According to Shannon's sampling theorem, the sampling frequency should be twice the frequency being sampled. The nyquist frequency is the maximum frequency that can be sampled without aliasing. In ultrasound imaging, it is defined as half of the pulse repetition frequency.
NF = PRF/2 (nyquist frequency = pulse repetition frequency/2)
This is the so-called Nyquist limit. If the velocity of flow exceeds the Nyquist limit, the direction and velocity are inaccurately displayed and appear to change direction. Color flow Doppler capitalizes on this effect. This allows detecting flow disturbances from laminar to turbulent flow.

See also Aliasing Artifact, Repetition Rate, and Sampling Rate.

Gynecologic ultrasound and obstetric ultrasound are two distinct applications of ultrasound imaging that serve different purposes in the field of women's health. While both involve the use of ultrasound technology to examine the pelvic region, they have different focuses and objectives.

Gynecologic [gynaecologic, Brit.] ultrasound primarily concentrates on the evaluation of the female reproductive organs, including the uterus, ovaries, fallopian tubes, and surrounding structures. It is commonly performed for various gynecological concerns, such as abnormal bleeding, pelvic pain, infertility investigations, and monitoring of reproductive disorders. It can identify signs of inflammation, the presence of free fluid, cysts, and tumors. This non-invasive technique aids in diagnosing and monitoring gynecological pathologies, facilitating early intervention and appropriate treatment. Typically, a transabdominal sonogram is performed with a full bladder to provide an initial assessment. However, if the pelvic ultrasound reveals any abnormalities or fails to provide a clear image of the organs, a more detailed evaluation can be achieved through a transvaginal sonography. This approach allows for improved visualization of the uterus and ovaries by placing the ultrasound probe inside the vagina.

Obstetric ultrasound, also known as prenatal, fetal or pregnancy ultrasound, is the branch of medical imaging that focuses on the use of ultrasound technology to assess the health and development of a fetus during pregnancy. Women with uncomplicated pregnancies commonly undergo an ultrasound examination between the 16th and 20th week of gestation. This routine assessment, performed with a real-time scanner, serves to determine accurate gestational age, monitor fetal size, and assess overall growth. The middle of the pregnancy trimester provides a crucial window for detecting many abnormalities of fetal anatomy. Advanced imaging techniques enable healthcare professionals to identify potential structural issues. Early detection of these abnormalities allows for timely intervention, counseling, and the implementation of appropriate management strategies.
See also Pregnancy Ultrasound, Pelvic Ultrasound, Hysterosalpingo Contrast Sonography and Vaginal Probe.

From GE Healthcare;;
Optison is the first 'second generation USCA' marketed in the US.
Ultrasound contrast agents used during an ultrasound imaging procedure, enable more accurate diagnosis of the patient's heart condition. The application of Optison allows to image the endocardial borders of the heart, to see cardiac wall motion abnormalities and to guide the selection and monitoring of treatment.
Optison represents a class of microbubbles with a shell formed by sonicating a solution of capsules filled with a perfluoropropane gas. The high molecular weight slows microbubble dissolution and prolongs the enhancement for several minutes. The human albumin-stabilized cavitation bubbles have a surface tension of 0.9 N/m and a surface dilatational viscosity 0.08 msP.

'August 06, 2001 Molecular Biosystems Inc., a subsidiary of Alliance Pharmaceutical Corp, announced the amendment of the Optison Product Rights Agreement (OPRA) dated May 9, 2000 with Mallinckrodt Inc, a unit of Tyco Healthcare. Optison, an intravenous ultrasound contrast agent, was developed by MBI and is being marketed by Mallinckrodt in the U.S. and Europe. Under the amended agreement, MBI will receive an immediate cash payment plus additional unspecified royalties for a two-year period. The amendment of OPRA coincides with an announcement by Nycomed Amersham Imaging that Nycomed and Mallinckrodt will terminate their joint commercialization and development agreement for ultrasound contrast agents, including Optison, effective Dec. 31, 2001. Effective Jan. 1, 2002, all selling and marketing activities will be resumed solely by Nycomed Amersham.'

A partial volume artifact is caused by the size of the image voxel. The loss of resolution is caused by multiple features present in the image voxel. In ultrasound imaging that occurs when the slice thickness is wider than the scanned structure. This artifact is also called slice thickness artifact or volume averaging artifact.

See also Ultrasound Picture.

Ultrasound is the ideal tool to examine children of all ages. It is fast, painless, uses no ionizing radiation, and does not require a baby to remain still for long periods. Real-time modes show movement of internal tissues and organs. Advanced ultrasound imaging techniques such as color Doppler, 4D ultrasound, harmonic imaging, and higher resolution, as well as the application of ultrasound contrast agents broaden the potential of ultrasound.
Pediatric [paediatric, Brit.] ultrasound can be used in all body regions and reduce the number of more invasive or radiating examinations that often additionally need sedation or intravenous iodinated contrast agents.

See also Fetal Ultrasound, Reflux Sonography, Ultrasound Safety, Abdominal Ultrasound and Pregnancy Ultrasound.