Wihelm Conrad Roentgen, a German physicist, is credited with discovering X-rays in 1895. He was experimenting with metallic salts, electrical current, and a vacuum tube. He passed high-voltage electric currents through the tubes, causing a screen in another area of the room to shine. This occurred even though his tube was covered with black paper. He had discovered a new form of radiation, imperceptible to the human eye, and different from cathode rays. He called them X-rays (unknown) because he himself did not know what they were. His first X- ray was of his wife's hand, showing her bones and wedding ring. He discovered that these invisible rays passed through wood, glass, and human flesh, but not bone or metal. Roentgen was awarded the first Noble Prize in physics in 1909 for his discovery of X-rays. It is now known that X- rays are part of the electromagnetic spectrum of energy. They are a type of electromagnetic radiation whose wavelength is smaller than visible light. They have higher frequency, and greater energy than light waves. They are very penetrating and pass through dense objects that absorb ordinary light.
To take an X-ray, the area to be looked at is placed between a metal cassette holding the film and X-ray tube. Electrical current passing through an X-ray tube produces a beam of ionizing radiation that can pass through the the body part being examined to produce an image on film. A lead shield is used to protect parts of the body which are not being X-rayed. X-rays pass easily through air and soft tissue, but stop when they encounter bone, which is made up of calcium, phosphate, and other minerals. A contrast medium, such as barium or other iodine-based compound, may be injected or inserted into the body to better define intestines, blood vessels, or other soft internal structures. When X-ray films are examined, bones appear white, and soft body tissues, muscles, and organs are grey to black because their density is similar. The contrast material introduced into the body helps to make the organ being examined stand out. Because X-rays are often somewhat difficult to read, it takes a trained radiologist to interpret to results with accuracy.
X-rays expose the body to ionizing radiation. This is a major drawback which poses certain health risks. Even low doses of X-rays can cause birth defects when a fetus is exposed to them during critical stages of development. Radiation exposure can also damage male sperm and female eggs and can result in genetic defects. Radiation exposure has a cumulative effect. Frequent exposure increases the risk of damage. X-rays are contraindicated during pregnancy unless they are absolutely necessary. If they are done at all, it is with the judicious use of a lead shield. Routine X-ray screening tests, such as chest X-rays, are no longer recommended.
British electronics engineer, Godfrey Houndsfield, won a Nobel Prize in 1979 for his invention of computerized axial tomography. Computed tomography combines the basic principles of radiology with computer technology. During a CT scan an X-ray tube rotates around the person being examined, and generates hundreds of images as it makes a 360-degree circle. These images are received on a series of special plates. Data on these detectors is then transmitted to a computer which processes them to create two-dimensional cross-sectional views of the body. An iodine substance is often used, as a contrast medium, as barium might be used in conventional X-rays.
Although a large number of images are taken during a CT scan, the total amount of radiation could be less than in an X-ray. However, there is still risk to a developing fetus; therefore, CT scans are not recommended during pregnancy.
Available since the early eighties, the diagnostic technique, magnetic resonance imaging, uses a magnetic field to create two-dimensional images which show a cross section of an internal organ or structure. These images are much like CT scans results, but do not require ionized radiation to produce them. MRI provides more detailed images than CT scans, often giving a much greater contrast between normal and abnormal tissue.
The technique is based on the principle that the most abundant atom in the body is hydrogen. When placed in a powerful magnetic field, the nuclei of these hydrogen atoms line up in one direction. When energy from radio waves is directed into the field of the body part being examined, the nuclei are temporarily moved out of alignment. When the radio waves stop, the nuclei return to their alignment. The machine's computers record the duration and the intensity of these signal changes and convert the data into information that produces an image which shows the internal structure of the part being examined.
MRI is most often used to examine the brain and spinal cord, the joints, and soft tissues of the body. It provides a non invasive method to evaluate inflammatory conditions and infections. It is also used to assess response to treatment, especially chemotherapy or radiation therapy. MRI can produce detailed images of the heart and major blood vessels, as well as the internal structure of the eye and ear. It is often used to examine sport injuries of the knee and shoulder joints.
MRI is not suitable for all individuals. The person being examined lies on a table that slides into a narrow tube and is surrounded by electromagnets. The procedure is not painful, but it is noisy and confining, and especially difficult for people who are claustrophobic. The procedure often takes from one to three hours. MRI cannot be used for individuals with pacemakers or other metal implants because the magnet may move the object and cause injury. The high cost of MRI (about $1,000 per examination) can also be a limiting factor of this technology. MRI evaluation during pregnancy should be carefully considered on an individual basis, with the decision being made between the patient and her doctor.
A Scottish doctor named Ian Donald is credited with building (with others) the first ultrasound machine in the late 1950s. Ultrasound or pulse-echo sonography is a medical diagnostic tool which uses high frequency sound waves to create a visual image on a screen. Obstetrical scans provide 'pictures' of the fetus within the mother's body.
The use of diagnostic ultrasound is based on the piezoelectric effect, which was discovered by Pierre and Jacques Curie in 1880. The application of a pulse of electric charge in a transducer produces a change in the thickness of the element. Repeated application of voltage results in the generation of pressure or sound waves. The transducer then converts one form of energy into another form. An ultrasound transducer converts electricity into mechanical energy in the form of vibrations by using the piezoelectric effect. The waves produced in diagnostic ultrasound are generated in short pulses, repeated 1,000 times a second. When the sound waves come in contact with the target object they bounce back and an amplifier amplifies the returning echo signals. These are then electronically processed and translated to dots on a screen for display on a cathode ray tube, as in a television screen. Computers are also used to process data, along with cameras, and video recorders to record images and data.
Doppler ultrasound is a development of ultrasound which can detect waves of moving fluid, because it can pick up moving structures, such as circulating blood. The returning echo contains a change or shift in tone and this can be used to measure blood flow. This information can then be used to interpret the baby's heartbeat.
Obstetrical ultrasound scans are safer than previous diagnostic techniques. They are non invasive, and their imaging does not involve X-ray radiation, which can be harmful to the fetus. It is a fast, easy procedure which should cause the mother no discomfort. Because results are often difficult to read and interpret, it takes a highly trained and skillful sonologist to complete the procedure.
An obstetrical ultrasound exam is not painful, although it may be somewhat uncomfortable because it is necessary to have a full bladder in order to view the uterus clearly. A gel is applied to the abdomen which enables the ultrasound waves to be conducted directly into the abdomen. The transducer box is moved slowly back and forth while the doctor views the the resulting image on an oscilloscope or computer screen.
Two types of ultrasound scans may be done during pregnancy. The first is referred to as a stage one examination. It is a short, simple exam which measures the widest dimension of the baby's head. This provides a good indication of the baby's gestational age. During this exam the location of the placenta, the amount of amniotic fluid, and the general position of the baby can be determined. Stage one ultrasound is also used to verify fetal growth if the baby seems to be growing either very rapidly or very slowly, and to confirm the diagnosis of multiple babies. Fetal anomalies or an ectopic pregnancy may also be discovered. The heart beating can be seen at about the 6th or 7th week. The baby's heartbeat can be heard at about 12 to 14 weeks with an auditory scan.
Stage two ultrasound is a longer examination, performed if there is the possibility of a potential problem with the pregnancy. It is used to rule out or confirm congenital malformations. Common defects of the neural tube, including spina bifida, hydrocephalus, and anencephaly may be detected; as well as anomalies of the gastrointestinal tract, renal tract, and heart and other soft tissues.
Diagnostic ultrasound is also used to guide the needle used in the amniocentesis procedure; a test which analyzes amniotic fluid for chromosomal abnormalities. This is generally performed around 16 weeks if there is an indication of a problem or if the mother is in a high risk category.
Ultrasound is also commonly used to examine other abdominal organs such as the liver, spleen, gallbladder, and pancreas; as well as the kidneys, bladder, heart, and thyroid gland.
Fetal monitoring devices
EFM, or electronic fetal monitoring, began to be used in the late 1960s. Up until that time, the fetal heartbeat was heard using a regular stethoscope, or later a fetoscope. The fetoscope has now largely been replaced by a portable ultrasound device which is easier to use and can pick up sounds that may be hard for the human ear to distinguish. During such monitoring, the fetal heartbeat is picked up and then recorded on a graph.
There are two types of fetal monitors. One type uses external leads that are taped or strapped to the mother's abdomen, the other uses an internal lead that is inserted under the baby's skin, usually on the scalp. They provide a continuous record of the baby's heartbeat. Monitors are used in conjunction with an electronic pickup which measures the motion of the uterus during contractions. When this is used during labor, the effect of each contraction on the baby's heart rate, can be clearly seen.
The external fetal monitor is more commonly used for low-risk pregnancies. With this device the fetal heart rate is measured with pulsed ultrasound. Two straps containing electronic transducers are placed around the mother's abdomen. One transducer records the baby's heartbeat, while the other measures the strength of her contractions. The monitor provides a continuous reading. New devices work by remote control, allowing the mother more freedom of movement as she is not attached to a machine.
Internal monitoring is considered to be the most accurate means of monitoring the baby's heart rate. It is used more often if the pregnancy is thought of as high-risk. During the procedure an electrode is inserted through the cervix into the baby's scalp. A safety feature prevents it from penetrating more than 2 millimeters. The heartbeat is recorded by picking up electrical impulses from the baby's heart, like an electrocardiogram. A transducer is strapped around the mother's abdomen to measure the pressure of the contractions. Once the leads are in place, they provide a continuous, detailed picture of the baby's heart rate in comparison to the mother's contractions. If the baby's heart rate drops too much during contractions, the baby is considered to be in danger. This situation would call for appropriate medical intervention, and the possibility of a cesarean section delivery.