MR imaging of the intervertebral disc: a quantitative study

Delineation of Inner Annulus Fibrosus and Nucleus Pulposus on Routine T2-weighted MR Images

STUDY DESIGN

Retrospective study of 150 IVDs.

OBJECTIVE

Assessment of costume algorithm ability to delineate the IAF and NP on routine T2 images.

SUMMARY OF BACKGROUND DATA

Central hyperintense region on T2-weighted MR images of normal lumbar IVDs represents a combination of IAF and NP. Ability to identify NP as distinct from IAF can help improve our understanding of IVD morphology in-vivo.

METHODS

Sagittal T2-weighted TSE MR images of 150 lumbar IVDs from 25 patients were analyzed. MR images were processed using a custom algorithm that markedly increased the signal intensity of structures with inherent signal intensity within 2 defined intensity thresholds. Signal intensity and contrast-to- noise ratio between outer annulus fibrosus, IAF, and NP were assessed at baseline and after processing. To assess consistency of underlying T2 differences, similar analysis was done on 108 discs from 18 patients in whom additional sagittal T2-weighted STIR images were available.

RESULTS

Following image processing, apparent IAF and NP were rendered visible in 86% and 84.3% IVDs on T2-weighted TSE and STIR images respectively. While signal intensity of these 2 regions was inherently different (P< 0.001) before processing on TSE and STIR images, their visualization was facilitated by a significant increase (P<0.001) in contrast-to-noise ratio after processing. Nonvisualization of NP was associated with disc degeneration (P<0.001).

CONCLUSION

Inherent differences exist in signal intensities of normal NP and IAF on T2-weighted MR images. Accentuating these differences using image postprocessing techniques can render these 2 structures visible.

A microstructure-based modeling approach to assess aging-sensitive mechanics of human intervertebral disc

BACKGROUND AND OBJECTIVE

The human body soft tissues are hierarchic structures interacting in a complex manner with the surrounding biochemical environment. The loss of soft tissues functionality with age leads to more vulnerability regarding to the external mechanical loadings and increases the risk of injuries. As a main example of the human body soft tissues, the intervertebral disc mechanical response evolution with age is explored. Although the age-dependence of the intervertebral disc microstructure is a well-known feature, no noticeable age effect on the disc stiffness is evidenced in the in-vitro experimental studies of the literature. So, if the disc intrinsic mechanics remains constant, how to explain the correlation of disc degeneration and disc functionality loss with age.

METHODS

A microstructure-based modeling approach was developed to assess in-silico the aging-sensitive mechanics of human intervertebral disc. The model considers the relationship between stress/volumetric macro-response and microstructure along with effective age effects acting at the lamellar and multi-lamellar scales. The stress-stretch and transversal responses of the different disc regions were computed for various age groups (13-18, 36, 58, 69 and 82 years old) and their evolution with age was studied.

RESULTS

While matching with in-vitro experimental data, the predicted stiffness was found to increase while passing from adolescent young discs to mature older discs and then to remain almost constant for the rest of life. Important age-related changes in the disc transversal behavior were also predicted affecting the flexibility of the disc, changing its volumetric behavior, and modifying its dimensions.

CONCLUSION

The developed approach was found able to bring new conclusions about age-dependent mechanical properties including regional dependency. The disc mechanics in terms of rigidity, radial and axial transversal responses were found to alter going from adolescent to middle age where the disc reaches a certain maturity. After reaching maturity, the mechanical properties undergo very slight changes until becoming almost constant with age.

MRI histogram analysis enables objective and continuous classification of intervertebral disc degeneration

PURPOSE

Magnetic resonance imaging (MRI) is the best diagnostic imaging method for low back pain. However, the technique is currently not utilized in its full capacity, often failing to depict painful intervertebral discs (IVDs), potentially due to the rough degeneration classification system used clinically today. MR image histograms, which reflect the IVD heterogeneity, may offer sensitive imaging biomarkers for IVD degeneration classification. This study investigates the feasibility of using histogram analysis as means of objective and continuous grading of IVD degeneration.

METHODS

Forty-nine IVDs in ten low back pain patients (six males, 25-69 years) were examined with MRI (T2-weighted images and T2-maps). Each IVD was semi-automatically segmented on three mid-sagittal slices. Histogram features of the IVD were extracted from the defined regions of interest and correlated to Pfirrmann grade.

RESULTS

Both T2-weighted images and T2-maps displayed similar histogram features. Histograms of well-hydrated IVDs displayed two separate peaks, representing annulus fibrosus and nucleus pulposus. Degenerated IVDs displayed decreased peak separation, where the separation was shown to correlate strongly with Pfirrmann grade (P < 0.05). In addition, some degenerated IVDs within the same Pfirrmann grade displayed diametrically different histogram appearances.

CONCLUSIONS

Histogram features correlated well with IVD degeneration, suggesting that IVD histogram analysis is a suitable tool for objective and continuous IVD degeneration classification. As histogram analysis revealed IVD heterogeneity, it may be a clinical tool for characterization of regional IVD degeneration effects. To elucidate the usefulness of histogram analysis in patient management, IVD histogram features between asymptomatic and symptomatic individuals needs to be compared.

High-Resolution Qualitative and Quantitative Magnetic Resonance Evaluation of the Glenoid Labrum

OBJECTIVE

This study aimed to implement qualitative and quantitative magnetic resonance sequences for the evaluation of labral pathology.

METHODS

Six glenoid labra were dissected, and the anterior and posterior portions were divided into normal, mildly degenerated, or severely degenerated groups using gross and magnetic resonance findings. Qualitative evaluation was performed using T1-weighted, proton density-weighted, spoiled gradient echo and ultrashort echo time (UTE) sequences. Quantitative evaluation included T2 and T1rho measurements as well as T1, T2*, and T1rho measurements acquired with UTE techniques.

RESULTS

Spoiled gradient echo and UTE sequences best demonstrated labral fiber structure. Degenerated labra had a tendency toward decreased T1 values, increased T2/T2* values, and increased T1rho values. T2* values obtained with the UTE sequence allowed for delineation among normal, mildly degenerated, and severely degenerated groups (P < 0.001).

CONCLUSIONS

Quantitative T2* measurements acquired with the UTE technique are useful for distinguishing among normal, mildly degenerated, and severely degenerated labra.

A statistical model for intervertebral disc degeneration: determination of the optimal T2 cut-off values

PURPOSE

The aim of this study was to investigate the possibility of quantitative classification in intervertebral disc degeneration using spin-spin relaxation time (T2) cut-off values with regard to morphological classifications.

METHODS

Lumbar magnetic resonance (MR) imaging was performed on 21 subjects (a total of 104 lumbar disks). The T2 relaxation time was measured in the nucleus pulposus using a sagittal multi-echo spin-echo sequence. The morphological classification of disc degeneration was assessed independently by three experienced neuroradiologists according to the Pfirrmann and Schneiderman classifications. Receiver operating characteristic analysis was performed among grades to determine T2 cut-off values in each classification. Intra- and interobserver differences were calculated using kappa statistics.

RESULTS

Moderate overall interobserver agreement was found between observers in both the Pfirrmann and Schneiderman classification schemes (kappa 0.46 and 0.51), while intraobserver reliability was substantial to almost perfect. The interobserver reliability was only fair in Pfirrmann grades III and IV (kappa 0.33 and 0.36), but the T2 cut-off values still indicated a significant difference between grades (p<0.05).

CONCLUSIONS

Interobserver agreement of MR evaluation in patients with intervertebral disc degeneration was only fair to moderate on the classification of more severe disc degeneration in the Pfirrmann and Schneiderman schemes. Based on our results, quantitative T2 cut-off values seem to be a more reliable method to define the degree of disc degeneration, which may help staging intervertebral disc degeneration (IVDD) even if the interobserver reliability is low.

New treatments and imaging strategies in degenerative disease of the intervertebral disks

Magnetic resonance (MR) imaging in patients with persistent low back pain and sciatica effectively demonstrates spine anatomy and the relationship of nerve roots and intervertebral disks. Except in cases with nerve root compression, disk extrusion, or central stenosis, conventional anatomic MR images do not help distinguish effectively between painful and nonpainful degenerating disks. Hypoxia, inflammation, innervation, accelerated catabolism, and reduced water and glycosaminoglycan content characterize degenerated disks, the extent of which may distinguish nonpainful from painful ones. Applied to the spine, "functional" imaging techniques such as MR spectroscopy, T1ρ calculation, T2 relaxation time measurement, diffusion quantitative imaging, and radio nucleotide imaging provide measurements of some of these degenerative features. Novel minimally invasive therapies, with injected growth factors or genetic materials, target these processes in the disk and effectively reverse degeneration in controlled laboratory conditions. Functional imaging has applications in clinical trials to evaluate the efficacy of these therapies and eventually to select patients for treatment. This report summarizes the biochemical processes in disk degeneration, the application of advanced disk imaging techniques, and the novel biologic therapies that presently have the most clinical promise.

Diagnostic tools and imaging methods in intervertebral disk degeneration

Low back pain has a negative impact on the economy and society. Intervertebral disk degeneration is linked to the occurrence of low back pain. MRI provides three-dimensional morphologic and biochemical information regarding the status of the disk. This article reviews new and evolving MRI disk-imaging techniques, including grading, relaxation-time measurements, diffusion, and contrast perfusion. In addition, high-resolution magic-angle spinning methods to correlate in vitro disk degeneration (with pain, etc) and in vivo spectroscopic results are discussed. With the potential for morphologic and biochemical characterization of the intervertebral disk, MRI shows promise as a tool to quantitatively assess disk health.

Labeling of lumbar discs using both pixel- and object-level features with a two-level probabilistic model

Backbone anatomical structure detection and labeling is a necessary step for various analysis tasks of the vertebral column. Appearance, shape and geometry measurements are necessary for abnormality detection locally at each disc and vertebrae (such as herniation) as well as globally for the whole spine (such as spinal scoliosis). We propose a two-level probabilistic model for the localization of discs from clinical magnetic resonance imaging (MRI) data that captures both pixel- and object-level features. Using a Gibbs distribution, we model appearance and spatial information at the pixel level, and at the object level, we model the spatial distribution of the discs and the relative distances between them. We use generalized expectation-maximization for optimization, which achieves efficient convergence of disc labels. Our two-level model allows the assumption of conditional independence at the pixel-level to enhance efficiency while maintaining robustness. We use a dataset that contains 105 MRI clinical normal and abnormal cases for the lumbar area. We thoroughly test our model and achieve encouraging results on normal and abnormal cases.

Monitoring of the effect of intervertebral disc nucleus pulposus ablation by MRI

In order to investigate intervertebral disc (IVD) degeneration and repair, a quantitative non-invasive tool is needed. Various MRI methods including qCPMG, which yields dipolar echo relaxation time (T(DE)), magnetization transfer contrast (MTC), and (1)H and (2)H double quantum filtered (DQF) MRI were used in the present work to monitor changes in rat IVD after ablation of the nucleus pulposus (NP), serving as a model of severe IVD degeneration. In the intact IVD, a clear distinction between the annulus fibrosus (AF) and the NP is obtained on T(2) and T(DE) weighted images as well as on MTC maps, reflecting the high concentration of ordered collagen fibers in the AF. After ablation of the NP, the distinction between the compartments is lost. T(2) and T(DE) relaxation times are short throughout the disc and MTC is high. (1)H and (2)H DQF signal, which in intact discs is obtained only for the AF, is now observable throughout the tissue. These results indicate that after ablation, there is an ingression of collagen fibers from the AF into the area that was previously occupied by the NP, as was confirmed by histology.

T2 relaxation times correlated with stage of lumbar intervertebral disk degeneration and patient age

BACKGROUND AND PURPOSE

T2 relaxation times provide a continuous measure of changes in intervertebral disk biochemistry. The purpose of this study was to correlate T2 relaxation times in lumbar disks with patient age and stage of degeneration.

MATERIALS AND METHODS

Sagittal T1- and T2-weighted images and axial images were acquired in 20 patients referred for MR imaging for back pain or radiculopathy. Two readers inspected these images and assigned a Pfirrmann grade to each disk. An additional sagittal multiecho FSE image sequence was obtained, and T2 relaxation times were calculated for a each lumbar disk. T2 relaxation times were correlated with Pfirrmann grade. T2 relaxation times in nondegenerated disks were correlated with patient age. Statistical significance was tested by ANOVA, ad hoc tests, and Pearson coefficients.

RESULTS

T2 relaxation times were calculated for 95 lumbar disks in 19 patients and discarded for 5 disks in 1 patient due to motion artifacts. Forty-four disks were classified as Pfirrmann grade II; 34, as grade III; 14, as grade IV; and 3, as grade V. Mean T2 relaxation times of the central region decreased from 108 ms for grade II to 53 ms for grade IV disks. T2 relaxation times correlated significantly with Pfirrmann grade. For grade II disks, T2 relaxation times of the central region decreased significantly from an average of 132 ms for patients in their 20s to 86 ms for those in their 60s.

CONCLUSIONS

T2 relaxation times in lumbar disks correlate with stage of degeneration and patient age.

Acute injury of an intervertebral disc in an elite tennis player: a case report

STUDY DESIGN

A case report.

OBJECTIVE

To present a previously not described rare case of intradiscal hematoma due to acute trauma in an elite tennis player.

SUMMARY OF BACKGROUND DATA

Several studies have demonstrated a high frequency of radiological changes in the spine of athletes, especially in sports with high loads on the back. Signs of disc degeneration without disc herniation have frequently been found in magnetic resonance imaging (MRI) studies of the spine of athletes. It has also been shown that radiological abnormalities of the spine in young athletes are correlated to back pain.

METHODS

An elite male tennis player experienced pain in the right buttock after a backhand stroke. He was successfully treated for hip problems and started to play competitive tennis, 2 weeks later. After few games, a backhand stroke again resulted in intense pain projected in the os coccyx region. At examination, there were no neurologic disturbances. At palpation over the spinal processes (Springing test) of L1-L2, the patient experienced intense pain projected to the os coccyx region.

RESULTS

MRI examination showed an injured L1-L2 disc with fluid inside the disc with a signal similar to blood. Four additional MRI examinations were performed 2 weeks and 2 years after the injury until disc degeneration is formed. Radiograph examination before and 2 years after the injury is available.

CONCLUSION

In conclusion, trauma in athletes can cause intradiscal hematoma, which probably is a new etiology for disc degeneration. Also that sudden onset of pain in the hip or the gluteal region may be caused by referred pain due to a disc lesion. Intradiscal hematoma can be visualized using MRI.

T2 relaxation times of intervertebral disc tissue correlated with water content and proteoglycan content

STUDY DESIGN

Human and bovine cadaver study in which biochemical measurements and magnetic resonance (MR) imaging of intervertebral discs were correlated.

OBJECTIVE

To measure the correlations between T2 relaxation time with water and proteoglycan (PG) content of intervertebral discs.

SUMMARY OF BACKGROUND DATA

Measuring T2 relaxation times may provide an accurate noninvasive method of detecting changes in disc water content and biochemistry due to aging or degeneration. Previous studies to validate the use of T1 or T2 relaxation times of intervertebral disc tissue have used MR relaxometers, lower field strength imagers, and in 1 case a 1.5-T imager. The dependence of T2 relaxation times on water and PG content needs further validation in high field clinical MR imagers.

METHODS

Multiecho MR images were obtained in 14 calf and 5 human cadaver discs. T2 relaxation times were calculated voxel by voxel for nucleus and anulus regions by fitting the decay of the signal intensity to an exponential model. Water and PG content were measured in samples of nucleus and anulus corresponding to the location of the T2 measurements. T2 relaxation times for calf and human specimens were correlated with water or PG content by regression analysis.

RESULTS

T2 relaxation times correlated significantly with water content in human nucleus pulposus, human anulus fibrosus, and calf anulus. T2 relaxation time correlated significantly with PG content only in the calf anulus. When the human and calf nucleus and anulus specimens were combined, T2 relaxation times correlated strongly with water (R = 0.81, P < 0.001) and less strongly with PG (R = 0.57, P < 0.001) content.

CONCLUSION

T2 relaxation times of intervertebral disc anulus fibrosus and nucleus pulposus correlate strongly with water content and weakly with PG content.

Lumbar disc localization and labeling with a probabilistic model on both pixel and object features

Repeatable, quantitative assessment of intervertebral disc pathology requires accurate localization and labeling of the lumbar region discs. To that end, we propose a two-level probabilistic model for such disc localization and labeling. Our model integrates both pixel-level information, such as appearance, and object-level information, such as relative location. Utilizing both levels of information adds robustness to the ambiguous disc intensity signature and high structure variation. Yet, we are able to do efficient (and convergent) localization and labeling with generalized expectation-maximization. We present accurate results on 20 normal cases (96%) and a promising extension to a pathology case.

Changes in T2 relaxation times associated with maturation of the human intervertebral disk

BACKGROUND AND PURPOSE

By calculating T2 relaxation times for intervertebral disks, we tested the hypothesis that disk water concentration increases between the first and second decades of life.

MATERIALS AND METHODS

In subjects younger than 10 years old (group 1) and subjects between 19 and 20 years old (group 2), a sagittal MR image of the lumbar spine was obtained with a modified 3D fast spin-echo (FSE) multi-echo sequence. T2 relaxation times for each voxel were calculated by fitting a logarithmic regression to the signal intensity in images at 16 different echo times. T2 times were averaged for each spinal disk in each group and differences tested for statistical significance by analysis of variance (ANOVA). T2 times along the vertical axis of the disk at the midline were plotted and inspected for evidence of a central lower signal intensity region (CLSIR) in the 2 groups. We tested the differences between groups for significance with the Student t test.

RESULTS

Maps of T2 relaxation times showed different patterns in groups 1 and 2. The mean T2 relaxation times in each disk level in group 1 ranged from 74-95 ms and in group 2, from 91-119 ms. Differences between the 2 groups were significant (P<.001, ANOVA, P=.0002, Student t test of means); differences between levels were not. In group 2, development of a CLSIR was significantly more common than in group 1 (P=.0001, Student t test).

CONCLUSIONS

T2 increases in the intervertebral disk between the first and second decades of life.

Imaging intervertebral disc degeneration

Magnetic resonance imaging provides excellent anatomic detail of spinal tissues, but fails to provide the type of information that permits a definitive diagnosis in many patients with back pain. New imaging strategies that can be applied to the study of intervertebral disc degeneration include diffusion-weighted imaging, magnetic resonance imaging, diffusion tensor imaging, magnetic resonance spectroscopy, functional magnetic resonance imaging, dynamic computed tomography and magnetic resonance imaging, and T2 relaxometry. With dynamic imaging, the relative motions of normal and degenerated lumbar motion segments can be evaluated noninvasively. With further evaluation of the technique, hypermobile segments may be distinguishable from those with normal relative motion. T2 measurements obtained by T2 relaxometry appear to have important advantages with regard to spinal imaging because this modality provides a continuous and objective measure of the content of free water in the disc, which decreases with aging and degeneration. Anatomic imaging of the spine is highly accurate in the evaluation of nonmechanical causes of back pain and less beneficial in the evaluation of back pain that is due to mechanical causes. The development of functional imaging strategies of the spine will likely improve the management of patients with back pain. This article outlines the current magnetic resonance imaging protocols for intervertebral disc degeneration, indicates deficiencies in current imaging, and describes functional imaging strategies for the spine that will likely improve the evaluation of patients with back pain. It also reviews recent published articles on magnetic resonance imaging and computed tomographic imaging of the spine and details the results of studies that have explored the future potential of spine imaging.

Single lamellar mechanics of the human lumbar anulus fibrosus

The mechanical behavior of the entire anulus fibrosus is determined essentially by the tensile properties of its lamellae, their fiber orientations, and the regional variation of these quantities. Corresponding data are rare in the literature. The paper deals with an in vitro study of single lamellar anulus lamellae and aims to determine (i) their tensile response and regional variation, and (ii) the orientation of lamellar collagen fibers and their regional variation. Fresh human body-disc-body units (L1-L2, n=11) from cadavers were cut midsagittally producing two hemidisc units. One hemidisc was used for the preparation of single lamellar anulus specimens for tensile testing, while the other one was used for the investigation of the lamellar fiber orientation. Single lamellar anulus specimens with adjacent bone fragments were isolated from four anatomical regions: superficial and deep lamellae (3.9+/-0.21 mm, mean +/- SD, apart from the outer boundary surface of the anulus fibrosus) at ventro-lateral and dorsal positions. The specimens underwent cyclic uniaxial tensile tests at three different strain rates in 0.15 mol/l NaCl solution at 37 degrees C, whereby the lamellar fiber direction was aligned with the load axis. For the characterization of the tensile behavior three moduli were calculated: E(low) (0-0.1 MPa), E(medium) (0.1-0.5 MPa) and E(high) (0.5-1 MPa). Additionally, specimens were tested with the load axis transverse to the fiber direction. From the second hemidisc fiber angles with respect to the horizontal plane were determined photogrammetrically from images taken at six circumferential positions from ventral to dorsal and at three depth levels. Tensile moduli along the fiber direction were in the range of 28-78 MPa (regional mean values). Superficial lamellae have larger E(medium) (p=0.017) and E(high) (p=0.012) than internal lamellae, and the mean value of superficial lamellae is about three times higher than that of deep lamellae. Tensile moduli of ventro-lateral lamellae do not differ significantly from the tensile moduli of dorsal lamellae, and E(low) is generally indifferent with respect to the anatomical region. Tensile moduli transverse to the fiber direction were about two orders of magnitude smaller (0.22+/-0.2 MPa, mean +/- SD, n=5). Tensile properties are not correlated significantly with donor age. Only small viscoelastic effects were observed. The regional variation of lamellar fiber angle phi is described appropriately by a regression line |phi|=23.2 + 0.130 x alpha (r(2)=0.55, p<0.001), where alpha is the polar angle associated with the circumferential position. The single anulus lamella may be seen as the elementary structural unit of the anulus fibrosus, and exhibits marked anisotropy and distinct regional variation of tensile properties and fiber angles. These features must be considered for appropriate physical and numerical modeling of the anulus fibrosus.

A pilot study of the prevalence of lumbar disc degeneration in elite athletes with lower back pain at the Sydney 2000 Olympic Games

OBJECTIVES

To observe the prevalence of lumbar intervertebral disc degeneration in elite athletes as compared with published literature of changes seen in non-athletes-that is, normal population.

METHODS

The lumbar spines of 31 Olympic athletes who presented to the Olympic Polyclinic with low back pain and/or sciatica were examined using magnetic resonance imaging. Three criteria were looked at: (a) the loss of disc signal intensity; (b) the loss of disc height; (c) the presence of disc displacement. The results were then recorded and correlated with the lumbar levels.

RESULTS

The disc signal intensity was progressively reduced the more caudal the disc space. It was most common at the L5/S1 level, and, of the abnormal group, 36% (n = 11) showed the most degenerative change. Disc height reduction was also found to be most common at the L5/S1 level. However, the most common height reduction was only mild. A similar trend of increased prevalence of disc herniation was noted with more caudal levels. At the L5/S1 level, 58% were found to have an element of disc displacement, most of which were disc bulges. Compared with changes seen in the normal population (non-athletes) as described in the literature, disc degeneration defined by the above criteria was found to be significantly more severe in these Olympic athletes.

CONCLUSIONS

Although the study was limited, the results suggest that elite athletes have a greater prevalence and greater degree of lumbar disc degeneration than the normal population. A more detailed follow up study should be considered to investigate which particular training activities have the most impact on the lumbar spine, and how to modify training methods so as to avoid the long term sequelae of degenerative disc disease of the lumbar spine.

Diurnal T2 value changes in the lumbar intervertebral discs

AIM

To investigate if there is any in vivo diurnal T2 value changes in the nucleus pulposus in normal and degenerated lumbar intervertebral discs.

MATERIALS AND METHODS

Eighteen volunteers (16 men, two women) with no symptoms related to lumbar disease were imaged in the morning before beginning daily work and in the evening after finishing work. Sagittal fast spin-echo T2-weighted images were obtained, following spin-echo transverse imaging for T2 analysis.

RESULTS

The normal disc group (n=71) showed statistically significant diurnal T2 value changes (p<0.001), whilst the degenerating disc group (n=19) showed no significant diurnal changes. The normal disc group up to age 34 years showed statistically significant diurnal T2 value changes. However no significant changes were demonstrated after the age 35 years.

CONCLUSION

Statistically significant diurnal T2 value changes in the normal lumbar intervertebral discs were demonstrated. Disappearance of the diurnal T2 value changes in the normal discs after the age 35 years was revealed for the first time and thought to be an aspect of aging, not caused by degeneration.

Correlation of diffusion in lumbar intervertebral disks with occlusion of lumbar arteries: a study in adult volunteers

PURPOSE

To evaluate the correlation of the diffusion values in lumbar intervertebral disks with lumbar artery status and the degree of disk degeneration.

MATERIALS AND METHODS

Sagittal T2-weighted images of the lumbar spine were obtained in 37 asymptomatic volunteers aged 22-68 years. The apparent diffusion coefficient (ADC) of 98 lumbar intervertebral disks was determined, and two-dimensional time-of-flight magnetic resonance angiography was performed on the corresponding 98 lumbar artery pairs (total arteries = 196). The degree of disk degeneration and the status of lumbar arteries were evaluated independently by two radiologists. ADC calculations were performed on the basis of the average signal intensities of the selected region of interest in lumbar disks. The association between ADC values of disks, the disk degeneration, and the status of lumbar arteries of the same level were analyzed with analysis of covariance, and pairwise analysis between groups (Scheffé post hoc multiple comparison) was performed with statistical software. P values less than .01 were considered significant.

RESULTS

The lumbar arterial status correlated strongly with the diffusion values of intervertebral disks, and the ADC values decreased with higher degrees of arterial narrowing. The correlation between disk degeneration and diffusion was not significant. Eight severely degenerated disks with normal lumbar artery status and diffusion values were found.

CONCLUSION

Impaired flow in lumbar arteries is significantly associated with decreased diffusion in lumbar disks and may play an important role in disk degeneration.

Magnetic resonance imaging measurement of relaxation and water diffusion in the human lumbar intervertebral disc under compression in vitro

STUDY DESIGN

Twelve lumbar intervertebral disc specimens were imaged with magnetic resonance imaging to estimate relaxation constants, T1 and T2, and tissue water diffusion, before and after applying compression.

OBJECTIVES

The objectives of the study were to measure T1, T2, and water diffusion for differences with loading state, region of the disc (anulus fibrosus or nucleus pulposus), and grade of degeneration.

SUMMARY OF BACKGROUND DATA

Magnetic resonance imaging can be used qualitatively to estimate water content and degeneration of the intervertebral disc. Beyond structural information of images, the relaxation times T1 and T2 may contain information on the changes occurring with degeneration. A modified spin-echo sequence can be used to estimate tissue water diffusion in cartilage and disc specimens with the ability to measure anisotropy.

METHODS

Specimens were imaged in a 1.5-Tesla clinical scanner. T1, T2, and water diffusion were estimated from midsagittal images. Magnetic resonance imaging parameters were calculated before and after axial loading. The measured T1, T2, and D (diffusion coefficient) were compared before and after compression, and for the diffusion data, also by direction to consider anisotropy.

RESULTS

For the T1 data, a significant difference was found by region, nucleus > anulus, and loading state, loaded > unloaded. For the T2 values, there was a significant difference by region, nucleus > anulus, and Thompson grade. For diffusion, significant differences were found by region, nucleus > anulus, Thompson grade, direction of diffusion, and state of compression, loaded > unloaded.

CONCLUSIONS

This study demonstrated that magnetic resonance imaging can be used to measure significant changes in T1, T2, or diffusion in intervertebral disc specimens by region, loading condition, or Thompson grade.

Apparent diffusion coefficient in thoracolumbar intervertebral discs of healthy young volunteers

Apparent diffusion coefficient values (ADC) of healthy intervertebral discs of young volunteers in the thoracolumbar spine were determined using a single-shot EPI sequence. ADC(z) was in the lumbar spine slightly higher than ADC(x) or ADC(y). In vivo diffusion measurements of intervertebral discs may offer a novel diagnostic tool to evaluate disc diseases in early phases.

Disc degeneration and cervical instability. Correlation of magnetic resonance imaging with radiography

STUDY DESIGN

An imaging study was designed to evaluate disc degeneration and segmental instability in the cervical spine.

OBJECTIVES

To compare the magnetic resonance imaging assessment of disc degeneration with the conventional plain radiographic evaluation of cervical segmental instability.

SUMMARY OF BACKGROUND DATA

No studies have been conducted to investigate the association of disc degeneration with cervical instability.

METHODS

Two hundred sixty consecutive patients with suspected cervical spine disorders were analyzed for horizontal and angular displacements on lateral flexion and extension radiographs and disc degeneration on T2-weighted magnetic resonance images of the cervical vertebrae.

RESULTS

In all intervertebral levels, the grade of disc degeneration increased significantly (P < 0.01) with age. Cervical instability was identified in 151 segments (14.5%) and correlated with Grade 1 and Grade 2 degeneration in the intervertebral discs (P < 0.01).

CONCLUSIONS

Cervical segmental instability may indicate early degeneration of intervertebral disc in the cervical vertebrae.

Plain film evaluation of degenerative disk disease at the lumbosacral junction

OBJECTIVE

Diagnosing degenerative disk disease (DDD) at the lumbosacral junction (LSJ) on plain films is often difficult, compared with other disk levels. The purpose of this study was to determine whether criteria for diagnosis of DDD at the LSJ can be established for plain films.

DESIGN AND PATIENTS

We retrospectively reviewed 100 lumbar MRI scans of patients who also had lumbar plain films. Using MRI as the reference standard, the LSJ was classified as normal (n=35) or exhibiting mild (n=45) or severe (n=20) DDD by two radiologists using accepted criteria. Measurements were performed on the plain films by two other radiologists and the average measurements were tabulated according to the three categories of DDD defined by MRI. Plain film measurements included the anterior and posterior disk heights (ADH, PDH), Farfan's ratio, determined by adding ADH to PDH and dividing that number by the measured anteroposterior (AP) length of the inferior end plate of L5 [(ADH+PDH)/AP length of L5], and lumbosacral angle (LSA). Subsequently, five additional radiologists interpreted the radiographs by visual inspection only, for DDD at the LSJ, both before and, several weeks later, after being provided with the quantitative data for normal versus DDD.

RESULTS AND CONCLUSION

There was a statistically significant difference between normal disk and increasing severity of DDD on radiographs using the parameters of PDH and Farfan's ratio. There was no statistically significant difference regarding ADH or LSA. Diagnostic accuracy by visual inspection was not significantly altered using the quantitative data for interpretation of DDD (68% correct before, 69.5% correct after). Analysis of results indicates that PDH is the most reliable and easily used criterion for detection of DDD at the LSJ. A PDH < or =5.4 mm on plain lateral film indicates DDD; PDH > or =7.7 mm indicates the absence of DDD on plain film.

Effect of Nd:YAG laser on experimental disc degeneration. Part I. Biochemical and radiographical analysis

Intervertebral disc herniation is an important health problem from both the social and economic aspect. It is often accompanied by a decrease in the content of water and proteoglycan (PG). The present study was undertaken to elucidate the effect of neodymium-yttrium-aluminum-garnet (Nd:YAG) laser on degenerated disc tissue. In this study a ventral disc herniation model in guinea pigs was performed to study the effects of ND:YAG laser on degenerated disc with low water and PG content. Effect of ND:YAG laser on degenerated cervical disc tissue is examined from the aspects of biochemistry and radiology. In the acute period water, PG, and collagen content decreased due to the ablative effect of ND:YAG laser on disc tissue. When changes in the degenerated disc in the post-laser chronic period were compared with degenerated disc findings, statistically significant changes could not be be found. From the results of this study, there is no question that the Nd:YAG laser offers many potential benefits, it remains to be proven whether or not this is of real benefit in the treatment of patients with degenerated disc disease.

Disc degeneration of pediatric patients in lumbar MRI

Magnetic resonance imaging (MRI) is widely used in pediatric spinal disorders, but the prevalence of associated lumbar disc degeneration (DD) has not been evaluated previously. In this study we investigated whether children with suspected spinal disease had increased tendency to early DD. We analyzed lumbar MRI scans of 32 patients and 49 control subjects under 15 years old. Only four patients (13%) had DD on T2-weighted MRI and they were all over 10 years old. Eleven subjects (22%) in the control group had DD. It seems that disc degeneration is seldom found in patients under 10 years old.

Lumbar disc degeneration and segmental instability: a comparison of magnetic resonance images and plain radiographs of patients with low back pain

We analyzed disc space height, angular displacement, tilting movement, and horizontal displacement in 109 patients with low back pain and/or sciatica, on plain radiographs of the lumbar spine. These parameters were compared with the grade of disc degeneration as evaluated by magnetic resonance imaging with the aim of studying lumbar segmental instability. Disc space height decreased in proportion to the grade of disc degeneration. Angular displacement was significantly less with severe disc degeneration, accompanied by a tendency to stabilization of the motion segment. Tilting movement and horizontal displacement did not correlate with the grade of disc degeneration. Lumbar segmental instability was recognized at all levels even in individuals who appeared to be normal or to have mild disc degeneration. The incidence of lumbar segmental instability at the L3-4 level was significantly higher in patients with normal discs or mild disc degeneration. At the L4-5 and L5-S levels it did not differ between different grades of disc degeneration.

Age-related MRI changes at 0.1 T in cervical discs in asymptomatic subjects

The age-dependent occurrence of cervical degenerative changes was studied using 0.1 T MRI in 89 asymptomatic volunteers aged 9 to 63 years. The degree of DD (disc darkening on T2*-weighted images), disc protrusions and prolapses, narrowing of disc spaces, dorsal osteophytes and spinal canal stenosis were assessed. Abnormalities were commoner in older subjects, 62% of being seen in those over 40 years old. In subjects aged less than 30 years there were virtually no abnormalities. DD was the most common abnormality, seen in 10% of discs; 57% DD was in subjects aged over 40. DD at the C5/6 level was the most common finding. No differences in abnormal findings between males and females was observed, nor any statistically significant association between DD and other abnormalities. Thus, DD begins later age in the cervical spine than in the lumbar region. Asymptomatic degenerative changes are common on MRI in the cervical spine after 30 years of age.

Correlating magnetic resonance imaging with the biochemical content of the normal human intervertebral disc

Magnetic resonance imaging was used to determine the T2 relaxation times of prepared proteoglycan solutions and of normal human intervertebral disc tissue from the annulus fibrosus (AF) and nucleus pulposus (NP). The collagen, proteoglycan, and water contents of the disc tissue samples were determined by biochemical assays after they were scanned. Correlations among 1/T2, collagen, proteoglycan, and water contents of the tissue samples and among 1/T2, water, and proteoglycan contents of the proteoglycan solutions were calculated. A moderate negative correlation between 1/T2 and water content was noted for the tissue samples, and a very high negative correlation was found between 1/T2 and water content for the proteoglycan solutions. The very high positive correlation between 1/T2 and proteoglycan content of the proteoglycan solutions is probably due to this negative correlation between 1/T2 and water content. There was no significant correlation between 1/T2 and proteoglycan content of the tissues. The moderate positive correlation between 1/T2 and collagen content is probably due to the high negative correlation between collagen content and water content. No significant correlation was found between the collagen and proteoglycan contents of the tissues. Thus it appears that the data confirm previous reports in the literature that the collagen of the disc tissue functions to control its water content.

High-intensity zone: a diagnostic sign of painful lumbar disc on magnetic resonance imaging

The prevalence, validity and reliability of high-intensity zones in the annulus fibrosus seen on T2-weighted magnetic resonance images of patients with intractable low-back pain were determined. This sign was readily recognized by two independent observers. It occurred in 28% of 500 patients undergoing magnetic resonance imaging for back pain. The presence of a high-intensity zone correlated significantly with the presence of Grade 4 annular disruption and with reproduction of the patient's pain. Its sensitivity as a sign of either annular disruption or pain was modest but its specificity was high, and its positive predictive value for a severely disrupted, symptomatic disc was 86%. This sign is diagnostic of painful internal disc disruption.

Differentiation of proliferating from resting cartilage in human fetal nasal septum by magnetic resonance imaging

Magnetic Resonance Imaging (MRI) has been used for the characterization of human fetal nasal septa. The images were made from fixed fetal heads from spontaneous abortions of different gestational age. The "in-plane" resolution of the images (at a pixel size of 312 x 312 microns2) allowed a detailed anatomical analysis of the midfacial structures of the fetal heads. In T2-weighted midsagittal sections a low signal intensity region of the septal cartilage could be seen. This part was shown to consist of immature proliferating cartilage by histochemical methods and contrasted to mature resting tissue at the rim of the septum. Direct comparison of the MR images with histological sections demonstrated the potential of MRI in pre- and postoperative evaluation of patients requiring surgical reconstruction of either traumatic or congenital defects of the face.

Disc degeneration and lumbar instability. Magnetic resonance examination of 16 patients

Flexion and extension radiographs of 75 young males with low back pain disclosed abnormal segmental motion of the lumbar spine in 16 patients with translational movements in 20 intervertebral segments. These 16 patients were further investigated by magnetic resonance imaging to assess disc degeneration in the unstable segments. On T2-weighted images of the 20 segments, the disc was normal in 13 and degenerated in only 7 patients. Thus, the initial factor in lumbar instability in young patients with low back pain is not always degeneration of the disc.

Quantitative magnetic resonance imaging of vertebral bodies: a T1 and T2 study

Multiple point T1 and T2 values of 424 vertebral bodies were measured and analysed. The influence of several factors including age, sex, location in the spine and status of neighbouring discs on the measured relaxation times were evaluated. The results indicate limitations in the region of interest approach. Vertebral bodies of different age, sex and location in the spine could not be distinguished. For heterogeneous tissues a more advanced form of image analysis appears to be essential. Diurnal factors resulting from the stress of normal ambulatory activity caused increased variation in vertebral body relaxation time values.

Quantitative magnetic resonance imaging in rectal carcinoma

T1 and T2 relaxation times have been calculated in 30 patients with rectal carcinoma and seven patients with a fibrotic pelvic mass. The relaxation times were calculated using a multipoint iterative method with data from seven total saturation recovery and six spin-echo sequences. The results show that the calculated T1 relaxation value is a useful discriminant between carcinoma and pelvic fibrosis and should improve the detection of early tumour recurrence.

Quantitative tissue characterisation in pancreatic disease using magnetic resonance imaging

Twenty-nine patients, 27 of whom had either inflammatory disease of the pancreas or pancreatic tumour, were studied by magnetic resonance imaging (MRI) and computed tomography (CT). Six healthy volunteers were studied by MRI alone. The pancreatic T1 and T2 relaxation times were calculated using a multipoint iterative method with data from seven total saturation recovery and six spin echo sequences. Magnetic resonance imaging can demonstrate the normal pancreas and a variety of pathological processes greater than 1-2 cm in size, but with less spatial resolution than CT. The relaxation-time results indicated no significant discrimination between chronic pancreatitis and pancreatic tumour. A significant elevation in the relaxation times was observed, however, in those patients with calcific chronic pancreatitis compared with the non-calcific chronic pancreatitic group and normal controls, suggesting a different pathophysiology for the two subgroups of chronic pancreatitis. The active phase of acute pancreatitis was associated with significantly elevated relaxation times, which returned to normal levels during the resolved phase of the disease. Associated extrapancreatic fluid collections were characterised by their very long relaxation times. The problems associated with spatial resolution, respiratory motion and lack of quantitative tissue characterisation suggest that MRI of the pancreas, using present methods, is unlikely to contribute to the overall management of patients with exocrine pancreatic disease.

Reproducibility of relaxation and spin-density parameters in phantoms and the human brain measured by MR imaging at 1.5 T

The reproducibility of T1, T2, and proton density, measured in phantoms and the human brain was evaluated by proton imaging techniques. The sequence used to derive T1 and density values was a multiple-saturation recovery which consists of four pairs of 90 degrees pulses, followed by a 180 degrees phase reversal pulse, generating four T1-weighted images. T2 was derived from a multiple-echo sequence, generating four T2-weighted images. The data were analyzed by fitting the pixel intensities to the respective equations by means of nonlinear multiparameter least-squares analysis. Short-term reproducibility between four consecutive scans was evaluated to be 1-4% depending on location with a phantom covering the entire span of physiologic T1 and T2 values. A second phantom containing a series of identical samples served to study the dependence of the apparent T1 and T2 on position, both radially and axially, with respect to magnet isocenter. Reproducibility across the field of view was found to be better than 7% (T1 and T2). This phantom was further used to evaluate effects of long-term reproducibility, which at each location varied from 5-14% (T1) and 2-10% (T2). Finally, interinstrument reproducibility, tested by means of the same protocol on three different instruments, all operating at the same magnetic field and using largely identical hardware for each location, was found to be 1-14% (T1) and 2-10% (T2). The positional dependence of the apparent relaxation times appears to be systematic and may be due to variations in the effective field, caused by magnet and rf inhomogeneity. Finally, brain tissue relaxation and spin-density data were determined using the same protocol in 37 scans performed on 27 normal volunteers. The tissues analyzed were putamen, thalamus, caudate nucleus, centrum semiovale, internal capsule, and corpus callosum. Excellent accordance was further obtained between left and right hemispheres.

A method for the clinical measurement of relaxation times in magnetic resonance imaging

A method for the determination of relaxation times in clinical magnetic resonance images is described. Three components are measured: the spin-lattice (T1) and spin-spin (T2) relaxation times and the proton density (M infinity). These components are separated in the algorithm to give increased tissue discrimination. Multiple data points are used to minimise error and increase reproducibility. Errors that arise in imaging data because of the short sequence repetition periods are considered and a technique for their reduction described. Clinical results obtained using the method are reviewed. These results demonstrate the clinical utility of the technique.