X-Ray — Purpose, Procedure & Normal Values | MyMedicPlus

An X-ray (radiograph) is a medical imaging examination that uses a precisely controlled beam of ionising electromagnetic radiation — X-rays, which are high-energy photons — to produce two-dimensional projected images of the body's internal structures on a digital detector or photographic film. X-ray photons interact with body tissues according to their atomic density and composition: highly dense structures such as cortical bone and calcified structures absorb most X-rays and appear white (radiopaque) on the image; intermediate-density soft tissues such as muscle and organs allow partial transmission and appear in shades of grey; air-filled structures (lungs, bowel, sinuses) absorb almost no X-rays and appear black (radiolucent). Digital radiography — the standard in modern radiology departments — uses flat panel detectors to capture X-ray images electronically, producing high-resolution images instantly, allowing immediate post-processing enhancement, and delivering substantially lower radiation doses than older screen-film systems. X-rays are the fastest, most widely available, and most cost-effective diagnostic imaging modality worldwide and remain the essential first-line investigation for fractures, chest disease, and a broad range of orthopaedic, thoracic, and abdominal conditions encountered in emergency and elective clinical practice.

The clinical indications for X-ray span virtually every medical specialty. Chest X-ray (the most frequently performed plain radiograph globally): diagnoses pneumonia (lobar or bronchopneumonia consolidation), congestive heart failure (cardiomegaly, upper lobe diversion, Kerley B lines, pleural effusion), spontaneous or traumatic pneumothorax (absent lung markings with a visible lung edge), pleural effusion (blunting of costophrenic angles, meniscus sign), lung cancer (pulmonary mass, hilar enlargement, lymphadenopathy), rib fractures, aortic widening or dissection, and foreign body aspiration. Bone and skeletal X-rays: detect and characterise fractures (location, type — transverse, spiral, comminuted, avulsion — and displacement or angulation), assess osteoporosis (vertebral crush fractures, trabecular changes), identify bone tumours (primary — osteosarcoma, giant cell tumour; secondary — metastatic deposits), diagnose osteomyelitis (periosteal reaction, bone destruction), evaluate joint degeneration in osteoarthritis (joint space narrowing, osteophytes, subchondral sclerosis), and localise foreign bodies. Abdominal X-ray: identifies bowel obstruction (dilated loops with air-fluid levels), free intraperitoneal gas under the diaphragm (bowel perforation — a surgical emergency), calcified renal or biliary calculi (though CT is more sensitive), large bowel volvulus, and abdominal aortic calcification. Spinal X-rays: assess scoliosis (Cobb angle measurement), vertebral fractures (osteoporotic wedge fractures), disc space narrowing, and spondylolisthesis. Dental X-rays (bitewing, periapical, panoramic OPG): detect dental caries, periapical abscesses, periodontal bone loss, and impacted teeth.

For most plain X-rays (chest, limbs, spine, pelvis), no preparation is required. Remove all metal objects from the area to be X-rayed, as these are fully radiopaque and create dense artefacts that obscure the underlying anatomy — metal jewellery, earrings, necklaces, rings, watches, body piercings, hair clips, and clothing with metal zips, buttons, underwires, or decorative metallic embellishments. You will usually be asked to change into a hospital gown for torso X-rays. Leave your watch and valuables securely in the changing room or with a companion. For barium contrast X-ray studies — barium swallow (oesophagus), barium meal (stomach and duodenum), or barium enema (colon) — specific, detailed preparation instructions are provided by the radiology department when the examination is booked, and typically include bowel preparation (laxatives) and fasting for variable periods. Always clearly inform the radiographer before any X-ray examination if you are pregnant or think you could be pregnant — even when the X-ray involves a body part distant from the uterus, the radiographer will apply a lead shield to the lower abdomen if feasible, or arrange an alternative imaging modality if the pelvic region must be imaged.

You are positioned by the radiographer in the specific anatomical position required for the views being taken — standing, sitting, or lying on the X-ray table, according to the clinical question and the patient's ability to cooperate. For a standard chest X-ray, you stand facing a vertical digital detector, arms positioned out of the lung fields, and take and hold a deep breath in — full lung inflation improves image quality and reduces cardiac magnification. The X-ray tube behind you emits a very brief burst of X-rays lasting less than one second. For an acute trauma or non-ambulant patient, a portable anteroposterior (AP) chest X-ray is taken with the patient supine in bed using a mobile X-ray unit. Two orthogonal views (at 90 degrees to each other) are standard for fracture assessment — for example, anteroposterior (AP) and lateral for a wrist, ankle, or knee. Oblique views or stress views may be added for specific joints (scaphoid wrist series, stress ankle views). The radiographer steps behind a lead-shielded protective screen or wall during the exposure. For children and patients who cannot cooperate, immobilisation or parental assistance (with lead apron protection) may be required. The appointment including positioning and any additional views typically takes 5–15 minutes.

A radiologist — a medical doctor specialising in imaging interpretation — reviews the digital images on a high-resolution diagnostic monitor (minimum 2-megapixel resolution for chest X-ray reporting) and issues a written, structured radiology report. For emergency and urgent studies, a preliminary report is communicated directly to the referring clinician within 30–60 minutes, with a final report following. Routine studies are reported within 24 hours in most radiology departments. The report describes each anatomical structure within the field of view systematically, notes any radiological abnormalities, and provides an impression with differential diagnoses and recommendations. Key chest X-ray landmarks and measurements: cardiac silhouette — cardiothoracic ratio above 0.5 on a PA film indicates cardiomegaly; pleural effusion — blunting of the costophrenic angle; pneumothorax — visible visceral pleural line with absent lung markings beyond it; consolidation — homogeneous opacification with air bronchograms; interstitial shadowing — Kerley B lines, ground-glass opacity. Fracture reporting includes: anatomical location, fracture pattern (transverse, oblique, spiral, comminuted, impacted, avulsion), displacement (angulation in degrees, shortening, rotation), and articular involvement. Your referring doctor receives the report and will discuss the findings at your clinical appointment.

Medical X-rays use very small doses of ionising radiation — the effective dose varies substantially by body region and view. Reference doses for common studies: chest X-ray (PA) approximately 0.02 mSv (equivalent to 2–3 days of natural background radiation from cosmic rays, soil, and radon); hand X-ray less than 0.001 mSv; lumbar spine X-ray (AP and lateral combined) approximately 1.5 mSv (6 months of background); pelvis X-ray approximately 0.7 mSv; abdominal X-ray approximately 0.7 mSv; mammogram approximately 0.4 mSv per breast. For comparison, a CT scan of the abdomen delivers approximately 8–10 mSv. All medical X-rays operate under the internationally accepted ALARA principle (as low as reasonably achievable) — each examination is justified only when the clinical diagnostic benefit clearly outweighs the very small but non-zero theoretical radiation risk from the dose delivered. The main diagnostic limitation of plain X-ray is its poor soft tissue contrast — CT and MRI provide far superior differentiation between soft tissue structures including organs, ligaments, tendons, cartilage, spinal cord, and cranial contents. Many important pathologies are invisible on plain X-ray: acute ischaemic stroke, pulmonary embolism, early osteomyelitis, cartilage damage, ligament tears, disc herniation, peritoneal metastases, and small lesions below 5–10 mm. Occult and hairline fractures, particularly of the scaphoid, hip (femoral neck stress fractures), ribs, and midfoot, may be completely invisible on plain X-ray and require MRI or CT for definitive diagnosis.