Cranial Ultrasound/Head Ultrasound
- What is cranial ultrasound?
- What are some common uses of the procedure?
- How should I prepare?
- What does the equipment look like?
- How does the procedure work?
- How is the procedure performed?
- What will I experience during and after the procedure?
- Who interprets the results and how do I get them?
- What are the benefits vs. risks?
- What are the limitations of cranial ultrasound?
What is cranial ultrasound?Head and transcranial Doppler are two types of cranial ultrasound exams used to evaluate brain tissue and the flow of blood to the brain, respectively.
Head UltrasoundA head ultrasound examination produces images of the brain and the cerebrospinal fluid that flows and is contained within its ventricles, the fluid filled cavities located in the deep portion of the brain. Since ultrasound waves do not pass through bone easily, this exam is most commonly performed on infants and babies, whose skulls have not completely formed. The gaps between those skull bones provide a "window," allowing the ultrasound beam to freely pass into and back from the brain. The ultrasound probe and some gel are placed on the outside of the head in one of those regions without bone.
Transcranial DopplerA transcranial Doppler (TCD) ultrasound evaluates both the direction and velocity of the blood flow in the major cerebral arteries of the brain. This type of ultrasound exam is also used during surgical procedures to monitor blood flow in the brain. TCD may also be used by itself or with other diagnostic exams such as magnetic resonance imaging (MRI), magnetic resonance angiography (MRA) and computed tomography (CT) scans.
Ultrasound imaging, also called ultrasound scanning or sonography, involves exposing part of the body to high-frequency sound waves to produce pictures of the inside of the body. Ultrasound examinations do not use ionizing radiation (as used in x-rays). Because ultrasound images are captured in real-time, they can show the structure and movement of the body's internal organs, as well as blood flowing through blood vessels.
Ultrasound imaging is a noninvasive medical test that helps physicians diagnose and treat medical conditions.
What are some common uses of the procedure?Head ultrasound is a routine exam for babies who were born prematurely. The procedure is used to diagnose and treat medical conditions related to premature birth, or to ensure that babies born prematurely do not develop complications.
In children, head ultrasound is used to:
- evaluate hydrocephalus, or an enlargement of the ventricles, a condition that can have a number of causes.
- detect bleeding within the brain tissue or the ventricles. The latter condition is called intraventricular hemomrrhage (IVH).
- assess whether there is damage to the white matter brain tissue surrounding the edges of the ventricles, a condition known as periventricular leukomalacia (PVL).
- evaluate for congenital abnormalities
- locate the site of an infection or tumor.
Transcranial Doppler ultrasound is used to assess the risk of stroke in adults and children with sickle cell disease. It is also used to measure conditions affecting blood flow to and within the brain, such as:
- Stenosis: a narrowing of a segment of a vessel, most commonly due to atherosclerosis (hardening of the arteries).
- Vasospasm: a temporary narrowing of a vessel, usually a reaction to blood being present in the spinal fluid spaces surrounding the brain. This condition is known as subarachnoid hemorrhage (SAH).
How should I prepare?No special preparation is required prior to head or transcranial Doppler ultrasound exams. However, the patient should wear comfortable, loose-fitting clothing
Adults may be asked to stop using nicotine-based products 30 minutes to two hours prior to a transcranial Doppler ultrasound exam. Products with nicotine may cause blood vessels to constrict and give inaccurate results.
Your doctor will provide specific instructions for you or your child prior to the exam.
What does the equipment look like?Ultrasound scanners consist of a console containing a computer and electronics, a video display screen and a transducer that is used to do the scanning. The transducer is a small hand-held device that resembles a microphone, attached to the scanner by a cord. The transducer sends out inaudible high frequency sound waves into the body and then listens for the returning echoes from the tissues in the body. The principles are similar to sonar used by boats and submarines.
The ultrasound image is immediately visible on a video display screen that looks like a computer or television monitor. The image is created based on the amplitude (strength), frequency and time it takes for the sound signal to return from the area of the patient being examined to the transducer and the type of body structure the sound travels through.
How does the procedure work?Ultrasound imaging is based on the same principles involved in the sonar used by bats, ships, fishermen and the weather service. When a sound wave strikes an object, it bounces back, or echoes. By measuring these echo waves, it is possible to determine how far away the object is and its size, shape and consistency (whether the object is solid, filled with fluid, or both).
In medicine, ultrasound is used to detect changes in appearance of organs, tissues, and vessels or detect abnormal masses, such as tumors.
In an ultrasound examination, a transducer both sends the sound waves and receives/records the echoing waves. When the transducer is pressed against the skin, it directs small pulses of inaudible, high-frequency sound waves into the body. As the sound waves bounce off of internal organs, fluids and tissues, the sensitive microphone in the transducer records tiny changes in the sound's pitch and direction. These signature waves are instantly measured and displayed by a computer, which in turn creates a real-time picture on the monitor. One or more frames of the moving pictures are typically captured as still images. Small loops of the moving “real time” images may also be saved.
Doppler ultrasound, a special application of ultrasound, measures the direction and speed of blood cells as they move through vessels. The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). A computer collects and processes the sounds and creates graphs or color pictures that represent the flow of blood through the blood vessels.
How is the procedure performed?
Head UltrasoundA head ultrasound is performed in the neonatal intensive care unit (NICU) at the baby's bedside. The baby is positioned lying face-up. A clear, water-based gel is applied to the transducer to help the transducer make secure contact with the body and eliminate air pockets that can block the sound waves from passing into the body. The sonographer (ultrasound technologist) or radiologist then gently presses the transducer against the fontanelle (soft spot of the baby's head, which has no bone to block the passage of the sound waves).
If head ultrasound is used during brain surgery, a portion of the skull will be removed and the exposed brain examined for brain masses with the use of a transducer.
Transcranial DopplerDuring a transcranial Doppler ultrasound, the patient is either positioned on his or her back on an examination table or seated upright in an examination chair. A clear water-based gel is applied on the back of the neck, above and lateral to the cheek bone, in front of the ear or over the eyelid, as these are sites for blood vessels that supply the brain. The transducer is gently pressed over one of these areas to measure the direction and speed of the flowing blood.
The patient will need to remain still during the examination, which may take between 20 and 30 minutes. However, if the patient needs to adjust his or her position on the examination table, there is usually no problem in pausing for that time. If the examination is being performed on a baby, a nurse or radiologic technologist may assist with keeping the baby still to ensure the best imaging quality.
What will I experience during and after the procedure?Most ultrasound examinations are painless, fast and easy.
There may be minimal discomfort from pressure, as the transducer is pressed against the area being examined. If the gel is not warmed prior to contact with the skin, it could produce a cold sensation.
If a Doppler ultrasound study is performed, you may actually hear pulse-like sounds that change in pitch as the blood flow is monitored and measured.
Once the imaging is complete, the gel will be wiped off your skin.
After an ultrasound examination, you should be able to resume your normal activities immediately.
Who interprets the results and how do I get them?A radiologist, a physician specifically trained to supervise and interpret radiology examinations, will analyze the images and send a signed report to your primary care physician or the physician who referred you for the exam, who will share the results with you. In some cases the radiologist may discuss results with you at the conclusion of your examination.
Follow-up examinations are often necessary, and your doctor will explain the exact reason why another exam is requested. Sometimes a follow-up exam is done because a suspicious or questionable finding needs clarification with additional views or a special imaging technique. A follow-up examination may be necessary so that any change in a known abnormality can be detected over time. Follow-up examinations are sometimes the best way to see if treatment is working or if an abnormality is stable over time.
What are the benefits vs. risks?
- Most ultrasound scanning is noninvasive (no needles or injections) and is usually painless.
- Ultrasound is widely available, easy-to-use and less expensive than other imaging methods.
- Ultrasound imaging does not use any ionizing radiation.
- Ultrasound scanning gives a clear picture of soft tissues that do not show up well on x-ray images.
- For standard diagnostic ultrasound there are no known harmful effects on humans.
What are the limitations of cranial ultrasound?Ultrasound examinations are very sensitive to motion, and an active or crying child will slow the examination process.
Large patients are more difficult to image by ultrasound, because greater amounts of tissue weaken the sound waves as they pass deeper into the body.
Exam results could be altered, due to:
- an open wound or recent surgical incision near the area being imaged.
- changes in blood flow pattern as a result of heart disease or irregular heart rhythms.