Intro to OB Gyn Sonography: Basic Principles (Part 1)

  • History of OB/GYN sonography begins with non-medical uses in the early 1900s (underwater navigation) and rapidly evolves into medical imaging.
  • Early equipment produced static black-and-white images using a B-scan with an articulated arm; images were not real-time.
  • The field grew with training programs like the HSC ultrasound program in 1988; key figures include Dr. Lyons and Denis Graton, who helped recruit and train X-ray techs to perform ultrasound.
  • Endovaginal ultrasound debuted in the late 1970s. Endovaginal (transvaginal) imaging uses a probe inserted into the vagina to get closer to the uterus; contrasted with transabdominal imaging, which passes through the anterior abdominal wall and bladder to reach the uterus.
  • In the 1980s, the first routine obstetrical scans began in Germany, followed by Canada in the early 1990s; many people born in the 1990s were scanned in utero.
  • Ultrasound became an integral part of women’s medical management; a sonographer in a generalist department typically performs scans daily.
  • Technology timeline:
    • Early: static B-scanners with transducers on an articulated arm; images were black-and-white and not live.
    • Real-time grayscale evolution followed, enabling live imaging.
    • Handheld devices began appearing, with limited success (Mobius SP One, first handheld but phone-dependent and with limited adoption).
    • 2016: Red River College demoed the GEV Scan with a dual-probe handheld unit that did not require a phone; used a flip screen for display; demonstrated real ultrasound (e.g., pancreas or liver) in a classroom setting.
    • Modern handhelds: Butterfly iQ (hooks to smartphone/tablet), Philips Lumify (also smartphone/tablet compatible) – Lumify is high quality but more expensive; Lumify offers multiple transducers (three) and strong performance akin to larger machines.
    • Clarius PA HD: wireless handheld ultrasound (no cable).
    • In Canada, the department acquired Butterfly iQ devices during the 2020-2021 school year in response to the COVID-19 pandemic.
  • Specific devices and impressions:
    • Philips Lumify (LumaFy/Luma five): praised for excellent image quality; many in generalist and cardiac programs consider it an excellent device; demoed with a pregnancy scan in class with a radiologist observing in a pop-up window.
    • Butterfly iQ: cost-effective and portable, hardware-agnostic (smartphone/tablet integration).
    • Clarius PA HD: wireless, no cable – potential benefits for mobility and ease of use.
  • Two-dimensional (2D), three-dimensional (3D), and four-dimensional (4D) imaging:
    • 2D ultrasound: real-time imaging in a single plane (width and height only; no depth).
    • 3D ultrasound: adds a depth dimension (length × width × height); not typically real-time.
    • 4D ultrasound: a moving 3D image in real time (requires powerful computing resources, RAM, and video processing).
    • A humorous aside in the talk notes a common misconception about time as a dimension; this is not addressed here.
  • Transducer basics:
    • The surface in contact with the patient is called the footprint.
    • The footprint has a heel and a toe; conceptual rule: what appears on the left side of the screen corresponds to the toe side of the patient.
    • The image is described as a sector; the sector width and depth can be adjusted.
  • Depth and field-of-view control:
    • Depth knob or setting allows deep or superficial imaging; depth is indicated on a scale (tick marks) along the bottom of the image.
    • The ultrasound machine computes true depths based on tissue sound speed, so measurements are accurate.
    • Sector width can be narrowed for faster frame rate when imaging moving targets (e.g., fetal heart) or widened to show more anatomy.
    • Magnification (zoom) is available to focus on a region within the sector.
  • Endovaginal vs transabdominal depth examples:
    • Endovaginal images are shallower than transabdominal images; in the example, a transabdominal image shows depth ~15 cm.
    • Endovaginal imaging positions the transducer much closer to the area of interest (e.g., uterus or mass) to obtain more detail with less depth.
  • Echoes, grayscale, and tissue interfaces:
    • Ultrasound echoes represent reflections at interfaces between tissues; sound that passes through body without reflection appears black (anechoic or low echoes).
    • Echogenicity terms used to describe relative brightness:
    • Echogenic: region contains echoes (generally brighter relative to surrounding tissue).
    • Anechoic: no echoes (appears black), e.g., amniotic fluid, urine in bladder, blood in fetal heart chambers, cystic areas.
    • Hyperechoic: brighter than surrounding tissue (e.g., bone).
    • Hypoechoic: darker than surrounding tissue (e.g., liver compared to bone).
    • Isoechoic: same echogenicity as reference tissue (same shade of gray).
    • Echotexture terms:
    • Homogeneous: uniform echo pattern (uniform brightness and texture).
    • Heterogeneous (inhomogeneous): nonuniform echo pattern (mixed brightness, textures).
    • Attenuation and enhancement (through transmission):
    • Attenuation: loss of acoustic energy as sound travels through tissue due to reflection, scattering, or absorption.
    • Enhancement: increased brightness behind a region with low attenuation (e.g., behind a cyst) due to more sound energy reaching deeper tissues.
    • Note: sometimes enhancement can create artifacts where deeper tissue looks brighter than it should due to the cyst’s non-attenuating path.
  • Practical image interpretation examples:
    • A fetus: amniotic fluid, bladder contents, stomach fluid, and bones produce characteristic echogenic patterns (black for fluid, white for ossified bone, grays for soft tissues).
    • Phantoms: regions labeled A, B, C illustrate relative echo strength (A strongest, then B, then C weakest) to practice comparing echogenicity.
  • Describing pathologies and concepts:
    • Lesion vs Mass:
    • Lesion: a focal area in tissue that appears different from surrounding tissue but does not necessarily occupy space.
    • Mass: a focal, space-occupying lesion; physically displaces or distorts surrounding structures (mass effect).
    • Signs of mass effect:
    • Displacement of vessels
    • Distortion of organ contour
    • Displacement of adjacent structures
    • Pelvic mass rule of thumb:
    • In the pelvis, 90% of masses arise from either the uterus or the ovary.
    • If a mass arises from the ovary, it is more likely cystic; if from the uterus, it is more likely solid.
    • Cystic vs solid masses:
    • Ovarian masses are usually cystic (fluid-filled).
    • Uterine masses are usually solid (tissue-based).
  • Anatomy and orientation terminology (to describe location in the body):
    • Cephalicus: head direction
    • Caudal: toward the feet; cauda means tail
    • Ipsilateral: on the same side
    • Contralateral: on the opposite side
    • Superficial: closer to the body surface
    • Deep: further from the body surface
    • Proximal: closer to a reference point (often the heart in anatomy discussions)
    • Distal: farther from the reference point
    • Medial: toward the midline
    • Lateral: away from the midline
    • Visceral: covering of an organ
    • Parietal: lining of a body cavity or wall
  • Common patient positions and orientations in OB/GYN imaging:
    • Prone: lying face down
    • Decubitus: lying on a side (e.g., right lateral decubitus)
    • Posterior oblique: between supine and decubitus
    • Trendelenburg (and reverse Trendelenburg): head lower than feet or head higher than feet, affecting pooling of fluids (e.g., pelvis region in some exams)
  • Practical tips and classroom notes:
    • Orange definition boxes introduce key terms (e.g., attenuation).
    • The instructor occasionally uses humorous placeholders (e.g., Cletus the fetus) to engage learners; these are contextual and not essential to the core concepts.
  • Summary concepts to remember:
    • Understand the evolution of ultrasound technology from static B-scans to real-time handheld devices and cloud-connected systems.
    • Distinguish endovaginal vs transabdominal approaches, including depth implications and image quality differences.
    • Master the basic imaging physics vocabulary: echogenicity (anechoic, hyperechoic, hypoechoic, isoechoic), echotexture (homogeneous vs heterogeneous), and phenomena like enhancement and attenuation.
    • Differentiate lesions from masses and recognize signs of mass effect.
    • Use pelvic mass heuristics to guide differential diagnosis (ovary cystic vs uterus solid) and look for connecting features (vessel presence, contour changes).
    • Be comfortable with anatomical and positional terms to describe findings accurately.
  • Quizzes and self-check prompts embedded in instructional content:
    • Rank the relative strength of echoes in phantom A, B, C.
    • Identify areas that are isoechoic and describe echotexture categories for a given image (homogeneous vs heterogeneous).
    • Describe enhancement behind a cyst and recognize it as an artifact if it misleads interpretation.
    • Apply the pelvic mass rule of thumb to distinguish likely origins (ovary vs uterus) based on cystic vs solid appearance.
  • Core practical takeaway: handheld ultrasound devices are increasingly capable and widely used in OB/GYN practice, but understanding imaging physics and anatomy remains essential for accurate interpretation and safe patient care.