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Ultrasonography in Animal Reproduction
- Ultrasound: High-frequency sound waves inaudible to humans
- Frequency: The frequency of sound waves audible to humans is much lower.
Ultrasound Equipment
- Transducer: Produces ultrasound waves
- Fitted with a piezoelectric crystal
- Emits ultrasound when stimulated by a high voltage current
- Scan Converter: Processes the ultrasound signals
History of Ultrasound
- Bats: Inspired the development of ultrasound technology
- Bats use ultrasound to navigate and locate objects
- Ultrasound Imaging: Visualizing internal structures using ultrasound waves
- Widely used in diagnostics today
Types of Probes
- Linear Array Probe: Used for trans-rectal diagnosis in large animals
Ultrasound Signal Processing
- Ultrasound Transmission:
- Transducer emits ultrasound waves into the patient's tissues.
- Echo Reception:
- Ultrasound waves encounter tissue structures and are:
- Reflected back
- Partially absorbed
- Entirely absorbed
- Echo Conversion:
- Returning echoes deform the piezoelectric crystal in the transducer.
- This mechanical energy is converted into an electrical signal.
- The signal's strength is proportional to the echo's strength.
- The signal's delay is proportional to the distance traveled.
- Scan Converter Interpretation:
- The scan converter analyzes the variations in the electrical signal.
- This information is displayed on a screen as:
- Brightness variations in a B-mode system
- Amplitude variations in an A-mode oscilloscope
- Images can be stored as needed.
Ultrasound Pulse-Echo Technique
- Pulse-Echo Principle: Ultrasound is emitted in short pulses, and the time it takes for the echoes to return is measured.
- This allows for the determination of the distance to the reflecting structures.
- The next pulse is emitted only after the previous echoes have been received.
Acoustic Impedance
- Definition: A physical property of tissue that describes its resistance to the passage of ultrasound waves.
- Factors Influencing Acoustic Impedance:
- Density of the tissue (ρ): Measured in kilograms per cubic meter (kg/m³)
- Speed of sound in the tissue (c): Measured in meters per second (m/s)
- Formula: Acoustic impedance (Z) = Density (ρ) × Speed of sound (c)
- Z = ρ × c
Acoustic Impedance Examples
- Low Impedance:
- Air: 0.004
- Lung
- High Impedance:
- Fat
- Water (fluids)
- Kidney
- Blood
- Liver
- Muscle
- Bone: Highest impedance
Ultrasound Instruments
- B-mode Real-time Ultrasonography: Used for most diagnostic veterinary purposes
- Transducers:
- Linear Array Transducers:
- Frequencies: 1 to 4 MHz
- Used in:
- Cattle
- Buffaloes
- Mares
- Female camels
- Sector Trans-abdominal Transducers:
- Frequencies: 5 to 10 MHz
- Used for:
- Early pregnancy diagnosis in small ruminants
Types of Probes
- Linear Array Probe:
- Used for trans-rectal diagnosis in large animals
- Produces a rectangular image
- Curvilinear Probe:
- Similar to linear array probe but with a curved shape
- Sector Scan Probe:
- Produces a pie-shaped image
- Used for trans-abdominal diagnosis in large and small animals
- Phased Array Probe:
- Uses multiple small crystals to focus the ultrasound beam
- Allows for greater flexibility in imaging
- A-mode (Amplitude Mode):
- Displays the amplitude of the ultrasound echoes as a function of time
- Used in pigs but less common in other species
Ultrasound Imaging Modes
- A-mode (Amplitude Mode):
- One-dimensional display with time on the horizontal axis
- Displays the amplitude of ultrasound echoes
- Used in pigs but less common in other species
- B-mode (Brightness Modulation):
- Compound A-mode scan with amplitude translated into brightness scale
- Location on the display is related to position and depth
- Color Doppler Ultrasound:
- Advanced ultrasound technique
- Detects movement of blood or other tissues
- When an ultrasound beam meets a moving object, the reflected ultrasound is either of increased or decreased frequency depending on whether the motion is towards or away from the transducer
- Different color codes are given based on the density and movement
Ultrasound Terminology
- Echogenic: Reflects ultrasound waves strongly
- Hypoechoic: Reflects ultrasound waves weakly
- Anechoic: Does not reflect ultrasound waves (appears black on the image)
- Structural: Refers to the physical structure of tissues or organs
Ultrasound Terminology
- Echogenicity: Describes how strongly a structure reflects ultrasound waves.
- Echogenic: Reflects ultrasound waves strongly.
- Hypoechoic: Reflects ultrasound waves weakly.
- Anechoic: Does not reflect ultrasound waves (appears black on the image).
- Changes in Echogenicity:
- A change in echogenicity within a homogeneous structure may indicate a pathological change.
- Hyperechoic: Increased echogenicity.
- Hypoechoic: Decreased echogenicity.
Attenuation
- Definition: The reduction in the amplitude of the ultrasound beam as it travels through the imaging medium.
- Factors Influencing Attenuation:
- Absorption: Ultrasound waves are absorbed by the tissue.
- Reflection: Ultrasound waves are reflected back from the tissue.
- Appearance: Structures that absorb the ultrasound beam will reflect no ultrasound back and will appear black on the image.
Ultrasound Terminology: Echogenicity
- Echogenicity: Describes how strongly a structure reflects ultrasound waves.
- Hyper-ecogenic: Reflects ultrasound waves strongly (appears bright on the image).
- Example: Bone
- Hypo-ecogenic: Reflects ultrasound waves weakly (appears darker on the image).
- Example: Fluid-filled structures
- Iso-ecogenic: Partially absorbs and partially reflects ultrasound waves (appears similar in brightness to surrounding tissues).
Ultrasound Artifacts
- Definition: Structures in an ultrasound image that do not directly represent the actual tissue being scanned.
- Types of Artifacts:
- Structures that are not actually present in the image.
- Objects that should be represented but are missing from the image.
- Structures that are mis-registered on the image.
Ultrasound Artifacts
- Definition: Structures in an ultrasound image that do not directly represent the actual tissue being scanned.
- Types of Artifacts:
- Operator-Related Artifacts:
- Wrong settings: Incorrect power gain, frequency, or other settings can affect image quality.
- Poor patient preparation: Inadequate preparation can lead to artifacts.
- Tissue-Related Artifacts:
- Reverberation: False echoes caused by repeated reflections between two interfaces.
- Mirror image artifacts: Structures appear mirrored on the opposite side of a strong reflector.
- Caustic shadowing or enhancement: Distortion of the ultrasound beam due to refraction or reflection.
- Beam width artifacts: The width of the ultrasound beam can cause blurring or distortion.
- Side load artifacts: Artifacts caused by the transducer being positioned at an angle.
- Refraction artifacts: Bending of the ultrasound beam as it passes through different tissues.
Reverberation Artifacts
- Cause: High acoustic impedance mismatch between the transducer and the tissue.
- External Reverberation: Air between the probe and the skin.
- Internal Reverberation: Reflectors such as intestinal gas and bones.
- Appearance:
- Multiple hyperechoic lines that are equally spaced and gradually attenuated.
- Example: Gas within the spiral colon.
Ultrasound Artifacts: Comet Tail Artifact
- Cause: Small reflective surfaces, such as gas bubbles or small metallic objects.
- Appearance: Narrow beam of closely spaced, discrete hyperechoic lines.
- Example: Gas bubbles in the intestines.
Ultrasound Artifacts: Acoustic Shadowing
- Cause: Structures that strongly attenuate the ultrasound beam, such as bone, mineralized tissue, or dense materials (e.g., metal, wood, fibrotic tissue).
- Appearance: Anechoic area distal to the attenuating structure.
Ultrasound Artifacts: Attenuation
- Cause: Dense material (mineralized or fibrous tissue) in the near field absorbs part of the ultrasound beam.
- Appearance: Hypoechoic band superimposed on the image.
Ultrasound Artifacts: Distal Acoustic Enhancement
- Cause: Structures with low attenuation (e.g., fluid-filled structures) augment the amplitude of echoes distally.
- Appearance: Increased echogenicity distal to the structure.
- Example: Gravid uterus.
- Benefit: Useful for identifying fluid-filled structures like cysts.
- Mitigation: Decreasing the differential gain at the affected level can reduce the artifact.
Diagnostic Uses of Ultrasonography
- Visualize:
- Structure: Internal anatomy of organs and tissues
- Motion: Movement of blood, fluids, or organs
- Structure Tomography: Detailed cross-sectional images
- Tissue Characteristics: Echogenicity, texture, and other properties
- Blood Velocity: Using color Doppler ultrasound
Reproductive Diagnostics in Domestic Animals
- Ovarian and Uterine Physiology and Pathology:
- Ovarian Follicle: Growth and development
- Corpus Luteum: Formation and function
- Cysts and Tumors: Detection and characterization
- Ovarian Blood Supply: Assessed using color Doppler
- Normal Uterine Ecotexture: Visualization of the uterus during estrus, pregnancy, or fluid accumulation
- Pathologies:
- Mucometra: Accumulation of mucus in the uterus
- Pyometra: Accumulation of pus in the uterus
- Tumors: Abnormal growths in the uterus
- Pregnancy and Gestational Physiology:
- Pregnancy Diagnosis: Early detection of pregnancy
- Fetal Heartbeat: Visualization of the fetal heart
- Fetal Sex: Determination of the fetal sex
Reproductive Diagnostics in Domestic Animals (Continued)
- Gestational Age and Fetal Viability:
- Determine gestational age using ultrasound.
- Count the number of fetuses.
- Assess fetal viability.
- Abnormal Pregnancies:
- Identify potential problems with the pregnancy.
- Monitor fetal growth.
- Detect early embryonic losses.
- Interventions:
- Ultrasound-Guided Ovum Pick-Up (OPU) for In Vitro Fertilization (IVF):
- Use ultrasound to guide the collection of oocytes for IVF.
- Ultrasound-Guided Aspiration of Fetal Contents:
- Reduce twin pregnancies in mares by aspirating fetal contents.
- Collect amniotic or fetal fluids for research or diagnosis.
Patient Preparation
- Transrectal Examination:
- Place the probe in a sleeve or condom with gel.
- Restraint the animal.
- Evacuate the rectum.
- Insert the probe into the rectum to visualize the ovaries and uterus.
- Transcutaneous Ultrasonographic Examination:
- Shave the area of interest.
- Clean the skin with water or alcohol.
Early Pregnancy Diagnosis in Domestic Animals
- Sheep and Goats:
- Fetal heartbeat first appears at 21 to 23 days using a transrectal linear array probe.
- Cotyledons can be visualized at 40 to 50 days using a sector transcutaneous or transabdominal probe.
- Other Species:
- Fetal heartbeats appear at 24 to 28 days in most species, except for mares.
- Mares may show fetal heartbeats earlier.
- Bitch and Cat:
- Ultrasound is particularly useful for confirming pregnancy in these species, as other methods are not readily available.
- Probe Requirements:
- Transrectal: Cattle, buffalo, mare
- Transcutaneous or Transabdominal: Small ruminants, bitch, cat
Ultrasound Imaging of Reproductive Structures
- Corpus Luteum:
- Appearance: Fluid-filled, anechoic (appears black)
- Visualization: Can be visualized and measured using ultrasound
- Vascularity: Evaluated using color Doppler ultrasound
- Red: Arterial blood flow
- Blue: Venous blood flow
- Ovarian Cysts:
- Types:
- Follicular Cysts: Fluid-filled follicles that have not ovulated
- Luteal Cysts: Cysts that develop from the corpus luteum
- Visualization: Can be identified using ultrasound
- Pregnancy Diagnosis in Cattle:
- Ultrasound Images:
- Fetus: Visible
- Fetal Appendages: Placenta, umbilical cord
- Fore and Hind Limbs: Can be identified
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