Uterine fibroids, endometriosis, and adenomyosis are gynecological disorders causing significant symptoms and have clinical struggles around diagnosis and treatment planning. The tissue changes associated with these disorders may support assessment via ultrasound shear wave elastography (SWE), an imaging method that estimates tissue stiffness. This dissertation examined the feasibility of gynecological SWE for the in vivo assessment of uterine tissues. Specifically, this thesis evaluated: 1) the validity and reliability of endoprobe SWE stiffness measured in tissue mimicking materials (TMMs), 2) the validity of indentation testing in TMMs, 3) the impact of indentation parameters on the agreement between indentation stiffness and stiffness parameters measured by SWE, and 4) the reliability of and confounders on in vivo SWE of the uterus.
First, to establish the reliability and validity of gynecological endoprobe SWE stiffness measures, 31 homogenous TMM phantoms were manufactured with a range of elastic moduli. SWE stiffness was measured at 1cm, 3cm, and 5cm depths using a linear, curvilinear, and endo- SWE probes. Quasi-static ramp compression stiffness was the validity benchmark. Phantom moduli ranged from 17.10 kPa to 88.12 kPa. Endoprobe SWE stiffness reliability was excellent at all depths, however endoprobe SWE validity was poorer at 1cm depths than that of both the linear and curvilinear probe. The validity of endoprobe SWE stiffness was lower at the 3cm depth compared to the 1cm depth, and outcomes were not valid at the 5cm depth.
Second, to establish the validity of indentation testing as a benchmark standard for SWE applications, indentation testing was conducted in TMM phantoms under a series of testing parameters with quasi-static ramp compression used as the benchmark. The best agreement between indentation and ramp compression outcomes was observed at low strain ranges with the lowest testing rate (0.01Hz). Higher strains required different material model and geometry parameters to improve validity. Regardless, indentation and ramp compression outcomes were highly correlated. It is recommended that researchers match testing parameters to in vivo loading conditions, while using this work to support material model and sample geometry selection.
Third, to identify the optimal indentation testing parameters to maximize agreement between SWE and indentation stiffness, several loading strain, loading rate, sample geometry, and indentation models were evaluated in TMM phantoms. Findings showed strong relationships between indentation and SWE stiffness outcomes, regardless of testing conditions. It is recommended to match loading parameters to in vivo conditions. Small sample geometries and low indentation rates appeared to optimize agreement between indentation and SWE outcomes.
The fourth and final study of this dissertation examined the in vivo reliability of uterine SWE. Institutional research ethics board approval was obtained (20170872-01H, H-08-18-790) and data were acquired from 32 participants with no active uterine disorders. SWE reliability was good to excellent, except in the anterior myometrium, where poor reliability was attributed to difficulty standardizing SWE sites between days. Phase in the menstrual cycle did not impact SWE outcomes. Site depth exhibited significant correlations with stiffness for multiple cases and heterogeneity in uterine stiffness was observed across sites. Anecdotal observations of confounding factors require further investigation.
The findings of this thesis suggest that quasi-static flat-tip indentation testing is a suitable benchmark standard to validate SWE under a variety of parameters. However, endoprobe SWE of the uterus does not appear to be valid at target depths of 3cm and beyond. Even at depths less than 3cm, linear or curvilinear probe SWE outperformed endoprobe SWE. Results suggest that further development of endoprobe SWE for uterine applications is required prior to clinical investigation of gynecological SWE for diagnostic and treatment planning purposes.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/43893 |
| Date | 09 August 2022 |
| Creators | Czyrnyj, Catriona |
| Contributors | Labrosse, Michel, McLean, Linda |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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