Poster No.:
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DOI:
C-644
ECR 2009
Educational Exhibit
Musculoskeletal
A. Kraus
1
, A. Farooq
1
, E. Buschmann
2
;
1
Bangor/UK,
2
Newcastle,
NSW/AU ct, soft tissue, ultrasound, Foreign body
10.1594/ecr2009/C-644
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The learning objective of this presentation is to demonstrate the appearance of different types of foreign bodies in different imaging modalities and therefore to help choosing the right imagingmodality for the detection of foreign bodies of various size, shapes and materials.
After penetrating there is often a suspicion of a foreign body remaining in situ. Not all imaging modalities are suitable for the detection of various types of foreign bodies.
Choosing the wrongmodality can lead to a foreign body being overlooked.
To examine the appearance of various types of foreign bodies in different imaging modalities we introduced the foreign bodies shown in the picture below into a piece of skin-covered chicken meat.
Fig.: Fig. 1: Foreign bodies used
Shown from left to right there are a tooth, a stone, a piece of glass (from a car window), a piece of fresh wood, a piece of dried wood (skewer tip), a tip of a pencil core, copper wire, steel wire, plastic covered steel wire, a staple, a thin piece of aluminium (from a drinks can), a piece of plastic covered by metal foil (from a tablet blister pack), a piece of rubber, thick black plastic, thin clear plastic, a (plastic) tooth brush bristle and a bristle from a natural brush. As the latter is difficult to see it is marked by the small red arrow.
Appearances on X-ray:
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Fig.: Fig. 2: Foreign bodies in the chicken piece
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Fig.: Fig. 3: X-ray with foreign bodies in situ
The images above show the foreign bodies in the chicken piece and the X-ray of the meat with the foreign bodies in situ. As expected the pieces of wire, the staple and the tooth are well visible, similarly the stone and the piece of glass. The aluminium strip was very thin and therefore does not show up as well. Pencil cores, containing graphite, also are easy to see. The wood pieces contain some air and are therefore just visible. The green arrow points to the fresh wood, the red arrow to the skewer tip. Surprisingly the blue rubber band also showed up vaguely (blue arrow), presumably it contains some radioopaque die.
Appearances on CT:
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Fig.: Fig. 4: Foreign bodies (for CT)
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Fig.: Fig. 5: Foreign bodies on CT (average attenuation image, slice thickness 2.5 cm, bone window)
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Fig.: Fig. 6: Foreign bodies on CT (average attenuation image, slice thickness 2.5 cm, soft tissue window window)
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Fig.: Fig. 7: Foreign bodies on CT (MIP)
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Fig.: Fig. 8: Foreign bodies on CT (volume rendered image)
On CT again the metallic structures, the tooth, the stone, the glass and the pencil core are well visualised and, similar to the X-ray, the rubber band is also seen. Due to the three-dimensional nature of CT thinner structures, like the aluminium strip and the rubber band, are more obvious than on plain X-ray, especially on the MIP and volume images.
Some air can again be seen in the two wooden foreign bodies. However as air is of lower density than the surrounding meat this can only be picked up on the "standard" average attenuation images (both on bone and soft tissue window), but not on the MIP.
Unfortunately, as the chicken had to be cut open to insert the foreign bodies, there is some air around the skewer tip, therefore it is difficult to appreciate the difference in attenuation of the wood (approximately 30 HU) compared to the surrounding meat (approximately
60 HU).
The plastic strips as well as the bristles could neither be seen on plain X-ray nor on CT.
Although one of the plastic pieces was covered by a layer of metal this was too thin and did not show up on X-ray or CT.
Appearances on ultrasound:
For the ultrasound examination the a 17.5 Mhz linear array probe was used. To avoid air surrounding the foreign body and interfering with the ultrasound image the foriegn bodies were pushed into the meat from the underside rather than placed in an open cut.
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Fig.: Fig. 9: Glass on ultrasound
Fig.: Fig. 10: Stone on ultrasound
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Fig.: Fig. 11: Tooth on ultrasound
Glass, stone and tooth, which were of relatively large volume, were very easy to visualise on ultrasound. The piece of glass displayed quite prominent posterior sonic enhancement
(similar to a fluid filled structure), where as the stone and the tooth showed a sonic shadow.
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Fig.: Fig. 12a: Aluminium on ultrasound - longitudial view
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Fig.: Fig. 12b: Aluminium on ultrasound - transverse view
Fig.: Fig. 13a: Copper wire on ultrasound - longitudinal view
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Fig.: Fig. 13b: Copper wire on ultrasound - transverse view
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Fig.: Fig. 14a: Steel wire on ultrasound - longitudinal view
Fig.: Fig. 14b: Steel wire on ultrasound - transverse view
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Fig.: Fig. 15: Staple on ultrasound - longitudinal view
The metallic foreign bodies were also very easy to see on ultrasound, especially when viewed along their longitudinal axis. Visualising them on transverse view is much more difficult. Interstingly, although of similar thickness, on transverse view the copper wire was much less obvious than the steel wire, causing considerebly less posterior echos.
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Fig.: Fig. 16: Plastic coated steel wire on ultrasound (longitudinal view)
The plastic coated steel wire was also easily visualised. The plastic coating surrounding the wire (red arrow) could be seen seperately from the wire itself (blue arrow).
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Fig.: Fig. 17a: Dry wood on ultrasound (longitudinal view)
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Fig.: Fig. 17b: Dry wood on ultrasound (transverse view)
Fig.: Fig. 18: Fresh wood on ultrasound (longitudinal view)
Wood is clearly seen, in transverse as well as longitudinal view. This finds a practical application for example in the detection of thorns.
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Fig.: Fig. 19: Pencil core on ultrasound
The pencil core is easily visualised. The tip of the pencil can be seen on the right.
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Fig.: Fig. 20: Thick black plastic on ultrasound
Fig.: Fig. 21: Thin clear plastic on ultrasound
Fig.: Fig. 22: Rubber on ultrasound
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The plastic pieces were slightly more difficult to see than the previous foreign bodies but are still visualised quite well. The rubber band shows up as two thin parallel lines.
Fig.: Fig. 23: Tooth brush bristle on ultrasound
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Fig.: Fig. 24: Natural bristle on ultrasound
The plastic tooth brush bristle and especially the natural brush bristle were difficult, but not impossible to visualise. The very thin natural bristle only shows up as a very fine line on ultrasound (arrow). They can really only be seen if visualised along their longitudinal axis.
MRI:
Unfortunately the piece of chicken was too small and our MRI scanner was not able to detect it, not even when it was placed on a phantom. Therefore we do not have any MRI images of our foreign bodies.
Clinical cases:
The following images show some examples of foreign bodies encountered in our clinical practice.
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Fig.: Fig. 25: Staple in index finger
The metallic staple in the index finger can clearly be seen on X-ray.
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Fig.: Fig. 26: Metallic foreign body in ear lobe
Fig.: Fig. 27a: Metallic foreign body in thenar
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Fig.: Fig. 27b: Metallic foreign body in thenar
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In these two cases plain X-rays helped to confirm the presence of a lost earring back in the earlobe and a piece of metal in the thenar.
Fig.: Fig. 28a: Swallowed coins (frontal view)
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Fig.: Fig. 28b: Swallowed coins (lateral view)
Plain X-ray can also detect metallic foreign bodies deep inside the body, in this case in the oesophagus.
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Fig.: Fig. 29: Glass foreign body on ultrasound
This glass foreign body near the index finger MCPJ after a glass cut injury, which did not show up on plain X-ray, was visualised on ultrasound.
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Fig.: Fig. 29: Piece of wood in sole of foot on ultrasound
A piece of wood in the sole of a foot localised by ultrasound.
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Fig.: Fig. 30a: Tiny metallic foreign body medially in the upper 1/3 of the lower leg
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Fig.: Fig. 30b: Artefact caused in MRI
This patient had a tiny metallic foreign body, of which he wasn not aware, medially in the soft tissues of the upper third of his left lower leg. This caused quite a significant artefact on a subsequent MRI scan.
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Fig.: Fig. 31: Sticky plaster on nose
The structure projected over the bridge of the nose is not a foreign body inside the patient but rather a sticky plaster with a stripey design applied to a wound over the bridge of the nose - as X-rays are two-dimensional images of three-dimensional structures it is important to make sure a potential foreign body seen on an X-ray is not an overprojection from something outside of the patient.
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Metallic foreign bodies are best seen on plain X-ray or CT in most cases, it might however be difficult if the foreign body is very thin. Wood, which almost always contains air, can be visualised onCT, where it shows a lower attenuation than the surrounding soft tissues.
Ultrasound can show almost all foreign bodies, even very thin ones, if a high frequency probe is used. This however limitsits use to relatively superficial foreign bodies.
Grainger RG, Allison D, Grainger & Allison's Diagnostic Radiology: A Textbook of Medical
Imaging, 3rd Edition, New York: Churchill Livingstone, 1997
McNally EG, Practical Musculoskeletal Ultrasound, Philadelphia: Elsevier, 2005
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