A mesh-based model of liver vasculature: implications for improved radiation dosimetry to liver parenchyma for radiopharmaceuticals

Abstract

Purpose To develop a model of the internal vasculature of the adult liver and demonstrate its application to the differentiation of radiopharmaceutical decay sites within liver parenchyma from those within organ blood. Method Computer-generated models of hepatic arterial (HA), hepatic venous (HV), and hepatic portal venous (HPV) vascular trees were algorithmically created within individual lobes of the ICRP adult female and male livers (AFL/AML). For each iteration of the algorithm, pressure, blood flow, and vessel radii within each tree were updated as each new vessel was created and connected to a viable bifurcation site. The vascular networks created inside the AFL/AML were then tetrahedralized for coupling to the PHITS radiation transport code. Specific absorbed fractions (SAF) were computed for monoenergetic alpha particles, electrons, positrons, and photons. Dual-region liver models of the AFL/AML were proposed, and particle-specific SAF values were computed assuming radionuclide decays in blood within two locations: (1) sites within explicitly modeled hepatic vessels, and (2) sites within the hepatic blood pool residing outside these vessels to include the capillaries and blood sinuses. S values for 22 and 10 radionuclides commonly used in radiopharmaceutical therapy and imaging, respectively, were computed using the dual-region liver models and compared to those obtained in the existing single-region liver model. Results Liver models with virtual vasculatures of ~ 6000 non-intersecting straight cylinders representing the HA, HPV, and HV circulations were created for the ICRP reference. For alpha emitters and for beta and auger-electron emitters, S values using the single-region models were approximately 11% (AML) to 14% (AFL) and 11% (AML) to 13% (AFL) higher than the S values obtained using the dual-region models, respectively. Conclusions The methodology employed in this study has shown improvements in organ parenchymal dosimetry through explicit consideration of blood self-dose for alpha particles (all energies) and for electrons at energies below ~ 100 keV.

Representing unsegmented vessels using available vascular data for bioheat transfer simulation

“…The blood entering the tissue domain is considered to be uniformly distributed 32,33,38,48 . Thus, the flow rates leaving the arterial terminal nodes 3 are considered to be equal.…”

“…The CCO method has undergone various modifications such as parallelizing the growth of blood vessels [35][36][37] to increase computational efficiency. An example of the application of the CCO model is found in Correa-Alfonso's work of vascularization on mesh liver model 38 . The minimum diameter of a blood vessel in this liver model is 100 µm.…”

In silico simulation of hepatic arteries: An open‐source algorithm for efficient synthetic data generation

“…1,2 Many CHPs incorporate detailed anatomy and physiological functions, such as respiratory and cardiac motion and find application in com-puted tomography (CT), magnetic resonance imaging (MRI), and nuclear medicine. Uses of these phantoms include internal and external dosimetry, [2][3][4][5][6][7][8][9] the development and testing of novel image reconstruction algorithms (e.g., motion compensation, artifact suppression, sparse reconstruction), 1,[10][11][12][13][14][15] image acquisition techniques (e.g., artifact avoidance, collimator and detector optimization), 1,16,17 post-processing techniques (e.g., noise reduction), 1,18,19 and more. 20 Furthermore, the Quantitative Imaging Biomarker Alliance (QIBA) has used the term digital reference object (DRO) for the use of CHPs and other phantoms to establish a minimum performance requirement for quantitative imaging algorithms and reduce inter-scanner variability.…”

“…Lastly, a group of algorithms based on the minimization of a physiologically motivated cost function have been used to form synthetic vasculature. 6,[43][44][45][46][47][48][49][50] Sauer et al 33 proposed a method for liver vasculature generation with corresponding contrast dynamics for virtual CT imaging studies of hepatic perfusion. However, the method assumes uniform contrast density throughout the hepatic arteries and thus would be unrealistic for the simulation of interventional x-ray images, which have a temporally and spatially varying contrast signal.…”

“…While this can be realistic, it limits data variability since the larger vessels are consistent across different arterial trees. Lastly, a group of algorithms based on the minimization of a physiologically motivated cost function have been used to form synthetic vasculature 6,43–50 . Sauer et al 33 .…”