Physics of MBI (~10 slides) Molecular Breast Imaging (MBI) physics and performance testing JW Hugg, BR Simrak, PD Smith, BE Patt Gamma Medica, Inc., Northridge, CA Molecular Breast Imaging (MBI) is an emerging radiotracer technique for detecting breast cancer, especially in women with radiographically dense breasts (about 40% of North American and European women; over 50% of Asian women). MBI uses an IV injection of 2-8 mci of 99m Tc-sestamibi (140 kev single gamma photon emissions, 6 hr half-life). Uptake in cancer lesions is rapid and imaging can begin within 5 minutes. Tracer washout is slow and uptake in normal tissue is much less avid. MBI evolved from scintimammography (SMM) which used a whole-body gamma camera to image the breast from a lateral position. Only lesions larger than 1 cm could be reliably detected by SMM because of the large distance from the collimator to the breast. MBI uses two small field-of-view gamma cameras in contact with the breast, which is mildly compressed between the two cameras to immobilize the breast during imaging. Typically two standard mammographic views are imaged for each breast: CC (cranio-caudal) and MLO (medio-lateral-oblique). The detectors for MBI are digital, solid-state, pixellated CZT (cadmium-zinc-telluride) modules. Multiple CZT detector modules are tiled to form a planar gamma camera. Pixel pitch is 1.5 mm (Gamma Medica LumaGEM) or 2.5 mm (GE Discovery 750b) and the crystal thickness is 5 mm. Energy resolution is typically 4.7% (LumaGEM) or 6% (Discovery). DRAFT Outline of presentation Self-Assessment Q1 What is the radiopharmaceutical (and its halflife) most commonly used for MBI or BSGI? a) 18 F-FDG (2 hr) b) 123 I-MIBG (13 hr) c) 99m Tc-Tetrofosmin (4 hr) d) 99m Tc-Sestamibi (13 hr) e) 99m Tc-Sestamibi (6 hr) Self-Assessment Q1 What is the radiopharmaceutical (and its halflife) most commonly used for MBI or BSGI? a) 18 F-FDG (2 hr) b) 123 I-MIBG (13 hr) c) 99m Tc-Tetrofosmin (4 hr) d) 99m Tc-Sestamibi (13 hr) e) 99m Tc-Sestamibi (6 hr) Reference: SJ Goldsmith, et al, SNM Practice Guideline for Breast Scintigraphy with Breast-Specific g-cameras 1.0, J Nuc Med Tech 2010: 38; 219-224. 1
BSGI & PEM (~5-6 slides) Self-Assessment Q2 Closely related techniques include BSGI (Breast Specific Gamma Imaging) and PEM (Positron Emission Mammography). BSGI (Dilon 6800 or Acella) is an older, less-sophisticated form of MBI using 3.0-3.2 mm pixel scintillators (NaI or CsI) and either PS-PMT or APD photodetectors. BSGI also uses only a single detector. PEM (Naviscan) uses 18 F-FDG and coincidence detection (paired 511 kev gamma emissions, 2 hour half-life) using small scintillator/pmt detectors that physically scan side-to-side to form a limited-angle PET scan. Patient preparation is lengthy for PEM: 12-24 hour fast, 1-2 hour quiet uptake delay after injection. This lecture will examine the physics of MBI, BSGI, and PEM and will compare the performance of the commercially available systems (all FDA 510(k) cleared). Objective 1: Understand the physics of MBI, BSGI, and PEM breast imaging. Compare BSGI and MBI: how many detector heads are used and what type of detectors? a) BSGI: 2 CZT detectors; MBI: 1 scintillator detector b) BSGI: 1 CZT detector; MBI: 2 scintillator detector c) BSGI: 1 scintillator detector; MBI 2 CZT detectors d) BSGI: 2 scintillator detectors; MBI 1 CZT detector e) BSGI: 1 scintillator detector; MBI 2 scintillator detectors Self-Assessment Q2 Compare BSGI and MBI: how many detector heads are used and what type of detectors? a) BSGI: 2 CZT detectors; MBI: 1 scintillator detector b) BSGI: 1 CZT detector; MBI: 2 scintillator detector c) BSGI: 1 scintillator detector; MBI 2 CZT detectors d) BSGI: 2 scintillator detectors; MBI 1 CZT detector e) BSGI: 1 scintillator detector; MBI 2 scintillator detectors Dose reduction (~6 slides) Patient and technologist radiation dose will be discussed. Reference: M O Connor, et al, Molecular Breast Imaging, Expert Reviews Anticancer Ther 2009; 9: 1073-80. 2
Self-Assessment Q3 What is the radiopharmaceutical dose recommended by the SNM for BSGI; and what is the dose currently used by the Mayo Clinic for MBI? a) 925 MBq (25 mci) for BSGI; and 148 MBq (4 mci) for MBI b) 925 MBq (25 mci) for BSGI; and 740 MBq (20 mci) for MBI c) 740 MBq (20 mci) for BSGI; and 370 MBq (10 mci) for MBI d) 1110 MBq (30 mci) for BSGI; and 296 MBq (8 mci) for MBI e) 370 MBq (10 mci) for BSGI; and 370 MBq (10 mci) for MBI Self-Assessment Q3 What is the radiopharmaceutical dose recommended by the SNM for BSGI; and what is the dose currently used by the Mayo Clinic for MBI? a) 925 MBq (25 mci) for BSGI; and 148 MBq (4 mci) for MBI b) 925 MBq (25 mci) for BSGI; and 740 MBq (20 mci) for MBI c) 740 MBq (20 mci) for BSGI; and 370 MBq (10 mci) for MBI d) 1110 MBq (30 mci) for BSGI; and 296 MBq (8 mci) for MBI e) 370 MBq (10 mci) for BSGI; and 370 MBq (10 mci) for MBI References: SJ Goldsmith, et al, SNM Practice Guideline for Breast Scintigraphy with Breast-Specific g-cameras 1.0, J Nuc Med Tech 2010: 38; 219-224. MK O Connor, et al, Comparison of radiation exposure and associated radiationinduced cancer risks from mammography and molecular imaging of the breast, Med Phys 2010; 37: 6187-98. Self-Assessment Q4 What are the most important factors leading to a dose reduction in MBI? a) Quantum efficiency of the detector, LEHS collimator b) Patient prep (fasting, delay for background washout), LEHS collimator c) LEHS collimator, noise reduction filter, CZT detectors d) Optimal pixel size, registered collimator, two detector heads, noise reduction filter e) Registered collimator, CZT detectors, two detector heads Dose Reduction for MBI, BSGI, PEM Objective 2: Understand how radiation dose can be lowered in MBI, BSGI, and PEM. 3
Self-Assessment Q4 What are the most important factors leading to a dose reduction in MBI? a) Quantum efficiency of the detector, LEHS collimator b) Patient prep (fasting, delay for background washout), LEHS collimator c) LEHS collimator, noise reduction filter, CZT detectors d) Optimal pixel size, registered collimator, two detector heads, noise reduction filter e) Registered collimator, CZT detectors, two detector heads Clinical Examples, Reimbursement (~10 slides) Clinical examples will be shown to demonstrate the application of MBI for secondary diagnosis and screening of radiographically dense breasts. Reimbursement issues will be briefly presented. Reference: AL Weinmann, et al, Design of optimal collimation for dedicated molecular breast imaging systems, Med Phys 2009; 36: 845-56. MBI-guided Biopsy (~5 slides) MBI-guided biopsy procedures will be discussed. Self-Assessment Q5 What advantages does MBI-guided biopsy (MBI-Bx) have over mammography-guided biopsy in women with dense breast tissue? a) MBI-Bx has higher resolution, higher reimbursement, and is faster b) MBI-Bx has higher specificity, instant specimen verification, and visualizes occult lesions c) MBI-Bx has higher photon energy, lower radiation dose, and higher reimbursement d) MBI-Bx has higher sensitivity, specificity, and resolution e) MBI-Bx has lower radiation dose, instant specimen verification, and higher reimbursement 4
Self-Assessment Q5 Performance tests (~5 slides) What advantages does MBI-guided biopsy (MBI-Bx) have over mammography-guided biopsy in women with dense breast tissue? a) MBI-Bx has higher resolution, higher reimbursement, and is faster b) MBI-Bx has higher specificity, instant specimen verification, and visualizes occult lesions c) MBI-Bx has higher photon energy, lower radiation dose, and higher reimbursement d) MBI-Bx has higher sensitivity, specificity, and resolution e) MBI-Bx has lower radiation dose, instant specimen verification, and higher reimbursement Several NEMA NU1 tests can be adapted to characterize the performance of the small-fov planar gamma cameras of MBI and BSGI, and NEMA NU2 tests can be adapted for PEM. A new lesion contrastdetectability phantom is under development and its use to compare system performance will be discussed. This lecture will examine the physics of MBI, BSGI, and PEM and will compare the performance of the commercially available systems (all FDA 510(k) cleared). Objective 3: Understand how to characterize the performance of MBI, BSGI, and PEM systems. Reference: M O Connor, et al, Molecular Breast Imaging, Expert Reviews Anticancer Ther 2009; 9: 1073-80. MBI Market (~3 slides) Finally, the potential market for MBI equipment and procedures will be discussed and the prediction will be made that by 2020 MBI could challenge myocardial perfusion imaging (MPI) as the most frequently used nuclear medicine procedure. Summary Learning Objectives Understand the physics of MBI, BSGI, and PEM breast imaging. Understand how radiation dose can be lowered in MBI, BSGI, and PEM. Understand how to characterize the performance of MBI, BSGI, and PEM systems. 5