- [click] Ultrasound Doppler method
When dealing with a case of fetal heart arrhythmias, the obstetrician has to answer some questions concerning its etiology or the best way to investigate the fetal well-being.
Modern obstetrics does not offer many alternatives. Besides the classical direct auscultation, the remaining non-invasive tools left for use are cardiotocography (CTG), and ultrasound.
Basicly the Huntleigh Diagnostic methodlogy deploys Cardiotocography (CTG) Fetal Monitoring technique as will be discussed. Such systems are useful to detect fetal heartbeat signals and also to monitor peripheral arterial and venous blood flow. These devices are for use in physicians' offices, vascular labs, extended care facilities, mobile labs, or anywhere documented vascular testing and reimbursement are important issues. The tasks these devices perform the spectral analysis for accurate visualization and quantification of blood flow parameters including velocity, directionality, and a number of calculated measurements. You have a choice of 4 or 8 MHz frequency continuous wave doppler transducers optimized for detecting blood flow throughout peripheral parts of the body. Optional display feature allows quantification, documentation and qualification of blood flow using a color frequency distribution spectral analysis for accurate determination of direction and velocity of blood flow. Fast, built-in printer for quality documentation of all information obtained.
Nevertheless, a general overview of the ultrasound methodology deserves mention.
GENERAL OVERVIEW OF ULTRASOUND METHODOLOGY
Ultrasonic imaging is the second most popular imaging modality in medicine (the first being x-rays). It is estimated that over 25% of all medical imaging procedures involve ultrasound. Ultrasonic imaging complements the other major imaging modalities, i.e. x-rays and magnetic resonance (MR) imaging etc.
Ultrasonic imaging is used extensively in obstetrics. For example, the size and weight of a baby can be estimated by measuring the diameter of the head, abdominal circumference and femur length on an ultrasound image. If the time since conception is known, then the projected weight of the baby at birth can be estimated. Two-dimensional (2D) ultrasound images such as the type can be combined together to produce three-dimensional (3D) images of a fetal face. Studies have shown that congenital abnormalities are easier to detect using 3D images than 2D images. Ultrasound is also used extensively to image the heart and to measure blood flow in arteries and veins (to detect blockages, for example).
There are many situations in which ultrasound is performed. Perhaps you are pregnant, and your obstetrician wants you to have an ultrasound to check on the developing baby or determine the due date. Maybe you are having problems with blood circulation in a limb or your heart, and your doctor has requested a Doppler ultrasound to look at the blood flow. Ultrasound has been a popular medical imaging technique for many years.
Ultrasound imaging (sonography) uses high-frequency sound waves to view soft tissues such as muscles and internal organs. Because ultrasound images are captured in real-time, they can show movement of the body's internal organs as well as blood flowing through blood vessels.
In an ultrasound exam, a hand-held transducer is placed against the skin. The transducer sends out high frequency sound waves that reflect off of body structures. The returning sound waves, or echoes, are displayed as an image on a monitor. The image is based on the frequency and strength (amplitude) of the sound signal and the time it takes to return from the patient to the transducer. Unlike with an x-ray, there is no ionizing radiation exposure with this test.
Ultrasound imaging is used in many types of examinations and procedures. Some examples include:
- Doppler ultrasound (to visualize blood flow through a blood vessel)
- Bone sonography (to diagnose osteoporosis)
- Echocardiogram (to view the heart)
- Fetal ultrasound (to view the fetus in pregnancy)
- Ultrasound-guided biopsies
- Doppler fetal heart rate monitors (to listen to the fetal heart beat).
Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. In ultrasound, the following events happen:
- The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe;
- The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone);
- Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected;
- The reflected waves are picked up by the probe and relayed to the machine;
- The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second); and
- The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.
In a typical ultrasound, millions of pulses and echoes are sent and received each second. The probe can be moved along the surface of the body and angled to obtain various views.
A basic ultrasound machine has the following parts:
- transducer probe - probe that sends and receives the sound waves;
- central processing unit (CPU) - computer that does all of the calculations and contains the electrical power supplies for itself and the transducer probe;
- transducer pulse controls - changes the amplitude, frequency and duration of the pulses emitted from the transducer probe;
- display - displays the image from the ultrasound data processed by the CPU;
- keyboard/cursor - inputs data and takes measurements from the display;
- disk storage device (hard, floppy, CD) - stores the acquired images; and
- printer - prints the image from the displayed data.
Different Types of Ultrasound
Most ultrasound machines presents a two dimensional image, or "slice," of a three dimensional object (fetus, organ). Two other types of ultrasound are currently in use, 3D ultrasound imaging and Doppler ultrasound.
3D Ultrasound Imaging
In the last several years, ultrasound machines capable of three-dimensional imaging have been developed. In these machines, several two-dimensional images are acquired by moving the probes across the body surface or rotating inserted probes. The two-dimensional scans are then combined by specialized computer software to form 3D images.
Doppler ultrasound is based upon the Doppler Effect. When the object reflecting the ultrasound waves is moving, it changes the frequency of the echoes, creating a higher frequency if it is moving toward the probe and a lower frequency if it is moving away from the probe. How much the frequency is changed depends upon how fast the object is moving. Doppler ultrasound measures the change in frequency of the echoes to calculate how fast an object is moving. Doppler ultrasound has been used mostly to measure the rate of blood flow through the heart and major arteries.
Major Uses of Ultrasound
Ultrasound has been used in a variety of clinical settings, including obstetrics and gynecology, cardiology and cancer detection. The main advantage of ultrasound is that certain structures can be observed without using radiation. Ultrasound can also be done much faster than x-rays or other radiographic techniques. Here is a short list of some uses for ultrasound:
Obstetrics and Gynecology
- measuring the size of the fetus to determine the due date;
- determining the position of the fetus to see if it is in the normal head down position or breech;
- checking the position of the placenta to see if it is improperly developing over the opening to the uterus (cervix);
- seeing the number of fetuses in the uterus;
- checking the sex of the baby (if the genital area can be clearly seen); - checking the fetus's growth rate by making many measurements over time;
- detecting ectopic pregnancy, the life-threatening situation in which the baby is implanted in the mother's Fallopian tubes instead of in the uterus;
- determining whether there is an appropriate amount of amniotic fluid cushioning the baby;
- monitoring the baby during specialized procedures - ultrasound has been helpful in seeing and avoiding the baby during amniocentesis (sampling of the amniotic fluid with a needle for genetic testing). Years ago, doctors use to perform this procedure blindly; however, with accompanying use of ultrasound, the risks of this procedure have dropped dramatically; and
- seeing tumors of the ovary and breast.
- seeing the inside of the heart to identify abnormal structures or functions; and
- measuring blood flow through the heart and major blood vessels.
- measuring blood flow through the kidney;
- seeing kidney stones;
- detecting prostate cancer early; and
- a growing use for ultrasound as a rapid imaging tool for diagnosis in emergency rooms.
About the Examination
For an ultrasound exam, you go into a room with a technician and the ultrasound machine.
You remove your clothes (all of your clothes or only those over the area of interest). The ultrasonographer drapes a cloth over any exposed areas that are not needed for the exam. The ultrasonographer applies a mineral oil-based jelly to your skin -- this jelly eliminates air between the probe and your skin to help pass the sound waves into your body. The ultrasonographer covers the probe with a plastic cover. He/she passes the probe over your skin to obtain the required images. Depending upon the type of exam, the probe may be inserted into you. You may be asked to change positions to get better looks at the area of interest. After the images have been acquired and measurements taken, the data is stored on disk. You may get a hard copy of the images. You are given a towelette to clean up.
Ultrasound imaging has been used for over 20 years and has an excellent safety record. It is non-ionizing radiation, so it does not have the same risks as x-rays or other types of ionizing radiation.
Even though there are no known risks of ultrasound imaging, it can produce effects on the body. When ultrasound enters the body, it heats the tissues slightly. In some cases, it can also produce small pockets of gas in body fluids or tissues (cavitation). The long-term effects of tissue heating and cavitation are not known.
Because of the particular concern for fetal exposures, national and international organizations have advocated prudent use of ultrasound imaging. Furthermore, the use of diagnostic ultrasound for non-medical purposes such as fetal keepsake videos has been discouraged.