radiology pt2 notes

VT120 Radiology

Positioning

  • Proper patient positioning is essential for diagnostic imaging.

    • This is the responsibility of the technician.

    • Proper positioning ensures:

    • Best image quality

    • Minimizes radiation exposure for the patient and personnel.

Principles of Positioning

  • Key considerations:

    • Know the anatomy.

    • Terminology is crucial.

    • Assess the patient's condition (sick or hurt).

    • Consider if the patient is scared.

    • Safety for all involved is the most important.

Terminology

  • Orthogonal views: Radiographs are 2D images taken of a 3D structure. At least two views, at least 90 degrees apart, are required to properly evaluate a body cavity or structure.

  • Dorsoventral View (DV):

    • Patient is laying in ventral or sternal recumbency (on its chest).

    • X-ray beam enters the dorsum (back) and exits the ventrum (front/chest/belly).

  • Ventrodorsal View (VD):

    • Patient is in dorsal recumbency (lying on its back).

    • X-ray beam enters the ventrum and exits the dorsum.

  • Lateral View (R or L Lat):

    • Named based on which side is recumbent (R for right, L for left).

  • Rostral: Towards the nose, used when working with the head and neck.

  • Skyline (or tangential) View: Evaluates the joint area when the joint is fully flexed.

  • Directional Terms:

    • Lateral: Towards the outside of the body (away from the midline).

    • Medial: Towards the midline.

    • Cranial: Towards the head (used if proximal to the carpus or tarsus).

    • Caudal: Towards the tail (used if proximal to carpus or tarsus).

    • Dorsal: Indicates a position at or distal to the carpus or tarsus towards the head.

    • Oblique: A projection where the beam does not follow the three major directional axes (mediolateral, craniocaudal or dorsopalmar/dorsoplantar).

    • Palmar: Towards the paw pads on the front limbs, at or distal to the carpus or tarsus.

    • Plantar: Towards the paw pads on the hind limbs, at or distal to the carpus or tarsus.

Directional Terminology (Complete List)

  • Rostral

  • Caudal

  • Cranial

  • Proximal

  • Carpus

  • Ventral

  • Dorsal

  • Medial

  • Lateral

  • Median plane

  • Tarsus

  • Plantar

  • Dorsal plane

  • Palmar

  • Transverse planes

Positional Naming Rules

  • Radiographic views are named using:

    • The anatomical direction that the beam enters the body.

    • The anatomical direction that the beam exits the body.

    • Example: In a ventrodorsal view (VD), the patient is in dorsal recumbency.

  • In lateral recumbency, the view is named based on the side that is down.

    • Example: In a right lateral view, the patient is lying on its right side.

  • Terms medial and lateral are secondary and used with other terms.

    • Example: dorsomedial.

  • Terminology changes when referring to the head and neck and distal limbs:

    • Rostral is used instead of cranial for the head.

    • For limbs distal to the carpus or tarsus, dorsal is used instead of cranial, and palmar/plantar replaces caudal.

Positioning/Prepping Your Patient

  • Use positioning tools when necessary: examples include gauze, tape, sandbags, troughs, wedges, etc.

    • Tools should be waterproof.

  • Do not hesitate to request sedation if needed.

  • Ensure the patient is:

    • Dry

    • Free from debris

    • Not wearing collars or harnesses (to avoid artifacts on x-ray).

Positioning Devices

  • If a patient is unwilling to stay still for x-rays or hands-free techniques are required, chemical restraint (sedation) may be necessary.

Rules for Taking Good X-rays

  1. Take at least two orthogonal views.

  2. The area of interest should be closest to the plate.

  3. When x-raying extremities, take images of the contralateral limb for comparative purposes.

  4. Center the area of interest in the beam.

  5. Take patient measurements at the widest part.

  6. Ideally, measure the patient in the same position as the x-ray will be taken.

  7. Position the patient with the thickest portion towards the cathode.

Prepping for X-ray

  1. Assemble all necessary equipment: Ensure the machine is turned on.

  2. Identify the anatomic landmarks.

  3. Measure the animal using calipers.

  4. Determine kVp and mAs using the technique chart and set the machine.

  5. Properly position the patient: Restraint should be firm and brief.

  6. Demonstrate proper collimation.

Motion Control

  • Patient positioning is critical as veterinary patients may resist staying still in awkward positions.

    • Apply firm restraint and work quickly.

    • Use chemical restraint if needed.

  • Exposure time should be as short as possible to reduce motion artifacts.

Distortion

  • The image of an object changes as the object's position relative to the film changes, leading to:

    • Foreshortening: Objects at an angle appear shorter.

    • End on view: Long objects appear as spots.

  • Ensure that the body part of interest is parallel to the film and not twisted.

Thoracic X-ray

  • Measurement:

    • At the thickest part of the thorax, near the level of the last rib/caudal border of the scapula.

  • Landmarks:

    • Cranial: Thoracic inlet.

    • Caudal: Last rib/1st lumbar vertebra.

  • Ideally taken on inspiration if possible.

    • Legs should be stretched enough to prevent superimposition over the chest.

    • Remember to use right and left markers.

Positioning: VD Thorax

  • Front and hind legs:

    • Should be extended and symmetrical.

  • Move front limbs away from the area of interest, ensuring:

    • Straight spine.

    • Thorax and head positioned in the trough.

    • Sternum directly above the spine.

Abdominal X-ray

  • Measurement:

    • At the thickest part of the abdomen, near the level of the last rib or thickest section if overweight.

  • Landmarks for positioning:

    • Cranial: Middle of the ribs/caudal aspect of T7/Xiphoid Process.

    • Caudal: Greater trochanter/pelvic outlet or joint.

  • Ideally taken on expiration if possible.

Positioning: VD Abdomen

  • Positioning requires:

    • Front and hind legs to be extended and symmetrical.

    • Move hind limbs away from the area of interest.

    • Straight spine using a trough; the sternum should align directly above the spine.

Extremities

  • Ensure the area of interest is closest to the cassette.

  • If not otherwise stated, radiograph joints at a 90-degree angle.

  • Common views include:

    • Lateral

    • AP (anterior/posterior)

  • Extra views may be taken in flexion or extension.

    • Always include an R/L marker to indicate the limb being x-rayed.

Extremities - Collimation

  • When imaging joints:

    • Include bones above and below the joint.

  • When imaging bones:

    • Include joints above and below the bone.

Oblique Positioning

  • An oblique radiograph is a type of radiograph taken at halfway between AP and lateral views.

    • The patient is rotated about 45 degrees from lateral.

    • Measure and collimate according to the bone being x-rayed.

    • Commonly used for paws and skulls/jaws.

Positioning: Pelvis

  • Positioning:

    • VD view must display perfect symmetry.

    • Legs should be extended and parallel with stifles rotated internally.

    • Patellas should be centered on the distal femurs.

  • Lateral positioning requirements:

    • Limb nearest the cassette is positioned most cranially.

    • Collimation:

    • Cranial: includes wings of ilium (with one vertebra).

    • Caudal: covers the caudal ischium (with about 1/3 of the femur).

Pelvic Radiographs (OFA)

  • OFA: Orthopedic Foundation for Animals

  • Landmarks for positioning:

    • Cranial: Wings of the ilium.

    • Caudal: Tibial crests.

    • Ventrodorsal: Medial rotation of the femurs, ensuring femurs are parallel and the tail does not obstruct areas of interest.

  • Labeling requires the registered name/AKC number, clinic identification, and date.

  • A lateral view is not required for OFA certification; sedation is often necessary.

Skull X-ray

  • Standard lateral and VD views are utilized.

  • Ensuring symmetry is crucial.

  • Rostrocaudal view: This is a VD with the nose pointed upwards.

  • All views can be performed with the mouth either open or closed.

    • Heavy sedation or anesthesia is often needed, especially for open-mouth views.

Spine X-ray

  • Standard VD and lateral views are utilized while keeping legs extended and symmetrical.

  • Use a trough on VD views to ensure the spine is straight.

  • Sedation and/or anesthesia may be required.

  • Collimation typically divides into sections (cervical, thoracic, lumbar, sacral, and coccygeal).

    • Collimate by narrowing down on the spine rather than the entire animal.

Viewing a Radiograph

  • In lateral view, position the patient's head to your left.

  • In VD/DV views, position as if you and the animal face each other, with the patient's head at the top.

    • The patient's right will be on your left hand side.

  • In lateral or oblique views of extremities, position the proximal portion up and the cranial or dorsal aspect to your left.

Evaluating a Radiograph

  • In lateral view:

    • Rib heads should be superimposed.

    • Intervertebral foramina should appear equal.

    • Transverse spinous processes should be superimposed.

  • In VD view:

    • Ribs should be symmetrical.

    • Spinous processes should be aligned in the center.

    • Wings of the ilium should be symmetrical.

    • Obturator foramina should also be symmetrical.

Contrast Studies: Terminology

  • Antegrade: Moving forward or directed along normal flow.

  • Barium Sulfate: A positive contrast medium commonly used to evaluate the gastrointestinal (GI) tract.

  • Contrast Medium: A substance introduced into the body (via injection or ingestion) to enhance visibility on a radiograph.

  • Cystography: Radiographic study highlighting the urinary bladder.

  • Double Contrast: Study using both positive and negative contrast media.

  • Esophagraphy: Radiographic study of the esophagus.

  • Excretory Urography: Radiographic evaluation of the upper urinary tract after IV injection of positive contrast medium.

  • Filling Defect: An abnormal area within an organ during a contrast study.

  • Gastrography: Study evaluating the stomach via radiography.

  • Ileus: Condition where intestines do not move contents along due to an obstruction.

  • Lower GI Study (Barium Enema): Contrast study examining the rectum and colon.

  • Myelography: Study evaluating the subarachnoid space around the spinal cord.

  • Negative Contrast Agent: Gas (such as air, CO2, nitrous oxide) that is radiolucent compared to soft tissues.

  • Nephrogram: Part of an excretory urogram detailing renal tissue blood supply and perfusion.

  • Pneumocystogram: Study of the urinary bladder using a negative contrast medium.

  • Positive Contrast Agent: Substance radiopaque compared to surrounding tissues.

  • Radiolucent: Area appearing black on a radiograph.

  • Radiopaque: Area appearing white on a radiograph.

  • Retrograde: Moving backwards against normal flow.

  • Upper Gastrointestinal Study: Study evaluating the stomach and small intestines.

  • Urethrography: Study assessing the urethra.

Positive-Contrast Media and Studies

  • Positive contrast media have higher atomic numbers or densities than the compounds in tissues and appear radiopaque (white) on radiographs.

  • Barium sulfate:

    • Available in powder, liquid, or paste forms.

    • Only used to evaluate the gastrointestinal tract, administered orally or rectally.

    • Not recommended if GI perforation is suspected.

  • Water-soluble organic iodides:

    • Administered via injection for intravascular studies or other body cavities.

    • Excreted through the kidneys.

Gastrointestinal Tract Studies (Barium Series)

  • Indications: Evaluates dangers in the gastrointestinal tract, often utilized when assessing GI foreign bodies or masses.

  • Patient Preparation: The affected area should ideally be clear of contents (may require fasting or enema), and hair must be dry and free of contrast.

  • Contraindications: Should not be conducted if GI perforation is suspected, the GI tract is distended, or ileus is noted. Not recommended if other imaging (ultrasound, endoscopy) is planned as it may obscure results.

Negative-Contrast Media and Studies

  • Negative contrast media have low atomic numbers or densities, appearing radiolucent (black) on radiographs.

  • Agents: Include air, nitrous oxide, oxygen, or carbon dioxide.

    • Care must be taken to avoid over-inflation of organs, which can lead to rupture and possible air embolism.

Double Contrast Media and Studies

  • These studies combine both positive and negative contrast media, often performed in the stomach, urinary bladder, and colon.

  • Negative contrast typically administered first to avoid excess bubbles formation.