ACCORDING TO MAYO CLINIC GUIDELINES FOR ULTRASOUND PROCEDURES:

FETAL ULTRASOUND:

A fetal ultrasound is an imaging technique that uses high-frequency sound waves to produce images of a baby in the uterus.
Fetal ultrasound images can help your physician to evaluate your baby's growth and development and determine how your pregnancy is progressing. A fetal ultrasound might also give you the chance to study your baby's profile months before delivery. In some cases, fetal ultrasound is used to evaluate possible problems or confirm a diagnosis.
Fetal ultrasound is often done during the first trimester to confirm and date the pregnancy and again during the second trimester — between 18 and 20 weeks — when anatomic details are visible. If your baby's health needs to be monitored more closely, ultrasounds might be repeated throughout the pregnancy.

Why it's done?
A fetal ultrasound can be done at any point during pregnancy, to:
Confirm the pregnancy and its location. Some embryos develop in the fallopian tube instead of in the uterus. A fetal ultrasound can help to detect a tubal (ectopic) pregnancy. Determine your baby's gestational age. Knowing the baby's age can help to determine your due date and track various milestones throughout your pregnancy.

Confirm the number of babies. If your doctor suspects a multiple pregnancy, an ultrasound might be done to confirm the number of babies.
Evaluate your baby's growth. Your doctor can use ultrasound to determine whether your baby is growing at a normal rate. Ultrasound can be used to monitor your baby's movement, breathing and heart rate as well.

Study the placenta and amniotic fluid levels. The placenta provides your baby with vital nutrients and oxygen-rich blood. Too much or too little amniotic fluid — the fluid that surrounds the baby in the uterus during pregnancy — or complications with the placenta need special attention.

Identify birth defects. An ultrasound can help to detect various birth defects.

Investigate signs or symptoms. If you're bleeding or having other complications, an ultrasound might help to determine the cause.

Perform other prenatal tests. Your doctor might use ultrasound to guide needle placement during certain prenatal tests, such as amniocentesis or chorionic villus sampling.

Determine fetal position before delivery. A C-section might be needed if the baby is in an abnormal position.

Fetal ultrasound isn't recommended simply to determine a baby's sex — but it might be a bonus for curious parents when an ultrasound is done for medical reasons. Similarly, fetal ultrasound isn't recommended solely for the purpose of producing keepsake videos or pictures.
Doppler Ultrasound It uses reflected sound waves to estimate the speed and direction of blood as it flows through the vessels. The Doppler scan is done to evaluate blood flow to placenta and fetus (fetus nourishment).

Cervix assessment To measures the length of cervix as cervical shortening may increase a women risk of preterm labor.

Risks:

Routine fetal ultrasounds are considered safe for both mother and baby. Researchers haven't noted any adverse effects of fetal ultrasounds in children followed for several years after birth.
Still, caution remains important. The use of fetal ultrasound solely to create keepsakes isn't recommended.
Fetal ultrasound also has limitations. Fetal ultrasound might not detect all birth defects.

How to prepare?
Full bladder, to drink plenty of water or clear fluid 1-hour prior to scan.

The bladder needs to be full enough to see the entire uterus in early pregnancy, to localize the lower margin of the placenta and its relation to the Os, and to make the fetus assessment easier.

In normal cases 3 scans are usually needed for a pregnant lady. However, the total number of scans will vary depending on whether the previous scan has detected certain abnormalities that require follow up assessment.

First trimester (begins from conception to 12th weeks of pregnancy)
A First scan is usually done at about 7 weeks to confirm pregnancy, to detect fetal movement, to detect if there were any ectopic or molar pregnancies, to estimate the fetal age and to determine whether there is more than one fetus (such as twins or triplets).

Second trimester (from 13th to 27th weeks of pregnancy)
A second scan is preformed at 18 to 20 weeks to monitor the fetus well-being, determine Fetal presentation, locate and evaluate placenta position, assess the amount of liquor (amniotic fluid), evaluate fetal growth, detect if there was any structure abnormalities (check the fetal limbs, brain, stomach, kidneys, urinary bladder, spine, 4 heart chambers and 3 vessel cord).

Third trimester (from 28th to 40th weeks of pregnancy)
A third scan may sometimes be done at around 34 weeks to evaluate fetal growth, placenta position, Doppler study for the placental and cerebral circulation and to confirm the estimated date of delivery.

Also be aware that fetal ultrasound can be done through the vagina (transvaginal) or over the abdomen (transabdominal), depending on why it's being done or the stage of your pregnancy. If you're having a transabdominal ultrasound, consider wearing loosefitting clothing so that you can easily expose your abdomen.

During the exam During a trans-abdominal fetal ultrasound, you'll recline on an exam table and expose your abdomen. The radiologist will apply a special gel to your abdomen. This will improve the conduction of sound waves and eliminate air between your skin and the transducer — the small plastic device that sends out sound waves and receives those that bounce back.
The radiologist will move the transducer back and forth over your abdomen. The sound waves reflected off your bones and other tissues will be converted into black-and-white or gray images on a monitor.
The radiologist will measure your baby's head, abdomen, thighbone and other structures. He or she might print or store certain images to document important structures. You'll likely be given copies of some of the images.

After the exam You can wipe off any residual gel or lubricant. If you had a full bladder during the ultrasound, you'll be able to urinate after the exam.

Results:
Typically, a fetal ultrasound offers reassurance that a baby is growing and developing normally.

A 2-D fetal ultrasound can help your physician to
evaluate your baby's growth and development.

A 3-D fetal ultrasound can provide images of a developing
baby with photo-quality details.

ULTRASOUND ABDOMEN AND KUB US:

Definition:
Although an abdominal ultrasound can be done to check for a number of conditions, it can be used to check for diseases that affect your kidneys, liver, gallbladder and pancreas, it can be also used to screen for an abdominal aortic aneurysm for men ages 65 to 75 who are current or former cigarette smokers.

Why it's done?
Your doctor may recommend that you have an abdominal ultrasound if he or she thinks you have a problem with the organs in your abdomen, including:
Kidneys
Liver
Gallbladder
Pancreas
Spleen

How you prepare?

Adults: nothing to eat or drink for 8 hours before the examination.
If the UB and the pelvis is needed , the UB must be full and patient must drink water or clear fluid (no milk), at least 1-hour prior the appointment time. Patient should Not Empty his/her bladder before completing the examination.

Infant 0-1 year: usually no preparation.
To fill the UB feed up the baby with formula or water, 1 hour prior to examination.

Children 13 months-14 years: nothing to eat or drink 3 hours prior to the examination.
Again if the UB is needed in the study the child must drink water or juice (no milk) 1 hour prior to examination. Patient should NOT empty his or her bladder before completing the examination.

What you can expect?
During the procedure A typical ultrasound exam is painless and takes about 20 minutes to complete. You may be asked to change into a hospital gown for the procedure.
Your abdominal ultrasound is usually performed by a radiologist. During the exam, you lie on your back on an examination table and a small amount of warm gel is applied to your abdomen. The gel helps eliminate the formation of air pockets between your skin and the instrument, called a transducer.The doctor presses the transducer against your skin over your abdomen, moving from one area to another. The transducer sends images to a computer screen.

PELVIC ULTRASOUND:

Examination of soft tissue organs and structures in the pelvis, to find the cause of pelvic pain, such as an ectopic pregnancy in women, or to detect tumors or masses.

Preparation:

Adults: Full bladder, patient must drink water or clear fluid (no milk), at least 1-hour prior the appointment time.

Infant 0-1 year: feed up of formula or water, 1 hour prior to examination.

Children 13 months-14 years: Drink water or juice (no milk) 1 hour prior to examination.

Patient should NOT Empty his or her bladder before completing the examination.

DOPPLER ULTRASOUND:

Evaluating blood flow, it can determine if there are any problems within the veins and arteries.

A Doppler ultrasound may help diagnose many conditions, including:
Blood clots
Poorly functioning valves in your leg veins, which can cause blood or other fluids to pool in your legs (venous insufficiency).
A blocked artery (arterial occlusion)
Decreased blood circulation into your legs (peripheral artery disease).
Bulging arteries (aneurysms).
Narrowing of an artery in your neck (carotid artery stenosis)

During a Doppler ultrasound, the radiologist presses a small hand-held device (transducer), about the size of a bar of soap, against your skin over the area of your body being examined, moving from one area to another as necessary. This test may be done as an alternative to more-invasive procedures such as arteriography and venography, which involve injecting dye into the blood vessels so that they show up clearly on X-ray images.
A Doppler ultrasound test may also help your doctor check for injuries to your arteries or to monitor certain treatments to your veins and arteries.

No added Preparation

TRANSCRANIAL US:

Cranial ultrasound uses high-frequency sound waves to obtain images of the brain. An ultrasound doesn't produce a detailed image, but it may be used because it's quick and inexpensive, and it can provide a valuable preliminary assessment of the brain. The ultrasound device is placed over the soft spot (fontanel) on the top of a baby's head.

No added Preparation

MUSCULOSKELETAL UTRASOUND:

Ultrasound Offers Advantages in Musculoskeletal Disorders Diagnosis and Treatment
Recent advances in high-resolution ultrasound imaging present new opportunities for improving the care of patients with musculoskeletal injuries. Ultrasound uses sound waves to provide real-time, high-resolution images of tendons, ligaments, muscles, and nerves throughout the body.

Ultrasound as a Diagnostic Tool:

Calcification in supraspinatus tendon

Use of ultrasound to identify the source of painful shoulder. The image shows an S-shaped calcification (arrows) within and deforming the supraspinatus tendon.
"Ultrasound is a readily available and cost-effective imaging technique that can help us evaluate tendons, muscles, ligaments, and nerves. Ultrasound can also be performed live, allowing dynamic evaluation of ligaments and tendons, as well as guiding needles to target areas throughout the body. Finally, ultrasound does not use radiation and is therefore safe during pregnancy.

No added Preparation

BREAST ULTRASOUND:
Your doctor may recommend an ultrasound to help determine whether a breast abnormality is likely to be a fluid-filled cyst or a solid mass, which may be either benign or cancerous.
Breast ultrasound is helpful to guide radiologic biopsy to get a sample of breast tissue if a solid mass is found.

No added Preparation

NECK/THYROID ULTRASOUND:

Ultrasonography is a safe and effective method of determining the size and the presence of solid or cystic components within a thyroid nodule. High-resolution ultrasonography can be used to determine the presence of non palpable nodules as small as 1 mm within the thyroid tissue. Unfortunately, malignant thyroid nodules cannot be differentiated from benign thyroid nodules by this technique. In a review of published studies, use of conventional thyroid ultrasonography did not allow accurate prediction of the histology of solitary thyroid nodules. Its main indications are accurate measurement of size and as a guide for FNAB.

No added Preparation