Current Concepts in Molecular Breast Imaging

Abstract

Molecular breast imaging (MBI) is a functional imaging modality that utilizes technetium 99m sestamibi radiotracer uptake to evaluate the biology of breast tumors. Molecular breast imaging can be a useful tool for supplemental screening of women with dense breasts, for breast cancer diagnosis and staging, and for evaluation of treatment response in patients with breast cancer undergoing neoadjuvant systemic therapy. In addition, MBI is useful in problem-solving when mammography and US imaging are insufficient to arrive at a definite diagnosis and for patients who cannot undergo breast MRI. Based on the BI-RADS lexicon, a standardized lexicon has been developed to aid radiologists in MBI reporting. In this article, we review MBI equipment, procedures, and lexicon; clinical indications for MBI; and the radiation dose associated with MBI.

Keywords: Tc-99m sestamibi; breast cancer screening; breast cancer staging; breast-specific gamma imaging; molecular breast imaging.

Figure 1

Dual-head molecular breast imaging (MBI) systems. A: Eve Clear Scan e750 (SmartBreast, Pittsburgh, PA) (arrows denote detectors). B: LumaGEM (CMR Naviscan, Carlsbad, CA). Figure 1B is provided courtesy of CMR Naviscan Corporation, Carlsbad, CA. Used with permission.

Figure 2

Normal molecular breast imaging findings in a 46-year-old woman with prepectoral silicone implants (photopenic regions, arrows). Shown are CC views of the right (A) and left (B) breast and MLO views of the right (C) and left (D) breast.

Figure 3

Patterns of radiotracer uptake in the background normal breast parenchyma relative to subcutaneous fat per the molecular breast imaging lexicon: photopenic (A), mild homogeneous (B), moderate homogeneous (C), and marked heterogeneous (D).

Figure 4

Patterns of radiotracer uptake in lesions per the molecular breast imaging lexicon: mass homogeneous (A), mass heterogeneous (B), nonmass segmental (C), and nonmass regional (D).

Figure 5

Importance of correlating molecular breast imaging (MBI) findings with findings on mammography. A 77-year-old woman with a history of microinvasive ductal carcinoma in situ (DCIS) of the left breast treated with breast conservation therapy (BCT) and benign findings on mammography after BCT had MBI performed for evaluation of the postsurgical region. On MBI, the CC view of the right breast (A) showed no abnormal uptake, but the MLO view of the right breast (B) showed linear nonmass uptake in the superior part of the breast (arrow). Retrospective review of the mammogram showed a corresponding focal asymmetry in the upper outer quadrant on the CC (C) and MLO (D) views of the right breast (arrows), which had been stable on prior mammograms over 2 years. US imaging (not shown) demonstrated no definite correlate. Tomosynthesis-guided biopsy was performed to target the mammographic correlate for the MBI finding (not shown). Postbiopsy CC (E) and lateral (F) mammographic views showed the clip (arrows) with surrounding hematoma corresponding to the abnormal MBI uptake. The final surgical pathology review revealed invasive ductal carcinoma and DCIS, grade 1.

Figure 6

Detection of breast cancer on supplemental screening molecular breast imaging (MBI). A 48-year-old women with BRCA2 mutation had normal findings on a screening mammogram of the right breast (A, MLO view). Subsequent MBI demonstrated moderate homogeneous mass uptake (arrow) in the right breast at the 10 o’clock position (B, MLO view). Grayscale longitudinal US imaging (C) showed a corresponding irregular, hypoechoic mass (arrows). US-guided biopsy (not shown) revealed invasive ductal carcinoma, grade 3. A postprocedure lateral mammogram (D) showed the clip (circle) correlating with the region of mass uptake on MBI.

Figure 7

False-positive molecular breast imaging (MBI) findings. A-C: False-positive MBI finding in a 71-year-old woman who presented with invasive ductal carcinoma of the right breast and underwent staging MBI. Craniocaudal (A) and MLO (B) MBI views of the left breast showed retroareolar mild heterogeneous mass uptake (arrows). A grayscale longitudinal US image (C) showed a correlating circumscribed oval mass (arrows). US-guided biopsy (not shown) revealed a fibroadenoma. D-F: False-positive finding in a 60-year-old woman with dense breast tissue presenting for screening MBI. Craniocaudal (D) and posterior MLO (E) MBI views of the right breast showed marked homogeneous mass uptake (arrows) at the 6 o’clock position, 4 cm from the nipple. (Anterior, not shown, and posterior MLO MBI views were obtained due to large breast size.) A grayscale transverse US image (F) showed a correlating oval, hypoechoic mass (arrow). US-guided biopsy (not shown) revealed an intraductal papilloma with apocrine metaplasia.

Figure 8

Detection of multicentric disease on staging molecular breast imaging (MBI). A 52-year-old woman with newly diagnosed right breast invasive ductal carcinoma with lobular features. A staging grayscale transverse US image (A) showed an irregular hypoechoic mass with an echogenic rim (arrows) at the 11 o’clock position, representing the known malignancy. Mediolateral oblique mammographic view (B) showed a clip (circle) denoting the malignancy and another clip (arrow) denoting a biopsy-proven fibroadenoma. Craniocaudal (C) and MLO (D) views from the staging MBI demonstrated marked regional nonmass uptake (arrows) in the upper outer quadrant of the right breast. A second-look US image showed additional masses at the 1 o’clock position (E, arrow) and 10 o’clock position (F, arrow). US-guided biopsy (not shown) confirmed multicentric disease. Craniocaudal (G) and lateral (H) mammographic views showed 3 clips with 3 magnetic seeds (arrows) placed at preoperative localization for surgical guidance, demonstrating the total extent of disease correlating with MBI uptake.

Figure 9

Evaluation of disease extent on staging molecular breast imaging (MBI). A 71-year-old woman presented with a palpable finding in the right breast at the 12 o’clock position. Craniocaudal (A) and MLO (B) mammographic views demonstrated dense breast tissue and a subtle focal asymmetry (arrow) in the area of the palpable finding (the triangle marker was placed to localize the palpable abnormality). A longitudinal grayscale US image (C) demonstrated a 6-cm hypoechoic mass with indistinct margins at the 12 o’clock position (arrows) correlating with the palpable finding. US-guided biopsy (not shown) revealed invasive mammary carcinoma. Staging CC (D) and MLO (E) MBI views showed an 8-cm area of marked regional nonmass uptake in the central/superior part of the breast (arrows) larger than the extent of disease seen on mammography or US imaging. Final surgical pathology revealed 7.5 × 5.5-cm invasive mammary carcinoma with mucinous features.

Figure 10

Molecular breast imaging (MBI) for evaluation of the response to neoadjuvant systemic therapy (NST)—partial imaging response for a 52-year-old woman with triple-negative invasive ductal carcinoma and ductal carcinoma in situ of the right breast treated with NST. Staging MLO mammographic view (A) demonstrated an irregular mass with an associated ribbon clip (arrow) in the upper outer quadrant representing the known malignancy. Staging grayscale radial US image (B) demonstrated a correlating irregular, hypoechoic mass (arrows) at the 10 o’clock position. Staging CC (C) and MLO (D) MBI views demonstrated marked mass uptake in the upper outer quadrant (arrows) compatible with unifocal malignancy. A post-NST mammogram (E) demonstrated a clip (arrow) with no discrete residual measurable mass. A correlating grayscale radial US image (F) showed a residual, hypoechoic mass (arrows) at the 10 o’clock position. Posttreatment CC (G) and MLO (H) MBI views demonstrated residual uptake (arrows) compatible with partial treatment response. The final surgical pathology review showed residual ductal carcinoma in situ.

Figure 11

Molecular breast imaging (MBI) for evaluation of the response to neoadjuvant systemic therapy (NST)—complete treatment response. A 63-year-old woman was diagnosed with multifocal poorly differentiated invasive ductal carcinoma of the right breast. A-E: Staging images. Mediolateral oblique mammographic view (A) showed 2 sites of biopsy-proven malignancy at the 9 o’clock position, 5 cm from the nipple, denoted by a wing clip (asterisk) and a second lesion at 9 o’clock, 3 cm from the nipple, denoted by a ribbon clip (arrow). A grayscale transverse US image showed an irregular, hypoechoic mass (arrows) at the 9 o’clock position, 5 cm from the nipple, representing the index malignancy (B) and an oval, hypoechoic mass (arrows) at the 9 o’clock position, 3 cm from the nipple, representing the second site of biopsy-proven malignancy (C). Cradiocaudal (D) and MLO (E) MBI views demonstrated 2 correlating lesions (arrows) with marked mass uptake. F-J: Post-NST images. Mediolateral oblique mammographic view (F) demonstrated 2 biopsy clips (asterisk, arrow) with no residual mass. A grayscale transverse US image showed a biopsy clip with a residual hypoechoic, ill-defined mass (arrows) at 9 o’clock, 5 cm from the nipple (G), and a biopsy clip (asterisk) with residual tumor bed (arrow) at 9 o’clock, 3 cm from the nipple (H). Craniocaudal (I) and MLO (J) MBI views showed no residual uptake, which was compatible with complete imaging response. Final surgical pathology review revealed no residual carcinoma.

Figure 12

Molecular breast imaging (MBI) as a problem-solving modality. A 70-year-old woman presented with left nipple retraction and palpable abnormalities. Craniocaudal (A) and MLO (B) mammographic views with 3 markers (triangles) placed to indicate the palpable abnormalities demonstrated tubular structures in the retroareolar region (arrows) suggestive of dilated ducts. A grayscale transverse US image (C) showed an isoechoic tubular mass (arrows) at the 9 o’clock position, correlating with 1 of the palpable findings. US-guided biopsy (not shown) revealed sclerosed adenotic papilloma, no atypia. A postbiopsy CC mammographic view (D) showed a biopsy clip (arrow) in the region of the palpable abnormality. Given the new nipple retraction and the patient’s inability to tolerate MRI, MBI was recommended. Craniocaudal (E) and MLO (F) MBI views demonstrate marked nonmass uptake in a segmental distribution at the 9–8 o’clock position extending posteriorly from the subareolar region (arrows). A grayscale transverse image from second-look US imaging (G) showed dilated ducts and a possible intraductal mass (arrow) at the 8 o’clock position, 1 cm from the nipple. US-guided biopsy (not shown) revealed an intraductal papilloma. A postbiopsy CC mammographic view (H) showed a new coil clip in the expected location (arrow). In light of the MBI findings, the biopsy pathology results were believed to be discordant with imaging, and surgical excision was performed. The final surgical pathology demonstrated ductal carcinoma in situ, low to intermediate grade.