Image guided biopsies are nowadays more and more applied in the diagnosis of a wide variety of disease. Different imaging modalities are used to guide the biopsy needle through the body to the target, computed tomography (CT), ultrasound (US) and magnetic resonance imaging (MRI)(1). Each guiding modality has its advantages and disadvantages. Ultrasound may be cost effective and provide real-time feed- back without radiation, although lesions can be obscured by bone or bowel gas and may be occult on ultrasound. MRI has excellent contrast resolution without radiation but is expensive and requires special equipment with limited availability at many centers(2). CT offers improved spatial resolution and is not limited by adjacent bones or bowel (2) gas but many procedures remain complicated in particular when an obstacle must be avoided (e.g., the posterior pleural cavity during adrenal gland punctures), meaning that the optimal needle path is on a plane that is oblique to the acquired axial images. An out-of-plane trajectory is associated with decreased needle placement accuracy, leading to trajectory errors which could cause perforation of neighboring organs or a non-diagnostic biopsy(3). Furthermore, radiation exposure increases, particularly in complex procedures performed by unskilled radiologists(4). 

A number of different auxiliary needle positioning devices have been developed. For example, laser targeting devices attached to the gantry or targeting devices which can be fixed directly to the patient. However, none of these auxiliary devices permits simultaneous real-time control of the needle, tremble-free needle advancement, and assistance for the implementation of an access path as planned in the patient data (5).

The IMACTIS company (Saint-Martin-d'Hères, France) has developed an electromagnetic navigation system for CT-guided interventional radiology procedures (FIG 1). The patient’s anatomy is visualized in 3D using a previously acquired CT scan. An electromagnetic transmitter is attached to the patient’s skin, which enables to identify the position of the needle used by the operator which is equipped with an electromagnetic receiver. The hypothetical needle trajectory can therefore be displayed in real time on the images of the patient. The operator can visualisethe trajectory of the needle during both the planning phase (determination of the optimal route before skin penetration) and the needle insertion phase of the procedure (1).

The feasibility of oblique trajectories means that the number of possible needle trajectories is increased when using the navigation system compared with conventional CT guidance. The navigation system should therefore increase both the accuracy of the gesture and the radiologist’s confidence in his gesture, whereas the radiation exposure and the duration and severity of the intervention should decrease (1).

The purpose of the current study was to compare the results of an electromagnetic navigation system with conventional CT guidance for CT-guided biopsies.