High-resolution three-dimensional contrast-enhanced blood oxygenation level-dependent magnetic resonance venography of brain tumors at 3 Tesla: first clinical experience and comparison with 1.5 Tesla

Prominent hypointense vessel on susceptibility-weighted images accompanying hyperacute and acute large infarction

BACKGROUND

Multiple prominent hypointense vessels on susceptibility-weighted image (SWI) have been found in the ischemic territory of patients with acute ischemic stroke. SWI is suitable for venous imaging.

PURPOSE

To evaluate the conditions of prominent hypointense vessel (PHV) in hyperacute and acute cerebral infarctions using susceptibility-weighted image (SWI).

MATERIALS AND METHODS

Magnetic resonance images, including SWI, of 284 patients with acute infarction were evaluated. Based on lesion size, the infarction was classified as a small (< 3 cm) or a large (> 3 cm) infarction. Stage of infarction was classified as hyperacute (< 6 h) or acute (> 6 h, < 1 week) on the basis of the onset of stroke. The site of infarction was categorised as a deep grey matter or a mixed (cortical and/or deep grey matter) infarction. The venous structures were analysed qualitatively for the calibre difference between ipsilateral and contralateral hemispheres. We quantitatively analysed the relationship between the size of areas with PHV on SWI and the abnormalities on MR angiography, apparent diffusion coefficient value, and signal intensity on T2WI in the 271 patients.

RESULTS

PHV over the infarction site was observed in 54.1% (137/253) of the large infarctions, and 19.3% (6/31) of the small infarctions on SWI. PHV was demonstrated in 63.1% (118/187) of mixed infarctions and 25.8% (25/97) of deep grey matter infarctions, and 59.2% (58/98) in hyperacute and 45.7% (85/186) of acute infarctions. The presence of PHV was statistically significant in the size and region of cerebral infarction (p < 0.05), and was not significant in the stage of infarction (p = 0.137). Quantitative analysis revealed significant differences in the MRA abnormalities and ADC values in the PHV ( +) group (p < 0.05) and no significant difference in the T2WI SI ratio in the PHV ( +) group (p = 0.086), compared with PHV (-) group.

CONCLUSION

PHV on SWI was more prominent at the portions with the large and mixed infarctions. PHV was observed both in hyperacute and acute infarction.

Emerging Techniques in Brain Tumor Imaging: What Radiologists Need to Know

Among the currently available brain tumor imaging, advanced MR imaging techniques, such as diffusion-weighted MR imaging and perfusion MR imaging, have been used for solving diagnostic challenges associated with conventional imaging and for monitoring the brain tumor treatment response. Further development of advanced MR imaging techniques and postprocessing methods may contribute to predicting the treatment response to a specific therapeutic regimen, particularly using multi-modality and multiparametric imaging. Over the next few years, new imaging techniques, such as amide proton transfer imaging, will be studied regarding their potential use in quantitative brain tumor imaging. In this review, the pathophysiologic considerations and clinical validations of these promising techniques are discussed in the context of brain tumor characterization and treatment response.

Susceptibility-weighted imaging using inter-echo-variance channel combination for improved contrast at 7 tesla

PURPOSE

To implement and optimize a new approach for susceptibility-weighted image (SWI) generation from multi-echo multi-channel image data and compare its performance against optimized traditional SWI pipelines.

MATERIALS AND METHODS

Five healthy volunteers were imaged at 7 Tesla. The inter-echo-variance (IEV) channel combination, which uses the variance of the local frequency shift at multiple echo times as a weighting factor during channel combination, was used to calculate multi-echo local phase shift maps. Linear phase masks were combined with the magnitude to generate IEV-SWI. The performance of the IEV-SWI pipeline was compared with that of two accepted SWI pipelines-channel combination followed by (i) Homodyne filtering (HPH-SWI) and (ii) unwrapping and high-pass filtering (SVD-SWI). The filtering steps of each pipeline were optimized. Contrast-to-noise ratio was used as the comparison metric. Qualitative assessment of artifact and vessel conspicuity was performed and processing time of pipelines was evaluated.

RESULTS

The optimized IEV-SWI pipeline (σ = 7 mm) resulted in continuous vessel visibility throughout the brain. IEV-SWI had significantly higher contrast compared with HPH-SWI and SVD-SWI (P < 0.001, Friedman nonparametric test). Residual background fields and phase wraps in HPH-SWI and SVD-SWI corrupted the vessel signal and/or generated vessel-mimicking artifact. Optimized implementation of the IEV-SWI pipeline processed a six-echo 16-channel dataset in under 10 min.

CONCLUSION

IEV-SWI benefits from channel-by-channel processing of phase data and results in high contrast images with an optimal balance between contrast and background noise removal, thereby presenting evidence of importance of the order in which postprocessing techniques are applied for multi-channel SWI generation.

LEVEL OF EVIDENCE

2 J. Magn. Reson. Imaging 2017;45:1113-1124.

Vascular malformation mimicking multiple sclerosis active plaque: Usefulness of susceptibility weighted imaging (SWI) to perform correct diagnosis

Brain focal hyperdensity areas are common findings in computed tomography examinations, often further evaluated in magnetic resonance imaging exams. These are usually haemosiderin and calcified perivascular clusters known as cerebral microbleeds and may be secondary signs of brain disorders. Cerebral microbleeds are paramagnetic and ferromagnetic substances determining magnetic field inhomogeneity. Susceptibility weighted imaging (SWI) performed at 3T with phase post-processing is very useful in evaluating this field variation. In fact in the past decade SWI has been increasingly reported for its clinical value in adults with neurologic disorders, traumas, arterial venous malformations, occult venous diseases, tumours and functional brain imaging. The occasional computed tomography findings of single or multiple focal hyperdense areas can mimic many of these brain disorders and lead to misinterpretations. For these reason it is useful to have a more detailed diagnosis with MRI brain examination. The authors highlight the role of SWI sequence in the differential diagnosis among active plaque, vascular malformation and haemorrhagic lesion in a case report of a 41-year-old woman suffering from multiple sclerosis with a focal hyperdense area reported in a computed tomography brain examination.

Variations of ITSS-Morphology and their Relationship to Location and Tumor Volume in Patients with Glioblastoma

BACKGROUND

Susceptibility weighted imaging and assessment of intratumoral susceptibility signal (ITSS) morphology is used to identify high-grade glioma (HGG) in patients with suspected brain neoplasm.

PURPOSE

The aim of this study was to outline variations in ITSS-morphology and their relationship to location as well as volume of the lesion in patients with glioblastoma (GB).

MATERIALS AND METHODS

Contrast-enhanced SWI (CE-SWI) images of 40 patients with histologically confirmed GB were analyzed retrospectively with particular attention to ITSS-morphology dividing all lesions into two groups. Considering the location of the lesion within brain parenchyma, lesions with and without involvement of the subventricular zone (SVZ+/SVZ-) were discerned. Additionally, the contrast-enhancing tumor volume was evaluated. Statistical analysis was based on a classification analysis resulting in a classification rule (tree) as well as Mann-Whitney-U test.

RESULTS

The distribution of ITSS-scores showed differences between the SVZ+ and SVZ- groups. While SVZ-GB showed only fine-linear or dot-like ITSS, in SVZ+ GB the ITSS-morphology changed with the tumor volume, that is, in larger tumors dense and conglomerated ITSS were the predominant finding.

CONCLUSION

Our findings indicate that ITSS-morphology is not a random phenomenon. Location of GB, as well as tumor volume, appear to be factors contributing to ITSS morphology.

Prominent hypointense veins on susceptibility weighted image in the cat brain with acute infarction: DWI, SWI, and PWI

BACKGROUND

The multiple prominent hypointense veins on susceptibility-weighted imaging (SWI) have been found in the ischemic territory of patients with acute ischemic stroke. Venous side is the unknown area in the hemodynamics of brain infarction.

PURPOSE

To evaluate the venous aspect in acute brain infarction through an animal study.

MATERIAL AND METHODS

The acute infarction in cat brains was induced with a bolus infusion of 0.25 mL of triolein through one side of the common carotid artery. The magnetic resonance (MR) images, including diffusion-weighted imaging (DWI), apparent diffusion coefficient (ADC) map, SW, and perfusion-weighted (PWI) images, were obtained serially at 2 h (n = 17), 1 day (n = 11), and 4 days (n = 4) after triolein infusion. The obtained MR images were evaluated qualitatively and quantitatively. For qualitative assessment, the signal intensity of the serial MR images was evaluated. The presence or absence and the location with serial changes of infarction were identified on DWI and ADC map images. The presence or absence of prominent hypointense veins and the serial changes of cortical veins were also evaluated on SWI. Quantitative assessment was performed by comparing the relative cerebral blood volume (rCBV), cerebral blood flow (rCBF), and mean transit times (MTT) of the lesions with those of the contralateral normal side calculated on PWI. The serial changes of rCBV, rCBF, and MTT ratio were also evaluated.

RESULTS

Acute infarction in the first and second medial gyrus of lesion hemisphere was found by qualitative evaluation of DWI and ADC map images. On the serial evaluation of SWI, the cortical veins of cat brain with infarction were obscured at 2 h and then re-appeared at 1 day. The hemorrhage transformation and prominent hypointense veins were seen at 4 days on SWI. The quantitative evaluation revealed increased MTT ratios and decreased rCBV and rCBF ratios on PWIs in the acute infarction of cat brain.

CONCLUSION

The prominent hypointense veins on SWI were seen in the half of the acute infarction at 4 days. The prominent hypointense veins on SWI may have good agreement with the increased MTT ratio.

In vivo quantification of white matter microstructure for use in aging: a focus on two emerging techniques

Human brain imaging has seen many advances in the quantification of white matter in vivo. For example, these advances have revealed the association between white matter damage and vascular disease as well as their impact on risk for and development of dementia and depression in an aging population. Current neuroimaging methods to quantify white matter damage provide a foundation for understanding such age-related neuropathology; however, these methods are not as adept at determining the underlying microstructural abnormalities signaling at risk tissue or driving white matter damage in the aging brain. This review will begin with a brief overview of the use of diffusion tensor imaging (DTI) in understanding white matter alterations in aging before focusing in more detail on select advances in both diffusion-based methods and multi-component relaxometry techniques for imaging white matter microstructural integrity within myelin sheaths and the axons they encase. Although DTI greatly extended the field of white matter interrogation, these more recent technological advances will add clarity to the underlying microstructural mechanisms that contribute to white matter damage. More specifically, the methods highlighted in this review may prove more sensitive (and specific) for determining the contribution of myelin versus axonal integrity to the aging of white matter in brain.

Benefits of contrast-enhanced SWI in patients with glioblastoma multiforme

INTRODUCTION

SWI can help to identify high-grade gliomas (HGG). The objective of this study was to analyse SWI and CE-SWI characteristics, i.e. the relationship between contrast-induced phase shifts (CIPS) and intratumoral susceptibility signals (ITSS) and their association with tumour volume in patients with glioblastoma multiforme (GBM).

MATERIALS AND METHODS

MRI studies of 29 patients were performed to evaluate distinct susceptibility signals comparing SWI and CE-SWI characteristics. The relationship between these susceptibility signals and CE-T1w tumour volume was analysed by using Spearman's rank correlation coefficient and Kruskal-Wallis-test. Tumour biopsies of different susceptibility signals were performed in one patient.

RESULTS

Comparison of SWI and CE-SWI demonstrated different susceptibility signals. Susceptibility signals visible on SWI images are consistent with ITSS; those only seen on CE-SWI were identified as CIPS. Correlation with CE-T1w tumour volume revealed that CIPS were especially present in small or medium-sized GBM (Spearman's rho r = 0.843, P < 0.001). Histology identified the area with CIPS as the tumour invasion zone, while the area with ITSS represented micro-haemorrhage, highly pathological vessels and necrosis.

CONCLUSION

CE-SWI adds information to the evaluation of GBM before therapy. It might have the potential to non-invasively identify the tumour invasion zone as demonstrated by biopsies in one case.

KEY POINTS

• MRI is used to help differentiate between low- and high-grade gliomas. • Contrast-enhanced susceptibility-weighted MRI (CE-SWI) helps to identify patients with glioblastoma multiforme. • CE-SWI delineates the susceptibility signal (CIPS and ITSS) more than the native SWI. • CE-SWI might have the potential to non-invasively identify the tumour invasion zone.

A systematic review of the utility of 1.5 versus 3 Tesla magnetic resonance brain imaging in clinical practice and research

OBJECTIVE

MRI at 3 T is said to be more accurate than 1.5 T MR, but costs and other practical differences mean that it is unclear which to use.

METHODS

We systematically reviewed studies comparing diagnostic accuracy at 3 T with 1.5 T. We searched MEDLINE, EMBASE and other sources from 1 January 2000 to 22 October 2010 for studies comparing diagnostic accuracy at 1.5 and 3 T in human neuroimaging. We extracted data on methodology, quality criteria, technical factors, subjects, signal-to-noise, diagnostic accuracy and errors according to QUADAS and STARD criteria.

RESULTS

Amongst 150 studies (4,500 subjects), most were tiny, compared old 1.5 T with new 3 T technology, and only 22 (15 %) described diagnostic accuracy. The 3 T images were often described as "crisper", but we found little evidence of improved diagnosis. Improvements were limited to research applications [functional MRI (fMRI), spectroscopy, automated lesion detection]. Theoretical doubling of the signal-to-noise ratio was not confirmed, mostly being 25 %. Artefacts were worse and acquisitions took slightly longer at 3 T.

CONCLUSION

Objective evidence to guide MRI purchasing decisions and routine diagnostic use is lacking. Rigorous evaluation accuracy and practicalities of diagnostic imaging technologies should be the routine, as for pharmacological interventions, to improve effectiveness of healthcare.

KEY POINTS

• Higher field strength MRI may improve image quality and diagnostic accuracy. • There are few direct comparisons of 1.5 and 3 T MRI. • Theoretical doubling of the signal-to-noise ratio in practice was only 25 %. • Objective evidence of improved routine clinical diagnosis is lacking. • Other aspects of technology improved images more than field strength.

Susceptibility-weighted imaging in patients with pyogenic brain abscesses at 1.5T: characteristics of the abscess capsule

BACKGROUND AND PURPOSE

SWI is a high-resolution 3D, fully velocity-compensated gradient-echo sequence that uses both magnitude and phase data. The purpose of this study was to investigate the phase behavior of the capsule of pyogenic brain abscesses with noncontrast SWI.

MATERIALS AND METHODS

Fourteen patients with pyogenic brain abscesses were studied at 1.5T. In all of the patients, SWI images were obtained and reviewed in addition to conventional MR images. Phase values within the abscess capsule were measured and compared with those from the abscess cavities and contralateral normal white matter using 1-way repeated measures ANOVA with post hoc Bonferroni analysis.

RESULTS

SWI phase images showed mild hypointesity in 6 patients, isointensity in 3 patients, and mixed iso- to mild hypointensity in 5 patients. The means of phase in the cavity, rim of abscesses, and contralateral normal white matter were -7.552 × 10(-3) ± 0.024, -0.105 ± 0.080, and +0.029 ± 0.011 radians, respectively. Post hoc comparisons showed significant differences between any pair of the 3 regions (abscess cavity, rim capsule, and normal white matter) in SWI (all Ps < .005).

CONCLUSIONS

SWI phase imaging shows evidence of paramagnetic substances in agreement with the presence of free radicals from phagocytosis. SWI may provide additional information valuable in the characterization of pyogenic brain abscesses.

Detection of cerebral microbleeds with quantitative susceptibility mapping in the ArcAbeta mouse model of cerebral amyloidosis

Cerebral microbleeds (CMBs) are findings in patients with neurological disorders such as cerebral amyloid angiopathy and Alzheimer's disease, and are indicative of an underlying vascular pathology. A diagnosis of CMBs requires an imaging method that is capable of detecting iron-containing lesions with high sensitivity and spatial accuracy in the presence of potentially confounding tissue abnormalities. In this study, we investigated the feasibility of quantitative magnetic susceptibility mapping (QSM), a novel technique based on gradient-recalled echo (GRE) phase data, for the detection of CMBs in the arcAβ mouse, a mouse model of cerebral amyloidosis. Quantitative susceptibility maps were generated from phase data acquired with a high-resolution T(2)(*)-weighted GRE sequence at 9.4 T. We examined the influence of different regularization parameters on susceptibility computation; a proper adjustment of the regularization parameter minimizes streaking artifacts and preserves fine structures. In the present study, it is shown that QSM provides increased detection sensitivity of CMBs and improved contrast when compared with GRE magnitude imaging. Furthermore, QSM corrects for the blooming effect observed in magnitude and phase images and depicts both the localization and spatial extent of CMBs with high accuracy. Therefore, QSM may become an important tool for diagnosing CMBs in neurological diseases.

MR phase imaging: sensitive and contrast-enhancing visualization in cellular imaging

The successful translation of stem-cell therapies requires a detailed understanding of the fate of transplanted cells. Magnetic resonance imaging (MRI) has provided a noninvasive means of imaging cell dynamics in vivo by prelabeling cell with T(2) shortening iron oxide particles. However, this approach suffers from a gradual loss of sensitivity since active cell mitosis could decrease the cellular contrast agent (CA) concentration below detection level. In addition, the interpretation of images may be confounded by hypointensities induced by factors other than this CA susceptibility effect (CASE). We therefore examined the feasibility of exploiting the phase information in MRI to increase the sensitivity of cellular imaging and to differentiate the CASE from endogenous image hypointensity. Phase aliasing and the B(0) field inhomogeneity effect were removed by applying a reliable unwrapping algorithm and a high-pass filter, respectively, thus delineating phase variations originating from high spatial frequencies due to the CASE. We found that the filtered phase map detects labeled cells with high sensitivity and can readily differentiate the cell migration track from the white matter, both of which are hypointense in T(2)-weighted magnitude images. Furthermore, an approximate fivefold contrast-to-noise ratio enhancement can be achieved with an MRI phase map over conventional T(2)-weighted magnitude images.

Decreased brain venous vasculature visibility on susceptibility-weighted imaging venography in patients with multiple sclerosis is related to chronic cerebrospinal venous insufficiency

Background

The potential pathogenesis between the presence and severity of chronic cerebrospinal venous insufficiency (CCSVI) and its relation to clinical and imaging outcomes in brain parenchyma of multiple sclerosis (MS) patients has not yet been elucidated. The aim of the study was to investigate the relationship between CCSVI, and altered brain parenchyma venous vasculature visibility (VVV) on susceptibility-weighted imaging (SWI) in patients with MS and in sex- and age-matched healthy controls (HC).

Methods

59 MS patients, 41 relapsing-remitting and 18 secondary-progressive, and 33 HC were imaged on a 3T GE scanner using pre- and post-contrast SWI venography. The presence and severity of CCSVI was determined using extra-cranial and trans-cranial Doppler criteria. Apparent total venous volume (ATVV), venous intracranial fraction (VIF) and average distance-from-vein (DFV) were calculated for various vein mean diameter categories: < .3 mm, .3-.6 mm, .6-.9 mm and > .9 mm.

Results

CCSVI criteria were fulfilled in 79.7% of MS patients and 18.2% of HC (p < .0001). Patients with MS showed decreased overall ATVV, ATVV of veins with a diameter < .3 mm, and increased DFV compared to HC (all p < .0001). Subjects diagnosed with CCSVI had significantly increased DFV (p < .0001), decreased overall ATVV and ATVV of veins with a diameter < .3 mm (p < .003) compared to subjects without CCSVI. The severity of CCSVI was significantly related to decreased VVV in MS (p < .0001) on pre- and post-contrast SWI, but not in HC.

Conclusions

MS patients with higher number of venous stenoses, indicative of CCSVI severity, showed significantly decreased venous vasculature in the brain parenchyma. The pathogenesis of these findings has to be further investigated, but they suggest that reduced metabolism and morphological changes of venous vasculature may be taking place in patients with MS.

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 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.

MRI in rodent models of brain disorders

Magnetic resonance imaging (MRI) is a well-established tool in clinical practice and research on human neurological disorders. Translational MRI research utilizing rodent models of central nervous system (CNS) diseases is becoming popular with the increased availability of dedicated small animal MRI systems. Projects utilizing this technology typically fall into one of two categories: 1) true "pre-clinical" studies involving the use of MRI as a noninvasive disease monitoring tool which serves as a biomarker for selected aspects of the disease and 2) studies investigating the pathomechanism of known human MRI findings in CNS disease models. Most small animal MRI systems operate at 4.7-11.7 Tesla field strengths. Although the higher field strength clearly results in a higher signal-to-noise ratio, which enables higher resolution acquisition, a variety of artifacts and limitations related to the specific absorption rate represent significant challenges in these experiments. In addition to standard T1-, T2-, and T2*-weighted MRI methods, all of the currently available advanced MRI techniques have been utilized in experimental animals, including diffusion, perfusion, and susceptibility weighted imaging, functional magnetic resonance imaging, chemical shift imaging, heteronuclear imaging, and (1)H or (31)P MR spectroscopy. Selected MRI techniques are also exclusively utilized in experimental research, including manganese-enhanced MRI, and cell-specific/molecular imaging techniques utilizing negative contrast materials. In this review, we describe technical and practical aspects of small animal MRI and provide examples of different MRI techniques in anatomical imaging and tract tracing as well as several models of neurological disorders, including inflammatory, neurodegenerative, vascular, and traumatic brain and spinal cord injury models, and neoplastic diseases.

Filtered deconvolution of a simulated and an in vivo phase model of the human brain

PURPOSE

To remove spatial patterns in gradient echo phase images which are caused by susceptibility differences between different tissue types using filtered deconvolution and to evaluate deconvolution effects.

MATERIALS AND METHODS

A realistic simulated susceptibility map of the human brain was built and used to evaluate the effects of filtered deconvolution. The simulated susceptibility map was convolved with a filter kernel representing a magnetic dipole resulting in a simulated phase map. The artificial phase map was superimposed with different noise levels and deconvolved using different deconvolution kernels. The resulting contrast-to-noise ratios between white and gray matter of the deconvolved data provide an estimate for an optimal deconvolution kernel for a given noise level. These results were used to deconvolve an in vivo phase model representing the average of 30 phase data sets and also individual phase data acquired at 7 Tesla.

RESULTS

The deconvolved phase model shows a better anatomical agreement with the corresponding magnitude than the original phase model (5% higher kappa coefficient). Visual inspection of the deconvolved individual phase shows a more consistent delineation of blood vessels.

CONCLUSION

Filtered deconvolution of SWI phase is possible when an appropriate filter kernel is used. This helps to improve region of interest definition as unrealistic phase patterns are removed.

Intracranial dural arteriovenous fistula with retrograde cortical venous drainage: use of susceptibility-weighted imaging in combination with dynamic susceptibility contrast imaging

BACKGROUND AND PURPOSE

SWI is a new MR imaging method that maximizes sensitivity to magnetic susceptibility effects with phase information for visualizing small cerebral veins. The purpose of this study was to report the use of SWI in combination with DSC in examining related RCVD in patients with intracranial DAVFs.

MATERIALS AND METHODS

Ten patients with angiographically confirmed DAVFs with RCVD underwent conventional MR imaging, SWI, and DSC. The ability of SWI to depict dilated cerebral veins was evaluated and then compared with DSC. The hemispheres of patients with DAVFs were grouped into affected (with RCVD) or nonaffected (without RCVD) categories by angiography. Four patients had bilaterally affected hemispheres. A total of 14 affected hemispheres in patients with DAVFs with RCVD were evaluated.

RESULTS

SWI showed dilated cerebral veins on the surface of the brain in all (100%) of the 14 affected hemispheres in patients with DAVFs with RCVD and deep in the brain in 9 (64%). T2-weighted imaging showed prominent flow-voids on the surface of the brain in 10 (71%) of the 14 affected hemispheres in patients with DAVFs with RCVD and deep in the brain in 5 (36%). DSC showed increased cerebral blood volume in all of the 14 affected hemispheres. The SWI findings regarding dilated veins on the surface of the brain corresponded well with the areas of increased cerebral blood volume.

CONCLUSIONS

SWI in combination with DSC could be used to characterize the presence of RCVD in patients with DAVFs.

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.

Windows on the human body--in vivo high-field magnetic resonance research and applications in medicine and psychology

Analogous to the evolution of biological sensor-systems, the progress in "medical sensor-systems", i.e., diagnostic procedures, is paradigmatically described. Outstanding highlights of this progress are magnetic resonance imaging (MRI) and spectroscopy (MRS), which enable non-invasive, in vivo acquisition of morphological, functional, and metabolic information from the human body with unsurpassed quality. Recent achievements in high and ultra-high field MR (at 3 and 7 Tesla) are described, and representative research applications in Medicine and Psychology in Austria are discussed. Finally, an overview of current and prospective research in multi-modal imaging, potential clinical applications, as well as current limitations and challenges is given.

Susceptibility weighted imaging (SWI) of the kidney at 3T--initial results

Susceptibility weighted imaging provides diagnostic information in strokes, hemorrhages, and cerebral tumors and has proven to be a valuable tool in imaging venous vessels in the cerebrum. The SWI principle is based on the weighting of T(2)* weighted magnitude images with a phase mask, therewith improving image contrast of veins or neighbouring structures of different susceptibility, in general. T(2)* weighted MRI is already used for assessment of kidney function. In this paper, the feasibility of SWI on kidneys was investigated. Translation of SWI from the brain to the kidneys comes along with two main challenges: (i) organ motion due to breathing and (ii) a higher oxygenation level of renal veins compared to the brain. To handle these problems, the acquisition time has been cut down to allow for breath-hold examinations, and different post-processing methods including a new phase mask were investigated to visualize renal veins. Results showed that by a new post-processing strategy SWI contrast was enhanced on average by a factor of 1.33 compared to the standard phase mask. In summary, initial experiences of SWI on the kidneys demonstrated the feasibility. However, further technical developments have to be performed to make this technology applicable in clinical abdominal MRI.

Combination of high-resolution susceptibility-weighted imaging and the apparent diffusion coefficient: added value to brain tumour imaging and clinical feasibility of non-contrast MRI at 3 T

The purpose of this study was to determine the benefit of high-resolution susceptibility-weighted imaging and the apparent diffusion coefficient for brain tumour imaging, and to assess the clinical feasibility of using a non-contrast MR protocol at 3 T. 73 patients with intra-axial tumours were enrolled into the study. Two experienced neuroradiologists reviewed three MRI sessions: (i) a non-contrast protocol including high-resolution susceptibility-weighted images and apparent diffusion coefficient; (ii) a contrast protocol including MR perfusion images; and (iii) combined contrast and non-contrast protocols. The two observers categorised tumours as glial or non-glial tumours, and then subcategorised the gliomas into low-grade or high-grade tumours. For semi-quantitative analysis, a scoring system based on the degree of intra-tumoral susceptibility signals and the visual apparent diffusion coefficient was used. The two observers diagnosed accurate tumour pathology in 52 (71%) of 73 tumours in the first review, 55 (75%) of 73 tumours in the second review and 61 (84%) of 73 tumours in the third review. The addition of the non-contrast protocol to the contrast protocol significantly differentiated glioblastoma multiforme and metastatic tumours, which was not possible with the contrast protocol alone. The sensitivity, specificity, positive predictive value and negative predictive value for glioma grading with the non-contrast protocol were 83.2%, 100%, 100% and 79.3%, respectively. The addition of both high-resolution susceptibility-weighted imaging and the apparent diffusion coefficient improved the diagnostic performance of the contrast MR protocol for brain tumour imaging and could be feasible in selected patients who cannot tolerate a contrast agent.

Susceptibility-weighted imaging: clinical angiographic applications

By combining filtered phase and magnitude information to create a novel and intrinsic source of contrast, susceptibility-weighted imaging (SWI) has shown great promise in clinical angiography and venography. SWI has contributed to new insights into traumatic brain injury, the role of calcification in atherosclerosis, and the possible relationship between blood settling and deep venous thrombosis. A further contribution from SWI to deep venous thrombosis research (and also stroke) involves its application to the noninvasive measurement of oxygen saturation in the brain and in other tissues. Altogether, SWI offers manifold and diverse avenues for further research using angiographic and venographic techniques.

Added value and diagnostic performance of intratumoral susceptibility signals in the differential diagnosis of solitary enhancing brain lesions: preliminary study

BACKGROUND AND PURPOSE

It has been reported that high-resolution susceptibility-weighted imaging (HR-SWI) is a promising tool for assessing brain tumor characterization noninvasively. The purpose of this study was to determine the added value and diagnostic performance of HR-SWI for differentiating solitary enhancing brain lesions (SELs) by assessing intratumoral susceptibility signals (ITSSs).

MATERIALS AND METHODS

Sixty-four consecutive patients with SELs, without previous surgery, were retrospectively reviewed. We performed 2 consensus reviews, by using conventional MR images alone and with adjunctive HR-SWI. We applied an ITSS grading system based on the degree of the ITSS. Then, we compared the presence and grade of the ITSSs among specific pathologic types of SELs.

RESULTS

Two observers diagnosed tumor pathology accurately in 43 (67%) of 64 SELs after reviewing the conventional images alone and 50 (78%) of 64 SELs after reviewing the adjunctive HR-SWI (P = .016, McNemar test). ITSSs were seen in 25 (100%) of 25 glioblastoma multiformes (GBMs), in 2 (40%) of 5 anaplastic astrocytomas, and in 11 (73%) of 15 metastatic tumors. Although the ITSSs were unable to distinguish between GBMs and solitary metastatic tumors, differentiation between GBMs and solitary metastatic tumors was achieved (P = .01) by using a high ITSS degree (grade 3). Moreover, the ITSSs could discriminate high-grade gliomas from lymphomas and nontumorous lesions with a specificity of 100% (P < .0001).

CONCLUSIONS

The use of ITSSs on HR-SWIs significantly improves the accuracy for the differential diagnosis of SELs compared with the use of conventional MR imaging alone.

Semiquantitative assessment of intratumoral susceptibility signals using non-contrast-enhanced high-field high-resolution susceptibility-weighted imaging in patients with gliomas: comparison with MR perfusion imaging

BACKGROUND AND PURPOSE

It has been reported that high-resolution susceptibility-weighted imaging (HR-SWI) may demonstrate brain tumor vascularity. We determined whether the degree of intratumoral susceptibility signal intensity (ITSS) on HR-SWI correlates with maximum relative cerebral blood volume (rCBVmax) and to compare its diagnostic accuracy for glioma grading with that of dynamic susceptibility contrast (DSC) perfusion MR imaging.

MATERIALS AND METHODS

Forty-one patients with diffuse astrocytomas underwent both non-contrast-enhanced HR-SWI and DSC at 3T. We correlated the degree and morphology of ITSS with rCBVmax within the same tumor segment. The degree of ITSS and rCBVmax were compared among 3 groups with different histopathologic grades. Spearman correlation coefficients were determined between the degree of ITSS, rCBVmax, and glioma grade. Receiver operating characteristic (ROC) curve analyses were performed to determine the diagnostic accuracy for glioma grading.

RESULTS

The degree of ITSS showed a significant correlation with the value of rCBVmax in the same tumor segments (r = 0.72, P < .0001). However, the areas of densely prominent ITSSs did not accurately correspond with those of rCBVmax. Spearman correlation coefficients between ITSS degree and glioma grade were 0.88 (95% confidence interval, 0.79-0.94). In the ROC curve analysis of histopathologic correlation by using the degree of ITSS, the optimal sensitivity, specificity, positive predictive value, and negative predictive value for determining a high-grade tumor were 85.2%, 92.9%, 95.8%, and 76.5%, respectively.

CONCLUSIONS

The degree of ITSS shows a significant correlation with the value of rCBVmax in the same tumor segments, and its diagnostic performance for glioma grading is comparable with that of DSC.

Signal intensity of the motor cortex on phase-weighted imaging at 3T

BACKGROUND AND PURPOSE

It is known that the motor cortex shows hypointensity on T2-weighted images in older patients. The goal of this study was to assess the signal intensity of the motor cortices on the phase-weighted imaging performed with a Windows-based software program that we developed ourselves.

MATERIALS AND METHODS

All studies were performed at 3T MR imaging. First, the TE for the phase-weighted image was optimized; the best contrast between the motor and other cortices was obtained with a TE of 40 ms. The study population consisted of 45 healthy subjects (23 females, 22 males; mean age, 32.1 years). The signal intensity of the motor cortices was divided into 3 grades by 2 neuroradiologists in comparison with that of the superior frontal cortex (SFC): In grade I, the motor cortex was isointense to the SFC; in grade II, the motor cortex was slightly hypointense to the SFC; and in grade III, the motor cortex was markedly hypointense to the SFC.

RESULTS

The motor cortex was classified as either grade II or III in all subjects older than 20 years of age on the phase-weighted images. Even at 10-19 years of age, the grade II or III appearance was found in 14 (88%) of 16 motor cortices (8 subjects) on the phase-weighted images.

CONCLUSION

In adolescents, the motor cortex is hypointense to other cerebral cortices on phase-weighted MR imaging, which probably reflects differences in the concentration of nonheme iron and/or in the tissue architecture.

Susceptibility-weighted MR imaging: a review of clinical applications in children

Susceptibility-weighted imaging (SWI) is a high-spatial-resolution 3D gradient-echo MR imaging technique with phase postprocessing that accentuates the paramagnetic properties of blood products such as deoxyhemoglobin, intracellular methemoglobin, and hemosiderin. It is particularly useful for detecting intravascular venous deoxygenated blood as well as extravascular blood products. It is also quite sensitive to the presence of other substances such as iron, some forms of calcification, and air. We have used this technique in the past several years to study a wide variety of pediatric neurologic disorders. We present a review with selected case histories to demonstrate its clinical usefulness in the improvement of the following: 1) detection of hemorrhagic lesions seen in various conditions, including traumatic brain injury and coagulopathic or other hemorrhagic disorders; 2) detection of vascular malformations such as cavernous angiomas, telangiectasias, or pial angiomas associated with Sturge-Weber syndrome; 3) demonstration of venous thrombosis and/or increased oxygen extraction in the setting of infarction, hypoxic/anoxic injury, or brain death; 4) delineation of neoplasms with hemorrhage, calcification, or increased vascularity; and 5) depiction of calcium or iron deposition in neurodegenerative disorders. SWI has provided new understanding of some of these disease processes. It is hoped that as SWI becomes more widely available, it will provide additional diagnostic and prognostic information that will improve the care and outcome of affected children.

High-field, high-resolution, susceptibility-weighted magnetic resonance imaging: improved image quality by addition of contrast agent and higher field strength in patients with brain tumors

INTRODUCTION

To demonstrate intratumoral susceptibility effects in malignant brain tumors and to assess visualization of susceptibility effects before and after administration of the paramagnetic contrast agent MultiHance (gadobenate dimeglumine; Bracco Imaging), an agent known to have high relaxivity, with respect to susceptibility effects, image quality, and reduction of scan time.

METHODS

Included in the study were 19 patients with malignant brain tumors who underwent high-resolution, susceptibility-weighted (SW) MR imaging at 3 T before and after administration of contrast agent. In all patients, Multihance was administered intravenously as a bolus (0.1 mmol/kg body weight). MR images were individually evaluated by two radiologists with previous experience in the evaluation of pre- and postcontrast 3-T SW MR images with respect to susceptibility effects, image quality, and reduction of scan time.

RESULTS

In the 19 patients 21 tumors were diagnosed, of which 18 demonstrated intralesional susceptibility effects both in pre- and postcontrast SW images, and 19 demonstrated contrast enhancement in both SW images and T1-weighted spin-echo MR images. Conspicuity of susceptibility effects and image quality were improved in postcontrast images compared with precontrast images and the scan time was also reduced due to decreased TE values from 9 min (precontrast) to 7 min (postcontrast).

CONCLUSION

The intravenous administration of MultiHance, an agent with high relaxivity, allowed a reduction of scan time from 9 min to 7 min while preserving excellent susceptibility effects and image quality in SW images obtained at 3 T. Contrast enhancement and intralesional susceptibility effects can be assessed in one sequence.

High-resolution contrast-enhanced, susceptibility-weighted MR imaging at 3T in patients with brain tumors: correlation with positron-emission tomography and histopathologic findings

BACKGROUND AND PURPOSE

The purpose of this work was to demonstrate susceptibility effects (SusE) in various types of brain tumors with 3T high-resolution (HR)-contrast-enhanced (CE)-susceptibility-weighted (SW)-MR imaging and to correlate SusE with positron-emission tomography (PET) and histopathology.

MATERIALS AND METHODS

Eighteen patients with brain tumors, scheduled for biopsy or tumor extirpation, underwent high-field (3T) MR imaging. In all of the patients, an axial T1-spin-echo (SE) sequence and an HR-SW imaging sequence before and after IV application of a standard dose of contrast agent (MultiHance) was obtained. Seven patients preoperatively underwent PET. The frequency and formation of intralesional SusE in all of the images were evaluated and correlated with tumor grade as determined by PET and histopathology. Direct correlation of SusE and histopathologic specimens was performed in 6 patients. Contrast enhancement of the lesions was assessed in both sequences.

RESULTS

High-grade lesions demonstrated either high or medium frequency of SusE in 90% of the patients. Low-grade lesions demonstrated low frequency of SusE or no SusE. Correlation between intralesional frequency of SusE and histopathologic, as well as PET, tumor grading was statistically significant. Contrast enhancement was equally visible in both SW and SE sequences. Side-to-side comparison of tumor areas with high frequency of SusE and histopathology revealed that intralesional SusE reflected conglomerates of increased tumor microvascularity.

CONCLUSIONS

3T HR-CE-SW-MR imaging shows both intratumoral SusE not visible with standard MR imaging and contrast enhancement visible with standard MR imaging. Because frequency of intratumoral SusE correlates with tumor grade as determined by PET and histopathology, this novel technique is a promising tool for noninvasive differentiation of low-grade from high-grade brain tumors and for determination of an optimal area of biopsy for accurate tumor grading.

Contrast enhanced susceptibility weighted imaging (CE-SWI) of the mouse brain using ultrasmall superparamagnetic ironoxide particles (USPIO)

Susceptibility weighted imaging (SWI) has been introduced as a novel approach to visualize the venous vasculature in the human brain. With SWI, small veins in the brain are depicted based on the susceptibility difference between deoxyhaemoglobin in the veins and surrounding tissue, which is further enhanced by the use of MR phase information. In this study we applied SWI in the mouse brain using an exogenous iron-based blood-pool contrast agent, with the aims of further enhancing the susceptibility effect and allowing the visualization of individual veins and arteries. Contrast enhanced (CE-) SWI of the brain was performed on healthy mice and mice carrying intracerebral glioma xenografts. This study demonstrates that detailed vascular information in the mouse brain can be obtained by using CE-SWI and is substantially enhanced compared to native SWI (i.e. without contrast agent). CE-SWI images of tumour-bearing mice were directly compared to histology, confirming that CE-SWI depicts the vessels supplying and draining the tumour. We propose that CE-SWI is a very promising tool for the characterization of tumour vasculature.

Detection of brain metastasis at 3T: comparison among SE, IR-FSE and 3D-GRE sequences

The objective of this study is to compare the detectability of brain metastases at 3T among three contrast-enhanced sequences, spin-echo (SE) sequence, inversion recovery fast SE (IR-FSE) sequence (both with section thickness of 6 mm), and three-dimensional fast spoiled gradient-echo (3D fast SPGR) sequence with 1.4 mm isotropic voxel. First, phantom studies were performed to quantify the contrast-enhancement ratio (CER) with three sequences. In 21 consecutive patients with brain metastases, axial images of three sequences at 3T were obtained after administration of gadoteridol. Two neuroradiologists assessed the detectability of brain metastases for the three sequences. In the phantom study, no evident difference in the CER was demonstrated among three sequences. Significantly more brain metastases were detected with 3D fast SPGR than with SE and IR-FSE (a total of 97 lesions with 3D fast SPGR vs. 64 with SE and 63 with IR-FSE). In particular, 3D fast SPGR was superior to the other two sequences in detection of the small lesions (<3 mm). At 3T, the contrast-enhanced 3D fast SPGR with 1.4 mm isotropic voxel is clinically more valuable for detecting small brain metastases than the SE and IR-FSE with section thickness of 6 mm.

Susceptibility Weighted Imaging: Data Acquisition, Image Reconstruction and Clinical Applications

Susceptibility-weighted imaging (SWI) is a novel method, that combines magnitude and phase information from a high-resolution, fully velocity compensated 3D T2-weighted gradient echo sequence. Phase images are unwrapped and high pass filtered to highlight phase changes associated with venous vessels and converted into a mask that is multiplied with the corresponding phase image. This technique has been applied thus far to the imaging of tumors, vascular malformations, trauma, stroke, micro-hemorrhages, and as a functional imaging method. The purpose of this paper is to present an overview of the current status of the technique and to illustrate its potential.

Proton magnetic resonance spectroscopic imaging in brain tumor diagnosis

The current state of standard tumor diagnostics using contrast-enhanced MRI and biopsy is assessed in this review, and the progress of proton magnetic resonance spectroscopy (MRS) over the last 15 years is discussed. We summarize MRS basics and describe a typical magnetic resonance session for noninvasive routine tumor diagnostics at 1.5 T, including two-dimensional magnetic resonance spectroscopic imaging (MRSI). The results that can be obtained from such procedures are illustrated with clinical examples. Attention is turned to cutting-edge methodologic and clinical research at 3 T, with examples using high-resolution or very short echo-time three-dimensional MRSI. The current status and limitations in proton MRSI are discussed, and we look to the potential of faster data collection and even higher field strength.