Tissue Biomechanical Properties Research Articles

Metabolic diversion of the phenylpropanoid pathway causes cell wall and morphological changes in transgenic tobacco stems

Studies involving transgenic plants with modifications in the lignin pathway reported to date, have received a relatively preliminary characterisation in relation to the impact on vascular integrity, biomechanical properties of tissues and carbon allocation to phenolic pools. Therefore, in this study transgenic tobacco plants (Nicotiana tabacum cv XHFD 8) expressing various levels of a bacterial 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL) gene have been characterised for cell wall and related morphological changes. The HCHL enzyme converts p-coumaroyl-CoA to 4-hydroxybenzaldehyde thereby rerouting the phenylpropanoid pathway. Plants expressing high levels of HCHL activity exhibited reduced lignin deposition, impaired monolignol biosynthesis and vascular integrity. The plants also exhibited reduction in stem toughness concomitant with a massive reduction in both the cell wall esterified and soluble phenolics. A notable result of redirecting the carbon flux was the wall-bound accretion of vanillin and vanillic acid, probably due to the shunt pathway. Intracellular accumulation of novel metabolites such as hydroxybenzoic and vanillic acid derivatives also occurred in the transgenic plants. A line with intermediate levels of HCHL expression conferred correspondingly reduced lignin deposition, toughness and phenolics. This line displayed a normal morphology but distorted vasculature. Coloration of the xylem has been previously attributed to incorporation of alternative phenolics, whereas results from this study indicate that the coloration is likely to be due to the association of low molecular weight phenolics. There was no evidence of increased growth or enhanced cellulose biosynthesis as a result of HCHL expression. Hence, rerouting the phenylpropanoid biosynthetic pathway quantitatively and qualitatively modifies cell wall-bound phenolics and vascular structure.

TU-D-ValB-03: MR-Guided Mechanically Assisted Interventions

Magnetic Resonance Imaging(MRI) has become the gold standard in the imaging of many soft tissues, osseous and joint conditions, but to date there has been limited success in harnessing this excellent imaging modality for interventional procedures. MRI is an ideal interventional guidance modality: it provides real‐time high‐resolution images at arbitrary direction and is able to monitor therapeutic agents, surgical tools, biomechanical tissue properties, and physiological function. At the same time, MRI poses formidable engineering challenges by limited access to the patient and a strong magnetic field that prevents the use of conventional materials and electronic equipment. Currently, no exigent technical solution exists to assist MRI‐guided needle placement procedures in an accurate, simple, and economical manner. A wide variety of procedures may be performed on open magnets but the trend is to use high field closed magnets, mainly because of improved imaging quality and wider availability of pulse sequences. The higher the field the higher the SNR and the higher SNR can be used to improve spatial and temporal resolution and can make techniques like temperature or flow sensitive imaging, functional brain MRI, diffusion imaging or MR spectroscopy more useful. Considering these trends, we believe that the use of conventional high‐field closed MRI scanners for guidance will allow more successful dissemination of MR‐guided techniques to radiology facilities throughout the country and eventually beyond. The talk will survey major trends and achievements in MR compatible interventional robotics, and present specific research projects and results currently in progress at the Johns Hopkins University and collaborators.

Coupling between elastic strain and interstitial fluid flow: Ramifications for poroelastic imaging

Elastography refers to a host of imaging techniques that enables the quantitative measurement of tissue displacement and strain in vivo. In its most common modality, ultrasound is used to map the displacement, and an inverse problem to find the tissue biomechanical properties results, based on the tissue’s constitutive equation, and the law of conservation of momentum. In most previous applications, the constitutive model for the tissue is assumed to be elastic or viscoelastic. It is well recognized, however, that soft tissues contain both fluid and solid phases. Furthermore, the fluid may flow within and between several different compartments. This paper addresses the question: Can ultrasound be used to image and quantify interstitial fluid flow in soft tissues from spatio‐temporal patterns of elastic strain? To answer this, we use the mathematical model of vascularized soft tissue, which includes the effects of fluid flow and the possibility of exchange between fluid compartments in conjunction with finite‐element modeling to predict the effects of fluid fluid flow on the spatio‐temporal patterns of soft‐tissue elastic strain.

What's New in Orthopaedic Research

Exciting advances continue to be made in numerous areas of orthopaedic research. One of the most important areas of research continues to be the discovery of biologic solutions to degenerative joint disease. Emerging information about the genetic basis of bone and cartilage pathology is being used to provide insight into the fundamental mechanisms of common conditions such as osteoporosis, degenerative disc disease, and arthritis. Other active areas of investigation include stem cells, growth factors, tissue engineering, biomaterials, and the biomechanical properties of tissues at the nanoscale. Another common theme is improving the understanding of the basic cellular mechanisms that control the response of musculoskeletal tissues to mechanical load. Investigations in these areas have the potential to improve current treatments and to lead to the development of novel therapies and implants. This paper reviews several major areas of active investigation. ### Bone and Skeletal Development A study of mice deficient in membrane-type 1 matrix metalloproteinase (MT1-MMP) showed that MT1-MMP plays a fundamental role in a novel mechanism of remodeling of unmineralized cartilage anlagen into membranous bone, ligament, and tendon1. While the most common mechanisms of remodeling in the skeleton (endochondral ossification and postnatal bone remodeling) involve replacement of a mineralized matrix by a newer mineralized matrix, in this newly discovered process MT1-MMP directs dissolution of unmineralized cartilage and apoptosis of nonhypertrophic chondrocytes. This process occurs without progression through the sequence of matrix mineralization. MT1-MMP also allows remodeling of cartilage into ligament at insertion sites. MT1-MMP is expressed at ligament insertion sites, implying that this molecule likely plays an important role in soft tissue-bone attachment. Human genetic diseases can provide a mechanism for identifying genes that are important for bone formation. Genetic studies also may shed light on the sensitivity of bone to mechanical loading. It is known that some individuals respond better to exercise …

Glaukomrisiko und Hornhautdicke

Intraocular pressure is still the most important risk factor for the development of glaucomatous optic nerve damage. There is growing evidence that corneal thickness is a risk factor for the development of glaucoma. This might be caused by the effect of corneal thickness on intraocular pressure (IOP) measurements. Goldmann applanation tonometry measurements are correlated with corneal thickness. Thick corneas lead to false high readings whereas thin corneas lead to false low readings. If corneal thickness as a risk factor for glaucoma is only related to the dependency of IOP measurements on corneal thickness or is related to possible different biomechanical tissue properties in glaucomatous eyes is not known. However, a large proportion of the corneal thickness effect seems to be related to the effect on IOP readings by applanation tonometry. Neglecting corneal thickness can lead to false measurements of IOP with consequent misdiagnosis and false treatment. Therefore, measurements of corneal thickness should be performed in glaucoma patients and suspects.

In Vivo Engineering of the Vocal Fold Extracellular Matrix with Injectable Hyaluronic Acid Hydrogels: Early Effects on Tissue Repair and Biomechanics in a Rabbit Model

A prospective, controlled animal study was performed to determine whether the use of injectable, chemically modified hyaluronic acid (HA) derivatives at the time of intentional vocal fold resection might facilitate wound repair and preserve the unique viscoelastic properties of the vocal fold extracellular matrix. We performed bilateral vocal fold biopsies on 33 rabbits. Two groups of rabbits were unilaterally treated with 2 different HA derivatives--Carbylan-SX and HA-DTPH-PEGDA--at the time of resection. Saline was injected as a control into the contralateral fold. The animals were painlessly sacrificed 3 weeks after biopsy and injection. The outcomes measured included histologic fibrosis level, tissue HA level, and tissue viscosity and elasticity. The Carbylan-SX-treated vocal folds were found to have significantly less fibrosis than the saline-treated controls. The levels of HA in the treated vocal folds were not significantly different from those in the controls at 3 weeks as measured by enzyme-linked immunosorbent assay. The Carbylan-SX-treated vocal folds had significantly improved biomechanical properties of elasticity and viscosity. The HA-DTPH-PEGDA injections yielded significantly improved viscosity, but not elasticity. Prophylactic in vivo manipulation of the extracellular matrix with an injectable Carbylan-SX hydrogel appears to induce vocal fold tissue regeneration to yield optimal tissue composition and biomechanical properties favorable for phonation.

A unified view of imaging the elastic properties of tissue

A number of different approaches have been developed to estimate and image the elastic properties of tissue. The biomechanical properties of tissues are vitally linked to function and pathology, but cannot be directly assessed by conventional ultrasound, MRI, CT, or nuclear imaging. Research developments have introduced new approaches, using either MRI or ultrasound to image the tissue response to some stimulus. A wide range of stimuli has been evaluated, including heat, water jets, vibration shear waves, compression, and quasistatic compression, using single or multiple steps or low-frequency (<10 Hz) cyclic excitation. These may seem to be greatly dissimilar, and appear to produce distinctly different types of information and images. However, our purpose in this tutorial is to review the major classes of excitation stimuli, and then to demonstrate that they produce responses that fall within a common spectrum of elastic behavior. Within this spectrum, the major classes of excitation include step compression, cyclic quasistatic compression, harmonic shear wave excitation, and transient shear wave excitation. The information they reveal about the unknown elastic distribution within an imaging region of interest are shown to be fundamentally related because the tissue responses are governed by the same equation. Examples use simple geometry to emphasize the common nature of the approaches.

Prosection vs. dissection, the debate continues: Rebuttal to Granger

Prosection vs. dissection, the debate continues: Rebuttal to Granger

Does Immobilization after Radiofrequency-Induced Shrinkage Influence the Biomechanical Properties of Collagenous Tissue?

Background Despite widespread use of radiofrequency-induced shrinkage of collagenous tissue, there have been no animal studies on the effects of postoperative immobilization on the biomechanical behavior of shrunken tissue. Purpose To examine the role of postoperative immobilization after radiofrequency-induced shrinkage, with special emphasis on the biomechanical properties of shrunken collagenous tissue. Study Design Controlled laboratory study. Methods One patellar tendon of 66 New Zealand White rabbits was shrunk. Six rabbits were sacrificed immediately after surgery. Twenty rabbits were not immobilized, twenty were immobilized for 3 weeks, and twenty were immobilized for 6 weeks. The biomechanical parameters failure strength, stiffness, and relaxation were tested. Results Nine weeks after surgery, biomechanical parameters were still low compared to control tendons. Shrunken tendons did not reach levels of normal tissue at any time after surgery, regardless of whether the animals had been immobilized. According to time-related development, all biomechanical parameters had the lowest levels 3 weeks after surgery. Immobilized tendons demonstrated a better and faster recovery than nonimmobilized tendons compared to the immediate postoperative level. Conclusion Postoperative immobilization supports recovery of biomechanical properties after shrinkage. Despite immobilization, biomechanical properties of shrunken tissue did not completely reach levels of normal tissue. Clinical Relevance Careful rehabilitation is imperative after radiofrequency-induced shrinkage. This animal model supports an immobilization period of at least 6 weeks after surgery.

A novel ultrasound indentation system for measuring biomechanical properties of in vivo soft tissue

Technologies for soft tissue analysis are advancing at a rapid place. For instance, elastography, which provides soft tissue strain images, is starting to be tried in clinical practice as a tool for diagnosing cancer. Soft tissue deformation modeling and analysis is also an active area of research that has application in surgery planning and treatment. Typically, quantitative soft tissue analysis uses nominal values of soft tissue biomechanical properties. However, in practice, soft tissue properties can vary significantly between individuals. Hence, for soft tissue methodologies to reach their full potential as patient-specific techniques, there is a need to develop ways to efficiently measure soft tissue mechanical properties in vivo. This paper describes a prototype real-time ultrasound (US) indentation test system developed to meet this need. The system is based on the integration of a force sensor and an optical tracking system with a commercial US machine integrated with a suite of analysis methodologies. In a study on a single-layer phantom, we used the system to compare various methods of estimating linear elastic properties ( via a theoretical approximation, 2-D finite element analysis, 3-D finite element analysis and a standard material-testing method). In a second study on a three-layer gelatin phantom, we describe a new finite-element-based inverse solution for recovering the Young’s moduli of each layer to show how the system can estimate properties of internal components of soft tissue. Finally, we show how the system can be used to derive a modified quasilinear viscoelastic (QVL) model on real breast tissue. (e-mail: noble@robots.ox.ac.uk)

Glucose-mediated in vitro glycation modulates biomechanical integrity of the soft tissues but not hard tissues

Glycation induced crosslinking of connective tissue collagen is thought to be involved in the pathogenesis of various disorders associated with diabetes and aging. Although the formation of the glycation related collagen crosslinks appears to be universal for all tissues, currently it is unknown whether differences exist between soft and hard tissue biomechanics in response to glucose-mediated in vitro glycation. In this study, the impact of non-enzymatic glycation was investigated on tendons and bones, using them as models for soft and hard tissue respectively. Achilles tendons from rabbits, and femur and tibia from rats, were subjected to in vitro glycation with glucose. Sixty days following glycation, the matrix integrity of the tendons and bones was evaluated and compared with the respective non-glycated tissue ( n=10 in each group). The results revealed that the impact of glycation was significant on the tendon but not on the bone. Measurements of the biomechanical stability of glycated tendons indicated a significant increase in maximum load (21%), Young’s modulus of elasticity (72%), energy to yield (35%) and toughness (68%) compared to the non-glycated tendons. No significant differences were found in breaking strength, bending stiffness, energy to yield and toughness between glycated and non-glycated femurs or tibias. The deformation of both soft and hard tissue was unaffected by the glycation. Measurements at ultimate tissue failure (break point) revealed that glycated tendons bore significantly higher load and energy absorption than non-glycated tendons. In contrast, the deformation of the glycated tendons at break point was considerably reduced as compared to control tendons. However, glycation had no significant effects on the hard tissue biomechanical properties at break point. The results of this study demonstrate that in vitro glycation influences the biomechanical properties of soft tissue but not hard tissue.

Antenatal pelvic organ mobility is associated with delivery mode.

Relaxation of pelvic ligaments may facilitate parturition in certain animal species. Biomechanical properties of pelvic connective tissue may also influence progress of labour in the human female. This study was designed to test whether peripheral joint mobility or pelvic organ mobility as measures of connective tissue biomechanical properties are associated with progress in labour and delivery mode. Prospective clinical observational study. Tertiary obstetric service. 200 nulliparous women recruited in antenatal clinic. Translabial ultrasound was used to obtain data on third trimester pelvic organ mobility. Upper limb joint mobility was assessed clinically. Gestational length, length of first and second stage of labour, delivery mode. Pelvic organ mobility was significantly associated with total length of second stage (P = 0.034 to P = 0.002). This was mainly due to the length of passive, not active second stage. There also was a statistically significant association between delivery mode and pelvic organ descent (P = 0.007 to P = 0.001), with the lowest mobility seen in women who required a Caesarean section in second stage. Joint mobility did not correlate with delivery data. Third trimester pelvic organ mobility is associated with duration of second stage and delivery mode.

A204 膝蓋腱治癒再生組織の力学的特性 : 両端骨片を含む中央 1/3 幅の組織を摘出した場合

A204 膝蓋腱治癒再生組織の力学的特性 : 両端骨片を含む中央 1/3 幅の組織を摘出した場合

Stiffness and passive peak force changes at the ankle joint: the effect of different joint angular velocities

Objective. To compare peak force and stiffness at the ankle joint in response to repetitive dorsiflexion at two joint angular velocities (5 and 25 deg s −1). Design. Pre- post-repeated measures design. Background. Stretching affects the biomechanical properties of tissues. In many instances, stretching is performed in a cyclic manner. An important factor that might influence the effects of stretching is the speed at which the tissues are lengthened. Methods. Eighteen healthy subjects participated. A dynamometer repeatedly moved the ankle joint from 0 deg of dorsiflexion to 80% of maximum dorsiflexion over a 2 min period. Two joint angular velocities were examined: 5 and 25 deg s −1. Force and angle data were recorded simultaneously. Electromyographic activity from plantar and dorsiflexor muscles was monitored. The variables of interest were peak passive force and average stiffness at the first and last repetition of motion. Results. Peak force was significantly higher ( P<0.05) at 25 deg s −1 for the first repetition. At both joint angular velocities, peak passive force decreased significantly over the 2 min of motion. The decreases were 13% and 21% at 5 and 25 deg s −1 respectively. Peak passive force was not significantly different ( P>0.05) across velocities at 2 min. Stiffness was greater at 25 deg s −1 initially ( P<0.05), however, it decreased significantly across time. The magnitude of the decrease was 20% and 31% at 5 and 25 deg s −1 respectively. After 2 min of motion, there was no significant difference ( P>0.05) in stiffness across the joint angular velocities examined. Conclusion(s). The findings showed that while significant differences existed in stiffness and peak force across angular velocities at the start of the stretching motion, the differences decreased considerably with repeated motion, and were relatively similar within 2 min. Relevance It has long been thought that greater speeds of stretch are more likely to lead to muscle injury. Our findings suggest that it is most beneficial to stretch at a slow speed initially, thereafter, the speed of stretch may be increased.

Injurious Mechanical Compression of Bovine Articular Cartilage Induces Chondrocyte Apoptosis

A bovine cartilage explant system was used to evaluate the effects of injurious compression on chondrocyte apoptosis and matrix biochemical and biomechanical properties within intact cartilage. Disks of newborn bovine articular cartilage were compressed in vitro to various peak stress levels and chondrocyte apoptotic cell death, tissue biomechanical properties, tissue swelling, glycosaminoglycan loss, and nitrite levels were quantified. Chondrocyte apoptosis occurred at peak stresses as low as 4.5 MPa and increased with peak stress in a dose-dependent manner. This increase in apoptosis was maximal by 24 h after the termination of the loading protocol. At high peak stresses (>20 MPa), greater than 50% of cells apoptosed. When measured in uniaxial confined compression, the equilibrium and dynamic stiffness of explants decreased with the severity of injurious load, although this trend was not significant until 24-MPa peak stress. In contrast, the equilibrium and dynamic stiffness measured in radially unconfined compression decreased significantly after injurious stresses of 12 and 7 MPa, respectively. Together, these results suggested that injurious compression caused a degradation of the collagen fibril network in the 7- to 12-MPa range. Consistent with this hypothesis, injurious compression caused a dose-dependent increase in tissue swelling, significant by 13-MPa peak stress. Glycosaminoglycans were also released from the cartilage in a dose-dependent manner, significant by 6- to 13-MPa peak stress. Nitrite levels were significantly increased above controls at 20-MPa peak stress. Together, these data suggest that injurious compression can stimulate cell death as well as a range of biomechanical and biochemical alterations to the matrix and, possibly, chondrocyte nitric oxide expression. Interestingly, chondrocyte programmed cell death appears to take place at stresses lower than those required to stimulate cartilage matrix degradation and biomechanical changes. While chondrocyte apoptosis may therefore be one of the earliest responses to tissue injury, it is currently unclear whether this initial cellular response subsequently drives cartilage matrix degradation and changes in the biomechanical properties of the tissue.

Age-associated changes in decorin in rat mandibular condylar cartilage

The small proteoglycan decorin strongly binds the fibrils of collagen types I and II; this interaction is thought to play a part in the maintenance of tissue integrity and biomechanical properties. In limb articular cartilage, there is evidence that decorin synthesis increases with age and that it is elevated in response to increased loading or in osteoarthritic cartilage. The aim here was to characterize the presence and relative amount of decorin in the condylar cartilage of the temporomandibular joint (TMJ) with maturation by Western blotting, and to assess its tissue localization by immunohistochemistry. Comparative data were obtained from tibial articular cartilage, which has been extensively studied. Cartilage from the mandibular condyle and tibial plateau was harvested from 24-day-old (growing) and 161-day-old (young adult) female Sprague–Dawley rats. In growing animals, decorin appeared slightly more abundant in the mandibular condylar cartilage than in articular cartilage, whereas in young adult animals the decorin content in the TMJ cartilage was noticeably less than in limb articular cartilage. Although there was an increase in decorin abundance with age at the TMJ, the increase in decorin with age in limb articular cartilage was considerably more pronounced. These data indicate that, although decorin is present in mandibular condylar cartilage, its abundance in adults is less than in limb articular cartilage; thus, maturation-associated changes may be dissimilar in magnitude from those documented for limb articular cartilage.

Trauma modifies strength and composition of retrodiscal tissues of the goat temporomandibular joint.

Temporomandibular pain is often accompanied by pathologic changes to joint retrodiscal tissues. The substantial representation of females in this condition has encouraged hypotheses which link genetic or hormonally induced abnormalities in tissue composition (type III collagen, type I collagen, type III/type I ratio) to the development of temporomandibular disorders. As this condition is often associated with a history of orofacial trauma, we investigated the functional impact of retrodiscal trauma on the composition and biomechanics of retrodiscal tissues. Retrodiscal tissue of female goats received trauma or sham trauma. Following a healing period of 30 days, the tissues were pulled to failure on an extensometer. Assessments were made of tissue biomechanical properties (failure force, elastic stiffness, strain distribution). Tissue fragments were assayed for collagens I and III. Thirty days after surgical section of retrodiscal tissues, the tissue had reformed, but the composition and biomechanics were substantially changed. Healed tissue manifested less than half the strength of normal tissue (P = 0.02). In addition, the development of tissue strain shifted from a relatively even distribution to a confined region near the retrodiscal-discal attachment zone. It appeared that a large increase in the expression of type III collagen (179.6%; P = 0.038) and the ratio of type III/type I collagen (180.9%; P = 0.011) accounted for these functional changes. We suggest that shifts in collagen expression following injury create shifts in strain development which focus tissue stresses near the interface of the disc and retrodiscal tissue, and that this shift dramatically weakens the tissue and increases the probability of re-injury, inflammation and pain.

Connective Tissues: Matrix Composition and Its Relevance to Physical Therapy

In the last 2 decades, the understanding of CT structure and function has increased enormously. It is now clear that the cells of the various CTs synthesize a variety of ECM components that act not only to underpin the specific biomechanical and functional properties of tissues, but also to regulate a variety of cellular functions. Importantly for the physical therapist, and as discussed above, CTs are responsive to changes in the mechanical environment, both naturally occurring and applied. The relative proportions of collagens and PGs largely determine the mechanical properties of CTs. The relationship between the fibril-forming collagens and PG concentration is reciprocal. Connective tissues designed to resist high tensile forces are high in collagen and low in total PG content (mostly dermatan sulphate PGs), whereas CTs subjected to compressive forces have a greater PG content (mostly chondroitin sulphate PGs). Hyaluronan has multiple roles and not only provides tissue hydration and facilitation of gliding and sliding movements but also forms an integral component of large PG aggregates in pressure-resisting tissues. The smaller glycoproteins help to stabilize and link collagens and PGs to the cell surface. The result is a complex interacting network of matrix molecules, which determines both the mechanical properties and the metabolic responses of tissues. Patients with CT problems affecting movement are frequently examined and treated by physical therapists. A knowledge of the CT matrix composition and its relationship to the biomechanical properties of these tissues, particularly the predictable responses to changing mechanical forces, offers an opportunity to provide a rational basis for treatments. The complexity of the interplay among the components, however, requires that further research be undertaken to determine more precisely the effects of treatments on the structure and function of CTs.

Differential Expression of Collagens XII and XIV in Human Skin and in Reconstructed Skin

Collagens XII and XIV localize near the surface of collagen fibrils and may be involved in epithelial-mesenchymal interactions as well as in the modulation of tissue biomechanical properties. Moreover, human skin fibroblasts cultured in monolayer are known to lose their ability to produce collagen XIV and to switch the transcription of collagen XII from the small splice variant (220 kDa) to the large (320 kDa), whereas the small form is the main form found in human skin. We have investigated the expression patterns of these two molecules in human skin as a function of donor age and anatomic site, by using immunohistology with specific monoclonal antibodies. We demonstrated changes in the expression patterns of collagens XII and XIV in human skin after birth. Moreover, in adult scalp skin, very strong staining of collagen XII fibril bundles was observed around hair follicles, in association with very low expression of collagen XIV. We also investigated the expression of collagens XII and XIV by fibroblasts and keratinocytes cultured in a reconstructed skin. In these culture conditions, fibroblasts recovered their ability to produce collagen XIV and re-expressed the small splice variant of collagen XII. These results could be explained by the deposition of large amounts of collagen fibrils by fibroblasts in this culture system. Thus, the re-expression of these collagens suggests that the deposition of banded collagen fibrils is a pre-requisite for the expression of collagen XIV and small variant of collagen XII.

Visualizing tissue compliance with MR imaging.

We propose a method for visualizing the mechanical properties of tissue based on the use of periodic mechanical compression in conjunction with phase-contrast MR imaging. A specialized mechanical transducer was used to provide programmable compression pulses to the surface of compliant phantoms. These compression pulses were synchronized to a spin-echo sequence with motion-sensitizing gradients to generate phase information reflecting spin displacement throughout the phantom. This sequence was tested with two agarose gel phantoms. The first was a cylinder containing three parallel layers of varying compliance and the second was composed of a semirigid sphere suspended in a uniform layer of decreased elastic modulus. Images showed complex patterns of motion throughout the phantom, which correlated with expected motion behavior of the phantom structures. This indicates that the biomechanical properties of tissues may be elucidated through the use of motion-sensitized MR imaging and suggests that a form of image contrast relating to tissue elasticity may be feasible.