Gerald D. Dodd III and Hayden Head

The process to biopsy or drain a mass or to perform percutaneous treatment such as radiofrequency ablation (RFA) of a tumor begins with a consultation request. This clinical request is part of a consultation between the requesting physician and the radiologist who will perform the procedure. This consultation should include a review of the patient’s pertinent clinical history, the objectives of the requested procedure, a review of pertinent imaging studies, an assessment of whether the procedure is indicated and technically feasible, the determination of the disposition of any tissue or fluid obtained, and an assessment of the patient’s willingness and ability to tolerate the procedure. After the decision to perform the procedure has been made, the radiologist must choose a method of guidance.

Mode of Image Guidance for Percutaneous Treatment

Three primary modalities can be used to guide percutaneous interventional procedures: fluoroscopy, computed tomography (CT), and sonography. In a few situations, the pathological condition or the patient’s anatomy may dictate a particular method of guidance. In most instances, however, sonographic guidance has proved to be quicker and easier than the other methods. In Asia and in many parts of Europe, sonography is the dominant method used to guide the performance of most nonvascular and interventional procedures. At several academic and private hospitals in the United States, sonography is used to guide 95% of all biopsies and drainages of abdominal, pelvic, pleural, and mediastinal masses. The advantages of sonography include real-time guidance, multidirectional imaging, identification and avoidance of major vessels, portability, excellent anatomical resolution, and reduced cost. The cost savings of sonography result from the lower capital expenses and operating costs of sonographic equipment and the potential use of CT scanners for diagnostic purposes, rather than for intervention.

Ultrasound-Guided Percutaneous Treatment

Methods

The two primary methods of performing sonographically guided intervention are the free-hand technique and the attached-guide technique. Advocates of the free-hand technique claim it allows for greater freedom in choosing needle placement and better needle visibility. Advocates of guides claim that they provide greater accuracy for deep biopsies, quicker needle localization, diminished teaching time, and improved coordination in procedures performed with nonradiologists. Because few companies manufacture needle guides for high-frequency probes, most near-field biopsies are performed with the free-hand technique. However, we believe that use of an attachable guide makes a biopsy or drainage of a mass more than 5 cm deep easier and quicker.

The success of sonographic guidance depends highly on optimization of the sonographic equipment. Important parameters that should be controlled are the type of probe, the gray scale, the field of view, and the focus. All of these variables have a direct effect on the visualization of the pathological condition and the needle. For near-field biopsies, the best results are usually obtained with 7 to 10 MHz linear probes. Most abdominal biopsies are best performed with 3.5 or 2.5 MHz sector probes. The field of view should be chosen to maximize visualization of the pathological condition and the needle. As a general rule, the field of view should be adjusted so that the needle traverses at least one third of the image. Under no circumstances should a large field of view be used when performing a biopsy of a small near-field lesion. The probes should be focused at the level at which the needle is expected to enter the lesion. Visualization of the needle can be improved by needle motion (use of an in-and-out motion with approximately a 1 cm excursion) and a slight rocking motion of the probe. This rocking motion can bring a needle that has deviated slightly out of the ultrasound plane back into the field of view.

With the attached-guide technique, the speed and success of the procedure can be improved by using two sets of hands: one person holds the probe and corrects it, and the second person places the needle catheter. Although the use of two people requires precise communication, it can produce less traumatic and more accurate results. In academic centers, the second person is usually a resident or fellow. In private practice, the most logical choice for the second person would be a sonographer. The most crucial task in the two-person technique is holding the probe, which is usually performed by the attending radiologist. The delivery of the anesthetic and placement of the needle are easier tasks and are usually done by the second person.

Percutaneously guided intervention may seem difficult and dangerous; however, in most instances, it is relatively simple and safe. Its success requires adherence to a few basic principles: