ABSTRACT
Interventional procedures in which needles and therapy applicators are introduced to either obtain a biopsy specimen or to deliver ablation therapy (e.g., liver) require real-time guidance of needles to their targets and knowledge of the applicators’ tip before ablation therapy can be initiated. Imaging techniques such as X-ray fluoroscopy, magnetic resonance (MR), computed tomography (CT), and ultrasound (US) are used for various applications; however, procedures that require real-time guidance use US imaging because of its ability to provide images at 15–60 Hz. Although this approach is useful, US imaging cannot provide sufficient lesion contrast to the organ or lesion for many applications. Thus, MR and CT are used to produce an image to identify a target, which is registered to the intraoperative US image thereby combining the benefit of real-time US imaging with the high-lesion contrast from MR or CT images. This approach is now used in a variety of interventional applications such as prostate biopsy and focal liver ablation. All interventional procedures require that the user views the needle as it is being directed to its target. Thus, the biopsy/therapy procedure requires that the user holds the US transducer in contact with the body with one hand, and the needle insertion tool or therapy tool in the other hand. The 2D US image stream is then aligned with the trajectory of the needle so that it is continuously visible in the US image stream as the needle is being advanced into the tissue. Typically, alignment is ensured by clip-on guides on the transducer causing the needle to be inserted inplane of the US image.
