Magnetic resonance 4D flow analysis of cerebrospinal fluid dynamics in Chiari I malformation with and without syringomyelia

Objective

To analyse cerebrospinal fluid (CSF) hydrodynamics in patients with Chiari type I malformation (CM) with and without syringomyelia using 4D magnetic resonance (MR) phase contrast (PC) flow imaging.

Methods

4D-PC CSF flow data were acquired in 20 patients with CM (12 patients with presyrinx/syrinx). Characteristic 4D-CSF flow patterns were identified. Quantitative CSF flow parameters were assessed at the craniocervical junction and the cervical spinal canal and compared with healthy volunteers and between patients with and without syringomyelia.

Results

Compared with healthy volunteers, 17 CM patients showed flow abnormalities at the craniocervical junction in the form of heterogeneous flow (n?=?3), anterolateral flow jets (n?=?14) and flow vortex formation (n?=?5), most prevalent in patients with syringomyelia. Peak flow velocities at the craniocervical junction were significantly increased in patients (?15.5?±?11.3 vs. ?4.7?±?0.7 ?cm/s in healthy volunteers, P?P?Conclusions 4D-PC flow imaging allowed comprehensive analysis of CSF flow in patients with Chiari I malformation. Alterations of CSF hydrodynamics were most pronounced in patients with syringomyelia.

Key Points

? Analysis of CSF flow is important in patients with Chiari I malformation ? 4D-PC MRI allows analysis of CSF in patients with Chiari I. ? Chiari I patients show characteristic qualitative and quantitative alterations of CSF flow. ? Alterations of CSF hydrodynamics are most pronounced in patients with associated syringomyelia.     

Imaging of the entire cerebrospinal fluid volume with a multistation 3D SPACE MR sequence: feasibility study in patients with hydrocephalus

Objectives

To evaluate the feasibility of imaging the entire cerebrospinal fluid (CSF) volume using the SPACE MR sequence.

Methods

The SPACE sequence encompassing the brain and spine was performed at 1.5 T in 12 healthy volunteers and 26 consecutive patients with hydrocephalus. Image contrast was estimated using difference ratios in signal intensity between CSF and its background. Segmentation of CSF was performed using geometrical features and a topological assumption of CSF shapes. Subarachnoid and ventricular CSF space volumes were assessed in volunteers and patients and linear discriminant analysis was performed.

Results

Image contrast was 0.94 between the CSF and the brain and 0.90 between the CSF and the spinal cord. According to the phantom study, the accuracy of CSF volume measurement was 98.5 %. A clear distinction between patients and healthy volunteers was obtained using the linear discriminant analysis. Significant linear regression was found in healthy volunteers between ventricular (Vv) and the whole subarachnoid CSF volume (Vs) with Vv?=?0.083 Vs.

Conclusions

Imaging of the entire CSF volume is feasible in healthy volunteers and patients with hydrocephalus. CSF volume can be obtained on a whole-body scale. This approach may be of use for the diagnosis and follow-up of patients with hydrocephalus.

Key Points

? MRI assessment of CSF volume is feasible in healthy volunteers/hydrocephalus patients. ? CSF volume can be obtained on a whole-body scale. ? The ratio of subarachnoid and ventricular CSF is constant in healthy volunteers. ? CSF linear discriminant analysis can distinguish between patients and healthy volunteers. ? Entire CSF volume imaging is useful for diagnosing and following hydrocephalus.     

Intracranial artery velocity measurement using 4D PC MRI at 3 T: comparison with transcranial ultrasound techniques and 2D PC MRI

Introduction

4D phase contrast MR imaging (4D PC MRI) has been introduced for spatiotemporal evaluation of intracranial hemodynamics in various cerebrovascular diseases. However, it still lacks validation with standards of reference. Our goal was to compare blood flow quantification derived from 4D PC MRI with transcranial ultrasound and 2D PC MRI.

Methods

Velocity measurements within large intracranial arteries [internal carotid artery (ICA), basilar artery (BA), and middle cerebral artery (MCA)] were obtained in 20 young healthy volunteers with 4D and 2D PC MRI, transcranial Doppler sonography (TCD), and transcranial color-coded duplex sonography (TCCD). Maximum velocities at peak systole (PSV) and end diastole (EDV) were compared using regression analysis and Bland–Altman plots.

Results

Correlation of 4D PC MRI measured velocities was higher in comparison with TCD (r?=?0.49–0.66) than with TCCD (0.35–0.44) and 2D PC MRI (0.52–0.60). In mid-BA and ICA C7 segment, a significant correlation was found with TCD (0.68–0.81 and 0.65–0.71, respectively). No significant correlation was found in carotid siphon. On average over all volunteers, PSVs and EDVs in MCA were minimally underestimated compared with TCD/TCCD. Minimal overestimation of velocities was found compared to TCD in mid-BA and ICA C7 segment.

Conclusion

4D PC MRI appears as valid alternative for intracranial velocity measurement consistent with previous reference standards, foremost with TCD. Spatiotemporal averaging effects might contribute to vessel size-dependent mild underestimation of velocities in smaller (MCA), and overestimation in larger-sized (BA and ICA) arteries, respectively. Complete spatiotemporal flow analysis may be advantageous in anatomically complex regions (e.g. carotid siphon) relative to restrictions of ultrasound techniques.     

Comparison of Blood Flow Velocity Quantification by 4D Flow MR Imaging with Ultrasound at the Carotid Bifurcation

BACKGROUND AND PURPOSE:4D flow MR imaging is an emerging technique that allows visualization and quantification of 3D blood flow in vivo. However, representative studies evaluating its accuracy are lacking. Therefore, we compared blood flow quantification by using 4D flow MR imaging with US within the carotid bifurcation.MATERIALS AND METHODS:Thirty-two healthy volunteers (age 25.3 ± 3.4 years) and 20 patients with ≥50% ICA stenosis (age 67.7 ± 7.4 years) were examined preoperatively and postoperatively by use of 4D flow MR imaging, with complete coverage of the left and right carotid bifurcation. Blood flow velocities were assessed with standardized 2D analysis planes distributed along the CCA and the ICA and were compared with US at baseline and postoperatively in patients. In addition, we tested reproducibility and interobserver agreement of 4D MR imaging in 10 volunteers.RESULTS:Overall, 101 CCAs and 79 ICAs were available for comparison. MR imaging underestimated (P < .05) systolic CCA and ICA blood flow velocity by 26% (0.79 ± 0.29 m/s vs 1.06 ± 0.31 m/s) and 19% (0.72 ± 0.21 m/s vs 0.89 ± 0.27 m/s) compared with US. Diastolic blood flow velocities were similar for MR imaging and US (differences, 9% and 3%, respectively; not significant). Reproducibility and interobserver agreement of 4D flow MR imaging was excellent.CONCLUSIONS:4D flow MR imaging allowed for an accurate measurement of blood flow velocities in the carotid bifurcation of both volunteers and patients with only moderate underestimation compared with US. Thus, 4D flow MR imaging seems promising for a future combination with MRA to comprehensively assess ICA stenosis and related hemodynamic changes.

Digital subtraction angiography is the current reference method for the assessment of ICA stenosis,¹ but less invasive techniques such as CE-MRA and CT angiography have emerged as reliable alternatives.^2,3 A recent meta-analysis revealed a pooled sensitivity and specificity of CE-MRA of ca. 94% and 93%, respectively, indicating that accuracy is lower compared with DSA and US.² In contrast to angiography, US provides limited morphologic information but detailed information regarding velocities at the carotid bifurcation and intracranial collateral blood flow.^3,4 A combination of such information as one 3D dataset provided by 1 technique (eg, CE-MRA plus PC MR imaging), would allow for a comprehensive assessment of the carotid bifurcation.Accordingly, carotid artery blood flow could be determined by use of time-resolved 2D PC MR imaging. It was recently used to quantify blood flow in the carotid and basilar arteries in healthy participants⁵ and in extracranial and intracranial vessels in patients with ICA stenosis.⁶ This approach, however, is restricted to single 2D planes and requires individual angulation of analysis planes perpendicular to the vessel lumen. 3D cine PC MR imaging with 3-directional velocity encoding (also termed 4D flow MR imaging) overcomes these limitations and was recently validated in a model of cerebral aneurysms with laser Doppler velocimetry and computational fluid dynamics.⁷ In vivo applications allow measurement and visualization of 3D blood flow at the arterial and venous vessels, the heart, and the liver.^8–10 Moreover, 4D flow MR imaging was applied to visualize complex 3D blood flow at the carotid bifurcation, analyze the shape of velocity-time curves, measure flow velocities at the CCA, and investigate the in vivo distribution of wall shear stress along the carotid bifurcation in volunteers and patients.^11,12Therefore, 4D MR imaging is an exciting imaging technique that provides a wide spectrum of potentially valuable information for clinical applications. However, data comparing the measurement accuracy of 4D flow MR imaging with sonography in vivo and in a larger number of normal and diseased vessels are sparse. Previous comparisons were conducted in the CCA of 8 volunteers¹¹; the intracranial arteries of 5 volunteers and a patient¹³; and, recently, in the liver vessels of 61 participants.¹⁰ Therefore, our purpose was to test the performance of carotid 4D flow MR imaging compared with US in more than 100 carotid arteries of both healthy volunteers and patients with high-grade ICA stenosis undergoing examinations preoperatively and postoperatively. Moreover, we systematically evaluated reproducibility and interobserver agreement of 4D flow MR imaging in a subgroup of 10 healthy volunteers undergoing repeated MR imaging examinations.     

Cervical high-intensity intramedullary lesions in achondroplasia: Aetiology, prevalence and clinical relevance

Objectives

In achondroplastic patients with slight complaints of medullary compression the cervical spinal cord regularly exhibits an intramedullary (CHII) lesion just below the craniocervical junction with no signs of focal compression on the cord. Currently, the prevalence of the lesion in the general achondroplastic population is studied and its origin is explored.

Methods

Eighteen achondroplastic volunteers with merely no clinical signs of medullary compression were subjected to dynamic magnetic resonance imaging (MRI). The presence of a CHII lesion and craniocervical medullary compression in flexed and retroflexed craniocervical positions was explored. Several morphological characteristics of the craniocervical junction, possibly related to compression on the cord, were assessed.

Results

A CHII lesion was observed in 39% of the subjects and in only one of these was compression at the craniocervical junction present. Consequently, no correlation between the CHII lesion and compression could be established. None of the morphological characteristics demonstrated a correlation with the CHII lesion, except thinning of the cord at the site of the CHII lesion.

Conclusions

CHII lesions are a frequent finding in achondroplasia, and are generally unaccompanied by clinical symptoms or compression on the cord. Further research focusing on the origin of CHII lesions and their clinical implications is warranted.

Key Points

? MRI now reveals exquisite detail of the cervical spinal cord. ? Cervical cord lesions are observed in one third of the achondroplastic population. ? These lesions yield high signal intensity on T2 weighted MRI. ? They are generally unaccompanied by clinical symptoms or cord compression. ? Their aetiology is unclear and seems to be unrelated to mechanical causes.     

Postoperative pulmonary and aortic 3D haemodynamics in patients after repair of transposition of the great arteries

Objectives

To characterise aortic and pulmonary haemodynamics and investigate the correlation with post-surgical anatomy in patients with dextro-transposition of the great arteries (d-TGA).

Methods

Four-dimensional (4D) MRI was performed in 17 patients after switch repair of TGA and 12 healthy controls (age, 11.9?±?5.4 vs 23.3?±?1.6 years). Patients were divided according to the pulmonary trunk (TP) position in relation to the ascending aorta (AAo): anterior (n?=?10) and right/left anterior position (n?=?7). Analysis included visual grading (ranking 0–2) of pulmonary and aortic vortical and helical flow, flow velocity quantification, blood-flow distribution to the right and left pulmonary arteries (flow ratio rPA:lPA), and vessel lumen areas.

Results

Anterior TP position was associated with increased vortices in six out of ten patients compared with right anterior TP position (one out of seven) and controls (none). Reduced systolic lPA and TP lumina in patients resulted in significantly increased peak systolic velocities (P?<?0.001). Flow ratio rPA:lPA was more heterogeneous in patients (rPA:lPA?=?1.56?±?0.78 vs volunteers 1.09?±?0.15; P?<?0.05) with predominant flow to the rPA. Eleven patients presented increased helices in the AAo (grade 1.6).

Conclusions

Evaluation of post-surgical haemodynamics in TGA patients revealed increased vortical flow for anterior TP position, asymmetric flow and increased systolic flow velocity in the pulmonary arteries owing to reduced vascular lumina.

Key Points

? 3D phase contrast MRI with velocity encoding (4D MRI) has numerous cardiovascular applications ? 4D MRI demonstrates postoperative haemodynamics following surgery for transposition of the great arteries ? Flow visualisation depicted enhanced pulmonary vortices in the anterior pulmonary trunk ? Narrow pulmonary arterial systolic lumina resulted in increased peak systolic velocities     

Value of "functional" magnetic resonance imaging in the diagnosis of ligamentous affection at the craniovertebral junction

Introduction

Objective of this investigation was to evaluate the rotational mobility at the craniocervical junction and changes in the width of the subarachnoid space during head rotation in healthy volunteers using Magnetic Resonance Imaging (MRI).

Materials and Methods

In 30 healthy volunteers axial 3 mm Half-Fourier Acquisition Single-Shot Turbo Spin-Echo (HASTE) sequences were obtained with the subject's head in neutral position, and in maximal rotation to the left and right respectively. All MRI examinations were evaluated by two neuroradiologists in consensus. The ranges of axial rotation at C0–C2 as well as the width of the subarachnoid space in neutral, and in maximal rotated position were measured. Student's t-tests were used to compare group differences.

Results

Total range of right-to-left-rotation at C0–C2 was 59–183° with mean rotation to the right and left side of 70° (±12.7°) and 75° (±13.0°). Difference between degrees of rotation to both sides was on average 4.9° (±7.1°) with a significantly greater rotational range to the left compared to the right. In neutral position, distance between the dura and the ventral wall of the cervical spinal cord was 1.6–4.2 mm. In active rotation interface between dura and myelon was evident in 19 volunteers with unilateral contact in 7, and bilateral contact in 12 cases.

Conclusions

High variablity of rotational mobility at the craniocervical junction and attenuation of width of the subarachnoid space during head rotation are frequent findings in an asymptomatic population. Our results indicate that the assessment of these parameters is of limited diagnostic value in patients with whiplash-associated disorders.     

Application of Spatial Modulation of Magnetization to Cervical Spinal Stenosis for Evaluation of the Hydrodynamic Changes Occurring in Cerebrospinal Fluid

Objective

To evaluate the hydrodynamic changes occurring in cerebrospinal fluid (CSF) flow in cervical spinal stenosis using the spatial modulation of magnetization (SPAMM) technique.

Materials and Methods

Using the SPAMM technique, 44 patients with cervical spinal stenosis and ten healthy volunteers were investigated. The degree of cervical spinal stenosis was rated as low-, intermediate-, or high-grade. Low-grade stenosis was defined as involving no effacement of the subarachnoid space, intermediate-grade as involving effacement of this space, and high-grade as involving effacement of this space, together with compressive myelopathy. The patterns of SPAMM stripes and CSF velocity were evaluated and compared between each type of spinal stenosis and normal spine.

Results

Low-grade stenosis (n = 23) revealed displacement or discontinuity of stripes, while intermediate- (n = 10) and high-grade (n = 11) showed a continuous straight band at the stenotic segment. Among low-grade cases, 12 showed wave separation during the systolic phase. Peak systolic CSF velocity at C4-5 level in these cases was lower than in volunteers (p < .05), but jet-like CSF propulsion was maintained. Among intermediate-grade cases, peak systolic velocity at C1-2 level was lower than in the volunteer group, but the difference was not significant (p > .05). In high-grade stenosis, both diastolic and systolic velocities were significantly lower (p < .05).

Conclusion

Various hydrodynamic changes occurring in CSF flow in cervical spinal stenosis were demonstrated by the SPAMM technique, and this may be a useful method for evaluating CSF hydrodynamic change in cervical spinal stenosis.     

Characteristics of CSF Velocity-Time Profile in Posttraumatic Syringomyelia

BACKGROUND AND PURPOSE:The development of syringomyelia has been associated with changes in CSF flow dynamics in the spinal subarachnoid space. However, differences in CSF flow velocity between patients with posttraumatic syringomyelia and healthy participants remains unclear. The aim of this work was to define differences in CSF flow above and below a syrinx in participants with posttraumatic syringomyelia and compare the CSF flow with that in healthy controls.MATERIALS AND METHODS:Six participants with posttraumatic syringomyelia were recruited for this study. Phase-contrast MR imaging was used to measure CSF flow velocity at the base of the skull and above and below the syrinx. Velocity magnitudes and temporal features of the CSF velocity profile were compared with those in healthy controls.RESULTS:CSF flow velocity in the spinal subarachnoid space of participants with syringomyelia was similar at different locations despite differences in syrinx size and locations. Peak cranial and caudal velocities above and below the syrinx were not significantly different (peak cranial velocity, P = .9; peak caudal velocity, P = 1.0), but the peak velocities were significantly lower (P < .001, P = .007) in the participants with syringomyelia compared with matched controls. Most notably, the duration of caudal flow was significantly shorter (P = .003) in the participants with syringomyelia.CONCLUSIONS:CSF flow within the posttraumatic syringomyelia group was relatively uniform along the spinal canal, but there are differences in the timing of CSF flow compared with that in matched healthy controls. This finding supports the hypothesis that syrinx development may be associated with temporal changes in spinal CSF flow.

Syringomyelia is a neurologic condition characterized by the development of a syrinx, a fluid cyst in the spinal cord. It is commonly associated with conditions that obstruct spinal CSF flow such as spinal cord injury,¹ Chiari type I malformation, and spinal tumors. Syrinxes form and enlarge in either the central canal of the spinal cord or in the cord parenchyma. For a syrinx to enlarge, the laws of mechanics require that the syrinx pressure exceed the pressure in the surrounding cord tissue and spinal subarachnoid space. However, the mechanism of CSF flow into a syrinx in the presence of this reverse pressure gradient is poorly understood and remains controversial. Computational models suggest that CSF could be driven by cardiac pulsations fromthe spinal subarachnoid space into the spinal cord via periarterial spaces, including toward a syrinx.² Besides CSF, another possible source of syrinx fluid could be extracellular fluid. It has recently been shown that after spinal cord injury, the blood–spinal cord barrier is damaged for an extended time³ and fluid could hence pass from the vasculature into a syrinx. However, the source of fluid in the syrinx has yet to be identified because the chemical composition of CSF and extracellular fluid is indistinguishable.⁴Understanding the characteristics of CSF dynamics in the spinal subarachnoid space and the way they change in conditions associated with syringomyelia may help elucidate the mechanism of the disease. Characterizing CSF flow in syringomyelia may also improve clinical management because syrinx morphology from MR anatomic images alone is insufficient to predict disease progression and surgical outcomes. Current treatment techniques for posttraumatic syringomyelia, such as shunting, are associated with syrinx recurrence. Therefore, understanding the CSF flow characteristics in these patients may help in developing effective techniques to manage this complex condition.CSF flow in the spinal subarachnoid space consists of pulsatile caudal and rostral flow during systole and diastole, respectively.⁵ Caudal flow in the spinal subarachnoid space commences approximately 100 ms after the onset of systole in healthy individuals, and the timing of its onset is affected by age and CSF obstructions in the spinal subarachnoid space. Detailed mechanisms that underpin the earlier onset of peak caudal CSF are not yet well-established and may be influenced by compliance in the craniospinal system. In the spinal subarachnoid space of healthy individuals, peak caudal and cranial velocities and their onset vary with spinal level. However, these variables are different in those with Chiari malformation.⁶Despite numerous studies in the literature of CSF flow in participants with Chiari type I malformation with and without syrinxes, there is a lack of understanding of spinal CSF dynamics in those who have sustained a spinal cord injury. Therefore, this study aimed to determine the CSF velocity-time profiles adjacent to the syrinx in participants with spinal cord injury and compare them with those in healthy controls. It is hypothesized that the peak CSF velocities and timing of the profile would be significantly altered in patients with posttraumatic syringomyelia.     

The Cervical Spinal Canal Tapers Differently in Patients with Chiari I with and without Syringomyelia

BACKGROUND AND PURPOSE:The cause of syringomyelia in patients with Chiari I remains uncertain. Cervical spine anatomy modifies CSF velocities, flow patterns, and pressure gradients, which may affect the spinal cord. We tested the hypothesis that cervical spinal anatomy differs between Chiari I patients with and without syringomyelia.MATERIALS AND METHODS:We identified consecutive patients with Chiari I at 3 institutions and divided them into groups with and without syringomyelia. Five readers measured anteroposterior cervical spinal diameters, tonsillar herniation, and syrinx dimensions on cervical MR images. Taper ratios for C1–C7, C1–C4, and C4–C7 spinal segments were calculated by linear least squares fitting to the appropriate spinal canal diameters. Mean taper ratios and tonsillar herniation for groups were compared and tested for statistical significance with a Kruskal-Wallis test. Inter- and intrareader agreement and correlations in the data were measured.RESULTS:One hundred fifty patients were included, of which 49 had syringomyelia. C1–C7 taper ratios were smaller and C4–C7 taper ratios greater for patients with syringomyelia than for those without it. C1–C4 taper ratios did not differ significantly between groups. Patients with syringomyelia had, on average, greater tonsillar herniation than those without a syrinx. However, C4–C7 taper ratios were steeper, for all degrees of tonsil herniation, in patients with syringomyelia. Differences among readers did not exceed differences among patient groups.CONCLUSIONS:The tapering of the lower cervical spine may contribute to the development of syringomyelia in patients with Chiari I.

Patients with a Chiari I malformation frequently develop syringomyelia, in theory the result of CSF flow obstructed by ectopic cerebellar tonsils. Phase-contrast MR imaging studies of CSF flow in the foramen magnum support this theory. Oscillatory CSF fluid flow has greater velocities and greater complexity in patients with Chiari I than in healthy subjects.¹ Why some patients with Chiari I develop syringomyelia and other do not has not yet been explained. How hyperdynamic CSF flow at the craniovertebral junction causes syringomyelia lower in the cervical spine has also not been elucidated.Abnormal tonsil position is not a necessary or a sufficient cause for syringomyelia because not all patients with Chiari I have syringomyelia and not all patients with syringomyelia have tonsillar herniation. The extent of tonsillar herniation does not predict the presence of syringomyelia. Therefore, factors other than tonsil herniation may have a role in the pathogenesis of syringomyelia. For example, one factor may be the size of the posterior cranial fossa; another pathogenetic factor may be the patency of the central canal within the cervical or thoracic spinal cord.^2,3The possibility that cervical spinal canal anatomy has a role in the pathogenesis of syringomyelia has not been extensively studied. The spinal canal narrows between C1 and C4 in healthy subjects⁴ and in patients with Chiari I.⁵ The tapering of the upper cervical spinal canal causes peak CSF velocities to increase from C1 to C4.^6,7 Taper ratios, the slope of a line fit to spinal canal diameters at multiple spinal levels, differ between patients with Chiari I and controls.^5,8 We designed this study to test the hypothesis that Chiari I patients with syringomyelia have different cervical spinal canal taper ratios than Chiari I patients without syringomyelia.     

Axial 3D gradient-echo imaging for improved multiple sclerosis lesion detection in the cervical spinal cord at 3T

Introduction

In multiple sclerosis (MS), spinal cord imaging can help in diagnosis and follow-up evaluation. However, spinal cord magnetic resonance imaging (MRI) is technically challenging, and image quality, particularly in the axial plane, is typically poor compared to brain MRI. Because gradient-recalled echo (GRE) images might offer improved contrast resolution within the spinal cord at high magnetic field strength, both without and with a magnetization transfer prepulse, we compared them to T2-weighted fast-spin-echo (T2-FSE) images for the detection of MS lesions in the cervical cord at 3T.

Methods

On a clinical 3T MRI scanner, we studied 62 MS cases and 19 healthy volunteers. Axial 3D GRE sequences were performed without and with off-resonance radiofrequency irradiation. To mimic clinical practice, all images were evaluated in conjunction with linked images from a sagittal short tau inversion recovery scan, which is considered the gold standard for lesion detection in MS. Two experienced observers recorded image quality, location and size of focal lesions, atrophy, swelling, and diffuse signal abnormality independently at first and then in consensus.

Results

The number and volume of lesions detected with high confidence was more than three times as high on both GRE sequences compared to T2-FSE (p?<?0.0001). Approximately 5 % of GRE scans were affected by artifacts that interfered with image interpretation, not significantly different from T2W-FSE.

Conclusions

Axial 3D GRE sequences are useful for MS lesion detection when compared to 2D T2-FSE sequences in the cervical spinal cord at 3T and should be considered when examining intramedullary spinal cord lesions.     

Evaluation of the supraaortic arteries using non-contrast-enhanced Velocity MR Angiography “Inhance”

Introduction

The aim of this study was to compare the recently developed phase contrast-based Inhance 3D Velocity magnetic resonance angiography technique (Inhance) to the contrast-enhanced standard method (CE-MRA) in the evaluation of the supraaortic arteries.

Methods

Inhance and CE-MRA were performed in ten consecutive patients with a suspected pathology of the supraaortic arteries on a 3-T MR scanner. Two neuroradiologists evaluated in consensus both sequences regarding the visualisation of the supraaortic arteries and their segments on a five-point score. Diagnostic certainty regarding the overall presence of a vascular pathology was rated on the same five-point score.

Results

On CE-MRA as well as on Inhance, a vascular pathology of the supraaortic arteries was detected in seven patients. There was no statistically significant difference in the overall diagnostic certainty regarding the presence or absence of pathologic findings for CE-MRA compared to Inhance. Furthermore, no statistically significant difference was found with regard to visualisation of the distal cervical and intracranial arterial segments, while CE-MRA was superior to Inhance in the visualisation of the origins of the cervical vessels from the aortic arch.

Conclusion

Non-contrast Inhance proved useful in the evaluation of the supraaortic arteries with limited assessment of the proximal supraaortic branches. Hence, this technique features a valuable alternative to CE-MRA in the visualisation of the supraaortic arteries, particularly in patients with renal insufficiency.     

Non-ECG-gated unenhanced MRA of the carotids: Optimization and clinical feasibility

Objectives

To optimise and assess the clinical feasibility of a carotid non-ECG-gated unenhanced MRA sequence.

Methods

Sixteen healthy volunteers and 11 patients presenting with internal carotid artery (ICA) disease underwent large field-of-view balanced steady-state free precession (bSSFP) unenhanced MRA at 3T. Sampling schemes acquiring the k-space centre either early (kCE) or late (kCL) in the acquisition window were evaluated. Signal and image quality was scored in comparison to ECG-gated kCE unenhanced MRA and TOF. For patients, computed tomography angiography was used as the reference.

Results

In volunteers, kCE sampling yielded higher image quality than kCL and TOF, with fewer flow artefacts and improved signal homogeneity. kCE unenhanced MRA image quality was higher without ECG-gating. Arterial signal and artery/vein contrast were higher with both bSSFP sampling schemes than with TOF. The kCE sequence allowed correct quantification of ten significant stenoses, and it facilitated the identification of an infrapetrous dysplasia, which was outside of the TOF imaging coverage.

Conclusions

Non-ECG-gated bSSFP carotid imaging offers high-quality images and is a promising sequence for carotid disease diagnosis in a short acquisition time with high spatial resolution and a large field of view.

Key Points

? Non-ECG-gated unenhanced bSSFP MRA offers high-quality imaging of the carotid arteries. ? Sequences using early acquisition of the k-space centre achieve higher image quality. ? Non-ECG-gated unenhanced bSSFP MRA allows quantification of significant carotid stenosis. ? Short MR acquisition times and ungated sequences are helpful in clinical practice. ? High 3D spatial resolution and a large field of view improve diagnostic performance.     

Clinical evaluation of aortic coarctation with 4D flow MR imaging

Purpose:

To show that 4D Flow is a clinically viable tool for evaluation of collateral blood flow and demonstration of distorted blood flow patterns in patients with treated and untreated aortic coarctation.

Materials and Methods:

Time‐resolved, 3D phase contrast magnetic resonance imaging (MRI) (4D Flow) was used to assess blood flow in the thoracic aorta of 34 individuals: 26 patients with coarctation (22 after surgery or stent placement) and eight healthy volunteers.

Results:

Direct comparison of blood flow calculated with 2D and 4D phase contrast data at standard levels for analysis in coarctation patients showed good correlation and agreement (correlation coefficient r = 0.99, limits of agreement = ?20% to 20% for collateral blood flow calculations). Abnormal blood flow patterns were demonstrated at peak systole with 4D Flow visualization techniques in the descending thoracic aorta of patients but not volunteers. Marked helical flow was seen in 9 of 13 patients with angulated aortic arch geometries after coarctation repair. Vortical flow was seen in regions of poststenotic dilation.

Conclusion:

4D Flow is a fast and reliable means of evaluating collateral blood flow in patients with aortic coarctation in order to establish hemodynamic significance. It also can detect distorted blood flow patterns in the descending aorta after coarctation repair. J. Magn. Reson. Imaging 2010;31:711–718. © 2010 Wiley‐Liss, Inc.

     

Sensory neuronopathy involves the spinal cord and brachial plexus: a quantitative study employing multiple-echo data image combination (MEDIC) and turbo inversion recovery magnitude (TIRM)

Introduction

Sensory neuronopathy (SNN) is a distinctive subtype of peripheral neuropathies, specifically targeting dorsal root ganglion (DRG). We utilized MRI to demonstrate the imaging characteristics of DRG, spinal cord (SC), and brachial plexus at C7 level in SNN.

Methods

We attempted multiple-echo data image combination (MEDIC) and turbo inversion recovery magnitude (TIRM) methods in nine patients with sensory neuronopathy and compared with those in 16 disease controls and 20 healthy volunteers. All participants underwent MRI for the measurement of DRG, posterior column (PC), lateral column, and spinal cord area (SCA) at C7 level. DRG diameters were obtained through its largest cross section, standardized by dividing sagittal diameter of mid-C7 vertebral canal. We also made comparisons of standardized anteroposterior diameter (APD) and left–right diameters of SC and PC in these groups. Signal intensity and diameter of C7 spinal nerve were assessed on TIRM.

Results

Compared to control groups, signal intensities of DRG and PC were higher in SNN patients when using MEDIC, but the standardized diameters were shorter in either DRG or PC. Abnormal PC signal intensities were identified in eight out of nine SNN patients (89 %) with MEDIC and five out of nine (56 %) with T2-weighted images. SCA, assessed with MEDIC, was smaller in SNN patients than in the other groups, with significant reduction of its standardized APD. C7 nerve root diameters, assessed with TIRM, were decreased in SNN patients.

Conclusion

MEDIC and TIRM sequences demonstrate increased signal intensities and decreased area of DRG and PC, and decreased diameter of nerve roots in patients with SNN, which can play a significant role in early diagnosis.     

Renal imaging at 7 Tesla: preliminary results

Objective

To investigate the feasibility of 7T MR imaging of the kidneys utilising a custom-built 8-channel transmit/receive radiofrequency body coil.

Methods

In vivo unenhanced MR was performed in 8 healthy volunteers on a 7T whole-body MR system. After B₀ shimming the following sequences were obtained: 1) 2D and 3D spoiled gradient-echo sequences (FLASH, VIBE), 2) T1-weighted 2D in and opposed phase 3) True-FISP imaging and 4) a T2-weighted turbo spin echo (TSE) sequence. Visual evaluation of the overall image quality was performed by two radiologists.

Results

Renal MRI at 7T was feasible in all eight subjects. Best image quality was found using T1-weighted gradient echo MRI, providing high anatomical details and excellent conspicuity of the non-enhanced vasculature. With successful shimming, B₁ signal voids could be effectively reduced and/or shifted out of the region of interest in most sequence types. However, T2-weighted TSE imaging remained challenging and strongly impaired because of signal heterogeneities in three volunteers.

Conclusion

The results demonstrate the feasibility and diagnostic potential of dedicated 7T renal imaging. Further optimisation of imaging sequences and dedicated RF coil concepts are expected to improve the acquisition quality and ultimately provide high clinical diagnostic value.     

Head and neck radiology: role of multidetector computed tomography in the evaluation of the tympanic canaliculus

Purpose

This study was undertaken to evaluate the potential of multidetector computed tomography (MDCT) for multiplanar visualisation of the tympanic canaliculus both in healthy individuals and in patients affected by chronic inflammatory disease of the middle ear.

Materials and methods

A preliminary study was performed on three dried skulls by placing a metal landmark inside the tympanic canal lumen with a view to optimising depiction by multiplanar CT. Subsequently, 50 patients were enrolled in a prospective study. Three of the 100 petrous pyramids studied were excluded owing to the presence of jugulotympanic glomus tumour with severe bone changes.

Results

The entire course of the tympanic canaliculus was identified in 80/97 petrous pyramids (82.4%), 57 of which were normal (75.4% detection rate) and 40 pathological (90% detection rate). To assess the tympanic canaliculus in the pathological petrous pyramids and evaluate its possible role in the disease process, some qualitative criteria were introduced: canal enlargement, loss of margin sharpness, focal erosion of canal margins and presence of pathological tissue.

Conclusions

MDCT represents the only technique allowing evaluation of the tympanic canal in vivo and with multiplanar images in a large number of cases (82.4%).     

Assessment of grating-based X-ray phase-contrast CT for differentiation of invasive ductal carcinoma and ductal carcinoma in situ in an experimental ex vivo set-up

Objective

Limited contrast between healthy and tumour tissue is a limiting factor in mammography and CT of the breast. Phase-contrast computed tomography (PC-CT) provides improved soft-tissue contrast compared with absorption-based techniques. In this study, we assessed the technical feasibility of grating-based PC-CT imaging of the breast for characterisation of ductal carcinoma in situ (DCIS).

Methods

Grating-based PC-CT was performed on one breast specimen containing an invasive ductal carcinoma and DCIS using monochromatic radiation of 23 keV. Phase-contrast and absorption-based images were compared qualitatively and quantitatively with histopathology in a blinded fashion.

Results

Grating-based PC-CT showed improved differentiation of soft-tissue components. Circular structures of high phase-shift contrast corresponding to the walls of the dilated ductuli of the DCIS were visualised with a contrast-to-noise ratio (CNR) of 9.6 using PC-CT but were not detectable on absorption-based images (CNR?=?0.27). The high phase-shift structures of the dilated ductuli were identifiable in the PC-CT volume data set allowing for 3D characterisation of DCIS.

Conclusions

Our results indicate that unlike conventional CT, grating-based PC-CT may allow the differentiation between invasive carcinoma and intraductal carcinoma and healthy breast tissue and provide 3D visualisation of DCIS.

Key Points

? Phase-contrast computed tomography (CT) yields improved soft-tissue contrast. ? The method can resolve the fine structure of a breast tumour. ? Invasive and intraductal carcinoma can be differentiated. ? Differentiation is possible by visual inspection and quantification. ? The method could improve early breast cancer diagnosis.     

Uterine cervical carcinoma: a comparison of two- and three-dimensional T2-weighted turbo spin-echo MR imaging at 3.0 T for image quality and local-regional staging

Objective

To compare three-dimensional (3D) T2-weighted turbo spin-echo (TSE) with multiplanar two-dimensional (2D) T2-weighted TSE for the evaluation of invasive cervical carcinoma.

Methods

Seventy-five patients with cervical carcinoma underwent MRI of the pelvis at 3.0 T, using both 5-mm-thick multiplanar 2D (total acquisition time?=?12 min 25 s) and 1-mm-thick coronal 3D T2-weighted TSE sequences (7 min 20 s). Quantitative analysis of signal-to-noise ratio (SNR) and qualitative analysis of image quality were performed. Local-regional staging was performed in 45 patients who underwent radical hysterectomy.

Results

The estimated SNR of cervical carcinoma and the relative tumour contrast were significantly higher on 3D imaging (P?<?0.0001). Tumour conspicuity was better with the 3D sequence, but the sharpness of tumour margin was better with the 2D sequence. No significant difference in overall image quality was noted between the two sequences (P?=?0.38). There were no significant differences in terms of the diagnostic accuracy, sensitivity, and specificity of parametrial invasion, vaginal invasion, and lymph node metastases.

Conclusion

Multiplanar reconstruction 3D T2-weighted imaging is largely equivalent to 2D T2-weighted imaging for overall image quality and staging accuracy of cervical carcinoma with a shorter MR data acquisition, but has limitations with regard to the sharpness of the tumour margin.

Key Points

? 3D T2-weighted MR sequence is equivalent to 2D for cervical carcinoma staging. ? Coronal 3D acquisitions can reduce the examination time. ? SNR and relative tumour conspicuity were significantly higher on 3D sequences. ? Reformatted 3D T2-weighted imaging had limitations in sharpness of tumour margin.     

Tapering of the Cervical Spinal Canal in Patients with Distended or Nondistended Syringes Secondary to Chiari Type I Malformation

BACKGROUND AND PURPOSE:Steeper tapering of the cervical spinal canal as documented in recent studies is thought to have a role in the pathophysiology of Chiari malformation-associated syringomyelia. This study aimed to determine whether taper ratio of the cervical spinal canal differs between patients with distended and nondistended syringes.MATERIALS AND METHODS:Seventy-seven adolescents (10–18 years) were divided into 2 groups: 44 with distended syrinx and 33 with nondistended syrinx. On T2-weighted MR images, anteroposterior diameter of the spinal canal was measured at each cervical level, and a linear trend line was fit by least squares regression to calculate the taper ratio. Taper ratios were compared between the 2 groups and further evaluated with respect to age and sex.RESULTS:In the nondistended group ND, the taper ratios for C1–C7, C1–C4, and C4–C7 averaged −0.73 ± 0.57, −1.61 ± 0.98, and −0.04 ± 0.54, respectively, all of which were significantly steeper than those observed in the distended group (P = .001, .004, and .033, respectively). Regarding the average diameters plotted by cervical level, the narrowest region of the canal was found to occur at C4 in both groups. In addition, no significant differences in taper ratio were noted between males and females, or between older (>14 years) and younger patients (≤14 years).CONCLUSIONS:Taper ratios of the cervical spinal canal were found to be different between patients with distended and nondistended syringes, indicating a reciprocal interaction between the syrinx and the cervical spine anatomy.

Chiari malformation type I (CMI) is the leading cause of syringomyelia (SM), a debilitating disorder that can give rise to neurologic impairments including motor weakness and sensory disturbance.^1–3 To date, the exact pathogenesis responsible for SM associated with CMI remains incompletely understood. Although numerous theories and hypotheses have been proposed to explicate the mechanisms underlying such pathologic entity,^4–7 none thoroughly elucidated the clinical and radiologic findings within the disease spectrum.According to a prevailing concept, altered CSF flow at the craniovertebral junction is one of the essential elements in the pathophysiology of SM and hypothetically causes the neurologic signs and symptoms associated with CMI.^8–11 Pinna et al¹² reported that the elongation of the systolic flow might prolong the condition of elevated spinal subarachnoid pressure in patients with CMI. Using computational flow analysis in an idealized 3D model of the subarachnoid space, Roldan et al¹³ and Linge et al¹¹ found that the peak CSF velocities increased progressively from the foramen magnum to C4 or C5. These findings, coupled with the mesodermal dysgenesis theory as evidenced by hypoplasia of the posterior cranial fossa,^14,15 imply an abnormal cervical spinal canal anatomy in patients with CMI. In an attempt to verify this hypothesis, Hirano et al¹⁶ and Hammersley et al¹⁷ investigated tapering of the upper cervical spinal canal, and as steeper taper ratio was found in patients with CMI as compared with healthy controls, they speculated that such bony variations might increase the pressure gradients between the cranial and caudal ends of the spinal canal, resulting in dysfunctional CSF flow and thus favoring the formation of a syrinx.Despite the elegance of the work of Hirano et al¹⁶ and Hammersley et al,¹⁷ which added an interesting twist to the pathomechanism of SM, their theory fails to account for the influence of a syrinx upon morphology of the cervical spinal canal. Clinically, it is observed that patients with a distended syrinx tend to have regional enlargement of the spinal canal. We, therefore, set out to determine whether taper ratio of the cervical spinal canal differs between patients with distended and nondistended syringes secondary to CMI.