Validating accurate placement of non-wire localization markers in non- palpable breast tumors using breast CT: a feasibility study

doi:10.21203/rs.3.rs-3313544/v1

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Validating accurate placement of non-wire localization markers in non- palpable breast tumors using breast CT: a feasibility study

https://doi.org/10.21203/rs.3.rs-3313544/v1

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Background

Dedicated photon-counting breast CT is an emerging imaging technology for imaging the breast without the need for compression of the breast and with a radiation dose comparable to that of mammography. In this study, we assessed the feasibility of using breast CT to confirm the accurate placement of localization markers in nonpalpable breast tumors before breast-conserving surgery.

Methods

We first evaluated the artifacts caused by 5 different metallic markers in 2 different phantoms and applied a computer algorithm to effectively remove the beam hardening artifacts. Next, we tested the potential of dedicated photon-counting breast CT combined with the artifact-removing algorithm to assess accurate marker placement in 5 patients with nonpalpable breast tumors.

Results

In the phantoms, all markers caused beam-hardening artifacts, but the computer algorithm successfully removed them. In the patients, the correct placement of the markers was visualized with breast CT and confirmed postsurgery, as all markers and tumors were present in the surgical specimen.

Conclusion

Dedicated photon-counting breast CT is an effective modality for demonstrating accurate placement of localization markers.

Health sciences/Oncology/Surgical oncology

Biological sciences/Biological techniques/Imaging/X ray tomography

Dedicated photon-counting breast CT is an emerging imaging technology for breast examination. Unlike mammography and limited angle tomosynthesis, it offers the advantage of high-resolution, isotropic 3D images without tissue overlap [1–5]. Additionally, the use of a photon-counting detector allows for radiation doses that are comparable to or possibly lower than those in mammography and tomosynthesis [3].

One of the key advantages of breast CT is that it eliminates the need for breast compression, greatly increasing patient comfort and compliance [6]. Additionally, image acquisition is fast, taking less than 20 seconds per breast.

As a patient-friendly method, breast CT holds promise in accurately confirming the placement of localization markers before breast-conserving surgery. After seed insertion, commonly guided by ultrasound, a postprocedure mammogram is usually obtained to verify proper marker placement and serve as a roadmap for the surgeon. However, in situations where patients decline mammography or have dense breast tissue and mammographic occult lesions, assessing accurate marker placement can be challenging. Breast-CT may solve this problem.

Metallic markers, however, cause beam-hardening artifacts in CT. In whole-body CT and cone beam CT, algorithms to reduce metal artifacts (MAR) have already been established [7, 8, 9].

In this feasibility study in phantoms, we evaluate the size of the beam-hardening artifacts caused by metallic markers in photon-counting spiral breast-CT and the efficacy of an MAR algorithm to reduce these artifacts. The potential of photon-counting breast CT combined with MAR to evaluate accurate marker placement was tested in 5 patients with nonpalpable breast tumors.

Breast-CT:

Examinations were performed on a dedicated CE-marked spiral Breast-CT system equipped with a photon-counting cadmium-telluride detector (nu:view; AB-CT–Advanced Breast CT GmbH, Erlangen, Germany). During one rotation around the object, up to 2,000 projection images are created without compression. A full spiral scan takes 7 to 12 seconds, and the scan length is chosen according to the object size (possible lengths are 80, 120, and 160 mm). A fixed X-ray tube voltage of 60 kV and a chosen tube current of 32 mA as well as the high-resolution (HR) mode “HighRes” were used for image acquisition, resulting in 0.15 mm thick slices.

After acquisition of images, the raw data were transferred to a dedicated research workstation for performing reconstructions and application of the metallic artifact reduction algorithm.

Phantom experiments:

Two types of phantom models were used to illustrate the presence of artifacts and the subsequent removal of artifacts using the algorithm.

Phantom 1 (Fig. 1) consisted of a 9 cm water cylinder in which 15 ml plastic centrifuge tubes were inserted and filled with low-density plastic pellets and water.

Four different metallic markers were inserted in the tubes: two different titanium tissue markers (UltraClip II Tissue Marker Ribbon (C.R. Bard, IJsselstein, The Netherlands) and a BIP O-Twist-Marker (BIP Medical, Türkenfeld, Germany)) and two different preoperative localization markers: one dummy radioactive I125 seed marker, of which the radioactivity had decayed (Pi Medical, Raamsdonkveer, The Netherlands), and one magnetic marker (Pintuition Seed, Sirius Medical, Eindhoven, the Netherlands).

Phantom 2 was a nonanatomical phantom that did not mimic the anatomy of the breast but mimicked breast and tumor tissue in terms of attenuation properties. In contrast-enhanced breast CT in patients with breast tumors, we found the attenuation property of fibroglandular tissue to be -27.5 ± 16.5 Hounsfield units (HU). The average HU of tumor tissue in contrast-enhanced breast CT was 101 ± 44.9. As a substance for mimicking the attenuation properties of fibroglandular tissue, we chose hairstyling gel, -51,99 ± 6,77 HU. Two layers of grapes of different sizes were inserted in the gel to represent contrast-enhancing breast cancers, 44,70 ± 6.59 HU. Two of the grapes were marked with a magnetic marker (Pintuition Seed, Sirius Medical, Eindhoven, the Netherlands) in horizontal or vertical orientation.

Metal artifact reduction

To remove the artifacts on CT created by the metallic markers, the method of 3D linear interpolation combined with edge-preserving attenuation-normalization was used as described by Prell et al. (10). This method consists of quasi-iterative correction steps after a first reconstruction of the acquired raw data, and in a final combination procedure, the metal implants are reinserted into the corrected images.

All reconstructions were made on a dedicated research workstation on which the MAR algorithm had been installed.

Patient cases

The potential value of breast CT to assess the position of inserted markers was examined in 5 patients who underwent presurgical placement of an 125I marker (n=3) or a magnetic marker (n=2). These patients refused to undergo mammographic confirmation of marker position, so we offered them a breast-CT examination instead. In 4 of the patients, localization seeds had been placed in an invasive ductal carcinoma under ultrasound guidance. In the fifth patient with biopsy-proven DCIS, a 125I marker was placed next to the calcifications under ultrasound guidance. In all patients, the presence of the marker in the surgical specimen after the operation was retrospectively retrieved from the pathology report.

Phantom 1

All the examined metallic markers cause beam-hardening artifacts, but the severity of the artifact is related to the size of the marker (Fig 2). The small UltraClip II marker only causes a very tiny artifact. With the other markers, the size of the artifacts is larger, especially with the magnetic marker (marker size 5 x 1.6 mm). After application of the MAR algorithm, all artifacts largely disappear.

Phantom 2

In our breast tissue mimicking phantom of styling gel and grapes, magnetic markers cause a large artifact rendering the grapes hardly visible anymore (fig. 3.1a and 3.1b). After application of the MAR algorithm, the artifacts disappear, while the background information of the grapes is preserved without decreasing the spatial resolution (fig. 3.2a and 3.2b). Fig. 3.3a and 3.3b show the calculated subtraction images between the uncorrected and corrected images by using a sharp reconstruction kernel. The orientation of the markers affects the orientation of the metallic artifacts, as seen on a coronal MIP (maximum intensity projection) reconstruction of the artifacts (fig. 3.4a and 3.4b).

On magnification images and after adjusting the contrast window width and level, a small hyperdense rim of 1 mm remained visible around the magnetic marker after application of the MAR algorithm (fig. 4).

Patient cases

We tested the potential value of breast CT in assessing the results of metallic marker placement in 5 patients scheduled to undergo surgical resection of an invasive breast carcinoma (4 patients) and DCIS (1 patient).

The magnetic markers cause significant beam-hardening artifacts, which are successfully removed by the MAR algorithm (fig. 5). The subtraction image shows the removed artifacts.

In the patient with DCIS, the calcifications remained visible after application of the MAR algorithm (Fig. 6) and removal of the artifacts from a 125I marker. Application of the MAR does not result in digital removal of calcifications.

Fig. 7 shows the volume-rendered image of a magnetic marker placed next to a previously inserted titanium marker in a tumor. This “virtual mammogram” was used as a roadmap by the surgeon during the operation.

In all patients, the localization marker was visible in the tumor in the surgical specimen, as stated in the pathology report.

Breast-conserving surgery is the treatment of choice in patients with early-stage nonpalpable breast malignancies and ductal carcinoma in situ (DCIS) (11). For optimal surgical outcomes, accurate preoperative localization of these tumors is essential.

Wire-guided localization (WL) is the most widely used method for the localization of nonpalpable breast lesions. However, the limitations of WL (patient discomfort, logistic challenges, possible wire migration and transection) have led to the development of alternative approaches, such as radioactive seed localization, radar reflector localization (SAVI SCOUT), magnetic seed localization and radiofrequency identification (RFID) (12).

In addition to logistic and patient-comfort related advantages, nonwire marking devices have the advantage that radiologists are allowed to place the device without concern for the surgical approach. As the surgical approach is not directed by the path of a wire, there is potential for limiting specimen volume and improving cosmetic outcome. A postprocedure mammography is usually performed for assessment of the correct location of the markers and for initial assistance of the surgeon in localizing the tumor in the operating room.

However, some women decline mammography, and in the case of a dense mammogram or mammographic occult tumor, it may be difficult to assess the correct position of the marker. This is important since the main challenge in the resection of nonpalpable tumors is to obtain clear resection margins while minimizing the resection of healthy breast tissue for good cosmetic outcomes.

MRI is not an alternative since these localization markers (except for the radar reflectors and the small 125I-markers) cause large susceptibility artifacts.

Breast-CT is an emerging 3D isotropic imaging technology for the breast that overcomes the limitations of 2D compression mammography. Moreover, the examination is pain-free and may be a patient-friendly alternative to mammography to confirm marker position. However, breast CT can only be used as an alternative to mammography if both the tumor and the marker can be simultaneously visualized. All metallic markers cause some beam-hardening artifacts on CT, which are size-dependent. In particular, the artifacts of the larger markers may be detrimental to the imaging of small tumors and calcifications.

In phantom experiments, we tested the potential of a computer algorithm to remove these artifacts. MAR can successfully remove even the large artifacts of relatively large magnetic markers. Only a small hyperdense rim of 1.5 mm remains visible around the marker. In 5 patients, we successfully demonstrated the potential of breast CT and MAR in confirming the position of localization markers in invasive tumors and DCIS. MAR only removed the beam-hardening artifacts, and calcifications remained visible after application of the algorithm.

Conclusion: Photon-counting breast CT is a promising modality to confirm the accurate placement of nonwire markers in nonpalpable breast tumors.

Ethics approval and consent to participate:
Approval by the Medical Research Ethics Committee (Leiden Den Haag Delft) (reference number nWMODIV2_2023019) was waived for this retrospective reconstruction of the breast CT data of the 5 patients on a separate workstation. These patients refused mammography and consented to undergo breast CT as an alternative modality for confirmation of the correct marker position. All experiments were performed in accordance with relevant guidelines and regulations.

Consent for publication:

All patients gave informed consent for publication of their data, although the images presented in this paper are entirely unidentifiable and there are no details on individuals reported within the manuscript..

Data availability:

All data generated or analyzed during this study are included in this published article.

Competing interests:

D. Kolditz is an employee of AB-CT – Advanced Breast-CT GmbH, Erlangen, Germany and provided the MAR software.

All other authors have no disclosures.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors’ contributions:

M.Wa.: conceptualization, methodology, formal analysis, investigation, writing - original draft, review & editing.

L.C.: phantom experiments, writing – original draft

D.K.: provided the MAR software, methodology, writing – review & editing

J.D.: methodology, writing – review & editing, supervision

M.We.: conceptualization, methodology, writing – review & editing

N.V.: conceptualization, methodology, patients investigation, writing – review & editing

J.H.: conceptualization, writing – review & editing

All authors have approved the submitted version and have agreed both to be personally accountable for the author's own contributions and to ensure that questions related to the accuracy or integrity of any part of the work, even those in which the author was not personally involved, are appropriately investigated, resolved, and the resolution documented in the literature.

Acknowledgements

Gerrit Kracht: photography of markers

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Competing interest reported. D. Kolditz is an employee of AB-CT – Advanced Breast-CT GmbH, Erlangen, Germany. All other authors have no competing interests.

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Validating accurate placement of non-wire localization markers in non- palpable breast tumors using breast CT: a feasibility study

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Abstract

Background

Methods

Results

Conclusion

Figures

INTRODUCTION

METHODS

RESULTS

Phantom 1

Phantom 2

DISCUSSION

Declarations

References

Additional Declarations

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