18.2 Stereotactic and Ultrasound-Guided Biopsy
Key Takeaways
- Stereotactic core biopsy (upright or prone) is the method for calcifications and other mammographic-only targets; a scout image is followed by a stereo pair, and vacuum-assisted cores are commonly used.
- Ultrasound-guided core biopsy is preferred for masses that are sonographically visible because the needle is watched in real time.
- A tissue-marker clip is typically placed after percutaneous sampling so the site can be found if the original finding is gone.
- Cyst aspiration and fine-needle aspiration biopsy were removed from ARRT Mammography Procedures in 2025; ultrasound guidance of a mass for core biopsy remains in.
- If the scout does not show the target in the biopsy window, reposition — do not sample blindly.
Why Guidance Modality Is a High-Yield Item
The 2025 Task Inventory still asks you to assist with two biopsies: ultrasound core biopsy with clip placement and stereotactic core biopsy with clip placement (prone or upright). ARRT tests basic knowledge: which method finds which target, what images prove you are on the finding, and what usually happens after the cores come out. The most common miss is treating ultrasound as a universal shortcut. Isolated mammographic calcifications do not become an ultrasound case "because ultrasound is real-time."
Keep the 2025 removals in view. Sentinel node mapping, cyst aspiration, and fine-needle aspiration (FNA) biopsy are not current mammography exam procedures. Ultrasound guidance of a mass for core biopsy is in. Do not confuse "this mass looks cystic on ultrasound" with "cyst aspiration is on the test."
Preparation, consent, and time-out for both rooms are in history, consent, time-out, setup, and postprocedure instructions. Clip films, core radiographs, and wire localization are in needle localization, specimen imaging, and clip placement.
Stereotactic Core Biopsy
Stereotactic guidance uses mammographic parallax. Two angled images let the system calculate the target's three-dimensional coordinates — X, Y, and depth (Z) — relative to the compressed breast in the biopsy window.
Scout, then stereo pair
The usual sequence is the sequence ARRT expects you to recognize:
- Position the breast so the finding sits in the biopsy window.
- Obtain a scout image (0°) and confirm the target is visible and not clipped by the window edge.
- Obtain a stereo pair — classically two images about 15° to either side of the scout plane (±15°).
- The physician (or targeting software under physician direction) marks the calcifications or mass on both stereo images.
- The system computes coordinates and needle depth.
- After the needle or vacuum probe is placed, repeat stereo images confirm that the aperture sits at the target before sampling.
If the scout does not show the finding, you do not biopsy. Reposition, change the projection (for example CC versus a lateral approach), or recognize that a tomosynthesis-only finding may need DBT-guided targeting rather than a 2D scout that never displayed the lesion. Stay at the basic level: stereotactic and tomosynthesis-guided work is for mammographic findings.
Upright versus prone
ARRT lists both platforms. Exam items often ask which one to choose, not how to service the table.
| Platform | Patient position | Practical strengths | Practical limits |
|---|---|---|---|
| Prone table | Face-down; breast through an aperture | Patient cannot see the needle; often fewer vasovagal events; breast hangs away from the chest wall | Posterior, axillary, or very inferior lesions may be out of reach; some patients cannot lie prone (respiratory disease, kyphosis, recent abdominal surgery, table weight limits) |
| Upright (sitting or lateral decubitus) | Seated or on the side, dedicated or add-on unit | Better access to many posterior lesions; option when prone is impossible | Vasovagal reactions are more common because the patient sees the work; motion if the patient is unsteady |
A patient with isolated UOQ calcifications who cannot lie prone is not an automatic surgical biopsy. Upright or lateral-decubitus stereotactic biopsy is the usual next thought.
What stereotactic is for, and how you sample
Stereotactic (or tomosynthesis-guided) biopsy is the method of choice for calcifications and for masses, asymmetries, or architectural distortion seen only on mammography or DBT with no reliable ultrasound correlate.
Vacuum-assisted core sampling is commonly used, especially for calcifications. A vacuum-assisted probe can collect multiple cores through one insertion and retrieve the tiny calcium flecks that prove you hit the cluster. Spring-loaded cores that work well for a sonographic mass often undersample a calcification cluster. You do not need a brand name. You do need "vacuum-assisted core is the usual stereotactic tool for calcs."
Stroke margin is the distance from the target to the far skin (toward the image receptor). If the calculated throw would exit the breast, you do not fire. Change approach, compression, or needle geometry until the margin is safe.
After cores are taken, intraprocedural specimen radiographs of the cores confirm that calcifications are in the tissue. If they are not, the physician retargets or takes additional samples before the patient gets off the table. A clip is typically deployed at the cavity so the site can be found later if the mammographic finding is gone.
Ultrasound-Guided Core Biopsy
Ultrasound guidance is real-time. The physician watches the needle enter the mass on the monitor. That is the method of choice for sonographically visible masses (and other ultrasound-visible targets, such as a solid-appearing nodule or a clip that can be seen with ultrasound).
Typical set-up: patient supine or posterior oblique, arm above the head, lesion documented in two planes, sterile probe cover, local anesthetic, a small nick if a larger device is used, then cores. Many mass biopsies use a spring-loaded core needle; vacuum-assisted devices are also used under ultrasound, especially for small masses. You do not need to memorize every gauge. You do need to know that ultrasound core biopsy with clip placement is an assist procedure on the 2025 task list.
Because the needle is visible in real time, ultrasound is a poor choice for isolated mammographic calcifications that have no ultrasound mass. "I will just look with ultrasound" is not a substitute for stereotactic targeting.
What was removed — and what was not
Cyst aspiration as a standalone mammography exam procedure was removed in 2025. Do not study it as a current 2.D task. If a cystic component is encountered while sampling a mass, handle any fluid as a body fluid under biohazard handling and follow the physician's on-table decision. Do not treat diagnostic cyst aspiration as a listed mammography procedure.
FNA biopsy was likewise removed. Sentinel node mapping was removed from Procedures. Those three belong in your "do not pick this" pile when an older-looking option appears.
Clip Placement After Percutaneous Biopsy
After adequate sampling, a radiopaque tissue marker (clip) is usually placed at the biopsy cavity. Clips matter most when vacuum-assisted sampling removes most or all of a small finding: the clip may be the only future target for localization. Post-clip mammograms document where the clip sits relative to the original finding. Displacement along the compression axis after the breast is released is the accordion effect — a reason the post-clip mammogram can look "off" compared with stereo images obtained under compression. Imaging of that clip is tested with specimen and localization films in the next section.
Choosing the Table: Stereotactic Versus Ultrasound
| Target type | Preferred guidance | Why |
|---|---|---|
| Isolated microcalcifications | Stereotactic (prone or upright) | Calcifications are mammographic findings; specimen radiographs prove they are in the cores |
| Mass, distortion, or asymmetry seen only on mammography/DBT | Stereotactic or DBT-guided | No reliable real-time ultrasound target |
| Mass clearly seen on ultrasound | Ultrasound core biopsy | Real-time needle visualization; no stereo pair required |
| Clip or cavity visible on ultrasound after a prior biopsy | Ultrasound if visible; mammographic/stereotactic if not | Use the modality that actually shows today's target |
Realistic Exam Scenario
Screening shows a tight cluster of pleomorphic calcifications in the left breast at 10 o'clock, 8 cm from the nipple. Diagnostic mammography confirms the cluster. Ultrasound of that quadrant shows no mass. The correct assist procedure is stereotactic vacuum-assisted core biopsy with clip placement, not ultrasound core biopsy and not FNA. After cores, the mammographer radiographs the specimens. If no calcium is on that film, sampling is not finished.
Common Traps
- Picking ultrasound for isolated calcifications.
- Forgetting the scout-then-stereo-pair sequence.
- Calling FNA or cyst aspiration a current ARRT mammography procedure.
- Omitting clip placement after a vacuum-assisted biopsy that may remove the entire mammographic finding.
- Firing when stroke margin is inadequate.
A diagnostic mammogram shows a cluster of suspicious calcifications with no sonographic mass. Which procedure should the mammographer be prepared to assist with on the 2025 ARRT Mammography outline?
After the breast is positioned in the stereotactic window, which imaging sequence is used to calculate target coordinates before the needle is placed?
Which statement correctly describes ultrasound's role on the current ARRT Mammography interventional outline?