Maharashtra HSC Radiology Technician (Vocational) key terms

Process in which an incoming X-ray photon transfers all its energy to an inner-shell electron, ejecting it and producing a photoelectron. It dominates at low kVp and in high-atomic-number tissues such as bone, and creates most subject contrast.

Interaction where a photon strikes an outer-shell electron, gives up part of its energy, and is deflected in a new direction. Scattered photons add fog to the image and dose to staff, so it is reduced by collimation and grids.

Reduction in intensity of an X-ray beam as it passes through matter, caused by absorption and scattering. It increases with tissue thickness, tissue density, atomic number, and lower photon energy.

Thickness of a specified absorber, usually aluminium, that reduces beam intensity to half its original value. It measures beam quality or penetrating power and is checked during routine equipment quality control.

Maximum voltage applied across the X-ray tube during exposure, expressed in kVp. It sets photon energy and penetrating power; raising kVp shortens the scale of contrast and reduces patient skin dose for a given receptor exposure.

Product of tube current in milliamperes and exposure time in seconds, giving total charge and therefore the number of X-ray photons produced. It controls receptor exposure and image density rather than beam penetration.

Uneven beam intensity across the X-ray field because photons produced deeper in the angled anode target are absorbed by the target itself. Intensity is lower on the anode side, so thicker patient parts are usually placed toward the cathode.

Small area on the anode target where X-rays are generated. A smaller focal spot gives sharper images but limits tube current, so large focal spots are used where heat loading is high.

Distance from the X-ray tube focal spot to the image receptor. It affects magnification, geometric unsharpness, and receptor exposure, since intensity falls with the square of distance.

Distance between the anatomical part being examined and the image receptor. Keeping it small reduces magnification and blur, so the part is placed as close to the receptor as the position allows.

Blurring of structure edges caused by the finite size of the focal spot and by the distances involved. It is reduced by a small focal spot, a long source-to-image distance, and a short object-to-image distance.

Enlargement of the projected image compared with the true object size, produced by divergence of the beam. It increases as the object moves away from the receptor and is calculated as the ratio of source-to-image to source-to-object distance.

Statement that radiation intensity from a point source is inversely proportional to the square of the distance from it. Doubling the distance reduces intensity to one quarter, which underpins distance protection and exposure calculations.

Path of the central ray through the patient onto the receptor, described by the entrance and exit points. Naming the projection precisely prevents wrong-side and wrong-view repeats in clinical practice.

Central axis of the X-ray beam, aimed at a specific anatomical point for each projection. Correct alignment of the central ray with the part and receptor controls distortion and ensures reproducible positioning.

Palpable surface point, such as the iliac crest, xiphoid process, or jugular notch, used to align the central ray and receptor. Reliable landmarks allow consistent positioning when body habitus varies.

Range of grey levels recorded on an image, from short scale with high contrast to long scale with low contrast. It is mainly influenced by kilovoltage and by the type of image receptor used.

Numeric value reported by a digital system that estimates receptor exposure. It guides correction of technique but is not a direct patient dose measurement and varies between manufacturers.

Digital display control that sets the range of pixel values mapped to visible grey levels. A wide window shows more soft-tissue shades, while a narrow window increases displayed contrast.

Digital display control that sets the central pixel value around which grey levels are distributed. Adjusting it brightens or darkens the displayed image without changing the stored data.

Computer-based alteration of stored digital image data after acquisition, including edge enhancement, smoothing, and grey-scale changes. It improves visibility but cannot recover information never captured.

Ratio of the height of lead strips in an anti-scatter grid to the distance between them. Higher ratios remove more scatter but demand more precise alignment and higher exposure factors.

Restriction of the X-ray beam to the area of clinical interest using adjustable shutters. It reduces patient dose, scatter, and fog, and the light field must match the exposed area.

Planned programme of checks and maintenance that keeps radiographic equipment and processing within accepted performance limits. It includes tests of output, kilovoltage accuracy, beam alignment, and image quality.

Measurement of a film's response to graded exposures, producing a characteristic curve of density against log exposure. It monitors developer activity, film speed, and contrast in darkroom quality control.

Degree of blackening of a processed radiograph, measured as optical density on a logarithmic scale. Adequate density is needed to see detail, and it depends on exposure and processing conditions.

Darkroom lamp fitted with a filter that emits light to which the film is least sensitive. It allows handling of film during processing, and its distance, wattage, and filter must be checked to avoid fog.

Tissue-weighted sum of equivalent doses across the body, expressed in sieverts, reflecting overall radiation risk. It allows comparison of different examinations and procedures with natural background exposure.

Energy deposited by ionising radiation per unit mass of material, measured in gray. It describes physical energy transfer and is the basis for calculating equivalent and effective dose.

Practice of keeping radiation doses as low as reasonably achievable, taking economic and social factors into account. It is applied through collimation, shielding, distance, and good technique.

Personal monitoring badge containing lithium fluoride crystals that store energy from radiation and release light when heated. It records cumulative dose over a wearing period and must be worn correctly.

Protective garment with lead or lead-equivalent material worn by staff and carers during exposures. It attenuates scattered radiation, and its integrity should be checked radiographically for cracks.

Structured measurement of radiation levels in and around an X-ray facility to confirm shielding and safe working practice. Results are documented and compared with regulatory dose limits.

Describes material or tissue that allows X-rays to pass readily, appearing dark on the image. Air in the lungs and gas in bowel are typical examples, in contrast to bone.

Describes material that absorbs X-rays strongly and appears white or light on the image. Bone, metal implants, and positive contrast agents are common examples.

Substance introduced into the body to increase difference in attenuation between structures. Barium sulphate and iodinated compounds are used for gastrointestinal and vascular studies respectively.

Examination using barium sulphate suspension to outline the gastrointestinal tract. It is preferred for suspected perforation because it is not absorbed, unlike water-soluble iodinated media.

Real-time X-ray imaging using a continuous or pulsed beam displayed on a monitor. It guides contrast studies and procedures, and staff must manage dose because exposure times can be long.

Severe, rapidly developing systemic allergic reaction with airway swelling, breathing difficulty, and falling blood pressure. It is a recognised risk of iodinated contrast injection and needs immediate adrenaline and emergency support.

Voluntary agreement to a procedure given after the patient receives and understands information about its purpose, risks, benefits, and alternatives. It must be documented and can be withdrawn at any time.

Duty to keep a patient's personal and clinical information private and share it only with those involved in care. Breach can harm trust and carries ethical and legal consequences.

Obligation of a radiographer to practise within competence, follow protocols, report errors, and put patient safety first. It includes accurate documentation and refusing tasks beyond one's training.