SUMMARY Susceptibility-weighted imaging (SWI) is a new neuroimaging technique, which uses tissue magnetic susceptibility differences to generate a unique contrast, different from that of spin density, T1, T2, and T2*. In this review (the first of 2 parts), we present the technical background for SWI. We discuss the concept of gradient-echo images and how we can measure local changes in susceptibility. Armed with this material, we introduce the steps required to transform the original magnitude and phase images into SWI data. The use of SWI filtered phase as a means to visualize and potentially quantify iron in the brain is presented. Advice for the correct interpretation of SWI data is discussed, and a set of recommended sequence parameters for different field strengths is given.

SUMMARY: Susceptibility-weighted imaging (SWI) has continued to develop into a powerful clinical tool to visualize venous structures and iron in the brain and to study diverse pathologic conditions. SWI offers a unique contrast, different from spin attenuation, T1, T2, and T2* (see Part 1). In this clinical review (Part 2), we present a variety of neurovascular and neurodegenerative disease applications for SWI, covering trauma, stroke, cerebral amyloid angiopathy, venous anomalies, multiple sclerosis, and tumors. We conclude that SWI often offers complementary information valuable in the diagnosis and potential treatment of patients with neurologic disorders. S usceptibility-weighted imaging (SWI) is a fully velocitycompensated high-resolution 3D gradient-echo sequence that uses magnitude and filtered-phase information, both separately and in combination with each other, to create new sources of contrast. With the advent of parallel imaging and the greater availability of clinical 3T MR images, it is now possible to image the entire brain with SWI in roughly 4 minutes. SWI has been found to provide additional clinically useful information that is often complementary to conventional MR imaging sequences used in the evaluation of various neurologic disorders, including traumatic brain injury (TBI), coagulopathic or other hemorrhagic disorders, vascular malformations, cerebral infarction, neoplasms, and neurodegenerative disorders associated with intracranial calcification or iron deposition. As neuroradiologists become more aware of these various applications and as advances in software technology permit easier acquisition and better interpretation, SWI will likely be incorporated into the routine diagnostic imaging evaluation. The technical concepts of SWI were outlined in Part 1 of this 2-part review and would be valuable reading as background to this article, especially the discussion about magnitude, SWI filtered phase, SWI processed data, and contrast available in SWI. 1 The following sections discuss different clinical applications of SWI predominantly in adults. An excellent clinical review by Tong et al 2 in the American Journal of Neuroradiology already covers many SWI applications in children. TBI: Diffuse Axonal InjuryTBI is a major cause of morbidity, mortality, disability, and lost years of productive life throughout the world.3 CT remains the primary imaging technique for the initial evaluation of patients who have sustained head trauma because it effectively allows detection of intracranial hemorrhages that require acute neurosurgical intervention. In recent years, however, MR imaging has been gaining popularity as an adjunctive imaging method in patients with TBI because it permits more precise identification and localization of smaller hemorrhages and can provide useful information regarding mechanisms of injury and potential clinical outcome. SWI is particularly helpful for the evaluation of diffuse axonal injury (DAI), often associated with punctate hemorrhages in the deep subcortical white ma...

Purpose:To investigate whether the variable forms of putative iron deposition seen with susceptibility weighted imaging (SWI) will lead to a set of multiple sclerosis (MS) lesion characteristics different than that seen in conventional MR imaging. Materials and Methods:Twenty-seven clinically definite MS patients underwent brain scans using magnetic resonance imaging including: pre-and postcontrast T1-weighted imaging, T2-weighted imaging, FLAIR, and SWI at 1.5 T, 3 T, and 4 T. MS lesions were identified separately in each imaging sequence. Lesions identified in SWI were reevaluated for their iron content using the SWI filtered phase images. Results:There were a variety of new lesion characteristics identified by SWI, and these were classified into six types. A total of 75 lesions were seen only with conventional imaging, 143 only with SWI, and 204 by both. From the iron quantification measurements, a moderate linear correlation between signal intensity and iron content (phase) was established. Conclusion:The amount of iron deposition in the brain may serve as a surrogate biomarker for different MS lesion characteristics. SWI showed many lesions missed by conventional methods and six different lesion characteristics. SWI was particularly effective at recognizing the presence of iron in MS lesions and in the basal ganglia and pulvinar thalamus. MULTIPLE SCLEROSIS (MS) is an inflammatory demyelinating and neurodegenerative disease of the central nervous system (1,2). Most patients start with a relapsing-remitting course, which has a clearly defined episode of neurologic disability and recovery. The pathologic hallmark of multiple sclerosis is the demyelinated plaque, a well-demarcated hypocellular area characterized by the loss of myelin, along with axonal loss due to (3,4), and the formation of astrocytic scars. The etiologic mechanism underlying MS is generally believed to be autoimmune inflammation (5). Nevertheless, what initiates the disease and the sequence of events underlying the development of MS is not yet well established (6).Conventional magnetic resonance imaging (MRI) has been used routinely to diagnose and monitor the disease spatially and temporally. The use of conventional MRI to measure disease activity and assess effects of therapy is now standard in clinical practice and drug trials (7). T2-weighted imaging (T2WI) is highly sensitive in the detection of hyperintensities in white matter. However, hyperintensities on T2WI can correspond to a wide spectrum of pathology, ranging from edema and mild demyelination to lesions in which the neurons and supporting glial cells are replaced by glial scars or liquid necrosis (8 -14). In addition to T2WI, Gadolinium enhancement on T1-weighted imaging (T1WI) can suggest acute inflammation, which is a marker of disease It is becoming a consensus among many studies that iron is enriched within oligodendrocytes and myelin in both normal and diseased tissue (20 -23). One explanation for such findings proposes that iron is associated with the biosynthetic enzymes ...

Susceptibility weighted imaging (SWI) is a new MRI technique that can identify calcification by using phase images. We present a single case with a partially calcified oligodendroglioma, multiple calcified cysticercosis lesions, and multiple physiologic calcifications in the same patient. SWI phase images and computed tomography (CT) images are compared. SWI phase images showed the same calcified lesions as shown on CT and sometimes some new calcifications. Our conclusion is that SWI filtered phase images can identify calcifications as well as CT in this case.

SummaryBackgroundCerebral cavernous malformations (CCMs) can cause symptomatic intracranial haemorrhage (ICH), but the estimated risks are imprecise and predictors remain uncertain. We aimed to obtain precise estimates and predictors of the risk of ICH during untreated follow-up in an individual patient data meta-analysis.MethodsWe invited investigators of published cohorts of people aged at least 16 years, identified by a systematic review of Ovid MEDLINE and Embase from inception to April 30, 2015, to provide individual patient data on clinical course from CCM diagnosis until first CCM treatment or last available follow-up. We used survival analysis to estimate the 5-year risk of symptomatic ICH due to CCMs (primary outcome), multivariable Cox regression to identify baseline predictors of outcome, and random-effects models to pool estimates in a meta-analysis.FindingsAmong 1620 people in seven cohorts from six studies, 204 experienced ICH during 5197 person-years of follow-up (Kaplan-Meier estimated 5-year risk 15·8%, 95% CI 13·7–17·9). The primary outcome of ICH within 5 years of CCM diagnosis was associated with clinical presentation with ICH or new focal neurological deficit (FND) without brain imaging evidence of recent haemorrhage versus other modes of presentation (hazard ratio 5·6, 95% CI 3·2–9·7) and with brainstem CCM location versus other locations (4·4, 2·3–8·6), but age, sex, and CCM multiplicity did not add independent prognostic information. The 5-year estimated risk of ICH during untreated follow-up was 3·8% (95% CI 2·1–5·5) for 718 people with non-brainstem CCM presenting without ICH or FND, 8·0% (0·1–15·9) for 80 people with brainstem CCM presenting without ICH or FND, 18·4% (13·3–23·5) for 327 people with non-brainstem CCM presenting with ICH or FND, and 30·8% (26·3–35·2) for 495 people with brainstem CCM presenting with ICH or FND.InterpretationMode of clinical presentation and CCM location are independently associated with ICH within 5 years of CCM diagnosis. These findings can inform decisions about CCM treatment.FundingUK Medical Research Council, Chief Scientist Office of the Scottish Government, and UK Stroke Association.