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Anatomical and Biological Imaging of Pediatric Brain Tumor
Published in David A. Walker, Giorgio Perilongo, Roger E. Taylor, Ian F. Pollack, Brain and Spinal Tumors of Childhood, 2020
Rob A. Dineen, Shivaram Avula, Andrew C. Peet, Giovanni Morana, Monika Warmuth-Metz
Perfusion MRI provides biomarkers of tumor vascularity such as cerebral blood flow (CBF), cerebral blood volume (CBV), and vascular permeability (ktrans). Several methods are used, each with its own properties, and each tends to be most accurate in measuring a specific biomarker. Dynamic susceptibility contrast (DSC) MRI is the most commonly used technique and is a rapid way to acquire CBV. Dynamic contrast-enhanced (DCE) MRI requires approximately 5 minutes and is particularly useful for obtaining ktrans. Both techniques require gadolinium-based contrast injection via a mechanical pump and these are commonly not compatible with a central venous catheter. Arterial spin labeling (ASL) measures CBF without contrast injection in about 5 minutes. An alternative method for acquiring information on perfusion without injecting contrast agent is multi-b value DWI, which can provide estimates of perfusion fraction (f), which has some equivalence to CBV. Some studies quote tumor blood volume (TBV) or tumor blood flow (TBF) which are equivalent to CBV and CBF respectively when the latter has been measured over the tumor. We use them interchangeably here.
Perfusion Imaging: Physical Principles and Applications in the Brain
Published in Andrei I. Holodny, Functional Neuroimaging, 2019
Perfusion MRI is able to characterize brain tumor biology and other central nervous system (CNS) disorders due to the underlying pathologic and physiologic changes that occur with tumor vasculature. Although the biology underlying brain tumor angiogenesis and vascular recruitment along with the feedback loop with tumor hypoxia and necrosis are extremely complex, there are some physiologic mechanisms that can be quantified using perfusion MRI. In particular, there are some perfusion metrics that can be used as surrogate markers of tumor angiogenesis and vascular permeability. The previous chapter describes the various techniques available for acquiring perfusion MRI data. The two major techniques currently used in both clinical and research settings are a T1-weighted steady-state dynamic contrast-enhanced MRI (DCE MRI) and a T2*-weighted dynamic susceptibility contrast (DSC) MRI (DSC MRI) method. The advantages and disadvantages of each technique with regard to characterizing tumor biology will be discussed; however, the majority of clinicians and investigators are currently utilizing the DSC MRI technique for brain tumor perfusion MRI.
IVIM MRI Analysis with Low Perfusion
Published in Denis Le Bihan, Mami Iima, Christian Federau, Eric E. Sigmund, Intravoxel Incoherent Motion (IVIM) MRI, 2018
Another common pathology with characteristically low perfusion is the ischemic stroke. Multiple disease mechanisms can result in a stroke, although they all share the aspect of disruption occurring in the cerebral blood flow [10]. In an ischemic stroke, the lack of blood flow due to a narrowed or blocked artery can result in cell death. Perfusion MRI has the potential to support the rapidly required treatment decisions for acute stroke patients. However, the relative ease of applicability of DWMRI, and its extraordinary ability to confirm the diagnosis of a stroke, has meant that DWMRI has become the “gold standard” for its detection [28]. Nevertheless, the diagnosis of transient ischemic attack, where an artery is temporarily blocked, was not always detectable by DWMRI, while changes were observed in a perfusion MRI [29, 30]. This presents a favorable role for the use of IVIM MRI, which is able to derive parameters of both diffusion and perfusion in a single protocol.
Detection of silent cerebral microcirculatory abnormalities in patients with manifest ischemic coronary disease: a perfusion brain MRI study combined with dipyridamole stress
Published in Scandinavian Cardiovascular Journal, 2021
Tihamer Molnar, Andrea Horvath, Zsuzsanna Szabo, Zoltan Vamos, Tamas Dóczi, Zsolt Illes
Patients underwent a baseline MRI session (T2, MPRAGE, T1, FLAIR) to exclude manifest structural brain pathologies including infarcts. Two months later, another MRI was performed when patient was already in the MR machine during dipyridamole administration. Dipyridamole was given intravenously in a 0.56 ml/kg dose for 4 min [8]. Dynamic susceptibility weighted (DSC) perfusion MRI was performed 7 min after administration, when dipyridamole reaches its peak concentration in the plasma. MR imaging was performed on a 3 T Siemens TIM Trio MRI scanner (Siemens AG, Erlangen, Germany) with a 12-channel head coil. Conventional anatomical imaging included T1-, T2-weighted, and FLAIR sequences. Three-dimensional T1-weighted MPRAGE images (TR/TI/TE = 2530/1100/3.37 ms, flip angle 7°, 176 sagittal slices, slice thickness 1 mm, field of view 256 × 256 mm2, matrix 256 × 256, receiver bandwidth 200 Hz/pixel, GRAPPA 2) served as structural scans. For DSC perfusion imaging, a T2*-weighted gradient echo planar sequence was used (TR/TE: 1400/33 ms, 20 axial slices, slice thickness: 3 mm, distance factor: 33%, FOV: 210 × 210 mm2, matrix: 88 × 88, receiver bandwidth: 1114 Hz/Px, GRAPPA 2.).
Important role of microglia in HIV-1 associated neurocognitive disorders and the molecular pathways implicated in its pathogenesis
Published in Annals of Medicine, 2021
A. Borrajo, C. Spuch, M. A. Penedo, J. M. Olivares, R. C. Agís-Balboa
A recent study explored the role of BBB disruption in the pathogenesis of HAND in the context of fully suppressive ART. They used dynamic contrast enhanced perfusion MRI to measure capillary permeability as an indicator for BBB integrity and found that the incidence of HAND in these patients was associated with BBB impairment. This work highlighted region-specific rather than global BBB disruption, and no correlation with neuroinflammation blood markers, suggesting that HIV and not systemic inflammation was driving this BBB disturbance. This would mean that the BBB disruption was a consequence of HIV already present in the brain as opposed to HIV impairing the BBB and then causing the brain disease [53]. Another study explored the establishment of abnormal BBB permeability and its relationship to neuropathogenesis during primary HIV infection by evaluating the CSF to serum albumin quotient (QAlb). To date, the QAlb remains the best-known fluid marker for BBB permeability in patients with primary HIV infection. They found after initiating ART during primary HIV infection, QAlb increases in association with neuronal damage, and this increase did not significantly improve during treatment over one year. Thus, they concluded, BBB-associated neuropathogenesis in HIV-infected patients may start during primary infection [52].
Magnetic resonance imaging features influencing high-intensity focused ultrasound ablation of adenomyosis with a nonperfused volume ratio of ≥90% as a measure of clinical treatment success: retrospective multivariate analysis
Published in International Journal of Hyperthermia, 2018
Bilgin Keserci, Nguyen Minh Duc
The following quantitative perfusion MRI features were assessed using the MR Permeability tool on the IntelliSpace Portal software (version 6.0, Philips): volume transfer constant, Ktrans; reverse reflux rate constant, Kep; volume fraction of extravascular extracellular space, Ve; and volume fraction of plasma, Vp. To quantify the time-SI curves on T1W perfusion MRI, which were derived from DCE-MRI data, the ratio of each quantitative perfusion parameter was defined as the ratio of the SI of the adenomyosis to that of the myometrium.