08/28 : image orientation

Sagittal Plane and Anterior-Window Orientation

• Sagittal plane basics
  • The sagittal suture in a newborn skull is the crack down the center; sagittal divides the body into left and right halves. A midsagittal slice runs exactly along the midline.
  • When imaging, imagine sliding a thin anatomical sheet out of the body and laying it on a screen to see the view, rather than physically cutting someone.
  • Cadaver example: a sagittal slice through the inferior vena cava (IVC) slightly to the right of midline shows the blue vessel (IVC) returning blood to the right atrium of the heart.
  • A subsequent sagittal slice slightly to the patient’s left shows the abdominal aorta (red vessel) staying ventral to the spine.
• Ultrasound probes and footprints
  • Curved footprint probe vs flat probe.
  • An anterior acoustic window is used when the transducer is placed on the abdomen; the top of the screen corresponds to the anterior surface of the patient, and the bottom corresponds to the posterior surface.
  • In sagittal imaging from an anterior window: the end near the patient’s head is labeled superior; the end near the feet is inferior.
• Quizzing and orientation practice
  • Example: If the question asks for the direction of the posterior side in a sagittal image, the answer is "posterior".
  • If the end near the head is superior and the other end is inferior, the opposite end is inferior; this uses deductive reasoning during practice.
• L test and terminology
  • L test = left testis. In ultrasound, terminology often uses “testis” rather than “testicle.”
  • Screen orientation remains anterior/posterior and superior/inferior even in non-abdominal views.
  • In sagittal from an anterior window, a midsagittal image is when the alignment is at midline; parasagittal means off-midline but still sagittal.
• Right upper quadrant anatomy in sagittal view
  • Parasagittal right lobe of the liver or long-right upper quadrant imaging can show the liver as a big smooth organ; the adjacent kidney may be identified.
• Pediatric and anatomical clues
  • Correlate with bones and ribs at the periphery; ribs create acoustic shadowing.
• Cine and CT context
  • CT (computed axial tomography) slices form a transverse dataset; a cine is a moving image through slices, starting superiorly and moving inferiorly.
  • Infused (enhanced) CT uses contrast; uninfused CT can make many structures hard to differentiate.
  • In infused CT, the aorta and kidneys often appear brighter due to contrast, whereas in uninfused CT they appear similarly gray to surrounding tissue.
• Pancreas and liver context in transverse scans
  • In transverse/axial views, the liver, kidney, and pancreas appear in particular cross-sections; the vertebral body serves as a home base landmark for orientation in transverse sections.
  • The diaphragmatic-liver interface near the posterior aspect separates liver from lung in high slices.
• Summary of typical organs visible in sagittal slices
  • IVC, abdominal aorta, liver, right kidney, kidney-adjacent fat, rectus abdominis, and pancreas can appear in sagittal scans depending on location.

Transverse (Axial) Plane and Vantage Point

• Definition and naming
  • Transverse (also called axial or horizontal) plane divides the body into superior and inferior halves; the image orientation is from the feet looking up toward the patient’s head.
  • In a transverse view from an anterior window, right side of the screen corresponds to the patient’s right side; left side of the screen to the patient’s left side.
• CAT scan context
  • CAT scan stands for Computed Axial Tomography; CT images are acquired in transverse (axial) sections, but the computer can reconstruct slices in other planes as well.
• The “toe” indicator and screen orientation
  • The toe/indicator on the ultrasound probe marks the patient’s right when viewing a transverse image from an anterior window.
  • If you see the right on the screen as you expect, you are looking from the feet up (inferior to superior orientation).
• Abdominal anatomy in transverse from anterior window
  • Starting with the vertebral body as a home base: vertebral body appears hyperechoic with shadowing behind it.
  • Deep to the vertebral body, identify the abdominal aorta (usually on the left of the IVC in the image depending on the view), and the IVC on the right.
  • Extrapyreneal fat appears as fat anterior to the peritoneal cavity (properitoneal fat is in front of the peritoneal cavity)
  • Rectus abdominis muscle appears as striated red/gray tissue; identify it and differentiate from fat.
  • The spleen and left kidney are commonly seen in left-sided coronal/transverse views; the liver is commonly seen on the right.
• Cine and dynamic imaging
  • A cine loop is a sequence of frames showing movement through the plane; e.g., CT cine through the chest to pelvis; ultrasound can also have cine loops.
  • A typical CT cine includes many frames spanning from superior to inferior.
  • Two example videos are provided in supplementary material (about 18 seconds and 2 minutes 43 seconds) to illustrate cross-sectional anatomy.
• Infused vs uninfused CT in practice
  • Infused CT: contrast highlights vessels and organs (e.g., aorta bright, kidneys bright).
  • Uninfused CT: vessels are not particularly brighter than surrounding tissue; only bone and calcifications are distinctly white.
• Practical imaging tips
  • Always start with the vertebral body to orient yourself before identifying the rest of the vasculature (IVC and aorta) and organs.
  • In longitudinal depth, the IVC and aorta orientation changes slightly with the level scanned; the liver sits on the right and the spleen on the left.
  • Color Doppler can be used to visualize blood flow in vessels like the IVC and hepatic veins.
• Two- and multi-plane principle in transverse imaging
  • Always view an organ in at least two planes to avoid misinterpretation; one view can be misleading.
  • When testing orientation, you can use a stuffed animal or doll to practice the transducer position and orientation.

Coronal (Frontal) Plane and Lateral Approaches

• Definition and orientation
  • Coronal plane divides the body into anterior (front) and posterior (back) sections; in coronal views, the body is oriented with the head toward the top and feet toward the bottom.
  • Coronal slices can be obtained from either the left lateral or right lateral aspects of the body depending on where the transducer is placed.
• Left-lateral decubitus (LLD) and right-lateral decubitus (RLD) examples
  • In a left lateral decubitus setup, placing the transducer on the left lateral surface and imaging coronal slices, the indicator should point toward the head (superior).
  • When rotating from coronal to transverse, rotate 90 degrees counterclockwise to maintain a consistent orientation (toe toward head in coronal, then rotate to become anterior in the transverse view from the left side).
  • In a right lateral decubitus setup, flip the probe to the right side and repeat with the indicator toward the head; rotation remains counterclockwise to convert to transverse.
• Key anatomy visible in coronal orientation
  • Spleen and left kidney are commonly visible when imaging from the left side; the liver and IVC are often visible on the right side.
  • In coronal left-sided views, the spleen tends to sit leftward with the left kidney nearby; in coronal right-sided views, the liver and IVC are more prominent.
• Plane-specific caveats
  • Coronal is specifically front/back orientation, not merely a side view; mislabeling side views as coronal is a common error.
  • The indicator should be toward the head for coronal; if rotated incorrectly, the image becomes a transverse view instead.
• Practical exemplars and landmarks
  • In coronal left-side imaging, the spleen and left kidney are prominent; you can identify the liver and right kidney on right-side coronal views.
  • The appearance of vessels and organs in coronal views helps distinguish which side you are imaging, based on the relative positions of the liver (right) and spleen (left).
• Rotation and orientation exercise
  • Start with coronal from the left side, then rotate 90 degrees counterclockwise to obtain a transverse view with the toe anterior and heel posterior.
  • Start with coronal from the right side, then rotate 90 degrees counterclockwise to obtain a transverse view with the toe posterior and heel anterior.
  • If the orientation feels confusing, model it with a prop (stuffy/doll) or mentally simulate patient positioning (e.g., right lateral decubitus vs left lateral decubitus).

Transducer Orientation and Techniques to Confirm It

• Transducer orientation recap
  • The transducer footprint can be on the anterior, posterior, or lateral surface of the patient.
  • The plane of section is defined by the transducer position and the orientation of the indicator (toe) on the footprint.
• Finger-shadow technique to confirm orientation
  • With live imaging, place a finger along the transducer piece in contact with the patient; you should see a shadow at the superior end of a sagittal image if orientation is correct (indicator toward the head).
  • If the shadow appears in the wrong location, the transducer may be backwards; rotate and recheck.
  • If the machine supports image reversal, you can flip the image electronically, but this can misalign the indicator with the actual footprint.
• Common pitfalls and fixes
  • A backwards probe leads to unusual shadow placement; rotate the probe to fix orientation.
  • If you must, you can use the image-reverse control, but be mindful of indicator alignment for future scans.
• Practical scanning rule: two-plane rule
  • Always scan any organ in at least two planes of section to avoid misinterpretation.
  • The rule of two planes is a central tenet of diagnostic imaging: one view is not enough.

Organs and Diagnostic Imaging: Practical Examples

• Liver, IVC, and hepatic veins
  • In transverse coronal-right views, you may encounter the liver, IVC, and abdominal aorta with visible branches such as the renal arteries.
  • The right hepatic vein drains into the IVC; diaphragmatic interface can separate liver from the lung in posterior views.
• Pancreas, stomach, and surrounding tissues
  • The pancreas can be imaged in transverse views; the body of the pancreas is visible in some slices with the surrounding retroperitoneal fat.
• Spleen and left kidney
  • Coronal left-sided views reveal the spleen and left kidney; splenomegaly refers to an enlarged spleen.
• Right kidney and adjacent organs
  • In right-sided views, expect to visualize the liver plus the right kidney, along with the IVC and aorta.
• Diaphragm and lung interface in high abdominal views
  • The diaphragm marks the boundary between liver and lung on posterior views; this is especially visible near the upper abdomen.
• Venous drainage in the liver
  • The hepatic veins (e.g., right hepatic vein) drain liver blood into the IVC; in some images you can identify these connecting vessels.
• Important heart-vascular interface in cross-sections
  • In higher slices, you may see the heart and the right atrium where the IVC drains.
• Color Doppler and vascular anatomy
  • Color Doppler helps visualize blood flow in vessels like IVC, hepatic veins, and renal vessels.
• Cadaver vs. imaging perspectives
  • Cadaver anatomy is used to illustrate planes of section; diagnostic imaging translates these planes into live anatomy with reverberation and shadowing artifacts.

Cross-Platform Imaging Concepts

• CT vs Ultrasound vs MRI
  • CT/transverse imaging provides cross-sectional anatomy with high bone and contrast differentiation when infused; ultrasound provides real-time imaging with dynamic motion and tissue echogenicity.
  • MRI shows different tissue contrasts and is particularly useful for muscles and soft tissues; CT is often superior for osseous structures.
• Cine loops and real-time anatomy practice
  • Cine allows observing movement through the dataset; a CT cine slides through from superior to inferior; ultrasound can have a live cine loop as well.
• Infused vs uninfused CT and practical interpretation
  • Infused CT enhances vasculature and organs; uninfused CT shows more uniform gray tissue where contrast is absent.
• Self-assessment and study resources
  • Supplementary materials include infused CT video demonstrations and cross-sectional anatomy walkthroughs (e.g., 18 seconds and 2 minutes 43 seconds). These are available under the Learn page’s supplementary materials.
• Foundational study strategies and ethics
  • The instructor emphasizes maintaining a relaxed, professional tone when interacting with patients; comfort and calmness help with patient history and successful scanning.
  • Practice with simulators and models (stuffed animals, dolls) to master orientation before real patients.

Summary of Core Concepts and Practical Rules

• Plane definitions and orientation
  • Sagittal: left-right division; midsagittal is at the midline.
  • Transverse: superior-inferior division; look from the feet upward.
  • Coronal: anterior-posterior division; viewer perspective from the side with proper orientation.
• Anterior window orientation rules
  • Top of the image corresponds to anterior; bottom to posterior; head toward the superior end; feet toward the inferior end.
• Transducer orientation and rotation rules
  • From sagittal to transverse: rotate the transducer 90° counterclockwise (CCW) to end up in transverse with the indicator toward the head for sagittal, and then maintain orientation as you switch planes.
  • From coronal to transverse: rotate 90° CCW to maintain consistent orientation; practice with left and right lateral decubitus to understand lateral-specific orientation.
• Pro tips for reliable scanning
  • Use the vertebral body as a home base in transverse views; identify IVC on the right and aorta on the left (relative to the image, depending on level).
  • Use the finger-shadow technique to confirm orientation; if wrong, rotate the probe.
  • Always view any organ in at least two planes to ensure correct interpretation.
• Practical anatomy focus for the abdominal course
  • Prioritize abdominal organs and recognizable landmarks (liver, gallbladder, pancreas, spleen, kidneys, aorta, IVC) during early weeks.
• Ethical and practical lab guidance
  • The instructor encourages a calm, conversational approach with patients to facilitate better history and scanning results.
• Optional resources
  • Digital diagrams and lab posters (Curry chapters) provide diagrams of planes of section, including sagittal, transverse, and coronal views and layering of anatomy.

Quick References (LaTeX-formatted)

• Sagittal plane divides left and right: ext{Sagittal plane}: ext{ left}
  eq ext{right}
• Midsagittal plane is the midline: ext{Midsagittal}: ext{ left} = ext{right}
• Transverse plane divides superior and inferior: ext{Transverse plane}: ext{ superior}
  eq ext{ inferior}
• Coronal plane divides anterior and posterior: ext{Coronal plane}: ext{ anterior}
  eq ext{ posterior}
• Rotation from sagittal to transverse (CCW): heta = 90^ ext{°}, ext{direction} = ext{CCW}
• Anterior window orientation: top = anterior, bottom = posterior; head = superior, feet = inferior: ext{Top}= ext{Anterior}, ext{Bottom}= ext{Posterior}, ext{Head}= ext{Superior}, ext{Feet}= ext{Inferior}
• Contrast-enhanced CT guidance: infused vs uninfused
  • Infused: $ ext{Contrast enhances vessels/organs: e.g., aorta, kidneys}$
  • Uninfused: $ ext{Only bone/calcifications are clearly white; vessels less distinct}$
• Cine loop terminology
  • Cine or cine loop: moving sequence of frames through a plane, similar to motion in cinema; root from Greek "kinesis" meaning movement.
• L test and anatomy terminology
  • L test = left testis; use the term "testis" rather than "testicle" in ultrasound notes when referring to anatomy.