Factors involved in the selection of the appropriate imaging modality for drainage of intrathoracic collections include the type of thoracic collection, patient condition, and operator preference.
The size, location, and contents of the collection are important considerations when selecting the appropriate imaging modality for guidance. In general, ultrasound is most useful for drainage of large free-flowing fluid collections . Ultrasound is the technique of choice because it lacks ionizing radiation, is portable, and allows real-time visualization of needle/catheter placement. At times, a free-flowing collection may be less accessible with CT guidance because the fluid collection tends to move to a dependent position in the chest. In contrast, complex fluid collections and air often cannot be distinguished from underlying aerated lung parenchyma by ultrasound and may require CT guidance . The location of the fluid collection may dictate the choice of modality. Structures that are located along the proposed route of catheter insertions such as internal mammary vessels or mediastinal structures may be easier to visualize and avoid with CT guidance. Patients whose condition precludes cessation of respiration present a challenge to the placement of large drainage catheters. The real-time capability of CT fluoroscopy allows visualization of the safest approach to the fluid collection throughout the respiratory cycle, which is important in preprocedure planning .
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