MRI-guided vacuum assisted breast biopsy – How I do it

Technical Requirements

The MRI-guided VABB is conducted in our setup with a dedicated open breast biopsy coil and a grid-type positioning device (BI320PA, NORAS, Germany, which can either be a grid or pillar-and post-positioning device) on a 1.5 T magnet. At least, 1.5 T MRI with an open coil (minimum four channels) is essential for doing MRI-guided VABB. Compression plates are fitted on the breast coil for gentle compression in the latero-medial direction. If both breasts need to be biopsied, then a positioning device allowing bilateral simultaneous compression is required; else, it can be done in different settings. A fiducial marker filled with diluted gadolinium is placed on the grid plate and serves as the reference point for calculating the coordinates for subsequent targeting [Figure 1]. The fiducial marker appears as linear hyperintensity on pre-contrast T1-weighted images.

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Figure 1:

Grid compression plates for positioning and mildly compressing the affected breast. The fiducial (blue arrow) serves as a reference point for calculating the coordinates.

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Postioning and MRI Sequences

The procedure is performed with the patient in a prone position, with their breasts positioned in the interventional breast coil and the target breast gently compressed between the medial and lateral plates. Although the needle is typically inserted from the lateral to medial direction, other approaches are feasible. Lesion localization involves the use of a pre-contrast T1 3D sequence and dynamic post-contrast T1-weighted spoiled gradient echo (FLASH-3D) sequence. Gadopentetate dimeglumine, 0.1 mmol/l/kg body weight, is injected intravenously as a rapid bolus, and axial images (1-mm slice thickness) are obtained immediately after contrast injection. Subtraction images are automatically generated by subtracting pre-contrast images from post-contrast images.

Targeting of the Lesion

The lesion and fiducial marker on the grid plate are identified, and the coordinates can be calculated either manually or using targeting software (like DynaCAD). The targeting software calculate all coordinates, which are transferred manually on the positioning device. When done manually, the T1 3D post-contrast sequence is loaded in the 3D format, and on sagittal reconstructed images, the target is marked with an “X” and transferred to the initial image displaying grid markings, along with the fiducial [Figure 2]. Both the fiducial and target appear on the same slice, allowing calculation of the number of grids separating the lesion from the fiducial grid in the craniocaudal and anteroposterior directions [Figure 2]. Depending on the location of the “X” within the grid, the position of the lesion on the needle guide block is estimated, and the appropriate hole on the grid block is determined [Figure 2]. These coordinates are written on a paper or on an MRI grid worksheet (provided by some vendors) and are transferred manually on the positioning device in the MRI room. The guide block (10G block) has four holes, allowing targeting from 13 positions based on the block’s rotation within the grid [Figure 3]. The block features a locking mechanism to stabilize it within the grid after installation. The lesion depth is measured from the skin to the abnormality on the axial or coronal images, with an additional 2 cm added to account for the grid plate thickness.

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Figure 2:

The 3D T1 post contrast axial sequence is loaded in 3D (axial, sagittal, coronal and MIP images with orange, pink & blue cross hair) and target (linear branching NME, marked as blue cross) and fiducial (marked as white arrow) are recognised and the target is transferred to first Sagittal image with grid markings. In this case the target (blue cross) is approached through the same grid as fiducial seen as white dot on first sagittal image and through mid hole on nipple side. NME: Non mass enhancement.

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Figure 3:

The grid block with four holes is placed in the desired grid in the required orientation as per the target calculation.

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VABB Procedure

Beneath the selected grid square, the skin is cleansed and anesthetized, and a vertical skin incision is made beneath the chosen needle-guide hole. The localizing set [Figure 4] is utilized to reach the lesion. It is crucial to ensure that the introducer passes through the incision before securing the grid block in the grid square. The plastic coaxial, along with the introducer, is advanced through the designated hole in the grid block to the desired depth [Figure 5]. The obturator replaces the introducer [Figure 6a], and a sequence is performed to confirm correct obturator positioning. Lesions may be displaced by local anesthetic, hemorrhage, or the “snowplow” effect of the advancing needle. Any necessary adjustments can be made before removing the obturator and replacing it with the probe through the coaxial [Figure 6b]. Images are reviewed to determine the lesion’s position relative to the obturator in terms of clock position [Figure 7], and multiple contiguous and directional samplings are performed using the VABB system (the ENCOR ENSPIRE™ Breast Biopsy System). Automated tissue excision and collection (ATEC) from Suros and Mammotome from Johnsons are the other VABB systems available in the market. Another repeat sequence confirms post-biopsy changes at the previously noted lesion site. Smaller lesions can be entirely removed with VABB.

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Figure 4:

Trolley for MRI-guided VABB. Requirements are (from L to R) gloves, specimen bottles, a clip marker, a localizing set (introducer, Visiloc, coaxial and grid block, blade, and forceps), local anaesthesia (2% Lignocaine, and diluted lignocaine with adrenaline), and an MRI-compatible 10G probe. VABB: Vacuum-assisted breast biopsy.

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Figure 5:

The introducer is placed through the (a) coaxial to the desired hole and to the required depth (b) in the grid block.

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Figure 6:

(a) The introducer is replaced by the Visiloc. If the MRI-sequence confirms the appropriate position of the Visiloc then it is replaced by the (b) probe and multiple samples are taken.

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Figure 7:

MRI Guided VABB performed in a case of metastastic left axillary nodes, (a) with linear NME in outer half of left breast as target. (b) The obturator was confirmed to be accurately placed in relation to the target. (c) Post biopsy changes confirmed accurate sampling of the target. VABB: Vacuum-assisted breast biopsy, NME: Non mass enhancement.

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Speed is vital to ensure that contrast does not wash out, making the lesion inconspicuous, and to maintain patient comfort, as prolonged procedures make it challenging for the patient to remain still.

Clip Placement

A metallic MRI-compatible breast clip marker can be placed to mark the biopsy site for future reference. If histopathological examination confirms a malignant or high-risk lesion, a stereo or ultrasound-guided wire can be placed with this marker serving as the surgical target. Even if benign findings are confirmed, the clip serves as a reference on follow-up MRI.

Post-procedure, manual compression for 10–20 minutes is applied to stop bleeding. A check mammogram is performed to ascertain the position of the marker clip. The most common complication encountered is a small hematoma, which is managed with ice application followed by a pressure dressing.

Challenges in Thin Breasts

Performing MRI-guided VABB in patients with thin breasts can be challenging due to the limited tissue available for compression and adequate needle placement. Insufficient tissue thickness may lead to difficulty in stabilizing the breast, affecting biopsy accuracy and sample retrieval. Plumping the breast with local anesthesia increases the thickness of the breast. The use of a petite needle with blunt ends available with the Atec Suros VABB machine and the use of half-notch option available in Encore Enspire machines are helpful.

Challenges with Posterior Lesions

Lesions located in the posterior aspect of the breast, close to the chest wall, pose a challenge for MRI-guided biopsy. Reaching these lesions with the biopsy needle while avoiding injury to the pectoral muscles or ribs requires precise imaging guidance and careful maneuvering. Additionally, limited needle angulation due to the proximity of the chest wall can make the procedure technically difficult.

Challenges with Anterior Lesions

Lesions located in the anterior breast region, near the skin, may be difficult to target due to the limited depth available for needle insertion. The risk of skin tenting or inadequate sampling increases in such cases. Additionally, maintaining accurate positioning within a shallow field can be challenging, requiring expertise in adjusting compression and needle trajectory.

Patient Positioning and Motion Artifacts

MRI-guided procedures require the patient to remain still for an extended period while lying in the prone position. Any movement can lead to motion artifacts, reducing image clarity and making lesion targeting difficult. Proper patient positioning and immobilization are crucial to ensure accurate needle placement and avoid procedural complications.

Access to Equipment and Expertise

MRI-guided breast biopsy is a resource-intensive procedure that requires specialized equipment and trained personnel. Limited availability of MRI-compatible biopsy devices and experienced radiologists can impact the feasibility and efficiency of the procedure, particularly in resource-limited settings.

Non-visualization of the Target

The target may not be seen on the day of the biopsy in of the cases. This could be due to excessive compression, so the lesion may not enhance due to compressed blood vessels. Mild release of pressure can help to see the target lesion. The other reason could be the lesion may not be a true lesion and enhancement due to hormonal changes may have been seen on the day of the diagnostic examination. Follow-up MRI in 6–12 weeks is advised in such cases.^[4]