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Radiology
Elasticity Imaging in Obstetrics
Built from Obstetric Imaging
What’s inside
9 sections · 84 slides
Overview
- Scope of this topic
From palpation to measurement
Why anyone wanted to image stiffness in the first place
- Palpation as a clinical stiffness test
- Diagnostic information carried by tissue stiffness
- Emergence of elasticity imaging
- Midsagittal section of the female pelvis
- Stiffness contrast versus echogenicity contrast
- Clinical status of elasticity imaging by organ
Elasticity: definitions and measures
Stress, strain, and the moduli that describe them
- Definition of elasticity
- Stress and strain
- Young’s modulus and shear modulus
- Why imaging relies on surrogate metrics
- Three approaches to elasticity imaging
- Summary and Descriptions of Elasticity Methods
- Reading the methods table
Strain (static) elastography
Squash the tissue, compare the frames
- Principle of strain elastography
- Sources of the applied force
- Steps in forming a strain elastogram
- Why the strain elastogram is qualitative
- Persistence and incremental strain
- Requirements for a diagnostic strain image
- The system quality metric and its misinterpretation
- Effect of small or non-uniform applied stress
- Boundary artefacts in strain imaging
- Strain ratio and strain heterogeneity
- Strain ratio in the breast versus the cervix
Strain elastography of the cervix
The most developed obstetric application so far
- Clinical questions for cervical strain elastography
- Early cervical elastography studies
- Reproducibility of cervical strain elastography
- Regions of interest on a cervical elastogram
- Reading the cervical elastogram
- Quantifying the force applied to the cervix
- Cervical projections used for strain quantification
- Cervical strain and subsequent preterm birth
- Force-measuring device and the cervical elasticity index
- Cervical elasticity index and dilatation time
- Limitations of cervical strain elastography
- Sources of variability in cervical elastography
- Strain elastography of the placenta
- Boundary conditions in the placenta
Dynamic elastography
Let the ultrasound beam do the pushing
- Principle of dynamic elastography
- Acoustic radiation force impulse imaging
- Strengths and limitations of acoustic radiation force imaging
- Shear-wave elasticity imaging
- From push pulse to shear-wave speed
- Shear-wave speed and tissue stiffness
- Point measurement versus shear-wave image
- Variance in shear-wave images
- Choosing the region for shear-wave measurement
- Absence of an objective data-quality metric
Shear-wave imaging of the cervix
A small, dense, awkwardly shaped target
- Why the cervix is a difficult target
- Transvaginal transducer limitations
- Transvaginal ultrasound of the cervix
- Cross-sectional shear-wave study in preterm labour
- Trimester differences in cervical shear-wave speed
- Elastography and B-mode images of the cervix in pregnancy
- What to notice in the paired cervical images
- Measurement location within the cervix
- Shear-wave elastography at the internal cervical os
- Reading the internal os elastogram
- Ex vivo cervix study design
- Why a linear transducer was chosen
- Shear-wave fronts across a cervix slice
- What the shear-wave front image shows
- Shear-wave speed along the length of the cervix
- Ripened versus unripened cervix
- Shear-wave speed around cervical ripening in vivo
- Cervical shear-wave speed across gestation
- Evidence still required for clinical use
Uterus, placenta and transient elastography
Beyond the cervix
- Myometrial stiffness during contraction
- Placental shear-wave speed in preeclampsia
- Transient elastography
- Probe applied to the body surface for stiffness measurement
What the clinician needs to know
Where the field stands, and what would move it
- Strain versus dynamic elastography
- What the referring clinician needs to know
- Requirements for a clinically meaningful tool
- Key points
- Suggested readings
- References
- References (continued)
- References (continued)
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- References (continued)
- Obstetric Imaging: Fetal Diagnosis and Care, 2nd Edition