What ultrasound can see, and what it honestly cannot
Ultrasound is brilliant at some questions and blind to others, and knowing which is which makes every scan make sense. Choose your scan type for the honest picture.
Abdominal ultrasound
Liver, gallbladder, pancreas, spleen, kidneys and the abdominal aorta.
Sees well
Gallstones and gallbladder wall changes
Liver size and texture, and many liver lesions
Kidney size, stones that are large enough, and blockage (swelling)
Fluid where fluid should not be
The width of the abdominal aorta
Honestly, less well
Organs hidden behind bowel gas, especially the pancreas
The bowel itself: air blocks sound almost completely
Very deep structures in larger bodies: sound weakens with distance
How it feels
Warm gel, firm but painless probe pressure, a few held breaths ("breathe in and hold").
How long
Usually 15 to 30 minutes.
Preparation in one line: Usually fasting for about 6 hours so the gallbladder is full and gas is low. Full prep checklist
Abdominal ultrasound
Liver, gallbladder, pancreas, spleen, kidneys and the abdominal aorta.
Sees well: Gallstones and gallbladder wall changes; Liver size and texture, and many liver lesions; Kidney size, stones that are large enough, and blockage (swelling); Fluid where fluid should not be; The width of the abdominal aorta
Less well: Organs hidden behind bowel gas, especially the pancreas; The bowel itself: air blocks sound almost completely; Very deep structures in larger bodies: sound weakens with distance
Prep: Usually fasting for about 6 hours so the gallbladder is full and gas is low.
Pelvic ultrasound
Bladder, womb and ovaries, or the prostate region, through the lower tummy.
Sees well: The womb lining and many ovarian cysts; Bladder wall and how well the bladder empties; Fibroids of meaningful size
Less well: Fine detail with an empty bladder: the full bladder is literally the viewing window; Ovaries hidden behind bowel gas; Early-stage or very small changes: sometimes an internal (transvaginal) scan is offered for a closer look
Prep: A full bladder: finish about a litre of water an hour before, and do not empty it.
Pregnancy ultrasound
The baby, the placenta, the fluid around the baby, and blood flow to the womb.
Sees well: Pregnancy dating in the first trimester (the most accurate time to date); Growth, position, placenta location and fluid volume later on; Heartbeat and movement, usually shown to you as you watch
Less well: Everything, when the baby faces the wrong way: some views simply require patience or a second visit; Guaranteeing normality: a normal scan is reassuring, not a promise; Keepsake-quality faces: clinical scans optimise for measurements, not portraits
Prep: Early pregnancy: full bladder. Later scans: usually no prep.
Thyroid and neck ultrasound
The thyroid gland, lymph nodes and salivary glands.
Sees well: Thyroid nodules, their size and their features; Enlarged lymph nodes and their shape; Guidance for a needle sample (FNA) if one is ever needed
Less well: Whether a nodule is active or lazy: that is blood-test and nuclear-medicine territory; Anything behind the breastbone: bone blocks sound
Prep: No preparation at all.
Vascular (Doppler) ultrasound
Blood flow: neck arteries, leg veins and arteries, and grafts or fistulas.
Sees well: Narrowing in the carotid arteries and how flow is coping; Clots in leg veins (the DVT question, answered without radiation); Flow through bypass grafts and dialysis fistulas
Less well: Vessels deep in the pelvis or chest; Heavily calcified arteries, where shadowing hides the channel
Prep: Usually none; abdominal Doppler studies may need fasting per your letter.
Muscles and joints ultrasound
Tendons, muscles, ligaments and the soft tissue around joints.
Sees well: Rotator cuff and Achilles tendon problems; Fluid collections, cysts and many soft-tissue lumps; Movement: ultrasound watches tendons glide live, which MRI cannot
Less well: Inside the joint and the bone itself: that is X-ray and MRI territory; Deep hip structures in larger bodies
Prep: No preparation; wear clothing that exposes the joint.
Reviewed against NHS ultrasound guidance and RadiologyInfo.org (ACR / RSNA) patient information.
Ultrasound builds its pictures from high-frequency sound waves and their echoes, the same physics a bat uses to fly in the dark. No ionising radiation is involved, which is why it is the first-line tool in pregnancy and can be repeated as often as needed without dose worries.
The trade-off is physics, not effort: sound will not cross air or bone, and it fades with depth. That is why the same scan can be crystal clear in one person and limited in another, and why an honest report sometimes says so out loud. When ultrasound hits its limits, CT and MRI take over: different physics, different strengths.
