Home About us Contact
|
Home About us Contact | ||
|
|
||
Diffusion-weighted MRI (diffusion-weighted + mri)
Selected AbstractsCerebral cortical laminar necrosis on diffusion-weighted MRI in hypoglycaemic encephalopathyDIABETIC MEDICINE, Issue 8 2005Y. Yoneda Abstract Background Laminar necrosis of the cerebral cortex characterized neuropathologically by delayed selective neuronal necrosis occurs in hypoglycaemic encephalopathy and other brain diseases. Case report A 37-year-old male with insulin-treated Type 1 diabetes mellitus developed hypoglycaemic encephalopathy associated with respiratory failure. Brain diffusion-weighted MRI during the subacute period demonstrated high signals along the cerebral cortex. Brain single-photon emission computed tomography showed diffuse, severe cerebral hypoperfusion. The patient remained comatose and died 1 month later. Conclusions High signals along the cortical bands on diffusion-weighted MRI suggest cortical laminar necrosis, although a postmortem examination was unavailable. Sustained hypoglycaemic brain injury, possibly associated with respiratory hypoxia, may be the underlying mechanism. [source] Addressing a systematic vibration artifact in diffusion-weighted MRIHUMAN BRAIN MAPPING, Issue 2 2010Daniel Gallichan Abstract We have identified and studied a pronounced artifact in diffusion-weighted MRI on a clinical system. The artifact results from vibrations of the patient table due to low-frequency mechanical resonances of the system which are stimulated by the low-frequency gradient switching associated with the diffusion-weighting. The artifact manifests as localized signal-loss in images acquired with partial Fourier coverage when there is a strong component of the diffusion-gradient vector in the left,right direction. This signal loss is caused by local phase ramps in the image domain which shift the apparent k-space center for a particular voxel outside the covered region. The local signal loss masquerades as signal attenuation due to diffusion, severely disrupting the quantitative measures associated with diffusion-tensor imaging (DTI). We suggest a way to improve the interpretation of affected DTI data by including a co-regressor which accounts for the empirical response of regions affected by the artifact. We also demonstrate that the artifact may be avoided by acquiring full k-space data, and that subsequent increases in TE can be avoided by employing parallel acceleration. Hum Brain Mapp, 2010. © 2009 Wiley-Liss, Inc. [source] Diffusion-weighted MRI for monitoring tumor response to photodynamic therapyJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2010Hesheng Wang MS Abstract Purpose: To examine diffusion-weighted MRI (DW-MRI) for assessing the early tumor response to photodynamic therapy (PDT). Materials and Methods: Subcutaneous tumor xenografts of human prostate cancer cells (CWR22) were initiated in athymic nude mice. A second-generation photosensitizer, Pc 4, was delivered to each animal by a tail vein injection 48 h before laser illumination. A dedicated high-field (9.4 Tesla) small animal MR scanner was used to acquire diffusion-weighted MR images pre-PDT and 24 h after the treatment. DW-MRI and apparent diffusion coefficients (ADC) were analyzed for 24 treated and 5 control mice with photosensitizer only or laser light only. Tumor size, prostate specific antigen (PSA) level, and tumor histology were obtained at different time points to examine the treatment effect. Results: Treated mice showed significant tumor size shrinkage and decrease of PSA level within 7 days after the treatment. The average ADC of the 24 treated tumors increased 24 h after PDT (P < 0.001) comparing with pre-PDT. The average ADC was 0.511 ± 0.119 × 10,3 mm2/s pre-PDT and 0.754 ± 0.181 × 10,3 mm2/s 24 h after the PDT. There is no significant difference in ADC values pre-PDT and 24 h after PDT in the control tumors (P = 0.20). Conclusion: The change of tumor ADC values measured by DW-MRI may provide a noninvasive imaging marker for monitoring tumor response to Pc 4-PDT as early as 24 h. J. Magn. Reson. Imaging 2010;32:409,417. © 2010 Wiley-Liss, Inc. [source] Ground truth hardware phantoms for validation of diffusion-weighted MRI applicationsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 2 2010Pim Pullens MSc Abstract Purpose: To quantitatively validate diffusion-weighted MRI (DW-MRI) applications, a hardware phantom containing crossing fibers at a sub-voxel level is presented. It is suitable for validation of a large spectrum of DW-MRI applications from acquisition to fiber tracking, which is an important recurrent issue in the field. Materials and Methods: Phantom properties were optimized to resemble properties of human white matter in terms of anisotropy, fractional anisotropy, and T2. Sub-voxel crossings were constructed at angles of 30, 50, and 65 degrees, by wrapping polyester fibers, with a diameter close to axon diameter, into heat shrink tubes. We show our phantoms are suitable for the acquisition of DW-MRI data using a clinical protocol. Results: The phantoms can be used to succesfully estimate both the diffusion tensor and non-Gaussian diffusion models, and perform streamline fiber tracking. DOT (Diffusion Orientation Transform) and q-ball reconstruction of the diffusion profiles acquired at b = 3000 s/mm2 and 132 diffusion directions reveal multimodal diffusion profiles in voxels containing crossing yarn strands. Conclusion: The highly purpose adaptable phantoms provide a DW-MRI validation platform: applications include optimisation of acquisition schemes, validation of non-Gaussian diffusion models, comparison and validation of fiber tracking algorithms, and quality control in multi-center DWI studies. J. Magn. Reson. Imaging 2010;32:482,488. © 2010 Wiley-Liss, Inc. [source] Predicting and monitoring cancer treatment response with diffusion-weighted MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2010Harriet C. Thoeny MD Abstract An imaging biomarker that would provide for an early quantitative metric of clinical treatment response in cancer patients would provide for a paradigm shift in cancer care. Currently, nonimage based clinical outcome metrics include morphology, clinical, and laboratory parameters, however, these are obtained relatively late following treatment. Diffusion-weighted MRI (DW-MRI) holds promise for use as a cancer treatment response biomarker as it is sensitive to macromolecular and microstructural changes which can occur at the cellular level earlier than anatomical changes during therapy. Studies have shown that successful treatment of many tumor types can be detected using DW-MRI as an early increase in the apparent diffusion coefficient (ADC) values. Additionally, low pretreatment ADC values of various tumors are often predictive of better outcome. These capabilities, once validated, could provide for an important opportunity to individualize therapy thereby minimizing unnecessary systemic toxicity associated with ineffective therapies with the additional advantage of improving overall patient health care and associated costs. In this report, we provide a brief technical overview of DW-MRI acquisition protocols, quantitative image analysis approaches and review studies which have implemented DW-MRI for the purpose of early prediction of cancer treatment response. J. Magn. Reson. Imaging 2010. © 2010 Wiley-Liss, Inc. [source] Feasibility of diffusion-weighted MRI for defining placental invasionJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2009Satoru Morita MD Abstract The purpose of this clinical note is to describe the feasibility of using diffusion-weighted imaging for diagnosing placental invasion with a case of placenta increta and six cases without it. Diffusion-weighted imaging (DWI) at a b-value of 1000 sec/mm2 can clearly define the border between the placenta and myometrium because only the placenta shows very high signal intensity. The corresponding image at a b-value of 0 sec/mm2 shows the myometrium with high signal intensity compared with the surrounding fat. Therefore, fusion of the two images can be used additionally to visualize thickness of the myometrium. As a result, DWI can be used to visualize the focal thinning of the myometrium caused by placenta increta, which has been difficult to diagnose on conventional magnetic resonance imaging sequences without contrast enhancement. However, the use of DWI for placental invasion should be determined following careful consideration of its risks and benefits, as fetus safety has not been established. J. Magn. Reson. Imaging 2009;30:666,671. © 2009 Wiley-Liss, Inc. [source] Functional MR imaging of the female pelvisJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2007Takashi Koyama MD Abstract Recent developments in MR techniques have magnified the roles and potential of MRI in the female pelvis. This article reviews the techniques and clinical applications of functional MRI (fMRI) of the female pelvis, including cine MRI, diffusion-weighted MRI (DWI), and dynamic contrast-enhanced (DCE)-MRI. Cine MRI is a useful tool for evaluating uterine contractility, including sustained contraction and peristalsis, in a variety of conditions and gynecologic disorders, and for evaluating pelvic-floor weakness. DWI can demonstrate abnormal signals in pathologic foci based on differences in molecular diffusion. It also enables the quantitative evaluation of the apparent diffusion coefficient (ADC), which may be useful for distinguishing malignant from benign tissues and monitoring therapeutic outcome. DCE-MRI has the potential to improve tumor detection and local staging, and can also provide quantitative information about perfusion of the tumor, which may be useful for both monitoring therapeutic effects and predicting therapeutic outcome. Understanding the roles played by functional MR techniques in the female pelvic region is beneficial not only for determining clinical applications, but also for developing further investigations with MRI. J. Magn. Reson. Imaging 2007;25:1101,1112. © 2007 Wiley-Liss, Inc. [source] Optimal acquisition orders of diffusion-weighted MRI measurementsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2007Philip A. Cook PhD Abstract Purpose To propose a new method to optimize the ordering of gradient directions in diffusion-weighted MRI so that partial scans have the best spherical coverage. Materials and Methods Diffusion-weighted MRI often uses a spherical sampling scheme, which acquires images sequentially with diffusion-weighting gradients in unique directions distributed isotropically on the hemisphere. If not all of the measurements can be completed, the quality of diffusion tensors fitted to the partial scan is sensitive to the order of the gradient directions in the scanner protocol. If the directions are in a random order, then a partial scan may cover some parts of the hemisphere densely but other parts sparsely and thus provide poor spherical coverage. We compare the results of ordering with previously published methods for optimizing the acquisition in simulation. Results Results show that all methods produce similar results and all improve the accuracy of the estimated diffusion tensors significantly over unordered acquisitions. Conclusion The new ordering method improves the spherical coverage of partial scans and has the advantage of maintaining the optimal coverage of the complete scan. J. Magn. Reson. Imaging 2007;25:1051,1058. © 2007 Wiley-Liss, Inc. [source] Controlling diffusion of 3He by buffer gases: A structural contrast agent in lung MRIJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2006Rodolfo H. Acosta PhD Abstract Purpose To study the influence of admixing inert buffer gases to laser-polarized 3He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. Materials and Methods The diffusion coefficient of 3He was altered by admixing buffer gases of various molecular weights (4He, N2, and SF6). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laser-polarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments. Results Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted and was experimentally validated. Images acquired under such conditions revealed improved resolution. The nature and concentration of the admixed gas defines a structural threshold for the observed apparent diffusion coefficient (ADC) as demonstrated with diffusion-weighted MRI on a pig's lung flooded with suitable gas mixtures. Conclusion A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. Their molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this enables images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] New developments of brain imaging for Parkinson's disease and related disorders,MOVEMENT DISORDERS, Issue 12 2006Paola Piccini MD Abstract Parkinson's disease (PD) and related disorders are subcortical degenerations targeting the nigrostriatal dopaminergic system and basal ganglia. Traditionally, MRI has been used to detect structural and positron emission tomography and single emission computed tomography functional neurochemical and metabolic changes associated with these disorders. Recently, advances in diffusion-weighted MRI, ultrasonography, and radiotracer-based imaging have yielded greater sensitivity for revealing structural change and allowed detection of changes in brain dopamine levels after levodopa and during behavioral tasks. This review focuses on these recent advances in neuroimaging technology and their use for the diagnosis and assessment of PD and other parkinsonian disorders. © 2006 Movement Disorder Society [source] Basilar artery atherosclerotic disease is related to subacute lesion volume increase in pontine base infarctionACTA NEUROLOGICA SCANDINAVICA, Issue 2 2009J. S. Kim Background,,, Although basilar artery atherosclerotic disease (BAD) is frequent in patients with pontine base infarction, it remains unknown whether BAD is related to the lesion size or clinical outcome. Methods,,, We studied 56 patients with unilateral pontine base infarction who underwent (i) diffusion-weighted MRI within 48 h after stroke onset and (ii) follow-up MRI and MR angiography in the subacute stage. Neurologic progression was defined as increased National Institutes of Health Stroke Scale score by , 2 during admission. Clinical outcome was dichotomized as good and poor (, 3) according to the modified Rankin Scale at 1 month after stroke onset. Results,,, Twenty-two patients (39%) had BAD and 15 patients (27%) had neurologic progression. Follow-up MRI performed at median 3.5 ± 1.1 days after the initial MRI showed the lesion volume significantly increased (P < 0.001). The BAD was not significantly related to demographic characteristics, risk factors, initial and follow-up lesion volume, neurologic progression and clinical outcome, but was closely related to the subacute increase in lesion volume (P = 0.004 for 20% increase, P = 0.029 for 50% increase). Conclusions,,, BAD is related to subacute increase in lesion volume, but not to ultimate poor clinical outcome in patients with pontine base infarction. [source] Using diffusion MRI for measuring the temperature of cerebrospinal fluid within the lateral ventriclesACTA PAEDIATRICA, Issue 2 2010LR Kozak Abstract Aim:, Hypothermia is often induced to reduce brain injury in newborns, following perinatal hypoxic,ischaemic events, and in adults following traumatic brain injury, stroke or cardiac arrest. We aimed to devise a method, based on diffusion-weighted MRI, to measure non-invasively the temperature of the cerebrospinal fluid in the lateral ventricles. Methods:, The well-known temperature dependence of the water diffusion constant was used for the estimation of temperature. We carried out diffusion MRI measurements on a 3T Philips Achieva Scanner involving phantoms (filled with water or artificial cerebrospinal fluid while slowly cooling from 41 to 32°C) and healthy adult volunteers. Results:, The estimated temperature of water phantoms followed that measured using a mercury thermometer, but the estimates for artificial cerebrospinal fluid were 1.04°C lower. After correcting for this systematic difference, the estimated temperature within the lateral ventricles of volunteers was 39.9°C. Using diffusion directions less sensitive to cerebrospinal fluid flow, it was 37.7°C, which was in agreement with the literature. Conclusion:, Although further improvements are needed, measuring the temperature within the lateral ventricles using diffusion MRI is a viable method that may be useful for clinical applications. We introduced the method, identified sources of error and offered remedies for each. [source] | ||||||||||