Susceptibility-weighted imaging: technical aspects and clinical applications, part 2

Simultaneous arteriovenous shunting and venous congestion identification in dural arteriovenous fistulas using susceptibility-weighted imaging: initial experience

In this short report, we describe the potential contribution of SWI in the noninvasive evaluation of DAVFs. SWI images were compared with DSA for the identification of the location of the fistulous point, the presence of CVR, and the presence of the PPP. In 5 of 6 patients, it was possible to identify the fistulous locations depicted as hyperintensity within venous structures. Cortical venous reflux was underestimated on SWI in 3 cases of robust CVR and not identified in 2 cases of less severe CVR. The PPP seen on angiograms correlated anatomically with increased number, caliber, and tortuosity of hypointense veins seen on SWI. Furthermore, SWI was superior to conventional MR imaging in the detection of these dilated veins. These preliminary results suggest an important role for SWI in the detection and assessment of the complex hemodynamics associated with DAVFs.

Widespread cerebral cortical mineralization in Wilson's disease detected by susceptibility-weighted imaging

Signal abnormalities of cortical gray matter, compared with the deep nuclear structures, have received less attention in Wilson's disease (WD). They nearly always accompanied white matter signal change, and commonly are associated with epilepsy and psychiatric features. We report herein two cases diagnosed as WD who, in addition to characteristic deep nuclear lesions on MR imaging, had widespread cerebral cortical paramagnetic signals dramatically detected by susceptibility-weighted imaging. T2-weighted MR images did not show any cortico-subcortical hyperintense lesions. To our knowledge, these findings have not been described before and may help to further characterize the disease.

Brain iron deposition and sequence characteristics in Parkinsonism: comparison of SWI, T₂* maps, T₂-weighted-, and FLAIR-SPACE

OBJECTIVES

To compare quantitatively T2- and T2*-based magnetic resonance imaging sequences in patients with symptoms of Parkinson disease and to evaluate the information content of those sequences regarding brain iron concentration.

MATERIALS AND METHODS

We imaged 51 patients with symptoms of Parkinson disease on 3-T magnetic resonance imaging with T2-weighted sampling perfection with application optimized contrasts using different flip-angle evolution (SPACE), fluid attenuation inversion recovery (FLAIR)-SPACE, susceptibility-weighted imaging (SWI), and parametric T2* sequence (MapIt). Signal analysis was performed in 22 regions of interest in the brain.

RESULTS

Correlations (r2 = 0.82...0.96) with brain iron concentration were excellent. Contrast and tissue separability ratios were best in the T2* maps and FLAIR-SPACE, respectively. Good correlations of contrast were reached between SWI and both T2-weighted SPACE and FLAIR-SPACE. Their relation to quantitative T2* values was reminiscent of a quadratic curve shape. However, separation into gray and white matter revealed a linear positive and negative correlation, respectively.

CONCLUSIONS

SWI showed potential in differentiating illnesses characterized by brain iron deposition. Closely similar information was given by T2-weighted SPACE and FLAIR-SPACE, whereas other sequence comparisons revealed dispersion from intersequence agreement.

Relaxation time mapping in multiple sclerosis

Several relaxation mapping techniques have been proposed to quantitatively assess disease-related brain tissue changes in multiple sclerosis. Newer developments also account for the distribution of hydrogen protons in different tissue compartments, and therefore provide markers for myelin and macromolecular content. This article will cover the broad spectrum of the pulse sequences and analysis techniques related to this topic that are currently available. Various technical and practical limitations linked with specific approaches will be discussed. These include acquisition time, accuracy and precision, radiofrequency absorption and limited coverage of the brain. Finally, the application of these techniques in the context of multiple sclerosis will be reviewed.

Cerebral microbleeds: detection, mechanisms and clinical challenges

In the last decade or so, cerebral microbleeds (CMBs) – tiny perivascular hemorrhages seen as small, well-demarcated, hypointense, rounded lesions on MRI sequences that are sensitive to magnetic susceptibility – have generated increasing interest among neurologists and clinical stroke researchers. As MRI techniques become more sophisticated, CMBs are increasingly detected in various patient populations (including all types of stroke, Alzheimer’s disease and vascular cognitive impairment) and healthy community-dwelling older people. Their presence raises many clinical dilemmas and intriguing pathophysiological questions. CMBs are emerging as an important new manifestation and diagnostic marker of cerebral small-vessel disease. They are a potential predictor of future intracerebral hemorrhage risk, a possible contributor to cognitive impairment and dementia and a potential key link between vascular and degenerative pathologies. In this article, we discuss the available pathological, neuroimaging and clinical studies in the field, and we provide a modern overview of the clinical and pathophysiological implications of CMBs in different disease settings.

Simultaneous visualization of nerves and vessels of the lower extremities using magnetization-prepared susceptibility weighted magnetic resonance imaging at 3.0 T

BACKGROUND

Identifying the extent of involvement of the vessel and nerve, particularly in regard to preoperative evaluation and precise localization of the tumor and its relation to the structures of the extremities, has important applications for advancing the treatment of lower extremity diseases.

OBJECTIVE

To review the technical feasibility of simultaneous visualization of nerves and vessels of the lower extremities by using magnetization-prepared susceptibility-weighted magnetic resonance (MR) imaging (MP-SWI) at 3.0T.

METHODS

Ten healthy volunteers and 10 patients were studied. Optimized MP-SWI, MR neurography (MRN) based on 3D diffusion-weighted steady-state free precession imaging and contrast-enhanced MR angiography (CE-MRA) sequences were performed for each subject. The means of signal-to-noise ratio (SNR)n, SNRv, SNRm, contrast-to-noise ratio (CNR)n,m and CNRv,m were calculated and the certainty of identifying nerves and vessels was determined. CNRn,m between MP-SWI and MRN, and CNRv,m between MP-SWI and CE-MRA were compared.

RESULTS

MP-SWI provides slightly poorer CNRv,m than CE-MRA, whereas MP-SWI provides a better CNRn,m than MRN. In thin-slice-thickness maximum-intensity projection arbitrary planes, the sciatic nerve and its branches were clearly identified (score 1 or 2 of 2) in 17 subjects (85%); the femoral artery and the main branches were identified (score 1 or 2 of 2) in all 20 subjects (100%). The nerves are isointense to slightly hypointense to muscle, and the vessels show a more obvious hyperintense signal than muscle in MP-SWI.

CONCLUSION

The proposed MP-SWI demonstrates the feasibility of simultaneously visualizing nerves and vessels of the lower extremities without using an exogenous contrast agent. It may enable straightforward localization of a disease process to a specific nerve and vessel.

Spin dephasing under nonlinear gradients: implications for imaging and field mapping

This work examines the prototypical MR echo that would be expected for a voxel of spins evolving in a strong nonlinear field, specifically focusing on the quadratic z(2) - ½(x(2) + y(2) ) field. Dephasing under nonlinear gradients is increasingly relevant given the growing interest in nonlinear imaging, and here, we report several notable differences from the linear case. Most notably, in addition to signal loss, intravoxel dephasing under gradients creating a wide and asymmetric frequency distribution across the voxel can cause skewed and nonlinear phase evolution. After presenting the qualitative and analytical origins of this difference, we experimentally demonstrate that neglecting these dynamics can lead to significant errors in sequences that assume phase evolution is proportional to voxel frequency, such as those used for field mapping. Finally, simplifying approximations to the signal equations are presented, which not only provide more intuitive forms of the exact expression but also result in simple rules to predict key features of the nonlinear evolution.

Pictorial essay: Susceptibility-weighted imaging in cerebral ischemia

The susceptiblity effect in magnetic resonance imaging (MRI) has been recognized for long and often has been considered undesirable, producing unnecessary noise. Susceptibility-weighted imaging (SWI) aims at exploiting this effect to provide a different type of contrast that is suited for vascular imaging. We describe five different cases in which SWI was found useful to delineate the underlying ischemia or to arrive at the corect diagnosis.

Neurodegeneration with brain iron accumulation - clinical syndromes and neuroimaging

Iron participates in a wide array of cellular functions and is essential for normal neural development and physiology. However, if inappropriately managed, the transition metal is capable of generating neurotoxic reactive oxygen species. A number of hereditary conditions perturb body iron homeostasis and some, collectively referred to as neurodegeneration with brain iron accumulation (NBIA), promote pathological deposition of the metal predominantly or exclusively within the central nervous system (CNS). In this article, we discuss seven NBIA disorders with emphasis on the clinical syndromes and neuroimaging. The latter primarily entails magnetic resonance scanning using iron-sensitive sequences. The conditions considered are Friedreich ataxia (FA), pantothenate kinase 2-associated neurodegeneration (PKAN), PLA2G6-associated neurodegeneration (PLAN), FA2H-associated neurodegeneration (FAHN), Kufor-Rakeb disease (KRD), aceruloplasminemia, and neuroferritinopathy. An approach to differential diagnosis and the status of iron chelation therapy for several of these entities are presented. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease.

Lumbar intraspinal arachnoid cyst superimposed by hyperacute spinal subdural hematoma: an unusual case

BACKGROUND CONTEXT

Lumbar intradural arachnoid cyst (AC) concomitant with hyperacute spinal subdural hematoma (SSDH) has never been reported in the literature.

PURPOSE

To report a case of lumbar AC superimposed by hyperacute SSDH, which was difficult to diagnose preoperatively using magnetic resonance imaging. Herein, we describe diagrams showing the proposed mechanisms underlying the formation of a symptomatic AC.

STUDY DESIGN/SETTING

The study was designed to be a case report and literature review.

METHODS

A 65-year-old man presented with acute onset of low back pain, followed by 5-day history of numbness and weakness in both legs before admission. Magnetic resonance imaging of the lumbosacral spine revealed an intradural extramedullary biconvex lesion at the L3-L4 level; the lesion compressed the cauda equina posteriorly. The lesion mainly appeared as hyperintense on T2-weighted images and hypointense on T1-weighted images. On the basis of these findings, the lesion was preoperatively diagnosed as a symptomatic lumbar subdural AC that compressed the cauda equina.

RESULTS

The patient underwent laminectomy from L2 to L4. After a dura incision, a partially organized subdural hematoma was noted. Beneath the subdural hematoma was an AC compressing the underlying nerve roots. The patient's back pain and muscle strength markedly improved after the operation.

CONCLUSIONS

Preoperative diagnosis of concomitant hyperacute SSDH and AC is difficult. In cases of patients who present with intraspinal AC accompanied by an acute onset of clinical presentation, an associated etiology should be considered until proven otherwise.

Evaluation of parenchymal neuro-behçet disease by using susceptibility-weighted imaging

BACKGROUND AND PURPOSE

Neurologic involvement in Behçet disease, also known as NBD, is one of the most devastating manifestations of the disease. The precise pathologic mechanism of parenchymal NBD lesions has not been established. We evaluated lesion characteristics and probable venous hemorrhage in parenchymal NBD by using SWI, and we compared the imaging results with conventional MR imaging sequences.

MATERIALS AND METHODS

We performed cranial MR imaging by using a 1.5T scanner in 23 patients with a definitive diagnosis of parenchymal NBD. We compared the proportion of lesion detection and the performance of hemorrhagic detection with the T2 FSE, T2*GE, and SWI magnitude, and SWI mIP by using the χ(2) test.

RESULTS

The proportion of lesion detection with both SWI magnitude and SWI MinMIP was significantly larger than that with T2*GE. The proportions of lesion detection among all other pairs of methods were not significantly different according to the corresponding P value (χ(2) = 17.4929, df = 3, P = .0006). Proportions of hypointense hemorrhagic lesions with T2 FSE and T2*GE were not significantly different, and likewise for the proportions of hypointense hemorrhagic lesions with SWI magnitude and SWI mIP. In contrast, the proportions of hypointense hemorrhagic lesions with SWI magnitude and SWI mIP were significantly larger than that with T2 FSE and T2*GE (χ(2) = 108.5396, df = 3, P < .0001).

CONCLUSIONS

Most of the lesions in parenchymal NBD were found to be hemorrhagic with SWI, supporting the proposed venous theory in pathology. In addition, compared with T2 FSE and T2*GE sequences, SWI was more successful in the determination of widespread involvement of the disease, particularly in nonchronic cases.

Susceptibility-weighted angiography (SWAN) of cerebral veins and arteries compared to TOF-MRA

PROBLEM

High resolution, non-contrast imaging of both cerebral veins and arteries by use of gradient echo T2 star weighted angiography (SWAN) is a new method for susceptibility-weighted imaging with short acquisition times. We assessed the potential of this sequence for the depiction of both cerebral veins and arteries.

METHODS

15 healthy volunteers were included in the study. MRI was performed on a 3T MR scanner using the following sequences: (1) a 3D multi-echo gradient echo T2 star weighted angiography (SWAN), (2) an arterial 3D TOF MR angiography and (3) a venous 2D TOF. With regard to the SWAN sequence, both MinIP and MIP images were reconstructed and systematically compared to MIP reconstructions of the artTOF and the venTOF. To suggest possible clinical implications of our findings, we additionally included two illustrative cases.

RESULTS

With regard to the visualization of the cerebral veins, the MinIP reconstructions of the SWAN sequence were considerably superior compared to the venTOF. Concerning the depiction of the main segments of the big cerebral arteries the value of the MIP reconstructions of the SWAN was comparable to that of the artTOF with limitations in the homogenity and in the depiction of smaller arteries.

CONCLUSIONS

SWAN allows for high-resolution visualization of both cerebral veins and arteries in one sequence without application of contrast agent and with significantly shortened scan time compared to the combined scan time of TOF-MRA and TOF-MRV. By use of either MinIP or MIP reconstructions, the arteries can be distinguished from the veins.

Clinical usefulness of the visibility of the transcerebral veins at 3T on T2*-weighted sequence in acute stroke patients

OBJECTIVES

The objective of this work was to investigate the clinical usefulness of the visibility of the transcerebral veins (VTV) in acute ischemic stroke patients at 3T.

METHODS

Sixty consecutive carotid artery territory stroke patients were included retrospectively. Two readers categorized the VTV on T2*-weighted sequence at 3T for each hemisphere, and asymmetry of this sign was assessed between each hemisphere by an asymmetry index (AI) using a three-item scale. The VTV and AI were correlated with clinical and radiological covariates. Particular interest was focused on patients for whom initial diffusion-weighted imaging alone was inconclusive.

RESULTS

VTV were detected in the stroke hemisphere in 58.3% (n = 35) and in the contralateral side in 10% (n = 6, p<0.0001). Asymmetry of the VTV between ischemic and contralateral hemispheres was present in 53.3% (n = 32). Intracranial artery occlusion, final infarct volume and symptomatic hemorrhagic transformation were correlated with a higher AI at baseline (ρ = 0.563, ρ = 0.291, and ρ = 0.285, p<0.05, respectively). Three hyperacute stroke patients with subtle DWI high signal intensity at admission demonstrated VTV.

CONCLUSIONS

The pathological value of the VTV seems to reside in its asymmetry between hemispheres, as it was correlated with important clinical parameters. This study also suggests that the VTV could be a supportive finding in stroke diagnosis, especially when DWI is unreliable.

New MR sequences in daily practice: susceptibility weighted imaging. A pictorial essay

Background

Susceptibility-weighted imaging (SWI) is a relatively new magnetic resonance (MR) technique that exploits the magnetic susceptibility differences of various tissues, such as blood, iron and calcification, as a new source of contrast enhancement. This pictorial review is aimed at illustrating and discussing its main clinical applications.

Methods

SWI is based on high-resolution, three-dimensional (3D), fully velocity-compensated gradient-echo sequences using both magnitude and phase images. A phase mask obtained from the MR phase images is multiplied with magnitude images in order to increase the visualisation of the smaller veins and other sources of susceptibility effects, which are displayed at best after post-processing of the 3D dataset with the minimal intensity projection (minIP) algorithm.

Results

SWI is very useful in detecting cerebral microbleeds in ageing and occult low-flow vascular malformations, in characterising brain tumours and degenerative diseases of the brain, and in recognizing calcifications in various pathological conditions. The phase images are especially useful in differentiating between paramagnetic susceptibility effects of blood and diamagnetic effects of calcium. SWI can also be used to evaluate changes in iron content in different neurodegenerative disorders.

Conclusion

SWI is useful in differentiating and characterising diverse brain disorders.

Susceptibility-weighted imaging (SWI): a potential non-invasive imaging tool for characterizing ischemic brain injury?

Susceptibility-weighted imaging (SWI) is a new high-resolution magnetic resonance imaging (MRI) tool that uses the paramagnetic susceptibility effects of deoxygenated blood to study the intracranial venous vasculature. We present SWI imaging findings in two children who suffered from acute arterial ischemia. Various patterns of normal/altered venous drainage could be identified. Our case study suggests that SWI assisted mapping of the regional changes of the cerebral venous drainage and correlation with diffusion weighted MRI may identify critically perfused brain at risk for infarct progression. Prospective studies are mandatory to further validate the value of SWI.

Imaging of acute ischemic stroke

In this article the individual components of multimodal computed tomography and multimodal magnetic resonance imaging are discussed, the current status of neuroimaging for the evaluation of the acute ischemic stroke is presented, and the potential role of a combined multimodal stroke protocol is addressed.

Suspicious neuroimaging pattern of thrombotic microangiopathy

The TMAs are a group of microvascular occlusive disorders characterized by thrombocytopenia and intravascular hemolysis. Literature review reveals a spectrum of neuroimaging findings, including a single case report of multifocal hemorrhagic infarctions. We present a series of 12 patients with TMA demonstrating a similar pattern of multifocal cortical and subcortical hemorrhagic infarctions.

Clinical Application of Susceptibility Weighted Imaging: Exploring from Routine Service

To evaluate the usefulness of susceptibility weighted imaging (SWI) in clinical brain MRI. Retrospective study was performed after approval from institution Ethical Committee. The brain MRIs with SWI were selected from data base of the radiology department. Only cases with no abnormality in extra-axial location were included into the study. Two neuroradiologists revealed the images without knowledge of patients' history and diagnosis. The SWI was first interpreted. Then conventional MRI (cMRI) was interpreted after finishing data collection from SWI. Clinical data and final diagnosis were collected from information given on requested forms and followed up imaging studies. Descriptive analysis was performed. From January 2007 to December 2009, 82 cases were satisfied the inclusion criteria. There were 40 males and 42 females with age 7–79 years old (means = 47.45). The final diagnosis were normal brain imaging 4 cases (4.9%), dementia/atypical Parkinson disease 2 cases (2.4%), cerebrovascular disease 24 cases (29.3%), parenchymal brain tumors 35 cases (42.7%), infection 4 cases (4.9%), multiple sclerosis (MS) 6 cases (7.3%) and inconclusive diagnosis 7 cases (8.5%). The abnormalities found on SWI were related to cMRI in 67 cases (81.7%). Three cases (3.7%) had lesions on SWI not demonstrated on cMRI The information got from SWI added on cMRI for interpretation and diagnosis in 43 cases (52.4%). SWI were shown more detectable microbleed and changing visualization of cortical and transmedullary veins. Microvascular structure inside the mass was demonstrated on SWI in brain tumor group. The increased transmedullary veins on SWI helped to confirm the non-neoplastic lesions. In selected cases with suspected or diagnosis of vascular disease and tumor, SWI added more information on cMRI especially microbleed and microvascular structure.

Susceptibility Weighted Imaging and Cerebrovascular Disorders

To investigate the correlation between the SWI findings and prognosis of the cerebrovascular disorders. From July 2008 to July 2010, 299 ischemic stroke patients were found in our hospital. The gender ratio is as male and female being 157 to 142. The mean age of all patients is 65.4, mean female age is 69.1, and mean male age is 62.6. There were 86 patients who had satisfactory pre-and post-treatment of CT, MRI with SWI. 23 of these 86 patients had catheter cerebral angiography. 50 of these 86 patients had MR angiogram or CT angiogram. 13 of these 86 patients did not have angiogram. We have also collected 7 severe cardiac arrested and cessation of cerebral circulation and 2 patients with chronic venous hypertension. Among the 86 patients, 23 patients who had negative with deoxygenated vessel on SWI were with small infarction on DWI Thirty-one patients had negative on initial CT head scan. CT finding did not accord with presence of hypointense vessel on SWI. Sixty-three patients had varied degree of abnormal hypointense vessels on SWI as deoxygenated vessels. The initial small foci on DWI may result with a larger infarction if there were with prominent hypointense vessels.

Susceptibility-weighted imaging of the brain: current utility and potential applications

BACKGROUND AND PURPOSE

Susceptibility-Weighted Imaging (SWI) is a relatively new magnetic resonance imaging (MRI) sequence relying on susceptibility differences between adjacent tissues to produce an image. It is extremely sensitive for detection of blood products (hemosiderin, ferritin), deoxygenated blood, calcium, iron, and small vein depiction. Little information is available in the literature to describe common findings seen using this imaging sequence. This article is an comprehensive review of appearances across the spectrum of brain pathology encountered in routine clinical practice.

MATERIALS AND METHODS

A retrospective review of 400 MRI Brain examinations was performed by one fellowship trained Neuroradiologist with 5 years experience (SB) and one general radiologist (RR). Agreement was by consensus observing normal and pathological imaging features seen in SWI sequences.

RESULTS

Results are presented as a comprehensive pictorial review highlighting the key imaging findings observed and new directions using SWI.

CONCLUSION

SWI is an extremely useful adjunct to current MRI sequences of the brain and is advocated for inclusion into routine Neuroimaging protocols.

Susceptibility weighted imaging in detecting hemorrhage in acute cervical spinal cord injury

BACKGROUND AND PURPOSE

Susceptibility weighted imaging (SWI) is sensitive to deoxyhemoglobin and blood products such as hemosiderin in detecting microbleeds in the brain. However, there are no studies on SWI in the spine cord injury so far. The purpose of this study was to evaluate the role of SWI in detecting hemorrhage in acute cervical spinal cord injury (SCI).

MATERIALS AND METHODS

Twenty-three patients with a history of acute cervical spine trauma were studied. High-resolution SWI, gradient-echo (GRE) T2* weighted-image (T2*WI) and conventional magnetic resonance imaging (MRI) were performed on all patients within 15 days of the onset of injury. On the basis of the MRI findings, the patients were classified into four patterns: normal cord, spinal cord edema, spinal cord contusion and spinal cord hemorrhage. Quantitative analysis was performed by calculating and comparing the signal ratio of the hemorrhage to normal spinal cord on the same slice of T2*WI and SWI. All patients were clinically evaluated in follow-up. Twenty volunteers were also scanned as a control group.

RESULTS

Out of 23 patients with a history of acute cervical spine trauma, 4 patients showed normal spinal cord on both conventional MRI and SWI, 8 had only spinal cord edema and 5 had contusion on conventional MRI, but SWI showed hemorrhage in 2 of the 5 patients with spinal contusion on conventional MRI; the other 6 patients had intraspinal hemorrhage on conventional MRI, and SWI proved hemorrhage in all these 6 patients. There was a significant difference between the signal ratios of hemorrhage to normal tissue on T2*WI and SWI (Z=2.34, P=.02).

CONCLUSION

Susceptibility weighted imaging is more sensitive than conventional MRI in detecting hemorrhage in acute cervical SCI. This technique could prove to be a useful tool in the routine evaluation of cervical SCI patients.

Quantitative susceptibility mapping of human brain reflects spatial variation in tissue composition

Image phase from gradient echo MRI provides a unique contrast that reflects brain tissue composition variations, such as iron and myelin distribution. Phase imaging is emerging as a powerful tool for the investigation of functional brain anatomy and disease diagnosis. However, the quantitative value of phase is compromised by its nonlocal and orientation dependent properties. There is an increasing need for reliable quantification of magnetic susceptibility, the intrinsic property of tissue. In this study, we developed a novel and accurate susceptibility mapping method that is also phase-wrap insensitive. The proposed susceptibility mapping method utilized two complementary equations: (1) the Fourier relationship of phase and magnetic susceptibility; and (2) the first-order partial derivative of the first equation in the spatial frequency domain. In numerical simulation, this method reconstructed the susceptibility map almost free of streaking artifact. Further, the iterative implementation of this method allowed for high quality reconstruction of susceptibility maps of human brain in vivo. The reconstructed susceptibility map provided excellent contrast of iron-rich deep nuclei and white matter bundles from surrounding tissues. Further, it also revealed anisotropic magnetic susceptibility in brain white matter. Hence, the proposed susceptibility mapping method may provide a powerful tool for the study of brain physiology and pathophysiology. Further elucidation of anisotropic magnetic susceptibility in vivo may allow us to gain more insight into the white matter micro-architectures.

Susceptibility-weighted imaging of the brain: does gadolinium administration matter?

OBJECTIVE

Susceptibility-weighted MR imaging (SWI) is usually obtained without administration of intravenous gadolinium (Gd). However, it is occasionally necessary to perform SWI after Gd is injected. The effects of Gd on SWI have not been systematically examined. The aim of this prospective study was to investigate whether performing SWI after Gd would influence the diagnostic image quality, parenchymal signal and vascular enhancement. An additional aim is to suggest potential future applications for Gd-enhanced SWI.

METHODS

SWI was performed in 31 subjects before and after Gd administration. 17 cases were examined in a 1.5T scanner and the remaining 14 were scanned at 3T. The pre- and post-Gd images were analysed for signal changes in the cerebral grey matter (GM), white matter (WM) as well as for enhancement in the superficial and deep venous system. The visibility of the veins was graded on subtraction maps.

RESULTS

The Gd-enhanced images showed no image quality degradation and no significant signal intensity change in the GM and WM as compared to the pre-Gd images (p>0.05). After Gd-administration significant enhancement of the venous sinuses was noticed (p<0.005), while the deep and cortical veins were poorly enhanced as confirmed by the calculated subtraction maps. The results showed no significant difference at variable MRI field strengths.

CONCLUSION

It is possible to perform SWI after Gd injection without information loss or signal change in the parenchyma. The most significant difference is the enhancement of the cerebral venous sinuses. Potential future applications are discussed.

Neuroimaging in rabies

Rabies remains a virtually incurable disease once symptoms develop. Neuroimaging studies demonstrate lesions in the different parts of the neuroaxis, even before brain symptoms are evident. These abnormalities have been detailed in both rabies virus-infected humans and dogs with magnetic resonance imaging (MRI). MRI disturbances were similar in both forms (furious or paralytic) in human rabies; however, they were more pronounced in paralytic than in furious rabies virus-infected dogs in which examination was done early in the disease course. Abnormalities were not confined only to neuronal structures of hippocampus, hypothalamus, basal ganglia, and brain stem but also extended to white matter. The blood-brain barrier (BBB) has been clearly shown to be intact during the time rabies virus-infected patients and dogs remained conscious, whereas leakage was demonstrated as soon as they became comatose. Although the location of MRI abnormalities can help diagnosing rabies, the intensities of signals are usually not very distinct and sometimes not recognizable. Newer techniques and protocols have been developed and utilized, such as diffusion-weighted imaging and diffusion tensor imaging, and the latter provides both qualitative and quantitative data. These techniques have been applied to normal and rabies virus-infected dogs to construct fractional anisotropy and mean diffusivity maps. Results showed clear-cut evidence of BBB intactness with absence of vasogenic brain edema and preservation of most neuronal structures and tracts except at the level of brainstem in paralytic rabies-infected dogs. Neuroimaging is one of the most useful tools for the in vivo study of central nervous system infections.

Cerebral microhemorrhages detected by susceptibility-weighted imaging in amateur boxers

BACKGROUND AND PURPOSE

SWI is a new technique for evaluating diffuse axonal injury associated with punctate hemorrhages. The aim of our study was to determine the prevalence of cerebral microhemorrhages in amateur boxers compared with nonboxers by using SWI and to evaluate the sensitivity of SWI compared with T2 FSE and T2*GE sequences.

MATERIALS AND METHODS

We performed cranial MR imaging with a 1.5T scanner in 21 amateur boxers and 21 control subjects. The study protocol included conventional MR images, T2 FSE, T2*GE, and SWI sequences. The proportions of boxers and controls having CSP, DPVS, cerebral atrophy, cerebellar atrophy, ventricular dilation, PSWMD, and microhemorrhages were computed and were compared by using the χ(2) test of proportions. The relationship between microhemorrhages and boxing-related covariates was assessed by using the Wilcoxon rank sum test. The association between the categories was tested by using the Fisher exact test.

RESULTS

Using SWI, microhemorrhages were found in 2 (9.52%) of 21 boxers. The microhemorrhages were not visible on T2 FSE or T2*GE images. The proportion of subjects with microhemorrhages did not differ significantly between the boxers and control subjects (χ(2) = 0.525, df = 1, P = .4688). The prevalence of CSP and DPVS was significantly higher in the boxers than in the control subjects.

CONCLUSIONS

More microhemorrhages were detected in amateur boxers than in controls, but this difference was not statistically significant.

Diagnostic neuroimaging by magnetic resonance imaging: update

Magnetic resonance (MR) imaging remains the most versatile technique in diagnostic imaging. In addition to conventional imaging sequences such as T(1)-weighted imaging, T(2)-weighted imaging, or fluid-attenuated inversion recovery imaging, various techniques specific for certain pathological conditions are being continuously introduced. Pulse sequences for various imaging contrasts are becoming mature, and studies on high (3 T), or even ultra-high (7 T) field systems are emerging as a golden standard for neurosurgical practices. MR spectroscopic imaging capable of providing a pictorial display of the chemical properties of the brain and microscopic imaging providing images with significantly high anatomical resolution equivalent to histological preparations are now becoming essential for presurgical evaluation.

Susceptibility weighted magnetic resonance imaging of cerebral cavernous malformations: prospects, drawbacks, and first experience at ultra–high field strength (7-Tesla) magnetic resonance imaging

High-resolution susceptibility weighted MR imaging at high field strength provides excellent depiction of venous structures, blood products, and iron deposits, making it a promising complementary imaging modality for cerebral cavernous malformations (CCMs). Although already introduced in 1997 and being constantly improved, susceptibility weighted imaging is not yet routine in clinical neuroimaging protocols for CCMs. In this article, the authors review the recent literature dealing with clinical and scientific susceptibility weighted imaging of CCMs to summarize its prospects and drawbacks and provide their first experience with its use in ultra–high field (7-T) MR imaging.

[Innovative MRI techniques in Parkinson's disease]

Brain imaging enables the investigation of brain morphology and function in patients with Parkinson's disease (PD). Innovative magnetic resonance imaging (MRI) techniques have recently been established as a new research tool in PD. They are based on the investigation of neuronal tissue properties (MR relaxometry, SWI, DWI, DTI, VBM) and of cerebral perfusion and neuronal activity (ASL, fcMRI). Besides a better understanding of the pathophysiology of PD, these innovative MR techniques might be suitable for measuring progression of PD and the effect of therapeutic interventions on brain functioning. In the clinical setting, they could help to advance the differential diagnosis of parkinsonian disorders.

[Application of susceptibility weighted imaging in revealing intratumoral blood products and grading gliomas]

OBJECTIVE

Susceptibility weighted imaging (SWI) is a novel imaging method that utilizes the magnetic susceptibility differences between tissues. The purpose of our study was to evaluate the application of SWI for revealing inratumoral blood products and diagnosing high-grade gliomas.

MATERIALS AND METHODS

Conventional MR sequences and SWI were performed in 32 patients, 10 low-grade gliomas (1 grade I and 9 grade II) and 22 high-grade gliomas (8 grade III and 14 grade IV). The ability of SWI for detecting inratumral blood products was analyzed and compared with conventional MR sequences. Logistic regression and Receiver operating characteristic (ROC) curve analysis were used to evaluate the diagnostic value of SWI for high-grade gliomas.

RESULTS

SWI was sensitive for showing intrtumoral blood products (P=0.00) and depicted much more micro bleeds. No statistical difference was found in detection rate of blood products between low-grade and high-grade group. According to the result of logistic regression, the frequency of blood products and the diameter of maximum blood products were significant determinants of high-grade gliomas. The result of ROC analysis indicated that with an optimal cut-off point (0.67), the sensitivity, specificity, positive predictive value and negative predictive value for diagnosing high-grade gliomas with blood products detected by SWI were 81.8%, 80.0%, 90.0%, and 66.6%, respectively.

CONCLUSION

SWI can accurately detect blood products with superlative contrast. With a high-grade gliomas risk estimation model based on two variables, satisfied sensitivity, specificity, PPV and NPV were obtained. Thus, SWI could be a useful adjunct sequence in glioma grading.

Susceptibility weighted imaging in cerebral hypoperfusion-can we predict increased oxygen extraction fraction?

INTRODUCTION

Increased concentrations of deoxyhemoglobin within veins can induce susceptibility changes resulting in increased conspicuity in susceptibility weighted imaging (SWI). Compensatory mechanisms following reduced cerebral perfusion due to carotid occlusive disease may not be sufficient to meet demands of ischemic tissue and increased tissue oxygen extraction ratio results in relative increase in deoxyhemoglobin levels in the venous blood draining affected hemisphere. We assessed whether patients with carotid disease display prominence of veins over affected cerebral hemisphere.

METHODS

Eighteen patients with unilateral carotid occlusion or critical carotid stenosis proven by magnetic resonance angiography (MRA) were selected. The medical records and MRI findings including SWI and MRA were reviewed. The SWI images were studied for the presence of asymmetry of veins over the cerebral hemispheres and were correlated with the site and severity of stenosis or occlusion. The veins were assumed to be conspicuous and asymmetric if there were more numerous veins and/or large veins with greater signal loss observed compared with opposite normal hemisphere.

RESULTS

In about half of patients, prominence of veins was noted in the cerebral hemisphere ipsilateral to side of occlusion. This was not observed in patients with significant extracranial carotid stenosis. The SWI abnormalities were seen extending beyond the boundaries of occluded vascular territory. There was good agreement between two observers in all the patients who showed positive finding. Also there was no interobserver variation in patients with negative findings.

CONCLUSION

The increased susceptibility arising out of increased deoxyhemoglobin to oxyhemoglobin ratio leads to visualization of prominent veins over the affected cerebral hemisphere on SWI.

Change in cortical vein appearance on susceptibility-weighted MR imaging before and after carotid artery stenting

OBJECTIVES

Susceptibility-weighted (SW) magnetic resonance (MR) imaging is a sensitive test to detect intravenous deoxygenated blood. On SW images, dilated appearing draining veins in tissue with perfusion impairment occur due to an increase in intravenous deoxyhemoglobin levels, and could indicate poor perfusion areas in which there is an elevated oxygen extraction fraction. In this study, patients with possible chronic ischemia caused by internal carotid artery stenosis underwent carotid artery stenting (CAS). Changes in cortical vein diameters were evaluated before and after CAS using SW imaging.

METHODS

Twenty-two patients with 25 lesions underwent 3 T SW imaging before and after CAS. The diameters of cortical veins were measured on SW images. Blood flow reduction and cerebrovascular reserve were examined before CAS using a single-photon emission computed tomography (SPECT) study, including an acetazolamide stress test.

RESULTS

Two of six patients with both decreased blood flow and reduced cerebrovascular reserve on SPECT showed significantly increased cortical vein diameters on pre-CAS SW images (P<0.05). After CAS, these same two patients demonstrated a significant decrease in their cortical vein diameters (P<0.05).

DISCUSSION

The present study demonstrates that dilated cortical veins as seen on SW imaging may reflect areas of altered oxygen extraction fraction due to chronic ischemia in patients with carotid artery stenosis, and that cortical venous dilatation is reversed after successful CAS. In the future, estimations of the cortical vein diameters on SW imaging may help to qualitatively evaluate areas of poor perfusion in chronic ischemia.

Three-dimensional susceptibility-weighted imaging at 3 T using various image analysis methods in the estimation of grading intracranial gliomas

OBJECT

Although three-dimensional (3D), high-spatial resolution susceptibility-weighted imaging (SWI) appears to be valuable in the evaluation of central nervous system gliomas, several evaluation methods are proposed in the literature. The purpose of this study was to evaluate the use of 3D SWI for grading intracranial gliomas with various analysis methods.

MATERIALS AND METHODS

Twenty-three patients suspected of having gliomas participated in this study. SWI was performed in addition to conventional MR sequences. In 15 cases, post-gadolinium enhanced SWI was also obtained. Imaging evaluation criteria were conventional grade, hypointensity ratio in the tumor-dominant structure of hypointensity on SWI (hemorrhage or vascular structure) and presence of abnormal enhancement surrounding the tumor.

RESULTS

Mean grading scores of conventional grade showed no statistically significant difference among WHO grades. Mean grading scores of hypointensity ratios in the tumor were higher for WHO Grades 3 and 4 than for lower grade tumors (P=.05, Mann-Whitney U test). Hemorrhagic foci were more frequently seen in the higher grade tumor. Post-contrast susceptibility-weighted images of five of 11 WHO Grade 3 and 4 cases showed bright enhancement surrounding the tumor, suggesting a breakdown of the blood-brain barrier.

CONCLUSIONS

SWI at 3 T may be a useful method to analyze the structural characteristics of gliomas and to evaluate pathology in vivo. Assessment of hypointensity ratios in the glioma was the most preferable method in grading glioma. However, more studies, specifically concerning a suitable method for image analysis, are needed to establish SWI at 3 T as a useful tool in clinical routine.

The imaging of the cerebral venous sinuses

The cerebral venous sinuses in the past have been relatively neglected during radiological, neurological, and neurosurgical scientific discourse. However modern imaging and radiological approaches to treatment are demonstrating that far from being rare, the cerebral venous sinuses are involved in the pathogenesis of a protean list of ailments. During the review we hope to illustrate the imaging of diseases of the cerebral venous sinuses as demonstrated on multislice computer tomography and magnetic resonance imaging.

Imaging of the meninges and the extra-axial spaces

The separate meningeal layers and extraaxial spaces are complex and can only be differentiated by pathologic processes on imaging. Differentiation of the location of such processes can be achieved using different imaging modalities. In this pictorial review we address the imaging techniques, enhancement and location patterns, and disease spread that will promote accurate localization of the pathology, thus improving accuracy of diagnosis. Typical and unusual magnetic resonance (MR), computed tomography (CT), and ultrasound imaging findings of many conditions affecting these layers and spaces are described.

Acute stroke magnetic resonance imaging: current status and future perspective

Cerebral stroke is one of the most frequent causes of permanent disability or death in the western world and a major burden in healthcare system. The major portion is caused by acute ischemia due to cerebral artery occlusion by a clot. The minority of strokes is related to intracerebral hemorrhage or other sources. To limit the permanent disability in ischemic stroke patients resulting from irreversible infarction of ischemic brain tissue, major efforts were made in the last decade. To extend the time window for thrombolysis, which is the only approved therapy, several imaging parameters in computed tomography and magnetic resonance imaging (MRI) have been investigated. However, the current guidelines neglect the fact that the portion of potentially salvageable ischemic tissue (penumbra) is not dependent on the time window but the individual collateral blood flow. Within the last years, the differentiation of infarct core and penumbra with MRI using diffusion-weighted images (DWI) and perfusion imaging (PI) with parameter maps was established. Current trials transform these technical advances to a redefined patient selection based on physiological parameters determined by MRI. This review article presents the current status of MRI for acute stroke imaging. A special focus is the ischemic stroke. In dependence on the pathophysiology of cerebral ischemia, the basic principle and diagnostic value of different MRI sequences are illustrated. MRI techniques for imaging of the main differential diagnoses of ischemic stroke are mentioned. Moreover, perspectives of MRI for imaging-based acute stroke treatment as well as monitoring of restorative stroke therapy from recent trials are discussed.