[Use of a newly developed piezoelectrically driven drilling machine for MR-guided bone biopsies]

PURPOSE

Development and clinical testing of an MR-compatible bone biopsy system, to enable the sample collection from osteosclerotic or subcortical lesions for histological investigation under MR control.

MATERIALS AND METHODS

A piezoelectrically driven drilling machine was constructed and tested in connection with an MR-compatible bone biopsy set in a vertical open MR scanner (0.5 T) on a phantom and 10 patients with ambiguous bone lesions. Images were obtained using T(1)-weighted spin-echo sequences and, in case of real-time imaging, a fast spoiled gradient-echo sequence.

RESULTS

The influence of the enabled motor (RF-interference) leads to a reduction of the signal to noise ratio of the images, but can be minimised by appropriate measures. The observed slight field distorsions do not affect the image quality during real time acquisition in a substantial manner. No complications occurred. The extracted biopsy material was sufficient and of good quality.

CONCLUSIONS

In spite of slightly restricted image quality, the described drilling machine combined with the bone biopsy set is well suited for MR-guided bone biopsies, which require the application of a motor driven drill. Its application within an interventional MR scanner is safe and its handling simple and manageable.

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.

123I-antileukoproteinase scintigraphy reveals microscopic cartilage alterations in the contralateral knee joint of rats with "monarticular" antigen-induced arthritis

OBJECTIVE

To assess the involvement of the contralateral knee joint in monarticular antigen-induced arthritis (AIA) by scintigraphy with the cationic (pI >10), 123I-labeled, serine proteinase inhibitor antileukoproteinase (123I-ALP) and to compare the scintigraphic findings with those of radiography and high-resolution ex vivo magnetic resonance imaging (MRI).

METHODS

Lewis rats with chronic AIA were examined 2.5 months following arthritis induction (injection of 500 microg of methylated bovine serum albumin/saline into the ipsilateral [arthritic] knee joint and injection of phosphate buffered saline into the contralateral knee joint following systemic immunization). 123I-ALP was injected intravenously into normal rats (n = 4) or rats with AIA (n = 6). The ipsilateral and contralateral knee joints and both ankles were examined by scintigraphy and radiography. Joint cartilage was examined by high-resolution ex vivo MRI, histopathology, and measurement of tissue radioactivity.

RESULTS

ALP accumulation (typically observed in normal articular cartilage) was lost in both the ipsilateral and the contralateral knee joints, but not in the clinically unaffected ankles of rats with AIA. In both knee joints, 123I-ALP target:background ratios and cartilage radioactivity correlated negatively with the loss of toluidine blue staining in cartilage, which documents the depletion of charged matrix molecules. Findings of histopathology confirmed mild alterations in the ipsilateral knee joint and even milder alterations in the contralateral knee joint, while the ankles were normal. Radiography and high-resolution ex vivo MRI failed to detect abnormalities in the contralateral knee joint.

CONCLUSION

Loss of ALP accumulation appears to document proteoglycan depletion, even in the microscopically altered cartilage of the contralateral knee joint in AIA. These findings underscore the high sensitivity of 123I-ALP for in vivo detection of biochemical cartilage alterations in arthritis, and furthermore, question the use of the contralateral knee joint as a normal control in AIA.

Effects of L-carnitine and its acetyl and propionyl esters on ATP and PCr levels of isolated rat hearts perfused without fatty acids and investigated by means of 31P-NMR spectroscopy

31P-NMR in vivo spectroscopy is a non-invasive and non-hazardous technique which investigates chemical composition and metabolism of living objects, for example by determining phosphocreatine (PCr) and ATP concentrations. In the present study we investigated the influence of L-carnitine, acetyl-L-carnitine and propionyl-L-carnitine on the energetic state of the Langendorff rat heart subjected to an ischemic period of 20 min followed by a reperfusion period of 60 min. To avoid an overlapping of the effects of fatty acids and glucose, the hearts were perfused with a Tyrode solution containing no fatty acids. Ischemia causes a rapid decrease in the PCr signal, followed by a decrease in the ATP signal after a prolonged period of ischemia. At the same time, a drastic increase in the Pi signal was observed. A partial recovery of the ATP and PCr signals was observed in the reperfusion period. With L-carnitine a markedly improved recovery of the high energy phosphates (e.g. increased PCr/P ratios) was found. With acetyl-L-carnitine this effect was enhanced in the first postischemic phase. It was followed, however, by a more rapid decrease in the PCr/Pi ratio in the late reperfusion period. The effect of propionyl-L-carnitine was not significantly improved in the first minutes of the reperfusion period, but during the whole reperfusion phase a stabilization of the PCr/Pi ratio was observed. Intracellular pH can be calculated from determination of the Pi-chemical shift. This shows that L-carnitine and its derivatives have a protective effect against intracellular pH decrease during ischemia. L-carnitine improves the energetic state of the heart, which leads to increased ischemia tolerance. Hearts under L-carnitine were able to tolerate up to four ischemia-reperfusion periods in succession, whereas the controls were not able to do so. These NMR results confirm the hypothesis that L-carnitine and its esters have a protective effect in the reperfusion period of the ischemic rat heart. This could be of importance for the treatment of ischemic cardiac diseases.

Visualization of collagenase-induced cartilage degradation using NMR microscopy

RATIONALE AND OBJECTIVES

There is an ongoing discussion about the role of collagenase as a specific cartilage-degrading enzyme in the course of osteoarthritis. Using NMR microscopy, the influence of collagenase on the cartilage structure was investigated.

METHODS

High-resolution MR imaging investigations were performed at 7.1 Tesla to study the influence of collagenase on the cartilage structure of pig femoral condyles. Two different contrast agents (polylysine-Gd-DTPA and liposome-entrapped contrast agents) were tested to improve the NMR microscopic visualization of the damaged cartilage regions.

RESULTS

The NMR microscopic investigations showed that collagenase affects only the cartilage surface. Changes within the cartilage layer were not detected. However, after the application of specific contrast agents, it was possible to detect with great sensitivity collagenase-induced damage to the collagen network on the cartilage surface and the superficial cartilage zones. The application of liposome-entrapped contrast agents improved the visualization of the collagenase-degraded superficial cartilage zone.

CONCLUSIONS

These findings could be of great importance when estimating the state of the articular cartilage. The degree of fibrillation of the cartilage surface in the course of osteoarthritic disease can be visualized by MR tomography with a high degree of sensitivity.

Calcium-induced structural changes of cartilage proteoglycans studied by H NMR relaxometry and diffusion measurements

1H transverse nuclear magnetic relaxation times (T2) and self-diffusion coefficients (SDCs) of water were measured in isolated proteoglycan aggregates from pig articular cartilage. The influence of varying osmotic pressure, as well as of different calcium concentrations, on the samples was investigated. Due to a structural transition of the proteoglycans that results from changed electrostatic interactions at higher calcium concentrations, an additional fraction of water protons is observable. These protons are characterized by a very long T2 value and low, restricted diffusion. Additionally, electron microscopic elemental analyses and XFA investigations were performed to estimate the amount of calcium taken up by the proteoglycans. A model for the calcium-mediated structural transition of the cartilage proteoglycans is proposed that explains the experimental results. The investigations suggest the ability of proteoglycans to act as a calcium-concentrating agent and suggest their important role in the calcification process of articular cartilage.

[Pressure devices for NMR microscopy studies of the loading behavior of articular cartilage]

High-resolution MRI offers a unique opportunity to non-invasively image collagen-mediated structures within articular cartilage. Visualization of the stress response of the anisotropic collagenous network in particular, provides more comprehensive knowledge of the biomechanical properties and integrity of articular cartilage, which in turn form a very promising starting point for the present ongoing developments in the noninvasive diagnosis of early stages or arthrosis. The detection of stress-induced changes in the collagenous network, however, requires an MRI probe that permits in vitro measurements under conditions similar to those in the joint, and different orientations relative to the static magnetic field. Here we describe two MR microimaging probes that enable the investigation of the viscoelastic properties of articular cartilage via visualization of the pressure-dependent modifications of anisotropic collagenous structures.

Rat antigen-induced arthritis: cartilage alterations assessed with iodine-123-antileukoproteinase

Imaging of cartilage alterations was attempted in joints of rats with chronic antigen-induced arthritis (AIA) using the cationic 123I-labeled serine proteinase inhibitor antileukoproteinase (123I-ALP; pI > 10), which selectively accumulates in normal cartilage, presumably through interaction with negatively charged proteoglycans.

METHODS

Iodine-123-ALP or 123I-myoglobin, a control protein of comparable size but with different isoelectric point (pI=7.3) was injected intravenously into normal or AIA rats. Joint accumulation was followed by scintigraphy for 14 hr. Tissue radioactivity was assessed by well-counter measurements after dissection. The content of charged molecules in articular cartilage was determined by toluidine blue staining; the degree of joint destruction was assessed in parallel by x-ray, ex vivo MRI and histopathology.

RESULTS

In intact articular cartilage, ALP accumulated to a significantly higher degree than myoglobin. This preferential accumulation was lost in rats with chronic AIA. The target-to-background ratio for 123I-ALP negatively correlated with the loss of toluidine blue staining in cartilage, which documents depletion of charged matrix molecules (r=-0.92, p < 0.01 at 4 hr; r=-0.97, p < 0.01 at 13 hr). ALP scintigraphy was sensitive in detecting cartilage alterations, even though the degree of joint destruction and inflammatory infiltration was mild, as demonstrated by x-ray, MRI and histopathology.

CONCLUSION

In rat AIA, loss of ALP accumulation appears to document proteoglycan depletion in mildly altered arthritic cartilage. ALP scintigraphy may represent a functional assay for early, premorphological cartilage alterations in human arthritis as well.

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.

[Operation of multidisciplinary, interventional 0.5 Tesla magnetic resonance tomograph. Technical and logistic problems and initial clinical results]

Multidisciplinary usage of a MRI system with a superconducting 0.5-T magnet (Signa SP, General Electric) with a vertical gap suited for diagnostic and therapeutic interventions raises complex problems. The MR equipment, including a special localizing system and the instruments for diagnostic and therapeutic interventions, is described. Before putting the system into operation tests were necessary to check MR compatibility of various materials and instruments and to build some auxiliary equipment. We report on the coordinating activities of the radiologist in the context of MR use by different medical specialities. Within the course of 12 months, 428 examinations/interventions of different kinds were carried out, among them 75 functional examinations of the spine or of joints, 31 diagnostic biopsies, 23 cerebral biopsies, and 23 operations. The special design of the Signa SP allows the whole scale of functional examinations, up to complete neurosurgical interventions, in the sitting position and under nearly real-time imaging control.

New gadolinium complexes as magnetic resonance imaging--contrast agents

We have investigated the physicochemical and paramagnetic properties of the new gadolinium complexes of N-(pyrid-2-yl-methyl)-ethylenediamine-N,N,N-triacetic acid (Gd-PEDTA) and N-tris(2-aminoethyl)amine-N,N,N,N,N,N+hexaacetic acid(Gd-TTAHA). The relaxivities as well as the thermodynamic and conditional stability constants of these complexes with respect to the physiological relevance were determined and discussed in comparison with the commercially available gadolinium (III) diethylenetriaminpentaacetic acid/gadopentate dimeglumine (Gd-DTPA, Magnevist). In case of Gd-TTAHA a twofold higher relaxivity and a complex stability similar to Gd-DTPA were determined. It is shown, that lower concentrations of Gd-TTAHA are sufficient for the same signal enhancement in the T1-weighted MR image compared with Gd-DTPA and, thus, the use of the new contrast agent Gd-TTAHA should diminish risks for health. Therefore, Gd-TTAHA might be used potentially as a new contrast agent for clinical MRI application.

Pulsed field gradient NMR and nuclear magnetic relaxation studies of water mobility in hydrated collagen II

Transverse nuclear magnetic relaxation and self-diffusion of water were measured in hydrated collagen II. Self-diffusion measurements were conducted by pulsed field gradient NMR (PFG NMR) and weighting of the different species in the signal by variable T2 relaxation in the experiment. Two fractions of water protons were detected, one with a short T2 value but high diffusivity and one with a long T2 value and low, completely restricted diffusion. The distance of the diffusion barriers was determined to be 2.3 microns. Possible reasons for the restriction in the movement of the water molecules in comparison with structural models of collagen II are discussed.

[Comparison of the effectiveness of sodium azide and merthiolate as bacteriocidal agents--a NMR study]

The pseudohalogenide sodium azide (NaN3) and the organometallic mercury compound merthiolate (sodium salt of ethyl mercurithiosalicylate) are commonly used as preserving solutions for biomaterials. In the present paper, these preserving solutions were compared for their efficacy in preserving porcine articular cartilage. For this purpose, porcine articular cartilage was incubated with phosphate buffer containing the corresponding amounts of NaN3 or merthiolate. Supernatants were assayed using NMR spectroscopy, and the content of soluble saccharides was determined using the dye Alcian blue. The results obtained clearly indicate that merthiolate is more effective than sodium azide. This makes the former a more suitable preserving agent for the storage of cartilage. A significant decrease in the lactate concentration, and enhancement of the acetate and the N-acetyl resonances indicate degenerative changes in the cartilage. However, when a large excess of sodium azide is used, its efficacy approaches that of merthiolate.

Action of compression and cations on the proton and deuterium relaxation in cartilage

In this paper, investigations are described on the influence of osmotic pressures and of varying cation concentrations on water relaxation times in cartilage (pig articular cartilage and bovine nasal cartilage). Both water content and relaxation times decrease strongly with increasing osmotic pressure. This relaxation behavior can be explained in terms of a fast chemical exchange between unbound and bound water. Na+ does not influence water content or relaxation times, whereas Ca2+ causes a small reduction in these parameters.

[The effect of temperature on preservation of swine articular cartilage--an NMR study]

The influence of temperature on stored porcine articular cartilage was studied and the factors underlying degradation identified. For these investigations, specimens measuring 18 mm in diameter were punched out of the articularis humeri of juvenile pigs. These samples were investigated by MR microimaging immediately after preparation, and after storage for three days at +4 degrees C and -18 degrees C. Five smaller (3 mm) cylindrical specimens were then obtained and compared with one another using MR-spectroscopy, relaxometry and biochemical assays. From the experiments we conclude that all analytical methods--with the exception of MR microimaging--are capable of detecting changes in cartilage, and that it is not advisable to keep cartilage frozen, since marked changes, presumably at the cellular level, occur. Storage at +4 degrees C also requires the use of preserving chemicals, as otherwise, the polymers of the extracellular matrix degrade.

The action of hypochlorous acid on polymeric components of cartilage

The action of sodium hypochlorite on N-acetylglucosamine, N-acetylgalactosamine, chondroitinsulfate and hyaluronic acid was studied by 1H-nuclear magnetic resonance (1H-NMR) in order to model some aspects of degradation processes caused by neutrophils on carbohydrate polymers of cartilage in rheumatoid arthritis. N-Acetyl side groups of carbohydrate monomers and chondroitinsulfate yield a resonance at 2.01-2.04 ppm in proton NMR-spectra. This resonance is observed in hyaluronic acid solutions only after a prolonged incubation to yield shorter polymeric chains. Sodium hypochlorite causes a continuous decrease of the line for N-acetyl groups. Two new resonances appear in the 1H-NMR spectra. An intermediate product, assumed as a chlorinated product of N-acetyl side chains, shows a chemical shift of about 2.35 ppm. This intermediate is hydrolyzed to a carbohydrate ring and acetate (1.90 ppm). Sodium hypochlorite acts in all systems investigated mainly on N-acetyl groups. Only small effects on the carbohydrate ring were found under our experimental conditions.

MR microimaging of articular cartilage and contrast enhancement by manganese ions

Saline solutions of manganese ions (Mn2+) were used as articular contrast agents in magnetic resonance microscopy (9.4 T) of cartilage of chicken femoral condyles and pig temporomandibular joints. The diffusion of Mn2+ from the articular surface into the cartilage matrix led to a strong contrast enhancement in the cartilage. The combination of the high spatial resolution and the contrast enhancement allowed the visualization of fine structures (tissue types) in the cartilage, which correlate with the tissue zones in histological sections stained with cationic dyes. We assume that the electrostatic interactions between the negatively charged groups of the proteoglycans and Mn2+ are most important for the mechanism of contrast enhancement. Hence, the different signal intensities of the various zones of cartilage indicate differences in density of proteoglycans. The intraarticular injection of the cationic contrast agent could improve the possibility of an early diagnosis of cartilage dysfunction and degeneration.

[The demonstration of cellular reactions in the temporomandibular condylar cartilage by NMR microscopy. The basic research for high-resolution NMR tomography of the temporomandibular joint]

The regional resolution of modern imaging methods is not good enough to clinically objectify changes to the cartilage of the temporomandibular joint, for example in functional orthodontic treatment. NMR microscopic studies of an intact temporomandibular joint preparation were done experimentally in the domestic pig on the basis of 1H-NMR relaxometric measurements in specimens of condylar cartilage. We succeeded in representing the cartilage of the temporomandibular joint down to the cellular level, and in demonstrating regeneration processes as a late sequela of surgery on the temporomandibular joint. The results are discussed with respect to their importance for future high-resolution magnetic resonance imaging of the temporomandibular joint.

The effect of O2-lack on the cerebrum in neonatal rabbits: first results of an in vivo NMR 31P-spectroscopic study

Two- and 10-day-old urethan anesthetized rabbits were investigated. The ATP content as well as the intracellular pH-value were analysed during hypoxia and following reoxygenation. In contrast to the 2-day-old animals, we found delayed decreasing ATP content in 10-day-old rabbits as well as a delayed increase during the reoxygenation. The return to normal pH-values during the reoxygenation takes more time in older animals.

[NMR-microscopic studies of the condylar cartilage of the temporomandibular joint]

The objectifying of growth mechanisms of the TMJ is very important for orthodontic diagnosis, treatment as well as clinical research. Condylar cartilage of the TMJ from neonatal pigs was investigated on in vivo preparations by NMR-microscopy. NMR-micro-pictures and histologic slide preparations of condylar cartilage were compared and discussed in connection with its implications for treatment with functional appliances.

[Biophysical research on condylar temporomandibular joint growth]

On the basis of results obtained from the study of mechanically induced potentials and pulsed 1H-NMR investigations of the condylar cartilage of the TMJ in vitro, the hypothesis is advocated that the internal regulation of condylar growth takes place with the aid of bioelectric signals. Reference in made to the importance of the studies for a future noninvasive diagnosis of condylar growth in the course of functional orthopedic treatment, using "dynamic" magnetic resonance imaging.

Nitrogen-15 NMR studies of rat liver in vitro and in vivo

In the present 2.1 T15N NMR study two different kinds of experiments are presented. In one we show that metabolic reactions of 15N-labelled glycine can be followed in the isolated rat liver. In the second we demonstrate that [15N]glycine can be detected using NMR in vivo. For quantification and identification of glycine and metabolites 15N-isotope analysis (emission spectrometry technique) was used. To our knowledge, this is the first demonstration of 15N NMR for study of the metabolism of 15N-labelled compounds in vivo.

31P-NMR spectroscopy and ultrastructural studies on nephrotoxicity of cyclosporine A

NMR-spectroscopy and electron microscopy were applied in order to find out whether nephrotoxic effects of cyclosporine A in combination with ischaemia on rat kidney are of significance for the energy metabolism of the organ. CSA was administered in daily doses of 15 mg/kg rat over 20 days. Use was made of the particular advantage of 31P-NMR-spectroscopy to follow up the dynamics of high-energy phosphate concentrations in the same tissue. Ultrastructural changes were observed in the region of the proximal tubule. Some mitochondria showed degenerative changes, others increased density of cristae. The total number of mitochondria was increased. This observation together with the coexistence of vacuolarly degenerated mitochondria and mitochondria with increased activity after CSA treatment is interpreted as expression of a compensatory mechanism that keeps constant the totality of high-energy phosphates despite damage to some mitochondria.