Purpose: MR-guided wireless localization became possible in 2022 with the development of an MR-compatible Scout deployment mechanism. We present our experience at a large academic medical center adopting MR-guided Scout localization and compare MR-guided Scout to MR-guided wire localization.
Materials and Methods: Informed consent was waived for this IRB-approved retrospective study. Patients who underwent breast MR-guided Scout or wire localization at our institution between October 2022 and July 2023 were identified using mPower search. Electronic medical records and imaging studies were reviewed. Differences regarding complication rate and device used for localization surgery were analyzed using a two-sample proportion test. Number of localization devices placed, days from site identified to surgery, and anesthesia start time were evaluated using a Wilcoxon ranksum test.
Results: 15 Scouts were placed at 14 sites in 12 patients and 37 wires were placed at 23 sites in 18 patients under MR-guidance during the study period. Each site was considered a case. 0% (0/14) of MR-guided Scout cases had complications. There was no significant difference in complication rate (p=0.25), number of localization devices placed (p=0.06), days lapsed from finding detection to surgery (p=0.82) or anesthesia start time (p=0.74) when comparing MR-guided Scout versus wire localization. Scouts were placed at time of biopsy for 71% (10/14) of cases. 86% (12/14) of Scout cases were removed at surgery, compared to 100% (23/23) of wire cases. Surgery was not performed for 14% (2/14) of Scout cases due to metastases (1) and benign concordant biopsy (1). 57% (8/14) of Scout cases were used for subsequent localization surgery compared to 100% (23/23) of wire cases (p < 0.01). Four Scout cases were removed at mastectomy.
Conclusion: MR-guided Scout localization is feasible and offers an alternative to MR-guided wire localization, without complications reported. While Scout placement facilitates surgical scheduling, there was no significant difference in days lapsed from finding detection to surgery or in operating room anesthesia start time. Scout placement at time of biopsy obviates the need for a separate localization procedure but poses a challenge in predicting appropriateness as 43% of Scout cases did not go on to localization surgery.
Clinical Relevance Statement: MR-guided Scout localization allows localization prior to the surgical date and is useful for MR findings not amenable to biopsy, where the biopsy clip is displaced, and for bracketing extent of disease. While Scout placement may be performed at time of biopsy, further evaluation is needed to determine best practices.