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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2024)

Extracting explainable flow metrics from cardiac flow imaging modalities for the use of clinical decision making is a challenge especially when our understanding of complex intraventricular hemodynamics is incomplete. We hypothesized that reduced-order models (ROMs) of intraventricular flow are a suitable strategy for deriving simple and interpretable clinical metrics suitable for further assessments. Combined with machine learning (ML) flow-based ROMs could provide new insight to help diagnose, risk-stratify, and monitor patients LV flow. We analyzed color-Doppler echocardiograms of 81 non-ischemic dilated cardiomyopathy (DCM) patients, 51 hypertrophic cardiomyopathy (HCM) patients, and 77 normal volunteers (Control). To test whether flow-based ROMs provide metrics that discriminate phenotypic differences, we used these ROMs to build three LV flow classifiers with different levels of supervision: supervised, weakly supervised, and quasi-unsupervised.

The first study applies proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) to obtain cohort-specific ROMs of LV flow. Each ROM aggregates a low number of components representing a spatially dependent velocity map. These components/hyperparameter were found using gridsearch to derive supervised ROMs that maximize classification power. POD-based and DMD-based ROMs stably represented each cohort through repeated 10-fold cross-validation. POD cohort-representative models slightly outperformed DMD cohort-representative ROM with POD mode captured >80% of the flow kinetic energy (KE) in all cohorts. This classifier performed favorably, with AUCs exceeding 0.75 and going up to 0.93.

The second part of the study explores whether there are intrinsic properties of patient-represented POD ROM that can differentiate among phenotypes. Semi-unsupervised classification using patient-specific ROMs revealed that KE ratio of these two principal modes, the vortex-to-jet (V2J) energy ratio, is a simple, interpretable metric that discriminates DCM, HCM, and Control patients. Receiver operating characteristic curves using V2J as classifier had areas under the curve ranging from 0.81-0.95 for distinguishing between phenotypes.

Modal decomposition of cardiac flow can be used to create ROMs of normal and pathological flow patterns, uncovering simple interpretable flow metrics with power to discriminate disease states, and particularly suitable for further processing using ML. Future work includes extending ROM for longitudinal studies by considering trajectory inference modeling for hemodynamic monitoring of patients with end-stage DCM.

    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2014)
    While it is well recognized that pulmonary deposition of inhaled particles is lowered in microgravity (μG) compared with gravity on the ground (1G), the absence of sedimentation causes fine particles to penetrate deeper in the lung in μG. Using quantitative magnetic resonance imaging (MRI), we determined the effect of gravity on peripheral deposition (DEPperipheral) of fine particles. Aerosolized 0.95-μm-diameter ferric oxide particles were delivered to spontaneously breathing rats placed in plethysmographic chambers both in μG aboard the NASA Microgravity Research Aircraft and at 1G. Following exposure, lungs were perfusion fixed, fluid filled, and imaged in a 3T MR scanner. The MR signal decay rate, R2*, was measured in each voxel of the left lung from which particle deposition (DEP) was determined based on a calibration curve. Regional deposition was assessed by comparing DEP between the outer (DEPperipheral) and inner (DEPcentral) areas on each slice, and expressed as the central-to-peripheral ratio. Total lung deposition tended to be lower in μG compared with 1G (1.01 ± 0.52 vs. 1.43 ± 0.52 μg/ml, P = 0.1). In μG, DEPperipheral was larger than DEPcentral (P < 0.03), while, in 1G, DEPperipheral was not significantly different from DEPcentral. Finally, central-to-peripheral ratio was significantly less in μG than in 1G (P ≤ 0.05). These data show a larger fraction of fine particles depositing peripherally in μG than in 1G, likely beyond the large- and medium-sized airways. Although not measured, the difference in the spatial distribution of deposited particles between μG and 1G could also affect particle retention rates, with an increase in retention for particles deposited more peripherally.
      Cover page: Increase in relative deposition of fine particles in the rat lung periphery in the absence of gravity
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