Molecular breast imaging: use of a dual-head dedicated gamma camera to detect small breast tumors

Abstract

Objective: Molecular breast imaging with a single-head cadmium zinc telluride (CZT) gamma camera has previously been shown to have good sensitivity for the detection of small lesions. To further improve sensitivity, we developed a dual-head molecular breast imaging system using two CZT detectors to simultaneously acquire opposing breast views and reduce lesion-to-detector distance. We determined the incremental gain in sensitivity of molecular breast imaging with dual detectors.

Subjects and methods: Patients with BI-RADS category 4 or 5 lesions < 2 cm that were identified on mammography or sonography and scheduled for biopsy underwent molecular breast imaging as follows: After injection of 740 MBq of technetium-99m ((99m)Tc) sestamibi, 10-minute craniocaudal and mediolateral oblique views of each breast were acquired. Blinded reviews were performed using images from both detectors 1 and 2 and images from detector 1 only (simulating a single-head system). Lesions were scored on a scale of 1-5; 2 or higher was considered positive.

Results: Of the 150 patients in the study, 128 cancers were confirmed in 88 patients. Averaging the results from the three blinded readers, the sensitivity of dual-head molecular breast imaging was 90% (115/128), whereas the sensitivity from review of only single-head molecular breast imaging was 80% (102/128). The sensitivity for the detection of cancers < or = 10 mm in diameter was 82% (50/61) for dual-head molecular breast imaging and 68% (41/61) for single-head molecular breast imaging. On average, 13 additional cancers were seen on dual-head images and the tumor uptake score increased by 1 or more in 60% of the identified tumors.

Conclusion: Gains in sensitivity with the dual-head system molecular breast imaging are partially due to increased confidence in lesion detection. Molecular breast imaging can reliably detect breast lesions < 2 cm and dual-head molecular breast imaging can significantly increase sensitivity for subcentimeter lesions.

Fig. 1

Photograph shows a dual-head molecular breast imaging system comprising two cadmium zinc telluride detectors mounted on modified mammographic gantry. To perform molecular breast imaging, the breast is lightly compressed between two detectors. When imaging the breast in craniocaudal position, detector 1 is located inferiorly and detector 2 is located superiorly to the breast. To image the breast in mediolateral oblique position, gantry is rotated so that detector 1 is located laterally and detector 2 is located medially to the breast.

Fig. 2

Bar graph shows sensitivity of molecular breast imaging for detection of breast tumors as function of tumor size. Results are shown for single-head molecular breast imaging system (lower detector), dual-head molecular breast imaging system, and scintimammography [49]. Note that no data were reported for detection of tumors 0–5 mm with scintimammography.

Fig. 3

70-year-old woman with 6-mm invasive ductal carcinoma (arrow) in upper inner left breast initially identified on mammography as BI-RADS category 4 lesion. Screening mammograms and craniocaudal and mediolateral oblique views from both molecular breast imaging detectors are shown. When inferior and lateral molecular breast imaging views acquired with detector 1 (middle images) were reviewed in blinded reading session, they were interpreted as showing negative findings. When both inferior and lateral views from detector 1 and superior and medial molecular breast imaging views from detector 2 (right images) were available for interpretation, cancer was identified in medial view alone. Average uptake score of lesion visualized with molecular breast imaging was 3 (moderate focal uptake). LMLO = left mediolateral oblique, LCC = left craniocaudal.

Fig. 4

46-year-old woman with two foci of mixed invasive ductal carcinoma with ductal carcinoma in situ in upper inner right breast: One is located at 1-o’clock position 7 cm from nipple and second is located at 2-o’clock position 3 cm from nipple. Cancers were initially identified on mammography and sonography as BI-RADS category 5 lesions. Screening mammogram and craniocaudal and mediolateral oblique views from both molecular breast imaging detectors are shown. During blinded readings, when inferior and lateral molecular breast imaging views acquired with detector 1 (middle images) were available for interpretation (corresponding to views from single-head molecular breast imaging), one focus of cancer was detected. When superior and medial molecular breast imaging views from detector 2 were available in addition to detector 1 views during separate blinded reading session, same cancer was identified but average lesion uptake score was increased from 3 to 5, indicating increase in reader confidence in identifying lesion. Also, with additional detector 2 views, second focus of cancer (arrow) was identified as blush of low-intensity uptake (uptake score of 2) visible in superior craniocaudal view only. RMLO = right mediolateral oblique, RCC = right craniocaudal.

Fig. 5

82-year-old woman with 4-mm invasive lobular carcinoma (arrows) in upper mid left breast at 12-o’clock position 6 cm from nipple. Cancer was initially identified on mammography as BI-RADS category 5 lesion; 5-mm benign intramammary lymph node in lower inner breast was also identified on mammography and sonography. Screening mammograms and craniocaudal and mediolateral oblique views from both molecular breast imaging detectors are shown. During blinded readings of only inferior and lateral molecular breast imaging views from detector 1 (middle images), molecular breast imaging findings were interpreted as negative. When superior and medial views from detector 2 (right images) were available for molecular breast imaging interpretation in addition to detector 1 views, cancer was identified and given uptake score of 4 (strong focal uptake) by two readers and score of 3 (moderate focal uptake) by third reader. Findings were otherwise negative on molecular breast imaging. LMLO = left mediolateral oblique, LCC = left craniocaudal.