Cross Sectional Imaging and Radiology Terminology

Traditional Anatomy vs Sectional Anatomy

  • Traditional Anatomy: study entire organ and systems to understand location, structure, and function.

  • Sectional Anatomy: study regions with emphasis on anatomical relationships of structures within regions.

  • Key directional cues in sectional anatomy include inferior/superior, medial/lateral.

  • Viewpoints are based on slices (cross-sections) rather than whole-organ perspectives.

Body Planes and Slices

  • Body Planes define how the body is divided for imaging and anatomy:

    • Transverse / Axial

    • Horizontal planes cut the body from right to left.

    • Define Superior (toward the head) and Inferior (toward the feet) relative positions along the plane.

    • Sagittal / Longitudinal

    • Vertical planes cut the body from superior to inferior.

    • Midline = Midsagittal plane.

    • Parasagittal planes are sagittal planes not along the midline; example: R3 = 3 cm to the right of midline.

    • Coronal / Frontal

    • Vertical planes at right angles to sagittal and transverse.

    • Divide the body into anterior and posterior portions.

    • Views are from right and left sides; also described as Superior and Inferior relative to other planes.

  • Note: Some slices may require multiple sections to evaluate a complete organ.

Sagittal and Coronal Slices

  • Sagittal Slices

    • Vertical planes that run from top to bottom (superior to inferior).

    • Used to view structures in a left-right orientation relative to the midline.

  • Coronal Slices

    • Vertical planes that run anterior to posterior.

    • Used to view structures in a front-to-back orientation.

Directional Terms Used in Imaging

  • Superior: closer to the head.

  • Inferior: closer to the feet. (Avoid using above/below to prevent ambiguity in some views.)

  • Transverse plane views may show slices from superior to inferior; may not be visible directly on the image.

  • In imaging, Sagittal and Coronal planes can view superior and inferior relationships.

  • Anterior (ventral): toward the front.

  • Posterior (dorsal): toward the back.

  • Medial: toward the midline.

  • Lateral: away from the midline.

  • Proximal: closer to the body (point of attachment or trunk).

  • Distal: farther from the body (point of attachment or trunk).

  • Superficial: near the surface.

  • Deep: away from the surface.

  • Cephalad: toward the head; synonymous with Superior.

  • Caudad: toward the feet; synonymous with Inferior.

Body Cavities: Open and Closed

  • Open Cavities (exposed to exterior):

    • Oral Cavity, Nasal Cavity, Orbital Cavity.

  • Closed Cavities (contain internal organs):

    • Dorsal Cavity: Cranial cavity and Spinal cavity; continuous with each other through the foramen magnum.

  • Ventral Body Cavity (divided by the diaphragm):

    • Thoracic cavity:

    • Right & Left Pleural Cavities – contain the Lungs.

    • Mediastinum – contains the Pericardial Cavity (heart).

    • Abdominopelvic cavity:

    • Abdominal cavity – contains stomach, liver, spleen, intestines (among other organs).

    • Pelvic cavity – contains the bladder and reproductive organs, rectum.

Quadrants and Regions of the Abdominopelvic Cavity

  • 4 Quadrants

    • Divided by a vertical plane through the midline and a horizontal plane through the umbilicus.

  • 9 Regions

    • The abdomen and pelvis can also be divided into 9 regions for more precise localization.

Membranes of Body Cavities

  • Functions: line cavities, cover organs within cavities, and line hollow organs.

  • Two main membrane types:

    • Connective Tissue Membranes

    • Dorsal body cavity membranes include the Meninges surrounding the brain and spinal cord (Dura Mater, Arachnoid, Pia Mater).

    • Joints have Synovial Membranes that secrete fluid for lubrication.

    • Epithelial Membranes

    • Mucous Membranes line open cavities (Nasal, Digestive Tract) and secrete mucus for lubrication and protection.

    • Serous Membranes (serosa) line ventral body cavities and cover organs in the cavity; consist of two layers:

      • Parietal Serosa (Parietal Layer): lines the cavity.

      • Visceral Serosa: covers organs within the cavity.

  • Specific Serous Membranes by Cavity:

    • Thoracic Cavity: Parietal Pleura lines the thoracic cavity; Visceral Pleura covers the lungs.

    • Pericardial Cavity: Parietal Pericardium lines the cavity; Visceral Pericardium covers the heart.

    • Abdominopelvic Cavity: Parietal Peritoneum lines the cavity; Visceral Peritoneum covers abdominal/pelvic organs.

  • Naming of membranes is generally by location.

  • Useful external reference: peritoneum areas and naming conventions.

Regional Terminology

  • Axial Portion: head, neck, and trunk.

  • Appendicular Portion: extremities (arms and legs).

  • Other Key Body Regions (examples):

    • Abdominal, Axillary, Cephalic, Costal, Inguinal, Pelvic, Plantar, Thoracic, Umbilical.

Radiology: Image Production and Views

  • Image Production (General):

    • X-ray Tube generates X-ray photons.

    • X-rays are directed toward the body; the object of interest is placed between the beam and film.

    • When the beam is turned off, there are no x-rays remaining in the room.

  • Image Formation Principles:

    • X-rays are absorbed by tissues; dense tissues appear white on film.

    • X-rays penetrate tissues; less dense tissues appear darker on film.

    • Object-to-film distance affects magnification; keep it as close as possible.

    • Left and Right sides of the image appear in mirror-like fashion (similar to ultrasound).

    • For diagnostic accuracy, two images at 90 degrees opposite are typically required.

  • Views and Projections:

    • Anterior-Posterior (AP) or Posterior-Anterior (PA).

    • Oblique views can be added (e.g., LPO, RPO).

    • Lateral views are named for the side examined.

    • Views are named for the anatomic structures included in the image.

  • Contrast Agents and Imaging Contrasts:

    • Contrast enhances visualization of blood flow, joint spaces, or organ perfusion.

    • Barium: oral or rectal, for GI tract visualization.

    • Iodinated contrasts: arterial, venous, or ductal imaging.

    • Air as a contrast agent.

    • Fluoroscopy, Endoscopic Retrograde Cholangiopancreatography (ERCP), and Digital Subtraction Angiography (DSA).

  • Practical considerations:

    • Contrast selection depends on the target structure and desired visualization.

    • Radiation exposure is a factor; CT delivers higher exposure than standard diagnostic radiography.

Computed Tomography (CT)

  • Mechanism:

    • Uses X-rays to create cross-sectional images.

    • The X-ray beam rotates around the patient; detectors measure transmitted X-rays at thousands of points.

    • Absorption data are used to reconstruct cross-sectional images.

  • Radiation: CT delivers about 10\sim 100 times more radiation than diagnostic radiography.

  • Image orientation:

    • Images are effectively viewed as if looking from the feet; the patient’s right side appears on the viewer’s left.

    • CT can produce images in transverse, sagittal, axial, or coronal planes.

  • Reference note (from source):

    • Image orientation and attribution context for a CT abdomen/pelvis image.

Sonography (Ultrasound)

  • Principles:

    • Uses high-frequency sound waves to produce images.

    • Images are in black, white, and shades of gray.

  • Advantages: no ionizing radiation; real-time imaging.

  • Characteristics:

    • Highly operator dependent.

    • Easily portable and relatively low-cost compared with other modalities.

Magnetic Resonance Imaging (MRI)

  • Basic Physics:

    • MRI relies on interactions between magnetic fields and radiofrequency waves with the nuclei of atoms (primarily hydrogen).

    • No ionizing radiation is used.

    • Patient is placed in a strong magnetic field; hydrogen nuclei align with the field.

    • Radiofrequency (RF) is applied to tip hydrogen nuclei out of alignment.

    • When RF is removed, nuclei realign and emit signals that are converted into images.

  • Contrast:

    • Gadolinium-based contrast is used to highlight structures.

  • Tissue contrast and weighting:

    • Hydrogen atoms provide fine detail of soft tissues (body ~75% water).

    • T1-weighted images: T_1-weighted contrast.

    • T2-weighted images: T_2-weighted contrast.

  • Planes:

    • Images can be obtained in transverse, axial, sagittal, and coronal planes.

  • Note: MRI provides superior soft-tissue contrast compared with many other modalities.

Summary of Imaging Planes and Common Practices

  • Common image planes include Transverse/Axial, Sagittal/Longitudinal, and Coronal/Frontal.

  • Different modalities use these planes to provide complementary views of anatomy and pathology.

  • Always consider the clinical question when selecting imaging modality, planes, and use of contrast.

Practical and Ethical Considerations

  • Radiation safety: CT involves higher radiation exposure; justify use and minimize dose.

  • Contrast safety: monitor for allergies and renal function when using iodinated contrasts or gadolinium.

  • Operator dependence: particularly relevant for ultrasound; technique affects image quality.

  • Patient comfort and accessibility: ultrasound is portable and low-cost, MRI is time-consuming and noisy, CT is fast but involves radiation.

  • Real-world relevance: imaging planes and membranes underpin surgical planning, diagnostic radiology, and cross-sectional anatomy education.

Notable Numbers, Terms, and References (from Transcript)

  • Midline reference: R3 = 3 cm to the right of midline (parasagittal example).

  • Quadrants: 4-quadrant division of the abdominopelvic cavity.

  • Regions: 9-region division of the abdominopelvic cavity.

  • CT radiation: approximately 10\sim 100 times more radiation than diagnostic radiography.

  • Membrane terminology: Parietal vs Visceral serosa; Dura vs Arachnoid vs Pia; Synovial membranes for joints.

  • Planes and orientations: AP, PA, LPO, RPO, Lateral; orientation depends on the beam and patient position.

  • Key contrasts: Barium (oral/rectal), Iodinated (arterial/venous/ducts), Air, Fluoroscopy, ERCP, DSA.

Additional References (as noted in the transcript)

  • Peritoneum naming conventions and regional anatomy references: https://teachmeanatomy.info/abdomen/areas/peritoneum/

  • Image attributions for CT abdomen/pelvis example: Wikipedia citation noted in slide