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In the context of neurologic disorders, dynamic susceptibility contrast (DSC) and dynamic contrast enhanced (DCE) MRI provide valuable insights into cerebral vascular function, integrity, and architecture. Even after two decades of use, these modalities continue to evolve as their biophysical and kinetic basis is better understood, with improvements in pulse sequences and accelerated imaging techniques and through application of more robust and automated data analysis strategies. Here, we systematically review each of these elements, with a focus on how their integration improves kinetic parameter accuracy and the development of new hemodynamic biomarkers that provide sub-voxel sensitivity (e.g., capillary transit time and flow heterogeneity). Regarding contrast mechanisms, we discuss the dipole-dipole interactions and susceptibility effects that give rise to simultaneous T(1), T(2) and [Formula: see text] relaxation effects, including their quantification, influence on pulse sequence parameter optimization, and use in methods such as vessel size and vessel architectural imaging. The application of technologic advancements, such as parallel imaging, simultaneous multi-slice, undersampled k-space acquisitions, and sliding window strategies, enables improved spatial and/or temporal resolution of DSC and DCE acquisitions. Such acceleration techniques have also enabled the implementation of, clinically feasible, simultaneous multi-echo spin- and gradient echo acquisitions, providing more comprehensive and quantitative interrogation of T(1), T(2) and [Formula: see text] changes. Characterizing these relaxation rate changes through different post-processing options allows for the quantification of hemodynamics and vascular permeability. The application of different biophysical models provides insight into traditional hemodynamic parameters (e.g., cerebral blood volume) and more advanced parameters (e.g., capillary transit time heterogeneity). We provide insight into the appropriate selection of biophysical models and the necessary post-processing steps to ensure reliable measurements while minimizing potential sources of error. We show representative examples of advanced DSC- and DCE-MRI methods applied to pathologic conditions affecting the cerebral microcirculation, including brain tumors, stroke, aging, and multiple sclerosis. The maturation and standardization of conventional DSC- and DCE-MRI techniques has enabled their increased integration into clinical practice and use in clinical trials, which has, in turn, spurred renewed interest in their technological and biophysical development, paving the way towards a more comprehensive assessment of cerebral hemodynamics.

When a briefly exposed target word is followed by a pseudoword mask, the disruptive masking effect is reduced when the mask shares graphemes with the target word and is further reduced when the mask shares phonemes with the target word (Perfetti, Bell, & Delaney, 1988,Journal of Memory and Language27, 59–70). These results implicate early (prelexical) phonemic activation during word identification. In Experiment 1, this phonemic masking effect was found to hold through target exposure durations ranging from 35 to 55 ms and to be independent of word frequency and spelling pattern consistency. In Experiment 3, completely convergent results were found in a masked priming paradigm that varied the exposure of a masked pseudoword prime from 25 to 65 ms. Phonemic priming effects were found by 45 ms correcting earlier conclusions favoring direct visual access based on this paradigm. Together, the masking and priming results strongly support a process of early phonemic activation prior to word identification. The results are most naturally handled by a single-mechanism activation model, but are also consistent with restricted versions of dual route theories.

Visual access to a printed word may be accompanied by a very rapid activation of phonetic properties of the word as well as its constituent letters. We suggest that such automatic activation during word identification, rather than only postlexical recoding, routinely occurs in reading. To demonstrate such activation, we varied the graphemic and phonetic properties shared by a word target and a following pseudoword mask. Graphemic ( mard ) and homophonic ( mayd ) masks, equated for number of letters shared with a word target ( made ), both showed a masking reduction effect relative to a control mask. There was an additional effect of the homophonic mask over the graphemic mask, attributable to phonetic activation. A second experiment verified this pattern of mask reduction effects using conditions that ruled out any explanation of the effect that does not take account of the target-mask relationship. We take the results to suggest that a phonetic activation nonoptionally occurs (prelexically) during lexical access.