Magnetic resonance imaging of the fetal brain

US remains the key imaging technique for prenatal screening of CNS pathology. However, MR imaging of the fetal brain is a powerful tool to further characterize CNS anomalies, especially during the third trimester. The prognosis of CNS anomalies detected at fetal MR imaging is not always known. As such, management may be problematic with regards to medical interruption of pregnancy. A multidisciplinary approach is essential in order to insure comprehensive evaluation and management of the pregnancy.     

Inflammation high-field magnetic resonance imaging

Multiple sclerosis (MS) is the most common inflammatory demyelinating disorder of the central nervous system (CNS). MS has been subject to high-field magnetic resonance (MR) imaging research to a great extent during the past years, and much data has been collected that might be helpful in the investigation of other inflammatory CNS disorders. This article reviews the value of high-field MR imaging in examining inflammatory MS abnormalities. Furthermore, possibilities and challenges for the future of high-field MR imaging in MS are discussed.     

Magnetic resonance imaging of the central nervous system

Magnetic resonance (MR) is a powerful new imaging modality which has recently become competitive with X-ray computed tomography (CT) for imaging of the central nervous system (CNS). The advantages of MR include lack of ionizing radiation and the necessity to use iodinated contrast. MR is able to image directly in the transaxial, coronal, and sagittal planes. With appropriate pulsing sequences, MR is more sensitive than CT in the detection of early disease associated with increased water content. Included in this category are multiple sclerosis, early infarcts, small tumours, and inflammatory lesions. MR is superior to CT in the posterior fossa due to beam hardening artifacts in the latter modality. In the cord, MR is useful in the evaluation of syringomyelia, spinal dysraphism, and intramedullary tumours. Due to its increased sensitivity in the detection of early disease, MR should generally be used as the initial screening procedure in the evaluation of possible intracranial disease. Current limitations of MR include longer single slice imaging times, thicker slices, inability to use contrast agents to define blood/brain barrier breakdown, and the inability to image calcification and cortical bone. Patients on cardiac monitors or on respirators and those with intracranial aneurysm clips and cardiac pacemakers are currently excluded from MR imaging.     

Significance of the T2*-weighted gradient echo brain imaging in patients with infective endocarditis

Background

Although aneurysm formation accompanying parenchymal hemorrhage is one of devastating complications in the central nerves system (CNS), imaging studies of the brain are not routinely warranted in patients with infective endocarditis (IE). To assess the clinical importance for detecting silent lesions in the central nervous system, we investigated hypointense signal spots detected on the brain T2*-weighted MR imaging in patients with IE.

Methods and results

Eleven patients with IE were retrospectively reviewed. Seven patients (63.6%) showed hypointense signal spots on T2*-weighted MR images. The number of hypointense signal spots increased within only a few weeks in five patients.

Conclusion

The brain T2*-weighted MR imaging in patients with IE may have a potential role to detect CNS lesions with clinical significance of potentially high risk of intracranial hemorrhage. T2*-weighted hypointense signal spots may be specific to brain involvement, and be quite useful in monitoring CNS lesions associated with IE, even if they are asymptomatic.     

Brain perfusion imaging

Recent advances in both computed tomography (CT) and magnetic resonance (MR) technology and a new emphasis on thrombolytic therapy for acute stroke have brought brain perfusion studies to the forefront of neuroimaging clinical practice and research. Although brain perfusion studies long have been possible with nuclear medicine techniques, singlephoton emission computed tomography (SPECT) and positron emission tomography (PET) imaging in particular, these techniques are not particularly amenable to the acute stroke setting. This article will review the basic concepts of brain perfusion imaging in the context of acute stroke. The focus will be on CT and MR perfusion. The methodology, technical aspects and the relative advantages and disadvantages of the individual techniques will be discussed. Additionally, xenon CT methods and perfusion imaging of other central nervous system (CNS) pathology will be briefly addressed.     

Diffusion tensor imaging (DTI) and its importance for exploration of normal or pathological brain development

Diffusion tensor MR imaging (DTI) can provide in vivo unique information on integrity of white matter structures (anisotropy) and connectivity (fiber tracking) in the human brain. This is made possible by means of non-invasive MR-based technique. The purpose of this article is to review the method and the current applications of diffusion tensor MR imaging. Studies of the past decade featuring relevant neuropsychiatric disorders as well as disorders in child psychiatry are reviewed. Furthermore, this report offers a summary of DTI-studies in children and adolescents showing alterations in brain or CNS structures including neurological, traumatological and oncological investigations. In particular, it focuses on the importance of this method with respect to exploration of normal and pathological brain development.     

New MR perfusion features in primary central nervous system lymphomas: pattern and prognostic impact

Journal of Neurology - Some MR perfusion features predict overall survival (OS) and progression-free survival (PFS) in glioblastomas. Prognostic value of MR perfusion in primary CNS lymphomas...     

Cerebral blood volume mapping by MR imaging in the initial evaluation of brain tumors

PURPOSE: To assess the contribution of magnetic resonance (MR) cerebral blood volume (CBV) mapping in the initial evaluation of brain tumors. METHODS: 63 patients presenting a brain tumor underwent dynamic susceptibility-contrast MR imaging before surgery or biopsy: 28 high grade gliomas, 8 low grade gliomas, 2 pilocytic astrocytomas, 4 lymphomas, 12 metastases, 9 meningiomas. The CBV maps were obtained for each patient and the relative CBV (rCBV) in different areas was calculated using the ratio between the CBV in the pathological area (CBVp) and in the contralateral normal tissue(CBVn). The maximum rCBV (rCBVmax) for each tumor was determined and the mean values of rCBVmax in each group of tumors were compared using an unpaired Student t test (p=0.05). RESULTS: The rCBVmax for high grade gliomas (mean +/- SD: 2.6 +/- 1,2) was statistically different from low grade gliomas (0.9 +/- 0.4) (p<0.001), lymphomas (0.7 +/- 0.2) (p=0.002), meningiomas (9.1 +/- 4.4) (p<0.001) and kidney metastases (8.9 +/- 2.1) (p<0.001). The two pilocytic astrocytomas had a much lower rCBVmax than high grade gliomas. No statistically significant difference was found between high grade gliomas and lung metastases (2.4 +/- 0.9) (p=0.72). CONCLUSION: CBV mapping provides additional information on the vascularity of the lesions, which is not available with conventional MR imaging. It might be useful for differentiating certain lesions showing contrast enhancement, mainly high grade gliomas from kidney metastases, meningiomas, lymphomas or pilocytic astrocytomas.     

Fetal central nervous system MR imaging

MR imaging of the fetal brain is rapidly being embraced in clinical practice. Fetal MR imaging is proving to be a powerful modality with which to evaluate the fetal brain and is a valuable complement to prenatal ultrasound. Structural abnormalities, such as cerebral malformations and destructive lesions, can be sonographically occult on prenatal ultrasound yet detectable by fetal MR imaging. Moreover, fetal MR imaging offers the promise of contributing to our understanding of normal as well as abnormal brain development with continued advances in MR imaging techniques, such as diffusion-weighted and parallel imaging.     

Clinical applications of intracranial perfusion MR imaging.

Dynamic susceptibility MR perfusion imaging of the brain offers clinically relevant physiological data not obtainable by conventional MR imaging. As new treatments continue to be developed for stroke, neoplasm, dementia, psychiatric illness, headache, and trauma, the potential clinical applications of perfusion MR imaging in the diagnosis, triage, and therapeutic monitoring of these diseases will increase. MR perfusion techniques are likely to be at least as sensitive and specific as radionuclide-based techniques, and offer the added advantage of higher intrinsic resolution, convenient coregistration with conventional MR imaging, as well as, time and cost-effective imaging in patients for whom a routine MR imaging is obtained.     

Hodgkin and non-Hodgkin lymphoma of the head and neck: clinical, pathologic, and imaging evaluation

Lymphomas are subdivided into HL and NHL and are more specifically classified into subtypes of HL or NHL according to the WHO classification. HLs involve the lymph nodes predominantly and only approximately 5% arise in extranodal sites, whereas 30% of NHLs present in extranodal sites. Imaging studies, including CT and MR imaging, cannot distinguish [figure: see text] HL from NHL, and cannot differentiate their various subtypes, necessitating a pathologic diagnosis. Clinical parameters, however, can be helpful in differentiating the two broad categories of lymphomas, and subtypes of lymphomas have predilections for different sites within the head and neck. HL is most commonly located in the lymph nodes of the neck and mediastinum. Marginal-zone lymphoma has an affinity for the ocular adnexa, salivary glands, larynx, and the thyroid gland. Diffuse large B-cell lymphoma is commonly encountered in the paranasal sinuses, mandible, maxilla, and Waldeyer ring. Burkitt lymphoma occurs more frequently in children and young adults and frequently affects the maxilla and mandible, with a greater distribution of involvement at a lower frequency. On imaging studies, the lymph nodes of HL and NHL are homogeneous and variable in size, with an average diameter from 2 to 10 cm. They may enhance slightly to moderately, display necrosis before and after treatment, and display calcification post-treatment. NHL in extranodal sites in the head and neck (nasopharynx, Waldeyer ring, oral cavity, and larynx) manifests frequently as a submucosal mass accompanied [figure: see text] by polypoid, bulky masses with a smooth mucosal surface. Clinically aggressive lymphomas, such as Burkitt lymphoma, diffuse large B-cell lymphoma, and NK-/T-cell lymphomas are characterized by destruction of the maxilla, mandible, and bones around the paranasal sinuses, which is indistinguishable from bony destruction in other malignant tumors, such as SCC. Contrast CT is indicated for evaluation of cervical lymph nodes; the chest, including the mediastinum; the pelvic cavity; paranasal sinuses; and orbits. CT is also useful for detection of bone destruction involving the base of the skull, paranasal sinuses, and the mandible or maxilla. MR imaging is preferred for the assessment of extension of lymphomas to different fascial spaces (parapharyngeal, masticator, infratemporal fossa, tongue, and nasopharynx) and for intracranial extension. Lymphomas are isodense to muscle on CT and circumscribed with distinct margins that occasionally display extranodal extension with less-well-defined margins and areas of necrosis within the tumor matrix. Lymphomas appear low in signal intensity on T1-weighted images and low to high in signal intensity on T2-weighted images, with variable, but usually low, enhancement following introduction of Gadolinium-DTPA (Gd-DTPA) contrast material.     

Orbital cavernous hemangioma: role of imaging

CT and MR imaging are particularly important in the diagnostic investigation of patients with vascular disorders of the orbit. The improved image quality of CT and MR imaging, along with dynamic CT angiography, MR angiography, MR venography, and multiphase dynamic contrast CT/MR imaging, has proven useful to delineate as well as differentiate various orbital vascular lesions. This article presents the current classification of orbital vascular disorders and describes the CT/MR imaging characteristics of orbital cavernous hemangiomas and simulating lesions.     

Wegener's granulomatosis of the paranasal sinuses with orbital and central nervous system involvement-diagnostic imaging

Wegener's granulomatosis (WG) is a systemic vasculitis that can affect any organic system, but primarily involves the upper and lower respiratory tracts and the kidneys. WG relatively frequently affects the nervous system (in 30-50%), usually in the form of peripheral or cranial neuropathy. Involvement of the brain is reported in a very small percentage of patients (2%-8%). Three major mechanisms have been described as the cause of central nervous system (CNS) disease in WG: contiguous invasion of granuloma from extracranial sites, remote intracranial granuloma and CNS vasculitis. CNS involvement caused by contiguous invasion of granuloma from extracranial sites is the rarest. We report the case of a 37-year-old man with WG, manifested as a pulmonary and paranasal sinuses disease, with orbital and CNS involvement, caused by contiguous invasion from the paranasal sinuses. In this report, the rich spectrum of findings achieved by computed tomography and magnetic resonance are demonstrated. The importance of computed tomography in bony destruction PNS findings, and the importance of MR imaging in evaluation of the direct intracranial spread from nasal, paranasal and orbital disease are also emphasized.     

Hypoxia imaging in brain tumors

Assessment of the oxygenation status of brain tumors has been studied increasingly with imaging techniques in light of recent advances in oncology. Tumor oxygen tension is a critical factor influencing the effectiveness of radiation and chemotherapy and malignant progression. Hypoxic tumors are resistant to treatment, and prognostic value of tumor oxygen status is shown in head and neck tumors. Strategies increasing the tumor oxygenation are being investigated to overcome the compromising [figure: see text] effect of hypoxia on tumor treatment. Administration of nicotinamide and inhalation of various high oxygen concentrations have been implemented. Existing methods for assessment of tissue oxygen level are either invasive or insufficient. Accurate and noninvasive means to measure tumor oxygenation are needed for treatment planning, identification of patients who might benefit from oxygenation strategies, and assessing the efficacy of interventions aimed to increase the radiosensitivity of tumors. Of the various imaging techniques used to assess tissue oxygenation, MR spectroscopy and MR imaging are widely available, noninvasive, and clinically applicable techniques. Tumor hypoxia is related closely to insufficient blood flow through chaotic and partially nonfunctional tumor vasculature and the distance between the capillaries and the tumor cells. Information on characteristics of tumor vasculature such as blood volume, perfusion, and increased capillary permeability can be provided with MR imaging. MR imaging techniques can provide a measure of capillary permeability based on contrast enhancement and relative cerebral blood volume estimates using dynamic susceptibility MR imaging. Blood oxygen level dependent contrast MR imaging using gradient echo sequence is intrinsically sensitive to changes in blood oxygen level. Animal models using blood oxygen level-dependent contrast imaging reveal the different responses of normal and tumor vasculature under hyperoxia. Normobaric hyperoxia is used in MR studies as a method to produce MR contrast in tissues. Increased T2* signal intensity of brain tissue has been observed using blood oxygen level-dependent contrast MR imaging. Dynamic blood oxygen level-dependent contrast MR imaging during hyperoxia is suggested to image tumor oxygenation. Quantification of cerebral oxygen saturation using blood oxygen level-dependent MR imaging also has been reported. Quantification of cerebral blood oxygen saturation using MR imaging has promising clinical applications; however, technical difficulties have to be resolved. Blood oxygen level dependent MR imaging is an emerging technique to evaluate the cerebral blood oxygen saturation, and it has the potential and versatility to assess oxygenation status of brain tumors. Upon improvement and validation of current MR techniques, better diagnostic, prognostic, and treatment monitoring capabilities can be provided for patients with brain tumors.     

Orbital and ocular imaging using 3- and 1.5-T MR imaging systems

The goal of this article is to familiarize general radiologists and clinicians (particularly ophthalmologists, neuro-ophthalmologists, neurologists, and neurosurgeons) with the recent introduction of clinical MR imaging scanners operating at a magnetic field strength of 3-T and to compare them with the more common standard scanners operating at 1.5-T. In this study, MR imaging at 3-T was found to offer superior depiction of orbital and intracranial anatomy and pathologic findings. Spin echo, high spatial resolution, T2-weighted, thin-section MR imaging sequences are especially useful and sensitive at 3-T for the evaluation of orbital, ocular, and intracranial anatomy and pathologic findings. The authors din that time-of-flight (TOF) MR angiography at 3-T surpasses the best MR angiography at 1.5-T and that two-dimensional TOF venography and three-dimensional contrast MR venography at 3-T offer superior visualization of intracranial and facial veins as compared with MR venography at 1.5-T. We believe that with further quality image production and efficient coil design, 3-T MR imaging should hold the promise of playing an important role in the diagnostic imaging evaluation of ocular, orbital, and optic pathway pathologic findings.     

Stroke imaging at 3.0 T

Stroke is a devastating disease with a complex pathophysiology. It is a major cause of death and disability in North America. To fully characterize its extent and effects, one requires numerous specialized anatomical and functional MR techniques, specifically diffusion-weighted imaging, MR angiography, and perfusion-weighted imaging. The advent of 3.0 T clinical scanners has the potential to provide higher quality information in potentially less time compared with 1.5 T stroke-specific MR imaging protocols. This article gives a brief overview of stroke, presents the principles and clinical applications of the relevant MR techniques required for diagnostic stroke imaging at high field, and discusses the advantages, challenges, and limitations of 3.0 T imaging as they relate to stroke.     

中枢神经系统炎性脱髓鞘性假瘤的诊断和治疗

目的:描述中枢神经系统炎性脱髓鞘性假瘤的临床表现,探讨该病的病理学特征以及MRI诊断价值,以期加强对本病的认识并提高诊断的正确性。方法:对2例经手术病理证实中枢神经系统炎性脱髓鞘性假瘤进行MRI检查,对其临床表现、影像学表现进行了回顾性分析。结果:MRI显示2例病变均表现为局限性肿块呈均匀长T1、长T2信号,临近未见伴有多发病灶。术前均被误诊为胶质瘤,经手术切除病变,病理证实为中枢神经系统炎性脱髓鞘性假瘤。结论:中枢神经系统炎性脱髓鞘性假瘤的临床和影像学诊断较为困难,常将本病误诊为肿瘤,此时可以先使用激素试验治疗,以避免手术或放射治疗造成的严重损伤。     

Perfusion MR imaging and MR spectroscopy of gemistocytic astrocytoma

This report is of a case of gemistocytic astrocytoma investigated by perfusion-weighted magnetic resonance (MR) imaging associated with proton MR spectroscopy. The conventional MR imaging presentation of gemistocytic astrocytoma is similar to that of HGG, metastasis or lymphoma. Nevertheless, a precise diagnosis is crucial as the prognosis and therapy of these diseases are different. Quantitative MR imaging sequences, which provide metabolic and vascular information, could be useful in the prevention of misdiagnosis.     

Parathyroid imaging

The most common indication for parathyroid imaging is hyperparathyroidism, which is caused by a solitary parathyroid adenoma in most patients. The primary function of parathyroid imaging is localization of the abnormal parathyroid gland, enabling the surgeon to pursue a minimally invasive resection. Ultrasound and (99m)Tc sestamibi scintigraphy are the mainstays for the preoperative localization of culprit lesions. The emerging modality of SPECT-CT can improve the sensitivity of (99m)Tc sestamibi scintigraphy and its use is encouraged when available. CT and MR imaging are useful as adjuncts, particularly as anatomic correlates to suspected ectopic glands on (99m)Tc sestamibi scintigraphy that are inaccessible to ultrasound. In cases of suspected parathyroid carcinoma, preoperative CT or MR imaging is recommended for surgical planning.     

Diffusion imaging in traumatic brain injury

Traumatic brain injury is a common cause of death worldwide, affecting mostly young people. The most feasible examination to be performed in the emergency room is computed tomography. Magnetic resonance (MR) imaging is becoming a significant tool in the evaluation of severe brain trauma. Diffusion-weighted imaging is an advanced MR imaging sequence that has been used to detect areas of ischemia and tumor malignancy. This article describes the recent advances in trauma based on diffusion-weighted MR imaging findings and in brain injury from head trauma based on diffusion-weighted MR imaging and diffusion tensor MR imaging findings. Current and potential clinical applications are discussed.