Diffusion tensor tractography in the head-and-neck region using a clinical 3-T MR scanner

Correlations of diffusion tensor imaging and clinical measures with spinal cord cross-sectional area measurements in pediatric spinal cord injury patients

PURPOSE

The purpose of this work was to employ a semi-automatic method for measuring spinal cord cross-sectional area (SCCSA) and investigate the correlations between diffusion tensor imaging (DTI) metrics and SCCSA for the cervical and thoracic spinal cord for typically developing pediatric subjects and pediatric subject with spinal cord injury.

METHODS

Ten typically developing (TD) pediatric subjects and ten pediatric subjects with spinal cord injury (SCI) were imaged using a Siemens Verio 3 T MR scanner to acquire DTI and high-resolution anatomic scans covering the cervical and thoracic spinal cord (C1-T12). SCCSA was measured using a semi-automated edge detection algorithm for the entire spinal cord. DTI metrics were obtained from whole cord axial ROIs at each vertebral level. SCCSA measures were compared to DTI metrics by vertebral level throughout the entire cord, and above and below the injury site. Correlation analysis was performed to compare SCCSA, DTI and clinical measures as determined by the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) examination.

RESULTS

In subjects with SCI, FA and SCCSA had a positive correlation (r = 0.81, P < 0.01), while RD and SCCSA had a negative correlation (r = -0.68, P = 0.02) for the full spinal cord. FA and SCCSA were correlated above (r = 0.56, P < 0.01) and below (r = 0.54, P < 0.01) the injury site. TD subjects showed negative correlations between AD and SCCSA (r = -0.73, P = 0.01) and RD and SCCSA (r = -0.79, P < 0.01).

CONCLUSION

The ability to quickly and effectively measure SCCSA in subjects with SCI has the potential to allow for a better understanding of the progression of atrophy following a SCI. Correlations between cord cross section and DTI metrics by vertebral level suggest that imaging inferior and superior to lesion may yield useful information for diagnosis and prognosis.

Diffusion tensor imaging of fetal spinal cord: feasibility and gestational-age-related changes

OBJECTIVES

Diffusion tensor imaging (DTI) of the fetal brain is a relatively new technique that allows evaluation of white matter tracts of the central nervous system throughout pregnancy, as well as in certain pathological conditions. The objectives of this study were to evaluate the feasibility of DTI of the spinal cord in utero and to examine gestational-age (GA)-related changes in DTI parameters during pregnancy.

METHODS

This was a prospective study conducted between December 2021 and June 2022 in the LUMIERE Platform, Necker-Enfants Malades Hospital, Paris, France, as part of the LUMIERE SUR LE FETUS trial. Women with a pregnancy between 18 and 36 weeks of gestation without fetal or maternal abnormality were eligible for inclusion. Sagittal diffusion-weighted scans of the fetal spine were acquired, without sedation, using a 1.5-Tesla magnetic resonance imaging scanner. The imaging parameters were as follows: 15 non-collinear direction diffusion-weighted magnetic-pulsed gradients with a b-value 700 s/mm2 and one B0 image without diffusion-weighting; slice thickness, 3 mm; field of view (FOV), 36 mm; phase FOV, 1.00; voxel size, 4.5 × 2.8 × 3 mm3 ; number of slices, 7-10; repetition time, 2800 ms; echo time, minimum; and total acquisition time, 2.3 min. DTI parameters, including fractional anisotropy (FA) and apparent diffusion coefficient (ADC), were extracted at the cervical, upper thoracic, lower thoracic and lumbar levels of the spinal cord. Cases with motion degradation and those with aberrant reconstruction of the spinal cord on tractography were excluded. Pearson's correlation analysis was performed to evaluate GA-related changes of DTI parameters during pregnancy.

RESULTS

During the study period, 42 pregnant women were included at a median GA of 29.3 (range, 22.0-35.7) weeks. Five (11.9%) patients were not included in the analysis because of fetal movement. Two (4.8%) patients with aberrant tractography reconstruction were also excluded from analysis. Acquisition of DTI parameters was feasible in all remaining cases (35/35). Increasing GA correlated with increasing FA averaged over the entire fetal spinal cord (r, 0.37; P < 0.01), as well as at the individual cervical (r, 0.519; P < 0.01), upper thoracic (r, 0.468; P < 0.01), lower thoracic (r, 0.425; P = 0.02) and lumbar (r, 0.427; P = 0.02) levels. There was no correlation between GA and ADC averaged over the entire spinal cord (r, 0.01; P = 0.99) or at the individual cervical (r, -0.109; P = 0.56), upper thoracic (r, -0.226; P = 0.22), lower thoracic (r, -0.052; P = 0.78) or lumbar (r, -0.11; P = 0.95) levels.

CONCLUSIONS

This study shows that DTI of the spinal cord is feasible in normal fetuses in typical clinical practice and allows extraction of DTI parameters of the spinal cord. There is a significant GA-related change in FA in the fetal spinal cord during pregnancy, which may result from decreasing water content as observed during myelination of fiber tracts occurring in utero. This study may serve as a basis for further investigation of DTI in the fetus, including research into its potential in pathological conditions that impact spinal cord development. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Probabilistic tractography of the extracranial branches of the trigeminal nerve using diffusion tensor imaging

PURPOSE

The peripheral course of the trigeminal nerves is complex and spans multiple bony foramen and tissue compartments throughout the face. Diffusion tensor imaging of these nerves is difficult due to the complex tissue interfaces and relatively low MR signal. The purpose of this work is to develop a method for reliable diffusion tensor imaging-based fiber tracking of the peripheral branches of the trigeminal nerve.

METHODS

We prospectively acquired imaging data from six healthy adult participants with a 3.0-Tesla system, including T2-weighted short tau inversion recovery with variable flip angle (T2-STIR-SPACE) and readout segmented echo planar diffusion weighted imaging sequences. Probabilistic tractography of the ophthalmic, infraorbital, lingual, and inferior alveolar nerves was performed manually and assessed by two observers who determined whether the fiber tracts reached defined anatomical landmarks using the T2-STIR-SPACE volume.

RESULTS

All nerves in all subjects were tracked beyond the trigeminal ganglion. Tracts in the inferior alveolar and ophthalmic nerve exhibited the strongest signal and most consistently reached the most distal landmark (58% and 67%, respectively). All tracts of the inferior alveolar and ophthalmic nerve extended beyond their respective third benchmarks. Tracts of the infraorbital nerve and lingual nerve were comparably lower-signal and did not consistently reach the furthest benchmarks (9% and 17%, respectively).

CONCLUSION

This work demonstrates a method for consistently identifying and tracking the major nerve branches of the trigeminal nerve with diffusion tensor imaging.

Update on MR Imaging of Soft Tissue Tumors of Head and Neck

This article reviews soft tissue tumors of the head and neck following the 2020 revision of WHO Classification of Soft Tissue and Bone Tumours. Common soft tissue tumors in the head and neck and tumors are discussed, along with newly added entities to the classification system. Salient clinical and imaging features that may allow for improved diagnostic accuracy or to narrow the imaging differential diagnosis are covered. Advanced imaging techniques are discussed, with a focus on diffusion-weighted and dynamic contrast imaging and their potential to help characterize soft tissue tumors and aid in distinguishing malignant from benign tumors.

Visualization of nerve fibers around the carotid bifurcation with use of a 9.4 Tesla microscopic magnetic resonance diffusion tensor imaging with tractography

Background

Precise imaging of nerves have been challenging in the head and neck region, mainly due to low spatial resolution. Here, we investigated how nerves in the head and neck region could be visualized using an ultra‐high magnetic field MR system.

Methods

We used formol‐carbol‐fixed human cadaveric necks and obtained MR diffusion tensor images (DTIs) using a 9.4 Tesla (T) ultra‐high magnetic field MR system. Afterward, we prepared tissue sections and checked the anatomic relationships between the neurons and the carotid artery in order to confirm that the visualized fibers are indeed neuron fibers.

Results

We were able to identify nerves, including the vagus nerve, the hypoglossal nerve, and the spinal‐accessory nerve. Hematoxylin‐eosin stained histological sections confirmed neuron fibers in the same anatomic position.

Conclusion

This technique has the feasibility to be applied for a more accurate anatomic understanding, maybe even close to a histological level.

High-contrast high-resolution imaging of posttraumatic mandibular nerve by 3DAC-PROPELLER magnetic resonance imaging: correlation with the severity of sensory disturbance

OBJECTIVE

Magnetic resonance neurography reveals abnormal morphologies of regenerated nerves and overgrown connective tissue in injured trigeminal nerves, suggesting neuroma formation. We hypothesized that such deformities and scar formation contribute to pain symptoms.

STUDY DESIGN

High-contrast high-resolution magnetic resonance imaging was utilized to evaluate the inferior alveolar nerve and lingual nerve following traumatic injury in 19 patients. The relationship between the morphologic classification and severity of the sensory disorder was assessed.

RESULTS

In all cases, 3-dimensional anisotropy contrast periodically rotated overlapping parallel lines with enhanced reconstruction (3DAC-PROPELLER) successfully revealed the inner structures within the lesion. The isolated type represented the normal course of the nerve isolated from scar-like tissue (8 cases), whereas the deformity type included the deformed nerve either within scar-like tissue or by itself, unassociated with surrounding scar-like tissue (9 cases). In the remaining 2 cases, the nerve tissue and scar-like tissue were incorporated. Patients with the deformity type exhibited significantly more severe pain symptoms compared with patients with the isolated type.

CONCLUSIONS

Overgrown connective tissue does not necessarily block regenerating nerves and itself may not cause pain. The morphologic findings on the 3DAC-PROPELLER were relevant to the severity of pain symptoms.

Diffusion tensor imaging of the inferior alveolar nerve using 3T MRI: a study for quantitative evaluation and fibre tracking

OBJECTIVES

Diffusion tensor imaging (DTI) can provide structural information and objective values for nerves. The aims of this study were to perform quantitative evaluation and fibre tracking of the normal inferior alveolar nerve (IAN) using DTI on 3.0-T MRI.

METHODS

DTI was applied to 92 IANs of 46 healthy volunteers. Circular regions of interest (ROIs) were placed on three different positions at the mandibular foramen, second molar and mental foramen of each nerve on apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps, and the ADC and FA of each ROI were measured. Differences in the values arising from the nerve positions were evaluated. Furthermore, fibre tracking of the IANs was performed by tractography, and the quality of visualization was evaluated.

RESULTS

There were no significant differences in the ADC and FA between the right and left sides regardless of the anteroposterior positions. Regarding differences arising from the anteroposterior measurement positions, the ADC and FA showed no significant differences (p > 0.017), except for the ADCs between the positions at the mandibular foramen and mental foramen in the left side (p = 0.0068). Overall, 70 (76%) of the 92 IANs could be visualized fully or partially by tractography.

CONCLUSIONS

The ADC and FA of the IAN were successfully obtained from healthy volunteers using DTI and were confirmed to be symmetrical regardless of the measurement positions. DTI is a feasible technique for the quantitative evaluation and visualization of the IAN.

Utility of MRI diffusion techniques in the evaluation of tumors of the head and neck

The use of diffusion-weighted imaging in the head and neck is an increasingly used technique that requires adaptation of the acquisition parameters. Parallel imaging and emerging techniques such as IVIM are playing a new role. The main indications for performing DWI are tissue characterization, nodal staging and therapy monitoring. Lower apparent diffusion coefficients have been reported in this region for malignant lesions such as SCC, lymphoma and metastatic lymph node, as opposed to higher ADC in benign lesions and lymph nodes. Follow-up and early response to treatment are reflected in an ADC increase in both primary tumor and nodal metastasis.

Diffusion tensor imaging in pediatric spinal cord injury: preliminary examination of reliability and clinical correlation

STUDY DESIGN

The design was a nonexperimental, repeated measures design.

OBJECTIVE

To examine the reliability of repeated diffusion tensor imaging (DTI) values of the pediatric cord and to compare DTI values with values obtained on the clinical examination and findings from conventional magnetic resonance imaging (MRI).

SUMMARY OF BACKGROUND DATA

DTI quantifies the diffusion of water molecules in directions parallel and transverse to the plane of neuronal axons. The unique characteristic architecture of the spinal cord allows DTI to examine the white matter and potentially separate white matter from gray matter and assess structural damage of the cord.

METHODS

Ten youths with cervical spinal cord injury (SCI) were evaluated using the International Standards for Neurological Classification of SCI (ISNCSCI) and had 2 scans using a 3.0T Siemens Verio MR scanner. The imaging protocol consisted of conventional sagittal fast spin echo T1- and T2-weighted scans, axial fast spin echo T2-weighted scans, and axial DTI acquisition. Intraclass correlation coefficient (ICC) and 95% confidence interval were calculated for mean, axial, and radial diffusivity (MD, AD, RD, respectively) and fractional anisotropy (FA). Relationships among DTI, MRI, and ISNCSCI were evaluated using Spearman correlation coefficients (rs) and differences were tested using Cohen's method.

RESULTS

There was moderate-to-strong reliability (ICC = 0.75-0.95) for MD, AD, and RD for all spinal levels. Reliability for FA for mid-C4 and between C5-C6 and C7-T1 was moderate (ICC = 0.75-0.80). Diffusivity values demonstrated moderate-to-good negative relationships (rs = -0.30 to -0.59), with 4 ISNCSCI values. FA values had a moderate-to-good (rs = 0.33-0.53) positive relationship, with 5 ISNCSCI values. Compared with MRI, DTI values had significantly stronger correlations (P ≤ 0.0001) with the majority of ISNCSCI values.

CONCLUSION

DTI values had good-to-strong reliability on repeated scans and moderate-to-good concurrent validity with clinical scores. When compared with conventional MRI, DTI values had statistically stronger correlations with the majority of values from the clinical examination.

Diffusion tensor imaging of the normal pediatric spinal cord using an inner field of view echo-planar imaging sequence

BACKGROUND AND PURPOSE

DTI in the brain has been well established, but its application in the spinal cord, especially in pediatrics, poses several challenges. The small cord size has inherent low SNR of the diffusion signal intensity, respiratory and cardiac movements induce artifacts, and EPI sequences used for obtaining diffusion indices cause eddy-current distortions. The purpose of this study was to 1) evaluate the accuracy of cervical spinal cord DTI in children using a newly developed iFOV sequence with spatially selective 2D-RF excitations, and 2) examine reproducibility of the DTI measures.

MATERIALS AND METHODS

Twenty-five typically developing subjects were imaged twice using a 3T scanner. Axial DTI images of the cervical spinal cord were acquired with this sequence. After motion correction, DTI indices were calculated using regions of interest manually drawn at every axial section location along the cervical spinal cord for both acquisitions. Various DTI indices were calculated: FA, AD, RD, MD, RA, and VR. Geometric diffusion measures were also calculated: Cp, Cl, and Cs.

RESULTS

The following average values for each index were obtained: FA = 0.50 ± 0.11; AD = 0.97 ± 0.20 × 10(-3)mm(2)/s; RD = 0.41 ± 0.13 × 10(-3)mm(2)/s; MD = 0.59 ± 0.15 × 10(-3)mm(2)/s; RA = 0.35 ± 0.08; VR = 0.03 ± 0.00; Cp = 0.13 ± 0.07; Cl = 0.29 ± 0.09; and Cs = 0.58 ± 0.11. The reproducibility tests showed moderate to strong ICC in all subjects for all DTI parameters (ICC>0.72).

CONCLUSIONS

This study showed that accurate and reproducible DTI parameters can be estimated in the pediatric cervical spinal cord using an iFOV EPI sequence.

Biologic imaging of head and neck cancer: the present and the future

While anatomic imaging (CT and MR imaging) of HNC is focused on diagnosing and/or characterizing the disease, defining its local extent, and evaluating distant spread, accurate assessment of the biologic status of the cancer (cellularity, growth rate, response to nonsurgical chemoradiation therapy, and so forth) can be invaluable for prognostication, planning therapy, and follow-up of lesions after therapy. The combination of anatomic and biologic imaging techniques can thus provide a more comprehensive evaluation of the patient. The purpose of this work was to review the present and future clinical applications of advanced biologic imaging techniques in HNC evaluation and management. As part of the biologic imaging array, we discuss MR spectroscopy, diffusion and perfusion MR imaging, CTP, and FDG-PET scanning and conclude with exciting developments that hold promise in assessment of tumor hypoxia and neoangiogenesis.

Different imaging techniques in the head and neck: Assets and drawbacks

In this review, the gold standard imaging techniques for the head and neck and the latest upcoming techniques are presented, by comparing computed tomography (CT), magnetic resonance imaging and positron emission tomography-CT, as well as ultrasound, depending on the examined area. The advantages and disadvantages of each examination protocol are presented. This article illustrates the connection between the imaging technique and the examined area. Therefore, the head and neck area is divided into different sections such as bony structures, nervous system, mucous membranes and squamous epithelium, glandular tissue, and lymphatic tissue and vessels. Finally, the latest techniques in the field of head and neck imaging such as multidetector CT, dual-energy CT, flash CT, magnetic resonance angiography, spectroscopy, and diffusion tensor tractography using 3 tesla magnetic resonance are discussed.