Cerebral MR venography

Optimization of 3D phase contrast venography for the assessment of the cranio-cervical venous system at 1.5 T

PURPOSE

The aim of this work was to optimize a three-dimensional (3D) phase-contrast venography (PCV) product MR pulse sequence in order to obtain clinically reliable images with less artifacts for an improved depiction of the cranio-cervical venous vessels.

METHODS

Starting from the product sequence, the 3D PCV protocol was optimized in eight steps with respect to the velocity encoding (V_enc) direction and value, slice thickness, reduction of susceptibility artifacts and arterial contamination, gradient mode and radio-frequency (RF)-spoiling, B₀-Shimming, asymmetric echo technique and RF-pulse type, and flip angle. The product and optimized protocol was used to perform 3D PCV in 12 healthy male volunteers with a median age of 50 years using a state-of-the-art 1.5-T MR system. For evaluation, the cranio-cervical venous system was divided into 15 segments. These segments were evaluated by three radiologists with experience in neuroradiology. An ordinal scoring system was used to access the overall diagnostic quality, arterial contamination, and the quality of visualization.

RESULTS

Image quality in the optimized 3D PCV was graded as "excellent" by all readers in 65.3% of the cases (p < 0.0001). The visualization of venous segments was strongly improved: it was considered diagnostic in 81.8% of all cases using the optimized sequence and in 47.6% for the product 3D PCV (p < 0.0001), respectively. The optimized protocol improved the imaging of all venous segments (p < 0.0001).

CONCLUSION

The optimized 3D PCV pulse sequence showed superior results compared to the product 3D PCV for the visualization and evaluation of the venous system in all healthy volunteers.

Intra- and Extracranial MR Venography: Technical Notes, Clinical Application, and Imaging Development

Scientific debate over chronic cerebrospinal venous insufficiency (CCSVI) has drawn attention to venous system involvement in a series of pathologic brain conditions. In the last few decades, the MRI venography (MRV) field has developed a number of valuable sequences to better investigate structural anatomy, vessel patency, and flow characteristics of venous drainage in the intra- and extracranial systems. A brief two-tier protocol is proposed to encompass the study of intra- and extracranial venous drainage with and without contrast administration, respectively. Contrast-enhanced protocol is based on time-resolved contrast-enhanced MRV of the whole region plus extracranial flow quantification through 2D Cine phase contrast (PC); non-contrast-enhanced protocol includes intracranial 3D PC, extracranial 2D time of flight (TOF), and 2D Cine PC flow quantification. Total scanning time is reasonable for clinical applications: approximately seven minutes is allocated for the contrast protocol (most of which is due to 2D Cine PC), while the noncontrast protocol accounts for around twenty minutes. We believe that a short though exhaustive MRI scan of the whole intra- and extracranial venous drainage system can be valuable for a variety of pathologic conditions, given the possible venous implication in several neurological conditions.

Noncontrast magnetic resonance angiography: concepts and clinical applications

Many noncontrast magnetic resonance angiography techniques have recently been developed in response to concerns about gadolinium in patients with renal impairment. This article describes the theory behind established and recently described techniques and how and where they can be performed in clinical practice.

Background-suppressed MR venography of the brain using magnitude data: a high-pass filtering approach

Conventional susceptibility-weighted imaging (SWI) uses both phase and magnitude data for the enhancement of venous vasculature and, thus, is subject to signal loss in regions with severe field inhomogeneity and in the peripheral regions of the brain in the minimum-intensity projection. The purpose of this study is to enhance the visibility of the venous vasculature and reduce the artifacts in the venography by suppressing the background signal in postprocessing. A high-pass filter with an inverted Hamming window or an inverted Fermi window was applied to the Fourier domain of the magnitude images to enhance the visibility of the venous vasculature in the brain after data acquisition. The high-pass filtering approach has the advantages of enhancing the visibility of small veins, diminishing the off-resonance artifact, reducing signal loss in the peripheral regions of the brain in projection, and nearly completely suppressing the background signal. The proposed postprocessing technique is effective for the visualization of small venous vasculature using the magnitude data alone.

Venous thromboembolism in Pakistan: a neglected research agenda

Venous thromboembolism (VTE) is an important cause of in-hospital mortality. A local understanding of disease burden, occurrence, etiology and successful preventive and therapeutic interventions is of vital import. We aimed to review the current literature of VTE originating from Pakistan to determine gaps in knowledge in order to prioritize future research. An electronic search was performed using Pakmedinet, Pubmed and Google Scholar to retrieve research articles on thrombosis, deep vein thrombosis and pulmonary thromboembolism in Pakistan. The search included all years and no limits were applied. All original research articles presenting primary data from Pakistan were selected. Full texts were reviewed and information synthesized and summarized in our review. Eighty-one studies were found, out of which we were able to retrieve and review 77 (95%) full texts. A total of 6,501 patients are included in this review. Among the studies, we found 25 case reports/series, 1 case-control, 3 cohort, 20 cross-sectional, 1 quasi-experimental, 2 randomized controlled trials, 4 retrospective file reviews and 21 review articles. Most of these were small studies with only eight having a patient population above 100. Six studies presented incidence of DVT which ranged from 2.6 to 12.82% depending on the population under study. Two articles studied risk factors for DVT. Six looked at different treatment modalities, often comparing one modality to the other, while another 15 articles assessed diagnostic strategies. Preventive aspects of VTE were addressed by only three studies and all found the rates of thrombo-prophylaxis grossly inadequate. There is a dearth of quality research on venous thromboembolism in Pakistan. We describe key areas of neglect and recommend prioritizing research on epidemiological and preventive aspects.

Color Doppler US of normal cerebral venous sinuses in neonates: a comparison with MR venography

BACKGROUND

Color Doppler US (CDUS) has been used for evaluation of cerebral venous sinuses in neonates. However, there is very limited information available regarding the appearance of superficial and deep normal cerebral venous sinuses using CDUS and the specificity of the technique to rule out disease.

OBJECTIVE

To determine the specificity, inter-modality and inter-reader agreement of color Doppler US (CDUS). To evaluate normal cerebral venous sinuses in neonates in comparison to MR venography (MRV).

MATERIALS AND METHODS

Newborns undergoing a clinically indicated brain MRI were prospectively evaluated. All underwent a dedicated CDUS of the cerebral venous sinuses within 10 h (mean, 3.5 h, range, and 2-7.6 h) of the MRI study using a standard protocol.

RESULTS

Fifty consecutive neonates participated in the study (30 males [60%]; 25-41 weeks old; mean, 37 weeks). The mean time interval between the date of birth and the CDUS study was 19.1 days. No cases showed evidence of thrombosis. Overall agreement for US reading was 97% (range, 82-100%), for MRV reading, 99% (range, 96-100%) and for intermodality, 100% (range, 96-100%). Excellent US-MRI agreement was noted for superior sagittal sinus, cerebral veins, straight sinus, torcular Herophili, sigmoid sinus, superior jugular veins (94-98%) and transverse sinuses (82-86%). In 10 cases (20%), MRV showed flow gaps whereas normal flow was demonstrated with US. Visualization of the inferior sagittal sinus was limited with both imaging techniques.

CONCLUSION

Excellent reading agreement was noted for US, MRV and intermodality. CDUS is highly specific to rule out cerebral venous thrombosis in neonates and holds potential for clinical application as part of clinical-laboratory-imaging algorithms of pre/post-test probabilities of disease.

Venous anatomy and imaging of the first centimeter

The outermost centimeter of the head contains multiple layers ranging from the skin to the meninges. The venous drainage of this region is complex and with wide anatomical variation. With advances in imaging techniques, delineation of this venous system has become better appreciated. Understanding the anatomy of the superficial venous system is fundamental in being able to differentiate pathology from normal variants and structures. This review aims to characterize the basic venous architecture of the first centimeter. In addition, it hopes to give an introduction to and examples of the methods employed to image it.

A new automatic phase mask filter for high-resolution brain venography at 3 T: theoretical background and experimental validation

To improve vessel contrast in high-resolution susceptibility-based brain venography, an automatic phase contrast enhancing procedure is proposed, based on a new phase mask filter suitable for maximizing contrast of venous MR signals. The effectiveness of the new approach was assessed both on digital phantoms and on acquired MR human brain images, and then compared with venographic results of phase masking methods in recent literature. The digital phantom consisted of a simulated MR dataset with given signal-to-noise ratios (SNRs), while real human data were collected by scanning healthy volunteers with a 3.0-T MR system and a 3D gradient echo pulse sequence. The new phase mask (NM) was more effective than the conventional mask (CM) both on the digital phantoms and on the acquired MR images. A quantitative comparison based on phantom venograms indicates how this phase enhancement can lead to a significant increase in the contrast-to-noise ratio (CNR) for all considered phase values as well as for all vessel sizes of clinical interest. Likewise, the in vivo brain venograms reveal a better depiction of the smallest venous vessels and the enhancement of many details undetectable in conventional venograms.

3D high-spatial-resolution cerebral MR venography at 3T: a contrast-dose-reduction study

BACKGROUND AND PURPOSE

The effect of various contrast-dose regimens for cerebral MR venography (MRV) has not been previously evaluated at 3T, to our knowledge. Our purpose was to evaluate and compare the diagnostic image quality resulting from half-versus-full-dose contrast regimens for high-spatial-resolution 3D cerebral MRV at 3T.

MATERIALS AND METHODS

Forty consecutive patients with known or suggested cerebrovascular disease underwent 3D high-spatial-resolution (0.7 x 0.6 x 0.9 mm(3)) cerebral contrast-enhanced MRV (CE-MRV) at 3T, by using an identical acquisition protocol. Patients were assigned to 1 of 2 groups: 1) full-dose (approximately 0.1 mmol/kg), and 2) half-dose (approximately 0.05 mmol/kg). Two readers evaluated the resulting images for overall image quality, venous structure definition, and arterial contamination. Signal intensity-to-noise-ratio (SNR) and contrast-to-noise-ratio (CNR) were evaluated in 8 consistent sites. Statistical analysis was performed by using Mann-Whitney U, Wilcoxon signed rank, and t tests and a kappa coefficient.

RESULTS

Both readers scored venous-structure definition as excellent or sufficient for diagnosis in approximately 90% of segments for the full-dose group (kappa = 0.87) and in approximately 80% of segments for the half-dose group (kappa = 0.85). Delineation grades were significantly lower for small venous segments, including the middle cerebral, septal, superior cerebellar, inferior vermian, posterior tonsillar, and thalamostriate veins in the half-dose group (P < .01). No significant difference existed for arterial contamination grades between the 2 groups (P > .05). SNR and CNR values were lower in the half-dose group (P < .01).

CONCLUSIONS

At 3T, high-spatial-resolution cerebral MRV can be performed with contrast doses as low as 7.5 mL, without compromising image quality as compared with full-dose protocols, except in the smallest veins, and without compromise of acquisition speed or spatial resolution.

Quantification of venous blood signal contribution to BOLD functional activation in the auditory cortex at 3 T

Most modern techniques for functional magnetic resonance imaging (fMRI) rely on blood-oxygen-level-dependent (BOLD) contrast as the basic principle for detecting neuronal activation. However, the measured BOLD effect depends on a transfer function related to neurophysiological changes accompanying electrical neural activation. The spatial accuracy and extension of the region of interest are determined by vascular effect, which introduces incertitude on real neuronal activation maps. Our efforts have been directed towards the development of a new methodology that is capable of combining morphological, vascular and functional information; obtaining new insight regarding foci of activation; and distinguishing the nature of activation on a pixel-by-pixel basis. Six healthy volunteers were studied in a parametric auditory functional experiment at 3 T; activation maps were overlaid on a high-resolution brain venography obtained through a novel technique. The BOLD signal intensities of vascular and nonvascular activated voxels were analyzed and compared: it was shown that nonvascular active voxels have lower values for signal peak (P<10(-7)) and area (P<10(-8)) with respect to vascular voxels. The analysis showed how venous blood influenced the measured BOLD signals, supplying a technique to filter possible venous artifacts that potentially can lead to misinterpretation of fMRI results. This methodology, although validated in the auditory cortex activation, maintains a general applicability to any cortical fMRI study, as the basic concepts on which it relies on are not limited to this cortical region. The results obtained in this study can represent the basis for new methodologies and tools that are capable of adding further characterization to the BOLD signal properties.

High-spatial-resolution contrast-enhanced MR angiography of the intracranial venous system with fourfold accelerated two-dimensional sensitivity encoding

Informed consent was obtained; the study was HIPAA compliant and institutional review board approved. Fourfold accelerated (FFA) two-dimensional (2D) sensitivity encoding (SENSE) (65 seconds) was prospectively compared with its nonaccelerated counterpart (4 minutes 20 seconds) for diagnostic image quality and sharpness of visualization of blood vessels at 1.5 T with three-dimensional (3D) intracranial contrast-enhanced magnetic resonance venography in 18 consecutive volunteers (10 men, eight women; mean age, 48.4 years) and two patients (55-year-old man, 30-year-old woman). Two readers compared FFA 2D SENSE results with results from its nonaccelerated counterpart; they rated visualization of large and medium sinuses as equivalent (P>.1) and that of small deep cerebral veins (P<.01) and superficial cerebral veins (P<.001) as superior. Overall diagnostic image quality ratings were excellent for 62% and 80% of nonaccelerated and FFA 2D SENSE results, respectively (P<.05). FFA 2D SENSE may become the method of choice for fast visualization of intracranial venous vasculature in clinical practice.

Thromboses veineuses cérébrales

Venous thromboses in the cerebrum are rare, within the context of both cerebrovascular disease and all of the venous thrombotic diseases. Its clinical aspects are polymorphic in their onset and in their acute phase, making diagnosis difficult. MRI with angiographic sequences can show the presence of a thrombus within a venous vessel and its consequences on the cerebral parenchyma. Hemostatic disorders are the leading causes of cerebral venous thrombosis, in particular, constitutional thrombophilia often associated with one or several promoting factors such as use of oral contraception. This explains the incidence peak among young women. The cause of approximately 20% of cerebral venous thromboses is never identified. Antithrombotic treatment must be prescribed on an emergency basis when the diagnosis is made, even if potentially hemorrhagic lesions are also present. The risk of permanent neurologic damage is approximately 13%.

Evaluation of petrosal sinus patency with 3-dimensional contrast-enhanced magnetic resonance venography in petroclival meningiomas for surgical strategy

BACKGROUND

The aim of this study was to perform a detailed anatomical analysis of petroclival venous structures as well as their patencies with 3D contrast-enhanced (CE) magnetic resonance venography (MRV) and to identify the potential contribution of these data to the therapeutic approach.

METHODS

Ten patients (8 women and 2 men) with unilateral petroclival meningioma were examined using 3D CE MRV in addition to conventional brain protocol. Both coronal source and multiplanar reconstructed images were evaluated for the anatomical orientation. Patency of the cavernous sinus, superior petrosal sinus (SPS), and inferior petrosal sinus (IPS) was assessed.

RESULTS

All the patients had a unilateral meningioma (7 on the right and 3 on the left) at the petroclival region. Both SPS and IPS were visualized with adequate intraluminal contrast enhancement in 6 patients, but IPS was absent in 3 on the lesion side, with a patent superior petrosal sinus as the drainage route. One patient had a partially occluded SPS, with IPS being the main course of cavernous sinus drainage.

CONCLUSIONS

Cerebral venous anatomy is a challenge to display with noninvasive methods because of flow dynamics, and CE 3D imaging seems to be the modality of choice to evaluate the variational anatomy and patency, which is essential in petroclival meningiomas. Because the cavernous sinus drains into either IPS or SPS, the patent sinus should be protected in surgery if there is tumoral occlusion of the others.

Transient global amnesia may be caused by cerebral vein thrombosis

Transient global amnesia (TGA) is a disorder of unknown aetiology, characterized by sudden loss of anterograde memory, in the absence other neurological signs or symptoms, followed by complete recovery in less than 24h. Precipitating actions such as strenuous physical activity or valsalva-like manoeuvres are frequently reported. Since first described in 1958, by Fisher and Adams, the possible pathophysiology has undergone much speculation. Nonconvulsive epileptic seizures, migraine, paradoxical embolism thorough a patent foramen ovale, and transient ischemic attacks have been proposed as potential mechanisms. One of the latest hypotheses is that venous congestion causes either ischemia or induces spreading depression in the medial temporal lobes. It has been demonstrated that retrograde flow in the internal jugular veins occurs more frequently during valsalva manoeuvres in TGA patients than in controls, supporting a dysfunctional venous circulation as part of the pathogenesis. However, earlier hypotheses typically fail to explain the relatively low recurrence rate of TGA, lack of comorbidity and the relation to precipitating events. If cerebral venous hypertension was the solely cause of TGA it would presumably be much more common with very high recurrence rates among those predisposed of the condition. Structural changes observed in MRI and SPECT studies along with reports of mild cognitive impairment lasting much longer than the amnestic episodes, indicate that TGA is less transient and perhaps somewhat less benign than earlier believed. Many cases of TGA seem to be associated with factors of increased risk of cerebral venous thrombosis, such as polycythemia, antiphospholipid antibodies, venous hypertension, female sex and more. We suggest that most cases of TGA may be due to small thrombi in the deep cerebral venous system. Small venous thrombi may difficult to visualize even when using modern imaging technology. Further studies of TGA patients with for example blood analysis of D-dimer together with MR venography or CT venography could be done to evaluate this new hypothesis.