Browsing by Author "Kapilamoorthy, Tirur Raman"
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Item A Ring Artifact in the Left Ventricle on Transesophageal Echocardiography After Mitral Valve Replacement(ANESTHESIA AND ANALGESIA, 2010)Item Applications of 3D CISS sequence for problem solving in neuroimaging.(The Indian journal of radiology & imaging, 2011)Three-dimensional (3D) constructive interference in steady state (CISS) is a gradient-echo MRI sequence that is used to investigate a wide range of pathologies when routine MRI sequences do not provide the desired anatomic information. The increased sensitivity of the 3D CISS sequence is an outcome of the accentuation of the T2 values between cerebrospinal fluid (CSF) and pathological structures. Apart from its well-recognized applications in the evaluation of the cranial nerves, CSF rhinorrhea and aqueduct stenosis, we have found the CISS sequence to be useful for the cisternal spaces, cavernous sinuses and the ventricular system, where it is useful for detecting subtle CSF-intensity lesions that may be missed on routine spin-echo sequences. This information helps in the management of these conditions. After a brief overview of the physics behind this sequence, we illustrate its clinical applications with representative cases and discuss its potential role in imaging protocols.Item Clinical applications of susceptibility weighted MR imaging of the brain - a pictorial review(NEURORADIOLOGY, 2008)Introduction Susceptibility-weighted imaging (SWI) is a novel magnetic resonance (MR) technique that exploits the magnetic susceptibility differences of various tissues, such as blood, iron and calcification. This pictorial review covers many clinical conditions illustrating its usefulness.Methods SWI consists of using both magnitude and phase images from a high-resolution, three-dimensional fully velocity-compensated gradient echo sequence. Phase mask is created from the MR phase images, and multiplying these with the magnitude images increase the conspicuity of the smaller veins and other sources of susceptibility effects, which is depicted using minimal intensity projection (minIP).Results The phase images are useful in differentiating between diamagnetic and paramagnetic susceptibility effects of calcium and blood, respectively. This unique MR sequence will help in detecting occult low flow vascular lesions, calcification and cerebral microbleed in various pathologic conditions and aids in characterizing tumors and degenerative diseases of the brain. This sequence also can be used to visualize normal brain structures with conspicuity.Conclusion Susceptibility-weighted imaging is useful in differentiating and characterizing diverse brain pathologies.Item Clinical utility of susceptibility-weighted imaging in vascular diseases of the brain(NEUROLOGY INDIA, 2010)Susceptibility-weighted imaging (SWI) is a rapidly evolving technique that utilizes both the magnitude and phase information to obtain valuable information about susceptibility changes between tissues. SWI is very sensitive to the paramagnetic effects of deoxyhemoglobin. SWI plays an important role in the diagnostic evaluation and management of acute stroke. In addition, it also plays an important role in the imaging of patients with chronic arterial occlusion and in understanding the effects of chronic infarction, like incomplete infarction and cortical laminar necrosis. The hemodynamic status and oxygen extraction fraction can also be evaluated. SWI is useful in evaluating cerebral venous sinus thrombosis by demonstrating the hemorrhagic venous infarction and thrombus in the sinus and the cortical veins, as well as secondary phenomena like venous stasis in the form of engorged cortical and transmedullary veins and collateral slow flow. Low-flow vascular malformations that are not visualized well on conventional sequences are depicted in exquisite detail along with the venous components on SWI. SWI is used for evaluating cavernomas, developmental venous anomalies, telangiactasias, dural arteriovenous fistulas and the various components of arteriovenous malformations. It has also evolved as a noninvasive technique for evaluating various anomalies of the venous system without administering contrast. Vasculopathies and vasculitis are associated with cerebral microbleeds which are detected on SWI. On the basis of the additional information provided by SWI, it can be included in the routine brain imaging protocol.Item Diffusion Tensor and Tensor Metrics Imaging in Intracranial Epidermoid Cysts(JOURNAL OF MAGNETIC RESONANCE IMAGING, 2009)Purpose: To explore the utility of diffusion tensor imaging (DTI) and diffusion tensor metrics (DTM) In characterizing the structural pathology of epidermoid cysts. DTI gives Information about the tissue structure: a high fractional anisotropy (FA) indicates a highly structured orientation of the tissue, fibers, or white matter tracts. Based on the tensor rank, a set of three metrics has been described that can be used to measure the directional dependence of diffusion: linear anisotropy (CL), planar anisotropy (CP), and spherical anisotropy (CS). DTM takes into account the shape of diffusion anisotropy and hence may provide better insight Into the orientation of structures than FA.Materials and Methods: DTI was performed in three patients with epidermoid cysts. FA, directionally-averaged mean diffusivity (Dav), exponential apparent diffusion coefficient (eADC), and DTM, such as CL, CP, and CS, were measured from the tumor core as well as from the normal-appearing white matter. Histopathological correlation was obtained.Results: Epidermoid cysts showed high FA with Dav values similar to that of normal white matter. eADC maps did not show any restriction of diffusion. FA values were. high, but not. as high as that for the white matter, CP values were higher and CL values were lower than those obtained for the white matter in various regions.Conclusion: High CP values suggest preferential diffusion of water molecules along a two-dimensional geometry, which could be attributed to the well-structured orientation of keratin filaments and flakes within the tumor as demonstrated by histopathology. Advanced imaging modalities like DTI with DTM can provide Information regarding the microstructural anatomy of the epidermoid cysts.Item Diffusion tensor mode in imaging of intracranial epidermoid cysts: one step ahead of fractional anisotropy(NEURORADIOLOGY, 2009)The signal characteristics of an epidermoid on T2-weighted imaging have been attributed to the presence of increased water content within the tumor. In this study, we explore the utility of diffusion tensor imaging (DTI) and diffusion tensor metrics (DTM) in knowing the microstructural anatomy of epidermoid cysts.DTI was performed in ten patients with epidermoid cysts. Directionally averaged mean diffusivity (D (av)), exponential diffusion, and DTM-like fractional anisotropy (FA), diffusion tensor mode (mode), linear (CL), planar (CP), and spherical (CS) anisotropy were measured from the tumor as well as from the normal-looking white matter.Epidermoid cysts showed high FA. However, D (av) and exponential diffusion values did not show any restriction of diffusion. Diffusion tensor mode values were near -1, and CP values were high within the tumor. This suggested preferential diffusion of water molecules along a two-dimensional geometry (plane) in epidermoid cysts, which could be attributed to the parallel-layered arrangement of keratin filaments and flakes within these tumors.Thus, advanced imaging modalities like DTI with DTM can provide information regarding the microstructural anatomy of the epidermoid cysts.Item Signal changes in cortical laminar necrosis-evidence from susceptibility-weighted magnetic resonance imaging(NEURORADIOLOGY, 2009)Two types of infarcts can be identified depending on the circumstances leading to its generation-infarcts with pannecrosis and infarcts with selective neuronal loss. Cortical laminar necrosis (CLN) can occur due to various etiologies of which infarctions and hypoxia are the commonest. Infarction results in pannecrosis whereas hypoxia and incomplete infarction result in selective neuronal loss with the presence of viable cells, glial proliferations, and deposition of paramagnetic substances. We investigated patients with CLN with susceptibility-weighted imaging (SWI), a technique highly sensitive to even traces of paramagnetic agents or hemorrhagic components.We retrospectively reviewed medical records of patients diagnosed with CLN as per standard criterion. Demographic characteristics and etiologies were recorded. Findings in magnetic resonance images including SWI were analyzed.We identified 11 patients with CLN, six males and five females with age range of 4-64 years. Etiologies included hypoxia in two patients and infarction in the nine patients. SWI detected diffuse linear hypointensities along the gyral margins in CLN due to hypoxic ischemic encephalopathy. Linear dot like hypointensities were identified in one patient with infarction.CLN due to hypoxic ischemic encephalopathy display linear gyral hypointensities and basal ganglia hypointensities that are identifiable in SWI and may represent mineralization. This might be related to iron transport across the surviving neurons from basal ganglia to the cortex, which is not possible in complete infarction. SWI may be helpful in understanding the pathophysiological aspects of CLN due to complete infarction and hypoxia.Item Spontaneous intracranial hypo and hypertensions: an imaging review.(Neurology India, 2011)Cerebrospinal fluid (CSF) pressure changes can manifest as either intracranial hypertension or hypotension. The idiopathic forms are largely under or misdiagnosed. Spontaneous intracranial hypotension occurs due to reduced CSF pressure usually as a result of a spontaneous dural tear. Idiopathic intracranial hypertension (IIH) is a syndrome of elevated intracranial tension without hydrocephalus or mass lesions and with normal CSF composition. Neuroimaging plays an important role in excluding secondary causes of raised intracranial tension. As the clinical presentation is varied, imaging may also help the clinician in arriving at the diagnosis of IIH with the help of a few specific signs. In this review, we attempt to compile the salient magnetic resonance imaging findings in these two conditions. Careful observation of these findings may help in early accurate diagnosis and to provide appropriate early treatment.Item Susceptibility weighted imaging in the diagnostic evaluation of patients with intractable epilepsy(EPILEPSIA, 2009)Aim: Dedicated magnetic resonance imaging (MRI) protocol can diagnose epileptogenic abnormalities in patients with intractable epilepsy. However, it is not sufficiently sensitive to detect small calcified lesions that may result from infections, tumors, or vascular malformations. This study aims to study the impact of the addition of T2*gradient echo/susceptibility weighted imaging (T2*GRE/SWI) sequence to a dedicated MRI protocol.Method: One hundred thirty-seven patients with intractable epilepsy underwent MRI using conventional epilepsy protocol with addition of T2*GRE/SWI sequence. Comparison of the images with and without these sequences was done for detection of calcified abnormalities/vascular abnormalities. In patients with calcified lesions, MRI findings were correlated either with histopathology or computerized tomography (CT) to confirm the presence of calcification.Results: In 16 patients the sequence gave additional information compared to conventional imaging protocol. The sequence helped in better characterization of lesions in all patients. In three patients it helped in detecting the lesion and in another three it appeared useful as it best characterized the lesions. Additional lesions were detected in two patients with old calcified granulomas. Important additional information was supplied in four patients, whereas in the remaining patients lesion conspicuity was increased.Conclusion: T2*GRE/SWI sequence should form part of routine epilepsy protocol as it increases sensitivity by detecting occult calcified lesions or vascular malformations that may be responsible for the patient's seizures. This is especially important in patients from developing countries who have post-infective calcified lesions responsible for seizures and who undergo only MRI as the imaging modality for intractable seizures.Item Susceptibility-weighted imaging in differentiating bilateral medial thalamic venous and arterial infarcts(NEUROLOGY INDIA, 2010)Bilateral medial thalamic infarcts may be due to thrombosis of internal cerebral veins or occlusion of artery of Percheron. Conventional MR imaging is often not helpful in differentiating the two. We discuss two cases in whom susceptibility-weighted imaging, including phase images contributed in demonstrating the thrombosed or patent internal cerebral veins.Item T1 Hyperintense Cystic Lesion - an Epidermoid or an Abscess?(CLINICAL NEURORADIOLOGY, 2010)