Meng Law

Magnetic Resonance Perfusion and Permeability Imaging in Brain Tumors

Recent evidence suggests that vascular permeability and the presence of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) are important mediators of brain tumor growth in addition to angiogenesis. Perfusion and permeability magnetic resonance (MR) imaging can now measure parameters such as cerebral blood volume and vascular permeability, which can be directly correlated with these histopathologic changes as well as molecular markers such as VEGF. The major techniques currently used in both the clinical and research settings are T1-weighted steady-state dynamic contrast-enhanced MR imaging (DCE MR imaging) and T2 *-weighted first-pass, dynamic susceptibility contrast MR imaging (DSC MR imaging). The advantages and disadvantages of each technique with regard to characterizing tumor biology are discussed in this article. Most clinicians and investigators are currently using the DSC MR imaging T2 *-weighted technique for brain tumor perfusion MR imaging. The existence of multiple approaches to pathologic classification of human glioma implies that there is a lack of consensus among experts as to which is the single best approach. These multiple grading systems do, however, agree on the histologic parameters that are important in the determination of glioma biology, namely hypercellularity, pleomorphism, vascular endothelial proliferation, mitotic activity, and necrosis.

Diffusion-weighted imaging, diffusion-tensor imaging, and fiber tractography of the spinal cord.

In the brain, diffusion-weighted imaging (DWI) is an established and reliable method for the characterization of neurologic lesions. Although the diagnostic value of DWI in the early detection of ischemia has not diminished with time, many new clinical applications of DWI have also emerged. Diffusion-tensor imaging and fiber tractography have more recently been developed and optimized, allowing quantification of the magnitude and direction of diffusion along three principal eigenvectors. Diffusion-tensor imaging and fiber tractography are proving to be useful in clinical neuroradiology practice, with application to several categories of disease, and to be a powerful research tool. This article describes some of the applications of DWI and diffusion-tensor imaging in the evaluation of the diseases of the spinal cord.

Imaging of Neurocysticercosis

Neurocysticercosis (NCC) is an infection of the central nervous system by the Taenia solium larvae, and is the most common cause of acquired epilepsy in endemic regions. The natural history of parenchymal NCC lesions can be divided into 4 stages with unique imaging and clinical features. Evaluation of cysticerci is challenging on conventional magnetic resonance (MR) imaging and computed tomography, and is significantly improved with MR cysternography techniques. Differentiation of NCC lesions from metastatic disease and pyogenic abscesses can be improved with advanced MR imaging including (1)H nuclear MR spectroscopy, diffusion-weighted imaging, and MR perfusion imaging.

Brain Tumors : A Multimodality Approach with Diffusion-Weighted Imaging, Diffusion Tensor Imaging, Magnetic Resonance Spectroscopy, Dynamic Susceptibility Contrast and Dynamic Contrast-Enhanced Magnetic Resonance Imaging

This article focuses on advanced magnetic resonance (MR) imaging techniques and how they can be used to help diagnose a specific tumor, suggest tumor grade and prognosis, follow tumor progression, evaluate tumor extension, suggest the ideal site for biopsy, and assess therapeutic response. Advanced MR imaging techniques may also help to distinguish between lesions that simulate brain tumors on conventional MR imaging studies.

Perfusion and permeability MR imaging of gliomas.

Conventional contrast-enhanced MR imaging is the current standard technique for the diagnosis and treatment evaluation of gliomas and other brain neoplasms. However, this method is quite limited in its ability to characterize the complex biology of gliomas and so there is a need to develop more quantitative imaging methods. Perfusion and permeability MR imaging are two such techniques that have shown promise in this regard. This review will highlight the underlying principles, applications, and pitfalls of these evolving advanced MRI methods.

Advanced techniques using contrast media in neuroimaging.

This article presents an overview of advanced magnetic resonance (MR) imaging techniques using contrast media in neuroimaging, focusing on T2*-weighted dynamic susceptibility contrast MR imaging and T1-weighted dynamic contrast-enhanced MR imaging. Image acquisition and data processing methods and their clinical application in brain tumors, stroke, dementia, and multiple sclerosis are discussed.

Posttreatment evaluation of central nervous system gliomas.

Although conventional contrast-enhanced MR imaging remains the standard-of-care imaging method in the posttreatment evaluation of gliomas, recent developments in therapeutic options such as chemoradiation and antiangiogenic agents have caused the neuro-oncology community to rethink traditional imaging criteria. This article highlights the latest recommendations. These recommendations should be viewed as works in progress. As more is learned about the pathophysiology of glioma treatment response, quantitative imaging biomarkers will be validated within this context. There will likely be further refinements to glioma response criteria, although the lack of technical standardization in image acquisition, postprocessing, and interpretation also need to be addressed.

Imaging of the Posttherapeutic Brain.

Abstract This review covers important topics relating to the imaging evaluation of glioblastoma multiforme after therapy. An overview of the Macdonald and Response Assessment in Neuro-Oncology criteria as well as important questions and limitations regarding their use are provided. Pseudoprogression and pseudoresponse as well as the use of advanced magnetic resonance imaging techniques such as perfusion, diffusion, and spectroscopy in the evaluation of the posttherapeutic brain are also reviewed.

FDG-PET/MRI fusion demonstrating cricoarytenoid muscle hypermetabolism due to contralateral true vocal cord paralysis

A 34-year-old female with recurrent papillary thyroid carcinoma who was previously treated with total thyroidectomy and cervical lymph node dissection was referred for imaging evaluation after treatment (Fig. 1). PET/CT was performed to evaluate for treatment response 8 weeks after the end of radiation therapy to the neck for recurrent disease. PET showed asymmetric focal hypermetabolism in the hypopharynx on the left at the edge of hyoid cartilage with a maximum SUV of 6.7. The activity was difficult to localize on PET/CT due to the lack of IV contrast. MRI was requested for further characterization and anatomic localization. MRI showed slight medialization of the right vocal cord and aryepiglottic fold but no enhancing mass in the area of focal increased FDG uptake. Physical examination did not reveal lymphadenopathy, neck masses, or tenderness. Laboratories, including thyroglobulin level were within normal limits. PET/MRI fusion facilitated the localization of focal FDG uptake to the left cricoarytenoid muscle that represented the compensatory increased movement of the left cricoarytenoid muscle due to contralateral true vocal cord paralysis.1 Major causes of vocal cord paralysis include trauma and malignancy, which more commonly affect the left recurrent laryngeal nerve due to its longer course through the aortopulmonary window.2 Our patient was confirmed by laryngoscopy to have right vocal cord paralysis presumably due to thyroidectomy. Her follow up MRI at 6 and 12 months showed no interval changes. Image fusion software can play an important role in defining the potential clinical applications for the emerging hybrid PET/MRI imaging systems.3

MR Perfusion Imaging: ASL, T2*-Weighted DSC, and T1-Weighted DCE Methods

State-of-the art imaging evaluation of brain tumors has extended beyond conventional contrast-enhanced MR imaging. Functional imaging assessment of brain tumor vascularity is important because there is a close association between angiogenesis and prognosis. MR perfusion imaging, including arterial spin labeling, T2*-weighted dynamic susceptibility contrast (DSC), and T1-weighted dynamic contrast-enhanced methods, can provide the radiologist with quantitative imaging biomarkers for characterization of tumor vascularity that can be helpful to determine tumor grading, predict prognosis, and evaluate therapeutic efficacy. This is particularly crucial as current and future anticancer agents may target specific aspects of tumor biology that may not be reflected by assessment of simple size measurement on conventional MRI. Technical factors including methods of image acquisition, data post-processing, and interpretation are also discussed.