Diffusion tensor imaging of cervical spinal cord: A quantitative diagnostic tool in cervical spondylotic myelopathy

Microstructural Characteristics of Cervical Spinal Cord Using High Angular Resolution Diffusion Imaging (HARDI) and Tractography in Healthy Subjects

PURPOSE

This study aimed to characterize spinal cord microstructure in healthy subjects using high angular resolution diffusion imaging (HARDI) and tractography.

METHODS

Forty-nine healthy subjects (18-50 years, divided into 2 age groups) were included in a prospective study. HARDI of the cervical spinal cord were acquired using a 3T MRI scanner with: 64 directions, b‑value: 1000s/mm2, reduced field-of-view (zonally magnified oblique multi-slice), and opposed phase-encoding directions. Distortions were corrected using the FSL software package. Fiber tracking was performed using a deterministic approach with DSI-Studio software. Tensor metrics-fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD)-and tractography statistics were then extracted, at each spine level, and after grey-white matter segmentation.

RESULTS

The microstructural organization of the spinal cord differed between upper and lower cervical spine levels: FA, and AD significantly decreased (p < 0.001); and RD significantly increased (p < 0.05) in lower levels, demonstrating changes in axonal density and myelinated fibers according to a cranio-caudal axis. FA, MD, AD, and RD values were significantly higher in spinal cord white matter (p < 0.0001), compared to grey matter. Age was not associated with a significant change in FA, while there is for MD, AD and RD (p < 0.05). Spinal cord tractography may provide information on the architectural organization of fibers and spinal tracts.

CONCLUSION

This study proposes a database in cervical spinal cord HARDI, allowing to study the microstructural organization of the spinal cord in healthy subjects, and providing a foundation for comparison with patients presenting spinal cord pathologies.

Metal artifact reduction around cervical spine implant using diffusion tensor imaging at 3T: A phantom study

PURPOSE

Diffusion MRI continues to play a key role in non-invasively assessing spinal cord integrity and pre-operative injury evaluation. However, post-operative Diffusion Tensor Imaging (DTI) acquisition of patients with metal implants results in severe geometric distortion. We propose and demonstrate a method to alleviate the technical challenges facing the acquisition of DTI on post-operative cases and longitudinal evaluation of therapeutics.

MATERIAL AND METHODS

The described technique is based on the combination of the reduced Field-Of-View (rFOV) strategy and the phase segmented EPI, termed rFOV-PS-EPI. A custom-built phantom based on a cervical spine model with metal implants was used to collect DTI data at 3 Tesla scanner using: rFOV-PS-EPI, reduced Field-Of-View single-shot EPI (rFOV-SS-EPI), and conventional full FOV techniques including SS-EPI, PS-EPI, and readout-segmented EPI (RS-EPI). Geometric distortion, SNR, and signal void were assessed to evaluate images and compare the sequences. A two-sample t-test was performed with p-value of 0.05 or less to indicate statistical significance.

RESULTS

The reduced FOV techniques showed better capability to reduce distortions compared to the Full FOV techniques. The rFOV-PS-EPI method provided DTI images of the phantom at the level of the hardware whereas the conventional rFOV-SS-EPI is useful only when the metal is approximately 20 mm away. In addition, compared to the rFOV-SS-EPI technique, the suggested approach produced smaller signal voids area as well as significantly reduced geometric distortion in Circularity (p < 0.005) and Eccentricity (p < 0.005) measurements. No statistically significant differences were found for these geometric distortion measurements between the rFOV-PS-EPI DTI sequence and conventional structural T2 images (p > 0.05).

CONCLUSION

The combination of rFOV and a phase-segmented acquisition approach is effective for reducing metal-induced distortions in DTI scan on spinal cord with metal hardware at 3 T.

Metal Artifact Reduction Around Cervical Spine Implant Using Diffusion Tensor Imaging at 3T: A Phantom Study

Diffusion MRI continues to play a key role in non-invasively assessing spinal cord integrity and pre-operative injury evaluation. However, post-operative Diffusion Tensor Imaging (DTI) acquisition of a patient with a metal implant results in severe geometric image distortion. A method has been proposed here to alleviate the technical challenges facing the acquisition of DTI in post-operative cases and to evaluate longitudinal therapeutics. The described technique is based on the combination of the reduced Field-Of-View (rFOV) strategy and the phase segmented acquisition scheme (rFOV-PS-EPI) for significantly mitigating metal-induced distortions. A custom-built phantom based on spine model with metal implant was used to collect high-resolution DTI data at 3 Tesla scanner using a home-grown diffusion MRI pulse sequence, rFOV-PS-EPI, single-shot (rFOV-SS-EPI), and the conventional full FOV techniques including SS-EPI, PS-EPI, and the readout-segmented (RS-EPI). This newly developed method provides high-resolution images with significant reduced metal-induced artifacts. In contrast to the other techniques, the rFOV-PS-EPI allows DTI measurement at the level of the metal hardware whereas the current rFOV-SS-EPI is useful when the metal is approximately 20 mm away. The developed approach enables high-resolution DTI in patients with metal implant.

Clinical and Research MRI Techniques for Assessing Spinal Cord Integrity in Degenerative Cervical Myelopathy-A Scoping Review

BACKGROUND

Degenerative cervical myelopathy (DCM) manifests as the primary cause of spinal cord dysfunction and is non-traumatic, chronic and progressive in nature. Decompressive surgery is typically utilised to halt further disability and neurological dysfunction. The limitations of current diagnostic options surrounding assessment and prognostic potential render DCM still largely a clinical diagnosis.

AIMS

To outline the limitations of current diagnostic techniques, present evidence behind novel quantitative MRI (qMRI) techniques for assessing spinal cord integrity in DCM and suggest future directions.

METHOD

Articles published up to November 2021 were retrieved from Medline, EMBASE and EBM using key search terms: spinal cord, spine, neck, MRI, magnetic resonance imaging, qMRI, T1, T2, T2*, R2*, DTI, diffusion tensor imaging, MT, magnetisation transfer, SWI, susceptibility weighted imaging, BOLD, blood oxygen level dependent, fMRI, functional magnetic resonance imaging, functional MRI, MRS, magnetic resonance spectroscopy.

RESULTS

A total of 2057 articles were retrieved with 68 articles included for analysis. The search yielded 2 articles on Quantitative T1 mapping which suggested higher T1 values in spinal cord of moderate-severe DCM; 43 articles on DTI which indicated a strong correlation of fractional anisotropy and modified Japanese Orthopaedic Association scores; 15 articles on fMRI (BOLD) which demonstrated positive correlation of functional connectivity and volume of activation of various connections in the brain with post-surgical recovery; 6 articles on MRS which suggested that Choline/N-acetylaspartate (Cho/NAA) ratio presents the best correlation with DCM severity; and 4 articles on MT which revealed a preliminary negative correlation of magnetisation transfer ratio with DCM severity. Notably, most studies were of low sample size with short timeframes within 6 months.

CONCLUSIONS

Further longitudinal studies with higher sample sizes and longer time horizons are necessary to determine the full prognostic capacity of qMRI in DCM.

Quantitative Analysis in Cervical Spinal Cord Injury Patients Using Diffusion Tensor Imaging and Tractography

Objective

To investigate the clinical usefulness of diffusion tensor imaging (DTI) and tractography in the prediction of outcomes after traumatic cervical spinal cord injury (SCI) and to assess whether the predictability is different between DTI and tractography administered before and after surgery.

Methods

Sixty-one subjects with traumatic cervical SCI were randomly assigned to preop or postop groups and received DTI accordingly. Among the patients who had DTI before surgery, we assigned 10 patients who had received repeated DTI examinations at 8 weeks after injury to the follow-up group. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were obtained from DTI, and imaginary fiber and crossing fiber numbers were calculated from the tractography. Neurological status and functional status were assessed at 4 and 8 weeks after SCI.

Results

The neurologic and functional statuses of both groups improved after 4 weeks. Out of the initial 61 patients who were enrolled in the study, the failure rate of DTI image analysis was significantly higher in the postop group (n=17, 41.5%) than in the preop group (n=6, 20%). The FA values and fiber numbers in the preop group tended to be higher than those in the postop group, whereas ADC values were lower in the preop group. When comparing the tractographic findings in the follow-up group, imaginary fiber numbers at the C6 and C7 levels and crossing fiber numbers from the C3 to C6 levels were significantly decreased after surgery. Several DTI and tractographic parameters (especially the ADC value at the C4 level and imaginary fiber numbers at the C6 level) showed significant correlations with neurologic and functional statuses in both the preop and postop groups. These findings were most prominent when DTI and physical examination were simultaneously performed.

Conclusion

Preoperative DTI and tractography demonstrated better FA and ADC values with lower interpretation failure rates than those obtained after surgery, whereas postoperative data significantly reflected the patient’s clinical state at the time of evaluation. Therefore, DTI and tractography could be useful in predicting clinical outcomes after traumatic cervical SCI and should be interpreted separately before and after spine surgery.

Magnetic resonance diffusion tensor imaging of acute spinal cord injury in spinal trauma

Background

It was important to develop a non-invasive imaging technique for early evaluation of spinal cord integrity after injury; MRI was the method of choice for evaluation of any cord abnormalities. However, some patients have symptoms with no detectable abnormalities by MRI. The purpose of our study was to assess the role of diffusion tensor MRI in evaluating the integrity of spinal cord fibers in case of spinal trauma.

Results

Out of the studied 30 patients, conventional MRI revealed abnormalities in the spinal cord in 23 patients (76.67%), diffusion tensor tractography revealed abnormalities in the spinal cord in 27 patients (90%), the mean FA value at the level of injury (0.326±0.135) was less than the mean FA value (0.532 ± 0.074) in control group (p value < 0.001), and the mean ADC value at the level of injury (1.319 ± 0.378) was less than the mean ADC value (1.734 ± 0.768) in the control group. FA was sensitive than ADC in the detection of the spinal cord abnormalities with a sensitivity of 93.33% versus 67.66% respectively.

Conclusion

DTI can be used to detect structural changes of spinal cord white matter fibers in acute spinal cord injury. A significant decrease of fractional anisotropy and apparent diffusion coefficient has been found at the site of spinal cord injury.

Quantitative Evaluation of the Diffusion Tensor Imaging Matrix Parameters and the Subsequent Correlation with the Clinical Assessment of Disease Severity in Cervical Spondylotic Myelopathy

Study Design

We performed a prospective observational study of 52 patients who were clinically suspected of cervical spondylotic myelopathy (CSM), based on the modified Japanese Orthopaedic Association (mJOA) score, and were referred for magnetic resonance imaging (MRI) of the cervical spine.

Purpose

To evaluate the quantitative parameters of the diffusion tensor imaging (DTI) matrix (fractional anisotropy [FA] and apparent diffusion coefficient [ADC] values) and determine the subsequent correlation with the clinical assessment of disease severity in CSM.

Overview of Literature

Conventional MRI is the modality of choice for the identification of cervical spondylotic changes and is known to have a low sensitivity for myelopathy changes. DTI is sensitive to disease processes that alter the water movement in the cervical spinal cord at a microscopic level beyond the conventional MRI.

Methods

DTI images were processed to produce FA and ADC values of the acquired axial slices with the regions of interest placed within the stenotic and non-stenotic segments. The final quantitative radiological derivations were matched with the clinical scoring system.

Results

Total 52 people (24 men and 28 women), mean age 53.16 years with different symptoms of myelopathy, graded as mild (n=11), moderate (n=25), and severe (n=16) as per the mJOA scoring system, underwent MRI of the cervical spine with DTI. In the most stenotic segments, the mean FA value was significantly lower (0.5009±0.087 vs. 0.655.7±0.104, p<0.001), and the mean ADC value was significantly higher (1.196.5±0.311 vs. 0.9370±0.284, p<0.001) than that in the non-stenotic segments. The overall sensitivity in identifying DTI metrics abnormalities was more with FA (87.5%) and ADC (75.0%) than with T2 weighted images (25%).

Conclusions

In addition to the routine MRI sequences, DTI metrics (FA value better than ADC) can detect myelopathy even in patients with a mild grade mJOA score before irreversible changes become apparent on routine T2 weighted imaging and thus enhance the clinical success of decompression surgery.

Microstructural Changes in Compressed Cervical Spinal Cord Are Consistent With Clinical Symptoms and Symptom Duration

STUDY DESIGN

A prospective study.

OBJECTIVE

To investigate the association between microstructural changes measured by diffusion tensor imaging (DTI) and clinical symptoms and their duration in patients with cervical spondylotic myelopathy (CSM) affected by single level.

SUMMARY OF BACKGROUND DATA

No report was reported regarding the association between the microstructural changes and the symptoms and their duration at single-level spinal cord compression.

METHODS

Twenty-nine consecutive patients with CSM and 29 normal subjects were enrolled in this study. DTI with tractography was performed on the cervical spinal cord. Clinical symptoms were evaluated using modified Japanese Orthopaedic Association (mJOA) scores for each patient, and the duration of clinical symptoms was noted based on the earliest instance of limb pain or numbness or weakness or bladder dysfunction. Mean fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values were calculated from tractography images.

RESULTS

The mean FA value of the cervical compressed spinal cord was significantly lower than the FA of the normal population (P < 0.001). The mean ADC value in the cervical compressed spinal cord was obviously higher than those of normal cervical spinal cord (P < 0.001). In the CSM patients, a significant positive association was observed between FA values and mJOA scores (P < 0.001). However, there were a notable negative association between mJOA scores and ADC values (P < 0.001), and between mJOA scores and symptom duration (P < 0.001).

CONCLUSION

These results illustrate DTI can measure the micostructural changes of cervical spinal cord and DTI parameters are potential biomarkers for spinal cord dysfunction in patients with CSM.

LEVEL OF EVIDENCE

3.

Apparent diffusion coefficient as an indicator of spinal cord compression due to anterior atlanto-axial subluxation in rheumatoid arthritis patients

PURPOSE

The aim of this retrospective study was to evaluate the apparent diffusion coefficient (ADC) as a potential parameter of spinal cord damage in cervical spine instability at the atlanto-axial level in rheumatoid arthritis (RA) patients.

METHODS

One hundred and six RA patients were included in the study. MRI examinations were performed with 1.5T scanner. The ADC was measured at six locations in the cervical spinal cord at the height of the first six cervical vertebrae (from C-1 to C-6). The ADC values were assessed in 2 groups: with and without anterior atlanto-axial subluxation (AAS) diagnosed on plain radiographs. Correlations between ADC values and radiographic measurements and RA activity indicators were evaluated.

RESULTS

The ADC values at C1 level (ADC₁) was higher in the group with anterior AAS than in the group without AAS (p < 0.001). Statistically significant moderate positive correlation between ADC₁ and anterior atlanto-axial diameter interval AADI (rho = 0.58; p < 0.008) was found as well as statistically significant weak negative correlation between ADC₁ and posterior atlanto-axial diameter interval PADI (rho =  - 0.34; p < 0.008).

CONCLUSIONS

The conducted study demonstrates the applicability of the ADC maps in the identification of spinal cord compression due to anterior AAS in RA patients. The results encourage the practical use of the ADC as an additional parameter in the qualification for surgical treatment. These slides can be retrieved under Electronic Supplementary Material.

Diffusion Tensor Imaging and Fiber Tractography Reveal Significant Microstructural Changes of Cervical Nerve Roots in Patients with Cervical Spondylotic Radiculopathy

OBJECTIVE

To delineate the fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of patients with cervical spondylotic radiculopathy by diffusion tensor imaging and fiber bundle tracing.

METHODS

Thirty patients with cervical spondylotic radiculopathy and 24 healthy volunteers were assessed using the International Standards for Neurological Classification of Spinal Cord Injury scale. All subjects underwent conventional sagittal T1- and T2-weighted imaging and horizontal 3-dimensional T2 driven equilibrium radiofrequency reset pulse and diffusion tensor imaging scan. The ADC and FA values were measured in the cervical nerve at most stenotic segment and heterolateral nonstenotic segment of patients.

RESULTS

Fiber tractography revealed thinned and sparse nerve roots and disruption of the fiber bundles in patients with cervical spondylotic radiculopathy. The FA values of C5-C8 in healthy volunteers or heterolateral nonstenotic nerve of patients with cervical spondylotic radiculopathy were significantly greater than those of the stenotic cervical segments of patients with cervical spondylotic radiculopathy (both P < 0.01). Furthermore, the ADC values of C5-C8 in healthy volunteers or heterolateral nonstenotic nerve of patients with cervical spondylotic radiculopathy were significantly lower than those of the stenotic cervical segments of cervical spondylotic radiculopathy patients (both P < 0.01).

CONCLUSIONS

Fiber tractography is capable of delineating microstructural changes of cervical nerve roots and cervical spondylotic radiculopathy exhibits significant changes in FA and ADC values.

Outcome factors in surgically treated patients for cervical spondylotic myelopathy

Context/Objective: To investigate prospectively preoperative parameters that might be related to the outcome of surgically treated patients for cervical spondylotic myelopathy (CSM).Design: Prospective study.Setting: Single Center in Ioannina, Greece.Participants: Thirty-six patients were included in the study. There were 21 males and 15 females, mean age 50.8 years, range 39-70 years. The mean BMI was 27.3.Outcome measures: From each patient, we recorded age, sex, BMI, symptoms, duration of symptoms, comorbidities, lifestyle, myelopathy grade based on MRI and levels of compression. All patients completed the modified JOA (mJOA) and NPE questionnaires preoperatively and at 1, 3, 12 months and 5-years postoperatively.Results: The mean mJOA score significant improved from 10.8 ± 1.9 points preoperatively to 16.6 ± 2.2 points at 12 months postoperatively. The mean mJOA score at 5-years postoperatively was 15.5 ± 3 points. The difference was still highly significant. The mean NPE score significant improved from 59.8 ± 12.2 points preoperatively to 28.2 ± 8.5 points at 1 month, to 35.8 ± 8.1 points at 3 month and to 28.2 ± 8.8 points at 12 months postoperatively. Younger patients had significant higher baseline mJOA scores and significant higher mJOA scores 5-year postoperatively. No correlation was found between sex, BMI, symptom duration, baseline mJOA or myelopathy grade and outcome at 12 months or 5-year postoperatively.Conclusion: Age was highly predictive factor of outcome for patients undergoing surgical treatment of CSM.

Minimisation of Signal Intensity Differences in Distortion Correction Approaches of Brain Magnetic Resonance Diffusion Tensor Imaging

OBJECTIVES

To evaluate the effects of signal intensity differences between the b0 image and diffusion tensor imaging (DTI) in the image registration process.

METHODS

To correct signal intensity differences between the b0 image and DTI data, a simple image intensity compensation (SIMIC) method, which is a b0 image re-calculation process from DTI data, was applied before the image registration. The re-calculated b0 image (b0_ext) from each diffusion direction was registered to the b0 image acquired through the MR scanning (b0_nd) with two types of cost functions and their transformation matrices were acquired. These transformation matrices were then used to register the DTI data. For quantifications, the dice similarity coefficient (DSC) values, diffusion scalar matrix, and quantified fibre numbers and lengths were calculated.

RESULTS

The combined SIMIC method with two cost functions showed the highest DSC value (0.802 ± 0.007). Regarding diffusion scalar values and numbers and lengths of fibres from the corpus callosum, superior longitudinal fasciculus, and cortico-spinal tract, only using normalised cross correlation (NCC) showed a specific tendency toward lower values in the brain regions.

CONCLUSION

Image-based distortion correction with SIMIC for DTI data would help in image analysis by accounting for signal intensity differences as one additional option for DTI analysis.

KEY POINTS

• We evaluated the effects of signal intensity differences at DTI registration. • The non-diffusion-weighted image re-calculation process from DTI data was applied. • SIMIC can minimise the signal intensity differences at DTI registration.

Spinal meningiomas: 61 cases with predictors of early postoperative surgical outcomes

BACKGROUND

Spinal meningiomas are benign, well-circumscribed and slowly-growing intradural tumors that compress the spinal cord. Hereby, a retrospective review of 61 spinal meningioma cases evaluated in terms of demographic, clinical, pathological and radiological features to predict the early postoperative functional outcomes.

METHODS

Patients' records and MRI images of all the histologically confirmed spinal meningioma cases that underwent surgical resection at two university hospitals from January 2005 to June 2016 were retrospectively reviewed. Demographic data, clinical findings, radiological features and pathology reports were reviewed. Univariate and multivariate logistic regression analyses were used to evaluate the impact of each factor on the early 3-month post-surgical functional outcome. A receiver operating characteristic (ROC) curve was used to predict the power of the model.

RESULTS

Sixty-one cases of spinal meningiomas were operated: 13 males (21%) and 48 females (79%). Mean age was 60.5 years and ranged from 24 to 92 years. Patients presented with back pain (57%), motor deficits (47.5%), sensory deficits (18%) and sphincteric dysfunction (11.5%). One case (1.6%) showed an additional extradural growth. There were 40 thoracic, nine cervical, five cervicothoracic, five thoracolumbar, and two lumbar cases. Only four cases (6.6%) showed atypical pathological features (WHO grade II). At 3-month follow-up, 46 patients (75.4%) had either functionally improved or remained stable. Fifteen patients (24.6%) had "worse" functional outcome. Three variables showed statistically significant odds ratio for improved outcomes (OR): pre-surgical motor deficit (OR=5; P=0.005); presurgical sensory disturbance (OR=3.5; P=0.026); pre-surgical myelopathy (OR=3.5; P=0.026). Multivariate analysis showed increased OR for cross-sectional ratio, pre-surgical myelopathy, pre-surgical radiculopathy and non-cervical location of tumor (1.59, 3.46, 3.2, 1.63/3.56, respectively). Although none has reached statistical significance (P>0.05), the receiver operating characteristic (ROC) curve showed an area under the curve (AUC) of 0.74.

CONCLUSIONS

The independent predictors of the early postoperative functional outcomes of spinal meningioma resections may include pre-surgical motor deficit, sensory deficit and myelopathy.

Signal intensity ratio on magnetic resonance imaging as a prognostic factor in patients with cervical compressive myelopathy

Patients with intramedullary signal intensity (SI) changes have a poor prognosis after surgical decompression in cervical compressive myelopathy (CCM); however, some patients show no clear relationship between the SI and postsurgical prognosis. This discrepancy may be because no comprehensive and proper quantitative evaluation exists to assess SI on magnetic resonance imaging (MRI). The purpose of this study was prospectively to evaluate the correlation between the clinical features, neurological outcome of patients with CCM, and the quantitative assessment of SI changes preoperatively and postoperatively, and the correlation with SI severity.A total of 112 patients with CCM at 1 or 2 levels underwent anterior cervical discectomy and fusion. We quantitatively analyzed MR signal changes on T1-weighted MR images (T1WI), gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) contrast-enhanced T1WI, and T2-weighted MR images (T2WI) using the signal intensity ratio (SIR). We evaluated the correlations between various variables and neurological outcome using the Japanese Orthopedic Association (JOA) scale, and the severity of SI change by grade (i.e., grade 0 ["none"], grade 1 ["light"], and grade 2 ["bright on T2WI"]).Significant differences between the 3 grades existed in symptom duration, preoperative JOA score, SIR on T2WI, and JOA recovery ratio. The JOA recovery ratio was negatively correlated with symptom duration and the SIR on T2WI, and positively correlated with the preoperative JOA score and cord compression ratio, but not with the SIR on T1WI and contrast-enhanced T1WI. On the postoperative 12-month follow-up MRI, the JOA recovery ratio and SIR on T2WI of the SI reversal patients were better than those of the nonreversal patients. On multiple regression analysis, the SIR on T2WI was the main significant prognostic factor of surgical outcome.The grading system on T2WI provided reliable predictive information for neurological outcome. Quantitative alterations in the SI on preoperative and postoperative T2WI, but not T1WI or contrast-enhanced T1WI, reflected the clinical features, surgical outcomes, and the correlation with SI severity. The patients with a longer duration of symptoms, lower cord compression ratio, severe myelopathy, intense signal change (i.e., grade 2) on the spinal cord, and an SIR greater than 1.55 had a poor recovery after a surgical operation.