Venous Perfusion Source Mapping “in Reverse” with Magnetic Resonance Imaging
Ekin Karasan
EECS Department, University of California, Berkeley
Technical Report No. UCB/EECS-2024-160
August 8, 2024
http://www2.eecs.berkeley.edu/Pubs/TechRpts/2024/EECS-2024-160.pdf
Magnetic resonance imaging (MRI) is a versatile medical imaging modality, which can be used for a variety of applications, including imaging soft tissue structure, measuring functional brain activity by probing blood oxygenation, assessing complex tissue dynamics, and quantifying tissue susceptibility. Measuring complex tissue dynamics such as perfusion and blood flow can offer essential information for diagnosis and provide insights into biophysical functions. Non-contrast enhanced methods to image these dynamics are particularly advantageous as they minimize the risk for patients and improve patient comfort.
While MRI tools for probing blood flow and perfusion are well-established for studying cerebral arterial disorders, the knowledge on the venous drainage mechanism of the brain is much more limited. This is largely attributed to the person-to-person variability in the cerebral venous physiology and the limitations of the current imaging technologies. Venous abnormalities play an important role in several important vascular and neurological conditions. Furthermore, venous effects also contribute significantly to functional MRI (fMRI) based on blood oxygenation level dependent (BOLD) contrast by reducing the spatial specificity of the BOLD signal.
Digital subtraction angiography (DSA) is currently the gold standard to image the venous system, however, it is an invasive procedure that has life-threatening risks. Primary non-invasive and non-contrast enhanced tools to probe the venous system with MRI are phase-contrast (PC) MRI, which probes the instantaneous velocity of blood and time of flight (TOF), which relies on inflow effects. TOF MRI is limited to imaging the venous structure and provides minimal information on flow dynamics. PC MRI requires very large velocity encoding gradients to capture slower flows, significantly increasing echo times, potentially leading to phase offset errors and reducing the accuracy of the measured velocities. Therefore, neither of the techniques can probe the venous system in its entirety.
To address current limitations in venous imaging, this dissertation proposes a novel venous perfusion source mapping method using Displacement Spectrum (DiSpect) MRI, a non-contrast method that uses blood water as an endogenous contrast agent. This technique encodes spatial information into the magnetization of blood water spins during tagging and remotely detects it once the tagged blood reaches the imaging region -- often near the brain's surface, where the signal-to-noise ratio is 3-4$\times$ higher. Through repeated spin-tagging and Fourier encoding, this method can resolve the sources of blood water entering the imaging slice across short (10ms) to long (3s) evolution times, effectively capturing venous perfusion sources in reverse. Blood sources can be traced regardless of their path and velocity, enabling measurement of slow blood flow in smaller veins and potentially in capillary beds.
The dissertation first introduces the theory behind DiSpect MRI and describes its application in venous perfusion source mapping in the superior cerebral veins. Next, the sensitivity of the proposed perfusion source mapping technique is established through perfusion modulation using caffeine and its specificity is demonstrated by measuring local perfusion changes during functional activation. Finally, the technique is validated with flow phantom experiments, and several advancements in acquisition techniques are presented.
Advisors: Michael Lustig
BibTeX citation:
@phdthesis{Karasan:EECS-2024-160,
Author= {Karasan, Ekin},
Title= {Venous Perfusion Source Mapping “in Reverse” with Magnetic Resonance Imaging},
School= {EECS Department, University of California, Berkeley},
Year= {2024},
Month= {Aug},
Url= {http://www2.eecs.berkeley.edu/Pubs/TechRpts/2024/EECS-2024-160.html},
Number= {UCB/EECS-2024-160},
Abstract= {Magnetic resonance imaging (MRI) is a versatile medical imaging modality, which can be used for a variety of applications, including imaging soft tissue structure, measuring functional brain activity by probing blood oxygenation, assessing complex tissue dynamics, and quantifying tissue susceptibility. Measuring complex tissue dynamics such as perfusion and blood flow can offer essential information for diagnosis and provide insights into biophysical functions. Non-contrast enhanced methods to image these dynamics are particularly advantageous as they minimize the risk for patients and improve patient comfort.
While MRI tools for probing blood flow and perfusion are well-established for studying cerebral arterial disorders, the knowledge on the venous drainage mechanism of the brain is much more limited. This is largely attributed to the person-to-person variability in the cerebral venous physiology and the limitations of the current imaging technologies. Venous abnormalities play an important role in several important vascular and neurological conditions. Furthermore, venous effects also contribute significantly to functional MRI (fMRI) based on blood oxygenation level dependent (BOLD) contrast by reducing the spatial specificity of the BOLD signal.
Digital subtraction angiography (DSA) is currently the gold standard to image the venous system, however, it is an invasive procedure that has life-threatening risks. Primary non-invasive and non-contrast enhanced tools to probe the venous system with MRI are phase-contrast (PC) MRI, which probes the instantaneous velocity of blood and time of flight (TOF), which relies on inflow effects. TOF MRI is limited to imaging the venous structure and provides minimal information on flow dynamics. PC MRI requires very large velocity encoding gradients to capture slower flows, significantly increasing echo times, potentially leading to phase offset errors and reducing the accuracy of the measured velocities. Therefore, neither of the techniques can probe the venous system in its entirety.
To address current limitations in venous imaging, this dissertation proposes a novel venous perfusion source mapping method using Displacement Spectrum (DiSpect) MRI, a non-contrast method that uses blood water as an endogenous contrast agent. This technique encodes spatial information into the magnetization of blood water spins during tagging and remotely detects it once the tagged blood reaches the imaging region -- often near the brain's surface, where the signal-to-noise ratio is 3-4$\times$ higher. Through repeated spin-tagging and Fourier encoding, this method can resolve the sources of blood water entering the imaging slice across short (10ms) to long (3s) evolution times, effectively capturing venous perfusion sources in reverse. Blood sources can be traced regardless of their path and velocity, enabling measurement of slow blood flow in smaller veins and potentially in capillary beds.
The dissertation first introduces the theory behind DiSpect MRI and describes its application in venous perfusion source mapping in the superior cerebral veins. Next, the sensitivity of the proposed perfusion source mapping technique is established through perfusion modulation using caffeine and its specificity is demonstrated by measuring local perfusion changes during functional activation. Finally, the technique is validated with flow phantom experiments, and several advancements in acquisition techniques are presented.},
}
EndNote citation:
%0 Thesis %A Karasan, Ekin %T Venous Perfusion Source Mapping “in Reverse” with Magnetic Resonance Imaging %I EECS Department, University of California, Berkeley %D 2024 %8 August 8 %@ UCB/EECS-2024-160 %U http://www2.eecs.berkeley.edu/Pubs/TechRpts/2024/EECS-2024-160.html %F Karasan:EECS-2024-160