Biopsy Instruments

The appropriate choice of the biopsy instrument depends on the clinical requirements. For corticosteroid injection or MR arthrography, MR compatible needles ranging from 18 to 22 g in size are obtainable. For biopsies, fine needles, cutting needles (Fig. 2), or MR-compatible drilling systems need to be used.

FIGURE 2 (A) Commercially available Tru-Cut needles, 14 and 18 g in size (Daum, Germany). (B) MR compatible, pneumatically driven hollow auger for MR-guided percutaneous biopsy of sclerotic lesions (Cook, Denmark). Pneumatically driven hand piece (top), and two different sizes of hollow augers with mandrel (bottom). In addition, a manual tool holder (right) is available. (C) Biopsy specimen acquired with the MR compatible biopsy system.

FIGURE 2 (A) Commercially available Tru-Cut needles, 14 and 18 g in size (Daum, Germany). (B) MR compatible, pneumatically driven hollow auger for MR-guided percutaneous biopsy of sclerotic lesions (Cook, Denmark). Pneumatically driven hand piece (top), and two different sizes of hollow augers with mandrel (bottom). In addition, a manual tool holder (right) is available. (C) Biopsy specimen acquired with the MR compatible biopsy system.

Needle selection rules similar to those followed in fluoroscopy- or computed tomography (CT)-guided biopsies are utilized. If the lesion is purely cystic with a thin cortical rim, a fine needle is sufficient, because it allows the penetration of the cortical bone and the aspiration of intralesional fluid. If the lesion is covered by a thick layer of cortical bone, or if the lesion is osteosclerotic, a drill is necessary.

MR-guided core biopsy needles are available in sizes ranging from 14 to 18 g. Drilling systems are either manually or mechanically driven (pneumatically, to ensure MR compatibility) (Fig. 2B and C) (26,27).

A problem specific to MR is difficulty secondary to susceptibility artifacts (28,29). Most of the MR compatible instruments are manufactured from nitinol alloys. Although these alloys are nonferromagnetic, they cause variable amounts of artifact. The artifact size depends on the size of the needle, the exact composition of the needle, whether it is used with a mandrel, the field strength of the MR scanner, the type of sequence used [GRE worst, fast spin echo (FSE) best], and the needle position with respect to the main magnetic field and to the phase- and frequency-encoding gradients (Table 1). In addition, the artifact size depends on the echo time (TE) and the bandwidth of the frequency-encoding gradient (Fig. 3).

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