As far as ultrasound is concerned, 4D ultrasound (also referred to as live 3D ultrasound or 4B-mode) is the latest ultrasound technology - the fourth dimension means length, width, and depth over time. 4D Ultrasound takes 3D ultrasound images and adds the element of time to the progress so that a moving three-dimensional image is seen on the monitor. A 4D scan takes the same amounts of time as a 2D or 3D scan; the difference is the ultrasound equipment being used. One advantage of a 4D fetal ultrasound to a 2D-mode is that parents can see how their baby will generally look like. However, there are different opinions over the medical advantages.
To scan a 3D ultrasound image, the probe is swept over the maternal abdomen. A computer takes multiple images and renders the 3D picture. With 4D imaging, the computer takes the images as multiple pictures while the probe is hold still and a 3D image is simultaneously rendered in real time on a monitor.
In most cases, the standard 2D ultrasound is taken, and then the 3D/4D scan capability is added if an abnormality is detected or suspected. The 3D/4D sonogram is then focused on a specific area, to provide the details needed to assess and diagnose a suspected problem. A quick 4D scan of the face of the fetus may be performed at the end of a routine exam, providing the parents with a photo.
See also Obstetric and Gynecologic Ultrasound, Pregnancy Ultrasound, Fetal Ultrasound and Abdominal Ultrasound.

Ultrasound technology has evolved significantly, providing sonographers with a wide range of ultrasound machines. As technology has advanced, portable ultrasound equipment, including handheld ultrasound systems, have emerged in the field of medical imaging. However, these devices may have limited imaging capabilities and reduced image quality compared to larger systems.
Types of ultrasound systems compiled according to their portability:

In summary, pros and cons of portable ultrasound machines:

See also Ultrasound Accessories and Supplies, Environmental Protection, Sonographer, Ultrasound Technology and Equipment Preparation.

Sonography [aka: ultrasonography] is a term that encompasses the entire process of performing ultrasound examinations and interpreting the obtained images.
Sonography involves the skilled application of ultrasound technology by trained professionals known as sonographers or ultrasound technologists. These specialists operate the ultrasound equipment, manipulate the transducer, and acquire the necessary pictures for diagnostic imaging purposes. Sonography requires in-depth knowledge of anatomy, physiology, and pathology to accurately interpret the ultrasound images and provide valuable information to the treating physician.
Sonography uses equipment that generates high frequency sound waves to produce images from muscles, soft tissues, fluid collections, and vascular structures of the human body. Obstetric sonography is commonly used during pregnancy. Sonography visualizes anatomy, function, and pathology of for example gallbladder, kidneys, pancreas, spleen, liver, uterus, ovaries, urinary bladder, eye, thyroid, breast, aorta, veins and arteries in the extremities, carotid arteries in the neck, as well as the heart.
A typical medical ultrasound machine, usually a real-time scanner, operates in the frequency range of 2 to 13 megahertz.

See also Musculoskeletal and Joint Ultrasound, Pediatric Ultrasound, Cerebrovascular Ultrasonography and Contrast Enhanced Ultrasound.

The main advantage of ultrasound is that certain structures can be observed without using radiation. However, ultrasound is energy and there are ultrasound safety regulations, because two bioeffects of ultrasound are heat and cavitation. Ultrasound is a mechanical energy in which a pressure wave travels through tissue. Reflection and scattering back to the transducer are used to form the image. As sound energy is transmitted through the tissue, some energy is reflected and some power is absorbed.
Possible physical effects with ultrasound:
The ultrasound safety is based on two indices, the mechanical index (MI) and the thermal index (TI). The WFUMB guidelines state that ultrasound that produces temperature rises of less than 1.5°C may be used without reservation. They also state that ultrasonic exposure causing temperature rises of greater than 4°C for over 5 min should be considered potentially hazardous. This leaves a wide range of temperature increases which are within the capability of diagnostic ultrasound equipment to produce and for which no time limits are recommended. However, it has not been determined that medical ultrasound causes any adverse reaction or deleterious effect.
The American Institute of Ultrasound in Medicine states that as of 1982, no independently confirmed significant biologic effects had been observed in mammalian tissue below (medical usage) 100mW/cm2.

See also Ultrasound Regulations and Ultrasound Radiation Force.

Urologic ultrasound includes the examination of the kidneys, renal vessels, urinary tract, bladder, prostate, and scrotum.
Usual gray scale ultrasound equipment and standard probes are sufficient to examine the kidney parenchyma and renal pelvis, the urinary tract and bladder. Doppler ultrasound is a useful adjunct to kidney ultrasound. High ultrasound system performance is desirable to show the arterial system, because advanced power Doppler is significantly more sensitive to blood flow than standard color Doppler.
Transurethral sonography may be used to examine the bladder and urethra. Transrectal sonography is used to scan and treat the prostate e.g., with brachytherapy or high intensity focused ultrasound. Very small probes are used for these applications. Reflux sonography is especially used in pediatric ultrasound.

See also Ultrasound Imaging Procedures, Ultrasound Picture, Ultrasound Imaging Modes, Lithotripsy, Thermotherapy, Brachytherapy and Ultrasound Therapy.