Every radiology resident scans in the first year, often alone on call. This guide covers the ultrasound basics you need on day one: choosing a probe, the knobs that matter, the artifacts that fool beginners, Doppler without tears and the normal measurements you will quote every day.
Choosing the right transducer
| Probe | Typical frequency | Use it for |
|---|---|---|
| Linear | about 5–15 MHz | Thyroid, neck, breast, scrotum, MSK, superficial lumps, vessels, appendix in thin patients |
| Curvilinear (curved) | about 2–6 MHz | Abdomen, pelvis, obstetrics, large patients |
| Phased array (sector) | about 1–5 MHz | Heart, between ribs, FAST views through small windows |
| Endocavitary | about 5–10 MHz | Transvaginal gynaecology and early pregnancy, transrectal prostate |
The rule is simple: higher frequency gives better resolution but less penetration. Use the highest frequency that still reaches the structure you need.
Knobology: the six controls that matter
- Depth: put the area of interest in the middle of the screen, with a little tissue below it. Too deep wastes resolution and frame rate.
- Gain: brightens the whole image after the echoes return. Fluid (bladder, gallbladder) should look black; if it looks grey, gain is too high.
- Time gain compensation (TGC): sliders that adjust brightness by depth so the image is even from top to bottom.
- Focus: place the focal zone at or just below the level of interest for the best lateral resolution.
- Frequency/preset: start with the correct exam preset (abdomen, thyroid, vascular) and adjust from there.
- Freeze, measure and label: label every image with side, organ and plane so someone else can follow your study.
Orientation: in radiology convention the probe marker points to the patient's head (longitudinal) or the patient's right (transverse), and that side appears on the left of the screen.
Artifacts every resident should know
| Artifact | Looks like | Why it matters |
|---|---|---|
| Acoustic shadowing | Dark band behind a strong reflector | Confirms gallstones, renal stones and calcification |
| Posterior enhancement | Bright band behind a structure | Fluid-filled lesions such as simple cysts |
| Reverberation | Equally spaced parallel lines | Seen near the skin and behind gas; can mimic debris in a cyst |
| Comet-tail | Short tapering bright tail | Cholesterol crystals in adenomyomatosis |
| Ring-down | Long continuous bright streak | Gas bubbles, for example in bowel or emphysematous infection |
| Mirror image | Duplicate structure across a strong reflector | Liver "above" the diaphragm; don't call a lung lesion |
| Twinkling | Rapid colour mix behind a rough surface on Doppler | Helps confirm small renal stones |
| Anisotropy | Tendon looks dark when the beam is not perpendicular | Can mimic tendinopathy or a tear in MSK scanning |
Doppler in five rules
- Colour Doppler shows direction and mean velocity; power Doppler is more sensitive to slow flow but shows no direction; spectral Doppler gives the waveform and velocities.
- Keep the angle of insonation at 60° or less for velocity measurements, and align the angle-correction cursor with the vessel.
- Aliasing (colour wrap or a cut-off spectral peak) means the scale/PRF is too low: raise the scale, lower the baseline, use a lower frequency or reduce depth.
- Set the colour box small and just over the vessel: a large box lowers the frame rate.
- Know the normal waveforms: low-resistance (internal carotid, renal, hepatic artery) versus high-resistance triphasic (resting peripheral limb arteries).
Normal measurements to memorise
| Structure | Usual upper limit of normal (adults) |
|---|---|
| Common bile duct | about 6 mm (wider after cholecystectomy and with age) |
| Gallbladder wall | 3 mm |
| Portal vein diameter | about 13 mm |
| Spleen length | about 12–13 cm |
| Kidney length | about 10–12 cm (a difference of more than 2 cm between sides is significant) |
| Abdominal aorta | under 3 cm (3 cm or more is an aneurysm) |
| Appendix | 6 mm outer diameter, compressible |
| Postmenopausal endometrium in a woman with bleeding | 4 mm or less is reassuring in most guidelines |
Ranges vary between textbooks and guidelines; use your department's reference values in reports.
A simple routine for on-call scans
- Right upper quadrant: gallbladder in two planes (stones, wall, pericholecystic fluid, sonographic Murphy's sign), CBD, liver, right kidney.
- Renal: both kidneys in two planes, measure length, look for hydronephrosis and stones, then the bladder.
- FAST: hepatorenal pouch (Morison's), splenorenal, pelvis and pericardium for free fluid.
- Write the report as you scan: answer the clinical question in the first line of the conclusion.
If you are preparing for a sonography registry, read our ARDMS SPI guide and try the free ARDMS questions.
Frequently asked questions
Which ultrasound probe should I use for the abdomen?
A curvilinear (curved) probe of about 2–6 MHz, because it penetrates deeply and gives a wide field of view. Switch to a linear probe for the bowel wall, appendix or abdominal wall.
How do I fix aliasing on colour Doppler?
Increase the scale (PRF), lower the baseline, use a lower transducer frequency, or reduce the depth so the PRF can rise.
What does posterior acoustic enhancement mean?
The tissue behind a structure looks brighter because sound passed through it with little attenuation. It is typical of fluid-filled structures such as simple cysts.
How long does it take to become good at ultrasound?
Most residents become safe at common abdominal scans after a few months of supervised daily scanning. Scan normal anatomy as often as possible: recognising normal is what makes abnormal stand out.
Written by the Radiology Boards team from standard ultrasound physics and practice. Normal values are typical adult reference ranges; follow local guidelines.