Collimator design for a dedicated molecular breast imaging‐guided biopsy system: Proof‐of‐concept

Abstract

Purpose: Molecular breast imaging (MBI) is a dedicated nuclear medicine breast imaging modality that employs dual-head cadmium zinc telluride (CZT) gamma cameras to functionally detect breast cancer. MBI has been shown to detect breast cancers otherwise occult on mammography and ultrasound. Currently, a MBI-guided biopsy system does not exist to biopsy such lesions. Our objective was to consider the utility of a novel conical slant-hole (CSH) collimator for rapid (<1 min) and accurate monitoring of lesion position to serve as part of a MBI-guided biopsy system. Methods: An initial CSH collimator design was derived from the dimensions of a parallel-hole collimator optimized for MBI performed with dual-head CZT gamma cameras. The parameters of the CSH collimator included the collimator height, cone slant angle, thickness of septa and cones of the collimator, and the annular areas exposed at the base of the cones. These parameters were varied within the geometric constraints of the MBI system to create several potential CSH collimator designs. The CSH collimator designs were evaluated using Monte Carlo simulations. The model included a breast compressed to a thickness of 6 cm with a 1-cm diameter lesion located 3 cm from the collimator face. The number of particles simulated was chosen to represent the count density of a low-dose, screening MBI study acquired with the parallel-hole collimator for 10 min after a ∼150 MBq (4 mCi) injection of Tc-99m sestamibi. The same number of particles was used for the CSH collimator simulations. In the resulting simulated images, the count sensitivity, spatial resolution, and accuracy of the lesion depth determined from the lesion profile width were evaluated. Results: The CSH collimator design with default parameters derived from the optimal parallel-hole collimator provided 1-min images with error in the lesion depth estimation of 1.1 ± 0.7 mm and over 21 times the lesion count sensitivity relative to 1-min images acquired with the current parallel-hole collimator. Sensitivity was increased via more vertical cone slant angles, larger annular areas, thinner cone walls, shorter cone heights, and thinner radiating septa. Full width at half maximum trended in the opposite direction as sensitivity for all parameters. There was less error in the depth estimates for less vertical slant angles, smaller annular areas, thinner cone walls, cone heights near 1 cm, and generally thinner radiating septa. Conclusions: A Monte Carlo model was used to demonstrate the feasibility of a CSH collimator design for rapid biopsy application in molecular breast imaging. Specifically, lesion depth of a 1-cm diameter lesion positioned in the center of a typical breast can be estimated with error of less than 2 mm using circumferential count profiles of images acquired in 1 min.

Direct-Conversion Molecular Breast Imaging of Invasive Breast Cancer: Imaging Features, Extent of Invasive Disease, and Comparison Between Invasive Ductal and Lobular Histology

“…In the diagnostic setting, prior studies have shown similar sensitivities (> 90%) in patients recommended for biopsy [1,4,[14][15][16]. In recent years, several innovations in detector and collimator configuration of the direct-conversion molecular breast imaging system allow the same performance at a substantially lower dose of 99m Tc-sestamibi-300 MBq compared with 740-1100 MBq previously used [7,[17][18][19][20]. Because of the high sensitivity achieved at lower doses, combined with relatively high specificity, ranging from 86% to 94%, breast gamma imaging may be a valuable tool in the evaluation of breast cancer [8,18].…”

Methodological aspects of 99mTc-sestamibi guided biopsy in breast cancer

“…An algorithm for determining the spatial location of the breast lesion was implemented in the software of the dedicated breast camera [ 37 ]. More recently, Weinmann et al developed a conical slant hole (CSH) collimator for MBI-guided biopsy with dual-head CZT, improving the accuracy of lesion depth determination [ 38 ]. To our knowledge, no full studies have yet been reported on clinical validation of MBI-guided biopsy procedures.…”

Integration of the function generation synthesis into the design of a multi-leaf collimator

“…Throughout the literature various authors have studied on characterization, parameter optimization and performance evaluation of collimator designs for different applications. Weinmann et al [1] optimized the design of novel conical slant hole collimator for molecular breast imaging (MBI) by utilizing Monte Carlo simulations. In their study, authors derived the initial design parameters from an existing parallel-hole collimator.…”