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MR Imaging–guided Breast Localization System with Medial or Lateral Access¹

¹ From the Departments of Medical Imaging (P.A.C., R.A.J., B.N.C., J.E.G.), Imaging Research (C.A.P., C.A.L., J.M., D.B.P.), Medical Biophysics (C.A.P., C.A.L., J.M., D.B.P.), Surgical Oncology (G.T.), and Anatomic Pathology (J.W.W.); and Division of Medical Oncology, Department of Medicine (E.W., K.H.), Sunnybrook Health Sciences Centre, 2075 Bayview Ave, MG166, Toronto, ON, Canada M4N 3M5. From the 2003 RSNA Annual Meeting. Received August 5, 2004; revision requested October 12; revision received March 21, 2005; accepted April 21; final version accepted September 1. Supported by the Canadian Breast Cancer Research Initiative, Terry Fox Foundation of the National Cancer Institute of Canada, the Ontario Research and Development Challenge Fund, and Amersham Health. Address correspondence to P.A.C. (e-mail: Petrina.causer{at}sw.ca).

Purpose: To evaluate the degree of error of the authors' magnetic resonance (MR) imaging–guided needle localization system for biopsy of suspicious lesions visualized only with MR imaging, by using both prospectively recorded and retrospectively reviewed data, including MR imaging lesion coordinates as the reference standard, and to determine whether any lesion or breast characteristics affect this error.

Materials and Methods: Institutional review board approval, along with informed consent, was obtained as directed by the board. In 31 patients (age range, 34–64 years; mean age, 54.5 years), 38 wires were placed for 35 lesions by means of an MR-guided needle localization system with medial or lateral access and computer software assistance for needle placement calculation. Needle and wire placement error measurements were calculated before and after necessary placement correction, accounting for tissue shift in the z plane. The error was statistically correlated with MR imaging lesion variables, breast density, and histopathologic findings by means of univariate and multivariate linear regression analyses or two-tailed paired t test. Procedure times and the frequency of medial or lateral approaches were recorded.

Results: Eleven of 35 localizations (31%) were medial, and 24 of 35 (69%) were lateral. The mean total magnet time was 61.6 minutes, and the mean needle deployment time was 9 minutes (range, 4–17 minutes). Sixteen of 35 lesions (46%) were malignant (seven ductal carcinoma in situ, six invasive ductal, two invasive lobular, and one lymphoma). The mean uncorrected needle placement error was 1.3 mm (range, 0–6 mm) for the x plane, 2.4 mm (range, 0–6.5 mm) for the y plane, and 5.6 mm (range, 0–15.6 mm) for the z plane. Fourteen of 38 needles (37%) required repositioning for z-plane error. The corrected z-plane error improved to 3.2 mm (range, 0–10.0 mm). Factors that significantly increased the uncorrected error included tissue shift in the z plane (R = 0.7), small lesion size (R = –0.59), and fatty breast density (P = .029).

Conclusion: The authors' system is accurate for performing MR-guided needle localizations for both medial and lateral approaches. Factors that increased the uncorrected needle placement error included small lesion size, fatty breast density, and tissue shift in the z plane.

© RSNA, 2006

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