Veterinary Specialized Diagnostic Imaging Techniques

Ultrasonography

• What it is

  • Uses sound waves to create images

  • A probe sends out sound waves that bounce off tissues and return to the probe, which the computer then translates into an image

• How it works

  • Sound waves go into the body, hit objects, and reflect back

  • The image color depends on the object's properties, like its shape and density, which affect how sound waves reflect.

• Key Concepts

  • Real-time imaging: you see the image as they are happening

  • Echogenicity: describes how tissues appear on ultrasound based on how they reflect sound waves

    • The appearance of the tissues on ultrasound based on the ability of the tissues to reflect sound waves

  • Anechoic: no echoes, appears very dark or black

  • Hyperechoic: reflects more intensely, appears brighter than surrounding tissue

  • Isoechoic: similar echogenicity

  • Hypoechoic: Reflects less intensely, appears darker than surrounding tissue

  • Transducers: the probes that send and receive sound waves

    • Different types exist for different uses

    • They are delicate and need care

    • Modes:

      • B-Mode

      • M-Mode

      • Doppler

    • Changes eletical energy into soundwaves

    • Wide variety of probes available

    • Small animal practices may require 3-4 probes

    • Equine practices may only require 1-2 probes

    • Handle with complete care

    • Avoid dropping or jarring them as crystals inside can become damaged

    • Wipe off after each use with soft cloth

    • Key concepts

      • Advantages

        • Real-time imaging

        • Allows viewing detailed pathology through tissues and fluid

        • Mobile probe

        • Safe because it uses no ionizing radiation

        • Can visualize internal organs, tendons and check for pregnancy

      • Limitations

        • Sound waves don't travel through bone or air

        • Artifacts can interfere with the image

      • Patient Prep

        • Fasting

        • Clipping fur

        • Using alcohol and gel for good probe contact

        • Keeping the patient still and straight

Ultrasound: Anatomy

• Liver

  • Located in cranial abdomen

  • Composed of 5 lobes

  • Gallbladder will be located between medial and quadrate lobes

• Gall Bladder

  • Located between right medial and quadrate lobes of liver

  • Appears as an anechoic, round or oval structure of variable size

  • Echogenic bile may be seen in a gravity dependent portion

• Kidneys

  • Located in retroperitoneal space in the cranial to mid-dorsal abdomen

  • Right kidney is more cranial to the left

  • Left kidney is best visualized immediately caudal to the last rib

• Spleen

  • Mostly in the left side of the abdomen

  • Divided into the head, body and tail

  • Head found by sliding 1-2 intercostal spaces cranial to the left kidney

  • After finding the head, rotate transducer 90 degrees and slide ventrally

  • Body is a rounded triangular shape

  • Follow the body towards the tail

  • Spleen has homogenous echogenicity with fine echotexture

• Urinary Bladder

  • Located in the caudoventral abdomen

  • Varies in size depending on distention

  • Normal bladder contains anechoic urine

  • In the transverse place the colon is seen as a semicircular highly echogenic structure that may deform the wall of the bladder

Fluoroscopy

• What it is:

  • A type of x-ray imaging that produces a continuous, moving image on a monitor

• How it works:

  • Like radiology, it uses x-rays, but in a continuous stream instead of a single shot

  • The x-rays pass through the patient to an image intensifier, creating a live video feed

• Key Concepts

  • Real-time

    • Provides live images

  • C-arm

    • A mobile type of fluoroscopy unit

  • Advantages

    • Allows real-time, interventional imaging

    • Vital for surgical procedures like placing plates and pins, especially in large animals

    • Useful for procedures where you need to see movement, such as catheter insertions or swallow studies

    • Static images can also be captured

  • Limitations

    • There is an increased radiation risk compared to standard radiology due to the continuous exposure

Computerized Tomography

• What it is:

  • Used and x-ray beam that rotates around the patient to take many thin cross-sectional slice images

  • A computer then processes this data to create 2D or 3D images

• How it works

  • It takes many x-rays from different angles around the body

  • The computer combines these images to show cross-sections, revealing structures that might be hidden in a single x-ray shot

• Key Concepts

  • Tomography

    • A technique to show detail in one plane while blurring other

  • Cross-sections

    • Images are viewed as slices through the body

  • Detectors

    • Collect the x-ray data after it passes through the patient

    • More detectors mean more slices

  • Advantages

    • Good for visualizing soft tissues and bone structures

    • Noninvasive way to look inside structures like the skull

    • Can be used for diagnosing neurological issues and equine lameness

    • Quickly show issues like brain bleeds, broken bones, and abdominal injuries

    • More readily available than MRI and less costly to manage

  • Limitations

    • Safety: uses x-rays

Magnetic Resonance Imaging

• What it is

  • MRI is the newest modality in veterinary medicine

• How it works

  • Uses non-ionizing electromagnetic field, protons, and contrast to view soft tissues in the body, especially the brain and spinal cord

  • Creates thin slice images

• Key Concepts

  • Used to view soft tissues, especially the brain and spinal cord, often with the help of contrast

Nuclear Medicine

• What it is

  • Radioisotopes are administered to the patient

  • It is a very effecting way to localize pathology or the results of trauma

• How it works

  • Radioisotopes are administered, typically intravenously

  • Certain isotopes are attracted to specific types of tissue

  • The patient then emits gamma rays from the radioisotope area of inflammation or increased metabolic activity that have taken up the radioisotope are detected by a gamma scintillation camera

  • Radioisotopes have a radioactive half-life and are mostly excreted in urine, with some feces

• Key Concepts

  • Advantages

    • Bone scan for tumor metastasis, injury, or infection

    • Lung scan for pulmonary function or embolism

    • Renal scan for perfusion and function

    • Thyroid scan for tumors and hyperthyroidism

    • Therapeutically, such as using radioactive iodine for the treatment of hyperthyroidism and thyroid tumors in felines

  • Limitations

    • Safety

      • Patient becomes a source of radiation excreted in urine, with some excreted in feces.

    • Requires specialized equipment, namely a gamma scintillation camera, to detect the emitted radiation

Lab Skill

• Barium Study

  • An upper gastrointestinal positive-contrast study is a diagnostic procedure performed in dogs and cats

  • It uses a contrast medium to help visualize the upper GI tract

  • Indications

    • Identifying gastric or intestinal foreign body

    • Confirming gastric outflow or intestinal foreign body

    • Identify possible mass

  • Patient Preparation

    • The patient ideally should be fasted for at least 12-24 hours to ensure the stomach and intestines are empty

    • Initial survey abdominal radiographs should be obtained to check preparation and establish a baseline

    • Sedation should ideally be avoided as it can affect GI motility, gastric emptying, and intestinal transit times

  • Contrast Administration

    • If a stomach or intestinal peroration is suspected, a water soluble organic iodide preparation should be used instead of barium

    • The recommended volume of barium is 6 mL/lb in dogs and cats

    • The start and finish times of administration must be noted

  • Radiograph Acquisition after Contrast

    • Immediate radiographs of the abdomen are taken including right and left lateral, ventrodoral

    • Subsequent radiographs are take at a specific time intervals depending on the species

      • Canine: Immediate, 30 and 60 minutes, then 2, 3, 5 hours, and every 2 hours thereafter until barium is out of the stomach and in the colon

      • Feline: Immediate, 15, 30, and 60 minutes, then every 30−60 minutes until barium is out of the stomach and in the colon