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Doppler Ultrasound

Doppler ultrasound is based upon the Doppler Effect. When the object reflecting the sound waves is moving, it changes the frequency of the echoes. It creates higher frequency when it moves towards the probe and lower frequency when moving away from the probe. The change in the frequency depends on how fast the object is moving. This is a special technique mainly used to examine blood flow. Problems in the veins and arteries are detected by Doppler ultrasound. Doppler ultrasound is also used to measure the blood flow through the heart. The direction of the blood flow is shown in different colors on the ultrasound machine screen. The Doppler images help the physician to see and evaluate blockages to blood flow, such as clots, narrowing of vessels, which may be caused by plaque and such diseases. Tumors and congenital malformation are also detected by Doppler ultrasound.

Ultrasound

Ultrasonography is a medical imaging technique that is also called ultrasound scanning or sonography. High frequency sound waves and their echoes and used in this technique for obtaining images from inside the human body. The echoes of sound waves reflected from the human body are recorded and displayed as a real-time visual image. This technique is similar to the echo location used by bats, whales and dolphins. The sonar used by submarines also operates with the same technique. Ultrasound is useful method to examine many of the body's internal organs like heart, liver, gallbladder, spleen, pancreas, kidneys and bladder.

Ultrasound Scanning

  1. Sound Waves: A transducer (a small handheld device) emits high-frequency sound waves.
  2. Echoes: These sound waves bounce off tissues, organs, and other structures inside the body.
  3. Image Formation: The transducer detects the echoes and sends this information to a computer, which creates images based on the patterns of the echoes.
echocardiogram

Types of Ultra sound:

  1. Abdominal Ultra sound: Evaluates organs in the abdomen, such as the liver, gallbladder, spleen, pancreas, and kidneys.
  2. Pelvic Ultra sound: Assesses reproductive organs (uterus, ovaries) and bladder.
  3. Obstetric Ultra sound: Monitors pregnancy and fetal development, to assess the risk of fetal abnormalities such as neural tube defects or Down's syndrome
  4. Cardiac Ultrasound (Echocardiogram): Evaluates heart structure and function.
  5. Doppler Ultra sound: Measures blood flow through vessels.
  6. Musculoskeletal Ultra sound: Examines muscles, tendons, and joints.
  7. Thyroid Ultra sound: Evaluates the thyroid gland.

Preparation:

  • Fasting: May be required for certain abdominal ultrasounds.
  • Full Bladder: Often necessary for pelvic ultrasounds.
  • Loose Clothing: Wear comfortable, loose-fitting clothes for easy access to the area being examined.

Procedure:

  1. Preparation: The patient may be asked to lie on a table and expose the area to be examined.
  2. Application of Gel: A special gel is applied to the skin to help transmit sound waves.
  3. Transducer Use: The healthcare provider moves the transducer over the area, capturing images.
  4. Image Review: The images are reviewed in real-time, and the provider may take multiple images from different angles.

Benefits:

  • Non-Invasive: No needles or incisions.
  • Safe: Uses sound waves, not radiation.
  • Real-Time Imaging: Allows dynamic assessment of moving structures.
  • Widely Available: Accessible in most healthcare settings.

Applications:

  • Diagnosis: Identifying and evaluating various medical conditions.
  • Monitoring: Tracking the progress of diseases or conditions.
  • Guidance: Assisting in procedures such as biopsies or fluid drainage.

Common Uses:

  • Pregnancy Monitoring: Checking fetal health and development.
  • Organ Assessment: Evaluating the liver, kidneys, and other organs.
  • Cardiac Evaluation: Assessing heart function and detecting abnormalities.
  • Blood Flow Analysis: Checking for blood clots or poor circulation.
  • Musculoskeletal Issues: Diagnosing tendonitis, bursitis, or tears.

Ultrasound examinations are versatile and essential tools in modern medical diagnostics, providing crucial information for the diagnosis and management of many health conditions.

Carotid Doppler ultrasound scanning is a diagnostic method used to assess blood flow through the carotid arteries, which are the primary vessels supplying the neck and head. This non-invasive modality is employed in the evaluation of various conditions, including:
1. Carotid artery stenosis (narrowing) - a common finding associated with increased risk of stroke. Doppler echocardiography image reveals any narrowing of the arteries or turbu￾lence in blood flow.
Echocardiography is a diagnostic tech￾nique used to evaluate structural and functional abnormalities of the heart including:
1. Heart wall: Detecting changes in thickness, texture or motion.
2. Heart chambers: Assessing size, shape, and function.
3. Heart valves: Evaluating valve leaflet movement, regurgitation and stenosis.
4. Large coronary arteries: Identifying narrowing or obstruction.
In addition to detecting cardiovascular lesions, echocardiography is also employed in the diagnosis of:
1. Congenital heart disease: Abnormalities present at birth.
2. Cardiomyopathy: Heart muscle disorders characterized by impaired function.
3. Aneurysms: Ballooning or dilation of the heart or blood vessel walls.
4. Pericarditis: Inflammation of the pericardial sac surrounding the heart.
5. Blood clots in the heart: Emboli that may have originated from other sources and traveled to the heart.

2. Transient ischemic attacks (TIAs), also known as "mini-strokes" or "warning strokes" - a temporary loss of blood flow to the brain.
3. Stroke - a neurovascular event characterized by permanent disruption of blood flow to the brain.
Doppler echocardiography is a valuable diagnostic tool that enables the measurement of blood flow velocity (speed) within the heart. This modality allows cardiologists to:
1. Assess structural abnormalities: Such as mitral valve prolapse, where the mitral valve leaflets protrude into the left ventricle.
2. Evaluate septal defects: Abnormal openings in the septum that separate the right and left sides of the heart.
By analyzing blood flow velocity, Doppler echocardiography can help diagnose and monitor various cardiovascular conditions, including those affecting the heart valves and septum.


Cataract Surgery: An ultrasound probe is inserted into the lens capsule through a small incision in the cornea. The incision is made using a diamond tipped instrument. The ultrasound probe softens the lens by emitting sound waves. It then sucks out the softened lens tissue. Only the front part of the lens capsule is removed.


Doppler ultrasound is a type of echocardiography that utilizes the principles of Doppler shift to measure the velocity of moving structures. This technique involves transmitting high-frequency ultrasonic waves from an emitter and detecting the frequency changes resulting from the interaction with moving targets, such as blood flowing through a blood vessel.
Doppler ultrasonography has become a widely accepted diagnostic modality for detecting various vascular conditions. Specifically, it is commonly employed to:
1. Identify arterial narrowing or stenosis in the neck, often resulting from atherosclerosis (the accumulation of fatty deposits on artery walls).
2. Detect blood clots (thrombi) within veins, as seen in deep vein thrombosis.
In addition to its vascular applications, Doppler ultrasound is also used for:
1. Fetal monitoring: To non-invasively assess fetal heart rate and detect any potential abnormalities.
2. Dialysis and cardiopulmonary bypass procedures: To monitor for air emboli (air bubbles) that may form during these interventions.
3. Blood pressure measurement: As a non-invasive means to estimate blood pressure, particularly in situations where direct measurement is not possible or practical.
The process begins with the emission of pulses of ultrasound at a specific frequency. As these pulses interact with moving objects, such as red blood cells in a vessel, the frequency of the reflected signals (echoes) shifts due to the Doppler effect. A sensor detects these frequency changes and converts them into meaningful data, providing valuable information about the velocity or flow characteristics of the target structure, for example, blood flow through an artery or vein.


Ancillary term used in ultrasound imaging to describe an anechoic region or structure that does not produce any reflective echoes (sonographic signals) when exposed to ultrasound waves. This is typically seen in structures containing clear fluid, such as:
1. Cysts: Fluid-filled cavities that do not reflect ultrasound signals.
In these cases, the lack of echogenicity allows for better visualization and differentiation from surrounding tissues.
"Echogenic" - A descriptive term used in ultrasound imaging to identify structures that produce reflective echoes or signals when exposed to ultrasound waves. In other words, an echogenic structure is one that generates a strong sonographic signal, allowing it to be visualized and characterized on the ultrasound image.


The frequency of ultrasound waves used in medical imaging varies depending on the type of examination and the depth of the tissue being imaged. Here are some general guidelines:

Common Frequencies:

  1. General Diagnostic Ultrasound:
    • Frequencies typically range from 2 MHz to 15 MHz.

  2. Abdominal Ultrasound:
    • Lower frequencies around 2 MHz to 5 MHz.
    • Lower frequencies provide deeper penetration but lower resolution.

  3. Pelvic Ultrasound:
    • Frequencies typically in the range of 3 MHz to 7.5 MHz.

  4. Obstetric Ultrasound:
    • Frequencies around 2 MHz to 5 MHz for deeper penetration to view the fetus.

  5. Cardiac Ultrasound (Echocardiogram):
    • Frequencies typically range from 2.5 MHz to 5 MHz.

  6. Vascular Ultrasound:
    • Frequencies around 5 MHz to 10 MHz.

  7. Musculoskeletal Ultrasound:
    • Higher frequencies around 7.5 MHz to 15 MHz.
    • Higher frequencies provide better resolution for superficial structures.

  8. Small Parts (Thyroid, Breast, Scrotal):
    • Frequencies in the range of 7.5 MHz to 15 MHz.

  • Penetration vs. Resolution: Lower frequencies penetrate deeper into the body but produce images with lower resolution. Higher frequencies provide higher resolution images but do not penetrate as deeply.
  • Tissue Characteristics: Different tissues reflect sound waves differently, so the frequency is chosen based on the specific characteristics and location of the tissue being examined.

Specific Frequency Ranges:

  1. 2-3.5 MHz: Deep structures like the liver, kidneys, and heart.
  2. 3.5-5 MHz: General abdominal and obstetric imaging.
  3. 5-7.5 MHz: Breast, thyroid, and vascular imaging.
  4. 7.5-10 MHz: Musculoskeletal and superficial structures.
  5. 10-15 MHz: Very superficial structures and detailed imaging of small parts.

Normally the term ultrasound refers to frequencies above 20 kHz (the maximum frequency a human can hear), medical ultrasound utilizes frequencies in the range of several MHz to achieve the necessary balance between resolution and penetration for effective imaging of different tissues and organs.

Frequency Range

Impact

Application

1 MHz to 3 MHz

Deep Tissue Imaging.

Deep structures like the liver, kidneys, and heart

3 MHz to 5 MHz

Provides a balance between penetration and resolution

General Abdominal and Obstetric Imaging

2.5 MHz to 5 MHz

Specifically chosen for adequate penetration and resolution

Cardiac Imaging (Echocardiography)

5 MHz to 10 MHz

Optimal for vascular imaging

Breast, thyroid, and vascular imaging

7.5 MHz to 15 MHz

Provides higher resolution images but less penetration depth

Musculoskeletal and Superficial Structures

Sonogram

As you can see from the table above, specific band of frequencies are chosen for optimal imaging.

  • Resolution: Higher frequencies provide better resolution, allowing for more detailed images of tissues and structures.
  • Penetration: The choice of frequency is a trade-off between penetration and resolution. Lower frequencies penetrate deeper but have lower resolution, while higher frequencies provide detailed images of superficial structures.

Movement of the internal tissues and organs are captured in ultrasound. Ultrasonography enables the physicians to diagnose a variety of disease conditions and also assess the damage caused to the systems. The ultrasound machine transmits high frequency sound pulses into the human body by using probes. These sound waves that travel into the body hit a boundary between the tissues inside the body and reflect the sound waves to the probe. Some waves travel even further and they reach another boundary and then get reflected back. The waves that are reflected are picked up by the probe and relayed back into the ultrasound machine.

The ultrasound machine in turn calculates the distance from the probe to the tissue or organ by using the speed of sound tissue and the time of each echo's return. The machine displays these distances and intensities of the echoes on the screen. Through the echoes that are produced the sonologist can identify how far away an object is, how large it is, its shape and consistency (fluid, solid or mixed). Two dimensional images are formed and reflected on the screen. Different types of ultrasound are used for different disease conditions. Ultrasound is used in a variety of clinical settings including obstetrics and gynecology, cardiology and cancer detection.


Amniocentesis

During the early days of pregnancy, amniocentesis is carried out on pregnant woman to find out if the developing fetus is free from certain abnormalities. This procedure involves certain invasive methods like inserting a hollow needle into the uterus of the woman through her abdominal wall to withdraw a sample of amniotic fluid that surrounds the fetus. Using ultrasound, the location of the fetus floating in the amniotic fluid is determined. The abdominal skin surrounding the area is cleaned. The procedure may be conducted either by injecting a local anesthetic in that area, or by just applying a tropical anesthetic around the area through which the needle is to be inserted. About 1 cc per week of gestation of the fetus is taken out from the amniotic fluid.

This procedure is used as a tool which can detect chromosomal disorders like Downs Syndrome and many rare metabolic disorders which are normally inherited. Some structural defects like spina bifida and anencephaly can be detected using this test. This procedure is normally carried out for women over the age of thirty five. It is recommended for women who had undergone a triple screen blood test during pregnancy and for those who have a family history of birth defects or some inherited metabolic disorders. This procedure may be conducted even in later stages of pregnancy to detect suspected problems like Rh incompatibility or infection. This test is also used to determine lung maturity of the infant in the last trimester.

A cell culture is done with the fetal cells taken out during the procedure and the analysis of the DNA is conducted to detect chromosomal abnormalities. It may take up to a month for the results to arrive. This is rated as a highly accurate procedure.

After the withdrawal of the amniotic fluid which takes only a few minutes, the pregnant woman is advised to be in bed for several hours, though the entire procedure will last for about 45 minutes. Doctors check the heart beat of fetus to ensure that it is normal. It is wise to call the health care provider, if the woman experiences fever, bleeding or leakage of amniotic fluid for a long time. Though the chances of infection or injury to the fetus are not ruled out, they are quite rare. There is also a slight chance of miscarriage, but the percentage is negligible. During later stages of pregnancy, a Doppler ultrasound is safer than amniocentesis because it is non-invasive. Anemia in the fetus can easily be detected using ultrasound by measuring the velocity of the blood flow in the middle cerebral artery.

Tags: #Doppler Ultrasound #Ultrasound #Amniocentesis
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Collection of Pages - Last revised Date: July 22, 2024