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These are commonly metal, glass or splinters of wood associated with industrial, road or domestic accidents and self-harm injuries.
Generally, two projections at right-angles to each other are reguired, without movement of the patient between exposures, particularly when examining the limbs. The projections will normally be antero-posterior or postero-anterior and a lateral of the area in question, as described in the appropriate chapters.
A radiopaque marker should be placed adjacent to the site of entry of the foreign body. The skin surface and a large surrounding the site of entry should be included on the images, since foreign bodies may migrate, example along muscle shealth, and high velocity foreign bodies may penetrates some distance through the tissues.
Compression must be applied to area under examination.
Oblique projections may be required to demonstrated the relationship of the foreign body to adjacent bone. A tangential (profile) projection may be required to demonstrated the depth of the foreign body and is particularly useful in examination of the skull, face, and thoracic and abdominal walls. Sometimes a single tangential projection maybe all that is required to show a superficial foreign body in the scalp or soft tissues in the face.
The exposure technique should demonstrate both bone and soft tissue to facilitate identification of partially opaque foreign bodies and to demonstrates any gas in the tissue associated with the entry of the foreign body.
The most usual exposure technique for conventional radiography are kVp sufficiently high to demonstrate bone and soft tissue on a single exposure, and use of two film/screen combinations of different speeds or a film/screen combination and non-screen film to demonstrate bony detail on one film and soft tissue on the other film with one exposure.
The use of digital images acquisition offers significant advantages in the localization of foreign bodies. CR and DR both allow soft tissue and bone to be visualized from one exposure using post-processing. The use of features such as edge enhancement and windowing enable much better demonstration of foreign bodies that have radio-opacity similar to that of the surrounding tissue.
INGESTED FOREIGN BODIES
A variety of objects, such as coins, beads, needle, dentures and fish bones, may be swallowed accidentally, or occasionally intentionally, particularly by young children. A technique used to smuggle drugs through costums involves packing the substance into condom, which are subsequently swallowed.
The patient should be asked to undress completely and wear hospital gown for the examination. The approximate time of swallowing the object and the site of any localized discomfort should be ascertained and noted on the request card, along with the time of examination. However, any discomfort may be due to abrasion caused by the passage of the foreign body. It is important to gain the patientâ€™s cooperation, especially in young children, since a partially opaque object may be missed if there is any movement during the exposure. The patient should practice arresting respiration before commencement of the examination.
If the patient is a young child, then the examination is usually restricted to a single antero-posterior projection to include the chest, neck and mid- to upper abdomen. The lower abdomen is usually excluded to reduce the dose to the gonads, as the examination is usually performed to confirm the presence of a foreign bodies lodged in the stomatch unable to pass through the pylorus. Care must be taken to ensure that the exposure selected is sufficient to adequately penetrate the abdomen as well as to visualized the chest.
The examination of older children and adults may require a lateral projection of the neck to demonstrate the pharynx and upper oesophagus, a right anterior oblique projection of the thorax to demonstrate the oesophagus, and an antero-posterior abdomen projection to demonstrate the remainder of the alimentar tract, exposed in that irder. Each image should, preferably, be inspected before the next is exposed, and the examination terminated upon discovery of the foreign body, to avoid unnecessary irradiation of the patient. The cassette should be large enough to ensure overlapping areas on adjacent images.
Non-opaque foreign bodies may be outlined with a small amount of barium sulphate. A few cases required a barium-swallow examination . If no foreign body is demonstrated within the alimentary tract, and particularly if there is doubt as to whether the foreign body has been ingested or inhaled, then a postero-anterior projection of the chest will be required to exclude an opaque foreign body in the respiratory tract or segmental collapse of the lung, which may indicate the presence of a non-opaque foreign body in the appropriate segmental bronchus. All projections should preferably be exposed in the erect position. A fast film/screen combination and short exposure time should be employed.
INHALED FOREIGN BODIES
Foreign bodies may be inhaled. Infants and young children habitually put object into their mouths, and these may be inhaled. Teeth maybe inhaled after a blow to the mouth or during dental surgery. Such foreign bodies may lodge in the larynx, trachea or bronchi.
The adult patient should be asked to undress completely to the waist and wear a hospital gown for the examination. A postero-anterior projection of the chest , including as much as possible of the neck on the image, and a lateral chest projection will be required initially. Alternatively, an antero-posterior chest image is acquired when examining children. A lateral projection of the neck, including the nasopharynx, may also be required. In the case of a non-opaque inhaled foreign body, postero-anterior projection of the chest in both inspiration and expiration will be required to demonstrate air trapping due to airway obstruction. This may manifest itself as reduced lung attenuation on expiration and/ or mediastinal shift. The kVp must be sufficiently high to demonstrate a foreign body that might otherwise be obscured by the mediastinum. A fast imaging system (film/screen combination) and short exposure time should be employed.
Cross-sectional imaging such as CT and MRI are additional technique that may provide useful information. NB: MRI is contraindicated in cases of suspected ferrous materials, since the examination may result in movement of the foreign body.
Bronchoscopy may be used to demonstrate the position of a foreign body, since the foreign body may be removed during this procedure.
INSERTED FOREIGN BODIES
Foreign bodies are sometimes inserted into any of the body orifices. Infants and young children, for example, may insert objects into the basal passages or an external auditory meatus. In these cases, radiography is required only occasionally, since most of the objects can be located and removed without recourse to radiography. When radiography is requested , two projections of the area concerned at right-angles to each other will be required.
Swabs may be left in the body following surgery. Such swabs contain a radio-opaque filament consisting of polyvinylchloride (PVC) impregnated with barium sulphate for radiographic localization.
Ultrasound should be the initial modality selected for the detection of an intrauterine contraceptive device. It is also very effective in the detection of soft tissue foreign bodies with the advantages of incurring no radiation burden where it is available.
There have been incidents where objects such as vibrators have become lodged in the rectum. In these cases, a single antero-posterior projection of the pelvis may be required.
Patients who are prone to self-harm may insert a variety of objects into their body cavities and under the skin.
TRANSOCULAR FOREIGN BODIES
Foreign bodies that enter the orbital cavity are commonly small fragments of metal, brick, stone or glass associated with industrial, road or domestic accidents.
Plain film imaging is the first modality for investigation of a suspected radio-opaque foreign body in the orbit. For further investigation, or assessment of an a non-opaque foreign body, CT scanning can be very useful. CT will give information about damage to the delicate bones of the medial and superior orbital margins and evidence of any damage suffered by the brain if the orbital roof has been breached. Ultrasound is useful for detecting foreign bodies and soft tissue damage but is less useful in the orbit in detecting very small foreign bodies. Access to ocular ultrasound expertise is less likely to be immediately available, and there is the extra harzard of introducing coupling gel into a possibly deep wound.
Radiographic localization may be carried out in two stages. First to confirm the presence of an intra-orbital radio-opaque foreign body. Second to determine whether the foreign body is intra- or extra-ocular.
Image showing fine detail are essential. A small focal spot (e.g 0.3mm2), immobilization with a head band and a high-definitions film/screen combination is recommended. Metal fragments down to 0.1x0.1x0.1 mm in size may be detected by conventional radiography.
Intesifying screens must be scrupulously clean and free of any blemishes producing artefacts that could be confused with foreign bodies. A cassette with perfectly clean screens may be set aside especially for these examinations.
CONFIRMATION OF RADIO-OPAQUE FOREIGN BODIES
A modified occipito-mental projection with the orbito-meatal base line (OMBL) at 30 degrees to the cassette is undertaken, with the patient either prone or erect. Whichever technique is adopted, the head must be immobilized. Ideally , a dedicated skull unit is selected as this will provide the maximum degree of resolution required for the visualization of a small foreign bodies.
The chin is raised so the OMBL is at 30 degree to either the vertical or horizontal beam. This position projects the petrous ridges to just below the inferior, anterior orbital margin with the walls of the orbit lying parallel to the cassette. Using a vertical or horizontal beam, the centray ray is directed to the interpupillary line. The beam is either collimated to include both orbits or just the orbit under examination, depending on the departmental protocol.
If it is suspected that a foreign body is obscured by the skull then a soft tissue lateral image may be necessary.
It may be necessary to repeat the examination if the artifact is suspected to be from possible dirty screen.
If radio-opaque foreign body is identified in the orbit, before proceeding with any further localization images it may be advisable to wait until the patient has been seen by the ophthalmologist who may decided to remove the foreign body or request CT or ultrasound in preference to radiography localization.
LOCALIZATION OF INTRA-ORBITAL FOREIGN BODY
The method described determines the position of the foreign body relative to the centre of the eye and whether it is intra- or extra-ocular. It should be ascertained that the patient is able to maintain ocular fixation, example like keep the eyes fixed on some given mark, since the exposures are required with the patient looking in different directions. The examination is preferably carried out using a skull unit.
The following projection are required is Occipito-mental modified with the centering adjusted to the middle of the interpupillary line. Two exposures are made , one with the eyes level and looking forward and the other with the eye under examination adducted (turned towards the nose). Lateral, with centering adjusted to the outer canthus of the eye. Three exposures are made , one with the eyes level and looking forward, one with the eyes raised and one with the eyes lowered.
In each case, the patient look stedily at some predetermined mark or small object during the exposures. A tracing is made from the lateral projections showing the three shadows of the foreign body. Straight lines are drawn to join them. The lines are then bisected at right angles midway between the shadows. The point of intersection of the bisectors indicates the center of the eyeball if the intersection is slightly anterior to the zygomatic border of the orbit. In this case the foreign body is in the eyeball.
If the intersection is remote from the zygomatic border it will indicate that the foreign body is in the surrounding tissue or muscles. A second tracing from the occipito-mental projections enables lateral movement of the foreign body to be plotted and shows its antero-posterior position relative to the centre of the pupil.
ORBITS: OCCIPITO-MENTAL MODIFIED PROJECTION
This is a frequently undertaken projection used to assess injuries to the orbital region.(e.g blow-out fracture ot the orbital floor) and to exclude the presence of metallic foreign bodies in the eyes before magnetic resonance imaging (MRI) investigations. The projection is essentially an under-tilted occipito-mental with the orbito-meatal baseline raised 10 degrees less than in the standard occipito-mental projection.
POSITION OF PATIENT AND CASSETTE
The projection is best performed with the patient seated facing the skull unit cassette holder or erect bucky. The patientâ€™s nose and chin are placed in contact with the midline of the cassette holder. The head is then adjusted to bring the orbito-meatal baseline to a 35 degree angle to the cassette holder. The horizontal central line of the erect bucky or cassette holder should be at the level of the midpoint of the orbits. Ensure that the median sagittal plane is at right-angles to the bucky or cassette holder by checking that the outer canthi of the eyes ant the external auditory meatuses are equidistant.
DIRECTION AND CENTERING OF THE X-RAY BEAM
The central ray of the skull unit should be perpendicular to the cassette holder and by design will be centered to the middle of the image receptor. If this is the case and the above positioning is performed accurately, then the beam will already be centered. If using erect bucky, the tube should be centered to the bucky using horizontal beam before positioning is undertaken. Again if the above positioning is performed accurately and the bucky height is not altered, then the beam will already be centered. To check that the beam is centered properly, the cross-lines on the bucky or cassette holder should coincide with the midline at the level of the mid-orbital region.
ESSENTIAL IMAGES CHARACTERISTICS
The orbits should be roughly circular in appearance (they will be more oval in the occipito-mental projection) The petrous ridges should appear in the lower third of the maxillary sinuses. There should be no rotation. This can be checked by ensuring that the distance from the lateral orbital wall to the outer skull margins is equidistant on both sides.
If the examination is purely to exclude foreign bodies in the eye, then tight â€˜letter boxâ€™ collimation to the orbital region should be applied.
A dedicate cassette should be used for foreign bodies . This should be cleaned regularly to avoid small artifacts on the screens being confused with foreign bodies.
If a foreign body is suspected, then a second projection may be undertaken with the eyes in a different position to differentiate this from an image artifact. The initial exposure could be taken with the eyes pointing up and the second with the eyes pointing down.
In cases of injury, this projection should be taken using horizontal beam in order to demonstrate any fluids levels in the paranasal sinuses. The patient may be positioned erect or supine.
POSITION OF PATIENT AND CASSETTE
The patient sits facing the vertical bucky or cassette holder of the skull unit. The head is rotated, such that the side under examination is in contact with the bucky or cassette holder. The arm on the same side is extended comfortably by the trunk, whilst the other arm may be used to grip the bucky for stability. The bucky height is altered, such that its centre is 2.5cm inferior to the outer canthus of the eye.
The patient lies on the trolley, with the arm extended by the sides and the median sagittal plane vertical to the trolley top. A grided cassette is supported vertically against theside under examination, so that the centre of the cassette is 2.5cm inferior to the outer canthus of the eye.
In either case, the median sagittal plane is brought parallel to the cassette by ensuring that the inter-orbital line is at right-angles to the cassette and the nasion and external occipital protuberance are equidistant from it.
DIRECTION AND CENTERING OF THE X-RAY BEAM
Center the horizontal ray to a point 2.5cm inferior to the outer canthus of the eye.
ESSENTIAL IMAGE CHARACTERISTICS
The image should contain all of the facial bones sinuses, including the frontal sinus and posteriorly to the anterior border of the cervical spine. A true lateral will have been obtained if the lateral portions of the floor of the anterior cranial fossa are superimposed.
This projection is often reserved for gross trauma, as the facial structures are superimposed. If a lateral is undertaken for a suspected foreign body in the eye, then additional collimation and alteration in the centering point will be required.