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
Types of Ultra sound:
Preparation:
Procedure:
Benefits:
Applications:
Common Uses:
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 turbulence in blood flow.
Echocardiography is a diagnostic technique 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:
Specific Frequency Ranges:
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 |
As you can see from the table above, specific band of frequencies are chosen for optimal imaging.
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.
Angiodynography
Angiodynography represents an innovative system that harnesses Doppler sonography for the creation of real-time, color-coded images of blood vessels within the conventional ultrasound slice image. This advancement incorporates a novel computerized technique, enabling the simultaneous display of both the traditional pulse-echo signal and the Doppler shift signal resulting from bodily movements at every point within the ultrasound slice plane. In this system, static tissue structures are depicted in the familiar grayscale image, while dynamic elements such as blood flow are represented in colors.
One study encompassed 453 patients, and it yielded valuable insights. The study culminated in acquiring normal and pathological flow measurements in various anatomical locations, including the carotid artery, jugular vein, renal transplants, thyroid, testis, and urethra. Additionally, it visualized abnormal flow velocities in conditions such as stenosis, tumors, and diffuse parenchymal alterations. This innovative technology offers a promising avenue for non-invasive vascular and tissue assessments, enhancing diagnostic capabilities in diverse clinical scenarios.
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Collection of Pages - Last revised Date: November 11, 2024