Side differences of knee joint cartilage volume, thickness, and surface area, and correlation with lower limb dominance--an MRI-based study

OBJECTIVE

To test the hypotheses that absolute side differences in knee joint cartilage morphology are substantially smaller than intersubject variability, and that systematic side differences are determined by (force) dominance of the lower limbs.

METHODS

Fifteen healthy volunteers with definite dominance of one lower limb were studied. Knees were imaged sagittally with a validated, high-resolution MR sequence. Transverse MR images of the thigh and calf were acquired with a spin echo sequence. Knee joint cartilage volume, thickness and joint surface areas, as well as muscle cross sectional areas were determined with in house post-processing software.

RESULTS

Absolute side differences amounted to 5.0+/-3.7% for the knee cartilage volume, 3.8+/-3.1% for cartilage thickness, and 3.4+/-1.7% for joint surface areas. The intersubject variability was 24.8%, 14.4%, and 14.1%, respectively. Volunteers with dominance of one of both lower limbs did not display significant side differences in cartilage morphology, but the side differences of the thigh musculature correlated positively with side differences of knee joint cartilage volume (r=+0.68; P< 0.01).

CONCLUSIONS

The results advocate the use of cartilage parameters from the contra-lateral limb for retrospectively estimating cartilage loss in patients with unilateral osteoarthritis (OA), and for determining local risk factors of OA in cross-sectional epidemiological studies, which are specific to pre-morbid cartilage morphology. Functional (force) dominance of one of both lower limbs does not explain side differences of articular cartilage morphology, but side differences are positively associated with side differences in muscle cross sectional areas.

Long-term and resegmentation precision of quantitative cartilage MR imaging (qMRI)

OBJECTIVE

Follow up of osteoarthritis (OA) and evaluation of structure modifying OA drugs require longitudinal data on cartilage structure. The aim of this study was to analyse the long term and resegmentation precision of quantitative cartilage analysis with magnetic resonance imaging (qMRI) in vivo, and to relate precision errors to the estimated cartilage loss in OA.

METHOD

Sagittal MR images of the knee were obtained in 14 individuals, four datasets being acquired in a first imaging session. In 12 subjects, two further datasets were acquired over the next months. Image analysis was performed in the same session for image data obtained under short-term and long-term imaging conditions, and in three different sessions (months apart) for the first data set (resegmentation precision).

RESULTS

Long-term precision errors ranged from 1.4% (total knee) to 3.9% (total femur) for cartilage volume and thickness and were only marginally higher than those under short term conditions. In the medial tibia, the error was 84 mm(3) compared with an estimated loss of >1,200 mm(3) in varus OA. Precision errors for resegmentation were somewhat higher, but considerably smaller than the intersubject variability.

CONCLUSIONS

Scanner drift and changes in imaging or patient conditions appear not to represent a critical problem in quantitative cartilage analysis with magnetic resonance imaging (qMRI). In longitudinal studies, image analysis of sequential data should be performed within the same post-processing session. Under these conditions, qMRI promises to be a very powerful method to assess structural change of cartilage in OA.

Fgf receptor signaling plays a role in lens induction

We describe experiments showing that fibroblast growth factor receptor (Fgfr) signaling plays a role in lens induction. Three distinct experimental strategies were used: (1) using small-molecule inhibitors of Fgfr kinase activity, we showed that both the transcription level and protein expression of Pax6, a transcription factor critical for lens development, was diminished in the presumptive lens ectoderm; (2) transgenic mice (designated Tfr7) that expressed a dominant-negative Fgf receptor exclusively in the presumptive lens ectoderm showed defects in formation of the lens placode at E9.5 but in addition, showed reduced levels of expression for Pax6, Sox2 and Foxe3, all markers of lens induction; (3) by performing crosses between Tfr7 transgenic and Bmp7-null mice, we showed that there is a genetic interaction between Fgfr and Bmp7 signaling at the induction phases of lens development. This manifested as exacerbated lens development defects and lower levels of Pax6 and Foxe3 expression in Tfr7/Tfr7, Bmp7+/– mice when compared with Tfr7/Tfr7 mice alone. As Bmp7 is an established lens induction signal, this provides further evidence that Fgfr activity is important for lens induction. This analysis establishes a role for Fgfr signaling in lens induction and defines a genetic pathway in which Fgfr and Bmp7 signaling converge on Pax6 expression in the lens placode with the Foxe3 and Sox2 genes lying downstream.

The upstream ectoderm enhancer in Pax6 has an important role in lens induction

The Pax6 gene has a central role in development of the eye. We show, through targeted deletion in the mouse, that an ectoderm enhancer in the Pax6 gene is required for normal lens formation. Ectoderm enhancer-deficient embryos exhibit distinctive defects at every stage of lens development. These include a thinner lens placode, reduced placodal cell proliferation, and a small lens pit and lens vesicle. In addition, the lens vesicle fails to separate from the surface ectoderm and the maturing lens is smaller and shows a delay in fiber cell differentiation. Interestingly, deletion of the ectoderm enhancer does not eliminate Pax6 production in the lens placode but results in a diminished level that, in central sections, is apparent primarily on the nasal side. This argues that Pax6 expression in the lens placode is controlled by the ectoderm enhancer and at least one other transcriptional control element. It also suggests that Pax6 enhancers active in the lens placode drive expression in distinct subdomains, an assertion that is supported by the expression pattern of a lacZ reporter transgene driven by the ectoderm enhancer. Interestingly, deletion of the ectoderm enhancer causes loss of expression of Foxe3, a transcription factor gene mutated in the dysgenetic lens mouse. When combined, these data and previously published work allow us to assemble a more complete genetic pathway describing lens induction. This pathway features (1) a pre-placodal phase of Pax6 expression that is required for the activity of multiple, downstream Pax6 enhancers; (2) a later, placodal phase of Pax6 expression regulated by multiple enhancers; and (3) the Foxe3 gene in a downstream position. This pathway forms a basis for future analysis of lens induction mechanism.

Gender differences in knee joint cartilage thickness, volume and articular surface areas: assessment with quantitative three-dimensional MR imaging

OBJECTIVE

To compare the cartilage thickness, volume, and articular surface areas of the knee joint between young healthy, non-athletic female and male individuals.

SUBJECTS AND DESIGN

MR imaging was performed in 18 healthy subjects without local or systemic joint disease (9 female, age 22.3 +/- 2.4 years, and 9 male, age 22.2 +/- 1.9 years.), using a fat-suppressed FLASH 3D pulse sequence (TR = 41 ms, TE = 11 ms, FA = 30 degrees) with sagittal orientation and a spatial resolution of 2 x 0.31 x 0.31 mm3. After three-dimensional reconstruction and triangulation of the knee joint cartilage plates, the cartilage thickness (mean and maximal), volume, and size of the articular surface area were quantified, independent of the original section orientation.

RESULTS AND CONCLUSIONS

Women displayed smaller cartilage volumes than men, the percentage difference ranging from 19.9% in the patella, to 46.6% in the medial tibia. The gender differences of the cartilage thickness were smaller, ranging from 2.0% in the femoral trochlea to 13.3% in the medial tibia for the mean thickness, and from 4.3% in the medial femoral condyle to 18.3% in the medial tibia for the maximal cartilage thickness. The differences between the cartilage surface areas were similar to those of the volumes, with values ranging from 21.0% in the femur to 33.4% in the lateral tibia. Gender differences could be reduced for cartilage volume and surface area when normalized to body weight and body weight x body height. The study demonstrates significant gender differences in cartilage volume and surface area of men and women, which need to be taken into account when retrospectively estimating articular cartilage loss in patients with symptoms of degenerative joint disease. Differences in cartilage volume are primarily due to differences in joint surface areas (epiphyseal bone size), not to differences in cartilage thickness.

Misexpression of IGF-I in the mouse lens expands the transitional zone and perturbs lens polarization

Insulin-like growth factor-I (IGF-I) has been implicated as a regulator of lens development. Experiments performed in the chick have indicated that IGF-I can stimulate lens fiber cell differentiation and may be involved in controlling lens polarization. To assess IGF-I activity on mammalian lens cells in vivo, we generated transgenic mice in which this factor was overexpressed from the alphaA-crystallin promoter. Interestingly, we observed no premature differentiation of lens epithelial cells. The pattern of lens polarization was perturbed, with an apparent expansion of the epithelial compartment towards the posterior lens pole. The distribution of immunoreactivity for MIP26 and p57(KIP2) and a modified pattern of proliferation suggested that this morphological change was best described as an expansion of the germinative and transitional zones. The expression of IGF-I signaling components in the normal transitional zone and expansion of the transitional zone in the transgenic lens both suggest that endogenous IGF-I may provide a spatial cue that helps to control the normal location of this domain.

FGF10 is an inducer and Pax6 a competence factor for lacrimal gland development

We investigated the mechanism of tissue induction and specification using the lacrimal gland as a model system. This structure begins its morphogenesis as a bud-like outgrowth of the conjunctival epithelium and ultimately forms a branched structure with secretory function. Using a reporter transgene as a specific marker for gland epithelium, we show that the transcription factor Pax6 is required for normal development of the gland and is probably an important competence factor. In investigating the cell-cell signaling required, we show that fibroblast growth factor (FGF) 10 is sufficient to stimulate ectopic lacrimal bud formation in ocular explants. Expression of FGF10 in the mesenchyme adjacent to the presumptive lacrimal bud and absence of lacrimal gland development in FGF10-null mice strongly suggest that it is an endogenous inducer. This was supported by the observation that inhibition of signaling by a receptor for FGF10 (receptor 2 IIIb) suppressed development of the endogenous lacrimal bud. In explants of mesenchyme-free gland epithelium, FGF10 stimulated growth but not branching morphogenesis. This suggested that its role in induction is to stimulate proliferation and, in turn, that FGF10 combines with other factors to provide the instructive signals required for lacrimal gland development.

Electromyography in MRI--first recordings of peripheral nerve activation caused by fast magnetic field gradients

Prior studies on the evaluation of stimulation by MRI were based on the subjective feeling of the volunteers. A wide variety of stimulation thresholds between the subjects was observed. In order to exclude subjective perception levels as a cause of this variation, we developed a method to investigate the activation of peripheral nerves after gradient switching by electromyography (EMG) within the MR-imager. Five healthy volunteers were positioned in the MR-scanner with the bridge of the nose at isocenter. The amplitude of sinusoidal pulse trains of the anterior-posterior gradient (rise-times: 200 or 300 micros, various numbers of oscillations) was increased stepwise. Four surface electrodes were placed on the region where a muscle-twitch was reported. Electric activity of the muscle during stimulation experiments was recorded with an MR-compatible electro-physiologic amplifier. Stimulation thresholds were defined by the appearance of an EMG-signal. Thresholds were sharp and consistent with the report of the subjects.

[Stimulation of peripheral nerves by time-varying magnetic field gradients in magnetic resonance tomography]

PURPOSE

The objective of this study is to explain how peripheral nerves can be stimulated by magnetic resonance imaging (MRI) and to describe the associated potential risk. Present knowledge on the bioeffects of time-varying magnetic fields used in MRI are summarized and discussed.

MATERIAL AND METHODS

This review summarizes current reports on peripheral nerve stimulation during MRI and studies which determine threshold values for stimulation effects.

RESULTS/DISCUSSION

The comparison of the different studies indicates that it is reasonable to express the stimulation threshold in terms of the gradient amplitude rather than in terms of the rate of change of the magnetic field gradient. Further studies are necessary to obtain reliable threshold values for peripheral nerve stimulation during MRI and, even more important, to find out how these results can be used to define threshold values in order to avoid excitation of the myocardium during MRI.

Effect of physical exercise on cartilage volume and thickness in vivo: MR imaging study

PURPOSE

To quantify, with magnetic resonance (MR) imaging, the in vivo changes in cartilage volume and thickness after physical exercise.

MATERIALS AND METHODS

The patellae of eight volunteers were imaged six times at physical test by using a spoiled fat-suppressed gradient-echo sequence with an acquisition time of 4.10 minutes. The volunteers then performed 50 knee bends, and two more data sets were acquired 3-7 minutes and 8-12 minutes after exercise. The patellar cartilage volume was determined after three-dimensional reconstruction, and the thickness was assessed with a three-dimensional minimal-distance algorithm.

RESULTS

Whereas repositioning had a small effect on the measurements (mean coefficient of variation, 1.4%), a statistically significant decrease in cartilage volume was observed 3-7 minutes (mean decrease, 6.0%; P < .05) and 8-12 minutes (mean decrease, 5.2%; P < .05) after exercise. The deformation was homogeneous throughout the joint surface. In one asymptomatic volunteer, a cartilage lesion became more pronounced after exercise.

CONCLUSIONS

MR imaging can be used to investigate the response of articular cartilage to physical exercise in vivo. Patients or volunteers should be allowed a sufficient period of physical rest if quantitative measurements of cartilage volume and thickness are to be undertaken in longitudinal studies.

Recent and future advances in high-speed imaging

Long acquisition times have long been a major drawback of magnetic resonance imaging (MRI) and have limited its use for all those organ systems with various types of movement, such as respiration, pulsation, and peristalsis. Recent advances in scanner hard- and software, most notably improvements in gradient and radio frequency coil design, in amplifier technology as well as in pulse sequence development, have created new fields of application for MRI. In this review article we give an overview of the development of pulse sequences from the spin echo technique through gradient echo techniques to the fastest imaging technique thus far developed, echo planar imaging (EPI). A variety of clinical applications for the different pulse sequences is included, along with a discussion on the advantages and drawbacks of each technique. The review ends with a discussion of possible future advances in the field of high-speed MR imaging.

Pathologic conditions in the small bowel: findings at fat-suppressed gadolinium-enhanced MR imaging with an optimized suspension of oral magnetic particles

Depiction of small-bowel pathologic conditions was optimized with use of a negative luminal contrast agent, spectral fat suppression, and gadolinium enhancement in an excised gut phantom. The method was applied in nine patients in conjunction with standard enteroclysis examinations. Bulk susceptibility effects of oral magnetic particles were canceled with use of a diamagnetic methylcellulose suspension. In the ileum, fat suppression and contrast between bowel wall and lumen was judged good or excellent in eight and nine patients, respectively. In eight of nine patients, additional mesenteric findings were depicted.