were observed.

CONCLUSION

A clinical trace element mixture was used as a novel double-contrast agent, and it exhibits selective MR contrast in articular cartilage.

Contrast enhanced cartilage imaging: Comparison of ionic and non-ionic contrast agents

Our objective was to compare relaxation effects, dynamics and spatial distributions of ionic and non-ionic contrast agents in articular cartilage at concentrations typically used for direct MR arthrography at 1.5T. Dynamic MR-studies over 11h were performed in 15 bovine patella specimens. For each of the contrast agents gadopentetate dimeglumine, gadobenate dimeglumine, gadoteridol and mangafodipir trinatrium three patellae were placed in 2.5mmol/L contrast solution. Simultaneous measurements of T(1) and T(2) were performed every 30min using a high-spatial-resolution "MIX"-sequence. T(1), T(2) and DeltaR(1), DeltaR(2) profile plots across cartilage thickness were calculated to demonstrate the spatial and temporal distributions. The charge is one of the main factors which controls the amount of the contrast media diffusing into intact cartilage, but independent of the charge, the spatial distribution across cartilage thickness remains highly inhomogeneous even after 11h of diffusion. The absolute DeltaR(2)-effect in cartilage is at least as large as the DeltaR(1)-effect for all contrast agents. Maximum changes were 5-12s(-1) for DeltaR(1) and 8-15s(-1) for DeltaR(2). This study indicates that for morphologically intact cartilage only the amount of contrast agents within cartilage is determined by the charge but not the spatial distribution across cartilage thickness. In addition, DeltaR(2) can be considered for quantification of contrast agent concentrations, since it is of the same magnitude and less time consuming to measure than DeltaR(1).

Magnetic resonance imaging of temperature-sensitive liposome release: drug dose painting and antitumor effects

BACKGROUND

In preclinical studies, lysolipid-based temperature-sensitive liposomes (LTSLs) containing chemotherapy drugs administered in combination with local hyperthermia have been found to increase tumor drug concentrations and improve antitumor efficacy of the drugs. We used a novel magnetic resonance imaging (MRI) method to measure the temporal and spatial patterns of drug delivery in a rat fibrosarcoma model during treatment with LTSLs containing doxorubicin and an MRI contrast agent (manganese) (Dox/Mn-LTSLs) administered at different times with respect to hyperthermia.

METHODS

Rats bearing 10- to 12-mm fibrosarcomas (n = 6-7 per group) were treated with Dox/Mn-LTSLs (at a dose of 5 mg doxorubicin/kg body weight) before and/or during 60 minutes of local tumor hyperthermia administered via a catheter inserted at the center of the tumor. Drug distribution was monitored continuously via MRI. Magnetic resonance changes were used to calculate intratumoral doxorubicin concentrations throughout treatment. Tumors were monitored until they reached five times their volume on the day of treatment or 60 days. Doxorubicin concentrations and times for tumors to reach five times their volume on the day of treatment were analyzed using the Kruskal-Wallis test and the Kaplan-Meier product-limit method, respectively. All statistical tests were two-sided.

RESULTS

Administration of Dox/Mn-LTSLs before, during, and both before and during hyperthermia yielded central, peripheral, and uniform drug distributions, respectively. Doxorubicin accumulated more quickly and reached higher concentrations in the tumor when Dox/Mn-LTSLs were administered during hyperthermia than when administered before hyperthermia (rate: 9.8 versus 1.8 microg/min, difference = 8.0 microg/min, 95% confidence interval [CI] = 6.8 to 12.8 microg/min, P = .003; concentration: 15.1 versus 8.0 ng/mg, difference = 7.1 ng/mg, 95% CI = 3.6 to 10.6 ng/mg, P = .028). LTSL administered during hyperthermia also yielded the greatest antitumor effect, with a median time for tumors to reach five times their volume on the day of treatment of 34 days (95% CI = 30 days to infinity) compared with 18.5 days (95% CI = 16 to 23 days) for LTSL before hyperthermia and 22.5 days (95% CI = 15 to 25 days) for LTSL before and during hyperthermia.

CONCLUSIONS

In this rat fibrosarcoma model, LTSLs were most effective when delivered during hyperthermia, which resulted in a peripheral drug distribution.

Quantitative imaging of proteoglycan in cartilage using a gadolinium probe and microCT

OBJECTIVE

Micro-computed tomography (microCT) imaging has the potential to allow the three-dimensional (3D) visualization of cartilage morphology. However, cartilage intensity on a microCT image is weak because cartilage does not strongly attenuate X-rays. This work was designed to demonstrate that exposure of cartilage to charged gadolinium compounds modifies the intensity to allow an improved visualization of cartilage morphology and the determination of proteoglycan content.

DESIGN

Trypsin was used to deplete proteoglycan in bovine nasal cartilage disks. Disks were then exposed to Gd(3+), gadopentetate (Gd-DTPA(2-)), or gadoteridol (Gd-HP-DO3A), and imaged with microCT. The intensities of the disks were measured from the images and compared to the actual proteoglycan content determined with a dimethylmethylene blue assay.

RESULTS

Treatment of naïve disks with 200 mM Gd(3+) for 24h at room temperature produced a 2.8-fold increase in intensity on microCT images. Similar treatment with 200 mM Gd-DTPA(2-) produced a 1.4-fold increase. After 2h of trypsin treatment at room temperature, the intensities of cartilage disks exposed to 20 0mM Gd(3+) decreased by 12%. Conversely, the intensities of trypsin-treated disks exposed to 200 mM Gd-DPTA(2-) increased by 15%. Trypsin treatment caused a 4% increase in the intensities of disks exposed to neutral Gd-HP-DO3A. The correlation between proteoglycan content and the microCT intensity of cartilage treated with Gd(3+) was very good (r(2)=0.81).

CONCLUSIONS

Gadolinium and microCT allow an improved 3D visualization of cartilage and quantification of its proteoglycan content.

Osteoarthritis: symptoms, signs and source of pain

Osteoarthritis is the most common form of arthritis. The condition is characterised by loss or failure of the functional and/or biochemical integrity of the joint. The clinical symptoms include joint stiffness, pain and dysfunction, but the principal problem for the majority of patients is the pain. Although there are no pain receptors in the cartilage, the origin of the pain is thought to be due to stimulation of the A delta mechanoreceptors and the C polymodal nerve endings in the synovium and surrounding tissues. However, some of the pain experienced in and around the joints is referred pain or sympathetic efferent pain. In addition, there is a poor correlation of clinical symptoms with radiological or imaging appearance. This lack of correlation of clinical evaluation and imaging makes attempts at treatment difficult and compromises attempts to design studies and to evaluate the outcome of osteoarthritis in clinical trials.

Patellar articular cartilage lesions: in vitro MR imaging evaluation after placement in gadopentetate dimeglumine solution

PURPOSE

To evaluate T1-weighted magnetic resonance (MR) imaging after diffusion of gadopentetate dimeglumine for visualization of articular cartilage lesions.

MATERIALS AND METHODS

MR imaging was performed in eight human cadaveric patella specimens immediately and 4 hours after placement into a vessel filled with gadopentetate dimeglumine solution (2.5 mmol/L). T1-weighted spin-echo and inversion-recovery turbo spin-echo MR sequences with nulled cartilage signal (inversion time of 300 msec) were used. In a total of 128 articular cartilage areas, MR imaging findings were compared with macroscopic and histopathologic findings. Pathologic evaluation was performed by one musculoskeletal pathologist. With knowledge of pathologic observations, MR images were analyzed by one musculoskeletal radiologist with regard to intrinsic signal intensity characteristics and surface abnormalities of articular cartilage.

RESULTS

Histopathologic findings demonstrated 67 areas of normal articular cartilage and 66 cartilage lesions (grade 1, n = 19; grade 2, n = 15; grade 3, n = 26; grade 4, n = 6). All grade 3 and 4 lesions could be identified on MR images obtained immediately after submersion and after 4 hours. Ninety-four percent of grade 1 and 2 lesions were identified as areas of predominantly decreased contrast enhancement on delayed MR images obtained with both sequences. MR images obtained immediately after submersion demonstrated abnormal signal intensity in only 9% and 12% of grade 1 and 2 lesions, respectively.

CONCLUSION

T1-weighted MR images obtained in vitro after gadopentetate dimeglumine diffusion allow demonstration of articular cartilage surface lesions and early stages of cartilage degradation.

In-vivo high resolution three-dimensional MRI studies of rat joints at 7 T

It is important to obtain high resolution images of joints for the study of disease, especially in rodent experimental models. We optimized (1)H magnetic resonance imaging three-dimensional sequences at 7 T, with lipid signal suppression, and T(1) and T(2) measurements for in-vivo experiments on rat joints, in order to assess the effectiveness of high-field MRI. The method was validated by applying it to the early diagnosis of arthritis. We studied the progress of rheumatoid arthritis in an arthritic rat model. We observed the rats' knees for 21 days after inducing arthritis. The images acquired over one hour had a high resolution of 1.75 x 10(-3) mm(3), (105 x 105 x 145 microm(3)) which allowed us to spot the early stages of joint degeneration, such as bone erosion, and to observe an apparent 'MRI' loss of cartilage thickness, attributed to dehydration of the cartilage tissue. The MR images obtained during the early stages of rheumatoid arthritis enabled us to study joint changes accurately before any histological signs of attack were visible.

In vivo assessment of macromolecular content in articular cartilage of the goat knee

Loss of proteoglycans (PGs) from the extracellular matrix of cartilage is an early event of osteoarthritis. The capability of Gd(DTPA)(2-)-enhanced MRI to quantitatively assess PG content was explored in a goat model of cartilage degeneration. Partial to total PG depletion was induced by an intraarticular injection of papain 1 day prior to the MRI session. A close correlation was found between the extent of the PG loss and the Gd(DTPA)(2-)-induced T(1) decrease. Papain-induced PG depletion was confirmed by post-mortem histological and biochemical assessments. A 2-hr delay after Gd(DTPA)(2-) injection was found to be optimal for an accurate quantitation of the cartilage defect. A series of knee flexions were performed post-Gd(DTPA)(2-) injection to facilitate penetration of the contrast agent into cartilage. However, DeltaT(1)'s observed in cartilage of exercised goat knees were not affected by papain or IL1beta pretreatment. Therefore, as long as a preinjection T(1) map was obtained, the Gd(DTPA)(2-)-enhanced MRI technique provided good sensitivity in detecting partial loss of PG in articular cartilage. This was true only when the animal was maintained in a resting state during diffusion of the Gd(DTPA)(2-). This approach is of particular interest for long-term evaluations of cartilage degeneration and regeneration.

Spatial assessment of articular cartilage proteoglycans with Gd-DTPA-enhanced T1 imaging

In Gd-DTPA-enhanced T(1) imaging of articular cartilage, the MRI contrast agent with two negative charges is understood to accumulate in tissue inversely to the negative charge of cartilage glycosaminoglycans (GAGs) of proteoglycans (PGs), and this leads to a decrease in the T(1) relaxation time of tissue relative to the charge in tissue. By assuming a constant relaxivity for Gd-DTPA in cartilage, it has further been hypothesized that the contrast agent concentration in tissue could be estimated from consecutive T(1) measurements in the absence or presence of the contrast agent. The spatial sensitivity of the technique was examined at 9.4 T in normal and PG-depleted bovine patellar cartilage samples. As a reference, spatial PG concentration was assessed with digital densitometry from safranin O-stained cartilage sections. An excellent linear correlation between spatial optical density (OD) of stained GAGs and T(1) with Gd-DTPA was observed in the control and chondroitinase ABC-treated cartilage specimens, and the MR parameter accounted for approximately 80% of the variations in GAG concentration within samples. Further, the MR-resolved Gd-DTPA concentration proved to be an even better estimate for PGs, with an improved correlation. However, the linear relation between MR parameters and PG concentration did not apply in the deep tissue, where MR measurements overestimated the PG content. While the absolute [Gd-DTPA] determination may be prone to error due to uncertainty of relaxivity in cartilage, or to other contributing factors such as variations in tissue permeability, the experimental evidence highlights the sensitivity of this technique to reflect spatial changes in cartilage PG concentration in normal and degenerated tissue.

23Na MRI accurately measures fixed charge density in articular cartilage

One of the initiating steps of osteoarthritis is the loss of proteoglycan (PG) molecules from the cartilage matrix. One method for assessing cartilage integrity, therefore, is to measure the PG content or fixed charge density (FCD) of cartilage. This report shows the feasibility of calculating FCD by (23)Na MRI and introduces MRI protocols for human studies, in vivo. (23)Na MRI was used to measure the sodium concentration inside bovine patellar cartilage. The sodium concentration was then converted to FCD (mM) by considering ideal Donnan equilibrium. These FCD measurements were compared to FCD measurements obtained through standard dimethylmethylene blue PG assays. There was a high correlation (slope = 0.89, r(2) = 0.81) between the FCD measurements obtained by (23)Na MRI and those obtained by the PG assays. These methods were then employed in quantifying the FCD of articular cartilage of human volunteers in vivo. Two imaging protocols were compared: one using a birdcage coil, the other using a transmit/receive surface coil. Both methodologies gave similar results, with the average sodium concentration of normal human patellar cartilage ranging from approximately 240 to 260 mM. This corresponds to FCDs of -158 mM to -182 mM.

(1)H double-quantum filtered MR imaging of joints tissues: bound water specific imaging of tendons, ligaments and cartilage

The (1)H double-quantum filtered (DQF) NMR and DQF MRI is applied to the joint tissues of rabbits for selective visualization of tendons, menisci and articular cartilage. The (1)H DQF NMR selectively filters double-quantum coherence arising from the (1)H dipolar interaction of the "bound" water in these tissues. The double-quantum creation time dependency of the DQF signal intensity is determined by the molecular environment of the "bound" water. Therefore, each tissue has a unique creation time at which the DQF signal reaches its maximum intensity, tau(max) (Achilles tendon: 0.46 +/- 0.02 ms, patella: 0.55 +/- 0.8 ms, anterior cruciate ligament: 0.60 +/- 0.05 ms, meniscus: 0.78 +/- 0.02 ms, skin: 0.81 +/- 0.07 ms). We have presented the creation-time-contrasted DQF images of the meniscus, patella, foot, and knee joint. Compared with conventional T(2)*-weighted gradient-echo (GRE) MR images, tendons, ligaments, menisci, and articular cartilage were more clearly seen in the DQF MR images. All these tissues were distinctly discriminated from each other by their creation times. DQF MR images of foot and knee joints can selectively demonstrated tendons, ligaments, and cartilage, which make it easier to understand the complicated anatomic structure of joints. Because the DQF NMR signal intensity and tau(max) are sensitive to the order structure of the "bound" water, it might be possible to introduce the creation-time dependent-contrast of (1)H DQF MR images as a new tool for analyzing the changes in the ordered structure of the tissue.

Sensitivity of MRI to proteoglycan depletion in cartilage: comparison of sodium and proton MRI

OBJECTIVE

The purpose of this work was to evaluate the results from sodium and proton magnetic resonance imaging (MRI) in detecting small changes in proteoglycan (PG) content in bovine articular cartilage specimens.

DESIGN

Articular cartilage from 15 specimens of bovine patellae were subjected to partial PG depletion with different concentrations of trypsin for 30 min. Sodium and proton MR images of the intact specimen were obtained on a 4T GE clinical MRI system. Two custom-built 7 cm-diameter solenoid coils tuned to proton and sodium frequencies were employed. Fast gradient echo and spin echo imaging sequences were used to determine sodium density, proton density and proton relaxation times (T(1)and T(2)) of the specimens. Spectrophotometric assay was performed after MRI to determine PG concentrations of the cartilage specimens.

RESULTS

The sodium signal change correlated well with the observed PG loss (R(2)=0.85, P< 0.01) whereas the proton signal change was inconsistent (R(2)=0.10, P< 0.8). The change in proton T(1)and T(2)between the two regions did not correlate with PG loss (R(2)=0. 07 and R(2)=0.06, respectively).

CONCLUSIONS

Results from these studies demonstrate that sodium MRI is both sensitive and specific in detecting small changes in PG concentration, whereas proton density and relaxation properties are not sensitive to small changes in PG content.

Visualization of pressure distribution within loaded joint cartilage by application of angle-sensitive NMR microscopy

High-resolution MRI measurements on knee joints show a multilaminar appearance of the cartilage. This intracartilaginar structure, visualized as hypointense zones in T(2)-weighted MR images is based on the dipolar interaction of water molecules within regions of anisotropic arrangement of collagen network. Using the different angle dependence of the MR signal, zones of radially and tangentially oriented network structures can be distinguished. Information equivalent to that from polarization light microscopy can be derived noninvasively. This is demonstrated by polarization light microscopic reference investigations. It is shown that this multilaminar MRI appearance is sensitively influenced by mechanical stress. A model explaining the contrary behavior of loaded tangential and radial network structures is given. Based on this pressure dependence, a noninvasive determination of mechanical properties is possible. Using the variation of size and intensity of the hypointense zones under pressure, dynamic high resolution MRI yields noninvasive information about the intracartilaginar pressure distribution similar to photoelastic measurements. Magn Reson Med 43:884-891, 2000.

MRI visualization of proteoglycan depletion in articular cartilage via intravenous administration of Gd-DTPA

The effect of intravenous administration of gadolinium diethylenetriamine-pentaacetic acid (Gd-DTPA) on MR images was studied in vitro, using pathologic osteochondral specimens removed during surgery for total endoprosthesis, and in vivo, on a group of volunteers. In ex vivo specimens, lesions of different shape having lower T1 were detected which corresponded to areas with depleted proteoglycans found histologically. In vivo experiments on young volunteers showed that the time course of cartilage enhancement was different for different anatomies. The time for maximum enhancement ranged from 45 min for the ventral femoral condyle to 270 min for patellar cartilage.

Nondestructive imaging of human cartilage glycosaminoglycan concentration by MRI

Despite the compelling need mandated by the prevalence and morbidity of degenerative cartilage diseases, it is extremely difficult to study disease progression and therapeutic efficacy, either in vitro or in vivo (clinically). This is partly because no techniques have been available for nondestructively visualizing the distribution of functionally important macromolecules in living cartilage. Here we describe and validate a technique to image the glycosaminoglycan concentration ([GAG]) of human cartilage nondestructively by magnetic resonance imaging (MRI). The technique is based on the premise that the negatively charged contrast agent gadolinium diethylene triamine pentaacetic acid (Gd(DTPA)2-) will distribute in cartilage in inverse relation to the negatively charged GAG concentration. Nuclear magnetic resonance spectroscopy studies of cartilage explants demonstrated that there was an approximately linear relationship between T1 (in the presence of Gd(DTPA)2-) and [GAG] over a large range of [GAG]. Furthermore, there was a strong agreement between the [GAG] calculated from [Gd(DTPA)2-] and the actual [GAG] determined from the validated methods of calculations from [Na+] and the biochemical DMMB assay. Spatial distributions of GAG were easily observed in T1-weighted and T1-calculated MRI studies of intact human joints, with good histological correlation. Furthermore, in vivo clinical images of T1 in the presence of Gd(DTPA)2- (i.e., GAG distribution) correlated well with the validated ex vivo results after total knee replacement surgery, showing that it is feasible to monitor GAG distribution in vivo. This approach gives us the opportunity to image directly the concentration of GAG, a major and critically important macromolecule in human cartilage.

In vivo magnetic resonance methods in pharmaceutical research: current status and perspectives

In the last decade, in vivo MR methods have become established tools in the drug discovery and development process. In this review, several successful and potential applications of MRI and MRS in stroke, rheumatoid and osteo-arthritis, oncology and cardiovascular disorders are dealt with in detail. The versatility of the MR approach, allowing the study of various pathophysiological aspects in these disorders, is emphasized. New indication areas, for the characterization of which MR methods have hardly been used up to now, such as respiratory, gastro-intestinal and skin diseases, are outlined in a subsequent section. A strength of MRI, being a non-invasive imaging modality, is the ability to provide functional, i.e. physiological, readouts. Functional MRI examples discussed are the analysis of heart wall motion, perfusion MRI, tracer uptake and clearance studies, and neuronal activation studies. Functional information may also be derived from experiments using target-specific contrast agents, which will become important tools in future MRI applications. Finally the role of MRI and MRS for characterization of transgenic and knock-out animals, which have become a key technology in modern pharmaceutical research, is discussed. The advantages of MRI and MRS are versatility, allowing a comprehensive characterization of a diseased state and of the drug intervention, and non-invasiveness, which is of relevance from a statistical, economical and animal welfare point of view. Successful applications in drug discovery exploit one or several of these aspects. In addition, the link between preclinical and clinical studies makes in vivo MR methods highly attractive methods for pharmaceutical research.

Effect of hydration on signal intensity of gelatin phantoms using low-field magnetic resonance imaging: possible application in osteoarthritis

Five gelatin phantoms were constructed to study the effect of matrical hydration on magnetic resonance imaging (MRI) signal intensity using a low-field strength imager. Water content of the phantoms ranged from 75 to 95% weight/weight. Signal intensity values of each phantom were measured using five imaging sequences: proton density, T1-weighted, T2-weighted, inversion recovery with short inversion time, and inversion recovery with long inversion time. There was significant positive correlation (p < .05) of signal intensity with differences in hydration using the T2-weighted sequence and the inversion recovery sequence with short inversion time. Significant negative correlations (p < .05) were found with T1-weighted imaging and the inversion recovery sequence with long inversion time. In a second part of the study, in vivo focal variations in MRI signal intensity were evaluated in a canine cranial cruciate ligament deficient model of osteoarthritis. Signal intensity measurements were obtained from multiple areas of articular cartilage to identify an initial stage in osteoarthritis that is characterized in part by increased hydration of articular cartilage. At 6 weeks post-transection of the cranial cruciate ligament, an increase in signal intensity was detected in the articular cartilage of the weight-bearing portion of the lateral femoral condyle and the caudal portion of the medial tibial condyle with T1-weighted imaging. The increase in signal intensity may reflect increased proteoglycan synthesis by chondrocytes that also occurs early in the pathogenesis of osteoarthritis.

Sodium MRI of human articular cartilage in vivo

Preliminary results from in vivo sodium MRI of human patellar articular cartilage are presented. Sodium images generated of an in vitro bovine patella clearly distinguish the region of proteoglycan depletion from the region of healthy cartilage. This provides the first evidence that sodium imaging may be used to detect changes due to osteoarthritis in vivo. The process of optimizing imaging time and signal-to-noise ratio, as well as potential implications in the detection of osteoarthritic change, are discussed.

Improved nuclear magnetic resonance microscopic visualization of joint cartilage using liposome entrapped contrast agents

RATIONALE AND OBJECTIVES

After intraarticular application of gadolinium (Gd)-DTPA the visualization cartilage surface roughness is limited because of diffusion into the cartilage. To improve the sensitivity of magnetic resonance (MR) arthrography to diagnose cartilage surface abnormalities, the authors have tested liposome-entrapped contrast agents.

METHODS

Using paramagnetic contrast agents (Gd-DTPA and manganese chloride) free and entrapped in liposomes, respectively, high resolution MR imaging investigations were performed at 7.1 tesla on intact pig temporomandibular and rabbit knee joints.

RESULTS

After intraarticular injection of the liposome-entrapped contrast agents an excellent contrast between cartilage surface and joint space was achieved. Diffusion of the contrast agent into the cartilage layer was prevented and the visualization of the cartilage surface was improved markedly. Small mechanically and enzymatically induced cartilage lesions could be assessed reliably.

CONCLUSIONS

Intraarticular injection of liposome-entrapped contrast agents can improve the potential of MR arthrography concerning the detection of early osteoarthritic cartilage changes.

MR-microscopic visualization of anisotropic internal cartilage structures using the magic angle technique

NMR microscopic studies of articular cartilage at 7.1 T are presented. Using a special experimental design, T2-weighted spin-echo images of cartilage-bone plugs were taken under variable angles with respect to the static magnetic field B0 to visualize the angular-dependent representation of internal matrix structures mediated by the collagen network arrangement. To quantify the observed orientational effect in the MR images, exact measurements of the transverse relaxation time T2 were taken using the CPMG sequence. The NMR experiments show the strong influence of the cartilage orientation with respect to the static magnetic field on the inhomogeneous appearance of the articular cartilage in the MR image. Additionally performed polarization light microscopic investigations demonstrate the direct relation between the oriented collagenous structures and the anisotropic regions observed in the MR images. A simple cartilage matrix model derived from the experimental findings is proposed, and consequences for the clinical assessment of the articular joint are discussed.

Short TE MR microscopy: accurate measurement and zonal differentiation of normal hyaline cartilage

The purpose of this study was to use MR imaging to accurately measure the thickness of hyaline cartilage and determine the MR contrast parameters for differentiation of cartilage zones in normal human cartilage samples. Cartilage samples were examined using three dimensional spin-echo MR microscopy at 9.4 T with a voxel size of 31 x 31 x 300 microns. Effects of T2 signal loss, susceptibility, and partial volume on measured thickness of cartilage were investigated. Thickness measurements were obtained on corresponding histological sections for comparison. Optimal contrast parameters for delineation of cartilage zones were evaluated using magnetization transfer, inversion recover, T1, and T2 contrast. T2 relaxation losses were identified as the primary source of discrepancy between the measured thickness of cortical bone and hyaline cartilage. Good contrast for zonal differentiation was obtained using T1 weighting. We conclude that images obtained using short TE MR microscopy can be used to accurately measure cartilage and bone thickness in human specimens, and can demonstrate zones within normal cartilage.

MRI contrast enhanced study of cartilage proteoglycan degradation in the rabbit knee

Early degeneration of cartilage is accompanied by a loss of proteoglycans and consequent changes in the content of water. Conventional magnetic resonance imaging (MRI) cannot reliably detect this change, since the relaxation properties of the cartilage are dominated by its collagen content. The applicability of a positively charged nitroxide as an MRI contrast agent in detection of the content of the negatively charged proteoglycans within the cartilage was investigated. The results from both MRI and electron paramagnetic resonance (EPR) spectroscopy indicate that the accumulation of the contrast agent reflects the amount of proteoglycans within the cartilage, presumably due to the electrostatic interactions between the negatively charged proteoglycans and the positively charged nitroxide. Such a contrast agent could be useful in the detection and study of early stages of the degeneration of joints.

Can magnetization transfer magnetic resonance imaging follow proteoglycan depletion in articular cartilage?

In this study we determined the efficiency of magnetization transfer magnetic resonance imaging (MT-MRI) to differentiate native and enzymatically degraded cartilage, using bovine sesamoid bones from the metacarpophalangeal joint as a model system. Gradual proteoglycan (PG) depletion was achieved by increasing incubation periods with testicular hyaluronidase. For native cartilage a Ms/Mo ratio of 0.303 +/- 0.09 (mean +/- SEM) was measured. Biochemically determined PG diminution up to 50% correlated strongly (r = 0.953) with changes in the Ms/Mo ratio. Further PG loss is not reflected in an equally drastic Ms/Mo increase, whereas subsequent treatment of PG-depleted cartilage samples with collagenase led to an additional rise in the Ms/Mo ratio. Proteoglycan depletion and the beginning destruction of the collagen structure were also assessed histochemically. Our study confirms that collagen contributes to the baseline MT effect observed in articular cartilage. However, the changes in the MT ratio in gradually PG-depleted cartilage with a largely intact collagen network indicate that PG contributes to the MT effect as well. Therefore MT-MRI might become a sensitive technique for the monitoring of subtle degradational changes in articular cartilage, the still inaccessible process in osteoarthritis.

Gd-DTPA2- as a measure of cartilage degradation

Glycosaminoglycans (GAGs) are the main source of tissue fixed charge density (FCD) in cartilage, and are lost early in arthritic diseases. We tested the hypothesis that, like Na+, the charged contrast agent Gd-DTPA2- (and hence proton T1) could be used to measure tissue FCD and hence GAG concentration. NMR spectroscopy studies of cartilage explants demonstrated that there was a strong correlation (r > 0.96) between proton T1 in the presence of Gd-DTPA2- and tissue sodium and GAG concentrations. An ideal one-compartment electrochemical (Donnan) equilibrium model was examined as a means of quantifying FCD from Gd-DTPA2- concentration, yielding a value 50% less but linearly correlated with the validated method of quantifying FCD from Na+. These data could be used as the basis of an empirical model with which to quantify FCD from Gd-DTPA2- concentration, or a more sophisticated physical model could be developed. Spatial distributions of FCD were easily observed in T1-weighted MRI studies of trypsin and interleukin-1 induced cartilage degradation, with good histological correlation. Therefore, equilibration of the tissue in Gd-DTPA2- gives us the opportunity to directly image (through T1 weighting) the concentration of GAG, a major and critically important macromolecule in cartilage. Pilot clinical studies demonstrated Gd-DTPA2- penetration into cartilage, suggesting that this technique is clinically feasible.

MR imaging

MRI is a tool of unprecedented capabilities for evaluating arthritis and its progression. Not only can it non-invasively delineate the anatomy of all components of a joint with unparalleled clarity, MRI is also capable of probing important functional and compositional parameters of disease in these tissues. Particularly intriguing is MRI's potential for identifying very early changes of joint disease when clinical symptoms may be minimal or absent. Early detection of patients who are at risk for developing progressive disease may allow appropriate treatment to be initiated earlier, when there may be a greater chance of favourable outcome. MRI can, furthermore, provide objective and quantitative measures of disease progression and treatment response. Certain parameters, such as articular cartilage volume, have been validated cross-sectionally; however, their longitudinal performance has yet to be established. Further work is, therefore, necessary to thoroughly validate and optimize some of these measures so that they can begin to be used in more powerful ways to explore the pathophysiology and potential therapies of arthritic disorders.

Magnetic resonance chondro-crassometry (MR CCM): a method for accurate determination of articular cartilage thickness?

A method for the assessment of articular cartilage thickness based on MRI is presented and its accuracy and reproducibility tested. Six specimens of human patellae were imaged, using a fat-suppressed FLASH 3D sequence, and sectioned with a high-precision band saw. The regional distribution of articular cartilage thickness was determined from the MR images and from the anatomical sections (intervals of 0.5 mm). With image analysis 50-90% of the image points were found to lie within exactly the same thickness interval in corresponding patterns, and less than 17% deviated more than 0.5 mm. More than 85% of all pixels were reproducible with MRI after new positioning of the joint. No influence of the read-out direction and no important differences between areas of thin and thick cartilage could be detected. The authors conclude that MR chondro-crassometry can provide accurate and reproducible information on cartilage thickness.

Visualisation of mass transport of small organic molecules and metal ions through articular cartilage by magnetic resonance imaging

Magnetic resonance imaging of water has been used to visualise the migration of three paramagnetic species, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO, 1), Cu2+ ions, and copper ethylenediamine-tetraacetate (CuEDTA, 2) through cartilage on the femoral condyle of the chicken knee. The migration of copper ions is dominated by strong binding with the cartilage. In contrast, both 1 and 2 bind weakly, and their diffusion can be followed as a progressive wave through the cartilage and subsequently into the trabecular bone structure.

The morphology of articular cartilage assessed by magnetic resonance imaging (MRI). Reproducibility and anatomical correlation

Quantitative assessment of cartilage volume and thickness in a formalin-alcohol fixed specimen of a human patella was conducted with magnetic resonance imaging (MRI), as it is still unclear whether the morphology of normal and damaged cartilage can be accurately demonstrated with this technique. MR imaging was carried out at 1.0 T (section thickness 2 mm, in-plane-resolution 0.39-0.58 mm) with the following pulse sequences: 1) T1-weighted spin-echo, 2) 3D-MPRAGE, 3) 3D-FISP, 4) 3D-MTC-FISP, 5) 3D-DESS, 6) 3D-FLASH. Following imaging, the patella was sectioned perpendicular to the articular surface at intervals of 2 mm with a diamond band-saw. The volume of its cartilage was determined from the anatomical sections and the MR images, using a Vidas IPS 10 image analysing system (Kontron). Measurements were carried out with and without the low-signal layer in the transitional zone between the articular cartilage and the subchondral bone. If the low-signal layer was included, the volume was overestimated with MRI by 16 to 19%. Without the low-signal layer the volumes were less than those determined from the anatomical sections: T1-SE-18.2%, MPRAGE -22.6%, FISP -17.1%, MTC-FISP -9.5%, DESS -9.3% and FLASH -6.1%. The coefficient of variation for a 6-fold determination of the volume amounted to between 6.2% (T1-SE) and 2.6% (FLASH). The FLASH sequence allowed the most valid and reproducible assessment of the cartilage morphology. The remaining difference from the real volume of the cartilage may be due to the fact that the calcified zone of the cartilage is not delineated by MRI.

Diffusion and relaxation mapping of cartilage-bone plugs and excised disks using microscopic magnetic resonance imaging

Spatially resolved maps of proton self-diffusion coefficients (D) and relaxation times (T1 and T2) were obtained on cartilage-bone plug samples and on excised disks of canine cartilage at a transverse resolution of 30 microns, using microscopic magnetic resonance imaging (micro-MRI). Results are compared for excised disks of cartilage and intact cartilage-bone plugs. Correlations between the absolute water concentration, the self-diffusion coefficient and the T1 relaxation are reported. The diffusion coefficient is not a linear function of water concentration. The thickness of the disks is 600 microns, compared with the ca. 900 microns observed for the cartilage-bone plugs, presumably due to the absence of the interfacial or tidemark layer of interdigitated cartilage and bone in the former samples. Our results suggest that excised disks of cartilage are excellent models for the articular surface and the first 500 or so microns of tissue. The molecular parameters of spin-spin and spin-lattice relaxation times, as well as the water self-diffusion coefficient, are virtually identical in the two types of samples. However, the cartilage-bone plugs have the additional feature of permitting the study of the tidemark region, a region that likely plays a major role in the transmission of mechanical force.

Variation in MR signal intensity across normal human knee cartilage

Signal intensity (SI) of individual pixels on sagittal magnetic resonance (MR) images of normal human knee cartilage was quantified to investigate whether it was related to cartilage proteoglycan content. In five subjects, images were acquired with spin-echo sequences with a TR msec/TE msec of 1,000 or 700/20 and a three-dimensional gradient-echo (GRE) sequence (60/15). In a sixth subject, the GRE sequence alone was used with 15 degrees, 30 degrees, and 50 degrees flip angles. In all subjects, SI was maximal in pixel layers of the medial zone and minimal at both cartilage edges, resulting in the presence of a bell-shaped curve of interpixel (zonal) SI variation across the cartilage thickness. The magnitude of SI was dependent on the pulse sequence and flip angle, but the bell shape of the SI variation curve was independent of them. For example, in the medial tibial cartilage, the peak SI was highest with the 1,000/20 spin-echo sequence, intermediate with the 700/20 sequence, and lowest with the GRE sequence. The differences were statistically significant. The bell-shaped SI variation curve resembled the curve for zonal variation in cartilage proteoglycan content but not the curves for collagen or free water content. The physiologic basis for this resemblance and the potential usefulness of the findings for early diagnosis of diseases such as osteoarthritis are discussed.