Susceptibility-weighted imaging (SWI) consists of using both magnitude and phase images from a high-resolution, three-dimensional, fully velocity compensated gradientecho sequence. Postprocessing is applied to the magnitude image by means of a phase mask to increase the conspicuity of the veins and other sources of susceptibility effects. This article gives a background of the SWI technique and describes its role in clinical neuroimaging. SWI is currently being tested in a number of centers worldwide as an emerging technique to improve the diagnosis of neurological trauma, brain neoplasms, and neurovascular diseases because of its ability to reveal vascular abnormalities and microbleeds.

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 ...

Purpose:To evaluate the diagnostic value of susceptibilityweighted imaging (SWI) for studying brain masses. Materials and Methods:SWI is a high-resolution, threedimensional, fully velocity-compensated gradient-echo sequence that uses both magnitude and phase data. Custom postprocessing is applied to enhance the contrast in the magnitude images between tissues with different susceptibilities. This sequence was applied to 44 patients (24 males and 20 females, 15-89 years old, mean age ϭ 50.3 years) with brain masses, pre-and/or postcontrast, and compared with conventional sequences (T1, T1 postcontrast, T2, proton density (PD), fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging (DWI) at 1.5T). Correlation with pathology was obtained in 12 cases. All images were reviewed independently by three radiologists. Results:In the evaluation of tumor visibility, boundary definition, blood products, venous vasculature, architecture, and edema, SWI gave better information than the standard T1-weighted postcontrast images in 11%, 14%, 71%, 73%, 63%, and 75% of the data, respectively, in a subgroup of 38 patients. This demonstrates that the information presented by SWI is complementary in nature to that available from conventional methods. On the whole, SWI was much more sensitive for showing blood products and venous vasculature. SWI showed a useful FLAIR-like contrast and complemented the information obtained by conventional T1 postcontrast sequences regarding the internal architecture of the lesions. Good pathologic correlations were found for blood products as predicted by SWI.Conclusion: SWI should prove useful for tumor characterization because of its ability to better highlight blood products and venous vasculature and reveal new internal architecture.

In this work, we present a new method for predicting changes in tumor vascularity using only one flip angle in dynamic contrast-enhanced (DCE) imaging. The usual DCE approach finds the tissue initial T 1 value T 1 (0) prior to injection of a contrast agent. We propose finding changes in the tissue contrast agent uptake characteristics pre-and postdrug treatment by fixing T 1 (0). Using both simulations and imaging pre-and postadministration of caffeine, we find that the relative change (NR50) in the median of the cumulative distribution (R50) is almost independent of T 1 (0). Fixing T 1 (0) leads to a concentration curve c(t) more robust to the presence of noise than calculating T 1 (0). Consequently, the NR50 for the tumor remains roughly the same as the ideal NR50 when T 1 (0) is exactly known. Further, variations in eating habits are shown to create significant changes in the R50 response for both liver and muscle. In conclusion, analyzing data with fixed T 1 (0) leads to a more stable measure of changes in NR50 and does not require knowl- Dynamic contrast-enhanced MRI (DCE-MRI) is a method for imaging the physiology of the microcirculation. A series of recent clinical studies have shown that DCE-MRIbased measures correlate well with tumor angiogenesis. DCE-MRI is performed after the administration of an intravenous contrast agent, gadolinium-DTPA, to noninvasively assess tumor vascular characteristics. Recently, DCE-MRI has been used to assess antiangiogenic cancer drug effectiveness in Phase I pharmaceutical trials (1-3) by acquiring data before and after drug treatment. The contrast enhancement patterns on DCE-MRI are influenced by tumor angiogenesis, as reflected by elevated vascular endothelial growth factor (VEGF) expression. Therefore, they become valuable indicators for assessing tumor angiogenic activity (4,5) and tumor neovascularization in vivo in hepatocellular carcinoma patients (6,7). The use of DCE has been so important that one would be hesitant to continue testing a drug in the absence of any volume or vascular changes appearing in DCE-MRI unless the patients' survival increased (8).Despite its promise, there are problems in the acquisition and processing of DCE data. Repeatability has been a major problem (9 -11). Given the wide clinical use of DCE-MRI, this is an important issue that must be directly addressed. One approach is to improve the methodology itself with more rapid high-resolution respiratory free scanning methods (12). And this will happen with the advent of parallel imaging (13,14). The other is to better process existing data.From our review of many DCE-MRI experiments and projects at the MRI Research facility in the Department of Radiology at Wayne State University, we have found that the causes of most of the DCE errors are related to noise in the T 1 estimates and to physiologic changes in the blood flow (BF) from one day to the next. Normally, an estimate for the baseline T 1 (referred to here as T 1 (0)) is obtained from multiple flip angle (FA) images (15). Any inconsist...

The high sensitivity but low specificity of breast MRI has prompted exploration of breast 1 H MRS for breast cancer detection. However, several obstacles still prevent the routine application of in vivo breast 1 H MRS, including poor spatial resolution, long acquisition time associated with conventional multi-voxel MRS imaging (MRSI) techniques, and the difficulty of "extra" lipid suppression in a magnetic field with relatively poor achievable homogeneity compared to the brain. Using a combination of a recently developed echo-filter (EF) suppression technique and an elliptical sampling scheme, we demonstrate the feasibility of overcoming these difficulties. It is robust (the suppression technique is insensitive to magnetic field inhomogeneity), fast (acquisition time of about 12 min) and offers high spatial resolution (up to 0.6 cm 3 per voxel at 1.5 T with a TE of only 60 ms). This approach should be even better at 3 T with higher resolution and/or shorter TE.