Sonography: Transducer Positions and Motions

• Sonographers utilize multiple acoustic windows, including subcostal, intercostal, and epigastric.
• They also employ various transducer motions like sweep, slide, rock, fan, and rotate, using both macro- and micromovements.

Transducer Positions

• Perpendicular: Transducer is straight up and down relative to the structure being imaged.
• Intercostal: Transducer is positioned between the ribs.
• Subcostal: Transducer is angled superiorly, just under the inferior costal margin.
• Angled: Transducer is tilted superiorly, inferiorly, or laterally at varying degrees.
• Rotated: Transducer is turned to oblique the scanning plane.

Transducer Motions

• Sliding/Sweeping: The entire probe is moved in a specific direction to find a better imaging window, move to different body areas, or follow a structure.
• Tilting: The transducer is moved side to side along its short axis, also known as "Fanning". Enables visualization of multiple cross-sectional images of a structure.
• Rotating: The transducer is turned clockwise or counterclockwise along its central axis. Primarily used to switch between long and short axes of a structure.
• Rocking: The transducer is rocked towards or away from the probe indicator along the long axis. Helps center the area of interest, also known as "in-plane" motion or "heeling/toe-ing".

Image Optimization

• High-quality images are obtained when the transducer is perpendicular to the reflector (structure).

Sonographic Appearance

• Echogenic or Hyperechoic: Tissue reflects sound with a bright intensity.
• Hypoechoic: Tissue has low-level echoes and appears darker than surrounding tissue.
• Isoechoic: Tissue has the same level of echoes as the surrounding tissue.
• Anechoic: Tissue is without internal echoes, usually indicates a cystic lesion with posterior enhancement.
• Anechoic or Sonolucent: The structure is fluid-filled and transmits sound easily. Examples include vascular structures, distended urinary bladder, gallbladder, and amniotic cavity.
• Infiltrating: Indicates an invading neoplasm or metastatic disease.
• Irregular borders: Borders are not well-defined or absent. Examples include abscess, thrombus, and metastases.
• Homogeneous: Tissue or parenchyma is completely uniform in texture or composition. Examples include the liver, thyroid, testes, and myometrium.
• Heterogeneous: Tissue or parenchyma is not uniform in texture or composition. Examples include metastasis in the liver, altered testicular tissue after torsion, and multiple thyroid nodules due to inflammation.
• Septated or Loculated collection: Well-defined borders with internal echoes; septa may be thin (likely benign) or thick (likely malignant).

Acoustic Artifacts

• Understanding the physical properties of sound is crucial for interpreting sonographic images and identifying artifacts.
• Posterior Shadowing: Lack of signal deep/posterior to a dense reflector; the dense structure reflects or absorbs transmitted sound waves completely. Seen posterior to stones, bones, and foreign bodies.
• "Dirty" Shadowing: Reverberation or ring-down artifact due to resonant vibrations in air bubbles. Can indicate normal bowel loop, bacterial infection, or abnormal presence of air.
• Posterior Enhancement: Increased through-transmission artifact when sound travels through a fluid-filled structure. The area beyond the posterior border appears brighter. Seen posterior to cystic structures like the gallbladder, cysts, urinary bladder, and ascites.

Ultrasound Criteria for Identifying Abnormal Structures

• Include description of the:
• Location
• Border
• Smooth, well-defined, or irregular
• Texture
• Homogeneous or heterogeneous
• Characteristics
• Anechoic, hypoechoic, isoechoic, hyperechoic, or echogenic
• Acoustic artifacts
• Transmission of sound may be increased, decreased, or unchanged
• Example:
• Intrahepatic mass
• Well-defined borders
• Homogeneous and hypoechoic to liver parenchyma
• Posterior enhancement is evident

Cysts & Tumors

• Simple Cyst: Smooth, well-defined borders, anechoic, thin walls, and increased through-transmission. Contains fluid.
• Complex Cyst: Characteristics of both fluid and solid components. Irregular, round, or oval shape with thick walls. May contain debris, septations, and solid components; shows posterior enhancement.
• Tumor/Neoplasm: Abnormal mass of tissue, usually without cysts or liquid areas. Shows irregular borders, internal echogenicity, and decreased through transmission; color Doppler shows blood flow.

Exam Preparation & Setup

• Review patient's clinical and imaging history.
• Begin with a transducer best suited to the structure of interest.
• Use a coupling agent (gel) to remove air between the transducer and skin.
• Consider patient comfort and transducer pressure.
• Perform comprehensive surveys of the area of interest without taking images.
• Adjust depth to best view the area of interest, which should be in the middle of the image.
• Adjust gain settings for well-defined borders.
• Compensate with an adjusted time gain compensation (TGC) slope.
• Be familiar with scanning protocols for different exams/organs.

Documentation

• Documentation must include:
• Patient's name and identification number
• Date and time
• Scanning site
• Sonographer's name or initials
• Area of interest (general and specific)
• Patient position
• Scanning plane
• Pertinent medical history and previous imaging findings.

Image Labeling

• Image labeling should be confined to the margins surrounding the image
• Documented areas of interest must be represented in at least two scanning planes.
• Documented areas of interest must be imaged in a logical sequence.
• The structure of the interest should be imaged in the center of the image, within a focal zone.
• Abnormalities are documented in at least two scanning planes following the general protocol images for a complete study of the area(s) of interest.
• Cine clips may be very useful to aid in the delineation of various abnormalities.
• Measuring organs and pathologic findings is done in two planes (sagittal and transverse) and in three dimensions:
• Longitudinal plane: from the most superior to most inferior margin and depth
• Transverse plane: third measurement
• Abdominal protocol may include an entire abdominal scan (Abdomen Complete study) that includes the survey of all the abdominal organs or limited abdominal exams dedicated only to specific organs.
• A broad-bandwidth transducer is used, with variations of 2.25 to 7.5 MHz, depending on the size of the patient and the depth of field.
• All organs are routinely imaged in at least two planes: transverse and longitudinal.
• Asking the patient to take a deep breath is useful, allowing you to see how the patient images appear with "routine" instrument settings and to observe where the organs are in relationship to the patient's respiration pattern.

Abdominal Imaging Examples

• Abdominal Aorta Sagittal View
• Abdominal Aorta Transverse
• Aorta Proximal - Sagittal and Transverse Images