Clinical Indications Biopsies

Percutaneous bone biopsies are common radiologic procedures for bone biopsy, including the histologic confirmation of suspected primary or secondary malignant and benign bone tumors. In addition, percutaneous bone biopsy may be used to confirm an infectious process and to determine the causative microorganism in suspected osteomyelitis (27,33,34). For these purposes, either core biopsy needles or fine needles may be used.

Until now, CT or X-ray fluoroscopy has been used mostly to guide biopsies. MR imaging offers superior soft-tissue contrast and lacks any radiation burden and can be also used to perform percutaneous biopsies. In our own series, we demonstrated that bone biopsies under MR

TABLE 1 Parameters Influencing the Artifact Size

Spin echo technique Low

Gradient echo technique High

TE: long High

TE: short Low

Frequency-encoding gradient alongside the instrument Low

Frequency-encoding gradient perpendicular to the instrument High

Bandwidth: broad High

Bandwidth: small Low

B0: high High

B0: low Low

Amount of metal: high High

Amount of metal: low Low

Abbreviation: TE, echo time.

FIGURE 3 (A) Influence of the increasing echo time on the magnetic resonance (MR) appearance of a 14 g (equal to 2 mm) core biopsy needle (Tru-Cut). At 1.5 msec, the needle is displayed a 8 mm thick structure and increases subsequently with increasing echo time up to 25 mm at an echo time of 20 msec. (B) Influence on the MR appearance of the an MR compatible 14 g needle, which is aligned to the phase-encoding gradient (arrow) (left) as well as perpendicular to the gradient (right). Abbreviation: TE, echo time.

FIGURE 3 (A) Influence of the increasing echo time on the magnetic resonance (MR) appearance of a 14 g (equal to 2 mm) core biopsy needle (Tru-Cut). At 1.5 msec, the needle is displayed a 8 mm thick structure and increases subsequently with increasing echo time up to 25 mm at an echo time of 20 msec. (B) Influence on the MR appearance of the an MR compatible 14 g needle, which is aligned to the phase-encoding gradient (arrow) (left) as well as perpendicular to the gradient (right). Abbreviation: TE, echo time.

imaging guidance provides results similar to those of biopsies performed under CT guidance (26,27). MR offers the unique feature of allowing histologic evaluation of nonspecific bone marrow edema (Fig. 4).

MR can be also used for percutaneous core decompression in patients with avascular necrosis of the femoral or humeral head (Fig. 5). However, the experience in this field is still limited and more clinical experience is required. The complications of MR-guided percutaneous biopsies of bone lesions are similar to those of any percutaneous biopsy. These include infection, bleeding, nerve injury, and breakage of the biopsy device. None of these complications has been observed in our own series.

MR guidance cannot be currently recommended for spinal lesions, which often require a transpedicular biopsy pathway. A safe access to the lesion depends here on a meticulous biopsy planning. In such cases, we still prefer CT as a guidance tool, because it offers the best spatial resolution. In addition, for the percutaneous ablation of the nidus in osteoid osteomas, CT is still the method of choice, because it allows more exact targeting of the nidus.

TABLE 2 Sequence Parameters for Fast Interventional MRI

GE

GE+seg. EPI

FSE

LoLo

FOV

450 x 450

375 x 275

375 x 275

250 x 250

Matrix

256 x 256

128x128

256x187

256 x 256

Slice thickn. (mm)

10

7

10

10

TR

8 msec

246 msec

576 msec minimum

592 msec minimum

TE

3.6 msec

4.6 msec

100 msec effective

104 msec effective

Flip angle

25°

80°

90°

90°

AC

2

2

2

1

Time

4.1 sec

15 sec for 16 slices

Turbo factor 79

Turbo factor 77

EPI factor 3

Note: Sequence parameters for fast imaging techniques used for interventional magnetic resonance imaging. LoLo applies the 90° excitation pulse, orthogonally rotated to the following 180° refocusing pulses. Only the spins first excited by the 90° pulse and then refocused by the 180° pulse will give signal to the image. No fold over artifacts can occur in this type of fast small field of view imaging.

Abbreviations: GE, gradient echo; GE + EPI, gradient echo planar; FSE, fast spin echo imaging; LoLo, Local look; TE, echo time.

Note: Sequence parameters for fast imaging techniques used for interventional magnetic resonance imaging. LoLo applies the 90° excitation pulse, orthogonally rotated to the following 180° refocusing pulses. Only the spins first excited by the 90° pulse and then refocused by the 180° pulse will give signal to the image. No fold over artifacts can occur in this type of fast small field of view imaging.

Abbreviations: GE, gradient echo; GE + EPI, gradient echo planar; FSE, fast spin echo imaging; LoLo, Local look; TE, echo time.

FIGURE 4 Bone-marrow edema of unknown origin in the right iliac bone. The patient underwent magnetic resonance-guided bone biopsy in prone position using a hollow auger under local anesthesia. On pathohistology, osteomyelitis was confirmed. Fast spin echo technique.

FIGURE 4 Bone-marrow edema of unknown origin in the right iliac bone. The patient underwent magnetic resonance-guided bone biopsy in prone position using a hollow auger under local anesthesia. On pathohistology, osteomyelitis was confirmed. Fast spin echo technique.

Percutaneous biopsies of the appendicular skeleton and pelvis, however, can be considered as safe, and based upon the still limited experience, accurate procedures (Fig. 6). For many lesions, it may be used as an alternative targeting modality to CT.

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