Ultrasound Scan — Procedure Guide, Recovery & Risks | MyMedicPlus

An ultrasound scan (sonography) is a non-invasive, real-time diagnostic imaging procedure that uses high-frequency sound waves — typically in the range of 2-18 MHz — transmitted from a piezoelectric transducer probe through a coupling gel applied to the skin surface. Sound waves are emitted in pulses that penetrate body tissues, where they are partially reflected at interfaces between tissues of differing acoustic impedance (density); the reflected echoes are detected by the same probe and processed by a computer to generate high-resolution grey-scale images displayed in real-time on a monitor. Higher frequency probes (7.5-18 MHz) provide higher spatial resolution for superficial structures — thyroid, breast, peripheral tendons, superficial lymph nodes — at the cost of reduced tissue penetration; lower frequency probes (2-5 MHz) penetrate deeper tissues such as the liver, kidneys, and gravid uterus with reduced resolution. Colour Doppler and spectral Doppler modes interrogate blood flow velocity and direction within vessels, enabling vascular assessment, cardiac function evaluation (echocardiography), and organ perfusion analysis. Contrast-enhanced ultrasound (CEUS) uses intravenously injected microbubble contrast agents to characterise liver lesions and assess vascularity. Endocavitary probes — endovaginal (transvaginal) and endorectal — provide high-resolution imaging of pelvic organs, early pregnancy, and the prostate from within body cavities. Ultrasound involves no ionising radiation whatsoever, is portable, widely available at the point of care, and is the first-line imaging modality for many clinical presentations including pregnancy assessment, abdominal pain, and deep vein thrombosis evaluation.

Ultrasound is indicated across virtually all medical specialties for organ evaluation and procedural guidance. In abdominal medicine it is the first-line investigation for gallstones, bile duct dilation, liver pathology (fatty liver, cirrhosis, liver lesions), pancreatic disease, kidney stones, and renal mass evaluation. In obstetrics it is the primary imaging modality throughout pregnancy — from early viability confirmation to the 12-week nuchal translucency screen, 20-week anomaly scan, and third-trimester growth monitoring. In gynaecology it evaluates the uterus (fibroids, endometrium, congenital anomalies), ovaries (cysts, ovarian torsion, PCOS), and monitors follicle development in fertility treatment cycles. In vascular medicine, Doppler ultrasound diagnoses deep vein thrombosis (DVT), assesses carotid stenosis, peripheral artery disease, and aortic aneurysm surveillance. Musculoskeletal ultrasound evaluates tendons, ligaments, bursae, and joints for injury or inflammation. Neck ultrasound characterises thyroid and parathyroid nodules. Ultrasound also guides real-time procedures including biopsies, drain insertions, nerve blocks, and joint injections.

The patient lies on an examination table or couch, exposing only the area to be scanned. A water-based acoustic conductive gel is applied to the skin surface — this eliminates air between the transducer and skin, as air strongly reflects ultrasound and would produce a blank image. The sonographer or radiologist selects an appropriate transducer frequency: higher frequencies (7.5–18 MHz) provide excellent surface detail for thyroid, breast, and musculoskeletal structures but limited penetration depth; lower frequencies (2–5 MHz) penetrate deeper for abdominal and obstetric scanning. The transducer is pressed gently against the skin and moved systematically across the area of interest in multiple planes. For pelvic structures, a full bladder is required to displace bowel gas and provide an acoustic window; a transvaginal probe may be introduced vaginally for superior uterine and ovarian resolution, or a transrectal probe used for prostate imaging. Doppler mode is activated to assess blood flow in vessels. The sonographer or radiologist captures standardised still images and video clips, takes measurements (organ dimensions, lesion size, foetal biometry, vessel flow velocities), and documents any abnormal findings. Total examination time is 15–45 minutes depending on the clinical question. A written report is sent to the referring clinician within 24–48 hours.

Ultrasound is highly accurate for a range of specific clinical indications. Sensitivity and specificity for gallstones exceed 95% in a fasted patient with a distended gallbladder. Accuracy for biliary duct dilation, renal collecting system dilation, and detection of significant abdominal free fluid (ascites) is similarly high. Thyroid nodule characterisation using validated reporting systems (EU-TIRADS, ACR-TIRADS) achieves 90–95% accuracy in stratifying malignancy risk. Doppler ultrasound provides 90–95% sensitivity and specificity for proximal DVT and significant carotid stenosis. Point-of-care ultrasound in emergency medicine rapidly diagnoses cardiac tamponade, pneumothorax, haemoperitoneum, and abdominal aortic aneurysm rupture. Obstetric ultrasound detects approximately 80% of major foetal structural anomalies at the 20-week anomaly scan. Limitations include reduced image quality in obese patients, when overlying bowel gas obscures abdominal organs, and inability to reliably penetrate bone or air-filled structures such as the lungs, where CT provides superior information.

Ultrasound at diagnostic frequencies and intensities used in clinical medicine has no known harmful biological effects and is considered the safest diagnostic imaging modality available. Unlike X-ray, CT, or nuclear medicine imaging, it emits no ionising radiation and carries no associated cancer risk with any number of repeat examinations. There is no documented harm to any foetal structure from obstetric diagnostic ultrasound performed at standard clinical settings. The transducer produces a mild warming effect from acoustic absorption at tissue interfaces, but this is well below any threshold of biological significance at diagnostic intensities. The main clinical limitations of ultrasound are operator-dependence (image quality and diagnostic accuracy are significantly influenced by the skill and experience of the sonographer), reduced penetration and resolution in obese patients and when bowel gas obscures structures, and inability to adequately image structures behind bone or containing air. These limitations may necessitate follow-up CT or MRI for definitive characterisation of complex lesions.

No recovery time whatsoever is required following an ultrasound scan. The acoustic gel is wiped off with a tissue and the patient may immediately resume all normal activities, dietary intake, and medication without restriction. Preparation before the scan depends on the body region: fasting for 4–6 hours is required for upper abdominal ultrasound to ensure the gallbladder is maximally distended (bile accumulates during fasting, distending the gallbladder and revealing gallstones clearly) and to minimise bowel gas. A full urinary bladder (drinking one litre of water 1 hour before the scan and not urinating) is required for transabdominal pelvic ultrasound of the uterus, ovaries, and bladder. Kidney, thyroid, musculoskeletal, breast, and vascular scans require no specific preparation. Results from the written radiology report are communicated to the referring clinician within 24–48 hours in most radiology departments, with urgent findings communicated by telephone immediately.