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However, less pain and shorter procedure time was reported in the ultra- sound group. Foreign body identification/localization Ultrasound can also be used to identify foreign bodies – either by direct visualization (metal) or by shadowing (wood, stones) or edema (inflamma- tion and secondary tissue effects from wood or organic material). Physical exam can be extremely challenging in these situations, and a patient’s own foreign-body sensation can often be misleading. Many common foreign Fluid Biceps Tendon (A) (B) Figure 16.14 ( A ) Shoulder probe position. ( B ) Ultrasound image obtained at this site. 308 Procedural ultrasound Ultrasound for procedure guidance
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bodies (e.g., wood) are not well visualized by x-ray, and triangulating the exact location of a small foreign body can be difficult and time-consuming using standard radiographic techniques. Focused questions 1. Is there a foreign body? 2. Are there vascular structures near the foreign body? Anatomy The appearance of normal superficial tissues is shown in Figure 16.15 . Note that the subcutaneous fat has a speckled appearance, which is slightly hypo- echoic when compared to the appearance of organs such as the liver or spleen. Muscle appears “marbled” because hypoechoic muscle tissue is divided by hyperechoic fascial planes. Vascular structures will appear anechoic and will be compressible. Bone will act as a strong reflector, creating a bright boundary beyond which only shadowing will be visible. Technique Probe selection Ultrasound of the superficial soft tissue should be performed with a high- frequency (5–10 MHz) linear probe. Epidermis/Dermis Hypodermis Subcutaneous fascia Muscle Bone Figure 16.15 Normal dermal tissue, with component layers. Procedural ultrasound 309 Ultrasound for procedure guidance
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Special equipment The following special equipment is required: ± Lidocaine or other local anesthetic ± Water bath or standoff pad for superficial structures Note: Be sure to check the manufacturer’s instructions regarding the safety of water-bath use with your particular transducer. Any transducer with a cracked housing should not be used, because the gel may conduct electrical signals to the operator or the patient. Thus, a cracked housing would be extremely dangerous when used with a water bath. ± Alligator forceps ( Figure 16.16 ) or other small grasping implement ± Sterile wire (e.g., Kopans wire) or needle if this will be used to guide a dissection Setup The patient should be placed in a comfortable position. As with other ultrasound-guided procedures, the ultrasound will be performed in the same position as the procedure itself. Scan over the area of suspected foreign body and note the appearance of bright reflectors and/or shadowing in the area. Familiarize yourself with the appearance of normal bony anatomy (bright reflector with shadowing, described previously) as well as soft tissue, tendons, and vascular struc- tures. Common foreign bodies such as wood or metal have a characteristic appearance on ultrasound ( Figures 16.17 –16.19). Glass is sometimes visual-
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