For CT-guided biopsies, a sterile field is set up on a movable procedure cart in the CT room. The interventional radiologist reviews existing images, and then the patient is placed in a position that facilitates needle insertion in a safe and efficient manner from the skin surface to the target. Patients can be placed in supine, prone, lateral, or lateral oblique positions as needed, but it is crucial to select a stable and comfortable position for the patient. The patient should remain in the same position after the initial planning images are obtained. Streak artifacts caused by the patient’s arms can be reduced by positioning the arms outside the imaging field (Fig. 2.4). Space within the gantry can be maximized by placing the table at the lowest position possible.

A radiopaque marker or grid is placed over the intended area of puncture. Radiopaque grids are commercially available; however, grids can be created on site using various types of catheters that are cut to a length of 10–20 cm, placed parallel at 1- to 2-cm intervals, and taped at the ends. The simplest radiopaque marker consists of a single piece of angiographic or drainage catheter placed on the patient in longitudinal fashion. Alternatively, one can use the laser lights that are built in the gantry together with the grid which can be displayed on the patient’s image to determine the needle puncture site.

For most interventions, a spiral scan of the area of interest is performed, including the marker or grid. In most cases, intravenous administration of contrast medium is unnecessary, but occasionally noncontrast images do not allow differentiation of the target from adjacent vascular structures. Tumors within solid organs may be isodense with their surrounding tissue on noncontrast images, in which case the contrast medium may be given intravenously to delineate the vascular structures or to differentiate the lesion from normal parenchyma (Fig. 2.5) [4].

The interventional radiologist identifies the target and then determines a path for placement of the biopsy needle or device. The needle path depends on the organ of interest and the intervening anatomy. In general, the path should be kept short, but it should also avoid certain anatomic structures such as bone, vessels, bowel, or other organs to render the procedure as safe as possible. Once the needle insertion site is determined, the patient is placed into the gantry. The positioning laser light and the radiopaque marker together provide adequate information to localize the exact site for needle insertion. A small ruler and a skin marker are often necessary to mark the puncture site accurately on the skin. The skin is then prepared in a sterile manner, and a keyhole drape is placed over the puncture site. A sterile cover may be applied to the table-side control panel so that the radiologist can operate the CT scanner during the procedure.

Most biopsies are performed under moderate sedation or local anesthesia. The skin entry site is infiltrated with local anesthetic agent (e.g., lidocaine 1 %), and sufficient local anesthetic agent should be injected at the interface of the pleura, peritoneum, or periosteum. A small stab incision is made to help the needle pass through the skin and subcutaneous tissues. CT guidance provides intermittent imaging, and thus the needle is inserted incrementally (1 to a few centimeters at a time) during CT-guided biopsy, and images are obtained after each manipulation to confirm proper advancement of the needle along the desired path.

CTF guidance provides continuous near-real-time imaging that allows monitoring of the needle insertion during CTF-guided biopsy. To avoid excessive radiation to the operator’s hand, needle-holding devices may be used [22]. Even with the use of needle-holding devices, radiation exposure to the operator and patient may not warrant real-time continuous-mode CTF. Alternatively, intermittent CTF can be performed after incremental advancement of the needle [23].

The operator must be cognizant of two angles when performing CT- or CTF-guided biopsy. Most CT-guided biopsies are performed in a true axial plane. This approach provides the easiest imaging protocol to confirm needle placement. Therefore, the operator has to keep the needle in one axial plane perpendicular to the Z axis. Cranial or caudal angulation of the needle can be detected on sequential CT images, and the path of the needle can be adjusted accordingly. One can take advantage of the laser light of the scanner for alignment of the needle in an axial plane. When the laser light shines on the skin entry site and the hub of the needle, it confirms the positioning of the needle in the imaging plane. The simplest CT-guided biopsy plan is one in which the needle is inserted perpendicular to the skin. However, this approach is not always feasible, depending on the intervening organs or structures that may have to be avoided. Therefore, the second angle that the operator should observe is the steepness of the approach with respect to the skin’s surface. Placement of the needle can be guided with the naked eye; however, this is more easily accomplished if the patient is taken out of the gantry and the puncture site is placed directly in front of the operator to avoid issues related to parallax.