Association between visual degeneration of intervertebral discs and the apparent diffusion coefficient

The value of apparent diffusion coefficient (ADC) measurements in intervertebral disc has been studied because ADC provides an estimate of free diffusion of unbound water and could be used as a quantitative tool to estimate degenerative changes. However, the challenging nature of diffusion imaging of spine and limited numbers of subjects in earlier studies has produced contradictory findings. We aimed to determine the relation between ADC and visual degenerative changes in lumbar intervertebral discs in a sufficiently large homogeneous study group. Lumbar spines of 228 volunteer middle-aged men were MR imaged at 1.5 T including anatomic and diffusion-weighted imaging. ADC values, T2 signal intensity and height, and width of the three lowest lumbar intervertebral discs were measured and disc degeneration visually graded. The calculated average ADC of 530 measured discs was 2.01×10⁻³ mm²/s±0.29 (±S.D.). The reduction in ADC between visually normal and moderately degenerated discs was 4%. Severely degenerated discs showed 5% larger ADC values than normal discs, presumably due to free water in cracks and fissures of those discs. T2 signal intensity of the disc was significantly correlated with the ADC values, whereas other measured parameters did not show correlation. There was no evident difference in ADC between the studied anatomic lumbar levels. Because there is considerable overlap between ADC values of normal and degenerated discs, we conclude that ADC measurements of intervertebral discs, at least with current technology, have limited clinical value.     

In vivo relaxation times of gray matter and white matter in spinal cord

In vivo relaxation times and relative spin densities of gray matter (GM) and white matter (WM) of rat spinal cord were measured. Inductively coupled implanted RF coil was used to improve the signal-to-noise ratio required for making these measurements. The estimated relaxation times (in milliseconds) are: T1(GM) = 1021+/-93, T2(GM) = 64+/-3.4, T1(WM) = 1089+/-126, and T2(WM) = 79+/-6.9. The estimated relative spin densities are: rho(GM) = (60+/-2.3)% and rho(WM) = (40+/-2.1)%. The T1 values of GM and white matter are not statistically different. However, the differences in T2 values and spin densities of GM and WM are statistically significant. These in vivo measurements indicate that the observed contrast between GM and WM in spinal cord MR images mainly arises from the differences in the spin density.     

A comparative study at 3 T of sequence dependence of T2 quantitation in the knee

Objective

T₂ mapping has been used widely in detecting cartilage degeneration in osteoarthritis. Several scanning sequences have been developed in the determination of T₂ relaxation times of tissues. However, the derivation of these times may vary from sequence to sequence. This study seeks to evaluate the sequence-dependent differences in T₂ quantitation of cartilage, muscle, fat and bone marrow in the knee joint at 3 T.

Methods

Three commercial phantoms and 10 healthy volunteers were studied using 3 T MR. T₂ relaxation times of the phantoms, cartilage, muscle, subcutaneous fat and marrow were derived using spin echo (SE), multiecho SE (MESE), fast SE (FSE) with varying echo train length (ETL), spiral and spoiler gradient (SPGR) sequences. The differences between these times were then evaluated using Student's t test. In addition, the signal-to-noise ratio (SNR) efficiency and coefficient of variation of T₂ from each sequence were calculated.

Results

The average T₂ relaxation time was 36.38±5.76 ms in cartilage and 34.08±6.55 ms in muscle, ranging from 27 to 45 ms in both tissues. The times for subcutaneous fat and marrow were longer and more varying, ranging from 41 to 143 ms and from 42 to 160 ms, respectively. In FSE acquisition, relaxation time significantly increases as ETL increases (P<.05). In cartilage, the SE acquisition yields the lowest T₂ values (27.52±3.10 ms), which is significantly lower than those obtained from other sequences (P<.002). T₂ values obtained from spiral acquisition (38.27±6.45 ms) were higher than those obtained from MESE (34.35±5.62 ms) and SPGR acquisition (31.64±4.53 ms). These differences, however, were not significant (P>.05).

Conclusion

T₂ quantification can be a valuable tool for the diagnosis of degenerative disease. Several different sequences exist to quantify the relaxation times of tissues. Sequences range in scan time, SNR efficiency, reproducibility and two- or three-dimensional mapping. However, when choosing a sequence for quantitation, it is important to realize that several factors affect the measured T₂ relaxation time.     

Two-exponential analysis of spin-spin proton relaxation times in MR imaging using surface coils

Proton relaxation time measurements were performed on a standard whole body MR imager operating at 1.5 T using a conventional surface coil of the manufacturer. A combined CP/CPMG multiecho, multislice sequence was used for the T1 and T2 relaxation time measurements. Two repetition times of 2000 ms (30 echoes) and 600 ms (2 echoes) with 180 degrees-pulse intervals of 2 tau = 22 ms were interleaved in this sequence. A two-exponential T2 analysis of each pixel of the spin-echo images was computed in a case of an acoustic neurinoma. The two-exponential images show a "short" component (T2S) due to white and gray matter and a "long" component (T2S) due to the cerebrospinal fluid. In the fatty tissue two components with T2S = 35 +/- 3 ms and T2L = 164 +/- 7 ms were measured. Comparing with Gd-DTPA imaging the relaxation time images show a clear differentiation of vital tumor tissue and cerebrospinal fluid.     

MR relaxometry on a whole-body imager: quality control.

Long-term monitoring of the average proton relaxation time T2 of phantoms measured on a Siemens MR whole-body imager showed very good repeatability and reproducibility. The repeatability (short-term precision) and reproducibility (long-term precision) of the average values of a relaxation time T2 approximately/= 81 ms, obtained by a standard 16-echo CPMG pulse sequence, were 2.6% and 9.7%, respectively. The Siemens Vision imager proved to be a suitable tool for T2 evaluation in vivo. Quality control was performed using the techniques of control diagrams developed by Shewhart, which proved to be an appropriate method for continuous quality control of relaxation time determination.     

The effect of varying echo spacing within a multiecho acquisition: better characterization of long T2 components

A 48-echo pulse sequence with five different echo-spacing combinations was examined to determine how one can most effectively measure the T2 relaxation characteristics of cerebral tissue containing a long T2 component. For each scan, the first 32 echoes had an echo spacing of 10 ms, while the spacing for Echoes 33-48 (DeltaTE2) was 10, 20, 30, 40 or 50 ms. In an in vivo study using 10 normal volunteers, it was found that the resolution of T2 distribution peaks for both myelin water (approximately 20 ms) and intracellular/extracellular (IE) water (approximately 80 ms) improved as DeltaTE2 increased. The geometric mean T2 values of the main peak agreed within the error for all DeltaTE2 values. A phantom study simulated T2 relaxation distributions that are expected in the brains of patients with demyelinating diseases. For phantoms in which the T2 values of the IE and lesion (200-500 ms) water compartments were separated by at least a factor of 3, each compartment in the distribution was better resolved when DeltaTE2=40 or 50 ms. On the basis of these results, we recommend the use of extended DeltaTE2 values for imaging patients with lesions, without the risk of losing valuable short T2 information.     

In vivo triple quantum filtered twisted projection sodium MRI of human articular cartilage

In this work, we present the first triple quantum filtered (TQF) sodium MR images of the human knee joint in vivo. A 3D TQF data set of 16 slices was obtained in 20 min using a TQF pulse sequence preencoded to a twisted projection imaging readout. Images clearly demarcate patellar cartilage and also demonstrate fluid signal suppressed by the triple quantum filter. Biexponential transverse relaxation times were calculated by fitting the TQF free induction decay to a theoretical signal expression. The average values from three healthy volunteers were T(2fall)(*) = 9.59 +/- 0.35 ms and T(2rise)(*) = 0.84 +/- 0.06 ms. Application of TQF imaging in biological tissues is discussed.     

Analysis of longitudinal relaxation rate constants from magnetization transfer MR images of human tissues at 0.1 T.

The human calf muscle was examined by using the magnetization transfer MR imaging technique. The time-dependent saturation transfer (TDST) method was applied at low magnetic field 0.1 T in order to measure the mobile water relaxation time T1w, the magnetization transfer rate Rwm from water to solid macromolecules, and the magnetization transfer contrast (MTC) of the human tissue. The magnetization transfer contrast of 0.67 was attained. The transfer rate Rwm was 4.5 sec-1 (+/- 0.3 sec-1) for the anterior tibial muscle and 5.0 sec-1 (+/- 0.4 sec-1) for the gastrocnemius muscles. The values of Rwm are considerably larger than the values of corresponding relaxation rates measured at high fields. The relaxation rate measurements of human tissues in vivo was shown to be possible at 0.1 T even within the framework of normal routine MR imaging. Magnetization transfer MR imaging is a very promising and practical method in order to assess the relaxation processes in heterogeneous human tissues in vivo, and it can improve the tissue characterization possibilities of MR imaging techniques.     

Apparent diffusion coefficient of intervertebral discs related to matrix composition and integrity

While tremendous work has been performed to characterize degenerative disc disease through gross morphologic, biochemical, and histologic grading schemes, the development of an accurate and noninvasive diagnostic tool is required to objectively detect changes in the matrix with aging and disc degeneration. In the present study, quantitative magnetic resonance was used to determine if the quality of the nutritional supply to the intervertebral disc at various ages and levels of degeneration could be assessed through measurement of the apparent diffusion coefficients (ADCs). Modifications of the nucleus pulposus matrix content, specifically of water and glycosaminoglycan contents, with age and disc degeneration, were reflected in correlating changes in the ADCs. From unforced stepwise linear regression analyses, relations were established showing that decreases in glycosaminoglycan or water contents in the nucleus pulposus resulted in direct decreases in the ADCs. Relations obtained for the ADCs of the nucleus pulposus were direction dependent, in conformity with the anisotropic diffusion in the intervertebral discs. Changes in matrix integrity, as evidenced by the percentage of denatured collagen, were also detected in the nucleus pulposus with a low positive correlation to the ADC along the height of the disc and an inverse statistically significant regression to the ADC along the anterior to posterior axis of the disc. Correlations between the matrix content and integrity of the annulus fibrosus and its ADCs were not as evident, with only the ADC in the lateral direction of the disc of the anterior annulus fibrosus able to reflect changes in matrix content. The information obtained by the ADCs, particularly of the nucleus pulposus, can potentially be used in combination with quantitative T1, T2, and MT parameters to noninvasively obtain a quantitative assessment of the disc matrix composition and structural integrity.     

Evaluation of water content by spatially resolved transverse relaxation times of human articular cartilage

Non-invasive assessment of cartilage properties, specifically water content, could prove helpful in the diagnosis of early degenerative joint diseases. Transverse relaxation times T(2) of human articular cartilage (34 cartilage slices of three donors) were measured on a pixel-by-pixel basis in a clinical whole body MR system in vitro. In vivo feasibility to measure quantitative T(2) maps was shown for human patellar cartilage. The relaxation times of cartilage with collagen in the radial zone oriented perpendicular to the magnetic field increased from approximately 10 ms near the bone to approximately 60 ms near the articular surface. Cartilage water content of the tibial plateau and femoral condyles could be determined from the correlation with T(2) (R(2) = 0.71) with an error of approximately 2 wt.%. In vivo, directional variation would need to be considered. If confirmed in vivo, T(2) measurements could potentially serve as a non-invasive tool for the evaluation of the status and distribution of water content in articular cartilage.     

Functional MRI of the human motor cortex using single-shot, multiple gradient-echo spiral imaging

In this study, we combined the advantages of a fast multi-slice spiral imaging approach with a multiple gradient-echo sampling scheme at high magnetic field strength to improve quantification of BOLD and inflow effects and to estimate T2* relaxation times in functional brain imaging. Eight echoes are collected with echo time (TE) ranging from 5 to 180 ms. Acquisition time per slice and echo time is 25 ms for a nominal resolution of 4 x 4 x 4 mm3. Evaluation of parameter images during rest and stimulation yields no significant activation on the inflow sensitive spin-density images (rho or I0-maps) whereas clear activation patterns in primary human motor cortex (M1) and supplementary motor area (SMA) are detected on BOLD sensitive T2*-maps. The calculation of relaxation times and rates of the activated areas over all subjects yields an average T2* +/- standard deviation (SD) of 46.1+/-4.5 ms (R2* of 21.8+/-2.2 s(-1)) and an average increase (deltaT2* +/- SD) of 0.93+/-0.47 ms (deltaR2* of -0.4+/-0.14 s(-1)). Our findings demonstrate the usefulness of a multiple gradient echo data acquisition approach in separating various vascular contributions to brain activation in fMRI.     

Early diagnosis of degenerative changes in the articular/fibrocartilaginous disc of the temporomandibular joint in patients with temporomandibular disorders using delayed gadolinium-enhanced MRI at 3 Tesla – preliminary results

BackgroundDelayed gadolinium enhanced MRI of cartilage (dGEMRIC) is a quantitative method for assessment of glycosaminoglycan content in connective tissues. We hypothesize that the early diagnosis of degenerative changes in the temporomandibular joint could be diagnosed using dGEMRIC technique.PurposeTo test the compositional MRI technique, dGEMRIC, at 3 Tesla to diagnosis early the degenerative changes in the fibrocartilaginous disc of the temporomandibular joint (TMJ) in patients with temporomandibular disorders (TMD) and to compare the dGEMRIC index of patients to the healthy volunteers.MethodsSix volunteers (two men, four women; 20.8÷28.1 years) and eleven patients (22 TMJs, seven women, four men; 24÷54 years) were recruited for this prospective trial. Only patients with no morphological abnormality on MRI and without disc dislocations were included. Volunteers were used as a control group. The PD-weighted FSE sequence and the 3D GRE (DESS) sequence protocols were performed for morphological assessment. The Inversion recovery (IR) sequence was performed for T1 relaxation time measurements and intra-venous (IV) contrast agent administration was used according to the dGEMRIC protocol. T1 maps were calculated offline and ROIs were drawn on TMJ discs by a specialist trained in TMD disorders. Statistical evaluation was performed by ANOVA and correlations were calculated.ResultsThe difference between the dGEMRIC values in the TMJ articular discs of the patients and the volunteers was statistically significant (P = .019). After contrast agent administration the T1 values dropped in both groups. In patient group was the T1 drop stronger (−54% from initial pre-contrast value), while in control group was the T1 drop less pronounced (−46% from initial pre-contrast value).ConclusionsdGEMRIC seems to be a useful, compositional, quantitative method, suitable also for small joints, such as the articular disc of the TMJ. The results of the dGEMRIC index in the articular disc of the TMJ imply a lower GAG content in patients with TMJ disorders.     

In vivo determination of 31P spin relaxation times (T1, T2, T1 rho) in rat leg muscle. Use of an off-axis solenoid coil

A probe using a solenoid coil tilted 45 degrees off-axis has been used to study the 31P NMR relaxation characteristics of the resonances arising from phosphorus metabolites in rats in vivo. T1, T1 rho and T2 values have been determined for phosphocreatine and ATP in leg muscle. The ratio of 31P T1(1700ms) to T2(12ms) for ATP was in excess of 200:1 compared with a ratio of 5:1 for 1H T1:T2. Of major significance was the observation that T2 values for phosphocreatine (230ms) were markedly longer than T2 values for ATP (12ms). Thus by use of appropriate delay times in spin echo sequences ATP signals can be nulled, and discrete 31P imaging of phosphocreatine in muscle may be possible provided the overall signal-to-noise is satisfactory.     

Magic sandwich echo relaxation mapping of anisotropic systems

The main objective of this article was (i) to refocus the residual dipolar and quadrupolar interactions in anisotropic tissues employing magic sandwich echo (MSE) imaging and to compare the results with that of conventional spin-echo (SE) imaging, and (ii) to quantify MSE relaxation and dispersion characteristics in bovine Achilles tendon and compare with spin-lattice relaxation time constant in the rotating frame (T(1rho)). Magic sandwich echo weighted images are approximately 75-100% higher in signal-to-noise ratio than the corresponding T(2)-weighted images. Magic sandwich echo relaxation times varied from 13+/-2 to 19+/-3 ms (mean+/-S.D.), depending upon the structural location of tendon. T(2) relaxation times only varied from 4+/-1 to 10+/-3 ms (mean+/-S.D.) on the same corresponding locations. Magic sandwich echo provides approximately 100% enhancement in relaxation times compared to T(2). Preliminary results based on bovine Achilles tendon and cartilage specimens suggest that the MSE technique has potential for refocusing residual dipolar as well as quadrupolar interactions in anisotropic systems and yields higher intensities than conventional SE imaging as well as T(1rho)-encoded imaging, especially at low-burst pulse amplitudes (250 and 500 Hz).     

Intervertebral disc modeling using a MRI method: migration of the nucleus zone within scoliotic intervertebral discs.

MRI is increasingly being used for etiologic examination of scoliosis and for intervertebral disc disorder analysis, but until now has not been applied to geometric modeling. The aim of this study was to develop a new geometric model of intervertebral discs using MRI and to quantify the migration of the nucleus zone within scoliotic intervertebral discs. Fourteen lumbar scoliotic children (Cobb angles 22 ± 7°) were examined using MRI. The protocol consisted of sagittal and coronal plane acquisitions of the entire spine. An image processing software allowed the outline detection of the nucleus zone (intervertebral high intensity portion). The vertebral bodies were also reconstructed. Using a pre-post processor, the nucleus zone migration and a wedging angle were quantified. Statistical tests showed the repeatability of the method (p > 0.4). Nucleus zone migration was correlated to the wedging angle (r² = 0.488, p < 0.0001) in the coronal plane. Our results were in agreement with the literature: when two vertebrae move deforming the disc, the nucleus moves into the convexity of the curvature. But should we talk about the nucleus? Despite image processing software allowing the highlighting of image features (automatic color lookup tables applied to grayscale images using pixel intensity measurements), it is impossible to differentiate the nucleus from the annulus on T2 weighting images of adolescent spine. This new geometric model of the intervertebral disc, used for the quantification of the nucleus zone migration, should be of interest for further investigation of stiffness parameters of spine.     

Age-related diffusion patterns in human lumbar intervertebral discs: a pilot study in asymptomatic subjects

Diffusion tensor imaging (DTI) may provide an accurate noninvasive method of detecting degenerative matrix alterations in human lumbar intervertebral discs (IVDs). This study aimed to investigate age-related degenerative changes in human lumbar IVDs using DTI. Thirty asymptomatic volunteers ranging in age from 25 to 67 years underwent single-shot diffusion weighted echo-planar imaging on a 3 T scanner. DTI-derived metrics including fractional anisotropy (FA) and mean diffusivity (MD) were analyzed by a histogram analysis method. A Mann-Whitney test was used to compare subject groups (young and elderly) with respect to the diffusion measures, and piecewise linear regression was used to characterize the change in each metric as a function of age. We found significant age-related changes in the elderly adult group, with decrease of MD (11%, P<.001) and increase of FA (20%, P<.001). Our results demonstrate that the degenerative-related changes taking place in the IVDs through aging can be quantitatively accessed by DTI-derived metrics, while the morphologic changes are difficult to be identified in conventional T(2)-weighted images. Our initial findings suggest that it would be worthwhile to validate the relationship between DTI metrics and the actual degenerative status of IVDs using extracted disc samples and to extend it to studies on patients with degenerative discs in order to further explore the clinical usefulness and relevance of DTI.     

Feasibility of MR elastography of the intervertebral disc

Low back pain (LBP) is a costly and widely prevalent health disorder in the U.S. One of the most common causes of LBP is degenerative disc disease (DDD). There are many imaging techniques to characterize disc degeneration; however, there is no way to directly assess the material properties of the intervertebral disc (IVD) within the intact spine. Magnetic resonance elastography (MRE) is an MRI-based technique for non-invasively mapping the mechanical properties of tissues in vivo. The purpose of this study was to investigate the feasibility of using MRE to detect shear wave propagation in and determine the shear stiffness of an axial cross-section of an ex vivo baboon IVD, and compare with shear displacements from a finite element model of an IVD motion segment in response to harmonic shear vibration. MRE was performed on two baboon lumbar spine motion segments (L3–L4) with the posterior elements removed at a range of frequencies (1000–1500 Hz) using a standard clinical 1.5 T MR scanner. Propagating waves were visualized in an axial cross-section of the baboon IVDs in all three motion-encoding directions, which resembled wave patterns predicted using finite element modeling. The baboon nucleus pulposus showed an average shear stiffness of 79 ± 15 kPa at 1000 Hz. These results suggest that MRE is capable of visualizing shear wave propagation in the IVD, assessing the stiffness of the nucleus of the IVD, and can differentiate the nucleus and annulus regions.     

Phosphorus-31 spin-lattice NMR relaxation in bone apatite and its mineral standards

Phosphorus-31 spin-lattice relaxation, both in the laboratory (B(0)=4.7 T) and rotating frame (B(1)=2.2 mT), was studied in the following samples: mineral of whole human bone (samples B1-B6), apatite prepared from bone (BHA), natural brushite (BRU), synthetic hydroxyapatite hydrated (HAh) and calcined (HAc), and synthetic carbonatoapatite of type B (CHA-B) with 9 wt% of CO(3)(2-). The T(1)(P) relaxation time was determined directly using the saturation recovery technique, while the T(1 rho)(P) relaxation time was measured via (1)H-->(31)P CP by incrementing the (31)P spin-lock. In order to avoid an effect of magic-angle spinning (MAS) on CP and relaxation, the experiments were carried out on static samples. The (31)P spin-lattice relaxation was discussed for trabecular and cortical bone tissue from adult subjects in comparison to the synthetic mineral standards. None of the reference materials has matched accurately the relaxation behaviour of the bone mineral. The most striking differences between the examined substances were observed for T(1)(P), which for human bone was sample dependent and appeared in the range 55-100 s, while for HAh, HAc, and CHA-B was 7.2, 10.0, and 25.8 s, respectively. Possible reasons of so large relaxation diversity were discussed. It has been suggested that T(1)(P) of apatites is to some extent dependent on the concentration of the structural hydroxyl groups, and this in turn is controlled by the material crystallinity. It was also found that T(1)(P) decreased on hydration by ca. 30%. For T(1rho)(P), both its magnitude and dependence on the CP contact time gave useful structural information. The dehydrated samples (HAc and BHA) had long T(1 rho)(P) over 250 ms. Those, which contained water, either structural (BRU) or adsorbed on the crystal surface (HAh, CHA-B, and B1-B6), had shorter T(1 rho)(P) below 120 ms. It was concluded that the effect of water on T(1 rho)(P) is much more pronounced than on T(1)(P). The interpretation has involved P-OH groups and adsorbed water, which cover the apatite crystal surface.     

Ex vivo magnetic resonance imaging of rat spinal cord at 9.4 T

The magnetic resonance (MR) properties of the rat spinal cord were characterized at the T9 level with ex vivo experiments performed at 9.4 T. The inherent endogenous contrast parameters, proton density (PD), longitudinal and transverse relaxation times T1 and T2, and magnetization transfer ratio (MTR) were measured separately for the grey matter (GM) and white matter (WM). Analysis of the measurements indicated that these tissues have statistically different proton densities with means PD(GM)=54.8+/-2.5% versus PD(WM)=45.2+/-2.4%, and different T1 values with means T1GM=2.28+/-0.23 s versus T1WM=1.97+/-0.21 s. The corresponding values for T2 were T2GM=31.8+/-4.9 ms versus T2WM=29.5+/-4.9 ms, and the difference was insignificant. The difference between MTR(GM)=31.2+/-6.1% and MTR(WM)=33.1+/-5.9% was also insignificant. These results collectively suggest that PD and T1 are the two most important parameters that determine the observed contrast on spinal cord images acquired at 9.4 T. Therefore, in MR imaging studies of spinal cord at this field strength, these parameters need to be considered not only in optimizing the protocols but also in signal enhancement strategies involving exogenous contrast agents.