Mark S. Shiroishi

Perfusion MRI: The Five Most Frequently Asked Technical Questions

OBJECTIVE This and its companion article address the 10 most frequently asked questions that radiologists face when planning, performing, processing, and interpreting different MR perfusion studies in CNS imaging. CONCLUSION Perfusion MRI is a promising tool in assessing stroke, brain tumors, and patients with neurodegenerative diseases. Most of the impediments that have limited the use of perfusion MRI can be overcome to allow integration of these methods into modern neuroimaging protocols.

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.

Clinical Applications of Diffusion Tensor Imaging

Advancements in diffusion-weighted imaging during the past decade have led to the use of diffusion tensor imaging to further characterize the structural integrity of neural tissue and to noninvasively trace neuronal tracts in the brain and spine. This has led to many clinical applications that have aided in surgical planning for brain and spinal cord tumors and has increased the diagnostic potential of magnetic resonance imaging in disorders such as multiple sclerosis, Alzheimer disease, and traumatic brain injury.

Principles of T2 *-weighted dynamic susceptibility contrast MRI technique in brain tumor imaging.

Dynamic susceptibility contrast magnetic resonance imaging (DSC‐MRI) is used to track the first pass of an exogenous, paramagnetic, nondiffusible contrast agent through brain tissue, and has emerged as a powerful tool in the characterization of brain tumor hemodynamics. DSC‐MRI parameters can be helpful in many aspects, including tumor grading, prediction of treatment response, likelihood of malignant transformation, discrimination between tumor recurrence and radiation necrosis, and differentiation between true early progression and pseudoprogression. This review aims to provide a conceptual overview of the underlying principles of DSC‐MRI of the brain for clinical neuroradiologists, scientists, or students wishing to improve their understanding of the technical aspects, pitfalls, and controversies of DSC perfusion MRI of the brain. Future consensus on image acquisition parameters and postprocessing of DSC‐MRI will most likely allow this technique to be evaluated and used in high‐quality multicenter studies and ultimately help guide clinical care. J. Magn. Reson. Imaging 2015;41:296–313.© 2013 Wiley Periodicals, Inc.

Retrograde Transvenous Neuroperfusion: A Back Door Treatment for Stroke

BACKGROUND AND PURPOSE Stroke is the third leading cause of death and the leading cause of adult disability in the United States. The clot-lysis drug tissue plasminogen activator is the only treatment that has been effective for acute stroke patients, yet there are significant limitations to its use and effectiveness. In this study retrograde transvenous neuroperfusion (RTN) was evaluated for its efficacy in reversing acute ischemia, preventing paralysis, and limiting pathological evidence of infarction in baboons. METHODS Ten adult male baboons underwent 3.5 hours of reversible middle cerebral artery occlusion (MCAO) under isoflurane (0.25% to 1.5%) anesthesia. Five randomly chosen animals received RTN treatment 1 hour after start of MCAO. Somatosensory evoked potentials were recorded during MCAO. Animals were assigned daily neurological scores. Animals were killed 6 days after MCAO, and brains were quantitatively analyzed for infarct volume. RESULTS Within 1 hour after RTN was started, treated animals showed significantly improved somatosensory evoked potentials (103.3% versus 75% of baseline; P<0.01). Likewise, the combined neurological score for the RTN-treated group was 99.2, while the combined mean score for the untreated group was 66.4 (P<0.015). The mean infarction volume was 8.8+/-3.1% (of contralateral hemisphere) for the control group and 0.3+/-0.2% for the RTN-treated group (P<0.01). No increased mortality was seen in the RTN-treated group. CONCLUSIONS We conclude that RTN treatment during MCAO effectively reverses the pathophysiological sequelae of ischemia, even when the treatment is initiated 1 hour after the onset of ischemia. Although the infarct volume in the control group was variable when quantitatively assessed 6 days after 3.5 hours of MCAO, virtually no evidence of infarcts was seen in the RTN-treated group.

ASFNR Recommendations for Clinical Performance of MR Dynamic Susceptibility Contrast Perfusion Imaging of the Brain

This article discusses the utility of DSC perfusion MR imaging in the setting of tumors and ischemia and suggests guidance on its implementation, processing, interpretation, and reporting. SUMMARY: MR perfusion imaging is becoming an increasingly common means of evaluating a variety of cerebral pathologies, including tumors and ischemia. In particular, there has been great interest in the use of MR perfusion imaging for both assessing brain tumor grade and for monitoring for tumor recurrence in previously treated patients. Of the various techniques devised for evaluating cerebral perfusion imaging, the dynamic susceptibility contrast method has been employed most widely among clinical MR imaging practitioners. However, when implementing DSC MR perfusion imaging in a contemporary radiology practice, a neuroradiologist is confronted with a large number of decisions. These include choices surrounding appropriate patient selection, scan-acquisition parameters, data-postprocessing methods, image interpretation, and reporting. Throughout the imaging literature, there is conflicting advice on these issues. In an effort to provide guidance to neuroradiologists struggling to implement DSC perfusion imaging in their MR imaging practice, the Clinical Practice Committee of the American Society of Functional Neuroradiology has provided the following recommendations. This guidance is based on review of the literature coupled with the practice experience of the authors. While the ASFNR acknowledges that alternate means of carrying out DSC perfusion imaging may yield clinically acceptable results, the following recommendations should provide a framework for achieving routine success in this complicated-but-rewarding aspect of neuroradiology MR imaging practice.

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.

Physiologic MRI for assessment of response to therapy and prognosis in glioblastoma

Aside from bidimensional measurements from conventional contrast-enhanced MRI, there are no validated or FDA-qualified imaging biomarkers for high-grade gliomas. However, advanced functional MRI techniques, including perfusion- and diffusion-weighted MRI, have demonstrated much potential for determining prognosis, predicting therapeutic response, and assessing early treatment response. They may also prove useful for differentiating pseudoprogression from true progression after temozolomide chemoradiation and pseudoresponse from true response after anti-angiogenic therapy. This review will highlight recent developments using these techniques and emphasize the need for technical standardization and validation in prospective studies in order for these methods to become incorporated into standard-of-care imaging for brain tumor patients.

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.

Malignant transformation of DNETs: a case report and literature review.

Dysembryoplastic neuroepithelial tumors (DNETs) have traditionally been thought of as lesions with a benign clinical course that generally do not undergo malignant transformation. However, cases are emerging of DNETs that progress to more malignant forms. We present a case of malignant transformation, and we compile and review all previously published cases to identify common characteristics that may confer a higher risk for malignant transformation. A PubMed search was performed of all English-language case reports of DNET transformations to malignant cancers. The demographic, clinical, and histologic features of these patients are compiled and analyzed. A separate case report with histologic descriptions is also presented. A total of 10 case reports of DNET malignant transformation were found. The majority of cases involved complex-type DNETs. A higher proportion of extratemporal lesions were observed. Almost all cases involved subtotal resection. Risk factors for malignant progression of DNET lesions include complex-type histologic features, extratemporal location, and subtotal resection. Malignant dedifferentiation of astrocytic or oligodendrocytic cells within the glial nodule of complex DNETs may be the source of these transformations. There are no radiographic features that differentiate DNETs that are at higher risk for transformation.