Biceps Tendon Sheath Injection

Excerpt

Ultrasound is well-suited for clinical practice given its affordability, portability, and lack of radiation exposure during image acquisition. These features allow clinicians from almost any specialty the ability to perform image-guided evaluations and interventions. Radiologists are uniquely suited to perform these evaluations and procedures, given their extensive training, knowledge of human anatomy, and understanding of the varied anatomical appearances across multiple imaging modalities.

Part of a radiologist’s training involves understanding medical physics, including how medical images are obtained. In ultrasound, the sonographer or physician utilizes a transducer to interrogate the area of interest. Within the transducer are piezoelectric crystals that vibrate when exposed to an alternating current. These vibrations generate sound waves transmitted into the patient’s soft tissues via a layer of ultrasound gel. The sound waves then interact with the tissue and are ultimately reflected to the transducer. Once the sound waves return to the transducer, they are converted back into an electric current. The computer then calculates the time interval between when the sound wave was initially generated and when the transducer received it to determine the location (depth) of the tissue that reflected the sound wave.

When planning a procedure, one must consider the type of transducer that yields the highest quality images. There are a variety of transducers that can be used with varied frequencies and shapes. In general, higher-frequency transducers are used for imaging more superficial structures, as they offer better resolution. However, the higher-frequency sound wave is more easily attenuated and has a decreased ability to penetrate tissue, limiting its use in the evaluation of deeper structures. For deeper structures or larger patients, one might choose a lower frequency or curved transducer. When imaging small body parts, such as a finger, a small transducer (hockey stick) may help.

Image guidance for procedures includes ultrasound, fluoroscopy, computed tomography, and, in some cases, magnetic resonance imaging (MRI). In general, ultrasound is particularly helpful in guiding soft tissue procedures such as therapeutic tendon sheath injection, soft tissue biopsy, and cyst or abscess aspiration/drainage. Ultrasound, computed tomography, and fluoroscopy guidance can be used for both joint aspiration and therapeutic injection. The chosen modality may depend on availability, user expertise, the body part to be treated, and the patient's body habitus. Advantages of ultrasound include the absence of ionizing radiation and direct, real-time visualization of the needle and surrounding soft tissues during the procedure. During fluoroscopic guidance, the needle is intermittently imaged, and its position is assessed only relative to the associated osseous structures. The involved soft-tissue structures must be inferred from anatomical knowledge. Also, fluoroscopy often requires a contrast agent to verify needle placement, whereas ultrasound allows direct visualization of the needle position. Computed tomography is useful for biopsy of osseous structures or therapeutic injection of deep anatomic structures, which can be difficult to visualize with ultrasound or palpate on physical examination.