Analysis of magnetic resonance images from normal and degenerate lumbar intervertebral discs

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.

[Evaluation of the intervertebral disc spaces with a low dose radiographic system]

PURPOSE

EOS is a new low dose radiographic system based on micro-pattern gaseous detector technology. The purpose was to compare the value of EOS and MRI in the evaluation of degenerative intervertebral disc disease.

METHODS AND MATERIALS

Thirty one fresh lumbar discs were studied with EOS, MRI, and discography. Finally, the discs were dissected for macroscopy. They were graded according to their degenerative level using each imaging modality. Osteophytes, herniations, calcifications, loss of disc height, discographic tears or ligamentous ossification were recorded as anomalies. Morphometric data were measured from the cadaveric sections and low-dose radiographs.

RESULTS

Thirty nine percent of the discs were narrowed, with a high correlation between EOS and MRI. Anterior and posterior disc margins were respectively depicted in 22% and 64% of cases with EOS vs 84% and 97% with MRI. MRI showed a disc herniation in 9 cases. The correlation between EOS and MRI was poor for the analysis of anterior and posterior disc margins, and disc herniation. Modic 2 abnormalities were present in 19% of disc levels at MRI. Osteophytes were visible in 65% of disc levels with EOS. The density of the disc space was homogeneous in 65% of cases. In the remaining cases, intradiscal calcifications were detected with EOS and confirmed at macroscopy.

CONCLUSION

The EOS low dose images allow a good characterisation of disc abnormalities. Especially, intervertebral disc height, density variations and finer bony details (osteophytes) were detected with high confidence. EOS is a promising new low dose radiographic method for 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.

Value of magnetic resonance imaging and discography in determining the level of cervical discectomy and fusion

STUDY DESIGN

The correlation between magnetic resonance imaging and discography of the cervical spine in degenerative disc disease was studied. In addition, the results of cervical discectomy and fusion were evaluated.

OBJECTIVES

To compare the value of cervical magnetic resonance imaging versus discography in selecting the level for discectomy and fusion and to evaluate the surgical outcome.

SUMMARY OF BACKGROUND DATA

The value of magnetic resonance imaging and discography in patients with cervical discogenic pain is less clear. Also, the status of a hypointense signal (dark) cervical disc and/or a small herniated disc on magnetic resonance imaging has not been determined.

METHODS

The magnetic resonance imaging studies and discography followed by computed tomography in 55 patients with cervical discogenic pain were evaluated. Surgical planning was based on the complete information of clinical symptoms, magnetic resonance imaging, and discography as well as computed tomography discography. Anterior cervical discectomy and keystone fusion was performed. Postoperative pain relief was assessed by the patients, and the follow-up radiographs were viewed by an independent reviewer. The overall surgical outcome was evaluated using Odom's criteria.

RESULTS

There were 161 disc levels that successfully underwent cervical discography with 79 positive levels. A positive discography result was found in 63% of dark (hypointense signal) discs and 45% of speckled discs. Fifty-nine percent of small herniated discs and 59% of torn discs had a positive discography, respectively. There were 100 abnormal cervical discs on magnetic resonance imaging. Magnetic resonance imaging had a false-positive rate of 51% and a false-negative rate of 27%. Successful cervical fusion was achieved in 95% of patients, and the overall satisfactory result was 76%.

CONCLUSIONS

Magnetic resonance imaging can identify most of the painful discs but still has relatively high false-negative and false-positive rates. There is a high chance that hypointense signal and small herniated discs are the pain generators, but they are not always symptomatic. Discography can save the levels from being unnecessarily fused. The combination of clinical symptoms, magnetic resonance imaging, and discography provides the most information for decision making and can improve the management of cervical discogenic pain.

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.

Structure and function of the lumbar intervertebral disk in health, aging, and pathologic conditions

This report is a comprehensive review of the basic and clinical science relating to the morphology and function of the intervertebral disc of the lumbar spine. The purpose is to review the anatomy, physiology, and biomechanics of the intervertebral disc of the lumbar spine in health, with aging, and in pathologic conditions. The complex morphology and ultrastructure of the intervertebral disc of the lumbar spine in the human provide the critical elements that permit normal mobility and transmission of force through the vertebral column. Alterations in this structure are manifest in a variety of clinical conditions routinely encountered in orthopaedic physical therapy practice. These structural and biomechanical changes are related to degenerative changes that occur in association with aging and trauma. Knowledge of the gross morphology and ultrastructure of the intervertebral disc and pathobiologic processes underlying associated conditions is essential to orthopaedic practice.

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.

Lumbar disc high-intensity zone. Correlation of magnetic resonance imaging and discography

STUDY DESIGN

This study correlated a specific lumbar disc abnormality described as the high-intensity zone observed on high-field magnetic resonance imaging with discography.

OBJECTIVES

To analyze the significance of high-intensity zones in lumbar discs of symptomatic patients with low back/radicular pain.

SUMMARY OF BACKGROUND DATA

Aprill and Bogduk described an 86% incidence of concordantly painful discography in lumbar discs exhibiting a posterior high-intensity zone on T2-weighted magnetic resonance imaging studies performed on back pain sufferers. They assert that the high-intensity zone is a reliable marker of discogenic pain in symptomatic subjects.

METHODS

Consecutive cases of lumbar spine high-field magnetic resonance imaging using T2-weighted images on symptomatic patients followed by discography at all high-intensity zone levels and at non-high-intensity zone control levels were reviewed until 100 high-intensity zone discs in 63 patients were found. Seventeen lifelong asymptomatic (for low back/radicular pain) adults were also scanned as magnetic resonance imaging controls. All magnetic resonance scans and discograms were agreed on by at least two of the radiologist authors.

RESULTS

Eighty-seven of 100 of the high-intensity zone discs proved concordantly painful at discography. All 87 painful and concordant discs exhibited abnormal morphology with anular tears extending either well into or through the outer third of the anulus fibrosus. Sixty-five of 67 non-high-intensity zone control discs were nonconcordant and of lower sensation intensity than the high-intensity zone discs. Only one high-intensity zone was found in the control subjects.

CONCLUSIONS

In patients with symptomatic low back pain, the high-intensity zone is a reliable marker of painful outer anular disruption.

Quantitative MR imaging of lumbar intervertebral disc and vertebral bodies: methodology, reproducibility, and preliminary results

Since relaxation times are influenced by the hydration of the tissue and the chemical environment of the water molecules, T1 and T2 measurements (quantitative MRI) could be used as an indicator for the water content and the biochemical composition of lumbar intervertebral discs. The discriminating power of quantitative MRI for tissue characterization in individuals (for clinical diagnosis) and in cohorts (e.g. for investigations on disc physiology or composition) relies on the reproducibility in relation to the expected tissue differences. We therefore investigated the reproducibility in vitro (lumbar spine phantom) and in vivo (10 volunteers). To estimate the differences between normal and pathologic tissues in vivo, 100 normal and 20 herniated intervertebral discs were examined by quantitative MRI in a first application of our method. The relaxation times were calculated from a set of 20 images obtained with five single-slice/multi-echo sequences at different TR values on a commercial whole-body system (1.5 T). We have found a satisfactory reproducibility in vitro (T1: 1.9%; T2: 6.2%), while the reproducibility was less satisfactory in vivo (T1: 16.4%; T2: 13.4%). Calculated from theses values, differences in relaxation times of various tissues must exceed 486 ms for T1 and 24 ms for T2 (tolerance limits) to allow discrimination with a 95% confidence in individuals. We observed statistically significant (p = 0.001) mean differences between normal (n = 100) and herniated (n = 20) intervertebral discs (delta T1: 196 ms; delta T2: 15 ms). Although statistical significant in cohorts, a discrimination of normal and herniated intervertebral discs is limited by quantitative MRI in individuals, since the differences are smaller than the tolerance limits necessary for a reliable clinical diagnosis. However, our results indicate that variations in the disc hydration and/or composition can be noninvasively detected by quantitative MRI in studies of cohorts with sufficient accuracy.

A simple model for the function of proteoglycans and collagen in the response to compression of the intervertebral disc

The nucleus pulposus of the intervertebral disc exerts a pressure which enables it to support axial compression when contained by the annulus fibrosus. The disc was modelled as a thick-walled cylindrical pressure vessel in which the nucleus was contained radially by the annulus. As a result, the stress in the annulus had radial (compressive) as well as tangential (tensile) components. The radial stress at a given point in the annulus was considered to be balanced by the internal pressure which is expected to arise from the attraction of water by proteoglycans. There was a reasonable agreement between the calculated radial stress distribution and published results on the distribution of water within the annulus. As the internal pressure is expected to be isotropic, the annulus was expected to contribute to the axial resistance to compression of the disc; this contribution would be equal, in magnitude, to the radial stress. Predictions of the pressure distribution within the annulus were similar to published experimental measurements made in the radial and axial directions. The tangential stress within the annulus was considered to arise from the restoring stress in its strained collagen fibrils.

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.

Imaging methods in examining the anatomy and function of the lumbar spine

Conventional plain radiography, with or without flexion and extension images, is still the primary imaging modality of the lumbosacral spine despite the modern imaging methods. This is due to the simplicity of the technique and the good anatomical detail of the bone structure. Despite the limited information content of the plain radiographs, they are needed to serve as anatomical maps in connection with computed tomography or magnetic resonance imaging. In some institutions magnetic resonance imaging is now the primary modality for the evaluation of the lumbosacral spine, in others computed tomography and myelography still have a primary role, often depending on the availability of the devices. Magnetic resonance imaging clearly shows the anatomy of the discs, spinal nerves and dural sac. The diagnostic precision achieved with computed tomography in the evaluation of a herniated disc may also be achieved with magnetic resonance imaging. Differentiation of epidural scar from recurrent or residual disc herniation in patients with previous laminectomy, which with computed tomography myelography has been unreliable, can be evaluated by using magnetic resonance imaging enhanced with gadolinium-DTPA. The identification of facet joint disease is, however, less efficient with magnetic resonance imaging. Computed tomography and magnetic resonance imaging are probably nearly comparable in their accuracy in the evaluation of patients with sciatica. If cost and availability were not limiting factors, magnetic resonance imaging could provide an excellent screening technique for identifying individuals who would benefit from the identification of risks or preclinical disease or from institution of preventive measures.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Magnetic resonance imaging in spinal disorders

The value of M.R.I. in diagnosing spinal disorders has been tested in a series of 100 patients. C.T., myelography, discography and the operative findings are compared with the M.R.I. findings. The results indicate that M.R.I. is a valuable diagnostic investigation.

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.