Fluoroscopy (General)

Fluoroscopy is the real time radiographic imaging of moving structures. It uses a continuous or pulsed x-ray beam and an image detector, usually a flat panel digital detector, with images displayed on monitors.

It is the basis of contrast studies (swallows, enemas, urography, cystography, arthrography, myelography and fistulography).

It is also the basis of procedures under image control (needle placement, drain and stent insertion, angiography, vascular and non-vascular interventions, pain injections, line placement, fracture reduction, orthopaedic surgery, endoscopic retrograde cholangiopancreatography, pacemaker and cardiac catheter lab work).

It supports functional assessment (diaphragm movement, joint motion, swallowing, and gastric emptying).

Images are acquired as continuous fluoroscopy (low dose rate), as pulsed fluoroscopy (3 to 15 pulses each second, lowering dose), as digital spot images and cine (higher dose), and as digital subtraction images.

The last image is held on screen after exposure ends (last image hold) so that the operator can review it without more radiation.

The dose rate in ordinary fluoroscopy is about 10 to 30 mGy each minute at the patient entrance surface. It may reach 100 mGy each minute or higher in large patients or in a high dose mode. Cine acquisition is 10 to 60 times higher than fluoroscopy.

Fluoroscopy is one of the largest contributors to medical radiation exposure for staff and patients, as procedure times can be long. Effective doses range from 1 to 10 mSv for diagnostic studies to 10 to 50 mSv or more for complex interventional procedures.

Staff doses are due to scatter from the patient, so the operator is exposed to the highest dose.

Deterministic effects (skin burns, hair loss, cataracts) occur at these skin doses:

• about 2 Gy: early erythema
• 3 to 5 Gy: epilation and moist desquamation
• over 10 Gy: necrosis

Cataract risk in staff is related to the cumulative lens dose. The principles are justification, optimisation (dose as low as reasonably achievable), and dose limits for staff.

Indications. Any examination or procedure where real time or dynamic imaging is needed:

• dynamic contrast studies of the gastrointestinal, urinary, genital and biliary tracts
• joint and spinal injections and arthrography
• vascular access and angiography
• drainage and biopsy under image control
• line, catheter, tube and drain placement and exchange
• orthopaedic fracture reduction and fixation in theatre
• swallow assessment
• assessment of diaphragm movement (sniff test) and tracheal motion
• localisation of foreign bodies
• pacing wire and cardiac device work
• endoscopic retrograde cholangiopancreatography
• ureteroscopy and stone treatment
• check of tubes and prostheses

Not when ultrasound, MR or a still radiograph answer the question without ionising radiation.

Contraindications and precautions.

• Pregnancy: avoid or use ultrasound or MR. When unavoidable, keep the beam away from the uterus and shorten the exposure.
• Children: lower dose settings, pulsed fluoroscopy at low rates, tight collimation, and no anti-scatter grid for small children.
• Previous high skin dose: avoid the same entry field.
• Allergy to the contrast agent where contrast is used.
• Women of reproductive age: a pregnancy test or a check of the menstrual dates as local policy requires.
• Unstable patients: monitoring and resuscitation equipment needed.

Staff protection:

• lead aprons (0.25 to 0.5 mm lead equivalent)
• thyroid collars
• lead glasses (reduce lens dose by a factor of about 5)
• ceiling suspended shields and table side curtains
• dosimeters at collar level and under the apron
• training

Preparation and technique.

• The patient is positioned on the table.
• The field is collimated tightly to the region of interest.
• The detector is placed as near as possible to the patient and the x-ray tube as far as possible.
• The lowest dose rate and pulse rate that give an adequate image are chosen, and magnification modes are avoided.

The beam angle is varied during long procedures to spread the skin dose over different areas. Fluoroscopy time and dose area product are recorded, and an alert is set at cumulative air kerma of 3 to 5 Gy.

Operators stay as far from the beam as practical, stand on the side of the detector (low scatter) rather than the tube side, and wear protection.

Normal appearances. Fluoroscopy shows the normal moving anatomy in real time:

• the diaphragm rises and falls symmetrically with breathing (excursion of 3 to 6 cm in quiet breathing, up to 10 cm in deep breathing, with the right hemidiaphragm usually 1 to 2 cm higher than the left)
• the heart and great vessels pulsate
• the pharynx and oesophagus show peristalsis
• the stomach shows peristaltic waves and the duodenal cap fills and empties
• the small bowel moves contrast steadily to the caecum
• joints move through a smooth range without clicks, catches or displacement

Contrast flows smoothly through the vessels, ducts and tracts, and fills hollow organs without leaks. Instruments, catheters and wires are seen as dense lines and are followed in real time. Metal implants appear as dense structures with their normal alignment.

Interpretation.

• Diaphragm movement: paradoxical movement on the sniff test (the diaphragm rises on sniffing instead of descending) indicates phrenic nerve palsy or paralysis.
• Reduced diaphragm movement suggests weakness, splinting from pain, basal disease or adhesions.
• A diaphragm that moves less than 1 cm on sniff in a unilateral palsy is abnormal. Bilateral palsy shows reduced movement on both sides, with abdominal paradox.
• Motility and function: delayed or disordered peristalsis, spasm, reflux, delayed emptying, retained contrast, and obstruction are judged by real time observation, which static films cannot show.
• Joint and spine instability: abnormal motion between vertebrae or between bones on flexion and extension, subluxation, and locking.
• Vascular and cardiac: calcification of valves or coronary arteries, pulsation of aneurysm, prosthetic valve motion (a restricted disc or leaflet suggests thrombus or pannus), and catheter position.
• Foreign body localisation: movement with respiration and swallowing helps decide whether a radio opaque object is within a lumen, a lung, or soft tissue.
• Tube, line and device position: the tip and course of a nasogastric tube, central line, pacemaker lead, drain, stent or catheter are confirmed, and any kinks, fractures, migration and malposition are identified.
• Procedural assessment: needle position and the spread of injected contrast confirm correct placement (for example, an epidural or facet joint injection with a vascular uptake pattern in a blood vessel, or intra-articular spread in a joint).
• Stone and urological treatment: stone fragmentation and positioning of stents are checked.
• Radiation dose data: the fluoroscopy time, the dose area product and the cumulative air kerma are recorded for each procedure and for audit.

Critical values and findings needing immediate action.

• Skin dose estimated at over about 2 to 3 Gy (long or complex procedure): record it in the notes, inform the patient, arrange skin follow up at 2 to 4 weeks, and give advice about skin care and delayed effects.
• Skin dose over 5 Gy needs specialist dermatology review.
• Contrast reaction during a procedure: stop injection, give adrenaline for anaphylaxis, oxygen and fluids, and call for help.
• Vascular injury, perforation, pneumothorax or haemorrhage during a procedure: resuscitation, tamponade or reversal, and surgical or interventional review.
• Equipment fault with continuous exposure: release the pedal, stop the procedure, and report the fault.
• Pregnancy discovered after exposure: estimate the foetal dose with a physicist, counsel the patient (most diagnostic doses are under the threshold for harm), and record.
• Staff dose over the investigation level on the dosimeter: review of practice, equipment and protection.

Limitations and artefacts.

• Radiation exposure is the chief limitation. Dose rises with patient size (a thick patient needs a higher dose, with scatter to staff), with long screening time, with magnification, with cine and subtraction runs, and with an oblique beam angle.
• Deterministic injuries are preventable and often unrecognised for weeks (the skin reaction may be delayed 2 to 4 weeks or longer).
• Image quality is limited by motion blur, scatter, and overlying bone, gas, barium, metal or ECG leads; the image intensifier or flat panel detector shows a limited field of view, with distortion at the edges in older equipment.
• Fluoroscopy shows only a two dimensional shadow of a three dimensional structure; cone beam CT, CT or ultrasound give the third dimension.
• Soft tissue contrast is low without contrast agents.
• Scatter radiation exposes staff: dose falls with the square of the distance, so stepping back one step halves the dose approximately; shielding and tight collimation matter more than any other measure.
• Over reliance on live images, missed lesions on last image hold, and inadequate documentation limit the interpretation; the operator should save images that document key findings.
• Contrast agents carry risks (reactions, nephropathy), and sedation carries its own risks.
• The principle of using the lowest possible dose for the question can degrade image quality, and operators should accept a noisier image if it answers the clinical question.

Special groups.

• Children: more sensitive to radiation (higher lifetime cancer risk for the same dose), with smaller bodies receiving a higher dose to the whole body; use paediatric dose settings, pulsed fluoroscopy at low rates, no grids for small children, immobilisation, and sedation or anaesthesia when needed.
• Pregnant women and staff: pregnant staff wear a second dosimeter at the waist under the apron, and the foetal dose limit for staff is a few mSv for the remainder of the pregnancy.
• Obese patients: high dose rates, scatter and image noise.
• Patients with repeated procedures (for example, cardiac, vascular, and urological procedures): cumulative skin dose and lens dose are monitored.
• Operators and staff: lens dose limits, protective glasses, and training.
• Regions: ageing equipment without dose reduction features, limited protective equipment and dosimetry, and shortage of trained radiographers raise risk for staff and patients; fluoroscopy is often the main imaging for orthopaedic and urological procedures.

Follow up tests.

• Records of fluoroscopy time, dose area product and cumulative air kerma for each procedure.
• Skin dose estimation and clinical follow up of the skin for high dose procedures (inspection at 2 to 4 weeks, and referral to dermatology and radiation physics when required).
• Dosimetry for staff, quality assurance and annual physics testing of the equipment.
• Audit against local reference dose levels.
• Ultrasound or MR as dose free alternatives, and cross-sectional imaging for three dimensional detail.
• Referral to a radiation protection officer or medical physicist.