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Related Concept Videos

Transfer Function to State Space01:23

Transfer Function to State Space

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State-space representation is a powerful tool for simulating physical systems on digital computers, necessitating the conversion of the transfer function into state-space form. Consider an nth-order linear differential equation with constant coefficients, like those encountered in an RLC circuit. The state variables are selected as the output and its n−1 derivatives. Differentiating these variables and substituting them back into the original equation produces the state equations.
In an RLC...
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State Space to Transfer Function01:21

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The conversion of state-space representation to a transfer function is a fundamental process in system analysis. It provides a method for transitioning from a time-domain description to a frequency-domain representation, which is crucial for simplifying the analysis and design of control systems.
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Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
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Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
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Related Experiment Video

Updated: Feb 5, 2026

Diffusion Tensor Magnetic Resonance Imaging in the Analysis of Neurodegenerative Diseases
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Comparing Glymphatic Function Measures: Diffusion Tensor Image Analysis Along Perivascular Spaces (DTI-ALPS) versus

Ingrid Mossige1,2,3, Lars M Valnes1,4, Tryggve H Storås1,3

  • 1Department of Physics and Computational Radiology, Division of Radiology and Nuclear Medicine, Oslo University Hospital, Sognsvannsveien 21, 0372 Oslo, Norway.

Radiology
|February 3, 2026
PubMed
Summary
This summary is machine-generated.

Diffusion-tensor image analysis along the perivascular space (ALPS) shows limited association with glymphatic function markers. This study found sparse cerebrospinal fluid tracer enhancement in ALPS regions, suggesting ALPS may not be a reliable indicator of glymphatic function.

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Area of Science:

  • Neuroimaging
  • Cerebrospinal Fluid Dynamics
  • Neurodegenerative Diseases

Background:

  • Diffusion-tensor image analysis along the perivascular space (ALPS) is a proposed noninvasive method to assess glymphatic function.
  • The validation of ALPS against established glymphatic function measures remains limited.

Purpose of the Study:

  • To evaluate ALPS indexes in different participant groups.
  • To compare ALPS indexes with cerebrospinal fluid (CSF) tracer enrichment and clearance measured by intrathecal contrast-enhanced MRI (gMRI).

Main Methods:

  • Secondary analysis of a prospective observational study involving 56 participants with CSF disorders and reference individuals.
  • Acquisition of MRI and diffusion-tensor imaging (DTI) scans before and after intrathecal gadobutrol injection.
  • Analysis of ALPS indexes and comparison with CSF tracer enrichment at 24 and 48 hours using regression analysis.

Main Results:

  • The ALPS index was significantly lower in the idiopathic normal pressure hydrocephalus (iNPH) group compared to the reference group.
  • A negative association was observed between the ALPS index and CSF tracer enrichment at 24 hours in deep white matter.
  • CSF tracer enrichment in ALPS regions of interest was minimal (10%), contrasting with substantial cortical enrichment (68-81%).

Conclusions:

  • CSF tracer enhancement within ALPS regions of interest was sparse across all participant groups.
  • The association between the ALPS index and gMRI markers of glymphatic function was found to be limited.
  • Further research is needed to validate ALPS as a reliable measure of glymphatic function.