Proof of concept for low‐dose molecular breast imaging with a dual‐head CZT gamma camera. Part II. Evaluation in patients

Abstract

Purpose: Molecular breast imaging (MBI) has shown promise as an adjunct screening technique to mammography for women with dense breasts. The demonstration of reliable lesion detection with MBI performed at low administered doses of Tc-99 m sestamibi, comparable in effective radiation dose to screening mammography, is essential to adoption of MBI for screening. The concept of performing low-dose MBI with dual-head cadmium zinc telluride (CZT) gamma cameras has been investigated in phantoms in Part I. In this work, the objectives were to evaluate the impact of the count sensitivity improvement methods on image quality in patient MBI exams and to determine if adequate lesion detection could be achieved at reduced doses. Methods: Following the implementation of two count sensitivity improvement methods, registered collimation optimized for near-field imaging and energy acceptance window optimized for CZT, MBI exams were performed in the course of clinical care. Clinical image count density (counts/ cm 2 ) was compared between standard MBI [740 MBq (20 mCi) Tc-99 m sestamibi, standard collimation, standard energy window] and low-dose MBI [296 MBq (8 mCi) Tc-99 m sestamibi, optimized collimation, wide energy window] in a cohort of 50 patients who had both types of MBI exams performed. Lesion detection at low doses was evaluated in a separate cohort of 32 patients, in which low-dose MBI was performed following 296 MBq injection and acquired in dynamic mode, allowing the generation of images acquired for 2.5, 5, 7.5, and 10 min/breast view with proportionately reduced count densities. Diagnostic accuracy at each count density level was compared and kappa statistic was used to assess intrareader agreement between 10 min acquisitions and those at shorter acquisition durations. Results: In patient studies, low-dose MBI performed with 296 MBq Tc-99 m sestamibi and new optimal collimation/wide energy window resulted in an average relative gain in count density of 4.2 6 1.3 compared to standard MBI performed with 740 MBq. Interpretation of low-dose 296 MBq images with count densities corresponding to acquisitions of 2.5, 5, 7.5, and 10 min/view and median lesion size of 1.4 cm resulted in similar diagnostic accuracy across count densities and substantial to near-perfect intrareader agreement between full 10 min-views and lower count density views. Conclusions: Review of patient studies showed that registered optimized collimation and wide energy window resulted in a substantial gain in count sensitivity as previously indicated by phantom results. This proof of concept work indicates that MBI performed at administered doses of 296 MBq Tc-99 m sestamibi with the applied count sensitivity improvements permits the detection of small breast lesions in patients. Findings suggest that further reductions in acquisition duration or administered dose may be achievable.

Nuclear imaging of the breast: Translating achievements in instrumentation into clinical use

“…169 Recent improvements in the CZT-based MBI technology used in this screening MBI trial have resulted in a ∼3 fold reduction in the administered dose of 99m Tc-sestamibi required for MBI. 170,171 Preliminary results from 600 patients screened with low-dose MBI performed with 300 MBq (8 mCi) 99m Tcsestamibi and mammography confirmed the findings of improved sensitivity of MBI relative to mammography in dense breasts at reduced administered dose. 172 Early findings from trials underway at Mayo Clinic indicate feasibility of performing screening MBI using administered doses as low as 150 MBq (4 mCi) 99m Tc-sestamibi.…”

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

“…Work from our institution has demonstrated ability perform MBI using 150-300 MBq Tc-99m sestamibi due to several count sensitivity improvement methods such as registered high sensitivity collimation and use of a wide energy window for CZT detectors. 23,24 Another advantage of the CSH collimator design is that the single-detector configuration would permit easier access to the breast than is possible with PEM, which requires a dualdetector configuration for positional information. Depending on the gantry design, a single-detector configuration would allow for theoretically infinite choices in positioning around the breast to optimize visualization and access to the lesion.…”

“…23 The number of particles generated was chosen so that simulations of the registered high-sensitivity MBI collimator (described below) generated images with background tissue count densities similar to what is observed clinically in patient MBI studies (median: 4.60 ± 1.13 counts/cm 2 /10 min/MBq). 24 Currently, we employ an administered dose of ∼300 MBq Tc-99m sestamibi, with a goal of reducing this dose to 150 MBq in the screening setting. Hence, the simulations were designed to achieve a count density of approximately 690 ± 170 counts/cm 2 , equivalent to the theoretical mean count density in a patient image acquired for 10 min with an administered dose of 150 MBq sestamibi.…”

Nuclear Breast Imaging: Clinical Results and Future Directions

“…Most published articles about BSGI reported injected doses of 555-1,110 MBq (15-30 mCi). With dual-head cadmium-zinc-telluride detector systems and optimized collimator and energy windows, an injected dose averaging 300 MBq (8.1 mCi) has been used while maintaining performance characteristics (12). Unlike mammography, radiation exposure during nuclear breast imaging is to the whole body, with the greatest accumulation of 99m Tc-sestamibi seen in the colon, kidneys, bladder, and gallbladder.…”