How does ultrasound produce an image

It increases if the propagation speed or the density of the medium is increased. Attenuation coefficient is the parameter used to estimate the decrement of ultrasound amplitude in certain media as a function of ultrasound frequency. The attenuation coefficient increases with increasing frequency; therefore, a practical consequence of attenuation is that the penetration decreases as frequency increases Figure 4. Ultrasound waves have a self-focusing effect, which refers to the natural narrowing of the ultrasound beam at a certain travel distance in the ultrasonic field.

It is a transition level between near field and far field. The beam width at the transition level is equal to half the diameter of the transducer.

At the distance of two times the near-field length, the beam width reaches the transducer diameter. The self-focusing effect amplifies ultrasound signals by increasing acoustic pressure.

In ultrasound imaging, there are two aspects of spatial resolution: axial and lateral. Axial resolution is the minimum separation of above-below planes along the beam axis.

It is determined by spatial pulse length, which is equal to the product of wavelength and the number of cycles within a pulse. It can be presented in the following formula:. The number of cycles within a pulse is determined by the damping characteristics of the transducer. The number of cycles within a pulse is usually set between 2 and 4 by the manufacturer of the ultrasound machines. As an example, if a 2-MHz ultrasound transducer is theoretically used to do the scanning, the axial resolution would be between 0.

For constant acoustic velocity, higher-frequency ultrasound can detect smaller objects and provide an image with better resolution. The axial resolution of current ultrasound systems is between 0. Figure 5 shows images at different resolutions when a 0. Lateral resolution is another parameter of sharpness to describe the minimum side-by-side distance between two objects.

It is determined by both ultrasound frequency and beam width. The higher frequencies have a narrower focus and provide better axial and lateral resolution. Lateral resolution can also be improved by adjusting focus to reduce the beam width. Temporal resolution is also important for observing a moving object such as blood vessels and heart. Like a movie or cartoon video, the human eye requires that the image is updated at a rate of approximately 25 times a second or higher for an ultrasound image to appear continuous.

However, imaging resolution will be compromised by increasing the frame rate. Optimizing the ratio of resolution to the frame rate is essential for providing the best possible image. As the ultrasound wave travels through tissues, it is subject to a number of interactions.

The most important features are as follows:. When ultrasound encounters boundaries between different media, part of the ultrasound is reflected and the other part is transmitted. Refection of sound waves is similar to optical reflection.

Some of its energy is sent back into the medium from which it came. The strength of the reflection from an interface is variable and depends on the difference of impedances between two affinitive media and the incident angle at the boundary. If the media impedances are equal, there is no reflection no echo. If there is a significant difference between media impedances, there will be nearly complete reflection.

For example, an interface between soft tissues and either lung or bone involves a considerable change in acoustic impedance and creates strong echoes. This reflection intensity is also highly angle dependent. In practical terms, it means that the ultrasound transducer must be placed perpendicular to the target nerve to visualize it clearly.

A change in sound direction when crossing the boundary between two media is called refraction. If the propagation speed through the second medium is slower than that through the first medium, the refraction angle is smaller than the incident angle.

Refraction can cause the artifact that occurs beneath large vessels on the image. During ultrasound scanning, a coupling medium must be used between the transducer and the skin to displace air from the transducer-skin interface. A variety of gels and oils are applied for this purpose. Moreover, they can act as lubricants, making a smooth scanning performance possible.

Most scanned interfaces are somewhat irregular and curved. If the boundary dimensions are significantly less than the wavelength or not smooth, the reflected waves will be diffused. Go Life needs your help to keep their mobile ultrasound units ready and available so women heading into abortion clinics can see their babies alive and moving. Together , we can be the first point of contact.

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Skip to content. Cherishing the Lives of Women. Schedule Appointment. Think of ultrasound imaging like the sonars you would find in submarines and boats. Great service and best regional pricing. May 06, Breast cancer: understanding the risks, symptoms, and ultimate prevention. Sep 26, If you want value in medical care, it pays to compare. This includes whether the object is solid or filled with fluid.

Doctors use ultrasound to detect changes in the appearance of organs, tissues, and vessels and to detect abnormal masses, such as tumors.

In an ultrasound exam, a transducer both sends the sound waves and records the echoing returning waves. When the transducer is pressed against the skin, it sends small pulses of inaudible, high-frequency sound waves into the body.

As the sound waves bounce off internal organs, fluids and tissues, the sensitive receiver in the transducer records tiny changes in the sound's pitch and direction.

A computer instantly measures these signature waves and displays them as real-time pictures on a monitor. The technologist typically captures one or more frames of the moving pictures as still images. They may also save short video loops of the images. Doppler ultrasound, a special ultrasound technique, 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. For most ultrasound exams, you will lie face-up on an exam table that can be tilted or moved. Patients may turn to either side to improve the quality of the images.

The radiologist a doctor specifically trained to supervise and interpret radiology exams or sonographer will position you on the exam table. They will apply a water-based gel to the area of the body under examination. The gel will help the transducer make secure contact with the body. It also eliminates air pockets between the transducer and the skin that can block the sound waves from passing into your body. The sonographer places the transducer on the body and moves it back and forth over the area of interest until it captures the desired images.

There is usually no discomfort from pressure as they press the transducer against the area being examined. However, if the area is tender, you may feel pressure or minor pain from the transducer. Very rarely, young children may need sedation to hold still for the procedure. Parents should ask about this beforehand and be made aware of prior food and drink restrictions that sedation requires.

Once the imaging is complete, the technologist will wipe off the clear ultrasound gel from your skin. Any portions that remain will dry quickly. The ultrasound gel does not usually stain or discolor clothing.

In some ultrasound exams, the doctor attaches a probe to the transducer and inserts into a body cavity. These exams include:. If the doctor performs a Doppler ultrasound exam, you may hear pulse-like sounds that change in pitch as they monitor and measure the blood flow. When the exam is complete, the technologist may ask you to dress and wait while the doctor reviews the ultrasound images.

A radiologist, a doctor trained to supervise and interpret radiology exams, will analyze the images. The radiologist will send a signed report to the doctor who requested the exam.

Your doctor will then share the results with you. In some cases, the radiologist may discuss results with you after the exam. You may need a follow-up exam. If so, your doctor will explain why.